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| Keywords: | CO2 reduction, plasmonic catalysis, nanomaterials, semiconductor heterojunctions, photoelectrochemical water-splitting, photovoltaics, optoelectronics, surface science, materials characterization |
FES Funded ProjectsOutputs
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| Doctoral Recruiting ScholarshipT12-P02 | Award | 2020-01-15 | Damini Vrushabendrakumar | | Synthesis, characterization, and visible light photocatalytic activity of solution-processed free-standing 2D Bi2O2Se nanosheetsOwing to their unique structural and electronic properties such as layered structure with
tuneable bandgap and high electron mobility, 2D materials have emerged as promising
candidates for photocatalysis. Recently, bismuth oxyselenide (Bi2O2Se), a member of bismuth
oxychalcogenide’s family has shown great potential in high-speed field-effect transistors,
infrared photodetectors, ferroelectric devices, and electrochemical sensors. However, the
potential of Bi2O2Se in photocatalysis has not yet been explored. In the current work, Bi2O2Se
nanosheets with an average size of ~170 nm and a lattice strain of 0.01 were synthesized at
room temperature using a facile solution-processed method and the as-synthesized material
was investigated with various characterization techniques such as XRD, FE-SEM, UV-Vis
spectroscopy. The bandgap for the indirect transition in Bi2O2Se nanosheets was estimated to
be 1.19 eV. Further, the visible-light-driven photocatalytic degradation of methylene blue
(MB) dye using Bi2O2Se as a photocatalyst is presented. The photocatalytic experiments
demonstrate the promising photocatalytic ability of Bi2O2Se as it leads to 25.06% degradation
of MB within 80 min of light illumination. The effect of active species trapping agents (carrier
and radical scavengers) on photocatalytic activity is also presented and discussed.T12-P02 University of Alberta | Publication | 2021-07-22 | Damini Vrushabendrakumar, Harshitha Rajashekhar, Saralyn Riddell, Aarat P Kalra, Kazi Alam, Shankar, K. | | Hot Carrier Photocatalysis Using Bimetallic Au@Pt Hemispherical Core-Shell NanoislandsWe report the fabrication of core-shell Au@Pt nanoislands grown on glass substrates using a facile and reproducible combination of magnetron sputtering and thermal annealing. Au@Pt NPs exhibit a lattice strain of ~0.2% and a slightly positively charged Au core due to electron transfer from Au to Pt during equilibration. The localized surface plasmon resonance peak of Au redshifts incrementally from 2.13 to 2.0 eV and broadens in a controllable manner with the addition of ultrathin Pt shells (1-3 nm). The quality factor of the LSPR resonance decreased gradually from ~13 to ~3 as bare Au nanoislands were coated with 3 nm of Pt. The Au@Pt nanoislands demonstrated superior methylene blue degradation performance due to the hot hole injection from the bimetallic nanoparticle into the dye molecule despite the absence of any semiconducting photocatalytic support. Raman thermometry studies involving Stokes and anti-Stokes spectra helped shed light on the hot electron dynamics of the composite system and validated hot carrier injection from Au to Pt.T12-P02 University of Alberta | Publication | 2017-01-01 | Ajay Manuel, Saralyn Riddell, Harshitha Rajashekhar, Damini Vrushabendrakumar, Kazi Alam, Pawan Kumar, "Sergey Gusarov ", "Alex Kobryn ", Mustafa Supur, "Rick McCreery ", Shankar, K. | | An Ultrasensitive Fluorescent Paper Based Acidic Gas Sensing PlatformAcidic gases are highly toxic for humans, wild animals and environment. Therefore, the development of easy-to-use, low cost, fluorescent paper-based rapid and selective sensing of acidic gas in open as well as closed environments is of great significance. In the present work, we have synthesized
red emissive sulfur using a two-step oxidation process and infused it into standard filter paper for the detection of acidic fumes. The as-prepared red emissive fluorescent paper exhibits significant change in emission color from red to dark brown upon exposure to acidic vapors. Therefore, the simple, portable and disposable analytical fluorescent paper-based sensing platform can be used as a next generation alternative technique for the effective detection of acidic gases with numerous
applications in food quality control, clinical determination and environment surveilling.T12-P02 University of Alberta | Activity | 2021-11-03 | Sachin Kadian, Narendra Chaulagain, Harshitha Rajashekhar, Damini Vrushabendrakumar, "Gaurav Manik ", Shankar, K. | | An Ultrasensitive Fluorescent Paper Based Acidic Gas Sensing PlatformT12-P02 University of Alberta | Publication | 2021-10-31 | Sachin Kadian, Narendra Chaulagain, Harshitha Rajashekhar, Damini Vrushabendrakumar, "Gaurav Manik ", Shankar, K. | | Remarkable CO2 photoreduction and photoelectrochemical water-splitting performance using narrow bandgap carbon-rich carbon nitride nanosheetsAbstract accepted for Oral Presentation in Symposium D:Carbon- and/or nitrogen-containing thin films and nanomaterials, at the prestigious 2023 Spring Meeting of the European Materials Research Society (E-MRS).
2,652 abstracts were submitted to the 2023 E-MRS, of which only a handful were accepted as oral presentations.
The 2023 Spring E-MRS Conference will be held at the Convention & Exhibition Centre of Strasbourg (France), from May 29 to June 2, 2023 and will consist of parallel symposia with invited speakers, oral and poster presentations assorted by three plenary sessions to provide an international forum for discussing recent advances in the field of materials science.
The high quality scientific program will address different topics organized into 21 symposia arranged in 6 clusters covering the fields of Energy materials; Nanomaterials and advanced characterization; Biomaterials and soft materials; Electronics, magnetics and photonics; Functional materials; Education and training.T12-P02 University of Alberta | Activity | 2023-05-31 | Narendra Chaulagain, Damini Vrushabendrakumar, Harshitha Rajashekhar, Navneet Kumar, Kazi Alam, Shankar, K. | | Effect of thiolate monolayers on CO2 photoreduction using CuPt nanoparticle decorated TiO2 nanoellipsoidsAbstract accepted for Poster Presentation in Symposium D:Carbon- and/or nitrogen-containing thin films and nanomaterials, at the prestigious 2023 Spring Meeting of the European Materials Research Society (E-MRS).
The 2023 Spring E-MRS Conference will be held at the Convention & Exhibition Centre of Strasbourg (France), from May 29 to June 2, 2023 and will consist of parallel symposia with invited speakers, oral and poster presentations assorted by three plenary sessions to provide an international forum for discussing recent advances in the field of materials science.
The high quality scientific program will address different topics organized into 21 symposia arranged in 6 clusters covering the fields of Energy materials; Nanomaterials and advanced characterization; Biomaterials and soft materials; Electronics, magnetics and photonics; Functional materials; Education and training.T12-P02 University of Alberta | Activity | 2023-05-31 | Narendra Chaulagain, Navneet Kumar, Damini Vrushabendrakumar, John Garcia, Kazi Alam, Shankar, K. | | ATUMS Visiting PhD StudentCompleted a 3-month research exchange visit in Summer 2022; worked in the labs of the Tom Nilges research group at the Technical University of Munich.T12-P02 | Activity | 2022-08-31 | Damini Vrushabendrakumar | | Sr-doped TiO2 nanotube arrays for CO2 photoreductionT12-P02 University of Alberta | Activity | 2022-05-17 | | | Tunable Absorption and Emission in Mixed Halide Bismuth Oxyhalides for Photoelectrochemical Water SplittingLayered materials such as bismuth oxyhalides (especially BiOBr and BiOI) are the focus of research attention as photocatalysts due to their visible light activity, unique electronic structure, excellent chemical and physical stability, and internal electric field effect. We report the solvothermal synthesis of BiOX solid solutions with continuously tunable optical absorption and photoluminescence spectra. We employed solid-state nuclear magnetic resonance (SSNMR) characterization to probe the local environment around Bi atoms. We determined that the synthesized BiOX solid solutions exhibit good agreement with Vegard’s law through refinement of the lattice parameters using powder X-ray diffraction (PXRD) and complementary atomic-level 209Bi SSNMR spectroscopy. The solid solution strategy makes it possible to modulate the light absorption of BiOX and tune the redox potentials corresponding to the electronic band edges to drive chemical reactions. The BiOX solid solutions demonstrated superior performance in sunlight-driven photoelectrochemical and photocatalytic water splitting. The best performing solid solution generated a photocurrent density of 1.5 mA cm–2 and a H2 evolution rate of 16.32 μmol g–1 h–1 for photoelectrochemical water splitting and photocatalytic hydrogen generation, respectively, and the enhanced performance is attributed to a higher specific surface area, a shorter carrier transit distance, and a higher electron density. The approximate order of magnitude performance improvement compared to pristine BiOBr and BiOI photoanodes was primarily due to optimal light harvesting combined with adequate thermodynamic driving force to drive water oxidation and proton reduction.T12-P02, T12-P03 University of Alberta | Publication | 2024-01-01 | Md Masud Rana, Kazi Alam, Narendra Chaulagain, John Garcia, Navneet Kumar, Damini Vrushabendrakumar, Harshitha Rajashekhar, Guy Bernard, Al Meldrum, Vladimir K Michaelis, Shankar, K. | | Visible Light Driven CO2 Photoreduction Using TiO2 Nanotube Arrays Embedded with Low Bandgap Carbon Nitride NanoparticlesThe extraordinary thermal and photochemical stability, superior charge transport, and tunable band positions of graphitic carbon nitride (g-CN), which is constituted of elements that are plentiful on Earth, renders g-CN an important semiconductor photocatalyst for heterogeneous catalysis [1,2]. Despite these advantages, carbon nitride-based semiconductors do not function effectively as freestanding photocatalysts or photoelectrodes due to a rapid carrier recombination rate and a slightly wide bandgap that only enables them to capture blue and UV photons [3,4]. Anodically formed TiO2 nanotube arrays (TNTAs) are semiconducting wide bandgap scaffolds with excellent photocatalytic properties due to the intrinsic orthogonalization of charge generation/transport and charge transfer processes. Herein, we use a novel in situ electrophoretic anodization to embed low bandgap carbon nitride nanoparticles (CNNPs) in the walls of titania nanotubes. The likelihood of the CNNPs leaching off the TNTA photoanode during photoelectrochemical processes was eliminated by encapsulating CN inside a TiO2 matrix. CNNPs were formed by the thermal condensation polymerization of carbon nitride utilizing citric acid and urea as the precursors, and exhibited some unusual properties, including a lower bandgap of 2.1 eV, a highly redshifted fluorescence emission maximum at 2.35 eV, surface carboxylate groups, and the emergence of unique structural characteristics corresponding to amorphous yet graphitic carbon [5]. In contrast to bulk g-CN, which has a C:N ratio of 0.75, the CNNPs possessed an elevated C:N ratio as high as 1.87 at the surface. The additional carbon was found to be both amorphous and graphitic, although the structural characteristics of g-CN were mostly unaffected, as validated by diffractometric and spectroscopic data. Even in the absence of a sacrificial agent, the CNNP@TNT nanocomposite demonstrated enhanced performance in sunlight-driven CO2 photoreduction. When compared to the freestanding TNT photocatalyst, the CO yield of photoreduction for the CN@TNT hybrid was more than three times higher. UV-filtered illumination of the CNNP@TNT heterojunction photocatalyst generated appreciable quantities of methane and CO (3.41 and 8.78 μmolg–1h–1 respectively). In situ electrophoretic anodization is an innovative approach to incorporate semiconductor quantum dots into TiO2 nanotubes or other electrochemically grown nanostructures.T12-P02 University of Alberta | Publication | 2023-01-01 | Damini Vrushabendrakumar, Kazi Alam, Narendra Chaulagain, Navneet Kumar, Shankar, K. | | Cathodically Inserted, Widely Dispersed Sr2+ Surface Dopants Produce a Threefold Improvement in the CO2 Photoreduction Activity of TiO2 Nanotube ArraysStrontium surface doping of anodic TiO2 nanotube arrays (TNTAs) is performed using an electrochemical cathodization method in an Sr2+-containing electrolyte. The doped strontium does not result in either phase-segregated Sr, SrO, or SrTiO3. Instead, Sr-doping results in modification of the crystallographic texture of anatase phase TNTAs, reduced crystal size, and increased lattice strain. Subtle changes are observed in the Fourier-transform infrared spectra (FTIR) of the carbon dioxide (CO2) adsorbed on the Sr-cathodized TNTA (Sr-C-TNTA), indicating a larger prevalence of monodentate carbonate and bidentate bicarbonate species on the surface. This is attributed to the higher alkalinity of surface hydroxyls bound to Sr in comparison to that of the Ti-bound hydroxyls. In addition to linearly adsorbed CO2, a population of bridging bidentate carbonate adsorbate is observed, suggesting an enhanced stabilization of the CO2 anion radical on the Sr-C-TNTA surfaces. Under AM1.5G 1 sun illumination, the Sr-C-TNTAs produce 25.0 μmol g–1 hr–1 carbon monoxide (CO), a greater than threefold improvement over the amount of CO generated by bare TNTAs (7.7 μmol g–1 hr–1). The spectroscopic characterization data are consistent with high-entropy surface-doping, creating relatively isolated and thermally stable Sr atoms on the surface of TiO2. These results highlight the potential of electrochemical cathodization in achieving high-entropy surface-doped semiconductors and single-atom catalysts.T12-P02 University of Alberta | Publication | 2023-12-19 | Damini Vrushabendrakumar, Kazi M Alam, Navneet Kumar, Harshitha Rajashekhar, Narendra Chaulagain, Saralyn Riddell, Alexander E Kobryn, Sergey Gusarov, Shankar, K. | | CO2 Photoreduction Activity Enhancement and Unexpected Observation of Carbon Monoxide Adsorbates on the Surface of TiO2 Nanotube Arrays Synthesized in Formamide ElectrolytesTiO2 nanotube arrays grown through electrochemical anodization in a formamide-based electrolyte (TNTA-FA) exhibited a whole host of unusual properties compared to nanotubes grown in the conventional ethylene glycol-based electrolyte (TNTA-EG). TNTA-FA exhibited shorter phonon lifetimes, lower lattice strain, more visible light absorption, lower work function, and a highly unusual adsorbate structure consisting of physisorbed and chemisorbed CO along with linearly adsorbed CO2 and various monodentate and bidentate carbonate species. The observation of adsorbed CO in the dark is highly unusual and indicates spontaneous deoxygenation of CO2 on the surface of TNTA-FA. The significance of this finding is that the formation of CO2•– is no longer the rate-limiting bottleneck for the reduction of CO2 on TNTA-FA surfaces as it is for all TiO2 surfaces. TNTA-FA samples are strongly colored (inclusive of a fluorescent green color) and consist of rounded, vertically oriented hollow cylinders as opposed to the honeycomb-like morphology of TNTA-EG arranged in an approximate triangular lattice. The photocatalytic activity was tested through the CO2 photoreduction and dye degradation tests. Formamide-based nanotubes outperformed the EG-based nanotubes by almost 1.7 and 2 times, respectively, in CO2 reduction and dye degradation tests done on methylene blue, brilliant green, and rhodamine B dyes. These results are attributed to stronger surface band bending in TNTA-FA which facilitates more efficient separation of photogenerated electron–hole pairs.T12-P02 University of Alberta | Publication | 2023-12-01 | Navneet Kumar, Kazi Alam, Damini Vrushabendrakumar, Atharva Shetty, John Garcia, Narendra Chaulagain, Shankar, K. | | Enhancement in the Rate of CO2 Photoreduction Using Divalent Strontium Cation (Sr2+) Doped TiO2 Nanotube ArraysWe explored the selective surface doping of anodically formed TiO2 nanotube arrays (TNTAs) with divalent Sr2+ cations using an electrochemical cathodization process in order to modify the basicity of the surface and modify the interactions of the surface with vapor phase CO2. The resulting Sr-doped TNTAs showed a 3-fold increase in CO2 photoreduction activity. Characterization using a broad suite of bulk- and surface-sensitive characterization techniques revealed the doped Sr atoms to be widely dispersed on the surface. Our results show a way forward to achieve single atom catalysts using cathodic doping of TiO2.T12-P02 University of Alberta | Publication | 2023-01-01 | Damini Vrushabendrakumar, Kazi Alam, Navneet Kumar, Narendra Chaulagain, Harshitha Rajashekhar, Saralyn Riddell, Shankar, K. | | Characterization of morphology-dependent transport in lead-halide perovskite printed films using time-resolved terahertz spectroscopyWe report on position-dependent measurements of photocarrier transport using time-resolved terahertz spectroscopy (TRTS) across a slot-die printed perovskite film of varying morphology. Using the Drude-Smith model for the photoconductivity spectra we report maximum intrinsic mobilities of $540 \pm 20$ $\mathrm cm ^2 \mathrm V^-1 \mathrm s^-1$. In addition, we measure variation across the film in the extracted mobilities and the localization c-parameter, correlated with complementary measurements of the film morphology and optical properties. To the best of our knowledge this is the first TRTS study performed on perovskite films produced using a slot-die printing technique.T12-P02 University of Alberta | Publication | 2023-10-31 | Nils Refvik, Lennart K Reb, Christoph Lindenmeir, Charles Jensen, Howe Simpson, Damini Vrushabendrakumar, Shankar, K., Peter Müller-Buschbaum, Frank Hegmann | | Doctoral Recruiting ScholarshipT12-P02 | Award | 2020-01-15 | Harshitha Rajashekhar | | MITACS GlobalinkT12-P02 | Award | 2022-02-20 | Harshitha Rajashekhar | | Hot Hole Utilization in Au-TiO 2 and Au-C3N4-TiO2 Core-Shell Heterojunctions for High Performance Photoelectrochemical Water SplittingGold nanoparticles (Au NPs) coated with TiO2 shells exhibit strong localized surface plasmon resonance (LSPR) peaks at ~550-600 nm. The Au plasmons decay in femtoseconds through both interband and intraband damping processes to produce hot electron-hole pairs. These hot carriers have excess energy at room temperature which can be utilized to generate electricity or drive a chemical reaction. However, the hot carriers experience ultrafast recombination and thermal relaxation in hundreds of femtoseconds to a few picoseconds due to electron-electron scattering and collisions with phonons. A Schottky barrier heterojunction between Au and a n-type semiconductor such as TiO2 is an ideal method to separate the hot carrier pairs. In Au-TiO2 Schottky junctions, hot electrons are injected into TiO2 through thermionic emission and/or field emission before recombination and thermal equilibration, at timescales of roughly 250 fs. However the harvesting of residual hot holes in Au remains problematic partly because of the difficulty in forming Schottky junctions between Au and p-type semiconductors. The harvesting of hot holes is particularly important considering that hot holes in Au are on average, more energetic than hot electrons.
