scholarly journals Synergistic Design of Anatase–Rutile TiO2 Nanostructured Heterophase Junctions toward Efficient Photoelectrochemical Water Oxidation

Coatings ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 557
Author(s):  
Sangwoo Lee ◽  
A. Young Cho ◽  
You Seung Rim ◽  
Jun-Young Park ◽  
Taekjib Choi
Keyword(s):  
Water Oxidation ◽  
Photocurrent Density ◽  
Band Alignment ◽  
Type Ii ◽  
Electron Hole ◽  
Rutile Tio2 ◽  
Photogenerated Electrons ◽  
Phase Alignment ◽  
Efficient Charge

Synergistically designing porous nanostructures and appropriate band alignment for TiO2 heterophase junctions is key to efficient charge transfer, which is crucial in enhancing photoelectrochemical (PEC) water splitting for hydrogen production. Here, we investigate the efficiency of PEC water oxidation in anatase–rutile TiO2 nanostructured heterophase junctions that present the type-II band alignment. We specifically prove the importance of a phase alignment in heterophase junction for effective charge separation. The TiO2 heterophase junctions were prepared by transferring TiO2 nanotube (TNT) arrays onto FTO substrate with the help of a TiO2 nanoparticle (TNP) glue layer. The PEC characterization reveals that the rutile (R)-TNT/anatase (A)-TNP heterophase junction has a higher photocurrent density than those of A-TNT/R-TNP junction and anatase or rutile single phase, corresponding to twofold enhanced efficiency. This type-II band alignment of R-TNT/A-TNP for water oxidation, in which photogenerated electrons (holes) will flow from rutile (anatase) to anatase (rutile), enables to facilitate efficient electron-hole separation as well as lower the effective bandgap of heterophase junctions. This work provides insight into the functional role of heterophase junction for boosting the PEC performances of TiO2 nanostructures.

scholarly journals Boosting the Activity and Stability of Copper Tungsten Nanoflakes toward Solar Water Oxidation by Iridium-Cobalt Phosphates Modification

Catalysts ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 913
Author(s):  
Chao Li ◽  
Peng Diao
Keyword(s):  
Water Oxidation ◽  
Collection Efficiency ◽  
Potassium Phosphate ◽  
Photocurrent Density ◽  
Charge Transfer Resistance ◽  
Buffer Solution ◽  
Hydrogen Electrode ◽  
Electron Hole ◽  
Transfer Resistance ◽  
Hole Recombination

Severe interfacial electron–hole recombination greatly limits the performance of CuWO4 photoanode towards the photoelectrochemical (PEC) oxygen evolution reaction (OER). Surface modification with an OER cocatalyst can reduce electron–hole recombination and thus improve the PEC OER performance of CuWO4. Herein, we coupled CuWO4 nanoflakes (NFs) with Iridium–cobalt phosphates (IrCo-Pi) and greatly improved the photoactivity of CuWO4. The optimized photocurrent density for CuWO4/IrCo-Pi at 1.23 V vs. reversible hydrogen electrode (RHE) rose to 0.54 mA∙cm−2, a ca. 70% increase over that of bare CuWO4 (0.32 mA∙cm−2). Such improved photoactivity was attributed to the enhanced hole collection efficiency, which resulted from the reduced charge-transfer resistance via IrCo-Pi modification. Moreover, the as-deposited IrCo-Pi layer well coated the inner CuWO4 NFs and effectively prevented the photoinduced corrosion of CuWO4 in neutral potassium phosphate (KPi) buffer solution, eventually leading to a superior stability over the bare CuWO4. The facile preparation of IrCo-Pi and its great improvement in the photoactivity make it possible to design an efficient CuWO4/cocatalyst system towards PEC water oxidation.

Insights into Charge Transfer at the Cluster/semiconductor Interface for In-Depth Understanding the Role of Atomically Precise Silver Cluster

2019 ◽  
Author(s):  
Yu Wang ◽  
Xiao-He Liu ◽  
Qiankun Wang ◽  
Martin Quick ◽  
Sergey Kovalenko ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Band Gap ◽  
Metal Clusters ◽  
Silver Cluster ◽  
Organometallic Complexes ◽  
Band Alignment ◽  
Transient Absorption Spectroscopy ◽  
Type Ii ◽  
Semiconductor Interface

