Investigation of electrochemical properties of various transition metals doped SnO2 spherical nanostructures for supercapacitor applications

A simple co-precipitation method has been used to synthesis SnO2 and different transition metal (Fe, Cu and Zn) doped SnO2 spherical nanostructures. The influence of doping concentration on the structural, optical, functional and morphological properties were carefully analysed by using X-ray diffraction, Fourier Transform Infrared Spectroscopy, UV-Visible spectroscopy and Scanning Electron Microscopy studies. The XRD pattern declared the formation of cassiterite rutile SnO2 with tetragonal structure. No impurity peaks correspond to the transition metal dopant was observed in the doped SnO2 samples. The average crystallite size was found to be 27.2, 24.1, 22.3 and 21.8 nm for pure and Fe, Cu and Zn-doped samples, respectively. The EDX spectra and element mapping assessed the presence of Sn, O, Fe, Cu and Zn species. The SEM images showed the spherical mor-phology for the synthesized pure and TM-doped samples. X-ray photoelectron spectra confirmed the electronic state and binding energy of the Sn, Cu, Zn, Fe and O. The electrochemical performance of the prepared electrodes were evaluated by galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The nanostructured Fe doped SnO2 electrode revealed a favorable specific capacitance of 270 F/g at a current density of 0.5 A/g and also it has excellent cycling stability of 98% retention over 2000 charging discharging cycles.