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

ABSTRACT 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/cm 2 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.