In this work, we use an innovative photoanode architecture to harvest hot holes. Our photoanode architecture consists of Au NPs coated with a thin layer of amorphous TiO2 and deposited on transparent conductive oxide (TCO)-coated glass substrates. Hot electrons are extracted from the Au into the TCO contact through the TiO2 shell. Hot holes tunnel through the TiO2 to reach the alkaline electrolyte whether they oxidize hydroxyl ions and dissolved oxygen species to generate oxygen. Another novelty is the use of a layer of graphitic carbon nitride (g-C3N4) quantum dots to pump the plasmon through exciton-to-plasmon energy transfer and increase the production of hot carriers. g-C3N4 works to enhance the plasmonic light harvesting due to the excellent overlap between the emission of g-C3N4 and the LSPR absorption band of Au. Photocurrent densities as high as 3.7 mA/cm2 were achieved under AM1.5G one sun illumination with concomitant high Faradaic efficiencies. Photoelectrochemical action spectra collected using filtered AM1.5G illumination and monochromatic LEDs revealed the prominent role of visible photons in water-splitting performed using Au-C3N4-TiO2 core-shell ternary heterojunctions. A key goal moving forward is to replace the noble metal (Au) with transition metal nitride plasmonic absorbers while sustaining the high level of photoelectrochemical performance.T12-P02 University of Alberta | Activity | 2022-07-01 | Narendra Chaulagain, Harshitha Rajashekhar, Navneet Kumar, Ehsan Vahidzadeh, Kazi Alam, Shankar, K. | | Alberta Innovates Graduate Student ScholarshipT12-P02 | Award | 2023-05-05 | Harshitha Rajashekhar | | Nano-Micro Letters Best Student Paper AwardHarshitha was awarded the Nano-Micro Letters Best Student Paper Award at the Canadian Symposium for Catalysis (CSC'2022) in Vancouver, BC for her presentation titled "Plasmonic catalysts and heterojunctions for CO2 reduction and dye photodegradation".T12-P02 | Award | 2023-05-05 | Harshitha Rajashekhar | | ATUMS Visiting PhD StudentCompleted a 3-month research exchange visit in Summer 2022; worked in the labs of the Ulrich Heiz, Aras Kartouzian and Tom Nilges research groups at the Technical University of Munich.T12-P02 | Activity | 2022-08-31 | Harshitha Rajashekhar | | Visiting PhD studentT12-P02 | Activity | 2023-02-28 | Harshitha Rajashekhar | | Photocatalytic CO2 reduction driven by porous metal nanoparticlesT12-P02 University of Alberta | Activity | 2022-05-26 | Harshitha Rajashekhar, Ehsan Vahidzadeh, Saralyn Riddell, Shankar, K. | | Plasmonic catalysts and heterojunctions for CO2 reduction and dye photodegradationT12-P02 University of Alberta | Activity | 2022-05-18 | | | 2024 Graduate Student Teaching AwardThe purpose of these awards is to recognize graduate students who are especially skillful and dedicated teachers at the University of Alberta. The graduate students are recognized for any in-person lectures delivered as well as teaching assistant duties. T12-P02 | Award | 2024-05-12 | Harshitha Rajashekhar | | Graduate Recruitment ScholarshipT12-P02 | Award | 2021-05-11 | Md Masud Rana | | Gerald J. Maier/NOVA Chemicals Corporation Graduate Recruitment AwardT12-P02 | Award | 2022-04-30 | Md Masud Rana | | Detecting Charge Separation in Optoelectronic Materials and Devices Using Planar Microwave Resonators: An OverviewThe advent of high Q-factor planar microwave resonators has opened up new possibilities for the electronic characterization of semiconductor heterojunctions and hot carrier plasmonic devices. The high sensitivity of planar microwave resonators to changes in the complex permittivity of semiconductor materials placed in the resonator coupling gap allows detection of both mobile and trapped carriers. Therefore, long-lived excess carriers in relaxation-type semiconductors occurring either due to photoexcitation or hot carrier injection from a plasmonic sensitizer can be detected
and quantified. Application of a large signal DC bias on top of the small-signal microwave bias further enables differentiation between trapped electrons and trapped holes. In most cases, characteristic lifetimes for trap-mediated processes can also be extracted.T12-P02 University of Alberta | Activity | 2021-11-03 | | | Detecting Charge Separation in Optoelectronic Materials and Devices Using Planar Microwave Resonators: An Overview Publisher: IEEE PDFT12-P02 University of Alberta | Publication | 2021-12-17 | | | Low bandgap carbon nitride nanoparticles incorporated in titania nanotube arrays by in situ electrophoretic anodization for photocatalytic CO 2 reductionWe report an in situ electrophoretic anodization process to realize a binary semiconductor heterojunction photocatalyst comprising green-emitting, water-soluble carbon nitride (CN) nanoparticles (NPs) embedded in TiO2 nanotube (TNT) arrays. Embedding CN inside a TiO2 matrix eliminates the possibility of the CNNPs leaching away during photocatalysis or photoelectro-chemistry. The synthesized CN exhibits visible light absorption down to 600 nm and an unusually redshifted green emission peak at 527 nm, which are attributed to a carbon rich g-C3N4 composition with a C:N ratio of ∼ 1.9 at the surface. Spectroscopy revealed the excess carbon to be both amorphous and graphitic while the structural features characteristic of g-C3N4 were preserved. Raman spectroscopy, transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) analysis verified the formation of the heterostructure as well as indicated strong interaction between the CN and TiO2 in the hybrid. The CNNP@TNT hybrid demonstrated superior performance in sunlight driven photocatalytic CO2 reduction without the need for a sacrificial agent. The CO yield of photo-reduction showed a more than threefold improvement for the CNNP@TNT hybrid compared to the stand-alone TNT photocatalyst. The synergistic enhancement of photocatalytic performance emerged due to the formation of a high-quality interface between the constituent semiconductors (TiO2 and CN) that facilitated efficient charge carrier separation. Density functional theory (DFT) calculations showed the feasibility of efficient photogenerated electron-hole pair separation at the heterointerface. Molecular dynamics (MD) simulations validated the facile dispersibility of CNNPs in water and polar solvents.T12-P01, T12-P02 University of Alberta | Publication | 2023-01-01 | Kazi Alam, Narendra Chaulagain, Ehsan Shahini, Md Masud Rana, John Garcia, Navneet Kumar, Alexander E Kobryn, Sergey Gusarov, Tian Tang, Shankar, K. | | Doctoral Recruitment ScholarshipT12-P02 | Award | 2021-05-13 | Navneet Kumar | | Synergistic Enhancement of the Photoelectrochemical Performance of TiO $\less$sub$\greater$2$\less$/sub$\greater$ Nanorod Arrays through Embedded Plasmon and Surface Carbon Nitride Co-sensitizationWe report a unique photoanode architecture involving TiO2, g-C3N4, and AuNPs wherein a synergistic enhancement of the photoelectrochemical (PEC) performance was obtained with photocurrent densities as high as 3 mA cm–2 under AM1.5G 1 sun illumination. The PEC performance was highly stable and reproducible, and a photoresponse was obtained down to a photon energy of 2.4 eV, close to the interband damping threshold of Au. The photocurrent enhancement was maximized when the Au plasmon band strongly overlapped the g-C3N4 emission band. Our photoanode architecture, which involved AuNPs buried under TiO2 and a plasmon-induced resonance energy transfer-like interaction between g-C3N4 quantum dots (CNQDs) and AuNPs, solved four major problems associated with plasmonic photoelectro-catalysis ─ it reduced recombination by limiting eliminating direct electrolyte access to AuNPs, it facilitated electron extraction through single-crystal TiO2 nanorod percolation pathways, it facilitated hole extraction through a defective TiO2 seed layer or canopy, and it expanded the range of visible light harvesting by pumping the Au surface plasmons from CNQDs through exciton-to-plasmon resonant energy transfer.T12-P02 University of Alberta | Publication | 2022-05-01 | Narendra Chaulagain, Kazi Alam, Sachin Kadian, Navneet Kumar, John Garcia, Gaurav Manik, Shankar, K. | | Photocatalytic mechanism control and study of carrier dynamics in CdS@C3N5 core-shell nanowiresWe present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low bandgap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, FDTD simulations, time-resolved terahertz spectroscopy (TRTS) and photoconductivity measurements. TRTS indicated high carrier mobilities > 450 cm2Vs-1 and carrier relaxation times > 60 ps for CdS-MHP while CdS-MHPINS exhibited much lower mobilities < 150 cm2Vs-1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J-V characteristics of CdS NWs disappeared in CdS-MHP confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low bandgap can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core-shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis. T12-P02, T12-P03, T06-Z01, T12-Z01 University of Alberta | Publication | 2021-04-30 | Kazi Alam, Charles Jensen, Pawan Kumar, Riley Hooper, Guy Bernard, Aakash Patidar, Ajay Manuel, "N Amer ", "A. Palmgren ", Narendra Chaulagain, David Purschke, John Garcia, Phillip Suwan Kirwin, Lian Shoute, "K. Cui ", "S. Gusarov ", "A. Kobryn ", Vladimir K Michaelis, Frank Hegmann, Shankar, K. | | Compositional and elemental descriptors for perovskite materialsIn this extended abstract we compare the performance of different families of descriptors – molar composition descriptor, weight composition descriptor and elemental descriptor – for regression task (prediction of bandgap) and include examples of a classification task for perovskite oxide materials with general formulas ABO3, A2BB′O6 and AxA′ 1−xByB′ 1−yO6. The best performance was observed for our elemental descriptor which consisted of -site and -site element information on: Shannon’s ionic radius, ideal bond length, electronegativity, van der Waals radius, ionization energy, molar volume, atomic number, and atomic mass. The weight composition descriptor showed superior results over a simpler molar composition descriptor. The results of principal component analysis, regression models with the hyperparameters optimized using an autoML software and Wasserstein autoencoders are briefly discussed for a possible use in inverse materials design.T12-P01, T12-P02 University of Alberta | Publication | 2023-04-21 | "Maicon Pierre ", "Jiri Hostas ", John Garcia, "Hatef Shahmohamadi ", "Alain Tchagang ", Shankar, K., "Venkataraman Thangadurai ", Dennis R Salahub | | Alberta Graduate Excellence ScholarshipT12-P02 | Award | 2023-05-05 | John Garcia | | Experimental progress on Bi-doped BCN and BZN perovskitesT12-P02 | Activity | 2023-04-22 | John Garcia | | Substitutional Cu doping at Ca and Nb sites in Ba3CaNb2O9 Towards Improved Photoactivity A First-principles HSE06 StudyT12-P02 University of Alberta | Publication | 2024-05-10 | "Sankha Ghosh ", John Garcia, "Bhavadharini Selvakumar ", "Amanda Ndubuisi ", Shankar, K., "Venkataraman Thangadurai ", Dennis R Salahub | | Tunable Syngas Production via Photoelectrochemical Reduction of CO2 Using Cu2O-SnO2 Z-Scheme PhotocatalystT02-P03 University of Alberta | Activity | 2018-08-13 | | | A Review on Photocatalytic CO2 Reduction using Perovskite Oxide NanomaterialsAs the search for efficient catalysts for CO2 photoreduction continues, nanostructured perovskite oxides have emerged as a class of high-performance photocatalytic materials. The perovskite oxide candidates for CO2 photoreduction are primarily nanostructured forms of titanates, niobates, tantalates and cobaltates. These materials form the focus of this review article because they are much sought-after due to their nontoxic nature, adequate chemical stability, and tunable crystal structures, bandgaps and surface energies. As compared to conventional semiconductors and nanomaterial catalysts, nanostructured perovskite oxides also exhibit an extended optical-absorption edge, longer charge carrier lifetimes, and favorable band-alignment with respect to reduction potential of activated CO2 and reduction products of the same. While CO2 reduction product yields of several hundred μmol−1 h−1 are observed with many types of perovskite oxide nanomaterials in stand-alone forms, yield of such quantities are not common with semiconductor nanomaterials of other types. In this invited review article, we present current state-of-the-art synthesis methods to form perovskite oxide nanomaterials, and procedures to engineer their bandgaps. This review also presents a comprehensive summary and discussion on crystal structures, defect distribution, morphologies and electronic properties of the perovskite oxides, and correlation of these properties to CO2 photoreduction performance. This review offers researchers key insights for developing advanced perovskite oxides in order to further improve the yields of CO2 reduction products.T12-P02 University of Alberta | Publication | 2018-01-05 | | | Core-shell titanium dioxide-titanium nitride nanotube arrays with near-infrared plasmon resonancesTitanium nitride (TiN) is a ceramic with high electrical conductivity which in nanoparticle form, exhibits localized surface plasmon resonances (LSPRs) in the visible region of the solar spectrum. The ceramic nature of TiN coupled with its dielectric loss factor being comparable to that of gold, render it attractive for CMOS polarizers, refractory plasmonics, surface-enhanced Raman scattering and a whole host of sensing applications. We report core–shell TiO2–TiN nanotube arrays exhibiting LSPR peaks in the range 775–830 nm achieved by a simple, solution-based,
low cost, large area-compatible fabrication route that does not involve laser-writing or lithography. Self-organized, highly ordered TiO2 nanotube arrays were grown by electrochemical anodization of Ti thin films on fluorine-doped tin oxide-coated glass substrates and then conformally coated with a thin layer of TiN using atomic layer deposition. The effects of varying the TiN layer thickness and thermal annealing on the LSPR profiles were also investigated. Modeling the TiO2–TiN core–shell nanotube structure using two different approaches, one employing effective medium approximations coupled with Fresnel coefficients, resulted in calculated optical spectra that closely matched the experimentally measured spectra. Modeling provided the insight that the observed near-infrared resonance was not collective in nature, and was mainly attributable to the longitudinal resonance of annular nanotube-like TiN
particles redshifted due to the presence of the higher permittivity TiO2 matrix. The resulting TiO2–TiN core–shell nanotube structures also function as visible light responsive photocatalysts, as evidenced by their photo-electrochemical water-splitting performance under light emitting diode illumination using 400, 430 and 500 nm photons.T12-P02, T12-P03 University of Alberta | Publication | 2018-02-01 | Samira Farsinezhad, Thariq Shanavas, Najia Mahdi, Abdelrahman M Askar, Piyush Kar, Himani Sharma, Shankar, K. | | Heterojunctions of mixed phase TiO2 nanotubes with Cu, CuPt, and Pt nanoparticles: interfacial band alignment and visible light photoelectrochemical activityAnodically formed, vertically oriented, self-organized cylindrical TiO2 nanotube arrays composed of the anatase phase undergo an interesting morphological and phase transition upon flame annealing to square-shaped nanotubes composed of both anatase and rutile phases. This is the first report on heterojunctions consisting of metal nanoparticles (NPs) deposited on square shaped TiO2 nanotube arrays (STNAs) with mixed rutile and anatase phase content. A simple photochemical deposition process was used to form Cu, CuPt, and Pt NPs on the STNAs, and an enhancement in the visible light photoelectrochemical water splitting performance for the NP-decorated STNAs was observed over the bare STNAs. Under narrow band illumination by visible photons at 410 nm and 505 nm, Cu NP-decorated STNAs performed the best, producing photocurrents 80% higher and 50 times higher than bare STNAs, respectively. Probing the energy level structure at the NP–STNA interface using ultraviolet photoelectron spectroscopy revealed Schottky barrier formation in the NP-decorated STNAs, which assists in separating the photogenerated charge carriers, as also confirmed by longer charge carrier lifetimes in NP-decorated
STNAs. While all the NP-decorated STNAs showed enhanced visible light absorption compared to the bare STNAs, only the Cu NPs exhibited a clear plasmonic behavior with an extinction cross section that peaked at 550 nm.T12-P02, T12-P03 University of Alberta | Publication | 2017-11-01 | Piyush Kar, Yun Zhang, Najia Mahdi, Ujwal Thakur, Benjamin Wiltshire, Ryan Kisslinger, Shankar, K. | | Top-Down Approaches Towards Single Crystal Perovskite Solar CellsThis project involved a collaboration between the Shankar Research Group at the UofA and the Muller-Buschbaum Group at TUM, Germany. Solar cells employing hybrid perovskites have proven to be a serious contender versus established thin-film photovoltaic technologies. Typically, current photovoltaic devices are built up layer by layer from a transparent substrate (bottom-up approach), while the deposition of the perovskite layer itself comes with many challenges including the control of crystal size, nucleation density and growth rate. On the other hand, single crystals have been used with great success for studying the fundamental properties of this new class of optoelectronic materials. However, optoelectronic devices fabricated from single crystals often employ different materials than in their thin film counterparts. Here, we demonstrate various top-down approaches for low-temperature processed organic-inorganic metal halide perovskite single crystal devices. Our approach uses common and well-established material combinations that are often used in polycrystalline thin film devices. The use of a polymer bezel allows easier processing of small crystals and the fabrication of solution-processed, free-standing perovskite single crystal devices. All in all these approaches can supplement other measurements of more fundamental material properties often requiring perovskite single crystals by rendering a photovoltaic characterization possible on the very same crystal with comparable material combinations as in thin film devices.T12-P02 University of Alberta | Publication | 2018-03-01 | Johannes Schlipf, Abdelrahman M Askar, Florian Pantle, Benjamin Wiltshire, Anton Sura, Peter Schneider, Linus Huber, Shankar, K., Peter Müller-Buschbaum | | Mechanochemical Synthesis of Methylammonium Lead Mixed\textendash Halide Perovskites: Unraveling the Solid-Solution Behavior Using Solid-State NMRMixed-halide lead perovskite (MHP) materials are rapidly advancing as next-generation high-efficiency perovskite solar cells due to enhanced stability and bandgap tunability. In this work, we demonstrate the ability to readily and stoichiometrically tune the halide composition in methylammonium-based MHPs using a mechanochemical synthesis approach. Using this solvent-free protocol we are able to prepare domain-free MHP solid solutions with randomly distributed halide ions about the Pb center. Up to seven distinct [PbClxBr6–x]4– environments are identified, based on the 207Pb NMR chemical shifts, which are also sensitive to the changes in the unit cell dimensions resulting from the substitution of Br by Cl, obeying Vegard’s law. We demonstrate a straightforward and rapid synthetic approach to forming highly tunable stoichiometric MHP solid solutions while avoiding the traditional solution synthesis method by redirecting the thermodynamically driven compositions. Moreover, we illustrate the importance of complementary characterization methods, obtaining atomic-scale structural information from multinuclear, multifield, and multidimensional solid-state magnetic resonance spectroscopy, as well as from quantum chemical calculations and long-range structural details using powder X-ray diffraction. The solvent-free mechanochemical synthesis approach is also compared to traditional solvent synthesis, revealing identical solid-solution behavior; however, the mechanochemical approach offers superior control over the stoichiometry of the final mixed-halide composition, which is essential for device engineering.T12-P02, T12-P04, T12-Z01 University of Alberta | Publication | 2018-03-01 | Abhoy Karmakar, Abdelrahman M Askar, Guy Bernard, Victor V Terskikh, Michelle Ha, Sahil Patel, Shankar, K., Vladimir K Michaelis | | Solution Processed Earth-Abundant Semiconductor Nanostructures for Sensing, Photocatalysis and PhotovoltaicsT12-P02 University of Alberta | Activity | 2017-06-22 | | | Au-Nanoparticle Embedded TiO2 Nanotube Arrays for Sensing, Photocatalysis and