Molecular Simulation of Gas Transport in Hydrated Nafion Membranes: Influence of Aqueous Nanostructure

Molecular simulation was used to investigate the nanoporous structure of hydrated Nafion membrane and its impact on gas transport The structural changes of Nafion induced by water uptakes were characterized in terms of the density and the pore size distribution. It was found that membrane hydration leads to a growth of separated water domains, which are gradually interconnected via newly formed water channels. The sorption and diffusion of H-2 and O-2 were studied at different temperatures and water contents of Nafion. Simulation results show that the water loading reduces gas solubilities as the adsorption site of gas molecules transforms from small cavities to large surfaces due to the enlargement of aqueous domains. However, such an opening of Nafion porous nanostructure effectively reduces gas diffusion barriers, and results in a 2-fold increase of O-2 diffusivities. Molecular configurations of gases inside Nafion nanoporous frameworks were examined on the basis of calculated radial distribution functions.