成果報告書詳細
管理番号20120000000658
タイトル*平成23年度中間年報 固体高分子形燃料電池実用化推進技術開発 基盤技術開発 酸化物系非貴金属触媒
公開日2012/8/2
報告書年度2011 - 2011
委託先名国立大学法人横浜国立大学 日本電気株式会社 日産自動車株式会社 住友化学株式会社 凸版印刷株式会社 旭硝子株式会社 太陽化学株式会社 国立大学法人北海道大学触媒化学研究センター
プロジェクト番号P10001
部署名新エネルギー部
和文要約和文要約等以下本編抜粋:
1.研究開発の内容および成果等
1.1 国立大学法人 横浜国立大学(物質・材料研究機構)
「部分酸化法を主とした非貴金属酸化物触媒の研究開発」
<平成24年度中間目標>
Ta及びZr酸化物をベースとした化合物で、単セル発電において0.6 Vでの電流密度100 mA/cm2が見通せる触媒を開発する。また、0.8 Vでの電流密度を増大させることを目的として、単極試験において0.8 Vで3 mA/cm2が見通せる値を得る。更に、酸素還元触媒能に影響を与える因子を特定し、その因子と酸素還元触媒能の相関の定量的評価を行う。
<平成23年度の実施内容>
酸化物粉末の微細化による電流値増加を目的として、4及び5族遷移金属を中心金属とする錯体化合物を出発物質に用いた。これまでの研究で、熱処理により酸化物触媒を作製するにあたり、出発物質に窒素と炭素を含むことが重要であることが明らかとなってきた。そこで、タンタル?窒素結合を持ちさらに炭素を含む化合物粉末としてオキシタンタルフタロシアニン(TaOPc)を触媒前駆体として用いた。
前駆体に、触媒粉末のマクロな電子導電パス形成のために導電補助担体として気相法炭素繊維を混合し、さらに触媒表面のカーボン被覆を目的としてサリチル酸を加え、乳鉢でよく混合した。この混合粉末をアルミナボートに載せ、4% H2/N2ガス雰囲気で、温度を800-1000oCまで変化させ電気炉で熱処理し触媒粉末を得た。この触媒には、窒素、炭素、酸素が含まれるので、本稿ではTa-CNO(Pc)と表記する。得られたTa-CNO(Pc)粉末から作製した触媒インクを、φ5.2 mmのGCロッド上に約1 mg担持し作用極とした。また、電気化学測定は、三電極式セルを用いて30oCに保った0.1 mol dm-3 H2SO4中で電位走査を行い、酸素還元電流(iORR)を求めた。電流値は炭素繊維を含んだ粉末触媒の質量基準とし、0.8 VにおけるiORR(|iORR @0.8V|)を用いてORR触媒能を比較した。また、触媒の結晶構造を調べるために、XRDを行
った。
英文要約Title:Strategic Development of PEFC Technologies for Practical Application / Non-precious metal oxide based cathode for PEFC (FY2010-FY2012) FY2011 Annual Report

Ta and Zr oxide-based catalysts have been investigated as non-precious metal oxide based cathode for polymer electrolyte fuel cells. It was promoted by the following two groups; Group 1: Fundamental research of oxygen reduction activity and durability, Group 2: Manufacturing of catalysts, and design and evaluation of catalyst layer. The results obtained in Group 1 are as follows; In order to increase oxygen reduction current, tantalum organic complexes containing nitrogen such as oxy-tantalum phthalocyanine, TaOPc, were used as starting materials. The heat decomposed oxy-tantalum phthalocyanine, Ta-CNO (Pc), had Ta2O5 structure and higher catalytic activity for oxygen reduction than partially oxidized tantalum carbonitride. We have used the conventional and the advanced first-principles calculation methods that can provide reliable atomic structure and electronic structure, respectively. The oxygen vacancy of inplane type was found to provide a relatively shallow level below the conduction band bottom, which can play a role as a conduction channel. When two monovacancies exist, they interact strongly and the stability increases by more than 2 eV. The level is deepened thereby possibly reducing the ability to conducting the electrons. A temperature programmed desorption of ammonia was used to estimate the real surface area of oxide-based catalysts. The amount of ammonia adsorption was probably correlated with the surface area of the oxide-based catalysts. The conversion-electron-yield (CEY) EXAFS measurements of the Ta-CNO catalysts prepared by partial oxidation of Ta-CN were performed. The analysis of radial structure around the Ta atoms shows that the change of the oxygen reduction activity with the oxidation time corresponds to that of the amount of oxygen vacancies. Additionally, we found that another type of oxygen vacancies than that formed at the initial stage can be generated by long oxidation. Controlling the types as well as the amount of oxygen vacancies seems to design the fabrication process of oxide-based catalysts. Structural change of Ta-CNO catalysts upon degradation was also investigated by using CEY EXAFS measurements. The results on the half cells and the CCMs indicate that oxygen vacancies increase in number upon degradation, which is accompanied by disordering. In order to estimate the density of active sites for oxygen reduction, the in-situ active site density measurement was tried using the difference of the oxygen adsorption behavior under electrochemical conditions. The results obtained in Group 2 are as follows; A new carbon in-situ method with hydrothermal decomposition in supercritical water was performed to inhibit the aggregation of the ZrO2/C catalysts. A drastic increase of oxygen reduction current of the ZrO2/C was observed and the current density reached 1.3 mA/cm2 at 0.8 V. We prepared a meso-porous carbon with pore size diameter of ca. 14 nm to improve the proton and gas diffusion behavior in the catalyst layer. The larger pore size caused the increase in the oxygen reduction current. Current density of 227 mA/cm2 was obtained at 0.6 V in a single cell using ZrO2/C cathode. It was found that the dispersion method of catalysts affected the performance of the single cell. In addition, the dependence of the gas pressure and degree of humidification on the initial single cell performance was investigated. These results indicated that the reaction mechanism which was different from the Pt/C catalyst was necessary to be considered and there would be suitable operation mode for oxide-based catalysts.
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