Effects of oxalic acid concentration on the microstructures and properties of nano-VO2(B)

In this work, a series of VO2(B) samples were synthesized via a hydrothermal process by reducing V2O5 with different concentrations of oxalic acid. The prepared samples were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry, and galvanostatic charge-discharge. Furthermore, the microdefects of VO2 samples were characterized by positron lifetime spectroscopy. The results revealed that VO2(B) was successfully prepared and the concentration of reducing agent had a certain influence on the microstructures and properties. The electrochemical performance measurements showed that all samples had good cycle stability in 2 mol/L KOH solution. The x = 1.50 sample displayed higher discharge capacitance of 149.5 F g(-1) at 30 mA g(-1) and the discharge capacitance remained about 67% even after 80 charge/discharge cycles. The positron lifetime spectra revealed that the main defects in VO2 samples were microvoids, and the defect concentration and size were affected by the C2H2O4 concentration.