Effect of Microwave Power and Cu Doping on MnO2 Nanostructures and Its Supercapacitor Performance

The enhanced specific surface area of electrode active materials provides a convenient way for the flow of electrolytic ions, resulting in improved electrochemical energy storage performance. In this study, synthesis of Cu-doped MnO2 nanomaterials was demonstrated using the microwave-assisted hydrothermal method. Upon reducing the microwave power from 400 to 250 W, the morphology of Cu-doped MnO2 nanostructures changed from nanorods (∼50–100 nm diameter) to nanoflowers with ∼10–20 nm thick petals on the surface. The flower-like morphology shows enhanced supercapacitor performance with a specific capacitance value of 433.15 F g–1 at 0.5 A g–1 current density. This feature is due to the synergistic effect of the enhanced conductivity by Cu doping and increased Brunauer–Emmett–Teller (BET) specific surface area (144.35 m2 g–1). Further, a two-electrode asymmetric supercapacitor (ASC) device was developed and it showed a maximum energy density of 77.78 Wh kg–1 at a power density of 1000 W kg–1. The device showed capacitance retention up to 102.86% after 20,000 charge–discharge cycles at 20 A g–1 current density. This study suggests that the Cu-doped MnO2 nanostructure is a promising electrode active material for enhanced supercapacitor performance with excellent rate capability.