Quaternized‐PAF Architecture Mediated Proton Channels to Enhance Ultra‐Robust Operation for 200 °C Proton Exchange Membrane Fuel Cells

Abstract In optimizing the trade‐off between power density and phosphoric acid (PA) retention in PA‐doped polybenzimidazole (PA‐PBI) membrane for improving performance of high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs), the self‐reinforcing network of interfacial interactions of the HT‐PEMs has to be deeply investigated. In this paper, a breakthrough strategy employing a quaternary ammonium (QA)‐functionalized porous aromatic framework (QPAF‐225) to synergistically integrate with sulfonated poly[2,2′‐(p‐oxydiphenylene)‐5,5′‐bibenzimidazole] (SOPBI) to form the robust HT‐PEM is successfully developed. The ionic interactions between the cationic QA moieties and anionic sulfonic acid groups can establish a self‐reinforcing proton‐conductive network, while the high‐density basic sites in QPAF‐225 act as the PA reservoirs and can mitigate the leakage. When benchmarked against QA‐deficient PAF‐225–10 (10% PAF‐225 in composite membrane) composite HT‐PEMs and pristine SOPBI, the QPAF‐225–10 composite delivers a high proton conductivity of 174 mS cm −1 at 200 °C and extremely high peak power density of 847 mW cm −2 of the HT‐PEMFC under ultralow Pt/C loading (0.3 mg cm −2 ) at 200 °C operation, which surpasses most of PA‐PBI systems reported in literatures. Critically, such a membrane exhibits ultralow voltage decay rate (0.04 mV h −1 over 904 h at 200 °C) and high PA retention ability, coupled with mechanical robustness exceeding industrial durability thresholds. This work transcends conventional additives by exploiting porous aromatic framework‐mediated proton channels and PA‐philic motifs, establishing a material paradigm for next‐generation HT‐PEMs that reconciles high‐power operation with long‐term stability in harsh electrochemical environments.