Nonlinear OpticsT12-P02 University of Alberta | Activity | 2017-04-20 | | | Charge Separation and Transport in Functional Heterojunctions Based on Solution-Grown TiO2 Nanotube & Nanowire ArraysT12-P02 University of Alberta | Activity | 2017-04-04 | | | Engineering Stable, High Efficiency Flexible Halide Perovskite Solar CellsT12-P02 University of Alberta | Activity | 2017-11-06 | | | Highly Structured Nanomaterials for High Performance Photocatalysts and Solar CellsT12-P02 University of Alberta | Activity | 2017-10-12 | | | Nanowire Electron Transport Layers (ETLs) for High Efficiency Halide Perovskite Solar Cells (HPSCs)T12-P02 University of Alberta | Activity | 2017-08-22 | | | Copper Sulfide Nanostructures and their utility in Photocatalytic CO2 ReductionT12-P02 University of Alberta | Activity | 2017-06-23 | Yun Zhang, Piyush Kar, "Xiaojiang Zhang ", "Samira Farsinezhad ", "Ling-hsuan Hsieh ", "Babak Amirsolaimani ", Shankar, K. | | One-Dimensional Solution-Processed TiO2 Nanostructures for Use in Photovoltaics, Photocatalysis, and Microwave Resonator SensorsT12-P02 University of Alberta | Activity | 2017-04-19 | Ryan Kisslinger, Ujwal Thakur, Benjamin Wiltshire, Najia Mahdi, "Mohammad Zarifi ", Piyush Kar, Shankar, K. | | Application of TiO2 Nanotubes and Nanowires in Photocatalytic CO2 ReductionT12-P02 University of Alberta | Activity | 2017-10-12 | | | Chalcogenide Semiconductor Nanomaterials for Photocatalytic ApplicationsT12-P02 University of Alberta | Activity | 2017-10-12 | | | 2D C-N Semiconductors: Graphitic, Earth-Abundant Photocatalysts with Tunable BandgapsT12-P02 University of Alberta | Activity | 2018-03-14 | Pawan Kumar, Ujwal Thakur, Guy Bernard, Ehsan Vahidzadeh, Shankar, K. | | Exploiting Nanophotonics and Plasmonic Hot Electrons for the Production of Solar FuelsT12-P02 University of Alberta | Activity | 2018-03-14 | | | CO2 reduction performance of TiO2 nanotube-based heterojunction photocatalystsT12-P02 University of Alberta | Activity | 2018-03-14 | | | Atomistic insights on Halide Composition in Mixed Halide Perovskite Systems: 207Pb solid-state NMR perspectiveT12-P02 University of Alberta | Activity | 2017-11-16 | "Abdelrahman Askar ", Abhoy Karmakar, Benjamin Wiltshire, Sahil Patel, Guy Bernard, Vladimir K Michaelis, Shankar, K. | | Preferentially Oriented Zn-Doped TiO2 Nanotubes Grown on Non-Native SubstratesT12-P02 University of Alberta | Activity | 2017-11-13 | | | Application of One Dimensional Metal Oxides as Electron transport layer for High Efficiency Halide Perovskite Solar Cells (HPSCs)T12-P02 University of Alberta | Activity | 2017-11-15 | | | Composition-Tunable Formamidinium Lead Mixed Halide Perovskites via Solvent-Free Mechanochemical Synthesis: Decoding the Pb Environments Using Solid-State NMR SpectroscopyMixed-halide lead perovskites are becoming of paramount interest in the optoelectronic and photovoltaic research fields, offering band gap tunability, improved efficiency, and enhanced stability compared to their single halide counterparts. Formamidinium-based mixed halide perovskites (FA-MHPs) are critical to obtaining optimum solar cell performance. Here, we report a solvent-free mechanochemical synthesis (MCS) method to prepare FA-MHPs, starting with their parent compounds (FAPbX3; X = Cl, Br, I), achieving compositions not previously accessible through the solvent synthesis (SS) technique. By probing local Pb environments in MCS FA-MHPs using solid-state nuclear magnetic resonance spectroscopy, along with powder X-ray diffraction for long-range crystallinity and reflectance measurements to determine the optical band gap, we show that MCS FA-MHPs form atomic-level solid solutions between Cl/Br and Br/I MHPs. Our results pave the way for advanced methods in atomic-level structural understanding while offering a one-pot synthetic approach to prepare MHPs with superior control of stoichiometry.T12-P02, T12-Z01, T12-Q01 University of Alberta | Publication | 2018-05-01 | Abdelrahman M Askar, Abhoy Karmakar, Guy Bernard, Michelle Ha, Victor V Terskikh, Benjamin Wiltshire, Sahil Patel, Jonathan Fleet, Shankar, K., Vladimir K Michaelis | | Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum dots (CNFQDs) for visible light driven water splittingGraphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and transfer of holes to the aqueous electrolyte. CNFQD-sensitized TiO2 nanorods exhibited a strong photoelectrochemical response up to 500 nm. Reuse experiments confirmed robustness and long term stability of the sample without exhausting the catalytic performance. The present work demonstrates a new pathway to sensitize TiO2 to visible photons by the in situ formation of embedded heterojunctions with fluorine doped carbon nitride quantum dots.T12-P02, T12-P03 University of Alberta | Publication | 2018-05-12 | Pawan Kumar, Ujwal Thakur, Kazi Alam, Piyush Kar, Ryan Kisslinger, Sheng Zeng, Sahil Patel, Shankar, K. | | Distinguishing between deep trapping transients of electrons and holes in TiO 2 nanotube arrays using planar microwave resonator sensorA large signal DC bias and a small signal microwave bias were simultaneously applied to TiO2 nanotube membranes mounted on a planar microwave resonator. The DC bias modulated the electron concentration in the TiO2 nanotubes, and was varied between 0 and 120 V in this study. Transients immediately following the application and removal of DC bias were measured by monitoring the S-parameters of the resonator as a function of time. The DC bias stimulated Poole-Frenkel type trap-mediated electrical injection of excess carriers into TiO2 nanotubes which resulted in a near constant resonant frequency but a pronounced decrease in the microwave amplitude due to free electron absorption. When ultraviolet illumination and DC bias were both present and then step-wise removed, the resonant frequency shifted due to trapping -mediated change in the dielectric constant of the nanotube membranes. Characteristic lifetimes of 60-80 s, 300−800 s and ~3000 s were present regardless of whether light or bias was applied and are also observed in the presence of a hole scavenger, which we attribute to oxygen adsorption and deep electron traps while another characteristic lifetime > 9000 s was only present when illumination was applied, and is attributed to the presence of hole traps.T12-P02 University of Alberta | Publication | 2018-05-16 | Mohammad H Zarifi, Benjamin Wiltshire, Najia Mahdi, Shankar, K., Mojgan Daneshmand | | Sunlight-driven water-splitting using two dimensional carbon based semiconductorsThe overwhelming challenge of depleting fossil fuels and anthropogenic carbon emissions has driven research into alternative clean sources of energy. To achieve the goal of a carbon neutral economy, the harvesting of sunlight by photocatalysts to split water into hydrogen and oxygen is an expedient approach to fulfill energy demand in a sustainable way along with reducing the emission of greenhouse gases. Even though the past decades have witnessed intensive research into inorganic semiconductor photocatalysts, the quantum efficiencies for hydrogen production from visible photons remain too low for the large scale deployment of this technology. Visible light absorption and efficient charge separation are two key necessary conditions for achieving the scalable production of hydrogen from water. Two-dimensional carbon based nanoscale materials such as graphene oxide, reduced graphene oxide, carbon nitride, modified 2D carbon frameworks and their composites have emerged as potential photocatalysts due to their astonishing properties such as superior charge transport, tunable energy levels and bandgaps, visible light absorption, high surface area, easy processability, quantum confinement effect, and high photocatalytic quantum yields. The feasibility of structural and chemical modification to optimize visible light absorption and charge separation makes carbonaceous semiconductors promising candidates to convert solar energy into chemical energy. In the present review, we have summarized the recent advances in 2D carbonaceous photocatalysts with respect to physicochemical and photochemical tuning for solar light mediated hydrogen evolution.T12-P02, T12-P03 University of Alberta | Publication | 2018-05-24 | | | TiO2 Nanotube - Noble Metal Nanoparticle Heterojunction Photocatalysts for CO2 ReductionThe sunlight-driven transformation of CO2 into hydrocarbon fuels is a highly challenging photocatalytic reaction which involves six to eight electron transfer steps. Even though titanium dioxide nanomaterials are currently some of the best performing photocatalysts for CO2 reduction, the reaction yields for CO2 photoreduction are currently limited by (i) Inadequate harvesting of visible photons (ii) Poor adsorption of reactants on to catalyst surfaces (iii) Inefficient charge transfer to adsorbates and (iv) Recombination losses. Amongst various types of titania nanomaterials, vertically oriented TiO2 nanotube arrays stand out for their self-organization and tunability of geometric dimensions (diameter, wall-thickness, tube length and intertubular spacing). When TiO2 nanotubes are decorated with noble metal nanoparticles (NPs), the resulting heterojunctions are able to overcome or mitigate the technical problems limiting higher CO2 reduction rates and we have been able to achieve methane yields as high as 3.7 mL g-1 h-1. Isotope labeled reactants were used to verify that the reaction products were indeed formed due to CO2 reduction. However the phase composition of TiO2, the nature of the noble metal NP deposition process, and the type of noble metal used play a critical role in determining the performance of CO2 reduction photocatalysts based on such heterojunctions. Our investigations showed that anatase-rutile mixtures perform better than either anatase or rutile alone. Similarly, photodeposition and grafting of colloidal NPs on to the nanotubes were found to be superior methods to form the heterojunction compared to direct vacuum deposition (sputtering) of noble metal islands followed by annealing. T12-P02 University of Alberta | Activity | 2018-06-20 | | | Optical Modelling of Non-Lithographically Fabricated Photonic Crystal- and Plasmonic- PhotocatalystsHigh performance photocatalysts need to make optimal use of incident light to drive chemical reactions. Photonic crystals are materials consisting of microscale- and submicron-scale periodicity in their refractive index wherein the propagation of light is prohibited in a certain frequency band (called the photonic stop-band). When pi-conjugated molecules or quantum dots are introduced into a photonic crystal whose absorption profile matches the photonic stop band, very strong absorption can result in such defect-doped photonic crystals, which is useful for photocatalysis. Likewise, nanoscale- and submicron-scale noble metal structures exhibit strong surface plasmon resonances (SPR) that result in an amplification of the local field and the generation of energetic carriers called "hot electrons". The exploitation of SPR in photocatalysis forms the basis for the rapidly expanding field of plasmonic photocatalysis. Herein, we present the results of three-dimensional finite difference time domain (3D-FDTD) electromagnetic simulations of solution grown photonic crystal and plasmonic materials for photocatalytic applications. These simulations are tremendously helpful in explaining experimental data and in obtaining predictive insights into the optimal geometries. Unlike lithographically patterned nanomaterials with deterministically positioned absorbers and scatterers, the underlying spatial configuration in non-lithographically fabricated photonic crystals and plasmonic materials is frequently unclear, thus requiring a heuristic and iterative modelling approach to obtain useful information.T12-P02, T12-P03 University of Alberta | Activity | 2018-06-20 | Sheng Zeng, Ajay Manuel, Ehsan Vahidzadeh, Collin VanEssen, Yun Zhang, Piyush Kar, Shankar, K. | | One Dimensional Metal Oxide Semiconductors as Electron Transport Layers for High Efficiency Halide Perovskite Solar Cells (HPSCs)Organometal trihalide perovskite semiconductor solar cells (HPSCs) have ushered in a new paradigm in the field of photovoltaics due to their high performance, facile synthesis, low cost and excellent optoelectronic properties. For optimal performance, HPSCs require an electron transport layer (ETL) that ensures efficient contact with the perovskite active layer and selectively transfers photogenerated electrons to the underlying electrode while also blocking holes. We report HPSCs with photoconversion efficiencies as high as 17.6 % using TiO2 nanorods (NR) as the ETL and a mixed halide, mixed cation organometal perovskite FAxMA1-xPbBryI3-y with optimized composition as the active layer. We found that one-dimensional TiO2 NR ETLs not only improved electron transport but also introduced nanophotonic enhancements through a more optimal management of incident light. We used two distinct geometric configurations of nanorods, one in which the NRs were oriented vertically to the transparent conductive oxide (TCO) substrate, and another in which the NRs were roughly horizontally oriented with their longer axes in the substrate plane. Both types of NRs exhibited superior quenching of the perovskite photoluminescence compared to flat, planar ETLs indicating improved electron extraction. However, the horizontal NRs also exhibited a higher photonic strength in the form of a more directional light scattering. The enhanced forward scattering of light by the horizontal nanorods compared to the suppressed backscattering improved the utilization of incident light within the perovskite layer and increased light harvesting across a wide spectral range.T12-P02 University of Alberta | Activity | 2018-06-20 | Ujwal Thakur, Sheng Zeng, "Ashwin Lele ", Al Meldrum, Shankar, K. | | Visible Light Responsive, Earth-Abundant Heterojunction PhotocatalystsT12-P02, T12-P03 University of Alberta | Activity | 2018-06-11 | | | Enhancing Photocatalyst and Solar Cell Performance Using Nanophotonic EffectsT12-P02 University of Alberta | Activity | 2018-06-11 | | | All-solid-state formation of titania nanotube arrays and their application in photoelectrochemical water splittingThe present work demonstrates for the first time the facile fabrication of TiO2 nanotube arrays (TNTAs) by a fluoride-free solid-state anodization process using LiClO4 containing solid polymeric electrolyte. The resulting nanotubes were tested for photoelectrochemical water splitting. The elimination of liquid electrolytes in electrochemical anodization constitutes a paradigm shift for the formation of nanoporous and nanotubular metal oxides. Our results open a new area of research that uses the distinctive properties of solid polymer electrolytes to achieve targeted doping and nano-morphologies. Characterization of the grown TNTAs indicated solid state anodized TNTAs to consist purely of the anatase phase of titania. The solid-state anodization process provides several advantages over conventional liquid electrolytes such as easy handling and processing, better charge transport, environmentally benign chemicals and methodology. Photoelectrochemical water splitting experiments were performed which confirmed the viability of TNTAs grown by the new solid-state process for photocatalytic applications.T12-P02, T12-P03 University of Alberta | Publication | 2018-08-08 | "Arezoo Hosseini ", Pawan Kumar, Najia Mahdi, Yun Zhang, Shankar, K. | | High Rate CO2 Photoreduction Using Flame Annealed TiO2 NanotubesThe photocatalytic reduction of CO2 into light hydrocarbons using sunlight and water is a challenging reaction involving eight electron transfer steps; nevertheless, it has great potential to address the problem of rising anthropogenic carbon emissions and enable the use of fossil fuels in a sustainable way. Several decades after its first use, TiO2 remains one of the best performing and most durable photocatalysts for CO2 reduction albeit with a poor visible light absorption capacity. We have used flame annealing to improve the response of TiO2 to visible photons and engineered a nanotubular morphology with square-shaped cross-sections in flame-annealed nanotubes. An enhanced CH4 yield was achieved in the photoreduction of CO2 using flame annealed TiO2 nanotubes, and isotope labeled experiments confirmed the reaction products to originate from the CO2 reactant. Flame-annealed TiO2 nanotubes formed in aqueous electrolyte (FANT-aq) yielded 156.5 µmol gcatalyst–1.hr–1 of CH4, which is in the top tier of reported performance values achieved using TiO2 as a stand-alone photocatalyst. This performance resulted because appreciable amounts of CH4 were generated under visible light illumination as well. TiO2 nanotubes exhibited CO2 photoreduction activity up to a wavelength of 620 nm with visible light driven photocatalytic activity peaking at 450 nm for flame annealed TiO2 nanotubes. Isotope labeling studies, using GC-MS and gas-phase FTIR, indicated photoreduction of 13CO2 to 13CH4. The detection of 13CO in the product mixture, and the absence of HCHO and HCOOH provides strong support for the photoreduction proceeding along a carbene pathway. The enhanced CO2 photoreduction performance of FANT-aq is attributed to increased visible light absorption, square morphology, and the presence of rutile as the only crystalline phase with (110) as the dominant plane.T12-P02 University of Alberta | Publication | 2018-08-08 | Piyush Kar, Sheng Zeng, Yun Zhang, Ehsan Vahidzadeh, Ajay Manuel, Ryan Kisslinger, Kazi Alam, Ujwal Thakur, Najia Mahdi, Pawan Kumar, Shankar, K. | | Enhanced Charge Separation in g-C3N4–BiOI Heterostructures for Visible Light Driven Photoelectrochemical Water SplittingT12-P02, T12-P03 University of Alberta | Publication | 2019-01-07 | Kazi Alam, Pawan Kumar, Piyush Kar, Ujwal Thakur, Sheng Zeng, "Kai Cui ", Shankar, K. | | Plexcitonics – Fundamental principles and optoelectronic applicationsThe nanoscale confinement and coupling of electromagnetic radiation into plexcitonic modes has drawn immense interest because of the innovative possibilities for their application in light harvesting and light emitting devices (LEDs). Plexcitons arise from the coupling between two types of quasiparticles, plasmons and excitons, and can be distinguished by the strength of the coupling into strong and weak coupling regimes. Plexcitons have been used to modulate the rate of Förster-type resonance energy transfer in quantum dot assemblies and enhance the spontaneous emission rate in quantum dot LEDs. The clearest examples of a plexcitonic enhancement of photocatalytic reaction rates have been evidenced in hybrid systems wherein the strongly bound exciton found in 2D sheet-like semiconductors is coupled to the surface plasmon resonance of close-lying noble metal nanoparticles. Plexcitonic photocatalysts and solar cells aim to increase the lifetime of hot carriers and thereby enhance the quantum yields for energy harvesting. Since plexcitonics requires the placement of plasmonic and excitonic components in close proximity with one another to facilitate their coupling, it provides a rich arena for chemists and materials scientists to form deterministic and non-deterministic arrays and heterojunctions involving noble metal thin films and nanostructures, quantum dots and dye molecules. This review summarizes the dynamics of plexcitons in the various composite systems and provides an overview of the latest theoretical and experimental developments in the field of plexcitonics.T12-P02, T12-P03, T12-P04 University of Alberta | Publication | 2019-01-02 | | | Melanin-based electronics: From proton conductors to photovoltaics and beyondT12-P02, T12-P04 University of Alberta | Publication | 2018-09-07 | | | Triplet excitons: improving exciton diffusion length for enhanced organic photovoltaicsT12-P02, T12-P04, T12-Z01 University of Alberta | Publication | 2019-01-05 | Bruno Luppi, "Darren Majak ", Manisha Gupta, Eric Rivard, Shankar, K. | | Preferentially Oriented TiO2 Nanotube Arrays on Non-Native Substrates and Their Improved Performance as Electron Transporting Layer in Halide Perovskite Solar CellsT12-P02, T12-P04 University of Alberta | Publication | 2019-10-19 | Ryan Kisslinger, "Abdelrahman Askar ", Ujwal Thakur, Saralyn Riddell, Darren Dahunsi, Yun Zhang, Sheng Zeng, Ankur Goswami, Shankar, K. | | Hexagonal Double Perovskite Cs2AgCrCl6Published in a special issue celebrating the 60th birthday of Thomas Fässler (a renowned main-group
inorganic chemist at the Technical University of Munich), this invited paper reports on a new double
