Efficient electrochemical performance of ZnMn2O4 nanoparticles with rGO nanosheets for electrodes in supercapacitor applications

Hydrothermally synthesized ZnMn2O4 and ZnMn2O4/rGO electrodes were investigated for its better performance in supercapacitors. The X-ray diffraction analysis revealed that ZnMn2O4 have spinel tetragonal crystal structure with average crystallite size calculated as 18 nm whereas ZnMn2O4/rGO crystallite size calculated as 20 nm. Functional groups and vibrations present in the samples were confirmed using Fourier transform infrared spectroscopy and Raman spectroscopy. X-ray photoelectron spectroscopy analysis confirmed the oxidation states and atomic concentrations present in the compound and composite. Spherical shape of the synthesized ZnMn2O4 nanoparticles and rGO nanosheets were seen by high resolution scanning electron microscopy studies. Spherical nanoparticles settled on rGO sheets can be viewed from high resolution transmission electron microscopy studies. Electrochemical performance of the nanomaterials was tested by cyclic voltammetry and galvanostatic charge-discharge analysis. ZnMn2O4 exhibits specific capacitance of 492 F/g at 5 mV/s scan rate in a potential window of 0-0.4 V. ZnMn2O4 wrapped with rGO showed specific capacitance of 1341 F/g at 5 mV/s in a potential window of 0-0.5 V. Electrochemical impedance spectra showed a charge transfer resistance of 1.78 and 1.43 Omega for ZnMn2O4 and ZnMn2O4/rGO composite respectively.