Porphyrin Helical Nanochannel-Assembled Polybenzimidazole Membranes Doped with Phosphoric Acid for Fuel Cells Operating in a Temperature Range of 25–200 °C

High-temperature proton-exchange membrane fuel cells (HT-PEMFCs) fabricated with phosphoric acid (PA)-doped polybenzimidazole (PBI) show apparent technical advantages. In practical automotive applications, achieving cold start-up capability is crucial. In this work, a kind of branched block proton exchange membrane (PEM) based on PBI with a low content of porphyrin ring (<1 mol.%) is reported as a branched monomer. Self-assembly into high-density helical nanochannels under the synergistic effect of phase separation and porphyrin π−π stacking, thus the PEM can maintain a high level of PA doping. Specifically, the PA/1.8TCPP-BrPy-OPBI membrane shows a proton conductivity of 0.169 and 0.071 S cm −1 , as well as an H 2 -O 2 fuel cell peak power density of 1077 and 357 mW cm −2 at 180 and 80 °C without humidification and backpressure, respectively. The membrane electrode assembly (MEA) can exhibit good fuel cell stability, with a voltage decay rate of only 7.0 µV h −1 at 80 °C. Furthermore, it maintains a peak power density of 93% even after 150 start-up/shut-down cycles at 25 °C. This work expands the operating temperature range of conventional PBI membranes between 25 and 200 °C and thus provides a novel strategy for high-performance PBI-based HT-PEMFCs.