Molecular Simulation of Equilibrium Solubility and Diffusion of Water in Polymer Electrolyte Membranes

摘要

The proton conductivity and the mechanical property of the polymer electrolyte membranes (PEMs) depend heavily on the equilibrium water content of the polymer systems. Molecular simulation method was used to investigate the equilibrium solubility and diffusion of water in hydrated Nafion 117. The simulations were based on the ab initio TEAM force field that was derived based on quantum mechanics data, liquid density and heat of vaporization of model compounds. The combination of the thermodynamic-integration approach and Widom's particle-insertion method was carried out to determine the excess chemical potential of water in the PEMs and then to estimate of their water sorption behavior. The dynamics of water molecules and hydronium ions in PEMs were investigated using molecular dynamics simulations. The calculated diffusion coefficients were in good agreement with experimental. These results should be useful in guiding the development of other membranes to replace Nafion in PEMs fuel cells.