MnO2/carbon nanowall electrode for future energy storage application: effect of carbon nanowall growth period and MnO2 mass loading

Abstract

Nanostructured MnO₂ films with 50 and 100 μg cm⁻² mass loadings supported on two dimensional (2D) stand-free carbon nanowalls (CNWs) were synthesized by anodic electrodeposition and investigated for supercapacitor application. The underlying CNW films of different growth periods, 12–24 s, were grown first by microwave plasma enhanced chemical vapor deposition on three dimensional (3D) nickel foam substrate. Tailoring the MnO₂/CNW/Ni hybrid nanocomposite electrode with an optimized CNW growth period of 18 s and a MnO₂ loading of 50 μg cm⁻² achieves the best capacitive performance; it exhibits a specific capacitance of 1170 F g⁻¹ at a galvanostatic charging–discharging current density of 1 mA cm⁻² and retains 110% of its initial capacitance after 2000 cycles at a current density of 3 mA cm⁻². The high density of atomic scale graphitic edges, large surface area with optimized defects and degree of crystallinity of CNWs in conjunction with an efficient utilization of MnO₂ nanoparticles facilitated rapid electron and ion transport and electrochemical cyclic stability, hence offering the potential of unique capacitive behavior. These results demonstrate an exciting commercial potential for high performance, environmentally friendly and low-cost electrical energy storage devices based on the MnO₂/CNW/Ni hybrid electrode.