Japan Technological Research Association of Artificial Photosynthetic Chemical Process ARPChem

Kashiwa, Japan

Japan Technological Research Association of Artificial Photosynthetic Chemical Process ARPChem

Kashiwa, Japan
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Kuang Y.,University of Tokyo | Kuang Y.,Japan Technological Research Association of Artificial Photosynthetic Chemical Process ARPChem | Jia Q.,University of Tokyo | Jia Q.,Japan Technological Research Association of Artificial Photosynthetic Chemical Process ARPChem | And 17 more authors.
Nature Energy | Year: 2017

Photoelectrochemical (PEC) water splitting offers a means for distributed solar hydrogen production. However, the lack of stable and cost-effective photoanodes remains a bottleneck that hampers their practical applications. Here we show that particulate Mo-doped BiVO 4 water oxidation photoanodes, without costly and complex surface modifications, can possess comparable stability to that of solar cells. The photoanode exhibits enhanced intrinsic photocorrosion inhibition and self-generation and regeneration of oxygen evolution catalysts, which allows stable oxygen evolution for >1,000 h at potentials as low as 0.4 V versus the reversible hydrogen electrode. The significantly improved photocorrosion resistance and charge separation are attributed to the unusual high-temperature treatment. In situ catalyst regeneration is found to be a site-specific and oxygen evolution rate change-induced process. Our findings indicate the potential of PEC water splitting to compete with other solar hydrogen production solutions, and should open new opportunities for the development of feasible PEC water splitting systems. © 2016 Macmillan Publishers Limited. part of Springer Nature. All rights reserved.


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.


Zhong M.,University of Tokyo | Zhong M.,Japan Technological Research Association of Artificial Photosynthetic Chemical Process ARPChem | Hisatomi T.,University of Tokyo | Hisatomi T.,Japan Technological Research Association of Artificial Photosynthetic Chemical Process ARPChem | And 28 more authors.
Journal of the American Chemical Society | Year: 2015

Photoelectrochemical (PEC) devices that use semiconductors to absorb solar light for water splitting offer a promising way toward the future scalable production of renewable hydrogen fuels. However, the charge recombination in the photoanode/electrolyte (solid/liquid) junction is a major energy loss and hampers the PEC performance from being efficient. Here, we show that this problem is addressed by the conformal deposition of an ultrathin p-type NiO layer on the photoanode to create a buried p/n junction as well as to reduce the charge recombination at the surface trapping states for the enlarged surface band bending. Further, the in situ formed hydroxyl-rich and hydroxyl-ion-permeable NiOOH enables the dual catalysts of CoOx and NiOOH for the improved water oxidation activity. Compared to the CoOx loaded BiVO4 (CoOx/BiVO4) photoanode, the ∼6 nm NiO deposited NiO/CoOx/BiVO4 photoanode triples the photocurrent density at 0.6 VRHE under AM 1.5G illumination and enables a 1.5% half-cell solar-to-hydrogen efficiency. Stoichiometric oxygen and hydrogen are generated with Faraday efficiency of unity over 12 h. This strategy could be applied to other narrow band gap semiconducting photoanodes toward the low-cost solar fuel generation devices. © 2015 American Chemical Society.


Ham Y.,University of Tokyo | Hisatomi T.,University of Tokyo | Hisatomi T.,Japan Technological Research Association of Artificial Photosynthetic Chemical Process ARPChem | Goto Y.,University of Tokyo | And 6 more authors.
Journal of Materials Chemistry A | Year: 2016

SrTiO3 is a photocatalyst that is well known for its activity for the overall water splitting reaction under UV light irradiation. In this study, the effects of SrCl2 flux treatments and Al doping on the photocatalytic properties of SrTiO3 were investigated. The SrTiO3, which showed an apparent quantum efficiency of 30% at 360 nm in the overall water splitting reaction, the highest value reported so far, was prepared by SrCl2 flux treatments in alumina crucibles. Scanning electron microscopy and X-ray diffractometry revealed that the flux-treated SrTiO3 consisted of well-crystalline particles with a cubic shape reflecting the perovskite-type structure. Inductively coupled plasma optical emission spectroscopy revealed that Al ions from the alumina crucibles were incorporated into the SrTiO3 samples. The SrTiO3 that was treated with SrCl2 flux in Al-free conditions showed a marginal improvement in photocatalytic activity despite the high crystallinity and the clear crystal habit. Doping SrTiO3 with Al improved the photocatalytic activity even without SrCl2 treatment. These results suggested that Al doping was a principal factor in the dramatic improvement in the water splitting activity of the flux-treated SrTiO3. The effects of flux treatments and Al doping on the morphology and water splitting activity of SrTiO3 were discussed separately. © The Royal Society of Chemistry 2016.