perovskite (belong to the family of halide perovskites that are of current popular interest as photovoltaic materials) that is unexpectedly not cubic but rather hexagonal.T12-P01, T12-P02 University of Alberta | Publication | 2018-10-31 | | | Nanophotonic enhancement and improved electron extraction in perovskite solar cells using near-horizontally aligned TiO2 nanorodsWhile vertically oriented metal oxide nanowires have been intensely researched for use as electron transport layers (ETLs) in halide perovskite solar cells (HPSCs), horizontal nanowires (oriented roughly parallel to the substrate) have received much less attention despite their higher photonic strength due to overlapping electric and magnetic dipolar Mie resonance modes. Herein, we demonstrate the fabrication of an assembly of horizontally aligned TiO2 nanorods (HATNRs) on FTO substrates via a facile hydrothermal route. The HATNRs are employed as the ETL to achieve 15.03% power conversion efficiency (PCE) in HPSCs which is higher than the PCE of compact TiO2 based devices (10.12%) by a factor of nearly 1.5. A mixed halide, mixed cation organometal perovskite FA0.83MA0.17Pb(Br0.17I0.83)3 with optimized composition is used as the active layer. The excellent refractive index matching between the perovskite and TiO2, coupled with strong Mie scattering in the nanorod geometry results in broadband near-zero backscattering and high forward scattering, upon coating of HATNRs with perovskite. The maximum suppression of backscattering is found at ∼600 nm. The HATNRs ETL also improves the extraction of electrons from the perovskite layer and results in superior blocking of carrier recombination at the perovskite layer/FTO interface.T12-P02 University of Alberta | Publication | 2019-01-29 | Ujwal Thakur, Sheng Zeng, Pawan Kumar, Sahil Patel, Ryan Kisslinger, Yun Zhang, Piyush Kar, Ankur Goswami, "Thomas Thundat ", Al Meldrum, Shankar, K. | | Organic-Inorganic Nanohybrid Materials for Photovoltaic ApplicationsThin film morphology is a key factor determining the performance of bulk heterojunction organic-inorganic solar cells through its influence on charge separation, charge transport and recombination losses in donor-acceptor blends. With this respect, both descriptive and predictive modeling of structural properties of blends of organic-inorganic perovskites of the type CH3NH3PbX3 (X=Cl, Br, or I) with P3HT or P3BT, including adsorption on TiO2 clusters having rutile (110) surface, is presented with the use of a methodo-logy that allows computing the microscopic structure of blends on the nanometer scale. The methodology is based on the integral equation theory of molecular liquids in the reference interaction site model and uses the universal force field. It provides a detailed microscopic insight into the organization of solvent molecules in the solvation shell structure and their contribution to the solvation thermodynamics. The calculated nanoscale morphologies serve as an instrument in rational design of hybrid photovoltaics.T12-P02 University of Alberta | Publication | 2019-01-29 | | | Novel Materials for Clean and Sustainable Energy CHALLENGE PROGRAM WORKSHOPThis was an INVITATION-ONLY workshop related to a major new funding initiative in Clean-Tech, spearheaded by NRC. The purpose of my participation in the workshop was to deliver input in helping to refine the R&D areas and start identifying key projects and partners that would help NRC to collaboratively deliver next generation materials for clean and sustainable energy technologies.T12-P02, T12-P03 University of Alberta | Activity | 2018-12-06 | | | C3N5: A Low Bandgap Semiconductor Containing an Azo-linked Carbon Nitride Framework for Photocatalytic, Photovoltaic and Adsorbent ApplicationsModification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of melem hydrazine precursor. Characterization revealed that in C3N5 polymer, two s-heptazine units are bridged together with azo linkage, which constitutes an entirely new and different bonding fashion from g-C3N4 where three heptazine units are linked together with tertiary nitrogen. Extended conjugation due to overlap of azo nitrogens and increased electron density on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum resulting in bandgap reduction down to 1.76 eV. XRD, He-ion imaging, HR-TEM, EELS, PL, fluorescence life time imaging, Raman, FTIR, TGA, KPFM etc clearly show that the properties of C3N5 are distinct from pristine carbon nitride (g-C3N4). When used as an electron transport layer (ETL) in MAPbBr3 based halide perovskite solar cells, C3N5 outperformed g-C3N4, in particular generating an open circuit photovoltage as high as 1.3 V, while C3N5 blended with MAxFA1-xPb(I0.85Br0.15)3 perovskite active layer achieved a photoconversion efficiency (PCE) up to 16.7 %. C3N5 was also shown to be an effective visible light sensitizer for TiO2 photoanodes in photoelectrochemical water splitting. Due to its electron- rich character, the C3N5 material displayed instantaneous adsorption of methylene blue from aqueous solution reaching complete equilibrium within 10 min, which is significantly faster than pristine g-C3N4 and other carbonbased materials. C3N5 coupled with plasmonic silver nanocubes promotes plasmon-exciton coinduced surface catalytic reactions reaching completion at much low laser intensity (1.0 mW) than g-C3N4 which showed sluggish performance even at high laser power (10.0 mW). The relatively
narrow bandgap and 2D structure of C3N5 make it an interesting air-stable and temperature resistant semiconductor for optoelectronic applications while its electron- rich character and intrasheet cavity make it an attractive supramolecular adsorbent for environmental applications. T12-P02, T12-Z01, T12-Q01 University of Alberta | Publication | 2019-02-14 | Pawan Kumar, Ehsan Vahidzadeh, Ujwal Thakur, Piyush Kar, Kazi Alam, Ankur Goswami, Najia Mahdi, "Kai Cui ", Guy Bernard, Vladimir K Michaelis, Shankar, K. | | CO2 photoreduction using earth abundant transition metal oxides & chalcogenidesInvitation Only Workshop related to the NRC Energy Materials ChallengeT12-P02 University of Alberta | Activity | 2019-02-21 | | | A Rational Design of Cu2O-SnO2 Core-Shell Catalyst for Highly Selective CO2-to-CO ConversionT02-P03, T12-P02 University of Alberta | Publication | 2019-04-16 | Sheng (Shawn) Nian Zhang, Meng Li, Bin Hua, "Nanqi Duan ", Shaochen Ding, Bergens, S., Shankar, K., Luo, J. | | Flame Annealed TiO2 and its Heterojunctions for the Production of Solar FuelsFlame annealed TiO2 received significant attention in the early 2000s as a method to improve the visible light responsivity of titania through the introduction of defects and dopants. In a highly cited but controversial paper, S.U.M. Khan and colleagues reported on highly efficient water-splitting using flame annealed TiO2 thin films
in the journal Science in 2002. Due to problems with the reproducibility of the reported results, spectral mismatch issues and potentially unphysical mechanisms, this line of research was abandoned. In the last few years, there has been a resurgence of interest in Black TiO2, which is a defect rich form of reduced titania exhibiting visible light absorption over a broad spectral range. Recently, the Shankar Lab found that flame annealing anodically formed TiO2 nanotube arrays produced an unusual morphological transition from circular to square-shaped cross-sections, which was accompanied by changes in the density of Ti3+ states and the phase composition. Using isotope-labeled mass spectrometry, we observed that flame annealed nanotubes significantly outperformed regular nanotubes in
the photoreduction of CO2 to methane while harvesting blue light. Flame annealed titania nanotubes also performed better than regular nanotubes in photoelectrochemical water splitting. This Invited Talk will focus on the use of flame annealed TiO2 nanotubes for the production of solar fuels.T12-P02, T12-P03 University of Alberta | Activity | 2019-03-06 | | | Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems Based on SnIPT12-P02, T12-P03 University of Alberta | Publication | 2019-03-13 | "Claudia Ott ", "Felix Reiter ", "Maximilian Baumgartner ", "Markus Pielmeier ", "Anna Vogel ", "Patrick Walke ", "Stefan Burger ", "Michael Ehrenreich ", "Gregor Kieslich ", "Dominik Daisenberger ", "Jeff Armstrong ", Ujwal Thakur, Pawan Kumar, "Shunda Chen ", "Davide Donadio ", "Lisa Walter ", "Thomas Weitz ", Shankar, K., "Tom Nilges " | | Vapor growth of binary and ternary phosphorus-based semiconductors into TiO2 nanotube arrays and application in visible light driven water splittingWe report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12) were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing vapor phase reaction deposition, the cavities of 100 μm long TiO2 nanotubes were infiltrated; approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water splitting performance compared to pristine materials and were found to be more active at higher wavelengths. SnIP@TiO2 emerged to be the most active among the polyphosphide@TiO2 materials. The improved photocatalytic performance might be due to Fermi level re-alignment and a lower charge transfer resistance which facilitated better charge separation from inorganic phosphides to TiO2.T12-P02, T12-P03 University of Alberta | Publication | 2019-05-24 | "Ebru Uzer ", Pawan Kumar, Ryan Kisslinger, Piyush Kar, Ujwal Thakur, Shankar, K., "Tom Nilges " | | Vapor Deposition of Semiconducting P Allotropes into TiO2 Nanotube Arrays for Photo-Electrocatalytic Water SplittingRecent evidence of exponential environmental degradation will demand a drastic shift in research and development toward exploiting alternative energy resources such as solar energy. Here, we report the successful low-cost and easily accessible synthesis of hybrid semiconductor@TiO2 nanotube photocatalysts. In order to realize its maximum potential in harvesting photons in the visible-light range, TiO2 nanotubes have been loaded with earth-abundant, low-band-gap fibrous red and black phosphorus (P). Scanning electron microscopy– and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV–vis measurements have been performed, substantiating the deposition of fibrous red and black P on top and inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular morphology of titania and a vapor-transport technique are utilized to form heterojunctions of P and TiO2. Compared to pristine anatase 3.2 eV TiO2 nanotubes, the creation of heterojunctions in the hybrid material resulted in 1.5–2.1 eV photoelectrocatalysts. An enhanced photoelectrochemical water-splitting performance under visible light compared with the individual components resulted for the P@TiO2 hybrids. This feature is due to synergistically improved charge separation in the heterojunction and more effective visible-light absorption. The electronic band structure and charge-carrier dynamics are investigated in detail using ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy to elucidate the charge-separation mechanism. A Fermi-level alignment in P@TiO2 heterojunctions leads to a more reductive flat-band potential and a deeper valence band compared to pristine P and thus facilitates a better water-splitting performance. Our results demonstrate effective conversion efficiencies for the nanostructured hybrids, which may enable future applications in optoelectronic applications such as photodetectors, photovoltaics, photoelectrochemical catalysts, and sensors.T12-P02, T12-P03 University of Alberta | Publication | 2019-05-09 | "Ebru Uzer ", Pawan Kumar, Ryan Kisslinger, Piyush Kar, Sheng Zeng, Shankar, K., "Tom Nilges " | | Exposing Halide-Mixing in Hybrid Perovskite Materials Using Solid-State NMRPoster PresentationT12-P02, T12-Z01 University of Alberta | Activity | 2018-07-22 | Abhoy Karmakar, Guy Bernard, Michelle Ha, Shankar, K., Vladimir K Michaelis, A M Askar,, V V Terskikh, | | Photoelectrochemical Reduction of CO2Poster presentation on "Photoelectrochemical Reduction of CO2" at the 2018 Future Energy System research symposium on March 14th, 2018.T02-P03 University of Alberta | Activity | 2018-03-14 | | | Syngas Production via Photoelectrochemical Reduction of CO2 with H2OPoster presentation titled "Syngas Production via Photoelectrochemical Reduction of CO2 with H2O" at the 2018 FEGRS research symposium on July 4th, 2018.T02-P03 University of Alberta | Activity | 2018-07-04 | | | Noble Metal Free, Visible Light Driven Photocatalysis Using TiO2 Nanotube Arrays Sensitized by P-doped C3N4 Quantum DotsBulk g-C3N4 is an earth-abundant, easily synthesizable, and exceptionally stable photocatalyst with an electronic bandgap of 2.7 eV. Herein, the concepts of P-doping and size quantization are combined to synthesize highly fluorescent P-doped carbon nitride quantum dots (CNPQDs) with a bandgap of 2.1 eV. CNPQDs are hosted on anatase-phase and rutilephase TiO2 nanotube array scaffolds, and examined as photoanodes for sunlight-driven water-splitting and as photocatalysts for surface catalytic reactions. Square-shaped rutile phase TiO2 nanotube arrays (STNAs) decorated with CNPQDs (CNPQD-STNA) generate 2.54 mA cm−2 under AM1.5 G simulated sunlight. A champion hydrogen evolution rate of 22 µmol h−1 corresponds to a Faradaic efficiency of 93.2%. In conjunction with Ag nanoparticles (NPs), the CNQPD-STNA hybrid is also found to be an excellent plexcitonic photocatalyst for the visible light-driven transformation of 4-nitrobenzenethiol (4-NBT) to dimercaptoazobenzene (DMAB), producing reaction completion at a laser power of 1 mW (532 nm) while Ag NP/TNA and Ag NP/STNA photocatalysts cannot complete this transformation even at 10 mW laser power. The results point the way forward
for photochemically robust, noble metal free, visible light harvesting photoacatalysts based on nanostructured heterojunctions of graphenic frameworks with TiO2.T12-P02, T12-P03 University of Alberta | Publication | 2019-10-17 | Pawan Kumar, Piyush Kar, Ajay Manuel, Ujwal Thakur, Kazi Alam, Yun Zhang, Ryan Kisslinger, Sheng Zeng, "Kai Cui ", Guy Bernard, Vladimir K Michaelis, Shankar, K. | | Multiscale modeling of active layer of hybrid organic-inorganic solar cells for photovoltaic applications by means of density functional theory and integral equation theory of molecular liquidsPhotovoltaic devices convert solar energy into electricity and are promising candidates to reduce carbon emission while providing an alternative way to meet increasing demand in energy consumption. In recent years, organic or hybrid organic-inorganic photovoltaic devices demonstrate steady increase in performance and stability and a promising tendency toward the low production cost. To make them attractive for commercial production, however, a deep understanding and ability to predict physical, chemical and electrochemical processes occurring in photovoltaic conversion layer is needed. Here, we present multiscale modeling of electronic and structural properties of hybrid organic-inorganic perovskites (OIP) of the type CH3NH3PbX3, X = Br, Cl, I, in contact with organic molecules of P3BT, P3HT, or SQ02, including adsorption on inorganic substrates of TiO2. Our methodology is based on Density Functional Theory (DFT) and integral equation theory of molecular liquids in the Reference Interaction Site Model (RISM). We apply it to study the photovoltaic thin film nanomorphology and determine the key factors affecting the performance of OIP-based bulk heterojunction solar cells through their influence on charge separation, charge transport and recombination losses in donor-acceptor blends. These factors include chemical composition of heterojunctions and mutual orientation of molecules on the border of the donor-acceptor or donor-acceptor-substrate systems. Since the formation of thin active layer of solar cells occurs in fluidic phase, we also provide a detailed microscopic insight into the organization of solvent molecules in the solvation shell structure and their contribution to the solvation thermodynamics. In total, these properties define charge transfer processes from donor to acceptor and are utilized in development of new generation organic and hybrid organic-inorganic solar cells. The calculated nanoscale morphologies serve as a guide in rational design of organic or hybrid photovoltaics.T12-P02 University of Alberta | Publication | 2019-09-01 | | | Heterojunctions of halogen-doped carbon nitride nanosheets and BiOI for sunlight-driven water-splittingA fluorine-doped, chlorine-intercalated carbon nitride (CNF-Cl) photocatalyst has been synthesized for simultaneous improvements in light harvesting capability along with suppression of charge recombination in bulk g-C3N4. The formation of heterojunctions of these CNF-Cl nanosheets with low bandgap, earth abundant bismuth oxyiodide (BiOI) was achieved, and the synthesized heterojunctions were tested as active photoanodes in photoelectrochemical water splitting experiments. BiOI/CNF-Cl heterojunctions exhibited extended light harvesting with a band-edge of 680 nm and generated photocurrent densities approaching 1.3 mA cm−2 under AM1.5 G one sun illumination. Scanning Kelvin probe force microscopy under optical bias showed a surface potential of 207 mV for the 50% BiOI/CNF-Cl nanocomposite, while pristine CNF-Cl and BiOI had surface photopotential values of 83 mV and 98 mV, respectively, which in turn, provided direct evidence of superior charge separation in the heterojunction blends. Enhanced charge carrier separation and improved light harvesting capability in BiOI/CNF-Cl hybrids were found to be the dominant factors in increased photocurrent, compared to the pristine constituent materials.T12-P02, T12-P03 University of Alberta | Publication | 2019-11-01 | Kazi Alam, Pawan Kumar, Piyush Kar, Ankur Goswami, Ujwal Thakur, Sheng Zeng, Ehsan Vahidzadeh, Kai Cui, Shankar, K. | | CVD grown nitrogen doped graphene is an exceptional visible-light driven photocatalyst for surface catalytic reactionsThe photocatalytic potential of large area CVD grown nitrogen doped graphene (NGr) has been explored though the chemical transformation of 4-nitrobenzene thiol into p,p'-dimercaptoazobenzene. Decoration of NGr with Ag nanocubes with rounded edges to form NGr/Ag nanohybrids resulted in a slight increase in the work-function and a decrease in the n-type character of NGr due to ground state transfer of negative charge from NGr to Ag. The Ag nanocubes exhibited a localized surface plasmon resonance (LSPR) at ~425 nm. When the NGr/Ag nanohybrids were illuminated with visible light of wavelength close to the LSPR peak, Kelvin probe force microscopy (KPFM) indicated a dramatic change in surface potential of −225 mV and Raman spectra detected electron accumulation in NGr, which are attributed to a high local field enhancement-mediated hot electron injection into NGr and the formation of long-lived charge separated states. Pristine nitrogen doped graphene and its coupled system with plasmonic Ag nanoparticles showed superior photocatalytic performance compared to bare plasmonic Ag catalyst. While standalone Ag NPs were unable to complete the transformation of 4-NBT into DMAB even at a laser power of 10 mW, NGr/Ag nanohybrids completed this transformation at a laser power of 1 mW, pointing to the high photoreduction strength of NGr/Ag. Density functional theory (DFT) based computational modeling was used to examine the electronic structure of graphene doped with graphitic, pyridinic and pyrrolic nitrogen dopant atoms. DFT results indicated an enhanced chemical reactivity of NGr due to stronger localization of charge at the dopant sites and a pronounced difference in the projected density of states (PDOS) for carbon atoms in proximity to, and distant from, the nitrogen dopant sites.T12-P02 University of Alberta | Publication | 2019-10-01 | Kazi Alam, Pawan Kumar, Ajay Manuel, Ehsan Vahidzadeh, Ankur Goswami, Sheng Zeng, Wenjie Wu, Najia Mahdi, Kai Cui, Alexander E Kobryn, Sergey Gusarov, Yenan Song, Shankar, K. | | Use of Periodic Pulses and Non-Native Substrates to Form Nanoporous Metal Oxide Films By AnodizationElectrochemical anodization is a robust and versatile fabrication method to form arrays of ordered nanopores and nanotubes in a number of metal oxides including Al2O3, TiO2, Ta2O5, Nb2O5, Fe2O3, ZnO, WO3, NiO and ZrO2 [1]. The key advantages of anodization are simplicity, low cost, solution-based processing, large area compatibility and mass-producibility. The anodic formation of oriented and aligned nanostructures has also been extended to metal chalcogenides [2]. A majority of the aforementioned metal oxide and chalcogenide compounds exhibit semiconducting behavior. Consequently, the anodically formed nanostructures in these compounds are high surface area semiconductors (typically after a crystallizing anneal) that are nearly ideal for the formation of electronic heterojunctions for sensing, photocatalysis, photovoltaics and light emission [3-5].
