Graphene And Graphene-Based Composites:Preparation, Characterization And Electrochemical Performance

Graphene with high conductivity and large specific surface area, when combine with single electrode materials of supercapacitor such as transition metal oxide and conductive polymer composite, can significantly improve the specific capacitance and capacitance characteristic (capacitance ratio, cycle stability, etc) at high current densities. Graphite oxide or reduced graphene oxide, which carries with a certain amount of polar functional groups including-OH,-COOH and epoxy group, has good embedded chemical properties that help it’s easy to composite with hydroxide, oxide and sulfide to graphene-based composites, thus the capacitance characteristic of single electrode material will be improved.In this paper, graphene nanosheet (GNS) as well as reduced graphene oxide (rGO) were prepared by the ultrasonic-stripping method and oxidation-reduction method, respectively. Graphene-based composites including Ni(OH)2/CoO/rGO, Ni(OH)2/rGO and Co9S8/rGO nanocomposites were synthesized by solvothermal method. Microstructure characterization displayed that nanoparticles in composites were not easy to agglomerate due to the presence of rGO, on the other hand, because of the absence of rGO. the synthesized Ni(OH)2/CoO and Co9S8nanoparticles severely agglomerated. It is easy to see that rGO is beneficial to prevent nanoparticles from severely agglomerating. Meanwhile, properties of the as-prepared graphene and graphene-based nanocomposites were reviewed in this paper.Measurement on in-situ electrical and electrochemical properties of as-prepared GNS and rGO were achieved. It reveals that electrical conductivity of GNS is better than that of rGO. but its specific capacitance is obviously lower than that of rGO. Besides, for the GNS and rGO. ratio characteristics and cycle stability are excellent.For as-synthesized Ni(OH)2/CoO/rGO nanocomposites with different reactant ratio, at the same scan rate (5mV/s), it reveals largest specific capacitance, as high as1056F/g, when the mass ratio of reactants is1:13:26(GO:Ni (CH3COO)2·4H2O:Co(CH3COO)2·4H2O), namely nickel acetate and cobalt acetate the molar ratio of1:2; the specific capacitance retention was84.8%after2000cycles at the scan rate of50mV/s. Furthermore, specific capacitance ratio and cycle stability of Ni(OH)2/CoO/rGO nanocomposites are both superior to the corresponding Ni(OH)2/CoO and Ni(OH)2/rGO nanocomposites.For as-synthesized CoS8/rGO nanocomposites with different reactant ratio, at the same scan rate (5mV/s), it reveals the largest specific capacitance (287F/g) when the mass ratio of reactants is1:10.4:17(GO:CH4N2S:Co(CH3COO)2·4H2O), namely the molar ratio of thiourea and cobalt acetate is2:1; the ratio is upto70.4%(Specific capacitance retention when scan rate increased from5to50mV/s) and specific capacitance retention was89.2%after1500cycles at the scan rate of50mV/s. In addition, the ratio and cycle stability are superior to the corresponding Co9S8nanoparticles. Variety of graphene-based composites have been synthesized, which illustrates solvothermal method is a universal method for the preparation of graphene nanocomposites.