J061033 フッ素系高分子電解質における側鎖分解プロセスの第一原理分子動力学シミュレーション(〔J061-03〕燃料電池・二次電池におけるナノ・マイクロ現象とマクロ性能(3):PEFC電極・電解質膜)

Abstract

To clarify the degradation mechanism of perfluorosulfonic acid (PFSA) membranes in polymer electrolyte fuel cells, we studied the decomposition process of PFSA side chain by radical species using the first-principles molecular dynamics method. This approach is possible to simulate real-time reactions from a viewpoint of atomic scale and reveal novel reaction pathways that traditional static methods may overlook. We investigated the reactions of OH and H radicals with the side chain model of CF_3CF_2CF_2SO_3H. In the reaction with a OH radical, a water molecule was generated when the OH radical abstracted the hydrogen atom from the side chain. An analysis of the interatomic distances and potential energy profiles revealed that the hydrogen bond between the OH radical and the oxygen atom in the sulfo group lowered the activation energy for the hydrogen abstraction. On the other hand, a H radical reacted with not the hydrogen atom but the oxygen atom in the sulfo group even though the activation energy for the reaction with the oxygen atom is higher than that with the hydrogen atom. This is because the hydrogen atom can escape from the approach of the H radical due to the small radius and mass, while the oxygen atom reacts with the radical due to the large radius and mass relative to the hydrogen atom. Moreover, this result indicates that it is important for clarification of the degradation mechanism to take account of not only statics but also dynamics.