High-performance and robust high-temperature polymer electrolyte membranes with moderate microphase separation by implementation of terphenyl-based polymers

Acid loss and plasticization of phosphoric acid (PA)-doped high-temperature polymer electrolyte membranes (HT-PEMs) are critical limitations to their practical application in fuel cells. To overcome these barriers, poly(terphenyl piperidinium)s constructed from the m- and p-isomers of terphenyl were synthesized to regulate the microstructure of the membrane. Highly rigid p-terphenyl units prompt the formation of moderate PA aggregates, where the ion-pair interaction between piperidinium and biphosphate is reinforced, leading to a reduction in the plasticizing effect. As a result, there are trade-offs between the proton conductivity, mechanical strength, and PA retention of the membranes with varied m/p-isomer ratios. The designed PA-doped PTP-20m membrane exhibits superior ionic conductivity, good mechanical strength, and excellent PA retention over a wide range of temperature (80–160 °C) as well as satisfactory resistance to harsh accelerated aging tests. As a result, the membrane presents a desirable combination of performance (1.462 W cm−2 under the H2/O2 condition, which is 1.5 times higher than that of PBI-based membrane) and durability (300 h at 160 °C and 0.2 A cm−2) in the fuel cell. The results of this study provide new insights that will guide molecular design from the perspective of microstructure to improve the performance and robustness of HT-PEMs.