Interface of Hydrated Perfluorosulfonic Acid Electrolyte and Platinum Catalyst: Dissipative Particle Dynamics Simulation Model

Abstract

Polymer electrolyte fuel cells (PEFC) are expected to be used widely in the future as a non-polluting power source in various applications. PEFC applications are only limited currently however, as PEFCs are still not competitive with existing power sources in energy efficiency and cost. One of the most popular forms of PEFC are composed of an electrolyte of hydrated perfluorosulfonic acid (PFSA), and carbon based electrodes that support small catalyst particles (typically Pt) on the surface. The global performance of PEFC of this type is governed by the rate of red-ox reactions on the catalyst surface, which are affected by molecular level dynamics of fuel, oxidants, and protons in the electrolyte near the catalyst surface. We need deeper understanding on this interfacial structures for new insights into the mechanisms that control the electrochemical surface processes. Several structure models have been proposed for the bulk electrolyte, while only little is understood as to its structure near the catalyst surface so far. In this study, to investigate the interfacial system of hydrated PFSA and platinum surface, we constructed models of this system for dissipative particle dynamics (DPD) simulations. DPD simulation is a kind of coarse-grained simulation which is used to study mesoscopic systems, typically consisting of macromolecules like polymers and biomolecules. We coarse grained the simulation system with DPD particles corresponding to PFSA segments A-C (see Fig.1), those grouping four water molecules (denoted as W), and those grouping ~8 platinum atoms (Pt). The catalyst surface was represented by a fixed slab of the Pt particles forming a simple lattice. We used soft potentials constructed via quantum chemical calculations by Okuwaki et al. [1] for interactions of DPD particles A-C and W; while we newly constructed soft potentials for the interactions of Pt with other DPD particles by analyzing their affinities via all-atom classical MD simulations for some small systems. For these all-atom MD simulations, we derived some intermolecular potential functions by first principles calculations. Details of our DPD simulations as well as the interaction model constructions will be presented in the conference session (a snapshot is displayed in Fig. 2). A portion of this research was supported by MEXT within the priority issue 6 of the FLAGSHIP2020 project (Project ID: hp160226, hp170253,hp180187). [1] K. Okuwaki et al., JSAP spring meeting (2016) 20a-W323-6. Figure 1