The Preparation And Electrochemical Performance Of MnO₂Base Composite For Supercapacitor

With the depletion of the energy and environmental problem in the process, thenew energy is drawn a lot attention. Supercapacitor is excited great public interest.Electrode materials are the key factor that influences the energy storage ofsupercapacitor. Transition metal oxides have the advantages of high energy density,high specific capacitance and excellent reversibility, which is used as the electrodematerials of supercapacitor. In the paper we chose the inexpensive MnO₂and C/MnO_xcomposite as our target product used for supercapacitor electrode materials. Thephysical properties were examined by Scanning electron microscopy （SEM）,Thermogravimetric/differential thermal analysis （TG/DTA）, X-ray diffraction （XRD）.Electrochemical properties were characterized by electrochemical impedancespectroscopy （EIS）, galvanostatic charge/discharge and cyclic voltammetry （CV）. Themajor contents of the paper are as follows:1. The Birnessite type δ-MnO₂was prepared by hydrothermal methods usingKMnO₄as oxidants and N₄（CH₂）₆as reducing agents. The SEM pictures depict thetypical agglomerate particles of morphologies. The effect on characteristics ofmaterials by reaction time was studied. The results show that the best electrochemicalproperties and the higher specific capacitance are obtained when the reactiontemperature is100℃and the reaction time is6h. Meanwhile the characteristics ofmaterials in different electrolyte were researched, indicating a better capacitivebehavior in the hybrid electrolyte and a high specific capacitance in the alkalineelectrolyte.2. The composite electrode materials of activated carbon/MnO_x（C/MnO_x） wereprepared by L9（34） orthogonal experiments and condition experiments usingphenol-melamine-formaldehyde resin as oxidants and manganese acetate asprecursors. The optimal conditions was as follows: the carbonization temperature was800℃, thecarbonization time was2h, the heating rate was4℃/min, the massfraction of manganese acetate was12％, the activation temperature was300℃, theactivation time was80min and the heating rate was7℃/min.Meanwhile comparingthe6M KOH electrolyte with the1M Na₂SO₄electrolyte, the specific capacitance ofthe composite in the6M KOH electrolyte is higher and it has a better capacitivebehavior. The results showed that the electrochemical performance of the activatedcomposite is obviously improved; the specific capacitance is up to179F/g.3. Polianiline/MnO₂nanorods were prepared by hydrothermal methods, in whichMnO₂nanorods oxidized the aniline monomer reductant. C/Mn₂O₃nanorods havebeen synthesized from these polyaniline/MnO₂nanorods by carbonization and airactivation for supercapacitors. The optimal conditions was as follows: thecarbonization temperature was800℃, the carbonization time is1h, the heating ratewas4℃/min, the activation temperature was350℃, the activation time was1h andthe heating rate was7℃/min. We compared the activated composite with carbonizedcomposite. The effect of the synergy of C and MnO_xon the electrochemical propertieshad been discussed. After activating in the air, the activated composite had a very high specific surface area, it was as high as468.3m²/g, its specific capacitance wasimproved to211F/g.