The impact of pre-swelling on the conductivity and stability of Nafion/sulfonated silica composite membranes

Nafion/sulfonated silica composite membranes were prepared by modifying Nafion NRE 212 membranes with 2-(4-chlorosulfonylphenyl) trimethoxysilane in a one step process. Prior to modification, one set of membranes were pre-swollen in methanol, while another set were not. The resultant composite membranes were characterized for their water retention capabilities and proton conductivity at various relative humidity conditions. Composites prepared from pre-swelled Nafion membranes had higher sulfonated silica (SS) content than those prepared from non-swelled Nafion membranes. Despite this higher SS content, composites prepared from non-swelled Nafion displayed higher proton conductivity and water contents under low relative humidity conditions. Furthermore, composites prepared from pre-swollen membranes were less stable, having a high propensity to leach SS after long-term immersion in water as determined by TG, which will severely limit their lifetime in fuel cell applications.