Redox Charge Transfer Kinetics and Reversibility of VO₂ in Aqueous and Non-Aqueous Electrolytes of Na-Ion Storage

The deep understanding about the electrochemical behavior of the nanostructured electrode in electrolytes provides crucial insights for the rational design of electrode for sodium (Na)-ion storage system (NIS). Here, we report redox charge transfer kinetics and reversibility of VO₂(B) nanorod electrodes in both aqueous and organic electrolytes for NIS. The as-synthesized VO₂(B) nanorods show the reversible redox reaction with the higher specific and rate capacitances at high current density in aqueous electrolytes than in organic electrolytes. Temperature-dependent impedance measurements demonstrate the more facile interfacial charge transfer of Na ions into VO₂(B) nanorods in aqueous electrolytes. The reversible evolution in oxidation state and chemical composition of VO₂(B) nanorods is observed in aqueous electrolytes, as confirmed by ex situ XRD and ex situ X-ray photoelectron spectroscopy analyses. Given by the facile and reversible pseudocapacitive feature, the electrochemical performances of VO₂(B) nanorods are further improved by constructing the hierarchical structure of the reduced graphene oxide-VO₂ composite for aqueous Na⁺ ion storage.