Manganese oxide on carbon as composite electrode materials for electrochemical of supercapacitors

The development of nanostructured electrodes for supercapacitors that exceed currently achieved energy storage capacity and display high charge/discharge rates is reported in this study. The energy stored in these electrodes can be increased compared to conventional electrodes by developing manganese oxide materials with controlled particle size, shape and surface. Manganese oxide was prepared by reacting in aqueous solution potassium permanganate (VII) with manganese (II) chloride. After precipitation, the oxide was recovered by filtering and drying. Three samples were prepared by different treatment at 70, 200 and 400 °C. The obtained materials have similar structural characteristic of spherical grain of about 300 nm. The particles appeared formed by small plate-like particles stuck each to other. The XRD analysis showed only a few broad peaks, which indicated an amorphous structure, whereas XPS evidenced that samples were a mixture of trivalent and tetravalent manganese compounds. Subsequently, these materials were used in preparation of electrodes, which were electrochemical characterized in a three-electrode cell. The characterizations showed that MnOx treated at 200 °C gave higher capacitance. A further optimization was made varying the content of MnOx, carbon conductive powder, graphite fibres and binding agent in the electrode. The optimization has given as result capacitance performance of 267 F/g(MnOx). Additionally, the study showed that the graphite fibres in the electrode allowed to improve their performance, especially for the higher charge/discharge rates. This results can be ascribed to the decreased electronic resistance into the electrode.