Novel crosslinked AB-type polyphenylquinoxaline membranes for high-temperature proton exchange membrane fuel cells

AB-type polyphenylquinoxaline (ABPPQ) membranes exhibit great mechanical properties and thermal properties for high-temperature proton exchange membranes (PEMs). However, they dissolve in high-concentration phosphoric acid (PA) during acid doping. In order to improve the PA resistant of ABPPQ, crosslinked ABPPQ membranes were prepared using sulfuric acid. The crosslinked ABPPQ membranes showed high PA resistance. The acid content of PA-doped membranes decreased slightly with crosslinking, but the crosslinked polyphenylquinoxaline (CPPQ)-20 membrane could reach 2.5 × 10⁻² S/cm proton conductivity at 160°C. Membrane electrode assemblies were fabricated with an active area of 4 cm² and Pt loading of 1 mg/cm². A startup and shutdown test (operated at 150°C with 0.2 A/cm² for 12 h and then 12 h off at room temperature) and a 30-day long-term durability test (150°C with 0.2 A/cm²) were conducted. In the startup and shutdown test, the crosslinked membranes showed a low open-circuit voltage decay rate of 0.15 mV/h. In the 30-day long-term durability test, the voltage decay rate was 0.039 mV/h. In both tests, the crosslinked membranes showed a stable performance. Therefore, the crosslinked ABPPQ membranes can be regarded as a novel material for high-temperature PEM fuel cells. POLYM. ENG. SCI., 59:2169–2173, 2019.