Gel-State Polyelectrolyte With Quaternized Hierarchical Channels Enables Subzero-Operable and High-Power PEMFCs From -20 to 240°C.

Despite the advantages of phosphoric acid (PA)-doped membranes in high-temperature proton exchange fuel cells (HT-PEMFCs), their limited low-temperature performance and acid leaching hinder further widespread deployment. Herein, we report a gel-state polyelectrolyte with quaternized hierarchical channels (QA-PBI-X-Gel) that overcomes these limitations through integrated structural and chemical design. The membranes feature a multiscale 3D porous architecture enriched with dual binding motifs: imidazole rings and quaternary ammonium (QA+) groups. This design enables efficient operation across a wide temperature range from -20°C to 240°C, fulfilling the dual role of an acid reservoir, where PA is stably retained through hydrogen bonding and ion-pair interactions, and a proton generator, which actively promotes acid dissociation even under subzero conditions. The membrane delivers a fivefold enhancement in low-temperature conductivity, achieves 0.411 S/cm at 240°C, and supports highly competitive peak power densities exceeding 2 W/cm2 while simultaneously enabling reliable subzero operation at -20°C, addressing a critical challenge of HT-PEMFCs in automotive applications. Durability tests confirm its robustness, with voltage degradation rates below 50 µV/h at both 40°C and 180°C. These findings establish a unified design that redefines the operational scope of PEMFCs, bridging the gap between existing low- and high-temperature technologies.