成果報告書詳細
管理番号20090000000018
タイトル*平成20年度中間年報 固体高分子形燃料電池実用化戦略的技術開発 要素技術開発 酸化物系非貴金属触媒
公開日2010/2/19
報告書年度2008 - 2008
委託先名国立大学法人横浜国立大学 国立大学法人東京大学 日本電気株式会社 パナソニック株式会社 日産自動車株式会社 株式会社アライドマテリアル 昭和電工株式会社 住友化学株式会社 太陽化学株式会社 凸版印刷株式会社 新日本石油株式会社
プロジェクト番号P05011
部署名燃料電池・水素技術開発部 燃料電池グループ
和文要約以下本編抜粋:1. 研究開発の内容及び成果等 1.1国立大学法人 横浜国立大学 「Ta, Zr系化合物を中心とした高機能酸化物系触媒設計及び酸素還元機能発現メカニズムの解析」 本年度は、主にTa化合物を中心とした酸化物系触媒を開発し、酸素還元開始電位の向上を目指した。タンタル炭窒化物(Ta-CN)を、微量のO2ガスを含む雰囲気で、1000℃で長時間部分酸化処理を行うことにより、酸素還元開始電位(EORR)が向上することを見出した。
英文要約Summary
Group 4 and 5 metal (Ta, Zr, Nb, and Ti) oxide-based catalysts have been investigated as non-precious cathode catalyst. The catalytic activity for oxygen reduction reaction (ORR) of heat-treated tantalum carbonitride (Ta-CN) was dramatically improved by partially oxidizing under nitrogen atmosphere containing traces of oxygen gas at 1000℃ for several 10 hours. The heat-treated Ta-CN was mixed with carbon black to have sufficient electrical conductivity as elextrocatalyst. The maximum onset potential for the ORR (EORR) of partially oxidized Ta-CN (Ta-CNO) reached 0.96V vs. RHE. In case of Nb and Ti, Nb and Ti based oxynitrides were highly dispersed on carbon support to enhance the catalytic activity for the ORR. In particular, the EORR of Nb-ON containing Zr and Ba as additives was ca. 0.91-0.96 V vs. RHE.
 Relation between the catalytic activity for the ORR and the structure of the catalysts has been examined using synchrotron radiation x-rays. The high-resolution XRD measurements revealed the presence of oxygen-vacancy defects and strain that they may have induced, both of which are presumably essential for the oxygen reduction activity. Theoretical molecular dynamics indicated that the Ta-CN had higher tolerance of partial oxidation than TaC and TaN. In addition, although the partial oxidation proceeded, carbon remained near the surface, and the remaining carbon might act as active site for the ORR. Because electrochemical behavior such as the Tafel slope for the ORR and the effect of the direction of the potential scan of Ta-CNO was different from that of platinum or platinum alloy catalysts, a mechanism of the ORR might be different between Ta-CNO and platinum alloys.
The trial of mass production of the catalysts resulted in the production of several ten grams of Ta-CNO. Ta-CNO heat-treated at 1050℃ had relatively large BET surface area and high catalytic activity for the ORR (EORR: 0.9 V). Partially oxidized niobium and titanium carbonitrides (Nb-CNO and Ti-CNO) had been also investigated. The EORR of the Nb-CNO and Ti-CNO was 0.88 and 0.85 V. In addition, high EORR of zirconia and titania exceeded 0.90 V by preparing the ultra-fine particles and modifying as carbon. The control of higher order structures such as nanoparticle catalyst supported on highly ordered mesoporous carbon was also examined to enhance the catalytic activity for the ORR.
A new preparation process of catalyst ink brought dramatic improvement of single cell performance, that is, the open circuit potential was over 0.90V and cell performance markedly improved under 0.5 V. The existence of coarse particle in the catalyst layer caused the decrease of the cell performance.
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