One-Step Solvothermal Preparation of Mn-Doped VO2(B) Nanosheets for High-Performance Supercapacitors

Pure and Mn-doped VO2(B) nanosheets were prepared using a simple one-step solvothermal reaction with V2O5 and H2O2 as precursors with Mn(CH3COO)(2)4H(2)O added directly into the precursor solution to obtain the Mn-doped variant. The powder morphology, local structures and cation oxidation states were investigated using scanning electron microscopy (SEM), powder X-ray diffraction (XRD), high-energy X-ray scattering, X-ray absorption near edge spectroscopy (XANES), and X-ray photoelectron spectroscopy (XPS). The electrochemical properties were studied using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The Mn-doped VO2(B) nanosheet sample, comprising a mixed phase of two polymorphs of VO2, exhibits 80% higher capacitance at 2 mV s(-1) scan rate, 2X smaller charge transfer resistance, and much improved cyclic stability compared with pure VO2(B). The improved electrochemical response is attributed to the enhanced mass transfer kinetics due to slightly differing microstructures and formation of more varied oxidation states of the V and Mn ions such that the charged defects increase the electrical conductivity and charge transfer efficiency.