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

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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 HxMoO3 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 MoO3j50 wt% H2SO4 aq.jHxMoO3 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.

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