Effects of Electrode Mass-loading on the Electrochemical Properties of Porous MnO2 for Electrochemical Supercapacitor

Porous MnO2 nanostructure with large surface area and large pore volume was prepared by a facial chemical method in large scale. The physical properties of the as-prepared MnO2 were characterized by X-ray diffraction (XRD) analysis, Brunauer-Emmett-Teller (BET) method and scanning electron microscope (SEM). The effect of electrode mass-loading on the electrochemical properties of MnO2 electrodes was studied by cyclic voltammetry (CV), impedance spectrum test and chronopotentiometry methods in 1.0M Na2SO4 solution. The results showed that the as-prepared MnO2 exhibited ideal capacitive behavior in a voltage window of 0~1.0V. With increasing of MnO2 mass from 5 to 25 mg cm-2 in electrode, the specific capacitance calculated from the CV curves at 2mV s-1 decreased from 452 to 205 F g-1. Impedance spectrum tests indicated that the reduction of specific capacitance was mainly due to the increase of charge transfer resistance and the slow ion diffusion in the thicker electrode. Ragone plots indicated that the MnO2 electrode with 5mg cm-2 mass-loading possessed good power-energy density characteristics. An energy density of 26.6Wh Kg-1 still remained 24Wh Kg-1 when the power density increased from 50 W Kg-1 to 5 KW Kg-1. These results indicated that porous MnO2 and thinner mass loading is benefit for applications in electrochemical supercapacitor.