Preparation And Properties Of S-doped Graphene-based Electrode Materials For Supercapacitor

With the development of science and technology,traditional energy is nearly exhausted,so it is urgent to develop environment-friendly and high-performance energy storage devices.Among them,supercapacitors combine the advantages of traditional capacitors and batteries,which have higher power density and can charge and discharge rapidly,becoming one of the most promising energy storage devices.Graphene,as a new two-dimensional nanomaterial,has been attracting much attention since it can be prepared in large quantities.Its extremely high theoretical specific surface area and conductivity indicate its wide application in supercapacitors.However,in practical applications,the structure of graphene is prone to change,making the capacitance much lower than the theoretical value.Therefore,graphene needs to be modified to improve the electrochemical performance.In order to solve the problem of agglomeration of graphene and improve its performance,it is one of the main research directions to dope and then compound metal oxides.Doping can effectively prevent graphene from stacking and increase the available specific surface area;change the electronic arrangement of the graphite lattice,provide more active sites,and facilitate the compounding of metal oxides.The synergistic effect between doped graphene and metal oxides was used to improve the electrochemical properties of the materials.The main results are as follows:Using PEDOT:PSS as sulfur source,and change the mass ratio of sulfur to graphene oxide,three doping materials with different sulfur contents were prepared by incubation and annealing treatment.Electrochemical tests proved that SG?1:1?has the best electrochemical performance.After the characterization analysis of SG?1:1?,it is concluded that the doped material has a wider interlayer distance and greater disorder,and defects on the edge of the material can be clearly observed.These characteristics indicated that the sulfur atom was successfully doped into the graphene lattice,so that the modified material obtained a higher specific capacitance of 254.35 F g^-1at a current density of 0.5 A g^-1and lower resistance.Based on r GO and SG respectively,the one-step hydrothermal method was used to prepare the manganese oxide compound and attach them to the substrates at the same time to prepare the rGO-MnO_xand SG-MnO_x.The structural characterization confirmed that the composite material contains the existence of Mn²⁺,Mn³⁺and Mn⁴⁺.The coexisting multivalent state was conducive to the rapid reversible redox reaction and provided a larger pseudocapacitance for the capacitor.Combined with the structural and morphology of SG,it can be seen that the doped graphene can compound more compounds,and the surface of SG-MnO_xshows a large number of uniformly distributed petal-shaped two-dimensional nanosheets.This structure provides the specific surface area of 635.184 m²g^-1,which is much larger than that of single doped or composite electrode materials.A larger specific surface area provides a larger electric double-layer capacitance,with the pseudocapacitance generated by Faraday reaction,the specific capacitance of SG-MnO_xat a current density of 0.5 A g^-1is as high as 1131 F g^-1,in addition,the long-life cycle retention after 5000 cycles is 81.2%.Furthermore,an asymmetric supercapacitor assembled with SG-MnO_xas the positive electrode and activated carbon as the negative electrode can obtain an adjustable voltage window of 1.5 V,and can reach an energy density of 21.23 Wh kg^-1at power density of 1.5 kW kg^-1.The capacity retention rate after5000 cycles is 83%.In summary,using the synergistic effect between SG and MnO_x,composite materials have excellent specific capacitance,power density,energy density and cycle stability,which can be widely used as electrode materials for supercapacitors.