Electrochemical Properties Of Polypyrrole Composites In Redox Electrolytes

Supercapacitors have excellent power density,good cycle life and non-pollution,which have been widely used in the field of electrical applications.Their electrochemical performance is mainly controlled by electrolyte and electrode materials.Compared with traditional electrolytes,redox electrolytes can provide additional pseudocapacitance for supercapacitors by redox reaction of active substances,and improve their specific capacitance and cycle stability.Conductive polymer polypyrrole has many advantages,such as good stability,high conductivity,low oxidation potential and simple synthesis process.It is often used as electrode material for supercapacitors.In this paper,carbon materials,binary and ternary composites of oxides and hydroxides with polypyrrole as the main body were prepared by various methods.The electrochemical properties of polypyrrole composites prepared in traditional electrolytes and redox electrolytes with active substances were systematically analyzed and compared.Specific research contents and conclusions are as follows:?1?Polypyrrole nanoparticles?PPy?and polypyrrole nanotubes?PPyNTs?electrode materials were prepared by chemical oxidation and soft template method.Polypyrrole nanotubes/carbon nanotubes?PM-3?composite materials were prepared by mixing method.The electrochemical properties of these materials in sulfuric acid?H₂SO₄?and carmine-sulfuric acid?AR18-H₂SO₄?electrolytes were studied.In H₂SO₄ electrolyte,the specific capacitance of PPy nanoparticles is 220 F g^-1,while in AR18-H₂SO₄ electrolyte,the specific capacitance can be increased to 445 F g^-1,which shows that AR18 in the electrolyte contributes greatly to the increase of the relative capacitance.The specific capacitance of PPyNTs in AR18-H₂SO₄ electrolyte increased to 579.2 F g^-1,indicating that the micro-morphology of PPyNTs has a great influence on its electrochemical properties.After composite with carbon nanotubes,the specific capacitance of PM-3 in AR18-H₂SO₄electrolyte was further increased to 674.2 F g^-1.?2?Polypyrrole nanotubes/cobalt hydroxide?PPyNTs/Co?OH?₂?composites were prepared by coprecipitation method using polypyrrole nanotubes as templates.The specific capacitances of PPyNTs,Co?OH?₂,PPyNTs/Co?OH?₂ were 13,708 and 838 F g^-1,respectively,in 2 mol L^-1 KOH solution with a current density of 1 A g^-1.When potassium ferricyanide?K₃Fe?CN?₆?was added to KOH electrolyte,the specific capacitance of PPyNTs/Co?OH?₂composites was significantly increased up to 4322 F g^-1,indicating that the active electrolyte provided additional specific capacitance.When the a current density is 1 A g^-1,after 5000cycles,the cycle retention rate in K₃Fe?CN?₆-KOH electrolyte is 95%,which is higher than that in KOH electrolyte.It shows that the introduction of K₃Fe?CN?₆ effectively improves the cycle stability of materials.?3?Firstly,MWCNTs/MnO₂ composites were prepared by coating manganese dioxide?MnO₂?on the surface of MWCNTs by impregnation method.Secondly,self-template method was used to coat PPy on the surface of MWCNTs/MnO₂ to form MWCNTs/MnO₂/PPy composite.The electrochemical properties of these materials in sodium sulfate?Na₂SO₄?and redox electrolyte?I^-/I₂-Na₂SO₄?were studied.In 1 mol L^-1 Na₂SO₄ electrolyte,the specific capacitances of MWCNTs,MWCNTs/MnO₂ and MWCNTs/MnO₂/PPy electrode materials are 50,238 and 316 F g^-1,respectively,when the a current density is 1 A g^-1.It shows that MnO₂ and PPy can provide Faraday pseudocapacitance for MWCNTs/MnO₂/PPy composite materials,respectively.In addition,the specific capacitance of MWCNTs/MnO₂/PPy composites was further increased to 806 F g^-1 by introducing I^-/I₂ redox species into Na₂SO₄electrolyte,indicating that the active electrolyte can also provide additional specific capacitance.