Improving the ohmic polarization of high-temperature proton exchange membrane fuel cells using crosslinked polybenzimidazole membranes containing acidophilic quaternary ammonium groups synthesized by one-step strategy

Ingenious crosslinked network structure in phosphoric-acid-doped polybenzimidazole membranes can mitigate the mutual restriction of proton conductivity and mechanical properties. However, the complicated synthesis of tailored macromolecular crosslinker and the time-consuming post-treatment hinder their practical application as high-temperature proton exchange membranes. Herein, crosslinked polybenzimidazole membranes are synthesized using small molecular crosslinkers containing acidophilic quaternary ammonium groups through a one-step crosslinking strategy. After doping with phosphoric acid, the quaternary ammonium-biphosphate ion-pair coordination and the crosslinked structure result in the improved anhydrous proton conductivity, oxidation stability, and mechanical strength of the formed membranes compared to the sample without the crosslinking structure. A membrane with the optimized degree of crosslinking exhibits an anhydrous conductivity of 72.27 mS/cm at 160 °C, with a tensile strength of 12.14 MPa. Benefiting from the crosslinked structure and high proton conductivity, the accordingly formed membrane electrode assembly possesses a high open-circuit voltage of 1.01 V and animproved ohmic polarization, delivering a peak power density of 0.66 W/cm2 using hydrogen as fuel and air as oxidant.