Preparation And Electrochemical Properties Of Ordered Mesoporous Carbon/Graphene Composites

As a new type of energy storage device,super capacitor is widely studied for its advantages such as long cycle life and fast charging and discharging speed.Energy density limits the widely using of capacitors.Whereas the energy density is proportional to the voltage and specific capacitance,so improving the voltage of electrolyte and the specific capacitance of electrode material can improve its energy density.In this paper,the effects of graphene composite on the structure and properties of mesoporous carbon materials are studied by means of mixing graphene and explored the electrochemical properties in different electrolyte.The main research contents and conclusions are as follows:With phenolic resin as carbon source,block copolymer F127 as soft templates,to join the different content of graphene oxide,the hierarchically ordered mesoporous carbon/graphene composites（OMC/G）was successfully prepared by solvent evaporation self-assembly method.The content of graphene has a great influence on its electrochemical properties.When the content of graphene is low,the specific surface area of some pore is hardly making full use of.When its content increased,its capacity is further reduced,because graphene ruined the carbon and make its effective specific surface area decrease.When the ratio of PF and GO is 8.5:0.15,OMC/G-K shows the best electrochemical performance of 276.8Fg^-1 at the current density of 1Ag^-1,while the OMC is 193.6 Fg^-1.After 5000 cycles,the capacitor retention is basical 100%.The specific surface area,micropore volume and mesoporous volume of the OMC and OMC/G after KOH activation increased by 222%,197%,204%,363%,330%and 299%,respectively,compared to OMC and OMC/G.In addition,since graphene is embedded in OMC matrix,the specific surface area of OMC/G-K composite material(²109.2m²g^-1)and pore volume(1.24m³g^-1)are far greater than the specific surface area of OMC-K(1474.6m²g^-1)and pore volume(0.84m³g^-1).The electrochemical properties of OMC/G-K were tested in acidic,alkaline and neutral electrolyte.It shows that the specific capacitance of OMC/G-K is 250 Fg^-11 in acidic and alkaline electrolyte slightly higher than the neutral electrolyte(200²50Fg^-1).The result is that their high ionic conductivity,small radius of ion hydration,and that H⁺and OH^-have a fast transfer rate compared with Na⁺,K⁺.In low current density,the capacitance of hierarchically ordered mesoporous carbon/graphene composites in water electrolytes is mainly determined by the conductivity of the electrolyte.In high current density,small hydrated ion radius and large migration rate can provide fast ion transport,which can easily absorbed/desorped,resulting in a large specific capacitance.However,the power density and energy density of OMC/G/K in neutral electrolytes are much higher than that of acid and alkaline electrolyte,because the operating voltage of neutral electrolyte（1.7 V）is larger than that of acidic and alkaline electrolyte（0.9 V）.For the leakage current after 2 hours,OMC/G-K in the acid electrolyte is greater than the alkaline and neutral electrolyte.The highest energy density of OMC/G-K is 27.23 Whkg^-1 in 0.5 M K₂SO₄ electrolyte and the corresponding power density is 425 Wkg^-1.