Analysis of Proton and Water Transfer in PFSA Membrane by Molecular Dynamics Simulation

Abstract

Protons transfer in polyelectrolyte membrane by both Vehicle and Grotthus mechanisms. This study describes the property of proton and water transfer in perfluorosulfonic acid (PFSA) membrane using molecular dynamics (MD) simulation in view of both Vehicle and Grotthus mechanisms. To treat Grotthus mechanism, Empirical Valence Bond (EVB) method was introduced to MD simulation. The potential energy barrier of proton hopping in EVB method was adjusted to the computational result of Density Functional Theory (DFT) to replicate the experimental value of diffusion coefficient of oxonium ions in water. The parameter for the simulation of PFSA membrane was water contents λ, which is defined as the ratio of water molecules and oxonium ions to sulfo groups, SO3-, obtained byλ=NH2O,H3O+/NSO3-. The structure of water and PFSA membrane was analyzed by Radial Distribution Function (RDF) and diffusion coefficient of proton was found out from Mean Square Displacement (MSD).