Preparation and electrochemical analysis of electrodeposited MnO 2 /C composite for advanced capacitor electrode

Mesoporous carbon (MPC) with uniform inner mesopore structure and high specific surface area prepared by an MgO-templated method has been employed for a substrate of MnO 2 /C composite. The MnO 2 /C composite was synthesized by anodic or cathodic electrodeposition of MnO 2 from MnSO 4 or KMnO 4 precursor, respectively, on the MPC substrate. The XRD patterns of the composite confirmed that MnO 2 was effectively deposited on the substrate under both anodic and cathodic electrodeposition processes. From the SEM images, sheet-like MnO 2 was deposited by anodic deposition (a-MnO 2 /C) while needle-like MnO 2 deposition was observed for the cathodic deposition (c-MnO 2 /C). The voltammetric experiments showed that the capacitive behavior of the composite depended on the preparation method. The difference in the specific capacitance between a-MnO 2 /C and c-MnO 2 /C is considered to be mainly due to the shape of MnO 2 deposited on the MPC substrate. The electrochemical capacitance of c-MnO 2 /C was much higher than that of the substrate carbon. The observed capacitance increase in c-MnO 2 /C was attributed to the pseudo-capacitance of MnO 2 that utilized effectively in controlled pore structure of MPC. The composite electrode, prepared by the cathodic deposition (c-MnO 2 /C), showed high specific capacitance and good durability for constant-current charge–discharge cycling.