Calcination removing soft template cetyl trimethyl ammonium bromide and its effects on capacitance performance of supercapacitor electrode MnO2

It is the first time to use calcination methods to remove the residual surfactant Cetyl Trimethyl Ammonium Bromide (CTAB) acting as soft template or structure directing agent for supercapacitor MnO2 electrodes. MnO2 was synthesized by liquid co-precipitation in the presence of CTAB. The as-prepared oxides heated at different heat treatment temperature are characterized systematically by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), N2 physical adsorption, cyclic voltammetry (CV) and galvanostatic charge/discharge tests. Results indicate that CTAB can be removed completely with the increase of heat treatment temperature, but the temperature also has great influences on the performance of MnO2. The free water, physical adsorption water and crystalline water lose successively, and the crystalline changes from amorphous α-MnO2⋅nH2O, first to crystalline MnO2, then to α-Mn2O3 and α-Mn3O4 accompanying with the oxygen loss process. Simultaneously, the specific capacitance and specific surface area of material exhibit similar variation trends being increase at first and then decrease as the heat calcination temperature increases. Sample MO-200 treated at 200 °C has the largest Brunauer-Emmett-Teller (BET) specific surface area (276.2 m2 g−1) and specific capacitance (240.1 F g−1) at 500 mA g−1. Therefore, in view of improving the capacitance performance, the relative low heat treatment temperature is suitable for MnO2 materials.