Synthesis Of Iron-based/Carbon Nanotubes And Their Electrochemical Properties In Supercapacitors

As a kind of energy storage equipment,supercapacitor is filled the gap between secondary batteries and traditional capacitors.Namely,it has higher power density and longer cycling life than secondary batteries,and higher capacitance and energy density than traditional capacitor,which has attracted extensive attention of researchers.As we all know,the electrode of supercapacitors is a key factor to determine its electrochemical performance.Currently,there are three kinds of common electrode materials for supercapacitors:carbon materials,metal oxides and conductive polymers.Among them,carbon based supercapacitor have high power density and long cycling life because of excellent conductivity of carbonaceous material.But their specific capacitance and energy density are relatively low.The metal oxides electrode can obtain high capacitance and energy density,but the cycling life is very poor due to its bad conductivity.Conductive polymer is a potential supercapacitor's electrode materials ascribe to its high conductivity,low cost,wide voltage window and highly reversible oxidation-reduction reaction.However,swelling and shrinking of conductive polymers may occur during the intercalating/de-intercalating process.These problems often lead to mechanical degradation of electrode and fading electrochemical performance during cycling.Iron-based oxides possess abundant resources and low cost and high theoretical specific capacity,which makes it become an excellent electrode material.In other hand,carbon nanotubes?CNTs?have unique one-dimensional hollow structure,good conductivity and high specific surface area,which is a typical double-layer capacitor electrode material.Consequently,combination of CNTs and iron-based oxide was adapted to improve the conductivity of hydride electrode in this work,leading to capacitance of electrode.The brief works of this paper are as follows:?1?The bare Fe₂O₃ and Fe₂O₃/CNTs composite were prepared via microwave-assisted Fenton's reagents,and its morphology and electrochemical performance were studied.As shown in SEM and TEM image,bare Fe₂O₃ nanoparticles were irregular spherical with a diameter of 1?m.In the composite,the Fe₂O₃ nanoparticles were evenly loaded on the surface of CNTs,and its diameter became small.The electrochemical performance of prepared materials was tested via three-electrode system in 1 M Na₂SO₄aqueous with the voltage window of-0.8^-0.3 V.The capacitance of Fe₂O₃/CNTs electrode was superior to bare Fe₂O₃ electrode.At current density of 0.5A/g,the specific capacitance of hydride electrode can achieve 232.6F/g,and Fe₂O₃ electrode only can obtain 131.9F/g.?2?The symmetrical supercapacitors were assemble used the bare Fe₂O₃electrode and Fe₂O₃/CNTs composite electrode,and the electrochemical performance were studied by CV,GCD and EIS.At current density of 0.5 A/g,the capacitance of the Fe₂O₃/CNTs supercapacitor was 51 F/g,while that of Fe₂O₃ supercapacitor was only 31 F/g.at the same power density,the energy density of Fe₂O₃/CNTs electrode was higher than bare Fe₂O₃ electrode.In addition,the capacitance retention of hybrid supercapacitor was better than that of Fe₂O₃ supercapacitor.?3?The bare CoFe₂O₄ and CoFe₂O₄/CNTs composite were synthesized by the solvothermal method and its morphology and electrochemical performance were studied.From the SEM and TEM image,it was clear obvious that the CoFe₂O₄ nanoparticles were uniformly anchored on the surface of CNTs,and its diameter was about 10 nm.In the 2 M KOH aqueous,the electrochemical performance of CoFe₂O₄ and CoFe₂O₄/CNTs electrode at 0⁰.5 V.the result indicated the specific capacitance of hybrid electrode was higher than bare CoFe₂O₄ electrode at same current density;and the EIS further demonstrate that the resistance of CoFe₂O₄/CNTs composite electrode was smaller than bare CoFe₂O₄ and the conductivity of ion was improved after introducing CNTs into CoFe₂O₄.?4?The asymmetric supercapacitor was assembled via CoFe₂O₄/CNTs hybrid electrode?positive electrode?and active carbon?negative electrode?.at current density of 2 A/g,the capacitance still remain 85.7%of original value and the coulomb efficiency was closed to 100%after cycling 1000.In addition,the energy density of CoFe₂O₄/CNTs//AC ACS can be achieves 30.4 W h/kg at power density of 400 W/kg.When the power density increased to 3986 W/g,the energy density of this device still remains 12.4 W h/kg.