Study of manganese oxide as a material for pseudocapacitor electrode

Manganese oxide is prepared by reacting in aqueous solution potassium permanganate (VII) with manganese (II) chloride. From the precipitated manganese oxide, obtained after filtering the solution and drying the residue at room temperature, three samples are prepared by thermal treatment at 70, 200 and 400 °C. The so-obtained materials are characterized by XRD, BET, SEM and TG analyses. Subsequently, these materials are used to prepare electrodes on which electrochemical tests are carried out in a threeelectrode cell configuration. Then, cyclic voltammetry and galvanostatic chargedischarge tests in a 0.1 M Na2SO4 electrolyte solution, have been carried out to investigate the effect of thermal treatment on capacitive performances. From these tests, it is found that the manganese oxide treated at 200 °C presents the best capacitive performance (250 F/g MnOx). For this reason, manganese oxide material treated at 200 °C is chosen for the preparation of several electrodes of different composition to investigate the influence of some preparative and operative parameters on electrode capacitance. In particular, it has been studied the influence of content of manganese oxide, carbon conductive powder, graphite fibres and binding polymer in the electrode composition and that of the concentration of electrolyte solution. The results of the electrochemical tests have allowed to identify the optimal electrode composition and concentration of electrolyte solution for our prepared manganese oxide. The results show that a high value of specific capacitance of about 300 F/g MnOx can be obtained from galvanostatic charge-discharge test carried out on the electrode with well defined composition of materials and concentration of electrolyte solution. Further, it is found that the presence of graphite fibres in the electrode and an optimal concentration of electrolyte improve the capacitive characteristic of manganese oxide, especially for the higher current densities. This because the former lowers the electronic resistance inside the electrode and, the latter increases the ionic conduction of electrolyte. Results on decay of the capacitive performance of manganese oxide during endurance test will be also reported during the meeting.