Research On The Controllable Synthesis Of Iron Oxide/Multilayer Graphene Composite And Their Supercapacitive Performance

Supercapacitors are one of the most concerned electrochemical energy storage devices currently,and they have excellent cycling performance and power density.Due to the characteristics of low redox potential,high theoretical capacity and low cost,Iron oxide is the most important negative electrode material for supercapacitors.The preparation of nanometer iron oxide and carbon material composite material is the main way to overcome the low conductivity of iron oxide and improve its Electrochemical performance.Different from the existing preparation technology,the thesis uses elemental iron as the iron source and ultrasonically stripped multilayer graphene as the carbon source to prepare evenly distributed iron oxide/multilayer graphene composite materials.The research contents of the thesis are as follows:(1)Using micron-sized iron powder as the iron source,a spherical?-Fe₂O₃nanoparticle/multilayer graphene composite material was prepared by water bath reaction.The prepared?-Fe₂O₃ nanoparticles have the same particle size and are evenly spread on the surface of the multilayer graphene to form a porous film structure.The thesis studied the effects of reaction time,sodium acetate addition and dilute nitric acid on the morphology and distribution of iron oxide,and explored the electrochemical performance of the composite material.The best performance of the composite material is as follow:the specific capacitance at a current densities of 2 A g^-1 and 10 A g^-1 are 1096 Fg^-1 and 822 Fg^-1 respectively.The specific capacity of 5000 cycles of charge and discharge at a current density of 2 A g^-1 is 32.2%of the initial capacity.The composite material is used as the negative electrode and activated carbon(AC)is used as the positive electrode to prepare an asymmetric supercapacitor.The maximum effective voltage window measured is 0-1.6 V,and the specific capacity is 60 Fg^-1 at a current density of 2 m A cm^-2.When the energy density is 21.3Wh kg^-1,the power density reaches 256 W kg^-1.The specific capacity retention rate is 22.2%after 1000cycles of charging and discharging at a current density of 4 m A cm^-2.(2)Using micron-sized iron powder as iron source and glycerol as structure directing agent,?-Fe₂O₃ nanosheet/multilayer graphene composite material was prepared by water bath reaction.The prepared sheet-like?-Fe₂O₃ has the same size and is staggered on the surface of the multilayer graphene,which improves the specific surface area of the composite material.The thesis studied the growth process of?-Fe₂O₃ nanosheets by changing the reaction time,and tested the electrochemical properties of the composite materials.Through process optimization,the performance of the best composite material obtained is as follow:the specific capacitance at a current densities of 2 A g^-1 and10 A g^-1 are 755 Fg^-1 and 415 Fg^-1 respectively.After 5000 cycles of charging and discharging at a current density of 2 A g^-1,the specific capacity is 16.3%of the initial capacity.