An emerging frontier in electrochemical anodization consists of imparting nanophotonic enhancement(s) to the semiconducting properties of highly ordered metal oxide nanopore (MONPAs) and nanotube arrays (MONTAs). Examples of such nanophotonic enhancements include the bottom-up, solution-based growth of photonic crystals, metamaterials and plexcitonic substrates. Nanophotonic enhancements enable light trapping in heterojunction photocatalysts and photovoltaic devices in order to harvest solar radiation more completely. Nanophotonic enhancements can also be used to control the directionality, intensity and lifetime of photoluminescence, and generate high Q-factor collective resonances to boost sensitivity in photodetectors, immunoassays and small molecules SERS-based sensing.
The use of low frequency pulses in the anodization process can be used to periodically modulate the diameter of nanopores and the wall-thickness of nanotubes in the depth direction [6]. Pulsed anodization of metal foils results in metal oxide nanostructures with a periodic refractive index which can be used to fabricate one-dimensional photonic crystals (1D-PhCs) by suitably adjusting the amplitude and pitch of the periodic features. Work in this area has focused on either using pulsed currents or pulsed voltages during anodization to form 1D-PhCs. One major limitation of the anodic growth of photonic crystals is the lack of control over the stop-band center frequency and the full width at half-maximum (FWHM) of the photonic stop-band resonances. We introduce a new technique, which involves periodically varying the charge supplied to the anodization process. The charge-controlled pulsed anodization process enables superior control over the morphology of the anodic 1D-PhCs and can be used to generate narrower resonances at desired wavelengths. Illustrative examples of the utility of these 1D-PhCs in photocatalysts and sensors are presented in this Invited Lecture.
Another frontier in the anodic formation of metal oxide nanostructures consists of the use of thin metal films on non-native substrates as anodization substrates. Currently, the overwhelming majority of anodization processes use metal foils that are hundreds of micrometers to millimeters in thickness as substrates. For optoelectronic applications, the use of such metal foils is highly limiting due to the opaque substrates preventing light in-coupling and light out-coupling into the nanopore/nanotube array from the substrate direction. Therefore, the formation of MONPAs & MONTAs on transparent substrates such as fluorine-doped tin oxide(FTO)-coated glass and indium tin oxide(ITO)-coated glass, is highly desirable [7]. This Invited Talk will showcase anodically formed MONPAs & MONTAs of TiO2, Ta2O5 and NiO on silicon and conductive glass substrates while also presenting prototypical optoelectronic applications of MONPAs & MONTAs on non-native substrates.
REFERENCES
[1] A. Ghicov and P. Schmuki, Chem. Commun. 0, 2791-2808 (2009).
[2] P. Kar, S. Farsinezhad, X. Zhang and K. Shankar, Nanoscale 6, 14305-14318 (2014).
[3] P. Kar, A. Pandey, J.J. Greer and K. Shankar, Lab on a Chip 12, 821-828 (2012).
[4] S. Farsinezhad, H. Sharma and K. Shankar, Phys. Chem. Chem. Phys. 17, 29723-29733 (2015).
[5] P. Qin, M. Paulose, M. I. Dar, T. Moehl, N. Arora, P. Gao, O. K. Varghese, M. Grätzel and M. K. Nazeeruddin, Small 11, 5533-5539 (2015).
[6] X. Zhang, F. Han, B. Shi, S. Farsinezhad, G.P. Dechaine and K. Shankar, Angew. Chem. Int. Ed. 51, 12732-12735 (2012).
[7] S. Farsinezhad, A. Mohammadpour, A. N. Dalrymple, J. Geisinger, P. Kar, M. J. Brett and K. Shankar, J. Nanosci. Nanotechnol. 13, 2885-2891 (2013).T12-P02 University of Alberta | Activity | 2019-10-14 | | | Planar microwave resonator with electrodeposited ZnO thin film for ultraviolet detectionA ZnO thin film is electrodeposited on the conducting strips of a planar microwave ring resonator to enable the formation of a novel sensor for ultraviolet irradiation. The fabrication of the sensor involves a low-cost process that basically utilizes a printed circuit board and an aqueous precursor solution. The resonator with no ZnO coating operates with a resonant frequency of 6.2 GHz and a quality factor of 170. The time-resolved microwave photoresponse of the sensor to UV illumination, under ambient conditions, is assessed through measurements of the resonance profile of the S21 parameter. The resonance frequency exhibited a highly sensitive downshift of ~ 6 MHz after a UV illumination time of ~ 3 min. This downshift is mostly attributed to the change in the dielectric constant of the ZnO film caused largely by the additional creation of bound charges. The usually reported long-lived and persistent post-illumination effects were not observed. The measurements of the resonance amplitude carried out at 20% and 70% relative humidities revealed average excess carrier relaxation lifetimes of 213 s and 185 s, respectively. Concomitantly, the measured resonance frequency downshifts increased with increased humidity. These results highlight the difference in the interaction mechanisms of photogenerated carriers with water and oxygen molecules on the surface and grain boundaries of the ZnO film. To our knowledge, this UV irradiation sensor is the first ZnO-based sensor device implemented with planar microwave circuit technology. In addition, the capabilities demonstrated by this simple photo-sensing method to determine induced carrier lifetimes make it a valuable technique for an in-depth investigation of the material properties.T12-P02, T07-P04, T07-P04NP University of Alberta | Publication | 2019-12-01 | | | Doped Graphene and Graphenic Semiconductors: Mass Producible, Earth- Abundant Materials for Photocatalysis and PhotovoltaicsT12-P02 University of Alberta | Activity | 2019-06-11 | | | High Voc halide perovskite solar cells using optimized charge transport layersT12-P02 University of Alberta | Activity | 2019-07-29 | Ujwal Thakur, "Sergey Gusarov ", Sheng Zeng, Pawan Kumar, Ankur Goswami, "Alexander Kobryn ", Shankar, K. | | Plasmon-Enhanced Semiconductor Photocatalysis: Using Hot Electrons to Drive Chemical ReactionsT12-P02 University of Alberta | Activity | 2019-07-30 | | | High Selectivity CO2 Photoreduction Using Earth Abundant Semiconductor PhotocatalystsT12-P02 University of Alberta | Activity | 2019-10-23 | Sheng Zeng, Ehsan Vahidzadeh, Ryan Kisslinger, Shankar, K. | | Anodic Fabrication of n- and p-type Metal Oxide Nanostructures on Non-Native SubstratesT12-P02 University of Alberta | Activity | 2019-10-22 | Ryan Kisslinger, Ujwal Thakur, Saralyn Riddell, Shankar, K. | | New frontiers in the anodic synthesis of self-organized TiO2 nanotube arraysT12-P02 University of Alberta | Activity | 2019-09-16 | | | Earth abundant 1D & 2D nanomaterial sensitized TiO2 nanotube arrays for visible light driven water-splittingT12-P02, T12-P03 University of Alberta | Activity | 2019-09-17 | Pawan Kumar, Ryan Kisslinger, Ujwal Thakur, Kazi Alam, "Ebru Uzer ", "Tom Nilges ", Shankar, K. | | Visible Light Driven Photocatalysts Based on New Graphenic Semiconductors and Their HeterojunctionsT12-P02 University of Alberta | Activity | 2019-07-16 | | | Life cycle assessment of mono-crystalline TiO2 nanorod array based halide perovskite solar cellsT12-P02, T13-P04 University of Alberta | Activity | 2019-05-07 | | | Plasmonic photocatalysis and SERS sensing using ellipsometrically modeled Ag nanoisland substratesSilver nano-islands are key platforms for plasmonic photocatalysis, SERS sensing and optical metamaterials due to their localized surface plasmon resonances. The low intrinsic loss in Ag enables high local electromagnetic field enhancements. Solution-based fabrication techniques, while cheap and compatible with high throughput, result in highly non-reproducible plasmonic substrates with wide sample-to-sample variability in geometry, optical resonances and Q-factors. Herein, we present a non-lithographic method of forming silver nano-islands based on sputter deposition of Ag films followed by elevated temperature annealing to induce spontaneous dewetting. The resulting plasmonic substrates show reproducible, well-defined LSPR resonances with high ensemble Q-factors whose optical properties could be modeled using spectroscopic ellipsometry to yield n and k values across the visible range. Our vacuum deposited Ag nanoislands demonstrated excellent photocatalytic activity for the transformation of 4-nitrobenzenethiol (4-NBT) and 4-aminothiophenol (PATP) into p,p'-dimercaptoazobenzene (DMAB).T12-P02 University of Alberta | Publication | 2020-06-01 | Ajay Manuel, Priyash Barya, Saralyn Riddell, Sheng Zeng, Kazi Alam, Shankar, K. | | Consistently High Voc Values in p-i-n Type Perovskite Solar Cells Using Ni3$\mathplus$-Doped NiO Nanomesh as the Hole Transporting LayerLeading edge p-i-n type halide perovskite solar cells (PSCs) severely underperform n-i-p PSCs. p-i-n type PSCs that use PEDOT:PSS hole transport layers (HTLs) struggle to generate open-circuit photovoltage values higher than 1 V. NiO HTLs have shown greater promise in achieving high Voc values albeit inconsistently. In this report, a NiO nanomesh with Ni3+ defect grown by the hydrothermal method was used to obtain PSCs with Voc values that consistently exceeded 1.10 V (champion Voc = 1.14 V). A champion device photoconversion efficiency of 17.75% was observed. Density functional theory modeling was used to understand the interfacial properties of the NiO/perovskite interface. The PCE of PSCs constructed using the Ni3+-doped NiO nanomesh HTL was ∼34% higher than that of conventional compact NiO-based perovskite solar cells. A suite of characterization techniques such as transmission electron microscopy, field emission scanning electron microscopy, intensity-modulated photocurrent spectroscopy, intensity-modulated photovoltage spectroscopy, time-resolved photoluminescence, steady-state photoluminescence, and Kelvin probe force microscopy provided evidence of better film quality, enhanced charge transfer, and suppressed charge recombination in PSCs based on hydrothermally grown NiO nanostructures.T12-P02 University of Alberta | Publication | 2020-01-06 | Ujwal Thakur, Pawan Kumar, Sergey Gusarov, Alexander E Kobryn, Saralyn Riddell, Ankur Goswami, Kazi Alam, Spencer Savela, Piyush Kar, Thomas Thundat, Al Meldrum, Shankar, K. | | Double peak emission in lead halide perovskites by self-absorptionDespite the rapidly increasing efficiencies of perovskite solar cells, the optoelectronic properties of this material class are not completely understood. Especially when measured photoluminescence (PL) spectra consist of multiple peaks, their origin is still debated. In this work, we investigate in detail double peak PL spectra of halide perovskite thin films and single crystals with different material compositions. By different optical spectroscopic approaches and quantitative models, we demonstrate that the additional PL peak results from an extensive self-absorption effect, whose impact is intensified by strong internal reflections. This self-absorption accounts for the unusual temperature dependence of the additional PL peak and it implies that absorption until far into the perovskite's Urbach tail is important. The internal reflections entail that even for thin films self-absorption can have a significant contribution to the PL spectrum. Our results allow for a clear assignment of the PL peaks by differentiating between optical effects and electronic transitions, which is a necessary requirement for understanding the optoelectronic properties of halide perovskites.T12-P02 University of Alberta | Publication | 2020-01-07 | Konstantin Schötz, Abdelrahman M Askar, Wei Peng, Dominik Seeberger, Tanaji P Gujar, Mukundan Thelakkat, Anna Köhler, Sven Huettner, Osman M Bakr, Shankar, K., Fabian Panzer | | Life Cycle Assessment of Monocrystalline TiO2 Nanorod Array Based Halide Perovskite Solar CellsT13-P04 University of Alberta | Activity | 2020-05-10 | | | Investigating the Tetragonal-to-Orthorhombic Phase Transition of Methylammonium Lead Iodide Single Crystals by Detailed Photoluminescence AnalysisHere we investigate the phase-transition from tetragonal to orthorhombic crystal structure of the halide perovskite methylammonium lead iodide single crystal. Temperature dependent photoluminescence (PL) measurements in the temperature range between 165 – 100 K show complex PL spectra where we can identify in total five different PL peaks. We can assign all observed PL features to different optical effects from the two crystal phases using detailed PL analyses. This allows us to quantify the fraction of tetragonal phase that still occurs below the phase transition temperature. We find that at 150 K, 0.015% tetragonal phase remains, and we observe PL signatures from tetragonal domains of 7-15 nm size down to 120 K. The tetragonal inclusions also exhibit an increased Urbach Energy, implying a high degree of structural disorder. Our results first illustrate how a careful analysis of the PL can serve to deduce structural information, and second, how structural deviations in halide perovskites have a significant impact on the optoelectronic properties of this promising class of semiconductors.T12-P02 University of Alberta | Publication | 2020-05-11 | "Konstantin Schotz ", "Abdelrahman Askar ", "Anna Kohler ", Shankar, K., "Fabian Panzer " | | Phase Evolution in Methylammonium Tin Halide Perovskites with Variable Temperature Solid-State 119Sn NMR SpectroscopyT12-P02, T12-P04, T12-Z01, T12-Q01 University of Alberta | Publication | 2020-07-01 | Michelle Ha, Abhoy Karmakar, Guy Bernard, Enoc Basilio, Arun Krishnamurthy, Abdelrahman M Askar, Shankar, K., Scott Kroeker, Vladimir K Michaelis | | Ultrafast Carrier Dynamics of CdS Nanowires Wrapped In C3N5 NanosheetsT12-P02, T06-Z01, T12-Z01 University of Alberta | Activity | 2020-11-13 | Charles Jensen, Kazi Alam, "A. Palmgren ", David Purschke, "N.Amer ", Shankar, K., Frank Hegmann | | Charge-accumulation-induced mixed photocorrosion in the Z-scheme PEC systemT02-P03, T12-P02 University of Alberta | Activity | 2020-11-23 | | | Water-splitting photoelectrodes consisting of heterojunctions of carbon nitride with a p-type low bandgap double perovskite oxideQuinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34-xFexO6-δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6-δ (BCNFCo), exhibited an optical absorption edge at ~ 800 nm, p-type conduction and a distinct photoresponse upto 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskite and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm-2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ~ 88%.T12-P02, T12-P03 University of Alberta | Publication | 2021-03-01 | Pawan Kumar, Suresh Mulmi, Devika Laishram, Kazi Alam, Ujwal Thakur, V Thangadurai, Shankar, K. | | Artificial Neural Network-Based Prediction of the Optical Properties of Spherical Core\textendash Shell Plasmonic MetastructuresThe substitution of time- and labor-intensive empirical research as well as slow finite difference time domain (FDTD) simulations with revolutionary techniques such as artificial neural network (ANN)-based predictive modeling is the next trend in the field of nanophotonics. In this work, we demonstrated that neural networks with proper architectures can rapidly predict the far-field optical response of