Acid‐Alkaline Double Electrolytes for High‐Energy Aqueous Proton Batteries

Abstract Aqueous proton batteries offer a promising energy storage solution due to their inherent safety, rapid ion mobility, and low cost. However, their performance is largely constrained by water's limited electrochemical stability, restricting operating voltage and energy density. This study addresses this challenge by introducing an innovative acid‐alkaline double electrolyte configuration to achieve high‐voltage aqueous proton batteries. Employing a high‐anodic‐limit acidic catholyte (7 M H 3 PO 4 ) and a low‐cathodic‐limit alkaline anolyte (6 M KOH), separated by a proton exchange membrane (PEM), significantly expands the full battery's electrochemical stability window (ESW) to 2.91 V. Cobalt‐doped Prussian blue (CoCuHCF) was selected as the cathode due to its superior proton kinetics and cycling durability, while benzo[c]cinnoline (BCC) was identified as an optimal anode via combined theoretical analysis and experimental validation. Consequently, the battery delivered exceptional electrochemical performance, achieving a high energy density of 329.6 Wh kg −1 at 1 A g −1 , a remarkable power density of 14788.3 W kg −1 at 10 A g −1 , and excellent cycling stability with 98.3% capacity retention after 1000 cycles. The proposed acid‐alkaline double electrolyte strategy provides efficient and valuable guidance for advancing aqueous energy storage technologies.