SiO2 nanoparticles-coated poly(paraphenylene terephthalamide) nonwovens as reinforcing porous substrates for proton-conducting, sulfonated poly(arylene ether sulfone)-impregnated composite membranes

We demonstrate a new reinforcing porous substrate for a proton-conducting composite membrane targeting proton exchange membrane fuel cells (PEMFC) applications. This porous substrate is based on hygroscopic SiO2 nanoparticles-coated poly(paraphenylene terephthalamide) (PPTA) nonwovens. The SiO2 nanoparticles (530 nm), which are interconnected by tetraethoxy silane (TEOS)-based silicate binders, play a crucial role in improving mechanical properties, hydrophilicity, and water retention capability of the substrate. The PPTA nonwoven serves as a support layer offering flexibility and toughness to the substrate. The SiO2 nanoparticles-coated PPTA nonwoven substrate is subsequently impregnated with sulfonated poly(arylene ether sulfone) (SPAES, degree of sulfonation = 49.3%) that acts as a proton-conducting electrolyte. In comparison to a pristine SPAES membrane, the porous substrate-reinforced SPAES composite membrane presents the substantially improved dimensional change, and more intriguingly, is effective in suppressing the steep decline of proton conductivity at a low humidity condition of 30 °C/50% RH.