scholarly journals Surface Electron-Hole Rich Species Active in the Electrocatalytic Water Oxidation

2021 ◽  
Author(s):  
Juan-Jesús Velasco-Vélez ◽  
Emilia A. Carbonio ◽  
Cheng-Hao Chuang ◽  
Cheng-Jhih Hsu ◽  
Jyh-Fu Lee ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Surface Electron ◽  
Electron Hole

Dynamical interaction of surface electron-hole pairs with surface defects: Surface spectroscopy monitored by particle emissions

1993 ◽  
Vol 70 (16) ◽  
pp. 2495-2498 ◽  
Author(s):  
Jun’ ichi Kanasaki ◽  
Akiko Okano ◽  
Ken’ ichi Ishikawa ◽  
Yasuo Nakai ◽  
Noriaki Itoh
Keyword(s):  
Surface Defects ◽  
Surface Electron ◽  
Electron Hole ◽  
Particle Emissions ◽  
Dynamical Interaction ◽  
Surface Spectroscopy

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.

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.

Metal Doped TiO2 Photocatalysts for CO2 Photoreduction

2013 ◽  
Vol 757 ◽  
pp. 243-256 ◽  
Author(s):  
Amir Al-Ahmed
Keyword(s):  
Chemical Reactions ◽  
Water Oxidation ◽  
Active Species ◽  
Electron Hole ◽  
Highly Active ◽  
Redox Active ◽  
Recent Developments ◽  
Metal Doped ◽  
Generate Electron ◽  
Hole Recombination

Greenhouse gases such as CO2, CH4 and CFCs are the primary causes of global warming. Worldwide, people are exploring techniques to reduce, capture, store CO2 gas and even convert this gas in to some useful chemicals. CO2 can be transformed into hydrocarbons in a photocatalytic reaction. The advantage of photo reduction of CO2 is to use inexhaustible solar energy. Knowledge of elementary steps in photocatalytic CO2 reduction under UV irradiation is required in order to improve the photo efficiency of the photocatalyst. A semiconductor photocatalyst mediating CO2 reduction and water oxidation needs to absorb light energy, generate electron hole pairs, spatially separate them, transfer them to redox active species across the interface and minimize electron hole recombination. This requires the semiconductor to have its conduction band electrons at higher energy compared to the CO2 reduction potential while the holes in the valence band need to be able to oxidize water to O2. A single semiconductor does not usually satisfy these requirements. Some recent developments in this field have been moves towards rational photocatalyst design, the use of highly active isolated Ti-species in mesoporous and microporous materials, metal-doping of TiO2, development of catalysts active at longer wavelengths than can be achieved with commercially available titania etc. The use of transition-metal loaded titanium dioxide (TiO2) has been extensively studied as a photocatalyst in photoreactions. Unlike traditional catalysts drive chemical reactions by thermal energy, semiconducting photocatalysts can induce chemical reactions by inexhaustible sunlight and convert CO2 in to the useful hydrocarbons. In this review article we will cover different aspects of metal doped nano structured TiO2 photocatalysts, used to convert/reduce CO2 in to useful hydrocarbons.

scholarly journals Fermi surface electron–hole instability of the (TMTSF)2PF6 Bechgaard salt revealed by the first-principles Lindhard response function

2020 ◽  
Vol 32 (34) ◽  
pp. 345701
Author(s):  
Bogdan Guster ◽  
Miguel Pruneda ◽  
Pablo Ordejón ◽  
Enric Canadell ◽  
Jean-Paul Pouget
Keyword(s):  
Fermi Surface ◽  
Response Function ◽  
First Principles ◽  
Surface Electron ◽  
Electron Hole ◽  
Bechgaard Salt

Status of Surface Electron/Hole Layer on Oxide Ferroelectrics

2007 ◽  
Vol 355 (1) ◽  
pp. 13-18 ◽  
Author(s):  
Yukio Watanabe ◽  
Yosuke Urakami ◽  
Sigeru Kaku ◽  
Daisuke Matsumoto
Keyword(s):  
Surface Electron ◽  
Electron Hole

scholarly journals Dynamics of photogenerated holes in undoped BiVO4 photoanodes for solar water oxidation

2014 ◽  
Vol 5 (8) ◽  
pp. 2964-2973 ◽  
Author(s):  
Yimeng Ma ◽  
Stephanie R. Pendlebury ◽  
Anna Reynal ◽  
Florian Le Formal ◽  
James R. Durrant
Keyword(s):  
Absorption Spectroscopy ◽  
Water Oxidation ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Electron Hole ◽  
Solar Water ◽  
Solar Water Oxidation ◽  
Oxidation Efficiency ◽  
Hole Recombination

We use transient absorption spectroscopy and photoelectrochemical methods to study the dynamics of photogenerated holes in BiVO4 for solar water oxidation. The back electron/hole recombination is found to be slow and therefore competes with water oxidation, limiting water oxidation efficiency.

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.

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.

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