Symmetric sponge-like porous polybenzimidazole membrane for high temperature proton exchange membrane fuel cells

Abstract

Conductive porous membranes are promising for environmental and energy applications. Here, a novel symmetric sponge-like porous poly[2,2’-(4,4′-oxybis(1,4-phenylene))-5,5′-bibenzimidazoles] (OPBI) membrane used for high temperature proton exchange membrane fuel cells was successfully fabricated by vapor-induced phase separation (VIPS). Typically, the symmetric sponge-like porous OPBI membrane exhibits thousands of micron-sized cells separated by ultra-thin walls, which are characterized by SEM micrographs. Porous membrane exhibits considerably enhanced acid doping level (ADL) of 9.6 and proton conductivity of 70.8 mS cm−2 at 180 °C compared with the corresponding dense membranes (OPBI: ADL = 4.1). Interestingly, with higher ADL, the porous OPBI membrane showed much lower swelling ratio in in-plane direction (50%) and thus higher dimensional stability than dense OPBI (74%) and mPBI (103%). Moreover, the open circuit voltage (OCV) of the fuel cell based on the porous membrane was 0.86 V indicating the low gas crossover and the fuel cell showed excellent peak power density of 485.3 mW/cm2 at 160 °C, higher than m-membrane of 353.1 mW/cm2 and OPBI membrane of 38.7 mW/cm2. Though the single cell durability is poor for porous OPBI membrane than that of m-PBI due to the leach of PA, the combination of the facile fabrication procedure, high performance and easy up-scaling enables the PBI porous membranes to be promising for high temperature proton exchange membrane fuel cells. Further work for us is to adjust the size of the pores and porous structure, thus improving the PA retention of porous membranes.