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成果報告書詳細
管理番号20190000000579
タイトル*2018年度中間年報 革新型蓄電池実用化促進基盤技術開発(国立大学法人北海道大学)
公開日2019/6/14
報告書年度2018 - 2018
委託先名国立大学法人北海道大学
プロジェクト番号P16001
部署名次世代電池・水素部
和文要約
英文要約Title: Research & Development Initiative for Scientific Innovation of New Generation Batteries 2 (RISING2); (FY2016-FY2020) FY2018 Annual Report

Brownmillerite-type Ca2FeCoO5 oxides, which have been discovered by us, are more active OER catalysts than noble metal catalysts, such as RuO2, under alkaline conditions. We found that bulk crystal structure of Ca2FeCoO5 was abruptly degraded by OER, with forming OER-catalytic active phase of Fe-doped γ-CoOOH nanoclusters comprising two-dimensionally connected MO6 octahedra with ridge sharing were developed inside the amorphous oxide matrix. This transformation involves the dissolution of Ca and Fe ions into electrolyte, which could suffer lowering battery performances. Accordingly, it is strongly motivated to synthesize directly the catalytic-active phase. Here, we successfully fabricated Fe-doped and Fe&Ni-codoped Co(OH)z catalysts with β-Co(OH)2 type structure by a simple coprecipitation methods without post-annealing at elevated temperatures. The Ni0.05Fe0.05Co0.90(OH)z catalysts show superior OER catalytic activity to Ca2FeCoO5 since the onset potentials of the former is lower than that of the latter by 0.02 V.
Carbon additives in the metal oxide-base cathodes in zinc air batteries are indispensable as a co-catalyst for ORR and electrical-conductive support, however, they are readily oxidized under strong alkaline condition. Normally, the oxidation of carbon materials is initiated at the edge plane rather than the basal plane of the hexagonal graphite sheet. We obtained a platelet structure carbon nanofiber (pCNF) with extremely little exposure of edge planes on the fiber wall by polymer pyrolysis using an anodic porous alumina template. The durability tests under OER galvanostatic conditions showed that increment of anodic overpotential for pCNF base electrode was much smaller than that of acetylene black, confirming the excellent durability of pCNF.
In order to improve the high durability and long life of the air electrode, it is desirable to use an electrode system that does not contain a carbon aid since it is thermodynamically unstable under an anodic potential for OER in alkaline media. Unfortunately, the oxide catalysts capable of conducting 4-electron ORR by themselves have not been established. Previously, we have discovered that La0.7Sr0.3Mn0.9Ni0.1O3-δ (LSMN) is highly-active ORR catalysts, exhibiting the ORR onset potential of only 0.05 V lower than that of Pt catalysts, and drives the 4-electron ORR without assistance of the carbon co-catalyst. In order to elucidate this reaction mechanism, the electrochemical measurements were conducted for an LSMN epitaxial thin film fabricated by the PLD on (100), (110) and (111) oriented Nb-dope SrTiO3 wafer, confirming that the (100) plane shows higher ORR activity than the other faces.
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