Proton Transport in Polymer Electrolyte Membranes. Theory and MD Simulations

摘要

In order to understand those chemical and physical parameters of a polymer electrolyte membrane (PEM) which lead to its optimum performance in a fuel cell, insight into microscopic mechanisms of the kinetic processes in the membrane is necessary. A simplified version of an empirical valence bond model for proton transfer in aqueous solutions has been developed recently, which is suitable for the high proton concentration present in acidic PEMs. The proton transport properties of this model in single pores of PEM materials are studied by molecular dynamics simulations and modified Poisson-Boltzmann theory. The PEM phase is described at several levels of complexity. Important material properties such as acid strength, counter charge delocalization and sulfonate head group as well as side chain mobility, are investigated,and those environmental effects, which influence the rate of proton transfer the most, are identified. The dependence of the mobility on operational parameters of the PEM fuel cell, such as temperature and water content, is also investigated. The results elucidate the molecular mechanisms of proton transport in sample water-filled pores of PEMs and highlight the main factors that speed up proton transport.