Electrochemical Properties of Manganese Oxide Surface-Modified Activated Carbon Electrode Materials

To improve electrochemical properties of activated carbon (AC), a commercial AC was modified by means of soaking in manganese nitrate solution and subsequent pyrolysis. Nitrogen adsorption at 77 K, SEM, and XRD were used to study the surface area, porosity, profile of modified AC, and the crystal structure of deposited manganese oxides. The performance of electrochemical capacitors using the modified AC as electrode materials was investigated by cyclic voltammograms, ac (alternating current) impedance, and constant current charge/discharge. Results showed that manganese oxides, especially alpha-Mn2O3, produced from the Mn(NO3)(2) decomposition had an obvious pseudo-capacitance effect. This effect was coupled with the electrical double layer capacitance of AC to form a complex capacitance so that the specific capacitance of modified AC could be as high as 254. F.g(-1) which is 54% higher than that of the unmodified AC. In addition, the tested capacitor with modified AC electrodes showed excellent performance during reversible charge discharge and also displayed high stability. Its equivalent series resistance was small at 0.10 Omega. After a long term test of 2000-cycles the capacitance retained nearly 100% of its original value.