A high voltage aqueous proton battery using an optimized operation of a MoO3 positive electrode

Abstract

Aqueous proton batteries have attracted increasing attention owing to their potential of high safety standard, high rate capability, and long cyclability. While some inorganic negative electrode materials for proton batteries have recently been found, inorganic positive electrode materials have rarely been reported. In this work, we investigate the proton insertion–extraction mechanism of MoO₃ using operando X-ray diffraction and density functional theory calculation to optimize its operating conditions as a positive electrode. It is found that the phase transition between MoO₃ and phase-I H_xMoO₃ can reversibly be utilized by preventing irreversible phase transition from phase-I to phase-III involving the change of proton accommodation from the intralayer to interlayer sites. A MoO₃ electrode using the phase transition between MoO₃ and phase-I shows an average reduction potential of 0.44 V vs. SHE with a maximum reversible capacity of 100 mA h g⁻¹. A MoO₃|50 wt% H₂SO₄ aq.|H_xMoO₃ full-cell exhibits a maximum discharge capacity of 73 mA h g⁻¹ and maintains nominal discharge voltage above 0.47 V, which is the highest voltage among aqueous proton batteries composed of insertion-type oxide active materials.