成果報告書詳細
管理番号20110000001105
タイトル*平成22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 次世代技術開発/ 固体高分子電解質膜の高感度劣化評価システムの研究開発
公開日2011/9/28
報告書年度2010 - 2010
委託先名国立大学法人大阪大学
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. 研究開発の内容及び成果等
電解質膜の劣化に関する研究はこれまでFenton 試験やOCV 試験により行われてきている。
特にFenton 試験は電解質膜のラジカルに対する耐性を調べる方法としてよく用いられているが、この試験ではいくつかのラジカル種が同時に生成されるため、ラジカル種の違いによる劣化過程の研究は困難であり、また、実際の燃料電池の運転による劣化と同種のプロセスを経るかもわからないという難点がある。そこで、本研究では選択的に特定のラジカル(OH・,O2-・,H・)を生成させ、これら反応ラジカル種による電解質膜に与える影響を、陽電子消滅法、溶液分析法等を用いて調べ、更に実際の燃料電池の運転で劣化した電解質膜との間で比較・検討を行うことで、電解質膜の劣化過程を明らかにするとともに、新たな劣化試験のプロトコルを作成することを目的としている。
英文要約 Title : Development of A New Evaluation System of Polymer Electrolyte Membrane for Fuel Cell (FY2010-FY2011) FY2010 Annual Report
In this study, we are aiming at the elucidation of degradation process of PEM caused by specialized radicals such as OH・, O2-・ and H・ mainly using positron annihilation spectroscopy and solution analysis, and also developing a new protocol for acceleration test of degradation. Three kinds of radicals, OH・, O2-・ and H・, were selectively produced with γ-irradiation in Nafion-117 membrane manufactured by DuPont. Irradiation was ranged from 0.1 kGy to 1 MGy. The ratio among the produced radicals was OH・ : O2-・ : H・ = 2 : 1 : 1.2. Proton conductivity was not affected by γ-irradiation below 100 kGy, but decreased around 1 MGy dose for all radicals. Especially the membrane was more damaged by the reductive radicals, O2-・ and H・. In positron annihilation spectroscopy, the key parameters are the lifetime of ortho-positronium (τ) and S-parameter. For the sample exposed to OH・, τ was not changed so much in the range below 100 kGy, however increased around 100 kGy. For the samples exposed to O2-・ and H・, τ increased gradually up to around 100 kGy. No significant change appeared on the S-parameter up to this dose, which was correlated with proton conductivity. Taking into account of the results of proton conductivity, it seems no significant change in the structure of cluster up to 100 kGy. In order to investigate the location of cleavage in membrane, dissociated elements were evaluated by solution analysis. The observed mole ratio of C to S was 2.7 for the sample exposed to OH・ of 100 kGy, indicating the scission would dominantly take place at around the terminal ether bond. The ratios were 5.1 and 5.7 for those exposed to O2-・ and H・, respectively, indicating the scission would take place around the ether bond close to the backbone. As OH・ is oxidative radical and the other two are reductive radicals, it can be inferred that the reaction of OH・ would be initiated from HOMO, and those of O2-・ and H・ would start from LUMO, according to frontier molecular orbital theory. For Nafion, HOMO and LUMO were found to be highly distributed around terminal ether bond and that close to the backbone, based on MO calculation. This is consistent with the results of solution analysis. Together with the results of higher dose experiments, it is concluded that the reductive radical is more serious for the membrane. Comparison between the degraded membranes with γ-irradiation and fuel cell operation was carried out. The degree of degradation was evaluated with eluted amount of sulfur, indicating that 3 kGy was equivalent with 6 hours operation of fuel cell under open circuit condition. The ratio of C/S for 4 hours operated membrane was 11.2, which was higher than that of γ-irradiated membrane, and the degradation relating to backbone seemed to be more advanced than γ-irradiated samples, though the voltage was kept constant even after the operation. This would be able to be attributed to the presence of permeated fuel gas. Further investigation must be carried out.
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