Boosting the Ionic Conductivity of Non-Aqueous Proton Electrolyte for Hybrid Capacitors

Proton batteries have emerged as promising alternatives for energy storage owing to their rapid H⁺ transport kinetics and environmental sustainability. However, state-of-art proton batteries using aqueous acid electrolytes suffer from severe hydrogen evolution, electrode dissolution, and narrow electrochemical windows. Non-aqueous electrolytes could obviate these challenges, while they are typically limited by low ionic conductivity. In this work, a hydrogen-bond-mediated proton transport mechanism is revealed in the phosphoric acid/ethyl acetate (H₃PO₄/EA) electrolytes with various concentrations. The optimized non-aqueous H₃PO₄/EA electrolyte (80 m) simultaneously achieves high ionic conductivity (21.8 mS cm^-1), wide electrochemical stability window (2.5 V), wide operational temperature range (-80 to 200 °C), and minimal corrosiveness. Using this electrolyte, the MoO₃//AC hybrid capacitor demonstrates ultrahigh power density (13292 W kg^-1), extended cycling stability (10 000 cycles), and unprecedented temperature adaptability (-50 to 60 °C). Our findings provide fundamental insights into non-aqueous proton conduction mechanisms and establish new design principles for practical proton energy storage systems.