A cluster/semiconductor model is built for exploring the role of noble metal clusters in a photocatalytic system. The incorporation of an atomically precise nanocluster, e.g. Ag<sub>44</sub>(SR)<sub>30</sub>, onto a large band gap semiconductor such as TiO<sub>2</sub> allows to obtain a clear interface and thus simplify the system. The composite is employed for photocatalytic H<sub>2</sub> generation. It’s found that changing the light source from visible light to simulated sunlight leads to an enhancement by three orders of magnitude. The H<sub>2</sub> production rate reaches 7.4 mmol/h/g<sub>catalyst</sub> which is five times higher than that of Ag nanoparticles modified TiO<sub>2</sub> and even comparable to that of the similar conditioned Pt nanoparticle modified TiO<sub>2</sub>. Energy band alignment and transient absorption spectroscopy, together with other studies, reveal that the role of the metal clusters is different from both organometallic complexes and plasmonic-nanoparticles. A type-II heterojunction charge transfer route is achieved under UV-vis irradiation, in which the cluster serves as small band gap semiconductor. The type-II photosystem has a more efficient charge separation ability, which contributes significantly to the enhanced catalytic performance. This finding endows the clusters a broad platform as cocatalysts rather than merely photosensitizers in the applications of light energy conversion.

scholarly journals A stable dye-sensitized photoelectrosynthesis cell mediated by a NiO overlayer for water oxidation

2019 ◽  
Vol 117 (23) ◽  
pp. 12564-12571 ◽  
Author(s):  
Degao Wang ◽  
Fujun Niu ◽  
Michael J. Mortelliti ◽  
Matthew V. Sheridan ◽  
Benjamin D. Sherman ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Photocurrent Density ◽  
Oxidation Catalysis ◽  
Oxidation Catalyst ◽  
Photoelectrochemical Cells ◽  
Half Cell ◽  
Dye Sensitized ◽  
Light Absorber ◽  
Water Oxidation Catalysis

In the development of photoelectrochemical cells for water splitting or CO2reduction, a major challenge is O2evolution at photoelectrodes that, in behavior, mimic photosystem II. At an appropriate semiconductor electrode, a water oxidation catalyst must be integrated with a visible light absorber in a stable half-cell configuration. Here, we describe an electrode consisting of a light absorber, an intermediate electron donor layer, and a water oxidation catalyst for sustained light driven water oxidation catalysis. In assembling the electrode on nanoparticle SnO2/TiO2electrodes, a Ru(II) polypyridyl complex was used as the light absorber, NiO was deposited as an overlayer, and a Ru(II) 2,2′-bipyridine-6,6′-dicarboxylate complex as the water oxidation catalyst. In the final electrode, addition of the NiO overlayer enhanced performance toward water oxidation with the final electrode operating with a 1.1 mA/cm2photocurrent density for 2 h without decomposition under one sun illumination in a pH 4.65 solution. We attribute the enhanced performance to the role of NiO as an electron transfer mediator between the light absorber and the catalyst.

Insights into Charge Transfer at the Cluster/semiconductor Interface for In-Depth Understanding the Role of Atomically Precise Silver Cluster

2019 ◽  
Author(s):  
Yu Wang ◽  
Xiao-He Liu ◽  
Qiankun Wang ◽  
Martin Quick ◽  
Sergey Kovalenko ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Band Gap ◽  
Metal Clusters ◽  
Silver Cluster ◽  
Organometallic Complexes ◽  
Band Alignment ◽  
Transient Absorption Spectroscopy ◽  
Type Ii ◽  
Semiconductor Interface

A cluster/semiconductor model is built for exploring the role of noble metal clusters in a photocatalytic system. The incorporation of an atomically precise nanocluster, e.g. Ag<sub>44</sub>(SR)<sub>30</sub>, onto a large band gap semiconductor such as TiO<sub>2</sub> allows to obtain a clear interface and thus simplify the system. The composite is employed for photocatalytic H<sub>2</sub> generation. It’s found that changing the light source from visible light to simulated sunlight leads to an enhancement by three orders of magnitude. The H<sub>2</sub> production rate reaches 7.4 mmol/h/g<sub>catalyst</sub> which is five times higher than that of Ag nanoparticles modified TiO<sub>2</sub> and even comparable to that of the similar conditioned Pt nanoparticle modified TiO<sub>2</sub>. Energy band alignment and transient absorption spectroscopy, together with other studies, reveal that the role of the metal clusters is different from both organometallic complexes and plasmonic-nanoparticles. A type-II heterojunction charge transfer route is achieved under UV-vis irradiation, in which the cluster serves as small band gap semiconductor. The type-II photosystem has a more efficient charge separation ability, which contributes significantly to the enhanced catalytic performance. This finding endows the clusters a broad platform as cocatalysts rather than merely photosensitizers in the applications of light energy conversion.