core–shell plasmonic metastructures. The results obtained with artificial neural networks are comparable with FDTD simulations in accuracy but the speed of obtaining them is between 100–1000 times faster than FDTD simulations. Further, we have proven that ANNs does not have problems associated with FDTD simulations such as dependency of the speed of convergence on the size of the structure. The other trend in photonics is the inverse design problem, where the far-field optical response of a spherical core–shell metastructure can be linked to the design parameters such as type of the material(s), core radius, and shell thickness using a neural network. The findings of this paper provide evidence that machine learning (ML) techniques such as artificial neural networks can potentially replace time-consuming finite domain methods in the future.T12-P01, T12-P02 University of Alberta | Publication | 2021-03-01 | | | Asymmetric Multipole Plasmon-Mediated Catalysis Shifts the Product Selectivity of CO 2 Photoreduction toward C2+ ProductsCu/TiO2 is a well-known photocatalyst for the photocatalytic transformation of CO2 into methane. The formation of C2+ products such as ethane and ethanol rather than methane is more interesting due to their higher energy density and economic value, but the formation of C–C bonds is currently a major challenge in CO2 photoreduction. In this context, we report the dominant formation of a C2 product, namely, ethane, from the gas-phase photoreduction of CO2 using TiO2 nanotube arrays (TNTAs) decorated with large-sized (80–200 nm) Ag and Cu nanoparticles without the use of a sacrificial agent or hole scavenger. Isotope-labeled mass spectrometry was used to verify the origin and identity of the reaction products. Under 2 h AM1.5G 1-sun illumination, the total rate of hydrocarbon production (methane + ethane) was highest for AgCu-TNTA with a total CxH2x+2 rate of 23.88 μmol g–1 h–1. Under identical conditions, the CxH2x+2 production rates for Ag-TNTA and Cu-TNTA were 6.54 and 1.39 μmol g–1 h–1, respectively. The ethane selectivity was the highest for AgCu-TNTA with 60.7%, while the ethane selectivity was found to be 15.9 and 10% for the Ag-TNTA and Cu-TNTA, respectively. Adjacent adsorption sites in our photocatalyst develop an asymmetric charge distribution due to quadrupole resonances in large metal nanoparticles and multipole resonances in Ag–Cu heterodimers. Such an asymmetric charge distribution decreases adsorbate–adsorbate repulsion and facilitates C–C coupling of reaction intermediates, which otherwise occurs poorly in TNTAs decorated with small metal nanoparticles.T12-P02 University of Alberta | Publication | 2021-02-01 | Ehsan Vahidzadeh, Sheng Zeng, Ajay Manuel, Saralyn Riddell, Pawan Kumar, Kazi Alam, Shankar, K. | | Hot Electrons in TiO2-Noble Metal Nano-Heterojunctions: Fundamental Science and Applications in PhotocatalysisPlasmonic photocatalysis enables innovation by harnessing photonic energy across a broad swathe of the solar spectrum to drive chemical reactions. This review provides a comprehensive summary of the latest developments and issues for advanced research in plasmonic hot electron driven photocatalytic technologies focusing on TiO2–noble metal nanoparticle heterojunctions. In-depth discussions on fundamental hot electron phenomena in plasmonic photocatalysis is the focal point of this review. We summarize hot electron dynamics, elaborate on techniques to probe and measure said phenomena, and provide perspective on potential applications—photocatalytic degradation of organic pollutants, CO2 photoreduction, and photoelectrochemical water splitting—that benefit from this technology. A contentious and hitherto unexplained phenomenon is the wavelength dependence of plasmonic photocatalysis. Many published reports on noble metal-metal oxide nanostructures show action spectra where quantum yields closely follow the absorption corresponding to higher energy interband transitions, while an equal number also show quantum efficiencies that follow the optical response corresponding to the localized surface plasmon resonance (LSPR). We have provided a working hypothesis for the first time to reconcile these contradictory results and explain why photocatalytic action in certain plasmonic systems is mediated by interband transitions and in others by hot electrons produced by the decay of particle plasmons.T12-P02, T12-P03 University of Alberta | Publication | 2021-05-01 | | | Nonlithographic Formation of Ta2O5 Nanodimple Arrays Using Electrochemical Anodization and Their Use in Plasmonic Photocatalysis for Enhancement of Local Field and Catalytic ActivityWe demonstrate the formation of Ta2O5 nanodimple arrays on technologically relevant non-native substrates through a simple anodization and annealing process. The anodizing voltage determines the pore diameter (25–60 nm), pore depth (2–9 nm), and rate of anodization (1–2 nm/s of Ta consumed). The formation of Ta dimples after delamination of Ta2O5 nanotubes occurs within a range of voltages from 7 to 40 V. The conversion of dimples from Ta into Ta2O5 changes the morphology of the nanodimples but does not impact dimple ordering. Electron energy loss spectroscopy indicated an electronic band gap of 4.5 eV and a bulk plasmon band with a maximum of 21.5 eV. Gold nanoparticles (Au NPs) were coated on Ta2O5 nanodimple arrays by annealing sputtered Au thin films on Ta nanodimple arrays to simultaneously form Au NPs and convert Ta to Ta2O5. Au NPs produced this way showed a localized surface plasmon resonance maximum at 2.08 eV, red-shifted by ∼0.3 eV from the value in air or on SiO2 substrates. Lumerical simulations suggest a partial embedding of the Au NPs to explain this magnitude of the red shift. The resulting plasmonic heterojunctions exhibited a significantly higher ensemble-averaged local field enhancement than Au NPs on quartz substrates and demonstrated much higher catalytic activity for the plasmon-driven photo-oxidation of p-aminothiophenol to p,p′-dimercaptoazobenzene.T12-P02 University of Alberta | Publication | 2021-01-01 | Ryan Kisslinger, Saralyn Riddell, Ajay Manuel, Kazi Alam, Aarat P Kalra, Kai Cui, Shankar, K. | | Unusual Surface Ligand Doping-Induced p-Type Quantum Dot Solids and Their Application in Solar CellsDoping quantum dots (QDs) is a problem that has been haunting researchers in the QD research community for years, even though doping techniques have been utilized for decades in conventional semiconductors. For the “self-purification” in colloidal QDs, engineering the surface ligands has emerged as an effective way to alter free carrier concentrations and doping types in colloidal QD solids. Halide-atomic ligands are the most popular ligands in producing PbS QD solids since they provide minimal dot-to-dot distance while maintain low in-gap trap states. However, previously reported halide surface treatment could only produce n-type QD solids. Here, we report the fabrication of p-type PbS QD solids using proton-assisted surface ligand exchange. We unveiled the origin of p-type doing in PbS QD solids, and it came from an unusual surface ligand; the HOH+ group formed using NH4X (X = Cl, Br, I) in methanol. We further fabricated QD solar cells using PbS–NH4Cl, a p-type QD solid predicted and proved by our theory and experiments. The champion device shows a high power conversion efficiency of 7.49%.T12-P02, T12-P04 University of Alberta | Publication | 2020-11-01 | | | Effect of morphology on the photoelectrochemical performance of nanostructured Cu2O photocathodesCu2O is a promising earth-abundant semiconductor photocathode for sunlight-driven water splitting. Characterization results are presented to show how the photocurrent density (Jph), onset potential (Eonset), band edges, carrier density (NA), and interfacial charge transfer resistance (Rct) are affected by the morphology and method used to deposit Cu2O on a copper foil. Mesoscopic and planar morphologies exhibit large differences in the values of NA and Rct. However, these differences are not observed to translate to other photocatalytic properties of Cu2O. Mesoscopic and planar morphologies exhibit similar Eg and Efb values of 1.93±0.04 eV and 0.48±0.06 eV respectively. Eonset of 0.48±0.04 eV obtained for these systems is close to the Efb indicating negligible water reduction overpotential. Electrochemically deposited planar Cu2O provides the highest photocurrent density of 5.0 mA cm−2 at 0 V vs RHE of all the morphologies studied. The photocurrent densities observed in this study are among the highest reported values for the bare Cu2O photocathodes. Although different deposition methods show a similar average photocurrent density 2.8±0.3 mA/cm2 at 0 V vs RHE, large variations in the photocurrent density are observed for samples prepared under nominally identical deposition methods.T12-P02, T12-P03 University of Alberta | Publication | 2020-07-01 | Lian Shoute, Kazi Alam, Ehsan Vahidzadeh, Ajay Manuel, Sheng Zeng, Pawan Kumar, Piyush Kar, Shankar, K. | | Plasmonic Catalysis: Fundamentals, Materials, Methods And ChallengesPlenary Lecture at International Online Conference on Nanomaterials (ICN’2021), April 9-11, 2021 which featured more than 200 participantsT12-P02, T12-P03 University of Alberta | Activity | 2021-04-11 | | | Heterojunctions based on 2D Carbon-Based Semiconductor Nanomaterials for Photocatalysis and PhotovoltaicsKeynote Lecture at Virtual International Conference on Hierarchically Structured Materials (ICHSM'2021), 08 - 10 April 2021, which featured over 100 participants.T12-P02, T12-P03 University of Alberta | Activity | 2021-04-10 | | | Nanosheets of carbon nitride and nitrogen doped graphene for photovoltaics and photocatalysisKeynote Lecture in Symposium on 2D Materials and Devices at International Conference on Emerging Electronics (ICEE-2020), 26-28 November 2020.T12-P02, T12-P03 University of Alberta | Activity | 2020-11-27 | | | Hot Electron-mediated Plasmonic Photocatalysis Using Heterojunctions of Noble Metal Nanoparticles and Semiconductor Nanowires/NanotubesKeynote Lecture in Session 3:Nanomedicine, Nanomaterials & Nanotechnology at the Vebleo Webinar. My lecture was sandwiched in-between those of Dr. Arthur Nozik (NREL) and Prof. Sanjay Banerjee (University of Texas at Austin), who are both legends in the field of semiconductor optoelectronics. My lecture was also posted on YouTube by the conference organizers. T12-P02, T12-P03 University of Alberta | Activity | 2020-08-18 | | | Introduction to plasmonics and the MEMS application of surface plasmonsInvited Industrial Guest Lecture in ECE 3038:MEMS and Nano Sensors on November 29, 2020 at Vellore Institute of Technology, India.T12-P02 University of Alberta | Activity | 2020-11-29 | | | Helped organize the 2D Materials symposium at ICEE'2020Part of 3-member organizing committee responsible for the 2D Materials track at the International Conference on Emerging Electronics (ICEE'2020). Made a list of suitable invited speakers and then proceeded to invite them. Our symposium had a number of expert speakers on materials and devices based on nanosheets of graphene, carbon nitrides, MoS2, GaSe, PtSe2, etc. Specific talks included, but were not limited to,:
(i) 2D materials and their nanocomposites as photocatalysts for the conversion of CO2 to chemicals
(ii) Platinum diselenide thin-film based field effect transistor for ammonia detection
(iii) Vertically aligned edge-oriented MoS2 hybrid thin films decorated with Pd nanoparticles for room temperature hydrogen sensor
(iv) Valley dichroism and exciton dynamics in semiconducting 2D-monolayer
(v) Plasmonic sensitization of graphene devices
(vi) Few-layer Transition Metal Dichalcogenides (TMDs) and their heterostructures for high performance photodetection
(vii) High-Temperature Performance of a GaSe Nanosheet-Based Broadband Photodetector
(viii) Tunability of thermoelectricity in twisted bilayer graphene
(ix) Electronic device integration of two-dimensional materials
(x) Plasmon triggered light-matter interactions in metal-2D quantum hybridsT12-P02 University of Alberta | Activity | 2021-05-13 | | | Robust Plasmonic Glasses using nanoporous TiO2 embedded with Au nanoparticlesPresented by Ajay Manuel in Symposium: S3: Optical and Electronic Materials and Devices - Fundamentals and Applications in the Session titled: Hybrid and Composite Optical Materials.
A high throughput, large area substrate-compatible, solution process namely electrochemical anodization has been used to grow highly ordered, vertically oriented, titania nanotube arrays (TNTAs). We introduced an innovation into the anodization process that enabled us to embed Au NPs into the nanostructured titania thin films. We call the resulting substrates Au NP-TNTAs. Au NP-TNTAs exhibited localized surface plasmon resonance (LSPR) peaks at ~600 nm characterized by very strong extinction coefficients and high ensemble Q-factors. The high surface area Au NP-TNTAs are excellent substrates for bioimaging and biosensing due to the strong enhancement of two-photon fluorescence observed in them. Au NP-TNTAs are also excellent plasmonic photocatalysts for sunlight-driven water-splitting.T12-P02, T12-P03 University of Alberta | Activity | 2020-08-03 | Sheng Zeng, Ryan Kisslinger, Ajay Manuel, Kazi Alam, Shankar, K. | | Core-shell titanium dioxide@titanium nitride nanotube arrays for optical limiters and near-infrared sensitive optoelectronicsPresented by Sheng Zeng in Symposium: S3: Optical and Electronic Materials and Devices - Fundamentals and Applications in the Session titled: Hybrid and Composite Optical Materials.
Electrochemical anodization was used to form glass-like TiO2 nanotube arrays (TNTAs) on native (Ti foil) and non-native (silicon) substrates. Atomic layer deposition (ALD) was used to conformally coat TNTAs with ceramic overlayers of transition metal nitrides (TiN, ZrN, HfN). Core-shell nanotubes resulted with a double-walled structure consisting of a TiO2 inner wall and a metal nitride outer wall, and exhibited strong near-infrared localized surface plasmon resonances (LSPR). The ~100 nm nanotube diameters and LSPR effects rendered the core-shell TiO2@TiN nanotubes(NTs) excellent optical limiters due to their strong Mie scattering and absorption effects. Compared to optical limiters based on noble metal nanoparticles, TiO2@TiN NTs displayed stronger resilience and higher damage threshold under intense laser irradiation because of their ceramic nature. Due to hot electron injection into TiO2 following plasmon decay in the nitride, the core-shell nanotubes are also good plasmonic photocatalysts.T12-P02, T12-P03 University of Alberta | Activity | 2020-08-03 | Sheng Zeng, Ajay Manuel, Saralyn Riddell, Ryan Kisslinger, Shankar, K. | | Plasmonic Photonic Crystal Photocatalysts Consisting of TiO2 Nanotube Arrays Decorated/Embedded with Noble Metal NanoparticlesPresented By Sheng Zeng in SYMPOSIUM S.EN06:Rational Designed Hierarchical Nanostructures for Photocatalytic System at the 2020 Fall Meeting of the Materials Research Society (2020 Virtual MRS) held November 27-December 04, 2020. For context, the MRS Fall and Spring Meetings are the premier conferences in the world for nanotechnology and materials science. In a convention (non-COVID19 affected) year, the MRS Meetings see as many as 10,000 attendees and have two dozen symposia running in parallel.
