Pre‐Protonated Vanadium Hexacyanoferrate for High Energy‐Power and Anti‐Freezing Proton Batteries

Abstract Proton batteries have been considered as an innovative energy storage technology owing to their high safety and cost‐effectiveness. However, the development of fast‐charging proton batteries with high energy/power density is greatly limited by feasible material selection. Here, the pre‐protonated vanadium hexacyanoferrate (H‐VHCF) is developed as a proton cathode material to alleviate the capacity loss of proton‐free electrode materials during electrochemical tests. The pre‐protonation process realizes fast and long‐distance transport of protons by shortening diffusion path and reducing migration barriers. Benefitting from the enhanced hydrogen bonding network combined with dual redox reactions of V and Fe in protonated H‐VHCF cathode, a high energy density of 74 Wh kg −1 at 1.1 kW kg −1 , and a maximum power density of 54 kW kg −1 at 65 Wh kg −1 is achieved for the asymmetric proton batteries coupling with MoO 3 /MXene anode. Proton transport and double oxidation‐reduction center are verified by theoretical calculations and ex situ experimental measurements. Considering the anti‐freezing availability of proton batteries, 82.5% of its initial capacity is maintained after 10000 cycles under −40 °C at 0.5 A g −1 . As a proof‐of‐concept, flexible device fabricated by optimized electrodes and hydrogel electrolytes can power up a light‐emitting diode even under a bent state.