Bifunctional Cationic Covalent‐Organic‐Framework for All‐Solid‐State Proton Batteries with High‐Rate and Ultra‐Stable Cyclability

Abstract Despite promising prospects afforded by high power density and abundant proton sources, proton batteries (PBs) face practical limitations. Liquid electrolytes induce anode dissolution and parasitic reactions, while solid electrolytes suffer from low proton conductivity and poor electrode compatibility. Herein, we introduce a bifunctional strategy for PBs using a cationic covalent organic framework (EB‐COF). Synthesized from ethidium bromide (EB) and 2,4,6‐triformylphloroglucinol (TP), this bifunctional host simultaneously stabilizes phosphomolybdate (PMo 12 ) clusters anode and confines H 3 PO 4 as a solid‐state electrolyte within its nanochannels. The resulting EB‐COF:H 3 PO 4 electrolyte exhibits superior proton conductivity (>10 −2 S cm −1 ) and a wide electrochemical stability window (3.3 V versus SCE). The assembled PB delivers exceptional rate capability and cycling stability, retaining 91% capacity over 15 000 cycles at 10 A g −1 , surpassing all reported solid‐state PBs. This performance stems from excellent electrode‐electrolyte compatibility and the high structural stability of the EB‐COF:H 3 PO 4 system. This study provides valuable insights for developing reliable all‐solid‐state PBs.