scholarly journals Radiative and Non-Radiative Recombination Pathways in Mixed-Phase TiO2 Nanotubes for PEC Water-Splitting

Catalysts ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 204 ◽  
Author(s):  
Rambabu Yalavarthi ◽  
Alberto Naldoni ◽  
Štěpán Kment ◽  
Luca Mascaretti ◽  
Hana Kmentová ◽  
...  
Keyword(s):  
Water Splitting ◽  
Water Oxidation ◽  
Transfer Rate ◽  
Electrochemical Impedance ◽  
Mixed Phase ◽  
Transfer Efficiency ◽  
Electron Hole ◽  
Surface Trap ◽  
Hole Transfer ◽  
Recombination Processes

Anatase and rutile mixed-phase TiO2 with an ideal ratio has been proven to significantly enhance photoelectrochemical (PEC) activity in water-splitting applications due to suppressing the electron–hole recombination. However, the mechanism of this improvement has not been satisfactory described yet. The PEC water oxidation (oxygen evolution) at the interface of TiO2 photoanode and electrolyte solution is determined by the fraction of the photogenerated holes that reach the solution and it is defined as the hole transfer efficiency. The surface and bulk recombination processes in semiconductor photoanodes majorly influence the hole transfer efficiency. In this work, we study the hole transfer process involved in mixed-phase TiO2 nanotube arrays/solution junction using intensity-modulated photocurrent and photovoltage spectroscopy (IMPS and IMVS); then, we correlate the obtained hole transfer rate constants to (photo)electrochemical impedance spectroscopy (PEIS) measurements. The results suggest that the enhanced performance of the TiO2 mixed-phase is due to the improved hole transfer rate across the TiO2/liquid interface as well as to the decrease in the surface trap recombination of the holes.

Mo-doped BiVO4 thin films – high photoelectrochemical water splitting performance achieved by a tailored structure and morphology

2017 ◽  
Vol 1 (8) ◽  
pp. 1830-1846 ◽  
Author(s):  
Martin Rohloff ◽  
Björn Anke ◽  
Siyuan Zhang ◽  
Ulrich Gernert ◽  
Christina Scheu ◽  
...  
Keyword(s):  
Thin Films ◽  
Water Splitting ◽  
Sol Gel ◽  
Surface Recombination ◽  
Photoelectrochemical Water Splitting ◽  
Transfer Efficiency ◽  
Hole Transfer ◽  
Structure And Morphology ◽  
Sol Gel Synthesis ◽  
Reduced Surface

Facile sol–gel synthesis of Mo:BiVO4 thin films with optimized morphology results in reduced surface recombination and enhanced hole transfer efficiency.

scholarly journals Identifying the Spectroelectrochemical Characteristics of Hematite Photoanodes for Water Oxidation

2021 ◽  
Author(s):  
Jifang Zhang ◽  
Qiyuan Lin ◽  
Zhenlei Wang ◽  
Haowen Liu ◽  
Yuegang Zhang
Keyword(s):  
Water Splitting ◽  
Water Oxidation ◽  
Surface States ◽  
Reaction Pathways ◽  
Reaction Intermediates ◽  
Fermi Level Pinning ◽  
Solar Water Splitting ◽  
Interfacial Processes ◽  
Active Reaction ◽  
Recombination Processes

Achieving efficient solar water splitting using hematite (α-Fe2O3), one of the most promising candidates for photoanodes, requires photogenerated holes to be efficiently used for water oxidation. However, this goal is obstructed by multiple undesirable recombination processes, as well as insufficient fundamental mechanistic understandings of water oxidation kinetics, particularly as to the nature of reaction pathways and possible reaction intermediates. Here we spectroelectro-chemically identify some of the most critical interfacial processes which determine the photoelectrocatalytic efficiencies of water oxidation, for hematite films with varied surface properties by tailoring the doping level of titanium. The spectroscopic signals of the processes inactive for water oxidation, including oxidation of intra-gap Fe2+ states and Fermi level pinning, are successfully distinguished from that of the active reaction intermediate, Fe(IV)=O. In addition, our kinetic analyses reveal two water oxidation pathways, of which the direct hole transfer mechanism becomes dominant over the surface states-mediated mechanism when the hematite surface is reconstructed by high levels of titanium dopants.

