An Improved EVB Model for Proton Transport in Polymer Electrolyte Membrane

We have performed a detailed analysis of proton solvation and transport properties in hydrated Nafion using molecular dynamics simulation. The revised EVB model predicts a significantly enhanced transport in comparison with the classical hydronium models, which largely improves the agreement with the available experimental data. The excess proton was found to have weaker interaction with the sulfonate groups in comparison with the classical hydronium ion, reflecting the delocalization nature of the proton charge defects in the EVB model. Our results suggest that the hopping transport has a large contribution to the proton diffusion even at lower hydration levels, as low as 3. It was also found that the Grotthuss component becomes more important and its contribution increases linearly as the hydration level increases.