Water self-diffusion anisotropy and electrical conductivity of perfluorosulfonic acid/SiO2 composite proton exchange membranes

Water self-diffusion anisotropy in perfluorosulfonic acid (PFSA)/SiO2 composite membranes was investigated by pulsed gradient spin-echo NMR as a function of diffusion time, temperature and relative humidity. The anisotropy of water diffusion that is related to the ion channel orientation decreases with the increase of silica content, diffusion time and relative humidity. Activation energies of water diffusion and proton conductivity were evaluated for the temperature range of 313-363 K. Empirical dependences for proton conductivity and proton diffusion coefficient as a function of water uptake were established and correlated with the silica content of membranes. The effect of in situ grown sulfonated silica nanoparticles on the orientation of water channels is also discussed. (C) 2012 Elsevier B.V. All rights reserved.