Ultralow‐Temperature (≤ −80 °C) Proton Pseudocapacitor with High Power‐Energy Density Enabled by Tailored Proton‐Rich Electrolyte and Electrode

Abstract Proton‐based energy storage systems provide a more sustainable alternative for large‐scale energy storage applications. However, conventional proton batteries/pseudocapacitors suffer from severe capacity loss because of reduced ionic conductivity and water‐to‐ice conversion at ultralow temperatures. Here, anti‐freezing proton‐rich electrolytes with ultralow freezing point (below −80 °C) and high conductivity (7.89 mS cm⁻¹ at −80 °C) are developed, combined with open framework‐structured Prussian blue analogous (VHCF) electrodes with proton‐rich binding sites, to construct a promising proton pseudocapacitor at ultralow temperatures. Hydrogen bond‐induced solvated structures and physicochemical properties are clarified by comprehensive characterization techniques and computational simulations. Temperature‐dependent structure and valence changes for VHCF electrodes at low temperatures are revealed, where the multi‐electron transfer reaction is affected by temperature to limit the capacity output. The proton pseudocapacitor (VHCF//6 m H₂SO₄//MoO_3‐x) achieves excellent electrochemical performance in the temperature range from −80 to 25 °C, and delivers a voltage window of 0 to 2.8 V and a high energy density of 74.9 Wh kg⁻¹ at −80 °C. This proton‐rich electrolyte‐electrode design principle suggests an effective strategy enabling next‐generation energy technology under extreme conditions.