Proton Exchange Membrane with Dual-Active-Center Surpasses the Conventional Temperature Limitations of Fuel Cells.

High temperature-proton exchange membrane fuel cells (HT-PEMFC) call for ionomers with low humidity dependence and elevated-temperature resistance. Traditional perfluorosulfonic acid (PFSA) ionomers encounter challenges in meeting these stringent requirements. Herein, this study reports a perfluoroimide multi-acid (PFMA) ionomer with dual active centers achieved through the incorporation of sulfonimide and phosphonic acid groups into the side chain. The fluorocarbon skeleton and multi-acid side chain structure facilitate the segregation of hydrophilic and hydrophobic microphases, augmenting the short-range ordering of hydrophilic nanodomains. Furthermore, the introduction of a rigid segment-benzene ring is employed to decrease side chain flexibility and raise the glass transition temperature. Notably, the prepared membrane exhibits a conductivity of 41 mS cm-1 at 40% relative humidity, showcasing a 1.8 times improvement over that of PFSA. Additionally, the power output of the H2-air fuel cell based on this membrane reaches 1.5 W cm-2 at 105 °C, marking a substantial 2.3 times enhancement compared to the PFSA. This work demonstrates the unique advantages of perfluorinated ionomers with multiple protogenic groups in the development of high-performance high-temperature electrolyte materials.