Collision induced charge separation in ground-state water splitting dynamics

2018 ◽  
Vol 20 (17) ◽  
pp. 12229-12240 ◽  
Author(s):  
Kentaro Yamamoto ◽  
Kazuo Takatsuka
Keyword(s):  
Water Splitting ◽  
Ground State ◽  
Charge Separation ◽  
Electron Hole ◽  
Hole Transfer ◽  
State Water ◽  
Induced Charge ◽  
State Charge

The pathway of one-way electron–hole transfer induced by proton reciprocating motions, thereby realizing the collision induced ground-state charge separation.

scholarly journals Identifying the Spectroelectrochemical Characteristics of Hematite Photoanodes for Water Oxidation

2021 ◽  
Author(s):  
Jifang Zhang ◽  
Qiyuan Lin ◽  
Zhenlei Wang ◽  
Haowen Liu ◽  
Yuegang Zhang
Keyword(s):  
Water Splitting ◽  
Water Oxidation ◽  
Surface States ◽  
Reaction Pathways ◽  
Reaction Intermediates ◽  
Fermi Level Pinning ◽  
Solar Water Splitting ◽  
Interfacial Processes ◽  
Active Reaction ◽  
Recombination Processes

Achieving efficient solar water splitting using hematite (α-Fe2O3), one of the most promising candidates for photoanodes, requires photogenerated holes to be efficiently used for water oxidation. However, this goal is obstructed by multiple undesirable recombination processes, as well as insufficient fundamental mechanistic understandings of water oxidation kinetics, particularly as to the nature of reaction pathways and possible reaction intermediates. Here we spectroelectro-chemically identify some of the most critical interfacial processes which determine the photoelectrocatalytic efficiencies of water oxidation, for hematite films with varied surface properties by tailoring the doping level of titanium. The spectroscopic signals of the processes inactive for water oxidation, including oxidation of intra-gap Fe2+ states and Fermi level pinning, are successfully distinguished from that of the active reaction intermediate, Fe(IV)=O. In addition, our kinetic analyses reveal two water oxidation pathways, of which the direct hole transfer mechanism becomes dominant over the surface states-mediated mechanism when the hematite surface is reconstructed by high levels of titanium dopants.

Defective ZnFe2O4 nanorods with oxygen vacancy for photoelectrochemical water splitting

Nanoscale ◽  
2015 ◽  
Vol 7 (45) ◽  
pp. 19144-19151 ◽  
Author(s):  
Ju Hun Kim ◽  
Youn Jeong Jang ◽  
Jin Hyun Kim ◽  
Ji-Wook Jang ◽  
Sun Hee Choi ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Oxygen Vacancy ◽  
Water Splitting ◽  
Water Oxidation ◽  
Oxygen Vacancies ◽  
Electron Donors ◽  
Surface Trap ◽  
Oxidation Activity ◽  
Vacuum Atmosphere ◽  
Photoelectrochemical Water Oxidation

A 1D ZnFe2O4 photoanode is treated under a hydrogen or vacuum atmosphere to improve the photoelectrochemical water oxidation activity up to 20 times. This post-treatment creates oxygen vacancies in the ZnFe2O4 lattice that serve as a source of electron donors and passivates surface trap sites, and as a result improves charge transfer.

scholarly journals Efficient Photoelectrochemical Water Splitting by Tailoring MoS2/CoTe Heterojunction in a Photoelectrochemical Cell

Nanomaterials ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 2341
Author(s):  
Effat Sitara ◽  
Habib Nasir ◽  
Asad Mumtaz ◽  
Muhammad Fahad Ehsan ◽  
Manzar Sohail ◽  
...  
Keyword(s):  
Water Splitting ◽  
Electrochemical Impedance ◽  
Linear Sweep Voltammetry ◽  
Photocurrent Density ◽  
Photoelectrochemical Water Splitting ◽  
Photoelectrochemical Cell ◽  
Electron Hole ◽  
Pair Separation ◽  
Electron Hole Pair ◽  
Electrochemical Impedance Spectroscopic

Solar energy conversion through photoelectrochemical water splitting (PEC) is an upcoming promising technique. MoS2/CoTe heterostructures were successfully prepared and utilized for PEC studies. MoS2 and CoTe were prepared by a hydrothermal method which were then ultrasonicated with wt. % ratios of 1:3, 1:1 and 3:1 to prepare MoS2/CoTe (1:3), MoS2/CoTe (1:1) and MoS2/CoTe (3:1) heterostructure, respectively. The pure materials and heterostructures were characterized by XRD, UV–vis-DRS, SEM, XPS, PL and Raman spectroscopy. Photoelectrochemical measurements were carried out by linear sweep voltammetry and electrochemical impedance spectroscopic measurements. A maximum photocurrent density of 2.791 mA/cm2 was observed for the MoS2/CoTe (1:1) heterojunction which is about 11 times higher than the pristine MoS2. This current density was obtained at an applied bias of 0.62 V vs. Ag/AgCl (1.23 V vs. RHE) under the light intensity of 100 mW/cm2 of AM 1.5G illumination. The enhanced photocurrent density may be attributed to the efficient electron–hole pair separation. The solar to hydrogen conversion efficiency was found to be 0.84% for 1:1 MoS2/CoTe, signifying the efficient formation of the p-n junction. This study offers a novel heterojunction photocatalyst, for PEC water splitting.

