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PHOTOCATALYST STRUCTURE AND PHOTOCELL

Foreign code F170008924
File No. (AF19P012)
Posted date Jan 19, 2017
Country WIPO
International application number 2016JP052531
International publication number WO 2016136374
Date of international filing Jan 28, 2016
Date of international publication Sep 1, 2016
Priority data
  • P2015-037227 (Feb 26, 2015) JP
Title PHOTOCATALYST STRUCTURE AND PHOTOCELL
Abstract In a heterojunction structure (50) employed in the present invention, a photocatalyst such as BiVO4 serves as a light-absorbing layer (40) and has a relatively small thickness of about several tens of nanometers or less. When a photocatalyst having such a small thickness as mentioned above is used, it becomes possible to collect almost all of electrons generated by the absorption of light with a nanorod (30) having excellent electric conductivity, and therefore the efficiency of collecting photogenerated carriers can be greatly improved. Thus, according to the present invention, it becomes possible to produce an excellent photocell having far superior properties compared with those of conventional photocells which utilize a photocatalyst such as BiVO4.
Outline of related art and contending technology BACKGROUND ART
Hydrogen, the main raw material in chemical industry, in addition, is also a source of clean energy. Most of the conventional hydrogen manufacturing techniques, steam reforming technology (non-patent document 1), coal gasification technology (non-patent document 2) (coal gasification), in biomass (biomass pyrolysis) (non-patent document 3) techniques such as in the present invention based on the prior art. In such a technique, the fossil fuel is used, hydrogen (H2) with the production of large quantities of carbon dioxide (CO2) will occur. However, fossil fuel is a problem that resource shortage, CO2 for discharge is a problem in the environment such as global warming.
On the other hand, a photocatalyst action using solar energy efficiently to obtain hydrogen by water splitting method, can be reproduced by the clean of the most attractive for making is believed to be one of the methods. The hydrogen technology, does not consume fossil fuel CO2 has less impact on the environment and the like for discharge. Therefore, sustainable and clean, dreams are of the hydrogen production technology.
Utilizing the fact that such a photocatalyst in the simplest configuration of the water splitting system, a combination of a photovoltaic cell and water electrolyzer. However, a photovoltaic cell and water electrolyzer and energy loss of both the high cost required for installation, practical use of such a system embodiment of the present invention hinder. For efficient hydrogen production as a selection of another, to directly utilize the solar energy in the production of hydrogen a photoelectrochemical cell (PEC: is photoelectrochemical cell).
A typical PEC device, semiconductor (photo anode) as a light absorber and a counter electrode consisting of a metal such as Pt, are immersed in the aqueous electrolytic solution in the weighing. Photons with energies higher than the bandgap of the photo anode is irradiated, the electron - hole pairs are generated. Among these, the holes, at the interface between the photo anode involved in a reaction with hydroxide and water. On the other hand, the electrons, through an external circuit from the photo anode Pt of back contact moves to the opposing electrode. In this way, using solar energy water solution contributes in the production of hydrogen.
Titanium oxide (TiO2) photocatalytic decomposition of water by (non-patent document 4) after it has been discovered that, the semiconductive oxide, most in the art of the photocatalytic activity is to be investigated which become one of the material. However, TiO2 and the band gap of the 3.2eV, the optical response of the solar spectrum region limited by ultraviolet (UV), the solar energy water can be used for decomposition with only slightly 4%. That is, the solar energy into hydrogen by the water to its wide band gap is essentially (solar-to-hydrogen conversion efficiency) efficiency limitation in some cases. From such a situation, the visible light region of the solar spectrum utilization is made of a material having a photocatalytic action and to be used for the development of the system, much effort has been made.
Of the solar spectrum in the visible light range in order to leverage the moisture in the solution, of about 2-2.4eV relatively small band gap the photocatalyst material is obtained, as such a material is, BiVO4 、α-Fe2 O3 、TaONand the like can be exemplified.
For example, bismuth vanadate salt (BiVO4) is, to the extent that the band gap of about 2.4eV (in the case of the monoclinic) and relatively narrow, and is excellent in stability to photo-corrosion (photocorrosion), since low cost, for the production of hydrogen by the photocatalyst as the most promising as a substance which is one of the (non-patent document 5, 6). BiVO4 theoretical STH(Solar-to-Hydrogen efficiency), i.e. solar energy into hydrogen by water to efficiency, the ground in the vicinity of the latitude of Japan is used as the average spectra of solar simulated light irradiation conditions (AM1.5) air mass (100mW/cm2) under, generally 7.5 mA/cm2 maximum optical current, may be as large as approximately 9.2%.
BiVO4 is thus excellent in light absorption on the other hand, the light absorption caused by the high recombination rate of electrons and holes, in a crystal of the carrier diffusion length as short as about 70 nm the electrical conductivity is low. Therefore, the light irradiation generated due to the recombination of electrons and holes to interfere with the dynamics of the water splitting is a problem. BiVO4 W or Mo to the conductivity and electric doping attempts been made to some (non-patent document 7, 8), both the result is not sufficient, BiVO4 still remains the problem of a low electrical conductivity remains.
Α-Fe2 O3 is a promising material, band gap is as small as about 2eV, the sunlight spectrum can be absorbed light in the range of about 40%, theoretical energy efficiency is as high as about 15%. However, in a crystal of low electronic conductivity and a high recombination rate of electrons and holes from the reasons, the amount of moisture to the solution in the visible light range is significantly limited the utilization efficiency of a problem.
