Study On The Characteristics Of Polypyrrole Supercapacitance And Its Decay Mechanism

Among various conducting polymers,Polypyrrole?PPy?is considered as one of most potential materials for several applications,such as supercapacitors,lith-ium batteries,biosensor and wearable electronics due to it?s ease synthesize,hypo-toxicity,high conductivity,environment friendly and good redox properties.How-ever,doped ions,thickness of PPy films and PPy doping/dedoping process are cru-cial to it?s capacitance and cycle stability in practical applications.In this paper,firstly,PPy films with different thickness and doped ions(Cl^-,SO₄^2-and TOS^-)were prepared by electrochemical methods under different poly-merrization charge densities and electrochemical workstation,XRD and SEM were used to study the effects of doped ions and thickness on it?s capacitance.Sec-ondly,the influence of PPy doping/dedoping process on it?s decay was investi-ngated.The main contents and conclusions of this paper are as follows:?1?Polypyrrole films with different thickness and different doped ions(Cl^-,SO₄^2-and TOS^-)were prepared by electrochemical methodes under different poly-merization charge densities(0.5,1,2 and 4 C·cm^-2).PPy/TOS^-films exhibited go-od electrochemical properties when their polymerization charge densities were 0.5C·cm^-2 and 1 C·cm^-2,that is,when the film thickness was relatively thin.However,PPy/Cl^-and PPy/SO₄^2-films exhibited markedly larger specific capacitance than that of PPy/TOS^-films when their polymerization charge densities increased to 2C·cm^-2 or 4 C·cm^-2,that is,when the film thickness was relatively thick.A simple model was suggested for explaining the relation between electrochemical propert-ies and thickness of PPy films.According to the model,the increment of PPy/TOS^-films from 1 C·cm^-2 to 2 C·cm^-2 is“inactive”,which resulted in the reduction of specific capacitance by half.XRD pattern indicated that PPy/TOS^-films possessed more ordered structure,which limited the ion diffusion in PPy matrix.Therefore,the high crystallinity of PPy films does not always mean good capacitance propert-yes.In the test of cycle stability,PPy/TOS^-films exhibited a better stability,which should be closely related to more ordered structure.It is noteworthy that we prese-nt a newly developed method to estimate the appropriate thickness of electrode material,which is significant to prepare energy storage devices.?2?PPy/Cl^-films were prepared by electrochemical polymerization and were tested in 1 M HCl and NaCl aqueous solutions.The results indicated that PPy cycle stability is closely related to PPy doping/dedoping process.After 5000 cycles,the specific capacitance of PPy films decreased by 8%in 1 M HCl solution.However,the specific capacitance of PPy films decreased by 75%in 1 M NaCl solution.The O/C ratio of PPy films in 1 M HCl had a small difference with that in 1M NaCl.The results of electrochemical quartz crystal microbalance?EQCM?indicated that the cations played an important role in PPy doping/dedoping process.The thicken-ss of PPy films increased by 15%and 60%in 1 M NaCl solution after 2000 cycles and 5000 cycles,respectively.The thickness increase of PPy films resulted from the accumulation of NaCl in PPy matrix.The capacitance decay of PPy films in 1M NaCl solution can be related to the accumulation of salts in PPy matrix.In addition,a novel equation was suggested to describe PPy doping/dedoping process.