Phase-pure VO2 nanoporous structure for binder-free supercapacitor performances

Abstract

Vanadium oxides are anticipated as a high-performance energy storage electrode due to their coupled double layer and pseudo-capacitative charge storage mechanism. In the present work, we investigated the influence of different structural phases of as-grown VO₂ nanoporous structure and corresponding oxidation states on the supercapacitor performance. This nanoporous structure facilitates fast ion diffusion and transport. It is shown that stoichiometric monoclinic VO₂, with V oxidation state of +4, provides superior charge storage capacity with a capacitance value of 33 mF/cm², capacitance retention of 93.7% and Coulombic efficiency of 98.2%, to those for VO₂ structures with mixed oxidation states of V⁵⁺ and V⁴⁺. A comparable high energy density is also recorded for the sample with all V⁴⁺. Scanning Kelvin probe microscopy results clarify further the formation of space charge region between VO₂ and carbon paper. These key findings indicate the potentiality of binder-free single phase monoclinic VO₂ porous structure towards the next-generation micro-supercapacitor application.