Rising global energy demands, environmental pollution, anthropogenic global warming and climate change have directed efforts toward the development of renewable and green energy sources. Photocatalytic solar energy conversion technologies are a promising alternative in this aspect, and provide for solar-to-chemical energy storage and conversion, water purification, and H2 generation etc. Engineering photocatalysts with greater performance efficiencies is crucial to the advancement of this technology. One approach towards optimizing photocatalysts involves the fabrication of well-designed nanophotonic structures such as photonic crystals and quantum dots etc. that can provide for large surface area catalysis, generate high intensity electric field hot spots, and optimal light utilization. We have successfully demonstrated this in our previous works involving TiO2 photonic crystals for CO2 photoreduction, and CNFQDs decorated square shape TiO2 nanotubes for water-splitting. The inclusion of plasmonic materials in these nanophotonic structures induces the generation of hot charge carriers to further promote photocatalytic reactions. Consequently, successful CO2 photoreduction using visible light illumination on large bandgap semiconductor materials is possible. Gas chromatography and isotope labeled CO2 tests help verify and validate these results. Plasmon driven thiol redox reactions, and enhanced hydrogen generation in photoelectrochemical water-splitting has also been achieved. Lumerical FDTD simulations are extensively used to guide nanostructure optimization, and supplement the experimental data generated in our work. T12-P02 University of Alberta | Activity | 2020-12-02 | | | Techno-economic assessment of titanium dioxide nanorod-based perovskite solar cells: from lab-scale to large-scale manufacturing Perovskite solar cells (PSCs) have shown remarkable progress in recent years. Different materials and structures have been developed to improve the photoconversion efficiency and operational stability of PSCs. However, the economic and technical impacts of materials and design choice on the large-scale deployment are not well addressed in the literature. In this research, a pathway for producing titanium dioxide (TiO2) nanorod-based perovskite solar modules was established and their manufacturing cost was estimated through the development of data-intensive, bottom-up techno-economic models. Material, utilities, and equipment requirements from available laboratory data to a mass production annual capacity of up to 21 MW were estimated through the development of scale factors. The minimum sustainable price and levelized cost of electricity were calculated. The direct manufacturing cost of the reference PSC module was estimated at $80.23/m2 and $0.73/W with a production capacity of 3.5 MWp. These costs decline to $47.15/m2 and $0.43/W at 21 MW production capacity. Material costs dominate the overall costs, fluorine-doped tin oxide glass being the most expensive material. The perovskite solar cell panels, when installed in residential homes in Alberta, Canada, were calculated to have a competitive levelized cost of electricity ranging from 7 to 17 cents per kWh. However, the cost was found to be extremely sensitive to the module efficiency, lifetime, and the solar insolation at the location of installation.T12-P02, T13-P04 University of Alberta | Publication | 2021-06-18 | | | The life cycle energy and environmental footprints of high-performance monocrystalline titanium dioxide nanorod-base perovskite solar cellsT12-P02, T13-P04 University of Alberta | Activity | 2020-11-23 | | | Development of life cycle GHG emissions of high-performance mono-crystalline titanium dioxide nanorod based perovskite solar cellsT12-P02, T13-P04 University of Alberta | Activity | 2020-10-14 | Harshadeep Kukkikatte Ramamurthy Rao, Eskinder Gemechu, Ujwal Thakur, Shankar, K. | | Life cycle assessment of high-performance mono-crystalline titanium dioxide nanorod based perovskite solar cellsT12-P02, T13-P04 University of Alberta | Activity | 2020-09-22 | | | Life cycle assessment of high-performance monocrystalline titanium dioxide nanorod-based perovskite solar cellsT12-P02, T13-P04 University of Alberta | Publication | 2021-07-23 | | | Heterojunctions based on 2D Carbon-Based Semiconductor Nanomaterials for Photocatalysis and PhotovoltaicsInvited Plenary Lecture at ISCMNB'21. T12-P02, T12-P03 University of Alberta | Activity | 2021-05-26 | | | Effect of sulfur‑doped graphene quantum dots incorporation on morphological, optical and electron transport properties of CH3NH3PbBr3 perovskite thin filmsT12-P02 University of Alberta | Publication | 2021-05-24 | Sachin Kadian, Naveen Kumar Tailor, Narendra Chaulagain, Shankar, K., "Soumitra Satapathi ", "Gaurav Manik " | | Harvesting Hot Holes in Plasmon-Coupled Ultrathin Photoanodes for High-Performance Photoelectrochemical Water SplittingThe harvesting of hot carriers produced by plasmon decay to generate electricity or drive a chemical reaction enables the reduction of the thermalization losses associated with supra-band gap photons in semiconductor photoelectrochemical (PEC) cells. Through the broadband harvesting of light, hot-carrier PEC devices also produce a sensitizing effect in heterojunctions with wide-band gap metal oxide semiconductors possessing good photostability and catalytic activity but poor absorption of visible wavelength photons. There are several reports of hot electrons in Au injected over the Schottky barrier into crystalline TiO2 and subsequently utilized to drive a chemical reaction but very few reports of hot hole harvesting. In this work, we demonstrate the efficient harvesting of hot holes in Au nanoparticles (Au NPs) covered with a thin layer of amorphous TiO2 (a-TiO2). Under AM1.5G 1 sun illumination, photoanodes consisting of a single layer of ∼50 nm diameter Au NPs coated with a 10 nm shell of a-TiO2 (Au@a-TiO2) generated 2.5 mA cm–2 of photocurrent in 1 M KOH under 0.6 V external bias, rising to 3.7 mA cm–2 in the presence of a hole scavenger (methanol). The quantum yield for hot-carrier-mediated photocurrent generation was estimated to be close to unity for high-energy photons (λ < 420 nm). Au@a-TiO2 photoelectrodes produced a small positive photocurrent of 0.1 mA cm–2 even at a bias of −0.6 V indicating extraction of hot holes even at a strong negative bias. These results together with density functional theory modeling and scanning Kelvin probe force microscope data indicate fast injection of hot holes from Au NPs into a-TiO2 and light harvesting performed near-exclusively by Au NPs. For comparison, Au NPs coated with a 10 nm shell of Al2O3 (Au@Al2O3) generated 0.02 mA cm–2 of photocurrent in 1 M KOH under 0.6 V external bias. These results underscore the critical role played by a-TiO2 in the extraction of holes in Au@a-TiO2 photoanodes, which is not replicated by an ordinary dielectric shell. It is also demonstrated here that an ultrathin photoanode (<100 nm in maximum thickness) can efficiently drive sunlight-driven water splitting.T12-P02, T12-P03 University of Alberta | Publication | 2021-09-04 | Ehsan Vahidzadeh, Sheng Zeng, Kazi Alam, Pawan Kumar, Saralyn Riddell, Narendra Chaulagain, "Sergey Gusarov ", Alexander E Kobryn, Shankar, K. | | Instantaneous Property Prediction and Inverse Design of Plasmonic Nanostructures Using Machine Learning: Current Applications and Future DirectionsAdvances in plasmonic materials and devices have given rise to a variety of applications in photocatalysis, microscopy, nanophotonics, and metastructures. With the advent of computing power and artificial neural networks, the characterization and design process of plasmonic nanostructures can be significantly accelerated using machine learning as opposed to conventional FDTD simulations. The machine learning (ML) based methods can not only perform with high accuracy and return optical spectra and optimal design parameters, but also maintain a stable high computing efficiency without being affected by the structural complexity. This work reviews the prominent ML methods involved in forward simulation and inverse design of plasmonic nanomaterials, such as Convolutional Neural Networks, Generative Adversarial Networks, Genetic Algorithms and Encoder–Decoder Networks. Moreover, we acknowledge the current limitations of ML methods in the context of plasmonics and provide perspectives on future research directions.T12-P01, T12-P02 University of Alberta | Publication | 2022-02-01 | | | Surface second harmonic generation spectra of titania coated Au NPs Surface second harmonic generation (s-SHG) spectra of supported Au nanoparticles (NPs) with titania coating are presented. Although the optical properties of these particles are in agreement with the predictions from Mie theory and previously reported literature, s-SHG spectra over a relatively broad spectral range, allows for the extraction of additional information regarding the morphology of the sample. These geometrical findings need to be considered while interpreting the observed spectra of supported NPs. In the case of atomic layer deposition of TiO2 onto Au NPs, it is found that for the titania layers thinner than 5 nm in nominal terms, Au NPs are not fully covered, as titania preferably accumulates at the space between the particles and at particles’ edges and corners. Full encapsulation of the Au NPs is achieved for titania films with a nominal thickness of more than 5 nm. Furthermore, s-SHG spectra can also be used to extract information on the size distribution of the NPs.T12-P02 University of Alberta | Publication | 2022-04-01 | Natalie Fehn, Ehsan Vahidzadeh, Shankar, K., Ueli Heiz, Aras Kartouzian | | Electrochemically reconstructed perovskite with cooperative catalytic sites for CO 2-to-formate conversionPerovskites are the promising catalysts for various reactions, yet their structure evolutions and the composition-function relation in the carbon dioxide reduction reaction (CO2RR) are not fully explored. In this study, we report that the reconstructed BaBiO3 (BBO) perovskite is able to facilitate CO2-to-formate (FA) conversion by both A- (Ba) and B- (Bi) site elements through the cooperative but distinct catalytic mechanisms. Specifically, the electrochemical reductions of BBO trigger the complete rearrangement of atoms with rapid kinetics at catalytically relevant voltages, giving rise to electricity-induced Bi metallene (eBBO) that efficiently generates FA with high selectivity and partial current densities. Moreover, the reconstructed BBO simultaneously enables Ba2+ release to the electrolyte, and the time-resolved FTIR and in situ Raman analysis collectively reveal that the Ba2+ adsorption enables easier CO2 adsorption, thereby leading to enhanced CO2-to-FA conversion. This work is of direct significance in elucidating the cooperative catalysis between A- and B- site elements in perovskites for room-temperature CO2RR.T02-P03, T12-P02 University of Alberta | Publication | 2022-06-01 | Mengnan Zhu, Bo-Wen Zhang, Minrui Gao, Pengfei Sui, Chenyu Xu, Lu Gong, Zeng, H., Shankar, K., Bergens, S., Luo, J. | | TiO 2-HfN Radial Nano-Heterojunction: A Hot Carrier Photoanode for Sunlight-Driven Water-SplittingThe lack of active, stable, earth-abundant, and visible-light absorbing materials to replace plasmonic noble metals is a critical obstacle for researchers in developing highly efficient and cost-effective photocatalytic systems. Herein, a core–shell nanotube catalyst was fabricated consisting of atomic layer deposited HfN shell and anodic TiO2 support layer with full-visible regime photoactivity for photoelectrochemical water splitting. The HfN active layer has two unique characteristics: (1) A large bandgap between optical and acoustic phonon modes and (2) No electronic bandgap, which allows a large population of long life-time hot carriers, which are used to enhance the photoelectrochemical performance. The photocurrent density (≈2.5 mA·cm−2 at 1 V vs. Ag/AgCl) obtained in this study under AM 1.5G 1 Sun illumination is unprecedented, as it is superior to most existing plasmonic noble metal-decorated catalysts and surprisingly indicates a photocurrent response that extends to 730 nm. The result demonstrates the far-reaching application potential of replacing active HER/HOR noble metals such as Au, Ag, Pt, Pd, etc. with low-cost plasmonic ceramics.T12-P02, T12-P03 University of Alberta | Publication | 2021-11-01 | Sheng Zeng, Triratna Parmeshwar Muneshwar, Saralyn Riddell, Ajay Manuel, Ehsan Vahidzadeh, Pawan Kumar, Ryan Kisslinger, Kazi Alam, Alexander E Kobryn, Sergey Gusarov, Ken Cadien, Shankar, K. | | Electrochemically Dismantled Perovskite with Cooperative Catalysis for CO 2-to-Formate ConversionElectrochemical reduction of carbon dioxide (CO2RR) driven by sustainable energy resources holds great promise for realizing the zero net emission of CO2 by converting them to value-added fuels.1–4 For the past few years, substantial efforts have been devoted to boosting CO2RR using different nanostructured catalysts. However, the complicated synthesis procedures and low product yields are usually associated with many of these catalysts, which hinder their scalability. More importantly, many catalysts suffer from the low catalytic activities, high overpotentials, and unsatisfactory selectivity, which collectively impede the large-scale applications of CO2RR technique. In this study, we pursue initiating the CO2 conversion on perovskite-based catalysts BaBiO3 (BBO) to selectively produce formate (FA). The structural/phase evolution of BBO under cathodic potentials, the catalytic performances of electrochemical and photoelectrochemical reduction of CO2RR, and the effect of non-active A-site element (Ba) will be investigated in detail.
Herein, BBO perovskite is fabricated by annealing the sol-gel Ba2+/Bi3+ nitrate mixture at high temperatures. Extensive physical characterizations show that under negative potentials, BBO pre-catalysts undergo irreversible structural and phase transformations, giving rise to Bi metallene with atomic-scale thickness and enlarged surface area, as supported by X-ray diffraction analysis and transmission electron microscopy (Figure 1a, and 1b). Using the fully electrochemically reduced BBO, a near-unity selectivity towards formate (FA) can be achieved at the potential of – 1.2 V vs. RHE in 0.1M KHCO3 solution with the typical H-type electrochemical cell. By coupling the state-of-the-art BiVO3 photoanode to the BBO dark cathode, FA can be generated at a of 80.0 % at a cell voltage of 2.5 V in a PEC cell. Contrarily, only < 1.0 % can be detected at 2.5 V without solar irradiation. Meanwhile, inductively coupled plasma optical emission spectrometry (ICP-OES) analysis suggests that A-site elements (Ba2+) are simultaneously released from the BBO lattice and diffuse to the electrolyte as a result of the complete reduction of BBO. The effect of Ba2+ - containing electrolytes on the CO2RR product distributions have been studied, and the results show that Ba2+ can either facilitate or impede FA production depending on both the external potential and the concentration of Ba2+ (Figure 1c). Specifically, high Ba2+ concentration and more negative potentials (i.e., 25 mM Ba2+ and -1.1 - -1.3 V vs. RHE) tend to favor HER over CO2RR due to the formation of BaCO3 precipitates, whereas low Ba2+ concentrations and more positive potentials (i.e., 2.5 and 7.5 mM Ba2+ and -0.9 - -1.1 V vs. RHE) can significantly enhance the selectivity towards FA. Density functional theory (DFT) calculations show that suitable barium ion adsorption promotes CO2-to-FA conversion by regulating the adsorption strength of *OCHO and *HCOOH intermediates. Our study utilizes both A- and B- site elements in BBO to benefit CO2 conversion, which may be extended to other perovskite electrocatalysts for CO2RR.T02-P03, T12-P02 University of Alberta | Activity | 2021-10-01 | Mengnan Zhu, Bowen Zhang, Minrui Gao, Chenyu Xu, Pengfei Sui, Zeng, H., Shankar, K., Bergens, S., Luo, J. | | Switchable CO2 Electroreduction Induced by the Bismuth Moiety with Tunable Local Structures on GrapheneT02-P03 University of Alberta | Activity | 2022-05-29 | | | Life cycle environmental and techno-economic assessment of perovskite solar cells. T12-P02, T13-P04 University of Alberta | Activity | 2021-07-16 | | | Air- and water-stable halide perovskite nanocrystals protected with nearly-monolayer carbon nitride for CO 2 photoreduction and water splittingHalide perovskites are exciting candidates for broad-spectrum photocatalysts but have the problem of ambient stability. Protective shells of oxides and polymers around halide perovskite nano- and micro-crystals provide a measure of chemical and photochemical resilience but the photocatalytic performance of perovskites is compromised due to low electron mobility in amorphous oxide or polymer shells and rapid charge carrier recombination on the surface. Herein an in situ surface passivation and stabilization of CsPbBr3 nanocrystals was achieved using monolayered graphenic carbon nitride (CNM). Extensive characterization of carbon nitride protected CsPbBr3 nanocrystals (CNMBr) indicated spherical CsPbBr3 nanoparticles encased in a few nm thick g-C3N4 sheets facilitating better charge separation via percolation/tunneling of charges on conductive 2D nanosheets. The CNMBr core-shell nanocrystals demonstrated enhanced photoelectrochemical water splitting performance and photocurrent reaching up to 1.55 mA cm−2. The CNMBr catalyst was successfully deployed for CO2 photoreduction giving carbon monoxide and methane as the reaction products.T12-P02, T12-P03 University of Alberta | Publication | 2022-08-01 | Devika Laishram, Sheng Zeng, Kazi Alam, Aarat P Kalra, Kai Cui, Pawan Kumar, Rakesh K Sharma, Shankar, K. | | Focused Session on "Microwave and Hot Carrier Sensors" at IEEE Sensors 2022, Dallas TXI am organizing a Focused Session on Microwave and Hot Carrier Sensors at IEEE Sensors 2022 together with Prof. Mohammad Zarifi from the University of British Columbia. IEEE Sensors is a large conference with multiple parallel tracks & sessions, and several thousand attendees every year. The conference is being organized in an in-person format in Dallas, TX from October 30 to November 03, 2022. T12-P02, T07-P04NP University of Alberta | Activity | 2022-04-29 | | | Plasmonic photocatalysis for high selectivity CO2 photoreduction and water-splitting driven by visible photonsIndustrial heterogeneous catalysis is dominated by thermally driven chemical reactions catalyzed by noble metal and transition metal micro- and nanoparticles (NPs) [1]. Most of these reactions require high temperatures and involve thermally excited phonon modes of the catalyst coupled to those of the reactant [2]. For such phonon-driven catalysis, catalytic action is described by a classical transition state through which reactant molecules acquire sufficient energy to overcome the activation energy barrier. In contrast, plasmonic photocatalysis offers the promise of using light as the energy source to selectively drive various chemical reactions close to room temperature [3]. Both carrier-driven catalysis (involving a non-classical transition state) and phonon-driven catalysis are possible with plasmons. Wholesale electricity prices worldwide are in a consistent long-term downward trend (due to increased adoption of renewables) and solid-state lighting is becoming increasing efficient and affordable as incandescent lamps are phased out. Therefore, plasmon-catalyzed chemical reactions in the future are likely to be driven not merely by sunlight but also by solid-state lamps, and this could usher in a paradigm shift in the field of heterogeneous catalysis.
Plasmons are coherent and collective oscillations of the conduction band electrons in metal nanoparticles [3]. When these oscillations are confined to interfaces of metals with air, liquids or dielectrics, they give rise to surface plasmon resonances (SPR). In coinage metals (Cu, Ag, Au), metal nitrides and metal sulfides, SPR is excited by visible light. Once excited, SPR decays at very short timescales to produce hot electrons, which can be directly utilized to perform carrier-driven catalysis. Alternatively, the hot carriers can equilibrate through collisions with phonons, and simulate the effect of thermally stimulated phonon-driven catalysis. Two reactions of particular interest for plasmonic catalysis are the transformation of CO2 into fuels, and water-splitting to generate hydrogen; rendering these two reactions efficient at scale, will simultaneously address global energy demand and global climate change [3].
References
1. Thomas, J. M. et al. Principles and practice of heterogeneous catalysis; John Wiley & Sons: 2014.
2. Linic, S. et al. Photochemical transformations on plasmonic metal nanoparticles. Nat. Mater. 14, 567-576 (2015).
3. Manuel, A.P. et al. Plexcitonics–fundamental principles and optoelectronic applications. J. Mater. Chem. C 7, 1821-1853 (2019).
