Functional Poly(<i>p</i>-terphenyl-<i>co</i>-4-acetylpyridine) Membranes for High-Temperature Proton Exchange Membrane Fuel-Cell Applications

The development of high-temperature proton exchange membranes (HT-PEMs) with low cost, simple synthetic pathways, and superior physicochemical performance is of paramount importance for their successful integration into fuel cells. Herein, we prepare HT-PEMs by grafting alkaline side-chain groups onto poly(p-terphenyl-co-4-acetylpyridine) membranes (PTAP-R), taking 2-chloromethylbenzimidazole (BIm) and (3-bromopropyl)trimethylammonium bromide (TAB) as functionalized reagents. Initially, PTAP is synthesized via a straightforward Friedel–Crafts polymerization process. For the purpose of increasing the phosphoric acid (PA) doping content along with improving conductivity, BIm or TAB with alkaline side chains is incorporated onto the PTAP backbones. Comparative analysis reveals that the PTAP-BIm membrane accomplishes an exceptional PA doping level of 289%, and the conductivity attains 122 mS/cm at 180 °C in nonhumidification conditions. Large amounts of PA molecules provide numerous active sites for proton transfer, leading to the development of extensive and dynamic hydrogen bonding networks along with densely interconnected transport pathways, which offer additional pathways for effective proton conduction. Furthermore, the H2-air fuel cell utilizing PTAP-BIm membrane with 289%PA achieves a peak power density of 324 mW/cm2 at 160 °C without backpressure. This study elucidates a cost-effective and mild approach for fabricating high-performance HT-PEMs that hold great potential in HT-PEM fuel-cell applications.