One-Step Solvothermal Preparation of Mn-Doped VO ₂ (B) Nanosheets for High-Performance Supercapacitors

Abstract

Pure and Mn-doped VO 2 (B) nanosheets were prepared using a simple one-step solvothermal reaction with V 2 O 5 and H 2 O 2 as precursors with Mn(CH 3 COO) 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 VO 2 (B) nanosheet sample, comprising a mixed phase of two polymorphs of VO 2 , exhibits 80% higher capacitance at 2 mV s −1 scan rate, 2X smaller charge transfer resistance, and much improved cyclic stability compared with pure VO 2 (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.