Channel orientation anisotropy in perfluorosulfonic acid/SiO2 composite proton exchange membranes: Water self-diffusion study using NMR

A diffusion-exchange model with the assumption of two water pools was applied to describe the water transport in perfluorinated sulfonic acid (PFSA)/SiO2 nanocomposites. The water diffusivity in-plane and through-plane in solution cast films was measured by NMR revealing higher in-plane mobility. Both diffusion coefficients reached maxima at ∼3%-wt. concentration in SiO2. The anisotropy of the PFSA channels orientation reflected in the diffusivity anisotropy decreased with the increase in the nanofiller content. Water exchange rates reached a maximum at low concentration of silica. Gaussian displacement distribution for water diffusion was detected in PFSA membrane at 40 °C independent of the direction of gradient for small concentration in silica.