Dual-Bond-Reinforced 3D Network Membrane with Nitrogen-Ratched Ionic Polymer for Enhanced Durability and High-Power HT-PEMFCs

Polybenzimidazole (PBI) membranes doped with phosphoric acid (PA) are promising electrolytes for high-temperature proton exchange membrane fuel cells (HT-PEMFCs) due to their excellent thermal stability and intrinsic mechanical strength. However, their practical performance is often constrained by insufficient PA uptake and retention, as well as mechanical degradation induced by acid plasticization. Herein, a synergistic modification strategy is proposed by incorporating chloromethylated polysulfone (CMPSF) as a covalent crosslinker and a nitrogen-rich ionic polymer (NIP) into an OPBI matrix to construct an OPBI/CMPSF-NIP (OPBI/C-I) composite membrane. CMPSF reacts with OPBI to form a robust three-dimensional crosslinked network, significantly enhancing mechanical integrity and dimensional stability. Simultaneously, the abundant basic nitrogen sites within NIP establish strong acid-base interactions with PA, improving PA uptake and retention while providing additional proton-hopping sites. As a result, the optimized OPBI/C-I membrane exhibits a high proton conductivity of 163.44 mS cm-1 at 160 °C under anhydrous conditions and delivers a peak power density of 1001.7 mW cm-2, far exceeding that of pristine OPBI membranes. Moreover, the composite membrane demonstrates enhanced oxidative stability and long-term PA retention. This work offers an effective and scalable strategy for balancing proton conductivity, mechanical robustness, and durability in PA-PBI-based HT-PEMs.