Crystalline Hydrogen Enhanced Dual‐Acid Quasi‐Solid‐State Proton Battery

Abstract Proton batteries are considered promising due to their high‐power output, cost‐effectiveness, and safety. However, they also face challenges such as low voltage, limited capacity, and poor cycle stability. To address these challenges, a dual‐acid quasi‐solid‐state electrolyte (SSAE) is developed by combining H 2 SiO 3 with H 2 SO 4 . This electrolyte has the decomposition voltage of 2.15 V and ultra‐high conductivity of 95 mS cm⁻¹ (1.5 mS cm⁻¹ at −70 °C). Leveraging this high decomposition voltage, the specific capacity of MoO 3 is successfully enhanced to 1.74 times than its original value at a current density of 5 A g −1 by harnessing the hydrogen evolution/oxidation reaction (HER/HOR) of lattice hydrogen (H· ad,s ) in MoO 3 at low potentials, which is typically regarded as a significant factor to suppress the gas evolution. Notably, the voltage achieved a record‐breaking 1.8 V in the Prussian Blue Analog //MoO 3 system at room temperature. The full cell consisting of HVFe‐PBA (pre‐protonated vanadium hexacyanoferrate)//SSAE//MoO 3 exhibited outstanding electrochemical performance at both room temperature and low temperatures. As a proof‐of‐concept, a pouch cell is assembled with an energy density of 72.3 Wh kg −1 , and even it maintained an energy density of 40.7 Wh kg −1 at −60 °C.