4. Kar, P. et al. High rate CO2 photoreduction using flame annealed TiO2 nanotubes. Appl. Catal. B-Environ. 243, 522-536 (2019).T12-P02 University of Alberta | Activity | 2022-05-16 | | | Plasmonic Photocatalysis for the Generation of Solar FuelsHeterogeneous catalysis is extensively used in industrial chemical reactions such as oil refining, ammonia production, steam reforming, Fischer-Tropsch synthesis, etc. These reactions are typically carried out at elevated temperatures (> 400 ℃) at a huge thermal and emissions cost. For instance, ammonia production is the single most greenhouse gas producing chemical process in the world and accounts for nearly 2% of world CO2 emissions. There is an urgent need to lower the energy cost and environmental footprint of industrial heterogeneous catalysis. Plasmonic catalysis is an emerging field of research that attempts to drive chemical reactions at close to room temperature using light as the energy source instead of heat. Surface plasmons are quantum quasiparticles representing the coherent and collective oscillations of conduction band electrons in metallic materials. In a handful of materials such as nanostructures or thin films of Au, Ag, HfN, TiN and Cu2S, these surface plasmons can be efficiently excited by visible or near-infrared light. Surface plasmons decay in a few femtoseconds to produce hot electron-hole pairs. Plasmonic photocatalysis attempts to use the energy of these hot carriers to drive chemical reactions under milder conditions through either carrier-mediated catalysis or phonon-mediated catalysis or a combination thereof. In this keynote lecture, the use of plasmonic catalysts in CO2 photoreduction and sunlight-driven water-splitting to generate solar fuels will be described.T12-P02 University of Alberta | Activity | 2022-02-17 | | | Hot Carrier-Mediated Generation of Solar Fuels Using Plasmon-Semiconductor NanoheterojunctionsSurface plasmons (or “plasmons”) are the quantized collective and coherent oscillations of conduction band electrons at metal-dielectric interfaces. Hot electron-hole pairs are generated by dephasing of plasmons. The excess energy of hot carriers can be used to drive chemical reactions. In this Invited Talk, we discuss strategies to harvest hot electrons and hot holes in plasmon-semiconductor heterojunctions to generate solar fuels. Examples of the successful use of hot carriers to drive CO2 photoreduction and water-splitting to generate fuels such as methane and hydrogen will be shown and discussed. Machine learning is playing an increasingly important role in the optimization of such nanoplasmonic architectures. T12-P01, T12-P02 University of Alberta | Activity | 2022-05-26 | | | Nanostructured Plasmonic Heterojunctions for the Production of Solar FuelsT12-P02 University of Alberta | Activity | 2022-01-27 | | | Optical and Optothermal Metamaterials: Fabrication, Characterization and Applications in Sensing and Energy HarvestingThe Shankar Lab at the University of Alberta has made pioneering contributions to self-organized vertically aligned nanorod or nanopillar array structures made of wide-bandgap metal oxide semiconductors. These metal oxides are also high index dielectrics and were used by the Shankar Lab to build various types of optical and optothermal metamaterials and photonic crystals using mostly bottom-up fabrication protocols. One type involves forming metallodielectric nanocomposites with plasmonic noble metals to achieve tailored optical and electronic properties. The presence of plasmons in the metallodielectric architecture modifies the optical density of states and also enables the generation of hot carriers through plasmon decay. These hot carriers, when appropriately harvested and utilized, can be used to perform photodetection or drive a chemical reaction. A second type of metamaterial, closely related to the first type, involves core-shell type nanocomposites consisting of a transition metal oxide core and a transition metal nitride shell. Transition metal nitrides such as TiN, HfN, TaN and ZrN exhibit plasmonic behavior as well as a suppressed Klemens decay process, which results in unique phonon behavior and long-lived carriers in such core-shell optothermal metamaterials. The third kind involves low loss all-dielectric metamaterials wherein the inherent optical anisotropy of vertically oriented metal oxide nanotube arrays affords a basis for metamaterial behavior. The potential parameter space to form the aforementioned types of metamaterials is vast. Therefore, mention will be made of machine learning approaches to accelerate optical property prediction and geometry optimization of core-shell metamaterials, which also attempt to obtain some insight into the thought process of the machine.T12-P02 University of Alberta | Activity | 2021-10-05 | | | Application of Machine Learning and Computer Vision in Obtaining the Optical Response of Plasmonic Heterostructures[Lecture Delivered Via Zoom] The profound and growing understanding of plasmonics has given rise to a variety of applications in photocatalysis, microscopy, nanophotonics, and metastructures. With the advancement of computing power and artificial intelligence, we have become aware that the characterization and design process of plasmonic nanostructures can be significantly accelerated using machine learning as opposed to conventional FDTD simulations. The artificial intelligence (AI) based methods can not only perform with high accuracy and return optimal design parameters, but also maintain a stable high computing efficiency without being heavily affected by the structural complexity. Recently, the Shankar Lab demonstrated that neural networks with proper architectures can rapidly predict the far-field optical response of core–shell plasmonic metastructures. The results obtained with artificial neural networks were comparable with FDTD simulations in accuracy but these results were obtained 100–1000 times faster than FDTD simulations. Further, ANNs do not have problems associated with FDTD simulations such as a dependency of the speed of convergence on the size of the structure. Another research success involved our use of a computer vision technique, namely convolutional neural network (CNN), in conjunction with artificial neural networks (ANN) to obtain the far-field optical response of concentric cylindrical plasmonic metastructures such as nanorods and nanotubes. In addition, we addressed an issue related to deep learning (DL) methods, namely explainability. The lack of explainability is one reason why conventional methods such as FDTD and are still prevalent. We probed deeper into these networks' architecture to explain how the optimized network could predict the final results. Our results suggest that the DL network learns the underlying physics governing the optical response of plasmonic core-shell nanocylinders, which in turn, builds trust in the use of DL methods in materials science and optoelectronics. T12-P02 University of Alberta | Activity | 2021-10-23 | | | Hot hole transfer from Ag nanoparticles to multiferroic YMn2O5 nanowires enables superior photocatalytic activityT02-P03, T12-P02, T06-Q02 University of Alberta | Publication | 2022-01-01 | Kazi Alam, Sergey Gusarov, Mustafa Supur, Pawan Kumar, Alexander E Kobryn, Kai Cui, Richard L McCreery, Shankar, K. | | Nanosecond Laser Confined Bismuth Moiety with Tunable Structures on Graphene for Carbon Dioxide ReductionT02-P03 University of Alberta | Publication | 2023-04-17 | Mengnan Zhu, "haoqing Jiang ", Bowen Zhang, Minrui Gao, Pengfei Sui, "renfei feng ", Shankar, K., Bergens, S., Gary J Cheng, Luo, J. | | Radial Nano-Heterojunctions Consisting of CdS Nanorods Wrapped by 2D CN:PDI Polymer with Deep HOMO for Photo-Oxidative Water Splitting, Dye Degradation and Alcohol OxidationSolar energy harvesting using semiconductor photocatalysis offers an enticing solution to two of the biggest societal challenges, energy scarcity and environmental pollution. After decades of effort, no photocatalyst exists which can simultaneously meet the demand for excellent absorption, high quantum efficiency and photochemical resilience/durability. While CdS is an excellent photocatalyst for hydrogen evolution, pollutant degradation and organic synthesis, photocorrosion of CdS leads to the deactivation of the catalyst. Surface passivation of CdS with 2D graphitic carbon nitrides (CN) such as g-C3N4 and C3N5 has been shown to mitigate the photocorrosion problem but the poor oxidizing power of photogenerated holes in CN limits the utility of this approach for photooxidation reactions. We report the synthesis of exfoliated 2D nanosheets of a modified carbon nitride constituted of tris-s-triazine (C6N7) linked pyromellitic dianhydride polydiimide (CN:PDI) with a deep oxidative highest occupied molecular orbital (HOMO) position, which ensures sufficient oxidizing power for photogenerated holes in CN. The heterojunction formed by the wrapping of mono-/few layered CN:PDI on CdS nanorods (CdS/CN:PDI) was determined to be an excellent photocatalyst for oxidation reactions including photoelectrochemical water splitting, dye decolorization and the photocatalytic conversion of benzyl alcohol to benzaldehyde. Extensive structural characterization using HR-TEM, Raman, XPS, etc., confirmed wrapping of few-layered CN:PDI on CdS nanorods. The increased photoactivity in CdS/CN:PDI catalyst was ascribed to facile electron transfer from CdS to CN:PDI in comparison to CdS/g-C3N4, leading to an increased electron density on the surface of the photocatalyst to drive chemical reactions.T12-P02 University of Alberta | Publication | 2023-04-01 | Pawan Kumar, Ehsan Vahidzadeh, Kazi Alam, Devika Laishram, Kai Cui, Shankar, K. | | Probe sonication-assisted rapid synthesis of highly fluorescent sulfur quantum dotsA new type of heavy-metal free single-element nanomaterial, called sulfur quantum dots (SQDs), has gained significant attention due to its advantages over traditional semiconductor QDs for several biomedical and optoelectronic applications. A straightforward and rapid synthesis approach for preparing highly fluorescent SQDs is needed to utilize this nanomaterial for technological applications. Until now, only a few synthesis approaches have been reported; however, these approaches are associated with long reaction times and low quantum yields (QY). Herein, we propose a novel optimized strategy to synthesize SQDs using a mix of probe sonication and heating, which reduces the reaction time usually needed from 125 h to a mere 15 min. The investigation employs cavitation and vibration effects of high energy acoustic waves to break down the bulk sulfur into nano-sized particles in the presence of highly alkaline medium and oleic acid. In contrast to previous reports, the obtained SQDs exhibited excellent aqueous solubility, desirable photostability, and a relatively high photoluminescence QY up to 10.4% without the need of any post-treatment. Additionally, the as-synthesized SQDs show excitation-dependent emission and excellent stability in different pH (2−12) and temperature (20-80 ℃) environments. Hence, this strategy opens a new pathway for rapid synthesis of SQDs and may facilitate the use of these materials for biomedical and optoelectronic applications. T12-P02 University of Alberta | Publication | 2023-04-01 | Sachin Kadian, Narendra Chaulagain, Naveen Narasimhachar Joshi, Kazi Alam, Kai Cui, Shankar, K., Gaurav Manik, Roger Narayan | | Active Learning for Optimum Experimental Design - Insight into Perovskite OxidesFinding the optimum material with improved properties for a given application is challenging because data acquisition in materials science and chemistry is time consuming and expensive. Therefore, dealing with small datasets is a reality in chemistry, whether the data is obtained from synthesis or computational experiments. In this work, we propose a new artificial intelligence method based on active learning (AL) to guide new experiments with as little data as possible, for optimum experimental design. The AL method is applied to ABO3 perovskites where a descriptor based on atomic properties was developed. Several regressor algorithms were employed: artificial neural network, Gaussian process and support vector regressor. The developed AL method was applied in the experimental design of two important materials: non-stoichiometric perovskites (Ba(1-x)AxTi(1-y)ByO3) due to substituting ionic sites with different concentrations and elements (A = Ca, Sr, Cd; B = Zr, Sn, Hf), aiming at the maximization of the energy storage density; stoichiometric ABO3 perovskites where different elements are changed in the A and B sites for the minimization of the formation energy. AL for experimental design is implemented in the machine learning agent for chemistry and design (MLChem4D) software; which has the potential to be applied in inorganic and organic synthesis (e.g.: search for the optimum concentrations, catalysts, reactants, temperatures and pH to improve the yield) and materials science (e.g.: search the periodic table for the proper elements and their concentrations to improve the materials properties). The latter marks the first MLChem4D application for the design of perovskites.T12-P01, T12-P02 University of Alberta | Publication | 2023-04-01 | Maicon Pierre Lourenco, Alain Tchagang, Shankar, K., Venkataraman Thangadurai, Dennis R Salahub | | Insights into the Machine Learning Predictions of the Optical Response of Plasmon@Semiconductor Core-Shell NanocylindersThe application domain of deep learning (DL) has been extended into the realm of nanomaterials, photochemistry, and optoelectronics research. Here, we used the combination of a computer vision technique, namely convolutional neural network (CNN), with multilayer perceptron (MLP) to obtain the far-field optical response at normal incidence (along cylinder axis) of concentric cylindrical plasmonic metastructures such as nanorods and nanotubes. Nanotubes of Si, Ge, and TiO2 coated on either their inner wall or both their inner and outer walls with a plasmonic noble metal (Au or Ag) were thus modeled. A combination of a CNN and MLP was designed to accept the cross-sectional images of cylindrical plasmonic core-shell nanomaterials as input and rapidly generate their optical response. In addition, we addressed an issue related to DL methods, namely explainability. We probed deeper into these networks’ architecture to explain how the optimized network could predict the final results. Our results suggest that the DL network learns the underlying physics governing the optical response of plasmonic core-shell nanocylinders, which in turn builds trust in the use of DL methods in materials science and optoelectronics.T12-P01, T12-P02 University of Alberta | Publication | 2023-03-01 | | | Liquid-phase exfoliation of graphitic carbon nitrides studied by molecular dynamics simulationHYPOTHESIS
The superiority of graphitic carbon nitride (g-C3N4) nanosheet results from its large specific surface area, which can be achieved by exfoliation of the bulk layered structure. Liquid-phase exfoliation (LPE) is the best-known method for the synthesis of two-dimensional (2D) g-C3N4 nanosheets. However, experimental investigations do not allow for a molecular-level understanding of the process. Molecular dynamics (MD) simulations are expected to provide microscopic insights and quantitative evaluation of the energy consumption during LPE, thus facilitating the search of effective solvents for the LPE of 2D materials.
SIMULATIONS
MD simulations are carried out to simulate the LPE process by performing potential of mean force calculations for the separation of two stacked g-C3N4 nanosheets. Free energy of exfoliation is evaluated and compared among nine common solvents with distinct molecular structures.
FINDINGS
The most probable path for the exfoliation process is identified. The free energy of exfoliation is found to correlate directly with the solvent free energy of a single g-C3N4 nanosheet. The solvation is enthalpy-driven and affected by the mobility of the solvent molecules around the nanosheet. Based on the MD results, several strategies are proposed to guide the selection of solvents for effective LPE.T12-P02 University of Alberta | Publication | 2023-01-01 | | | C3N4 and C3N5 Nanosheets As Passivation Layers and Carrier Extractors for Inorganic Semiconductor Nanowires and Quantum DotsInorganic semiconductor nanowires and quantum dots made of chalcogenides, III-V semiconductors and halide perovskites offer exciting potential for optoelectronic devices. The orthogonalization possible in nanowires between the normally competing processes of charge generation and charge separation have been used to project very high operating performance exceeding that of thin films and single crystals in light harvesting devices such as solar cells, photodetectors, photocatalysts and photoelectrolyzers. Likewise, inorganic quantum dots with size-tunable absorption and emission spectra are excellent candidates for light emitting devices as well as light harvesting devices. However, the practical performance of inorganic nanowire based optoelectronic devices has significantly lagged theoretical predictions. A major reason for the discrepancy between theory and experiment is the presence of surface traps and defects in nanowires and quantum dots, which exhibit a large surface area to volume ratio. Several chemical treatments and annealing regimens have been employed to heal surface defects in nanowires and quantum dots. One popular strategy involves wrapping nanowires and/or quantum dots with a thin coating of a molecular monolayer (e.g. alkanethiols) or an atomic layer deposited conformal oxide. While such core-shell architectures are frequently effective in reducing surface defects, the surface passivation is invariably accompanied by a deterioration in optoelectronic properties due to the difficulty experienced by charge carriers in tunneling through the thin shell layer. The resulting trade-off between surface passivation and carrier extraction limits performance improvements in light harvesting devices. Thus there is a strong need for passivating layers that do not negatively impact carrier extraction.
Herein, we show that graphitic carbon nitride coatings are highly effective in passivating the surfaces of inorganic nanowires and quantum dots while preserving excellent carrier transport and extraction. Three illustrative examples are provided together with in-depth spectroscopic and electrical characterization:
(1) Cesium lead bromide (CsPbBr3) quantum dots passivated by g-C3N4 nanosheets and performing spectacularly as CO2 photoreduction catalysts and water-splitting photoanodes
(2) The double helical ternary semiconductor SnIP passivated by g-C3N4 nanosheets which experienced a remarkable improvement in photoelectrochemical performance
(3) Cadmium sulfide (CdS) nanowires passivated by C3N5 nanosheets resulting in a superior photocatalytic performanceT12-P02 University of Alberta | Activity | 2022-07-01 | Kazi Alam, Pawan Kumar, Devika Laishram, Charles Jensen, Annabelle Degg, Narendra Chaulagain, Frank Hegmann, Tom Nilges, Rakesh Sharma, Shankar, K. | | Plexcitons for Solar Energy Harvesting and Sensing DevicesThe 2023 MRS Fall Meeting & Exhibit will be held November 26 through December 1, 2023, in Boston, Massachusetts, at the Hynes Convention Center and adjacent Sheraton Boston Hotel. The world's foremost international scientific gathering for materials research, the MRS Fall Meeting showcases leading interdisciplinary research in both fundamental and applied areas presented by scientists from around the world.
Prof. Shankar will be delivering an Invited Talk in Symposium F23-044: Excitonic Materials. He will be speaking about the lab's recent fundamental studies and device results in Au nanoparticle-carbon nitride heterojunctions, Au-nanoisland cyanine J-aggregates, plasmon-CdS nanorod heterostructures and Ag decorated YMn2O5 nanowires.T12-P02 University of Alberta | Activity | 2023-11-26 | | | The importance of charge carrier dynamics for oxide photocatalysts and photoelectrocatalystsT12-P02 University of Alberta | Activity | 2023-04-21 | | | Life Cycle Assessment of High-Performance Monocrystalline TiO2 Nanorod Based Perovskite Solar CellsT12-P02, T13-P04 University of Alberta | Activity | 2022-07-28 | | | Extraction of hot carriers in plasmon coupled TiO2 nanoheterojunctions for high performance photoelectrochemical water splittingHybrid nanostructured photoanodes decorated with plasmonic gold nanoparticles (Au NPs) and carbon nitride quantum dots (CNQD) exhibited superior photoelectrochemical performance for water splitting in the visible-light regime because of the successful harvesting of plasmonic hot carriers. In this work, we demonstrate the efficient harvesting of hot holes generated in Au NPs for two different TiO2-based photoanode architectures.T12-P02 University of Alberta | Activity | 2022-05-26 | Narendra Chaulagain, Ehsan Vahidzadeh, Kazi Alam, Shankar, K. | | Metallophthalocyanine conjugated cellulose nanocrystals as a non-volatile memory and photocatalyst T12-P02 University of Alberta | Activity | 2022-05-26 | Narendra Chaulagain, Pawan Kumar, Kazi Alam, Shankar, K. | | Synergistic Enhancement of the Photo-electrochemical Performance of TiO2 Nanorod Arrays Through Embedded Plasmon and Surface Carbon Nitride Co-SensitizationT12-P02 University of Alberta | Activity | 2022-05-16 | | | Dendritic Copper Current Collectors as a Capacity Boosting Material for Polymer-Templated Si/Ge/C Anodes in Li-Ion BatteriesDendritic copper offers a highly effective method for synthesizing porous copper anodes due to its intricate branching structure. This morphology results in an elevated surface area-to-volume ratio, facilitating shortened electron pathways during aqueous and electrolyte permeation. Here, we demonstrate a procedure for a time- and cost-efficient synthesis routine of fern-like copper microstructures as a host for polymer-templated Si/Ge/C thin films. Dissolvable Zintl clusters and sol–gel chemistry are used to synthesize nanoporous coating as the anode. Cyclic voltammetry (CV) with KOH as the electrolyte is used to estimate the surface area increase in the dendritic copper current collectors (CCs). Half cells are assembled and tested with battery-related techniques such as CV, galvanostatic cycling, and electrochemical impedance spectroscopy, showing a capacity increase in the dendritic copper cells. Energy-dispersive X-ray spectroscopy is used to estimate the removal of K in the bulk after oxidizing the Zintl phase K12Si8Ge9 in the polymer/precursor blend with SiCl4. Furthermore, scanning electron microscopy images are provided to depict the thin films after synthesis and track the degradation of the half cells after cycling, revealing that the morphological degradation through alloying/dealloying is reduced for the dendritic Cu CC anodes as compared with the bare reference. Finally, we highlight this time- and cost-efficient routine for synthesizing this capacity-boosting material for low-mobility and high-capacity anode coatings.Other, T12-P02 University of Alberta | Publication | 2024-01-01 | Christian L Weindl, Christian E Fajman, Zhuijun Xu, Tianle Zheng, Gilles E Möhl, Narendra Chaulagain, Shankar, K., Ralph Gilles, Thomas F Fässler, Peter Müller-Buschbaum | | Predicting Free Energies of Exfoliation and Solvation for Graphitic Carbon Nitrides Using Machine LearningAs a metal-free and visible-light-responsive photocatalyst, graphitic carbon nitride (g-C3N4) has emerged as a new research hotspot and has attracted broad attention in the field of solar energy conversion and thin-film transistors. Liquid-phase exfoliation (LPE) is the best-known method for the synthesis of 2D g-C3N4 nanosheets. In LPE, bulk g-C3N4 is exfoliated in a solvent via high-shear mixing or sonication in order to produce a stable suspension of individual nanosheets. Two parameters of importance in gauging the performance of a solvent in LPE are the free energy required to exfoliate a unit area of layered materials into individual sheets in the solvent (ΔGexf) and the solvation free energy per unit area of a nanosheet (ΔGsol). While approximations for the free energies exist, they are shown in our previous work to be inaccurate and incapable of capturing the experimentally observed efficacy of LPE. Molecular dynamics (MD) simulations can provide accurate free-energy calculations, but doing so for every single solvent is time- and resource-consuming. Herein, machine learning (ML) algorithms are used to predict ΔGexf and ΔGsol for g-C3N4. First, a database for ΔGexf and ΔGsol is created based on a series of MD simulations involving 49 different solvents with distinct chemical structures and properties. The data set also includes values of critical descriptors for the solvents, including density, surface tension, dielectric constant, etc. Different ML methods are compared, accompanied by descriptor selection, to develop the most accurate model for predicting ΔGexf and ΔGsol. The extra tree regressor is shown to be the best performer among the six ML methods studied. Experimental validation of the model is conducted by performing dispersibility tests in several solvents for which the free energies are predicted. Finally, the influence of the selected descriptors on the free energies is analyzed, and strategies for solvent selection in LPE are proposed.T12-P02 University of Alberta | Publication | 2023-11-08 | Ehsan Shahini, Narendra Chaulagain, Shankar, K., Tian Tang | | Nanostructured Heterojunctions for Quantum Sensing, Generation of Solar Fuels and Low Cost PhotovoltaicsT12-P02 University of Alberta | Activity | 2024-03-25 | |
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