Ordered Mesoporous Carbon Composites Fabricated By Dual-template Method For Supercapacitor Applications

As a new type of electrochemical energy storage device,supercapacitors have attracted widespread attention due to their advantages such as high power density,long cycle life,and environmental friendliness.The electrode materials have been regarded as the key factor to affect capacitive performance.Mesoporous carbon materials have become the research focus of supercapacitors electrode materials because of advantages of well developed pore structure,large specific surface area and appropriate pore size.However,there is still the problem of low energy density for the use of pure ordered mesoporous carbon in supercapacitors.Graphene and MnO2 have a very high theoretical specific capacitance.It is expected that they can be combined with ordered mesoporous carbons to take advantage of their respective advantages,to make up for the disadvantages of easy agglomeration of graphene itself,low conductivity of MnO2,and achieve the purpose of improving the energy density of supercapacitors.In terms of the problems existed in low energy density of supercapacitors,this paper proposes to prepare a high-performance supercapacitor electrode materials by combining sulfonated graphene,MnO2 and ordered mesoporous carbon.The main contents and conclusions are described as follows:(1)In order to increase the specific surface area of ordered mesoporous carbons.Highly ordered mesoporous carbon-silica nanocomposites have been successfully synthesized by the evaporation method,wherein phenolic resin prepolymer is used as carbon source,tetraethyl orthosilicate(TEOS)and triblock copolymer F127 were selected as the dual templating agents in the second chapter,and then removes the SiO2 skeleton with NaOH solution to further form pores to obtain ordered mesoporous carbon materials(OMC).The optimum conditions were obtained by comparing the electrochemical properties of the electrode materials prepared at different temperatures and different carbon and SiO2 ratios.The porosity of the preparation material OMC-40 is as high as 1794.09 m2/g.The test results show that the specific capacitance of the electrode material is 196.6 F/g at a current density of 1 A/g,and the capacitance is 98.9%of the initial specific capacitance after 5000 cycles.The interconnected mesoporous channels of OMC provide better penetration and transport of electrolyte ions,and have much better rate performance than conventional high specific surface area activated carbons.Therefore,they are very promising supercapacitor electrode materials.(2)To increase the conductivity of OMC,on the basis of OMC,the third chapter selects highly conductive graphene and ordered mesoporous carbon composite to prepare OMC/SG with excellent electrochemical properties.The structures of OMC/SG and OMC are characterized by X-ray diffraction,transmission electron microscopy,X-ray photoelectron spectroscopy and nitrogen adsorption-desorption.These results indicate that OMC/SG composites possess the hierarchically ordered hexagonal p6mm mesostructure with the lattice unit parameter and porous diameter close to 10 nm and 4 nm,respectively.Sulfonated graphene is also demonstrated to be integrated into the interpenetrating network structures via covalent bonding and hydrogen bonding,as well as be highly dispersed in OMC matrix.The specific surface area of the OMC/SG composite is found high up to 1708.78 m2/g,and a mesoporous ratio in OMC/SG shows as high as 80%.Meanwhile,supercapacitor electrode based on the obtained OMC/SG exhibits a specific capacitance as high as 314.2 F/g at the current density of 1.0 A/g,while OMC based electrode is only 196.6 F/g.In addition,the resultant OMC/SG composites display good rate capability(70%of the capacitance retained at current density high up to 100 A/g),and an excellent cycling stability(no capacitance loss over 5000 cycles).In particular,after the incorporation of sulfonated graphene,the surface capacitance of OMC/SG(Cs)increases up to 18.4 F/cm2 at 1 A/g,which is far larger than that of carbon-based materials.These optimized interconnected porous structures in the OMC/SG composites are favorable to the accessibility,rapid diffusion of aqueous electrolytes,while sulfonated graphene can also facilitate the transport of electrons and provide better interface wettability of electrodes with electrolytes,thereby leading to an excellent energy storage performance.(3)To further increase the specific capacity of OMC/SG,because MnO2 has a very high theoretical specific capacitance(1370 F/g),an ordered mesoporous carbon/MnO2 composite(C/MnO2)is obtained on the surface of the OMC/SG material through a KMn04 redox reaction.The OMC/SG with high specific surface area and high conductivity serve not only as the substrate for the growth of MnO2 nano wires,but also as the electrically conductive channel for electrochemical performance enhancement.SEM,TEM,XRD and nitrogen adsorption-desorption results show that MnO2 is a monoclinic ?-MnO2 nanowire with a diameter of about 5 nm.C/MnO2-110 has a bimodal pore structure and a high specific surface area(684.25 m2/g).Besides,manganese dioxide shows high pseudocapacitive behaviour due to faradaic redox reaction.The electrochemical properties of the C/MnO2 composite were significantly enhanced as compared with C/MnO2-0.The asymmetric supercapacitors(ASCs)assembled with C/MnO2-110 anodes and C/MnO2-0 cathodes exhibited a high energy density of 34.56 Wh/kg at a power density of 450 W/kg.The ASCs also show superior cycling stability for 5000 cycles.The enhanced electrochemical performance of the C/MnO2 makes them a promising electrode material for application in supercapacitors.