Design,Preparation Of Iron-based Composite Materials As Supercapacitor Electrode Material

In the 21st century,with the exhaustion of fossil fuels,human beings are gradually trying to develop new energy sources to solve problems such as energy shortages and environmental pollution.At the same time,some new energy conversion devices have emerged,such as solar cells,lithium-ion batteries and supercapacitors.Among many energy conversion devices,supercapacitors have attracted much attention from researchers because of their high energy density,high power density and fast charge and discharge rate.Considering these advantages,it will have great potential application value in electronic communication,industrial power equipment,electric vehicles,aerospace and defense technology.For supercapacitors,the choice of electrode materials determines the performance of the capacitors.At present,electrode materials are mainly divided into three categories:metal oxide materials,conductive polymer materials and carbon materials.Therefore,this study mainly prepared iron-based nanomaterials,and their composite materials with carbon materials and conductive polymer materials,and studied the electrochemical properties of the composites.1.Preparation and electrochemical properties of different kinds of ferriteDifferent kinds of ferrite nanomaterials?including:?-Fe₂O₃?Fe₃O₄ and Fe-glycerate?had been synthesized by one-pot hydrothermal method FeCl₃·6H₂O as the only iron source,urea as a precipitant glycerol and water as solvent by changing the ratio of glycerol and water.And the growth process of?-Fe₂O₃ was investigated and passed by controlling different reaction times.?-Fe₂O₃ and C-?-Fe₂O₃ were obtained by heat treatment of iron glycerate in air and nitrogen,respectively.The scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray diffraction?XRD?,and X-ray photoelectron diffraction?XPS?and other analytical methods were used to analyze the morphology and structure of the material.Finally,the electrochemical performance of the material was tested by electrochemical workstation.The results show that the mass specific capacity of Fe₃O₄ can reach 427F/g at current density of 1 A/g.The capacity retention rate can reach 79.5%after5,000 charge and discharge cycles.2.Preparation and Electrochemistry Performance of Nitrogen,Sulfur Co-doped Iron oxide@N-Doped Porous Carbon?NS-Fe₃O₄@N-pC?Nanocomposites.?-FeOOH@PPy core-shell Nanococoons had been synthesized by a oxidative polymerization reaction on the surface of?-FeOOH obtained by experiment 1 pyrrole?Py?as a monomer,p-toluenesulfonic acid?p-TSA?as a dopant and a surfactant,by the dropwise addition of ammonium persulfate?APS?initiator.Finally,NS-Fe₃O₄@N-PC nanocomposites were obtained by heat-treating?-FeOOH@PPy at different temperatures in a nitrogen atmosphere.Electrochemical studies show that the prepared?-FeOOH,?-FeOOH@PPy and NS-Fe₃O₄@N-PC have tantalum capacitance behavior during charge and discharge.The mass specific capacity can reach 325 F/g,617 F/g and 866 F/g,respectively at a current density of 1 A/g.NS-Fe₃O₄@N-PC has a mass specific capacity of 383 F/g at a current density of 10A/g,and still has a capacity retention rate of 78.2%after 5000 charge and discharge cycles.Moreover,the asymmetric supercapacitor devices were constructed based on NS-Fe₃O₄@N-PC anodes and commercial carbon nanotubes cathodes.Under the two-electrode system,the specific capacity is up to 117 F/g at a current density of 1A/g.The energy density can reach 38.9 Wh/Kg at a power density of 700.2 W/Kg,and the capacity retention rate can reach 91.6%after 5000 cycles at 4 A/g.3.Preparation and Electrochemical Properties of Core-Shell Structure Fe₃O₄@N-pCFe₃O₄@N-pC materials produced by Fe₃O₄@PDA under high temperature and nitrogen conditions.Fe₃O₄ nanospheres had been synthesized by one-pot hydrothermal method using ethylene glycol as solvent,polyvinylpyrrolidone as surfactant,FeCl₃·6H₂O as iron source,sodium acetate as precipitant.Then the surface of the microspheres was coated with a layer of polydopamine through in-situ polymerization reaction.Last,then the Fe₃O₄@N-pC nanocomposite were obtained by high temperature heat treatment under a nitrogen atmosphere.The thickness of the N-pC was adjusted by adjusting the thickness of the polydopamine shell.Electrochemical studies have shown that the pure Fe₃O₄ nanospheres have a specific capacity of 425 F/g and a potential window of 0.4 V.After coating the carbon layer,the specific capacity can reach 630 F/g,and the potential window is slightly improved to 0.42 V.After 5,000 cycles,the capacity retention rate was 79.5%.4.Preparation of Fe₃O₄@MnO₂ Yolk@Shell Microspheres for Improved Pseudocapacitive PerformanceAs a consecutive work of the last chapter,yolk@shell Fe₃O₄@MnO₂ composites were prepared using the reaction between PDA derived carbon in Fe₃O₄@N-pC and KMnO₄ under hydrothermal condition.The electrochemical results show that the specific capacitance of Fe₃O₄@MnO₂ is 715 F/g at a current density of 1 A/g,which is further improved compared with the specific capacity of pure Fe₃O₄ of 442 F/g.Fe₃O₄@MnO₂ has an excellent rate performance of 450 F/g at a current density of 10A/g.In addition,in order to study the practical application of Fe₃O₄@MnO₂,the asymmetric supercapacitor device,assembled by the N-pC and Fe₃O₄@MnO₂ was constructure and it offers an energy density of 31.3 Wh/kg at a power density of 750W/kg and long-term stability with only 5.3%initial capacitance loss after 5000 cycles at 4 A/g.