The optimization of specific capacitance of amorphous manganese oxide for electrochemical supercapacitors using experimental strategies

The optimal deposition conditions for plating the amorphous manganese oxide (denoted as a-MnOx·nH2O) with a maximum specific capacitance were approached by using the experimental strategies, including the fractional factorial design (FFD), the path of steepest ascent and the central composite design (CCD) coupled with the response surface methodology (RSM). The anodic deposition variables such as current density of deposition, pH, MnSO4 concentration and temperature of the plating bath were found to be the key factors influencing the specific capacitance of a-MnOx·nH2O in the FFD study. These variables were subjected to the path of the steepest ascent study to approach the vicinity of optimal conditions for plating the a-MnOx·nH2O deposit with a maximum specific capacitance. Effects of the current density and the MnSO4 concentration were further examined using a regression model in the CCD study. This model, represented as response surface contour plots, showed that a-MnOx·nH2O deposited under pH of 5.6, a current density of 3.7 mA cm−2, a passed charge of 0.3 C cm−2, a MnSO4 concentration of 0.16 M and a deposition temperature of 24 °C exhibited the highest specific capacitance of ca. 220 F g−1.