Fabrication And Investigation Of Polyaniline Doped With Metal Ions And Graphene Oxide For Electrochemical Supercapacitors

Polyaniline（PANI） is an attractive candidate among the various conductive polymers and has been become a research focus on the supercapacitor electrode materials in recent years based on its good environmental stability, high pseudo-capacitance energy storage characteristic, unique proton doping mechanism and its low-cost raw material. However, for a long time with the ions continuous embedding and emergence during the process of charging and discharging cycle, the volume of PANI expansion and contraction repeatedly which can cause the damage to the polymer chain. Therefore, the doped PANI do not have a satisfactory cycleability. This has become barrier of its potential applications. The chemical and electrochemical synthesis of transition metal ions and carbon-based materials as dopants with PANI can improve its capacitance properties and exhibit good cycle stability. This article is mainly about synthesis of PANI by doped with Zr⁴⁺, Ag⁺ and composite with graphene oxide. The effects of Zr⁴⁺, Ag⁺ and graphene oxide on morphologies and electrochemical properties of PANI were investigated. The main research contents are as follows:（1） Polyaniline doped with zirconium ions(PANI/Zr⁴⁺) and polyaniline doped with silver ions（PANI/Ag⁺） were synthesized by interfacial polymerization processes, which used aniline as starting material in toluene and ammonium persulfate（APS） as the oxidant in contact with an aqueous solution of zirconium ions(Zr⁴⁺) and silver ions（Ag⁺） in sulfuric acid（H2SO4） and nitric acid（HNO3）, respectively. The synthesized PANI/Zr⁴⁺ and PANI/Ag⁺ were subjected to the physico-chemical characterization by fourier transforminfrared（FT-IR）, X-ray diffraction（XRD） and scanning electron microscopy（SEM） and X-ray photoelectron spectroscopy（XPS） techniques, respectively. The electrochemical behaviors of different doping concentrations of Zr⁴⁺ and Ag⁺ on PANI have been investigated. It indicates that the PANI/0.08 M Zr⁴⁺ and PANI/0.12 M Ag⁺ show larger specific capacitances of 416 F g-1 and 529 F g-1 and maintain 54% and 51% of the initial capacitances after 500 cycles at a current density of 5 m A cm-2, respectively. While the specific capacitances of undoped Zr⁴⁺ and Ag⁺ with PANI exhibit only 297 F g-1 and 256 F g-1 at a current density of 5 m A cm-2 and the cycle stability are 9% and 4%, respectively. It illustrate that the electrochemical characteristics such as capacitive characteristics and the cycle stability of PANI are enhanced by doping of Zr⁴⁺ and Ag⁺.（2） PANI/Ag⁺ was synthesized by cyclic voltammetry（CV） with aniline（An） as monomer, Ag⁺ as dopants in nitric acid（HNO3） electrolyte and the concentration of the dopants were also investigated. The structure and morphology of PANI and PANI/Ag⁺ films were characterized by fourier transform infrared（FT-IR）, X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The electrochemical behaviors of different doping concentrations of Ag⁺ on PANI have been investigated. The results suggest that the PANI/0.12 M Ag⁺ films show a larger specific capacitance of 1000 F g-1 at a current density of 3 m A cm-2 and better cycle stability of 71% after 1000 cycles compared with that of PANI, whose specific capacitance and cycle stability are 591 F g-1 and 46%, respectively. That is, when doped Ag⁺ with PAMI, the electrochemical properties have been improved significantly.（3） Zn²⁺/polyaniline/graphene oxide(Zn²⁺/PANI/GO) composites were synthesized in H2SO4 solution containing homemade graphene oxide（GO） and zinc ions(Zn²⁺) via electrochemical polymerization. The structure and morphology of Zn²⁺/PANI/GOs were characterized by fourier transform infrared（FT-IR）, scanning electron microscopy（SEM）, Raman, X-ray diffraction（XRD）, and transmission electron microscope（TEM）, respectively. The influence of different concentrations o f GO on the electrochemical behaviors of Zn²⁺/PANI/GO composites were investigated. When the concentration of GO is 15 mg L-1, that is, the Zn²⁺/PANI/15 GO show larger specific capacitance of 1266 F g-1 at a current density of 3 m A cm-2 and better cycle stability of 86% after 1000 cycles. It indicates that both the conductivity of PANI and the cycle stability of PANI have been improved significantly by dop ing with Zn²⁺ and composite with graphene oxide.