Phase-pure VO nanoporous structure for binder-free supercapacitor performances.

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 VO 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 VO, with V oxidation state of +4, provides superior charge storage capacity with a capacitance value of 33 mF/cm, capacitance retention of 93.7% and Coulombic efficiency of 98.2%, to those for VO structures with mixed oxidation states of V and V. A comparable high energy density is also recorded for the sample with all V. Scanning Kelvin probe microscopy results clarify further the formation of space charge region between VO and carbon paper. These key findings indicate the potentiality of binder-free single phase monoclinic VO porous structure towards the next-generation micro-supercapacitor application.