Atomistic simulation study of the hydrated structure and transport dynamics of a novel multi acid side chain polyelectrolyte membrane

Abstract

Perfluoroimide acid (PFIA) belongs to a new class of Multi Acid Side Chain (MASC) polyelectrolyte membranes. Classical molecular dynamics simulations were carried out to study the hydrated nanostructure of PFIA and transport of water molecules and hydronium ions at T = 300 K and T = 353 K for a range of hydration levels. The radial distribution functions showed negligible change with temperature. The PFIA chain radius of gyration was minimally influenced by hydration and temperature which makes it suitable for fuel cells. Our simulations showed the formation of a large continuous water phase cluster in PFIA at high hydration levels which has also been observed in conductive probe atomic force microscopy experiments. These large continuous clusters lead to significantly higher vehicular diffusion rates for water molecules and hydronium ions at higher hydration levels. The vehicular diffusivity constants for water molecules and hydronium ions for PFIA were comparable to those for Nafion at both T = 300 K and T = 353 K. The vehicular proton conductivity values for PFIA were observed to be higher than those for Nafion at both T = 300 K and T = 353 K which agrees qualitatively with the experimental trends.