Galvanostatic deposition of manganese oxide films for super capacitive application and their fractal analysis

Abstract

Manganese oxide (MnO2) thin films were electrodeposited on stainless steel substrates through galvanostatic mode at different current densities of 2.0 mA cm−2, 1.0 mA cm−2, and 0.5 mA cm−2. Morphology of the films was controlled by controlling current density during deposition. The surface morphology and compositional analysis of deposited films were studied through scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) respectively. SEM images revealed a porous morphology of the deposited films, while discontinuity of film surface was observed for films deposited at higher growth rate. X-ray diffraction patterns for the deposited films revealed a weak orthorhombic crystal system corresponding to the di-pyramidal structure of MnO2. The specific capacitance of MnO2 films, as determined through cyclic voltammetry, was found to range from 90 Fg−1 to 170 Fg−1. The electrochemical impedance spectroscopy (EIS) data was used for obtaining a modified Randles equivalent circuit for identifying the series resistance, charge-transfer resistance, double-layer capacitance, and ion diffusion. Fractal dimensions of the deposited films were determined through image processing software and EIS data. The study also investigates the effect of texture, roughness, and anisotropy of the thin films on their electrochemical capacitive performance.