scholarly journals Quantum dot and electron acceptor nano-heterojunction for photo-induced capacitive charge-transfer

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Onuralp Karatum ◽  
Guncem Ozgun Eren ◽  
Rustamzhon Melikov ◽  
Asim Onal ◽  
Cleva W. Ow-Yang ◽  
...  
Keyword(s):  
Heavy Metal ◽  
Charge Transfer ◽  
Quantum Dot ◽  
Electron Acceptor ◽  
Band Alignment ◽  
Fullerene Derivative ◽  
Type Ii ◽  
Trap States ◽  
Electron Hole ◽  
Donor Acceptor

AbstractCapacitive charge transfer at the electrode/electrolyte interface is a biocompatible mechanism for the stimulation of neurons. Although quantum dots showed their potential for photostimulation device architectures, dominant photoelectrochemical charge transfer combined with heavy-metal content in such architectures hinders their safe use. In this study, we demonstrate heavy-metal-free quantum dot-based nano-heterojunction devices that generate capacitive photoresponse. For that, we formed a novel form of nano-heterojunctions using type-II InP/ZnO/ZnS core/shell/shell quantum dot as the donor and a fullerene derivative of PCBM as the electron acceptor. The reduced electron–hole wavefunction overlap of 0.52 due to type-II band alignment of the quantum dot and the passivation of the trap states indicated by the high photoluminescence quantum yield of 70% led to the domination of photoinduced capacitive charge transfer at an optimum donor–acceptor ratio. This study paves the way toward safe and efficient nanoengineered quantum dot-based next-generation photostimulation devices.

Role of Transition Metal-Hydroxide (M-OHx , M=Mn, Fe, Ni, Co) Co-catalyst Loading : Efficiency and Stability of CdS Photoanode

2015 ◽  
Vol 1776 ◽  
pp. 1-6 ◽  
Author(s):  
Alka Pareek ◽  
Pradip Paik ◽  
Pramod H. Borse
Keyword(s):  
Transition Metal ◽  
Water Oxidation ◽  
Photocurrent Density ◽  
Chemical Precipitation ◽  
Metal Hydroxide ◽  
Photoelectrochemical Cell ◽  
Precipitation Method ◽  
Catalyst Loading ◽  
Co Catalyst

ABSTRACTIn this work we have synthesized the colloidal particles of transition metal-hydroxide (M= Ni, Co, Mn, Fe) by a simple chemical precipitation method. The surface of spray deposited CdS thin films were modified using nano-colloids to utlize them as water oxidation catalysts (WOC) for the photoelectrochemical cell (PEC). A systematic comparison of the PEC performance of modified and unmodified film is carried out to understand the role of co-catalyst. Ni(OH)2 modification yields 3.4 times higher photocurrent density than bare CdS photoanode, and exhibits hydrogen-evolution rate of 600 μmol/hr. Fe(OH)2 modified film shows best stability of 8 hours as compared to the others.

Surface-reduced Si-doped TiO2 nanotubes for high-efficiency photoelectrochemical water splitting

2019 ◽  
Vol 12 (06) ◽  
pp. 1940004
Author(s):  
Dawei Si ◽  
Zhenbiao Dong ◽  
Ting Li ◽  
Dongyan Ding ◽  
Congqin Ning
Keyword(s):  
Water Splitting ◽  
High Efficiency ◽  
Photocurrent Density ◽  
Reduction Reaction ◽  
Photoelectrochemical Water Splitting ◽  
Defect States ◽  
Photogenerated Electrons ◽  
Long Time ◽  
Si Doped

TiO2 is a promising photocatalyst in the reaction of water splitting for hydrogen. Here, we used NaBH4 reduction reaction to introduce [Formula: see text]/VO defect states into Si-doped TiO2 nanotubes and investigated the photoelectrochemical water splitting properties. It was found that the photocatalytic activity was improved through NaBH4 reduction because of the existence of [Formula: see text]/VO. The defect states ([Formula: see text]/VO) could play a role of capture trap and accelerate the separation of photogenerated electrons and holes. The photocurrent density of the Si-doped TiO2 nanotubes reduced for 3[Formula: see text]h was 1.5[Formula: see text]mA/cm2 compared to 0.7[Formula: see text]mA/cm2 of the unreduced nanotubes. The conversion efficiency was 0.7%, which was almost 4 times than that of pure TiO2. On the other hand, reduction for a long time would generate excess defect states and thus cause the decrease of photocurrent density. Excess defect states could act as the recombination centers of photogenerated electrons and holes.

scholarly journals Tunable Electronic Properties of Type-II SiS2/WSe2 Hetero-Bilayers

