| This paper reviews characteristic, applications of supercapacitors and recent research progress about supercapacitor electrode materials. Meanwhile, Co3O4 with controllable morphologies and its applications are reviewed. Preparation and performance of Co3O4 for supercapacitors is studied in this paper. The main contents are as follows:RuO2 has been found to possess high specific capacitance. However, high cost inhibits its applications. RuO2/Co3O4 thin films with different RuO2 content are first prepared by spray pyrolysis method and applied in supercapacitors to reduce amount of RuO2. The results show that the specific capacitance of pure Co3O4,15.5%,35.6% and 62.3% RuO2-composites at the current density of 0.2 A g"1 are 394±8,453±9, 520±10 and 690±14 F g-1, respectively. The specific value of 62.3% RuO2-composite is nearly that of pure RuO2 reported in literature (720 F g-1). This reduces the amount of RuO2.62.3% RuO2-composite presents the highest specific capacitance value at various current densities, whereas 35.6% RuO2-composite exhibits not only the largest specific capacitance contribution from RuO2 (CspRuO2) at the current density of 0.5, 1.0,1.5 and 2.0 A g-1 but also the highest specific capacitance retention ratio (46.3±2.8%) at the current density ranging from 0.2 to 2.0 A g-1. The specific capacitance contribution from RuO2 in 62.3% RuO2-composite is 869±23 F g-1 at the current density of 0.2 A g-1. The value is higher that of of pure RuO2 reported in literature (720 F g-1).Porous transition metal oxides have attracted widely attention due to their excellent supercapacitive performance. However, researchers focus only on synthesizing single-sized pore supercapacitor electrode materials. Compared with single-sized pore materials, hierarchical porous materials can enhance properties due to improved mass transport through the material and maintenance of a specific surface area on the level of fine pore. Meso-macroporous Co3O4 supercapacitor electrode is first synthesized by polystyrene spheres and carbowax in this paper. For comparison, non-porous Co3O4 and mesoporous Co3O4 electrodes are prepared under the same condition. The results show that meso-macroporous Co3O4 electrode exhibits larger specific capacitance than those of non-porous Co3O4 electrode and mesoporous Co3O4 electrode at various current densities. The specific capacitance of meso-macroporous Co3O4 electrode at the current density of 0.2 A g-1 is 453 F g-1, which is the highest value of all porous Co3O4 supercapacitor materials. Meanwhile, meso-macroporous Co3O4 electrode possesses the highest specific capacitance retention ratio at the current density ranging from 0.2 to 1.0 A g-1, indicating that meso-macroporous Co3O4 electrode suits to high-rate charge-discharge. Further, this study provides a simple and available method to prepare other meso-macroporous transition metal oxides in supercapacitors.Co3O4 materials for electrochemical capacitors are powders, which have to be mixed with conducting agent and binder during the electrode preparation process. The use of insulating binder will result in an increase in the internal resistance of electrode. Co3O4 thin film is synthesized by a chemical bath deposition in this paper. Scanning electron microscopy images show that Co3O4 thin film is composed of spherical-like coarse particles, together with some pores among particles. Electrochemical studies reveal that Co3O4 thin film exhibits a maximum specific capacitance of 227 F g-1 at the current density of 0.2 A g-1. The value is higher than those of Co3O4 thin film prepared by spray pyrolysis (74 F g-1) and by successive ionic layer adsorption and reaction method (165 F g-1). The specific capacitance reduces to 152 F g-1 when the current density increases to 1.4 A g-1. The specific capacitance retention ratio is 67% at the current density range from 0.2 to 1.4 A g-1. Compared with other methods, chemical bath deposition is a method with low cost, low temperature and convenient for large-area deposition.In view of Co3O4 film prepared by chemical bath deposition for supercapacitor material, the specific capacitance retention rate is not high at high current density and needs to be further improved. Co(OH)2 thin films are prepared by electrodeposition, and then Co(OH)2 thin films are calcined to obtain Co3O4 thin films. Capacitive property of these thin films is measured. The results show that the specific capacitance of Co(OH)2 thin film, Co3O4 thin film obtained by calcineing at 200?and 300?at the current density of 0.2Ag-1 are 153.4,150.4 and 129.1 F g-1, respectively. The specific capacitance retention ratio of three thin film electrodes is above 97% at the current density range from 0.2 to 1.0 A g-1. The specific capacitance retention ratio of above 88% is obtained in three thin film electrodes when the current density increases to 2.0 A g-1. These values are higher than those of Co3O4 thin film prepared by chemical bath deposition (67%).Colloidal carbon spheres are prepared using glucose as precursor by hydrothermal synthetic route, and then novel Co3O4/CoO/Co/graphite composites with multilayered structure are synthesized by colloidal carbon spheres. The composites possess different structures in comparison to materials prepared by other researchers with similar method. They consist of multilayer materials with spherical structures. The first, second, third and inner layer are Co3O4, CoO, Co and graphite, respectively. Electrochemical property of Co3O4/CoO/Co/graphite is studied by cyclic voltammetry and constant current charge-discharge. The results show that capacitive performance of the composites results from pseudo-capacitance caused by redox reactions and electric double-layer capacitance. The specific capacitance of the material is 25.2 F g-1, which is lower than that of Co3O4. However, the potential windows is -1.0-0.46 V, which is higher than that of Co3O4. |
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