Hyperbranched Interpenetrating Hydrogen Bond Network (HIHBN) Proton Exchange Membrane for Fuel Cells Above 220 °C

Abstract High‐performance proton exchange membranes (PEMs) play a vital role in the efficiency of high‐temperature proton exchange membrane fuel cells. In this study, a novel PEM with a hyperbranched interpenetrating hydrogen bond network (HIHBN) is developed by incorporating hyperbranched poly(benzyl‐triptycene) (PBT) and SnP₂O₇ hydrogen bond networks. This innovative design significantly enhances the proton conductivity. Additionally, the unique structure of the hyperbranched PBT polymer with a branching point (triptycene, a π‐conjugated aromatic ring compound with a three‐cyclic configuration) contributes to an impressive glass transition temperature exceeding 400 °C, enabling the membrane to operate at elevated temperatures (above 220 °C) in fuel cell applications. This membrane shows promise as an alternative to commonly used polybenzimidazole (PBI)‐based membranes, offering improved mechanical strength and a reduced swelling ratio. When applied in fuel cells, the HIHBN PEM achieves an excellent through‐plane proton conductivity of 0.108 S cm⁻¹ and a peak power density of 0.75 W cm⁻² at 220 °C under dry H₂/O₂ conditions. Notably, it exhibited minimal degradation after ≈33 h under harsh operating conditions, demonstrating its stability and long‐term durability. These findings highlight the potential of HIHBN PEMs for high‐efficiency, durable performance in high‐temperature fuel cell environments.