Superior Room‐Temperature Anhydrous Proton Conduction in 3D Porous Benzimidazole Membranes Enabled by Strong Acid Confinement

Phosphoric acid-doped polybenzimidazole (PA-PBI) is a leading anhydrous proton exchange membrane (APEM) material for non-aqueous electrochemical technologies. However, its flexible linear backbone results in poorly defined and acid-sensitive proton conduction pathways, compromising durability and limiting the use of stronger acids for conductivity enhancement. To overcome these limitations, we designed and synthesized a novel self-standing, 3D benzimidazole-functionalized covalent triazine framework membrane (OBI-CTFM) via a sol-gel approach. This membrane exhibits exceptional mechanical strength, strong acid resistance, and an intrinsic microporous structure with alkaline imidazole groups that enable effective acid uptake and confinement. Remarkably, the methanesulfonic acid-treated membrane (MSA@OBI-CTFM) achieved a record-high anhydrous proton conductivity (>10^-2 S cm^-1) near room temperature, surpassing most reported anhydrous proton conductors. As an APEM in proton batteries, this membrane enabled remarkable cycling stability (∼7000 cycles) and high specific capacity. Our work demonstrates the critical role of 3D porous structures in APEMs and paves the way for advanced PBI membranes in electrochemical applications.