Continuous Proton Channels in Vanadium Hexacyanoferrate Enable All‐Round Improved Ultra‐Low‐Temperature Energy Conversion

Proton-based batteries emerge as a promising candidate for low-temperature energy conversion and storage, yet their practical implementation is constrained by cathode performance limitations. Herein, [Fe(CN)₆] vacancies-mediated vanadium hexacyanoferrate (VFeCN-VHCF) with contiguous proton channels is pioneered as a proton cathode material for all-round improved ultra-low-temperature energy conversion. Through operando characterization and density functional theory calculations, we reveal that the [Fe(CN)₆] vacancies induce the formation of V═O bonds, which serve as the active sites to store protons and endow V_FeCN-VHCF to reach a high capacity. More crucially, the interaction between interstitial water and V═O─H groups constructs continuous proton channels within the V_FeCN-VHCF framework, which enables rapid and unimpeded Grotthuss-type proton conduction during redox reactions. By employing V_FeCN-VHCF as the proton cathode and hydrogen gas as the anode, the fabricated V_FeCN-VHCF‖H₂ proton full battery demonstrates an unprecedented specific capacity of 165.16 mAh g^-1 at 0.1 Ag^-1. Notably, even at an ultralow temperature of -80 °C, this battery maintains a high capacity of 86.63 mAh g^-1 at 0.1 A g^-1, which is significantly superior to previously reported low-temperature batteries. This work offers a promising avenue for the advancement of high-power energy storage systems designed to operate in extreme environmental conditions.