Interface of Hydrated Perfluorosulfonic Acid Electrolyte with a Platinum Catalyst: Structural Analyses with Dissipative Particle Dynamics Simulations*

Dissipative particle dynamics (DPD) simulations were performed to study structures of hydrated perfluorosufuonic acids (PFSA) in contact with platinum surfaces. Two types of interfacial systems were simulated, where PFSA molecules interact with a cube and a slab of platinum, respectively representing a small catalyst particle used in a regular fuel cell and a platinum substrate popularly used in a model system experiment. The calculated results suggest that the two systems form a shell structure and a layer structure, respectively, of PFSA components near the platinum surfaces. The water component covers the platinum surfaces popularly in both systems, of which the coverage depends on the hydration levels of PFSA. Detailed analyses revealed that the water component networks are quite different in the two systems, which are three-dimensionally connected in the systems with a platinum cube, while disrupted by hydrophobic components in the systems with a platinum slab.