Preparation And Electrochemical Energy Storage Performances Of Transition Metal Oxide-based Composite Materials

With the deleption of fossil fuels,people begin to develop new energy such as wind energy,solar energy and tidal energy.Therefore,we need to develop new types of energy storage devices.Among various energy storage systems,supercapacitors gain attractive attention because of their high power density,fast charging capability,long life,wide temperature range,environmental protection,and superior rate capability.As a new type of energy storage device,supercapacitors show great application prospects in the field of wearable electronic devices,electric cars and so on.Electrode material is one of the key factors that determine the performance of supercapacitors.Currently,carbon materials,metal oxides and conductive polymers are the main electrode materials for supercapacitors.With the above consideration,this paper designs the following work:1)?-Fe₂O₃@C composite materials had been synthesized by one-pot hydrothermal method using water as solvent,FeCl₃·6H₂O as the only iron source,C₆H₁₂O₆ as carbon source and sodium acetate as precipitant.The structure,composition and morphology of the composite materials were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscope?TEM?and Raman spectroscopy?Raman?.The electrochemical performance of?-Fe₂O₃@C composite materials were tested by cyclic voltammetry,galvanostatic charge and discharge and alternating current impedance in electrochemical workstation.In the experiment,the different dosage of glucose promoted that the surface roughness of?-Fe₂O₃@C composite materials were different,so the electrical properties were quite different.The results showed that?-Fe₂O₃@C composite materials had the best supercapacitive performance when the dosage of glucose was 1mmol.When the current density was 1A/g,the specific capacitance was 288 F/g.After 2000 such cycles,the specific capacitance of?-Fe₂O₃@C-1.0 electrode decreased to 72.3%of the initial level.2)In the presence of urea,MnCO₃@C composite materials was prepared by one-pot hydrothermal method using MnCl₂·4H₂O as the only manganese source,C₆H₁₂O₆ as carbon source and water as solvent.When the precursor MnCO₃@C was put into different atmospheres and temperature,the different phases of manganese oxides?MnO₂?Mn₂O₃?MnO and Mn₃O₄?were obtained.And we studied the electrochemical properties of the precursor and four manganese oxides.The experiment results showed that the specific capacitance of MnCO₃@C was 119.2 F/g when the current density was 1A/g.The precursors have excellent cycling stability.After 2000such cycles,the specific capacitance decreased to 64.8%of the initial level.Mn₂O₃ had the best electrochemical performance among manganese oxides.When the density was 1A/g,the specific capacitance is 248.8 F/g.After 2000 such cycles,the specific capacitance still retained 76.1%of the initial level.3)MOFs are organic-inorganic hybrid materials,which have large specific surface areas and can control the structure of pores.Thus,MOFs have attracted extensive attention.In this article,ZIF-67@ZIF-8 composite materials which were pentagonal dodecahedron were prepared by epitaxial growth.The composite materials were pyrolyzed in nitrogen and air to obtain Co₃O₄@N-doped porous carbon composite materials?Co₃O₄@N-PC?.We controlled the pore size by adjusting the dosage of zinc salt.Once employed as electrode for supercapacitor,the as-prepared Co₃O₄@N-PC exhibited a high specific capacitance?422.8 F/g at 1A/g?and excellent long-term cycling stability?87.9%retention after 5000 cycles?.These findings open up opportunities to explore efficient metal oxide/carbon electrode materials,and to improve the supercapacitance performance of metal oxide/carbon composite materials by structural and compositional modifications.