Mechanochemically Synthesized Covalent Organic Framework‐Based Protonic Electrolytes with Superior Proton Conduction for Solid‐State Proton Batteries

Comprehensive Summary The development of solid‐state protonic electrolyte is essential for safe and durable energy storage, yet their practical application remains limited by insufficient proton conductivity and narrow electrochemical stability windows. Although covalent organic frameworks (COFs) have emerged as promising platform for proton conduction owing to their ordered porous channels and tunable functionalities, conventional solvothermal synthesis generally requires harsh conditions, long reaction times, and large amounts of organic solvents. Herein, we report a simple and efficient mechanochemical ball‐milling strategy for facile synthesis of a phosphoric acid‐loaded COF protonic electrolyte (PA@TP‐COF). Benefiting from the ordered nanochannels of TP‐COF and the strong acid‐base interactions between the framework and H 3 PO 4 , continuous hydrogen‐bonding networks are constructed to facilitate efficient proton transport. Consequently, the PA@TP‐COF electrolyte exhibits a high proton conductivity of 6.24 × 10 −2 S·cm −1 with a low activation energy of 0.14 eV. Moreover, the electrolyte delivers a wide electrochemical stability window of 5.6 V. Solid‐state proton batteries assembled with PA@TP‐COF electrolyte achieve remarkable cycling durability with 72.2% capacity retention after 1500 cycles at 1.0 A·g −1 , together with excellent rate capability.