Preparation And Electrochemical Properties Of Graphene/Nickel-cobalt Compound Composite Materials

Human beings are now facing with problems such as energy shortages and environmental pollution.It is an effective way to actively develop renewable energy into electrical energy.It is essential to develop high-efficiency energy storage devices,which are energy-saving and environmentally friendly.Supercapacitors are promising in the storage and conversion of energy.Nickel-cobalt bimetallic compound electrode materials have received extensive attention in the field of supercapacitors.In this thesis,a Ni-Co bimetal combination was selected and graphene/nickel-cobalt compound composite?NCS/rGO?was prepared on the basis of graphene.It is expected that the supercapacitor electrode material with excellent electrochemical performance can be synthesized under the synergistic effect of graphene and nickel-cobalt compound.The main research contents are as follows:?1?Reduced graphene oxide and nickel-cobalt sulfide composites?NCS/rGO?were prepared with different sulfur sources and solvents by the solvothermal method.When thiourea?THU?is used as the sulfur source and the volume ratio of ethylene glycol?EG?to deionized water?DI?water is 1:1,NiCo₂S₄ particles with relatively uniform distribution and smaller particle diameter are arrayed on the surface of rGO in the NCS/rGO composite.The specific capacitance of NCS/rGO-1 composite is 1648 F/g at the first charged and discharged.After the first 20 charge/discharge cycles,the electrode material is activated,and the specific capacitance is increased to 1672 F/g;after 300 charge/discharge cycles,the specific capacitance is reduced to 1580 F/g,and the cycle performance is relatively good.?2?The ratio of cobalt nitrate to nickel nitrate is unchanged,and the dosage is changed to investigate the effect of graphene content in the composite on the electrochemical performance of NCS/rGO.As the content of graphene in the composite increases,the specific capacity of the composite increases first and then decreases.When the content of rGO is high,the pseudocapacitance of the nickel-cobalt sulfide as an active component is reduced by the Faraday reaction.The composite NCS/rGO-1.00 with rGO content of 17.54wt%exhibited a higher specific capacitance?1406 F/g?.The capacitance retention rate was 63.73%after300 cycles of charge and discharge at a current density of 1.0 A/g.?3?Nickel-cobalt double hydroxide supported on the surface of reduced graphene oxide?Ni-Co LDH@rGO?was obtained,with ZIF-67 grown on the surface of graphene oxide?ZIF-67@GO?as the precursor.Ni-Co LDH@rGO retains a cubic structure with a rough surface and stacked sheets.Ni-Co LDH@rGO-10 with a rGO content of 25.50wt%has a higher specific capacitance of 1246 F/g,and the specific retention rate was 82.5% after 300 charge/discharge cycles at a current density of 1 A/g.?4?Nickel-cobalt bimetallic sulfide supported on the surface of reduced graphene oxide?Ni-Co-S@rGO?was obtained,with ZIF-67 grown on the surface of graphene oxide?ZIF-67@GO?as the precursor and thioacetamide as a sulfur source.Ni-Co-S@rGO-10 with a rGO content of 35.41wt%has the larger specific capacitance of 1240 F/g,and the specific capacitance retention was 86.93%after300 cycles of charge and discharge at a current density of 1 A/g.