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Suzuki Y.,Japan National Institute of Advanced Industrial Science and Technology | Furube A.,Japan National Institute of Advanced Industrial Science and Technology | Singh R.B.,Japan National Institute of Advanced Industrial Science and Technology | Matsuzaki H.,Japan National Institute of Advanced Industrial Science and Technology | And 5 more authors.
Journal of Physical Chemistry C | Year: 2015

The survival probability of electron-hole pairs decays following a power law given by t-1/2 at long times when geminate recombination proceeds under diffusion and Coulomb interaction. Although the power law decay was known, the dependence of the decay amplitude on the strength of the Coulomb interaction, distance dependence of the intrinsic recombination rate, and the diffusion coefficient has not yet been fully understood. In this manuscript, we show analytical expressions on the amplitude of the asymptotic decay and compare the results with the overall kinetics obtained by numerical calculations. The results were applied to the measured data on the kinetics of carriers in LaTiO2N (LTON) solid photocatalyst measured using time-resolved diffuse reflectance spectroscopy (TRDR). The kinetic parameters of carriers were estimated and the presence of trap states was suggested. We also discuss the generalization of the results to the case that the diffusion is dispersive. The dispersive transport of carriers is considered to originate from the carrier transport by successive transitions among trap states with various release times. © 2015 American Chemical Society. Source


Hisatomi T.,University of Tokyo | Katayama C.,Japan Technological Research Association of Artificial Photosynthetic Chemical Process ARPChem | Katayama C.,Fujifilm Co. | Moriya Y.,University of Tokyo | And 5 more authors.
Energy and Environmental Science | Year: 2013

BaNbO2N was activated for photocatalytic sacrificial water oxidation and reduction by modifying the starting material for nitridation and loading appropriate cocatalysts. Addition of BaCO3 to the Ba 5Nb4O15 precursor improved the crystallinity and uniformity of BaNbO2N as a nitridation product, leading to higher oxygen evolution activity. BaNbO2N generated oxygen from an aqueous AgNO3 solution under illumination up to 740 nm. © 2013 The Royal Society of Chemistry. Source


Xu J.,Japan National Institute of Materials Science | Xu J.,University of Tokyo | Xu J.,Bohai University | Pan C.,Japan National Institute of Materials Science | And 4 more authors.
Chemical Communications | Year: 2015

Overall water splitting was achieved on a simple perovskite oxynitride photocatalyst, CaTaO2N, with an absorption edge at 510 nm. This photocatalyst, modified with a Rh-Cr bimetallic oxide cocatalyst, produced stoichiometric H2 and O2 steadily under UV and visible light irradiation after coating of the photocatalyst particles with amorphous Ti oxyhydroxide. This journal is © The Royal Society of Chemistry 2015. Source


Kumagai H.,University of Tokyo | Minegishi T.,University of Tokyo | Sato N.,Japan Technological Research Association of Artificial Photosynthetic Chemical Process ARPChem | Sato N.,Fujifilm Co. | And 3 more authors.
Journal of Materials Chemistry A | Year: 2015

The effects of a phosphate buffer electrolyte and surface modification with thin conductor layers on the photoelectrochemical properties of CdS and Pt-modified polycrystalline Cu(In,Ga)Se2 (CIGS) photocathodes were investigated. The photocurrent obtained from Pt/CdS/CIGS electrodes, in which the CIGS layer was fabricated by co-evaporation using a three stage method, clearly increased in a phosphate buffer electrolyte solution as a result of promotion of the hydrogen evolution reaction. The half-cell solar-to-hydrogen efficiency (HC-STH) of this device reached a maximum of 5.4% at 0.30 VRHE even under neutral conditions. Furthermore, significant enhancement of the hydrogen evolution reaction on a CIGS photocathode by surface modification with thin conductor layers was observed. The enhancement was due to the promoted charge transfer between the underlying photocathode and water through the Pt catalyst. The HC-STH of a CIGS photocathode modified with a conductive Mo/Ti layer (Pt/Mo/Ti/CdS/CIGS) was as high as 8.5% at 0.38 VRHE, a value that exceeds those previously reported for photocathodes based on polycrystalline thin films. © The Royal Society of Chemistry 2015. Source


Takata T.,Japan National Institute of Materials Science | Pan C.,Japan National Institute of Materials Science | Nakabayashi M.,University of Tokyo | Nakabayashi M.,Japan Technological Research Association of Artificial Photosynthetic Chemical Process ARPChem | And 4 more authors.
Journal of the American Chemical Society | Year: 2015

The design of optimal surface structures for photocatalysts is a key to efficient overall water splitting into H2 and O2. A unique surface modification method was devised for a photocatalyst to effectively promote overall water splitting. Photodeposition of amorphous oxyhydroxides of group IV and V transition metals (Ti, Nb, Ta) over a semiconductor photocatalyst from corresponding water-soluble metal peroxide complexes was examined. In this method, amorphous oxyhydroxide covered the whole surface of the photocatalyst particles, creating a core-shell structure. The water splitting behavior of the novel core-shell-type photocatalyst in relation to the permeation behavior of the coating layer was investigated in detail. Overall water splitting proceeded successfully after the photodeposition, owing to the prevention of the reverse reaction. The photodeposited oxyhydroxide layers were found to function as molecular sieves, selectively filtering reactant and product molecules. By exploiting the selective permeability of the coating layer, redox reactions on the photocatalyst surface could be suitably controlled, which resulted in successful overall water splitting. © 2015 American Chemical Society. Source

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