Yi Baolian

Influence of Electrolyte Concentration and Temperature on the Capacitance of Activated Carbon

Influence of Electrolyte Concentration and Temperature on the Capacitance of Activated Carbon

Lanthanum Doped Manganese Dioxide/Carbon Nanotube Composite Electrodes for Electrochemical Supercapacitors

Although higher specific capacitances have been achieved for manganese dioxide/multi-walled carbon nanotubes (MnO2/MWCNTs), the low conductivity of MnO2 is still the main obstacle in increasing its loading or film thickness. Another problem is that the cycling stability of MnO2/MWCNTs is much lower than that of activated carbon electrodes. Therefore, this new type of electrode material is still limited in application until now. In this paper, lanthanum doped MnO2/MWCNTs composites were prepared by an in situ redox method. The surface morphology and phase structure of the as-prepared samples were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectrometry. The electrochemical properties were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy (ETS). The La-doped MnO2 could be formed on the MWCNTs by the reduction of MnO(superscript - subscript 4). The resistance of the composite electrodes decreased because La doping increases the number of imperfections in the MnO2 lattice, which improves the electrical conductivity and the electrochemical activity of the electrode. La doping is, therefore, an effective way to overcome the intrinsic low electric conductivity of MnO2, which facilitates an increase in the loading or the film thickness of MnO2 without increasing electrode resistance. The major effect of La doping is a significant improvement in the charge/discharge cycling performance of a symmetric electrochemical supercapacitor with electrodes composed of MnO2/MWCNTs. The specific capacitance of the composite electrodes was improved by La doping.

Electrochemical Capacitance of Composites with MnOx Loaded on the Surface of Activated Carbon Electrodes

Activated carbon/manganese oxide (MnOx) composites were prepared by the thermal decomposition of Mn(NO3)(2) that was impregnated on the surface of activated carbon XC-72 with a specific surface area of 250 m(2) . g(-1) and on YEC-8 with a specific surface area of 1726 m(2) . g(-1) at 200 degrees C. The surface morphology and crystalline structure of the composites were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The electrochemical properties of the composites were tested by cyclic voltammetry, galvanostatic charge. discharge, and impedance spectroscopy. We found that alpha-Mn2O3 and alpha-Mn3O4 were formed when the composites were annealed at 200 degrees C. At mass ratios of C and MnOx of 2:1 and 9:1, the specific capacitance of MnOx in the composites of XC-72/MnOx was 499 and 435 F . g(-1) and the specific capacitance of MnOx in the composites of YEC-8/MnOx was 554 and 606 F . g(-1), respectively. This suggests a significant contribution of pseudocapacitance from MnOx to the specific capacitance of the electrode.