Preparation Of Graphitic Porous Carbons And Their Electrochemical Performance

Carbon materials are widely used in electrode materials of supercapacitors because of the advantages such as low cost, electrochemical stability, and work at wide range of temperature. We have prepared highly graphitic nanocarbons by a simple catalytic graphitization, while sucrose and glucose were employed as the carbon source, and nickel acetate and nickel nitrate are employed as nickel catalyst precursor, respectively. The morphology, nanostructures and electrochemical performance were studied. The major contents of this paper are as follows:1. Hydrothermal carbons were prepared from sucrose and glucose as the carbon source. Afterwards, the resulted hydrothermal carbons were further activated in mixed gas of oxygen and nitrogen(the volume percent of oxygen is 5 %). The optimum technological condition for sucrose-derived activated carbon(SAC): the concentration of sucrose was 1 mol L-1, the reaction time was 12 h, the reaction temperature was 200 ℃ and the loading ratio was 50﹪. The optimum technological condition for glucose-derived activated carbon(GAC): the concentration of glucose was 0.5 mol L-1, the reaction time was 6 h, the reaction temperature was 180 ℃ and the loading ratio was 30﹪. Both SAC and GAC are of spherical shape and well dispersed. The diameter ranges for SAC and GAC are 0.8-1 μm and 0.4-0.7μm, respectively. GAC shows the larger specific surface area(715 m2 g-1) than SAC(654 m2 g-1). At 0.5 A g-1, the specific capacitance of GAC can reach 225 F g-1, comparing with the value 198 F g-1 for SAC.2. Highly graphitic activated carbons(HGAC) are synthesized by a simple hydrothermal method followed by catalytic graphitization. The optimum technological condition for HGAC: the weight ratio of nickel nitrate to sucrose was 0.2, the concentration of sucrose was 0.75 mol L-1, the reaction temperature was 190 ℃ and the reaction time was 6 h. The interplanar distance(d002) and the graphitization degree parameter(g) are 0.339 nm and 0.58, respectively. HGAC shows the larger specific capacitance(232 F g-1) than activated carbon(AC)(198 F g-1) At 0.5 A g-1.3. Highly graphitic clew- like nanocarbons(HGCN) are synthesized by a simple hydrothermal method followed by impregnation and catalytic graphitizat ion, while sucrose and nickel acetate are employed as the carbon source and nickel catalyst precursor, respectively. The optimum technological condition for HGCN: the weight ratio of nickel acetate to activated carbon was 0.2, the heating rate was 10 ℃ min-1, the reaction temperature was 900 ℃ and the reaction time was 2 h. HGCN is composed of interconnected and curled carbon nanowires with sizes ranging from 10 to 25 nm and these nanowires twist around each other to form clew- like nanostructures. The interplanar distance(d002) and the graphitization degree parameter(g) are 0.337 nm and 0.81, indicating a highly graphitic structure. At 0.5 A g-1, the specific capacitance of HGCN can reach 248 F g-1, higher than the value 198 F g-1 for AC.