Applied Surface Science, Vol.483, 785-792, 2019
Phosphoric acid doped high temperature proton exchange membranes based on comb-shaped polymers with quaternized graft architectures
A series of poly(arylene ether ketone)-g-quaternized 4-vinylbenzyl chloride copolymers (PAEK-g-QVBC-x) containing locally and densely quaternized side chains were synthesized. The PAEK-g-QVBC membranes were obtained by solution casting from their reaction mixture and then doped with phosphoric acid (PA) to be used as advanced anhydrous high temperature proton exchange membranes. Compared to the commercial PA doped polybenzimidazole membrane and other main-chain-type quaternized hydrocarbon polymer membranes with the similar proton conductivity, these PA-PAEK-g-QVBC-x membranes possess much lower PA doping level, extremely lower volume swelling ratio, and higher dimensional and oxidative stability. Among them, PA-PAEK-g-QVBC-6.4 membrane with the PA doping level in weight of 101.7% has the highest proton conductivities of 31 mS cm(-1) at 120 degrees C and 65 mS cm(-1) at 200 degrees C, respectively. Surprisingly, its volume swelling ratio is only 7.8%, which is far less than other reported PA doped membranes. The preliminary fuel cell test shows that PA-PAEK-g-QVBC-6.4 membrane has the peak power density of 53 m W cm(-2) at 100 degrees C without any humidification. The results indicate that the anhydrous proton exchange membranes based on comb-shaped polymers with quaternized graft architectures have the potential to resolve the dilemma between demand of high PA doping levels to achieve high proton conductivity and the dimensional and mechanical stability of largely swollen membranes for high temperature fuel cells.