Scope of claims (In Japanese)[請求項1]
表面が導電性を有する基体上に、
導電性を有する円柱状のナノロッドであって平均半径がR1のナノロッドが単位面積(μm2)当たりN本の密度で実質的に均一にアレイ状に設けられており、
前記ナノロッドの表面は、光触媒作用を有する光吸収体膜により、平均表面被覆率Cで80%以上が被覆されて平均半径がR2のヘテロ接合ナノロッドを構成しており、
前記ナノロッドのバンドギャップEgAは前記光吸収体のバンドギャップEgBより広く(EgA>EgB)、且つ、前記ナノロッドの価電子バンドのエネルギーEcAは前記光吸収体の価電子バンドのエネルギーEcBよりも低く(EcA<EcB)、
前記ヘテロ接合ナノロッドの相互の平均間隔をLとしたときに前記平均半径R2がR2<L/2を満足している、光触媒構造体。
[請求項2]
前記光吸収体膜の表面はナノ粒子状の凸部を複数有しており、該複数の凸部が前記ヘテロ接合ナノロッドの平均半径R2を規定する、請求項1に記載の光触媒構造体。
[請求項3]
前記ナノロッドの表面を被覆する前記光吸収体膜の凸部を除く部分の平均厚みは、該光吸収体中における電子および正孔の拡散長よりも薄い、請求項2に記載の光触媒構造体。
[請求項4]
前記光吸収体膜は、バンドギャップが3eV以下の直接遷移型の半導体材料である、請求項1~3の何れか1項に記載の光触媒構造体。
[請求項5]
前記ナノロッドの主成分は、WO3、MoO3、ZnOの何れかである、請求項1~3の何れか1項に記載の光触媒構造体。
[請求項6]
前記光吸収体の主成分は、BiVO4、BiFeO3、BiNbO4、BiTaO4、SbVO4、SbNbO4、SbTaO4、CrVO4、CrNbO4、CrTaO4、FeVO4、FeNbO4、FeTaO4、InVO4、InNbO4、InTaO4、LaVO4、LaNbO4、LaTaO4、CeVO4、CeNbO4、CeTaO4、α-Fe2O3、TaONの何れかである、請求項1~3の何れか1項に記載の光触媒構造体。
[請求項7]
前記ナノロッドの主成分は酸化タングステン(WO3)であり、前記光吸収体の主成分は酸化ビスマスバナジウム(BiVO4)である、請求項6に記載の光触媒構造体。
[請求項8]
前記光吸収体はリン酸コバルトを含む、請求項1~3の何れか1項に記載の光触媒構造体。
[請求項9]
前記ヘテロ接合ナノロッドの平均半径R2と前記ナノロッドの平均半径R1の差ΔRが25nm<ΔR<40nmの範囲にある、請求項1~3の何れか1項に記載の光触媒構造体。
[請求項10]
前記ナノロッドの平均半径R1は40nm<R1<100nmの範囲にある、請求項1~3の何れか1項に記載の光触媒構造体。
[請求項11]
前記ナノロッドの高さHは500nm<H<2500nmの範囲にある、請求項1~3の何れか1項に記載の光触媒構造体。
[請求項12]
前記ヘテロ接合ナノロッドの相互の平均間隔Lは190nm<L<320nmの範囲にある、請求項1~3の何れか1項に記載の光触媒構造体。
[請求項13]
前記ナノロッドの単位面積(μm2)当たりの本数Nは10<N<30の範囲にある、請求項1~3の何れか1項に記載の光触媒構造体。
[請求項14]
前記基体の表面は酸化インジウムスズ(ITO)である、請求項1~3の何れか1項に記載の光触媒構造体。
[請求項15]
前記光吸収体膜は電着膜である、請求項1~3の何れか1項に記載の光触媒構造体。
[請求項16]
請求項1~3の何れか1項に記載の光触媒構造体がアノードとして用いられている光電池。
  • Applicant
  • ※All designated countries except for US in the data before July 2012
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
  • Inventor
  • PIHOSH, Yuriy
  • MAWATARI, Kazuma
  • KAZOE, Yutaka
  • KITAMORI, Takehiko
  • TURKEVYCH, Ivan
IPC(International Patent Classification)
Specified countries National States: AE AG AL AM AO AT AU AZ BA BB BG BH BN BR BW BY BZ CA CH CL CN CO CR CU CZ DE DK DM DO DZ EC EE EG ES FI GB GD GE GH GM GT HN HR HU ID IL IN IR IS JP KE KG KN KP KR KZ LA LC LK LR LS LU LY MA MD ME MG MK MN MW MX MY MZ NA NG NI NO NZ OM PA PE PG PH PL PT QA RO RS RU RW SA SC SD SE SG SK SL SM ST SV SY TH TJ TM TN TR TT TZ UA UG US UZ VC VN ZA ZM ZW
ARIPO: BW GH GM KE LR LS MW MZ NA RW SD SL SZ TZ UG ZM ZW
EAPO: AM AZ BY KG KZ RU TJ TM
EPO: AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR
OAPI: BF BJ CF CG CI CM GA GN GQ GW KM ML MR NE SN ST TD TG
Reference ( R and D project ) CREST Creation of Nanosystems with Novel Functions through Process Integration AREA
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