Simplified controlled phosphoric acid doping in polybenzimidazole membranes for improved high-temperature fuel cell performance

Gel-type polybenzimidazole membranes prepared by the Polyphosphoric acid method are widely used in high-temperature proton exchange membrane fuel cells. However, uncontrollable acid content will lead to membrane dissolution at high temperatures. This work proposes a facile and efficient sodium bicarbonate-assisted post-treatment modification strategy to precisely tune the phosphoric-acid doping level of naphthalene-containing polybenzimidazole (NPBI) membranes. The in-situ-formed sodium bicarbonate microcrystals can suppress the drastic shrinkage of gel membranes during drying, reduce the shrinkage rate to 72.5%. Meanwhile, sufficient internal microporous cavities are retained to realize controllable optimization of phosphoric-acid doping content, and mitigate the drawbacks including structural collapse and doping imbalance of gel membranes. The membrane exhibited a proton conductivity of 272 mS cm −1 and reaches a peak power density of 1758.6 mW cm −2 at 200 °C. After 200 h of operation at 160 °C, the voltage decay rate reaches 16.5 μV h −1 , which provides an efficient technical strategy for HT-PEMFCs.