In-site pulse electrodeposition of manganese dioxide/reduced graphene oxide nanocomposite for high-energy supercapacitors

Manganese dioxide/reduced graphene oxide (MnO2/RGO) nanocomposite material was synthesized by the in-situ anodic pulse electrodeposition method to fabricate symmetric supercapacitors. The effects of the pH value of the electrodeposition bath were considered on the properties of fabricated electrodes. Three pH values ​​of 4, 7, and 10 were evaluated, and physicochemical properties were studied using field-emission scanning and transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, nitrogen gas sorption isotherm, and thermogravimetric analysis. The electrochemical evaluation was performed by galvanostatic charge/discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy techniques. The results revealed that the MnO2/RGO nanocomposite prepared at pH = 7 (i.e., MGO7) exhibited a maximum specific capacitance of 693.4 F g−1 at a current density of 0.5 A g−1. The symmetric supercapacitor based on MGO7 was also assessed using GCD and CV tests. Its specific capacitances at current densities of 0.5 and 20 A g−1 were 577.9 and 290.0 F g−1, respectively. The symmetric supercapacitor maintained 79.2% of initial capacitance after 5000 consecutive charge/discharge cycles at a current density of 4 A g−1. The highest energy density of 80.3 Wh kg−1 at the power density of 0.625 kW kg−1 and the highest power density of 25 kW kg−1 at the energy density of 40.3 Wh kg−1 was achieved by the fabricated supercapacitor.