Arylether-type polybenzimidazole-based composites containing imidazole-substituted heteropolyacid salts for high-temperature proton exchange membrane fuel cells

Phosphoric acid-doped polybenzimidazole (PA-PBI) membranes are one of the most promising candidates for practical applications in high temperature proton exchange membrane fuel cells. In the field of the proton exchange membranes, a key target is to develop the membranes possessing high proton conducting ability, and meanwhile maintaining good mechanical integrity. It is extremely hard for PBI-based membranes at a high acid doping level (ADL) to have good strength due to the strong “plasticization effect” caused by PA molecules to PBI backbones. In order to obtain high-proton-conductivity membranes with a good comprehensive performance, three imidazole-substituted heteropolyacid salts (imi-HPAs) were synthesized and then incorporated into an arylether-type polybenzimidazole (Ph-PBI) matrix to fabricate some composite membranes via a solution blending process. Since both Ph-PBI matrix and imidazole-substituted heteropolyacid salts contained the functional imidazole groups, some preferred mixed effects and performance enhancements of the organic-inorganic composite membranes were observed. The morphology of the composite membranes revealed that imidazole-substituted heteropolyacid salts were homogenously dispersed in the Ph-PBI matrix. The membrane Ph-PBI/imi-HPA-3-15% at ADL∼290.4% had the highest conductivity of 166.6 mS·cm^-1 at 200 °C. A H₂/O₂ fuel cell based on one membrane showed a peak power density of 454 mW·cm^-2 at 160 °C, without humidification.