Fig. 4
Electrochemical characterization of electrodes in aqueous electrolyte. a Cyclic voltammetry (CV) curves of NP c-V2O3, r-VO2 and c-V2O3/r-VO2−x (x = 0.22) electrodes in three-electrode configuration at a scan rate of 50 mV s−1 in 1 M Na2SO4. b Gravimetric and volumetric capacitances for NP c-V2O3, r-VO2 and c-V2O3/r-VO2−x electrodes at various scan rates, comparing with the volumetric values previously reported for Ti3C2Tx MXene clay36, N-doped mesoporous few-layer carbon (MFLC-N)37 and bare MnO2 electrodes20, as well as the gravimetric values of mesoporous RuO29, hydrogenated-TiO2/MnO2 (H-TiO2/MnO2)19 and nanostructured hexagonal WO338. c Plot of normalized capacitance versus scan rate−1/2 for the separation of diffusion-controlled intercalation pseudocapacitance from surface-controlled redox pseudocapacitance in the scan rates from 5 to 1000 mV s−1. d Evolution of volumetric capacitances of NP c-V2O3/r-VO2−x electrodes at a scan rate of 5 mV s−1 as a function of x. The gray solid circles and lines are the theoretically volumetric capacitances for NP c-V2O3/r-VO2−x based on the atomic structures with x = 0, 0.167, 0.25 and 0.5, which correspond to r-VO2, metastable r-VO2−x and c-V2O3, respectively
