PNNL

Abstract

The effects of level of hydration and temperature on the nanostructure of an atomistic model of a NafionTM (Du Pont) membrane and the vehicular transport of hydronium ions and water molecules were examined using classical molecular dynamics simulations. Through the determination and analysis of structural and dynamical parameters such as density, radial distribution functions, coordination numbers, means square deviations, and diffusion coefficients, we identify that hydronium ions themselves play a role in modifying the interfacial structure in the membrane at the sulfonate pendants. In the regime of low level of hydration, short hydrogen bonded linkages made of water molecules and also hydronium ions give a more constrained structure to the sulfonate pendants. The diffusion coefficient for water was found to be in good accord with experimental data. The diffusion coefficient for hydronium ions was determined to be much smaller (6 to 10 times) than for water. Temperature was found to have a significant effect on the absolute value of the diffusion coefficients for both water and hydroniums.