Influence of the surface-chemistry of modified mesoporous carbon on the electrochemical behaviour of solid-state supercapacitors

This paper reports on the synthesis of the mesoporous CMK-3 carbon carried out using the SBA-15 silica as a template and its chemical modification by nitric acid treatment at room temperature. The nitric-acidmodified carbon, CMK-3AN, was used to prepare other carbon samples by thermal treatments at 700 and 900 C, which modify the surface properties of carbons by a partial removal of oxygenated surface groups. A series of composite electrodes was prepared from modified and unmodified carbons and used as the active material for solid-state supercapacitors. The electrochemical study carried out in two electrode configurations showed that the insertion of oxygen-containing functional groups in template carbon imparted changing on the capacitance features, enhancing also the electrode/electrolyte interface. However, the one disadvantage of acid treatment was that the carbon and electrodes showed a slight higher electronic resistance. The nitric-acid-modified carbon electrodes (CMK-3AN) showed better capacitive performances (162 F g-1; on the basis of the weight of the active carbon materials for one electrode) than those of the untreated CMK-3 carbon (132 F g-1) and much higher values than the carbon samples treated at 700 C (CMK-3AN7) and 900 C (CMK-3AN9), which showed values of 82 and 49 F g-1, respectively. The high total capacitance of the former carbon originates from its higher pseudocapacitance, which derived from the presence of electrochemically active oxygen-containing functional groups. These groups were partially eliminated during the thermal treatments at 700 and 900 C. As a consequence to this, the supercapacitor using the carbon treated at the highest temperature (CMK-3AN9) showed a specific capacitance of about 250% lower than that with the nitric-acid-treated carbon (CMK-3AN).