Electrochemical Synthesis And Investigation Of Electrochemical Performance Of Doped Polypyrrole And Its Composites

With the increasing of energy shortage problems,people are eager to find an efficient energy storage device to use the existing energy effectivel.As a new kind of energy storage device,supercapacitor has become a hot research in the field of new chemical power because of its high energy density,fast charge /discharge rate and good cycle stability compared with secondary battery and capacitor.Electrochemical supercapacitors?ES?based on conducting polypyrrole?PPy?electrode material are currently attracting significant interest due to its low cost,easy synthesis,low oxidation potential and good stability.In order to optimize the electrochemical performance of polypyrrole electrode materials,doped and multi-walled carbon nanotubes?MWCNTs?modified polypyrrole electrode materials were synthesized by cyclic voltammetry in acid solution.The morphology and structure of PPy composites were characterized by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,fourier transform?FI-IR?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?.The electrochemical properties of electrode were investigated by cyclic voltammetry?CV?,galvanostatic charge–discharge?GCD?and electrochemical impedance spectroscopy?EIS?.The main research results and conclusions are as follows:?1?Polypyrrole?PPy?was synthesized by cyclic voltammetry on the stainless steel mesh with sulfuric acid?H₂SO₄?and nitric acid?HNO₃?as the electrolyte and dopants,respectively.The structure,morphology and electrochemical properties of PPy/H₂SO₄ and PPy/HNO₃ were investigated.The results show that the PPy/HNO₃ has a coral-like structure with loose and porous while the PPy/H₂SO₄ exhibits a cauliflower-like structure.At a current density of 5 m A cm^-2,the specific capacitance of PPy/0.5 M HNO₃ is 596 F g^-1 in 0.5 M H₂SO₄ electrolyte.During cycle life test,the capacitance retention of PPy/HNO₃ is 95.9% after 1000 cycles.Meanwhile,the specific capacitance of PPy/H₂SO₄ is 442 F g^-1 in 1.0 M HNO₃ electrolyte,and the specific capacitance remains 70.6% after 1000 cycles.In comparison with PPy/H₂SO₄,PPy/HNO₃ possesses the excellent electrochemical properties.The polypyrrole in eigenstate has poor conductivity,but it is remarkably improved in conductivity when in the doped state,and the electrical activity is enhanced.?2?Transition metal ions doped PPy were synthesized by cyclic voltammetry onto the stainless steel wire mesh with various concentration of MSO₄(M:Ni²⁺,Fe²⁺ and Cu²⁺)in electrolyte.The structure,morphology and electrochemical properties of electrode materials were investigated.The relationship between electrochemical properties of transition metal ions doped PPy/M²⁺(M: Ni²⁺,Fe²⁺ and Cu²⁺)and the properties of ions has also been researched.The PPy/M²⁺ electrode materials show a larger specific capacitance of 517,679 and 764 F g^-1 at a current density of 5 m A cm^-2 and lower resistance compared with the pure PPy electrode,and the specific capacitance remains 80.5%,82.7% and 83.8% after 1000 cycles.The lower the ionic radius and the bigger the ionic potential of transition metal cation is,the higher the specific capacitance of PPy/M²⁺ is.?3?On the basis of the above?2?,PPy doped with Cu²⁺ and multi-walled-carbon nanotubes?MWCNTs?composite was synthesized by cyclic voltammetry onto the stainless steel wire mesh immersed by CM.The effects of MWCNTs on the electrochemical properties of PPy were investigated.The results illustrate that PPy and MWCNTs formed a core-shell structure and at a current density of 5 m A cm^-2 the highest capacitance of 1269 F g^-1 of PPy/MWCNTs composites was achieved in the presence of 0.8% amount MWCNTs,which were modified by mixture acid reflux 1h.And the specific capacitance remains 88.1% after 1000 cycles at a scan rate of 50 m V s^-1.