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

Abstract 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‖H 2 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.