Novel Electrode Materials Of Carbon Modified By Metal/Metal Oxide And Electrochemical Characteristics

Electrochemical capacitor is a new device for electrical energy storage. It possesses not only much more energy than conventional capacitors, but also much higher power density than batteries. Supercapacitor fills up the gap between batteries and conventional capacitors. According to the principles of electrical energy storage, electrochemical capacitors are classified into two catalogues of electric double-layer capacitor and faradic pseudocapacitor. Electrode material is one of the most important components of a supercapacitor. It is a key factor influencing the performance of supercapacitor. Research and development of electrode materials have been a hot topic in both academe and industry field in recent years.In the present dissertation, high performance and cost-effective carbon electrode materials were prepared using agricultural waste materials as precursor. In order to improve the electrochemical properties of activated carbon (AC), a commercial AC was modified by nickel oxide and hydrous ruthenium oxide, respectively, so that the modified electrodes were able to produce simultaneously electric double-layer capacitance and pseudocapacitance. Main work was done as following:Activated carbons were prepared by a chemical activating method using walnut shells as precursor and ZnCl₂ as activating agents. They were characterized by the nitrogen adsorption, XRD, FT-IR, SEM, TEM, and TGA. The resultant carbons were of highly microporous materials with numbers of oxygen-containing functional groups on the surface. The results show that the carbon electrode-based capacitors have excellent electrochemical properties: high specific capacitance of 271.0F/g, low leakage current of 0.25mA, small equivalent series resistance (ESR) of 0.39Ω.A commercial AC was modified by means of soaking in Ni(NO₃)₂ solution and subsequently thermal treatment. The results showed that NiO produced from Ni(NO₃)₂ decomposition had obvious pseudo-capacitance effect. Thus both electrical double layer capacitance of carbon and pseudo-capacitance of NiO had contribution to the total capacitance. As a result, the specific capacitance of the modified AC could be as high as 237.9 F/g, 42.5% higher than of original carbon. The corresponding volume and surface specific capacity increased also significantly.It is well know that amorphous hydrous RuO₂·nH₂O has highly electrochemical reversibility and high specific capacitance. So RuCVAC electrode material was prepared by sol-gel method. The results showed that RuO₂ particles were uniformly dispersed in the surface of activated carbon. Due to its mixed electronic-protonic conductivity, hydrous RuO₂ on the carbon surface displayed an obvious pseudocapacitve behaviour. As a result, the specific capacitance of RuO₂/AC electrode material was as high as 306.7F/g, much higher than that of original one, increased by 51.5%. The modified electrode material also had the advantage of high power density.The results showed that the modification by depositon of NiO/Ni and RuO₂ on the carbon surface could effectivley improve the electrochemical properties of conventional activated carbon. The present study provides simple, feasible and cost-effective ways to produce high-perfomance carbon electocde materials for supercapacitor.