Reactive Molecular Dynamics Study of Proton Transport in Polymer Electrolyte Membranes

Dynamical properties of water and protons in Nafion with an equivalent weight of 1144 are studied using the recently developed reactive molecular dynamics (RMD) algorithm at various water contents. The structural diffusion of a proton along the aqueous domains is modeled via a mechanism similar to that observed in bulk aqueous systems. The algorithm implements reactivity in classical MD simulations by three steps: (i) satisfaction of the trigger, (ii) instantaneous reaction, and (iii) local equilibration. Two different schemes (Method 1 and Method 2) of execution of the algorithm are investigated, which differ in terms of the range of the local environment involved in the reaction. Both methods are parametrized to the experimental rate constant of proton transport in bulk water. The mean lifetime of the protons increased with the water content in Nafion. Water diffusivities of the reactive systems using the two schemes increased with the hydration level and were higher than the diffusion coefficients in t...