Molecular Dynamics Simulation of 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 empirical valence bond (EVB) method was developed in order to treat the excess proton transport through the Grotthuss mechanism. The new EVB model predicts a significantly enhanced transport in comparison with previous hopping models as well as the classical hydronium diffusion, which largely improves the agreement with the available experimental data. Our results suggest that a proton hopping mechanism has a small effect on the proton dissociation from the first solvation shell of sulfonate groups, namely that protons are not enhanced to separate from the sulfonate groups by the hopping mechanisms. From diffusion comparison between the Grotthuss and vehicular mechanism, the Grotthuss mechanism dominates the proton diffusion at the studied hydration levels including a hydration level of 3. It was also found that the vehicular mechanism dominates the electroosmotic transport of water molecules at the studied hydration levels.