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 H2‐O2 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. [ABSTRACT FROM AUTHOR]