Graphene-based Co₃O₄ Composites:Synthesis And Electrochemical Performance Application

Hydrocarbon fossil fuels such as petroleum oil,coal and natural gas are accounted for the most significant portion of the global electricity generation.However,the increasing consumption and the rapid depletion of fossil fuels has driven the major research focus to exploitation and utilization of renewable energy such as wind energy,tidal energy and solar energy for the past few decades.To provide widespread usage of renewable energies,efficient energy storage and conversion technologies are required.Inspired by this,the electrochemical systems available for energy storage and conversion including lithium ion batteries,electrochemical capacitors are designed and developed for advanced energy conversion and storage devices.Transition metal oxide nanostructures is one of the current investigation focuses for supercapacitors.Self-assembled graphene-constructed Co3O4 microspheres(GCM)with controllable diameters,have been successfully synthesized by a one-pot hydrothermal treatment,in which the Co3O4 microspheres were simultaneously grown on a large scale on graphene nanosheets.When used as electrode materials for aqueous supercapacitors,the composites of GCM(the volume ratio of graphene oxide and 0.01 M NaOH solution is 15:1)exhibited a high specific capacitance of 568.8 F g-11at a discharge current density of 1 A g-1 in 6 mol L-1 KOH aqueous solution,as well as a good rate capability.It also showed high stability and a high capacitance retention behavior of 95.6%of its initial capacitance was retained even after 2000 cycles.We also synthesized graphene-constructed flower Co3O4(GFC)composites by one-pot hydrothermal process.The morphologies of Co3O4 ranged from leaf-cluster to flower.The GFC,as electrode material for lithium battery,showed a high specific capacitance of 1148 mAh g-1 at 0.1 A g-1 and 606 mAh g-1 at 5 A g-1.It turns out that GFC-2 manifests outstanding cycling performance with 98.9%capacity after 500 cycles.The extraordinary electrochemical performance of the GFC-2 can be attributed to not only the hierarchical graphene structure,but also the strong synergistic effect between the uniformly Co3O4.