Construction Of Transition Metal/Polyaniline Complexation System And Study On Its Electrochemical Properties

In recent years,both the Internet and clean energy have both developed at a rapid pace,giving rise to hybrid cars,portable electronic devices,the Internet of Things,and more.The development and promotion of these equipment are inseparable from efficient and practical energy storage equipment to provide energy.Therefore,supercapacitors(SC)have attracted wide attention and are expected to replace batteries as the mainstream energy storage equipment.Polyaniline(PANI)material has a very high theoretical specific capacitance and a variety of oxidation reduction states,which has a great development potential in the field of supercapacitor electrode materials.However,in practice,the specific capacitance value of PANI is much lower than the theoretical one,and the cycle stability is poor,which greatly limits the application of PANI in the field of electrochemistry.3,3’-diamino-2,2’-bipyridine(BPY)is a kind of organic small molecule material with unique structure.The pyridine nitrogen in BPY structure can be complexed with metal ions,and the aniline group can also undergo chemical oxidation copolymerization with aniline,which is expected to enhance the electrochemical performance of PANI.Transition metal ion and BPY coordination,doping into the polyaniline material,can obtain a uniform stable transition metal complex system.Transition metal ions can not only improve the conjugation degree of polyaniline materials,but also change the electron cloud density to improve the electrochemical properties of polyaniline materials.In this study,PANI/BPY+M(M=Cu,Fe,Ni)composites were obtained by copolymerization of transition metal ions after coordination of BPY.The coordination of BPY was used to introduce transition metal ions into PANI,thus improving its capacitance performance and cyclic stability.In the first part of this paper,BPY was complexed with different transition metals and then copolymerized with aniline by chemical oxidation to obtain PANI/BPY+M(M=Cu,Fe,Ni)composites.FT-IR,XRD,Raman and XPS tests showed that the BPY and aniline copolymerized,and the composite was successfully prepared.The morphology of the composite materials was characterized by SEM and TEM.It was observed that the surface of the composite materials formed a spongy porous structure.Cyclic voltammetry(CV),galvanostatic charge-discharge(GCD),and electrochemical impedance spectroscopy(EIS)were measured using a three-electrode system in 1M H2SO4 using the Princeton Electrochemistry Workstation.The reference system of direct transition metal doping without ligand were PANI,PANI+Cu,PANI+Fe and PANI+Ni,and the capacitance values of them at the current density of 1 A/g are 361.3F/g,834.9F/g,1535F/g and 647.5F/g,respectively.It can be seen that the capacitance values of the composite materials doped with transition metals have excellent improvement.It shows that the transition metal ions can participate in the REDOX reaction and thus increase the capacitance value.But at the same time,it shows poor cyclic stability,indicating that the metal ions complex in the system is not stable,with the process of charge and discharge,a large number of removal occurs.After the addition of BPY ligand copolymerization,the capacitances of PANI/BPY,PANI/BPY+Cu,PANI/BPY+Fe,PANI/BPY+Ni at the current density of 1 A/g are all greater than PANI,which were 620 F/g,1142.1 F/g,559.6 F/g and 987.5 F/g,respectively.However,the capacitance value of PANI/BPY+Fe is slightly lower than that of PANI/BPY.This is because the structure of PANI/BPY is destroyed in the process of iron ion complexation,resulting in a decrease in the amount of free ions in the REDOX reaction,which is shown as a lower energy density.However,after adding metal ions to PANI/BPY+Cu and PANI/BPY+Ni,copper ions and nickel ions successfully coordinate in the PANI/BPY system and participate in the REDOX reaction,which greatly enhances the capacitance value of the material.In addition,transition metal ions are complexed in the system by coordination,which shows high reversibility in the process of REDOX reaction,which solves the problem of poor cycling stability of polyaniline materials.In the second part of this paper,the influence of the content of transition metal ions on the electrochemical properties of PANI/BPY+Cu was investigated on the basis of the first part.Firstly,organic small molecule BPY ligands with different copper ion content(molar mass:0,0.25,0.5,0.75 and 1)were prepared and copolymerized with aniline by traditional chemical oxidation polymerization method.Finally,PANI/BPY+Cu composites with different copper ion content were prepared.The results of FT-IR,XRD and Raman show that the composites have been successfully synthesized.The PANI/BPY+Cu was characterized by BET,SEM and TEM.The PANI/BPY+Cu exhibited a spongy network structure,which was conducive to the full contact of the electrolyte.CV,GCD,and EIS were performed using a three-electrode system in 1M H2SO4 using the Princeton Electrochemistry Workstation.According to CV curve,the electrochemical performance of PANI/BPY+Cu gradually improved with the increase of copper ion content,but when the addition amount exceeded 0.5,the electrochemical performance did not improve further.The results of GCD test show that the discharge time of the composites obtained by complexing copper ions increases.PANI/BPY+Cu(0.5)has the longest discharge time of 914s,PANI/BPY+Cu(0.25)and PANI/BPY+Cu(0.75)are 850s and 842s,respectively.However,the difference in discharging time between PANI/BPY and PANI/BPY+Cu(1)is not significant.According to EIS analysis,the internal resistance of the composites increases to varying degrees after different amounts of Cu2+ions are complexed by PANI/BPY.However,in the process of REDOX,the doping of metal ions improves the electron transfer rate,and the final superposition shows that the electrochemical performance of the composites is improved.