Nanomaterials ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 2037
Author(s):  
Yue Guan ◽  
Xiaodan Li ◽  
Ruixia Niu ◽  
Ningxia Zhang ◽  
Taotao Hu ◽  
...  
Keyword(s):  
Band Gap ◽  
Electronic Properties ◽  
Density Functional ◽  
Photogenerated Electron ◽  
Strain Range ◽  
Band Alignment ◽  
Type Ii ◽  
Electron Hole ◽  
Structural And Electronic Properties ◽  
Indirect Band Gap

First-principle calculations based on the density functional theory (DFT) are implemented to study the structural and electronic properties of the SiS2/WSe2 hetero-bilayers. It is found that the AB-2 stacking model is most stable among all the six SiS2/WSe2 heterostructures considered in this work. The AB-2 stacking SiS2/WSe2 hetero-bilayer possesses a type-II band alignment with a narrow indirect band gap (0.154 eV and 0.738 eV obtained by GGA-PBE and HSE06, respectively), which can effectively separate the photogenerated electron–hole pairs and prevent the recombination of the electron–hole pairs. Our results revealed that the band gap can be tuned effectively within the range of elastic deformation (biaxial strain range from −7% to 7%) while maintaining the type-II band alignment. Furthermore, due to the effective regulation of interlayer charge transfer, the band gap along with the band offset of the SiS2/WSe2 heterostructure can also be modulated effectively by applying a vertical external electric field. Our results offer interesting alternatives for the engineering of two-dimensional material-based optoelectronic nanodevices.

Theoretical investigation on the photoelectrochemical anticorrosion mechanism of SnO2–TiO2nanotube

2019 ◽  
Vol 18 (03) ◽  
pp. 1950016 ◽  
Author(s):  
Yang Meng ◽  
Jianjun Zhang ◽  
Zhunzhun Wang ◽  
Jin-Xia Liang ◽  
Chun Zhu
Keyword(s):  
Density Functional ◽  
Composite Films ◽  
Photocurrent Density ◽  
304 Stainless Steel ◽  
Functional Theory ◽  
Photogenerated Electrons ◽  
Theoretical Investigations ◽  
Charge Analysis ◽  
Good Agreement

In this work, the calculated electron density difference, Bader charge analysis and the density of states (DOS) of SnO2–TiO2-nanotubes (NTs) indicate that the electrons are transferred from the Ti atoms of TiO2into the O atoms of (SnO[Formula: see text] in SnO2–TiO2-NTs and the supported (SnO[Formula: see text] cluster acts as the role of storage for photogenerated electrons excited from TiO2-NTs, which is in good agreement with experimental results that the SnO2–TiO2-NTs composite films have higher photocurrent density for photocathodic protection of 304 stainless steel (304SS). The theoretical investigations provide a plausible explanation for the photoelectrochemical anticorrosion mechanism of SnO2–TiO2-NTs using periodic density functional theory (DFT).

scholarly journals Electron–hole superfluidity in strained Si/Ge type II heterojunctions

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Sara Conti ◽  
Samira Saberi-Pouya ◽  
Andrea Perali ◽  
Michele Virgilio ◽  
François M. Peeters ◽  
...  
Keyword(s):  
Quantum Well ◽  
Device Fabrication ◽  
Band Alignment ◽  
Einstein Condensation ◽  
Type Ii ◽  
Electron Hole ◽  
Strained Si ◽  
Step Procedure ◽  
Bose Einstein ◽  
Lattice Matched

AbstractExcitons are promising candidates for generating superfluidity and Bose–Einstein condensation (BEC) in solid-state devices, but an enabling material platform with in-built band structure advantages and scaling compatibility with industrial semiconductor technology is lacking. Here we predict that spatially indirect excitons in a lattice-matched strained Si/Ge bilayer embedded into a germanium-rich SiGe crystal would lead to observable mass-imbalanced electron–hole superfluidity and BEC. Holes would be confined in a compressively strained Ge quantum well and electrons in a lattice-matched tensile strained Si quantum well. We envision a device architecture that does not require an insulating barrier at the Si/Ge interface, since this interface offers a type II band alignment. Thus the electrons and holes can be kept very close but strictly separate, strengthening the electron–hole pairing attraction while preventing fast electron–hole recombination. The band alignment also allows a one-step procedure for making independent contacts to the electron and hole layers, overcoming a significant obstacle to device fabrication. We predict superfluidity at experimentally accessible temperatures of a few Kelvin and carrier densities up to ~6 × 1010 cm−2, while the large imbalance of the electron and hole effective masses can lead to exotic superfluid phases.

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