Singh R.B.,Japan National Institute of Advanced Industrial Science and Technology | Matsuzaki H.,Japan National Institute of Advanced Industrial Science and Technology | Suzuki Y.,Japan National Institute of Advanced Industrial Science and Technology | Suzuki Y.,University of Tokyo | And 8 more authors.
Journal of the American Chemical Society | Year: 2015

In addition to the process of photogeneration of electrons and holes in photocatalyst materials, the competitive process of trapping of these charge carriers by existing defects, which can both enhance the photocatalytic activity by promoting electron-hole separation or can deteriorate the activity by serving as recombination centers, is also very crucial to the overall performance of the photocatalyst. In this work, using femtosecond diffuse reflectance spectroscopy we have provided evidence for the existence of energetically distributed trapped states in visible-light responsive solid photocatalyst powder material LaTiO2N (LTON). We observe trapped state sensitive kinetics in bare-LTON. CoOx cocatalyst loading (2 wt % CoOx-LTON) shows effect on the kinetics only when presence of excess energy (for above bandgap excitation) results in the generation of surface carriers. Thus, the kinetics show appreciable excitation wavelength dependence, and the experimental results obtained for different λexc have been rationalized on this basis. In an earlier work by Domen and co-workers, the optimized CoOx/LTON has been reported to exhibit a high quantum efficiency of 27.1 ± 2.6% at 440 nm, the highest reported for this class of photocatalysts (J. Am. Chem. Soc. 2012, 134, 8348-8351). In the present work, the mechanism is addressed in terms of picosecond charge carrier dynamics. © 2014 American Chemical Society.


Wang Q.,University of Tokyo | Li Y.,University of Tokyo | Hisatomi T.,University of Tokyo | Hisatomi T.,Japan Technological Research Association of Artificial Photosynthetic Chemical Process ARPChem | And 5 more authors.
Journal of Catalysis | Year: 2015

A major challenge in developing high-performing Z-scheme water splitting systems lies in achieving efficient transfer of electrons between the H2 and O2 evolution photocatalysts. Here, we report a Z-scheme system consisting of H2 evolution photocatalyst (HEP)/metal layer (M)/O2 evolution photocatalyst (OEP), taking SrTiO3:La,Rh/Au/BiVO4 as a prototype. SrTiO3:La,Rh/Au/BiVO4 systems exhibit photocatalytic activities for overall water splitting that are 6 and 20 times higher than powder suspensions and SrTiO3:La,Rh/BiVO4 systems without metal layers, respectively. The SrTiO3:La,Rh/Au/BiVO4 system achieves an apparent quantum yield of 5.9% under monochromatic light irradiation at 418 nm and a solar-to-hydrogen conversion efficiency of 0.2%. The high performance of this system is due to the presence of the Au layer that transfers photogenerated electrons from BiVO4 to SrTiO3:La,Rh in an effective manner. The present study offers a new design concept for HEP/M/OEP solid-state devices to overcome the limitations of earlier Z-scheme systems and thus enable efficient photocatalytic water splitting. © 2014 Elsevier Inc. All rights reserved.


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.


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.


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.


PubMed | Japan Technological Research Association of Artificial Photosynthetic Chemical Process ARPChem, Tokyo University of Science and University of Tokyo
Type: Journal Article | Journal: Journal of the American Chemical Society | Year: 2015

Photoelectrochemical (PEC) devices that use semiconductors to absorb solar light for water splitting offer a promising way toward the future scalable production of renewable hydrogen fuels. However, the charge recombination in the photoanode/electrolyte (solid/liquid) junction is a major energy loss and hampers the PEC performance from being efficient. Here, we show that this problem is addressed by the conformal deposition of an ultrathin p-type NiO layer on the photoanode to create a buried p/n junction as well as to reduce the charge recombination at the surface trapping states for the enlarged surface band bending. Further, the in situ formed hydroxyl-rich and hydroxyl-ion-permeable NiOOH enables the dual catalysts of CoO(x) and NiOOH for the improved water oxidation activity. Compared to the CoO(x) loaded BiVO4 (CoO(x)/BiVO4) photoanode, the 6 nm NiO deposited NiO/CoO(x)/BiVO4 photoanode triples the photocurrent density at 0.6 V(RHE) under AM 1.5G illumination and enables a 1.5% half-cell solar-to-hydrogen efficiency. Stoichiometric oxygen and hydrogen are generated with Faraday efficiency of unity over 12 h. This strategy could be applied to other narrow band gap semiconducting photoanodes toward the low-cost solar fuel generation devices.

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