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OXYGEN REDUCTION CATALYST, FUEL CELL, AIR CELL, AND METHOD FOR PRODUCING OXYGEN REDUCTION CATALYST

Foreign code F210010304
File No. (S2019-0488-N0)
Posted date Jan 29, 2021
Country WIPO
International application number 2020JP022723
International publication number WO 2020250898
Date of international filing Jun 9, 2020
Date of international publication Dec 17, 2020
Priority data
  • P2019-109815 (Jun 12, 2019) JP
Title OXYGEN REDUCTION CATALYST, FUEL CELL, AIR CELL, AND METHOD FOR PRODUCING OXYGEN REDUCTION CATALYST
Abstract Provided is a novel oxygen reduction catalyst that has excellent stability and high oxygen reduction capability. This oxygen reduction catalyst includes a complex oxide formed of a conductive tin oxide including Zr.
Outline of related art and contending technology BACKGROUND ART
Fuel cells and air cells are electrochemical energy devices that extract, as electrical energy, energy generated by a chemical reaction between a compound serving as fuel and an anode active material, using oxygen or the like in the air as an oxidizer. Fuel cells and air cells have a theoretical energy capacity higher than that of secondary batteries such as Li-ion batteries, and can be used as a vehicle onboard power source, a stationary distributed power source at home or factory, or a power source for portable electronic devices, or the like.
An electrochemical reaction that reduces oxygen occurs on the oxygen electrode side of a fuel cell or an air cell. The oxygen reduction reaction is difficult to proceed at a relatively low temperature, and the reaction can generally be promoted by a noble metal catalyst such as platinum (Pt). However, the energy conversion efficiency of fuel cells and air cells is not yet sufficient. In addition, because the oxygen reduction reaction occurs in a high potential region, even noble metals such as Pt dissolve and degrade, which leads to problems in ensuring long-term stability and reliability. Furthermore, catalysts containing noble metals such as Pt as the main component are expensive, increasing the price of the overall system of fuel cells and air cells, and preventing widespread use thereof. Therefore, development of a catalyst that is inexpensive and does not use noble metals such as platinum and has high oxygen reduction capability is desired.
Organometallic complexes, nitrogenated carbons, transition metal chalcogenides, transition metal carbides, transition metal nitrides, and the like are known as Pt-free catalysts. however, all of these catalysts are insufficient from the perspectives of catalytic activity and durability, and performance exceeding that of Pt-based catalysts has not been achieved.
Among these, Non-Patent Documents 1 and 2 disclose that some of the transition metal oxides of group 4 and group 5 elements have activity with respect to oxygen reduction reactions. In addition, Non-Patent Document 3 and Patent Document 1 indicate that some structural defects may function as active sites for oxygen reduction reactions. Furthermore, Non-Patent Documents 4 and 5 and Patent Document 1 disclose imparting electrically conductive carbon or the like when configuring an electrode.
Since an oxygen reduction reaction on an air electrode catalyst of a fuel cell or an air cell is a reaction involving electron transfer from an electrode, electrons need to rapidly transfer from the electrode to the vicinity of a reactive active site on the catalyst in order to obtain favorable oxygen reduction catalyst performance. In addition, oxygen and protons, which are reactants, must be able to quickly reach the reactive active site. However, the transition metal oxides of group 4 and group 5 elements described in Non-Patent Documents 1 to 3 and Patent Document 1 generally have an insulator electronic state, and therefore have poor electrical conductivity and are difficult to react quickly. Therefore, although relatively high performance is exhibited when operating the battery at a low current value, there is a problem in that the operating voltage decreases in the high current region.
In addition, with the methods described in Non-Patent Documents 4 and 5 and Patent Document 1, it is difficult to construct and control an effective electron conduction pathway in the vicinity of an active site at a nano-level, and performance remains low. In addition, the introduction of a large amount of electrically conductive carbon inhibits the supply of oxygen to the catalytic active site, and there is a demand to improve oxygen reduction performance by achieving both the provision of electrical conductivity and the effective transport of oxygen.
Patent Document 2 discloses an oxygen reduction catalyst containing an electrically conductive oxide and an oxide of at least one type of transition metal selected from the group consisting of Ti, Zr, Nb, and Ta having oxygen vacancies provided on at least a surface of the electrically conductive oxide. Furthermore, it is described that such a configuration can provide an oxygen reduction catalyst having good stability and high oxygen reduction performance.
Scope of claims (In Japanese)[請求項1]
 Zrを含む導電性酸化スズで構成された複合酸化物を含む酸素還元触媒。

[請求項2]
 前記導電性酸化スズは、酸化数が+3.0以上+4.0未満であるジルコニウムを含み、
 前記酸化スズが組成式:SnO x1で表される請求項1に記載の酸素還元触媒。
 (上記式中、x1は1~2である。)

[請求項3]
 前記複合酸化物のBET比表面積が10~200m 2/gである請求項1または2に記載の酸素還元触媒。

[請求項4]
 前記複合酸化物において、質量%比で、Zr/Sn=0.001~0.095である請求項1~3のいずれか一項に記載の酸素還元触媒。

[請求項5]
 前記複合酸化物の体積抵抗率が10,000Ωcm以下である請求項1~4のいずれか一項に記載の酸素還元触媒。

[請求項6]
 請求項1~5のいずれか一項に記載の酸素還元触媒を空気極として用いた燃料電池。

[請求項7]
 請求項1~5のいずれか一項に記載の酸素還元触媒を空気極として用いた空気電池。

[請求項8]
 導電性酸化スズに、アークプラズマ蒸着法を用いてZrをドープする工程を備えた請求項1~5のいずれか一項に記載の酸素還元触媒の製造方法。
  • Applicant
  • ※All designated countries except for US in the data before July 2012
  • YOKOHAMA NATIONAL UNIVERSITY
  • Inventor
  • ISHIHARA Akimitsu
  • NAGAI Takaaki
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 DJ DK DM DO DZ EC EE EG ES FI GB GD GE GH GM GT HN HR HU ID IL IN IR IS JO JP KE KG KH KN KP KR KW 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 ST SV SY TH TJ TM TN TR TT TZ UA UG US UZ VC VN WS 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
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