Preparation And Properties Of Graphene/Phthalocyanine/Polyaniline Composites As Electrode Materials

Up to now, it has been proved that incorporating graphene into materials of pseudo-capacitor properties is an effect route to obtain better supercapacitor. Phthalocyanines(Pcs), consisting of 18 π-electron, are synthetic analogues with planar aromatic macrocycles derived from porphyrins. Pcs possess outstanding photoelectric properties so that they have been employed in supercapacitor, being physically mixed with CNTs or covalently combined with graphene oxide by amide bond. In this work, NiTAPc was combined with rGO by –N=N- and the product rGO-p-Pc was incorporated into PANi to give binary or ternary composites for excellent electrode material.Graphene oxide(GO) was prepared via chemical oxidation, and p-phenylenediamine(pPD) was used as a reducing agent to produce functionalized reduced graphene rGO-pPD with the aid of concentrated aqueous ammonia. The rGO-pPD was bonded with 2, 9, 16, 23-nickel(II) tetraamino phthalocyanine(NiTAPc) with outstanding optical and electrochemical properties by azo coupling reaction, to obtain binary composite rGO-p-Pc through covalently grafting method. By FTIR, the formation of-N=N- double bonds was proved; Raman spectra also indicated the covalent grafting on rGO-pPD. XRD suggested the generation of substance with new crystalline, and UV-vis tests showed that charge transfer occured between two species of rGO-p-Pc; in addition, the morphologys were examined by SEM.Herein, the electrochemical properties of the binary complex with different rGO-pPD contents(reaction ratios of rGO-pPD and NiTAPc respectively were 4:1, 3:1, 2:1, 1:1, 1:2, 1:3) were explored by cyclic voltammetry(CV), galvanostatic charge/discharge(GCD), and AC impedance(EIS) in 1 mol·L-1 H2SO4 solution. The results showed that the binary complex rGO-p-Pc(3:1) was closest to ideal capacitor behavior, and it has the largest specific capacitance up to 553.7 F·g-1 at 1 A·g-1, so that it was of the best electrochemical properties. Moreover, its specific capacitance still remained as high as 423.9 F·g-1 at high current density of 30 A·g-1. In addition, the stability of rGO-p-Pc(3:1) was tested by 500 charge/discharge runnings, and the specific capacitance remained 500 F·g-1, which decresed only by 10.3% of.In 1 mol·L-1 Na2SO4 and 1 mol·L-1 NaOH solutions, the CV and GCD curves of rGO-p-Pc(3:1) became much different. In neutral electrolyte solution the capacitance dropped to 240.9 F·g-1 which was less than half of the original, while the voltage working range in base electrolyte solution became very narrow. Therefore, NaOH was no longer available as an electrolyte for binary complex prepared in this work.In situ chemical oxidative polymerization was carried out by using binary complex rGO-p-Pc(3:1) and aniline monomer(content ratio of 3:1, 2:1,1:1, 1:2, 1:3) as the raw materials, to prepare a ternary complex consisted of graphene, metal phthalocyanine and conductive polyaniline, named as rGO-p-Pc/PANi. The synthesis was characterized via FTIR, XRD, Raman, and UV-vis. CV, GCD and EIS tests of various ternary complexes were also conducted to study the effects of different content ratios of rGO-p-Pc and aniline. Primary studies of electrochemical properties in acidic and neutral electrolyte solution were also carried out. The capacitance of ternary composites reduced much as polyaniline covering its electrochemical active sites. With increasing polyaniline content, the capacitance increases, among which rGO-p-Pc/PANi(1:2) has the maximum capacitance of 333.8 F·g-1(at 1 A·g-1), and the value has decreased to 137 F·g-1 in 1 mol·L-1 Na2SO4. The result in both electrolyte solutions also indicates that the acidic electrolyte is more suitable as electrolyte for ternary composites.