Stable de/protonation-assisted hydrogen vanadium oxide cathodes for aqueous zinc-ion batteries

Abstract

H₂V₃O₈ (denoted as HVO) is introduced to achieve high reversible capacity for aqueous zinc-ion batteries, and we investigate the fundamental charge-storage mechanism. Given the importance of the proton-associated reaction, the crystalline K₂V₃O₈ is ion exchanged in HCl aqueous solution to yield HVO nanowires. These nanowires ultimately result in an open porosity, thereby promoting the electrochemical reaction with protons by shortening the ion/electron transport pathways and reducing both the charge-transfer resistance and activation barrier. Comprehensive analyses indicate that the charge-storage process is governed by a reversible de/protonation reaction rather than conventional Zn²⁺ intercalation. Notably, the HVO electrode delivers a reversible capacity of 467 mAh g⁻¹ at 0.1 A g⁻¹ and retains 96% of its initial capacity over 900 cycles at 1.5 A g⁻¹, resulting in superior specific capacity, rate capability, and cyclability, which are attributed to the selected nanostructure. Operando and ex situ characterization confirm the formation and reversibility of intermediate phases such as zinc hydroxytriflate and vanadium oxides. The observed pH evolution during cycling further validates the key role of H⁺ in enabling fast charge storage. This acid-engineered amorphous HVO thus demonstrates clear viability as a practical cathode for aqueous zinc-ion batteries.