Preparation And Electrochemical Properties Study Of Modified Carbon-based Electrode Materials

Supercapacitor,devices with high power density and good cyclability,has great application prospect in the fields of automotive energy,consumer electronics and communication devices.Benefiting from these advantages,it is becoming a hotspot in recent scientific research.Since the energy density of supercapacitors is much lower than that of commercial energy storage devices such as lithium-ion batteries,which would limit its commercialization,the development of supercapacitor electrode materials with both high energy density and high-power density is urgently needed.In order to improve the energy density of supercapacitors,this paper further investigates the enhancement of specific capacitance of carbon materials by doping heteroatoms and preparation of carbon materials/transition metal oxide composites.The main methods and results are as follows:1)It is important to improve the specific capacitance of activated carbon,which is one of best commercialized carbon materials nowadays.In this paper,nitrogen-doped activated carbon was prepared.The existence of nitrogen element in activated carbon materials and the electrochemical properties of nitrogen-doped activated carbon in different electrolyte solutions were investigated respectively.It was verified that the doping of nitrogen element introduces pseudocapacitance into activated carbon and enhances the specific capacitance of activated carbon.The characterization results indicate that the forms of nitrogen present in activated carbon is mainly pyridinic N,pyrrolic N and graphitic N.The electrochemical test results under the three-electrode system show that the specific capacitance of the nitrogen-doped activated carbon in the sulfuric acid electrolyte solution is 297.2 F/g at a current density of 1 A/g,which is 12.1%higher than that of the activated carbon.The specific capacitance retention is80.8%at a current density of 10 A/g,demonstrating an excellent rate ability.Meanwhile,a considerable cyclability can be observed that 98.7%of capacity can be kept after 10000 charge/discharge cycles.2)Graphene is extremely suitable as a carbon substrate for composite materials due to its great electrical conductivity,high specific surface area and two-dimensional structure.In this thesis,a reduced graphene oxide/molybdenum oxide composite was prepared.The structures and electrochemical properties of rGO,MoO₃ and rGO/MoO₃ were further detected.During the hydrothermal process,different temperatures were studied towards the nucleation process of MoO₃ and different acid solutions were also investigated towards microstructure of rGO/MoO₃ composite.We finally select an optimized condition to prepare rGO/MoO₃ composite by one-step hydrothermal method.In the hydrothermal process,ammonium molybdate is converted to molybdenum oxide on the surface of the graphene oxide,while the graphene oxide is simultaneously reduced.The molybdenum oxide existed as?-molybdenum oxide nanowires.The hybrid structure provides MoO₃ higher specific area and faster electron pathway.The electrochemical test results under the three-electrode system show that the specific capacitance of the composite is 313.5 F/g at a current density of 1 A/g in 1 mol/L H₂SO₄ solution,which is 187%higher than that of the reduced graphene oxide and 76.6%higher than that of MoO₃.rGO/MoO₃ has a better rate ability than MoO₃,the specific capacitance retention is 54.5%at a current density of 8 A/g,which is much higher than that of MoO₃?37.7%?.