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

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 at 200 °C and extremely high peak power density of 847 mW cm of the HT-PEMFC under ultralow Pt/C loading (0.3 mg cm) 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 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.