scholarly journals Ab Initio Studies of Bimetallic-Doped {0001} Hematite Surface for Enhanced Photoelectrochemical Water Splitting

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 940
Author(s):  
Joseph Simfukwe ◽  
Refilwe Edwin Mapasha ◽  
Artur Braun ◽  
Mmantsae Diale
Keyword(s):  
Water Splitting ◽  
Water Oxidation ◽  
Density Functional ◽  
Doping Concentration ◽  
Visible Region ◽  
Photon Absorption ◽  
Electron Hole ◽  
Functional Theory ◽  
Valance Band Maximum ◽  
Electron Holes

First-principles calculations based on density functional theory (DFT) were carried out to study the energetic stability and electronic properties of a bimetallic-doped α-Fe2O3 photoanode surface with (Zn, Ti) and (Zn, Zr) pairs for enhanced PEC water splitting. The doped systems showed negative formation energies under both O-rich and Fe-rich conditions which make them thermodynamically stable and possible to be synthesised. It is found that in a bimetallic (Zn, Ti)-doped system, at a doping concentration of 4.20% of Ti, the bandgap decreases from 2.1 eV to 1.80 eV without the formation of impurity states in the bandgap. This is favourable for increased photon absorption and efficient movement of charges from the valance band maximum (VBM) to the conduction band minimum (CBM). In addition, the CBM becomes wavy and delocalised, suggesting a decrease in the charge carrier mass, enabling electron–holes to successfully diffuse to the surface, where they are needed for water oxidation. Interestingly, with single doping of Zr at the third layer (L3) of Fe atoms of the {0001} α-Fe2O3 surface, impurity levels do not appear in the bandgap, at both concentrations of 2.10% and 4.20%. Furthermore, at 2.10% doping concentration of α-Fe2O3 with Zr, CBM becomes delocalised, suggesting improved carrier mobility, while the bandgap is altered from 2.1 eV to 1.73 eV, allowing more light absorption in the visible region. Moreover, the photocatalytic activities of Zr-doped hematite could be improved further by codoping it with Zn because Zr is capable of increasing the conductivity of hematite by the substitution of Fe3+ with Zr4+, while Zn can foster the surface reaction and reduce quick recombination of the electron–hole pairs.

Towards zero bias photoelectrochemical water splitting: onset potential improvement on a Mg:GaN modified-Ta3N5 photoanode

2018 ◽  
Vol 6 (31) ◽  
pp. 15265-15273 ◽  
Author(s):  
Ela Nurlaela ◽  
Yutaka Sasaki ◽  
Mamiko Nakabayashi ◽  
Naoya Shibata ◽  
Taro Yamada ◽  
...  
Keyword(s):  
Water Splitting ◽  
Photoelectrochemical Water Splitting ◽  
Electron Hole ◽  
Zero Bias ◽  
Hole Transfer ◽  
Potential Shift ◽  
Onset Potential ◽  
Potential Improvement ◽  
Mg Doped

A remarkable onset potential shift has been demonstrated on Ta3N5 modified with a Mg:GaN layer. The Mg-doped GaN band positions facilitate more efficient electron/hole transfer to/from Ta3N5, inducing a negative onset potential shift to 0 vs. RHE.

Electrochemical and photoelectrochemical water splitting with a CoOx catalyst prepared by flame assisted deposition

2020 ◽  
Vol 49 (3) ◽  
pp. 588-592 ◽  
Author(s):  
Fusheng Li ◽  
Ziqi Zhao ◽  
Hao Yang ◽  
Dinghua Zhou ◽  
Yilong Zhao ◽  
...  
Keyword(s):  
Cobalt Oxide ◽  
Water Splitting ◽  
Water Oxidation ◽  
Oxide Catalyst ◽  
Photoelectrochemical Water Splitting ◽  
Deposition Method ◽  
Photoelectrochemical Water Oxidation

A cobalt oxide catalyst prepared by a flame-assisted deposition method on the surface of FTO and hematite for electrochemical and photoelectrochemical water oxidation, respectively.

scholarly journals Au decorated BiVO4 inverse opal for efficient visible light driven water oxidation

RSC Advances ◽  
2021 ◽  
Vol 11 (15) ◽  
pp. 8751-8758
Author(s):  
Xiaonong Wang ◽  
Xiaoxia Li ◽  
Jingxiang Low
Keyword(s):  
Visible Light ◽  
Water Splitting ◽  
Water Oxidation ◽  
Inverse Opal ◽  
Photocatalytic Water Splitting ◽  
Visible Light Driven

Photocatalytic water splitting provides an effective way to prepare hydrogen and oxygen.

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