Supercapacitors Performance Of Heterojunction Based Composites

Transition metal oxides are considered to be excellent supercapacitor electrode materials because of their high theoretical capacitance,good stability,environmental friendliness and tunable structure.By compounding two transition metal oxides,a nano-heterojunction structure can be formed at the van der Waals interface of the two substances.The unique electronic effect of heterojunctions can enhance the electrical conductivity of the materials under certain conditions,which can prepare high-performance supercapacitor electrode materials.Finding suitable heterojunction materials requires careful selection of materials and design of processes in order to prepare morphological structures that match the characteristics of supercapacitor electrodes.To this end,in this thesis,we prepare transition metal compound nanoheterojunction materials and investigate their supercapacitor performance by preferring different materials and selecting suitable synthetic routes from electrode materials and structures as follows:（1）The NiCo₂O₄nanoneedle coated with Bi₂O₃nanosheets was successfully prepared using a two-step hydrothermal method to produce electrodes that could be used in supercapacitors.The electrode was analyzed using a series of experimental measurement techniques and density functional theory simulations.NiCo₂O₄Nanoedles provide an ideal skeleton for improving the specific surface area and an electroactive site for the Faraday reaction,while the Bi₂O₃nanosheets also show A·good specific capacitance potential.The specific capacitance of the NiCo₂O₄@Bi₂O₃electrode at 1A·g^-1was 766 F·g^-1.Asymmetric supercapacitor devices（ASC）were assembled with cathodic activated carbon（AC）and anode NiCo₂O₄@Bi₂O₃.The operating voltage of 1.6V,NiCo₂O₄@Bi₂O₃//AC ASC achieved a high energy density of 24 Wh·kg^-1at 800W·kg^-1and demonstrated good cycle stability with capacitance retention of 82%after10000 cycles at 10 A·g^-1.（2）The composite of CoMn₂O₄needle cluster loaded Fe₂O₃particles structure was made by two-step hydrothermal method.CoMn₂O₄is A·good electrode material for bimetallic oxide supercapacitors,and this time it serves as a skeleton to further improve the performance after loading the Fe₂O₃particles.CoMn₂O₄@Fe₂O₃exhibits a high specific capacitance of 710 F·g^-1at 1 A·g^-1.CoMn₂O₄@Fe₂O₃//GO ASC achieved a high energy density of 36.2 Wh·kg^-1at 801 W·kg^-1and a capacitance retention rate of 84%after 10000 cycles.（3）The Cu₂O-CoO heterojunction grown on graphene（GO）nanosheets was successfully prepared to produce electrodes that can be used for supercapacitors.The porous structure and high surface area of the graphene aerogel provide an ideal backbone for the electrode,while the Cu₂O-CoO heterojunction contributes the major capacitance as the main structure that participate in the Faraday reaction.The high capacity of the prepared Cu₂O-CoO electrode at 1 A·g^-1was 723 F·g^-1.The Cu₂O-CoO/GO//GO ASC achieved a high energy density of 44.1 Wh·kg^-1at 794 W·kg^-1,and the capacitance retention rate was 89.3%after 10000 cycles.In conclusion,the first system we utilized the needle two-metal oxide NiCo₂O₄as a substrate,with a large surface area and good specific capacitance.In the second system,we used the needle double metal oxides of Mn and Co as the substrate,which also achieved good results.In the third system,we tried to use the carbon material（graphene oxide）as the substrate,and the material also reached a high specific capacitance.