Factors influencing MnO2/multi-walled carbon nanotubes composite's electrochemical performance as supercapacitor electrode

Poor crystallined α-MnO2 grown on multi-walled carbon nanotubes (MWCNTs) by reducing KMnO4 in ethanol are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and Brunauer–Emmett–Telle (BET) surface area measurement, which indicate that MWCNTs are wrapped up by poor crystalline MnO2 and BET areas of the composites maintain the same level of 200 m2 g−1 as the content of MWCNTs in the range of 0–30%. The electrochemical performances of the MnO2/MWCNTs composites as electrode materials for supercapacitor are evaluated by cyclic voltammetry (CV) and galvanostatic charge–discharge measurement in 1 M Na2SO4 solution. At a scan rate of 5 mV s−1, rectangular shapes could only be observed for the composites with higher MWCNTs contents. The effect of additional conductive agent KS6 on the electrochemical behavior of the composites is also studied. With a fixed carbon content of 25% (MWCNTs included), MnO2 with 20% MWCNTs and 5% KS6 has the highest specific capacitance, excellent cyclability and best rate capability, which gives the specific capacitance of 179 F g−1 at a scan rate of 5 mV s−1, and remains 114.6 F g−1 at 100 mV s−1.