Electrochemical Proton Intercalation Properties of Bronze-Type Vanadium Dioxide in Nonaqueous Protic Electrolyte

Proton (H+) serves as an energy carrier in various electrochemical systems because of its ubiquity and unique characteristics originating from its small size and lightness. Consequently, solid-state proton conduction and Faradaic proton storage are pivotal for high-capacity fast-charging electrochemical systems. However, the use of acidic electrolytes in proton-related systems requires electrodes capable of resisting acidity. In this study, we explored the electrochemical proton intercalation of bronze-type vanadium dioxide (VO2(B)) using a nonaqueous protic electrolyte, specifically the pseudoprotic ionic liquid (pPIL) composed of 1-methylimidazole (C1Im) and acetic acid (AcOH). VO2(B) exhibits a reversible electrochemical capacity of 260 mAh g–1 at 150 mA g–1, retaining 75% capacity even after 200 cycles at 500 mA g–1 in pPIL electrolytes. The interslab pillar oxygen atoms provide the dense hydrogen-bond donor–acceptor array realizing the two-dimensional proton transport pathways. These insights will aid in identifying emerging electrode materials that enable stable proton (de)intercalation with a high rate and high capacity.