| Electrochemical capacitor (EC) also called supercapacitor, is a new storing energy device in-between batterie and conventional capacitor. It has advantages of high specific power and specific energy. According to different principles of electrical energy stored, electrochemical capacitor are classified as two kinds, electric double-layer capacitor (EDLC) and faradic pseudocapacitor. Electrode material is one of important factors influencing the performance of supercapcitor. Therefore, research concerning electrode materials has been a hot topic in both academe and industry.In this dissertation, in order to improve electrochemical properties of AC, commercial AC was modified by metallic oxide, so that the modified AC is able to form simultaneously electric double-layer capacitance and pseudocapacitance. The main work was following:A commercial available AC was modified by means of soaking in Ni(NO3)2 solution and subsequently pyrolysis. The nitrogen adsorption, SEM, XPS, TEM XRD, TGA were used to charcterize carbon materials. The performance of electrochemical capacitors using resultant carbons as electrode material was investigated by cyclic voltammetry, constant current charge/discharge, leakage current and alternating current inpedence. The results showed that nano-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 modified AC could be as high as 246.1 F/g, 89.2% higher than of original carbon. The corresponding volume and surface specific capacity are extremely high, 169.7F/cm3 and 30.1μF/cm2, respectively. The ECs with modified carbon electrode exhibited high electrochemical stability, low leakage current of 0.23 mA, and endured charge/discharge of large current change. Furthermore, it could maintain the capacitance about 90% after 10000 cyclic charge/discharge.Another type of modified NiO-AC was made by means of deposition- transformation through the procedure of Ni(NO3)2→NiC2O4→Ni(OH)2→NiO. The resultant NiO-AC based ECs also had obvious pseudo-capacitance behavior.. Thus both effects of electrical double layer capacitance of carbon and pseudo-capacitance of NiO had contribution to the capacitor. The modified AC has a specific capacitance of 171.0F/g, 31.5% higher than that of original carbon, 117.4F/cm3 and 24.1μF/cm2, respectively. The stable property of EC was approved by cyclic voltammetric tests. The capacitance could be kept 87% after 10000 cyclic charge-dischang.The AC was also modified by using Co(NO3)2 solution through soaking and pyrolysis to form CoO2-AC. The modification had obvious significance. The resultant CoO2-AC had a high specific capacitance of 198.8F/g, 52.8% higher than that of original carbon. The corresponding volumetric and surface specific capacity were increased from 89.3 F/cm3 and 16.2/μF/cm2 to 136.9F/cm3 and 25.3.4μF/cm2, respectively, 53.3% and 56.2% higher than the AC.Activated carbon is usually suitable as cathode material, but not good enough for anode. Therefore, we utilized the modified AC as anodal materials and a lab-made AC as cathodal material to fabricate hybrid capacitors. The pefromace of hybrid EC was better than that of capacitor made with symmetrical electrode, reflected by high stability, low leakage current and high capcitance. The mixed carbons had an average specific capacitance as high as 265.1F/g.The results showed that nano-NiO and nano-CoO modified AC could be significantly improve the electrochemical properties of conventional activated carbon. The present study had important significance for development and application of electrode material of high performance in supercapacitor.
|
PDF Full Text Request