Computer Simulation Study of Model Nafion Membrane in Water/Methanol Solvent

Abstract

Using NPT and NVT molecular dynamics simulation techniques, we have simulated an atomistic model of solvated Nafion in the lithium salt form, with the following three main objectives: (i) to obtain details on the local environment of the lithium cations and to assess the solvent effect on their binding, (ii) to investigate the translational and rotational motion of solvent molecules (water and methanol) absorbed in the polymer matrix, and (iii) to elucidate details of the ionic transport though the hydrophilic regions of the membrane and to study the ionic conductivity as a function of solvent (water/methanol) composition. A property which is of central importance for understanding the functional features of Nafion materials, including direct methanol fuel cells, is the ionic conductivity and methanol crossover. We have found that conductivity parameter is strongly dependent on the solvent composition and determined by the solvation effects and the spatial distribution of polar sulfonate groups in ion-conductive channels.