Synthesis And Electrochemical Properties Of N-substituted Carboxyl Polyanilline Covalently Grafted Graphene Composites

Supercapacitors as a new candidate device for energy storage, due to their high powerdensity, high specific capacitance, long cycling life, energy conservation and environmentalprotection have recently attracted significant attention in vehicles, communications, powergeneration and military fields. Wherein, the electrode material is the key to performance ofsupercapacitors, graphene and the conductive polyaniline due to excellent performance andcommonly used as electrode materials. As a family of carbon-based materials, graphenepossesses excellent mechanical, thermal, electrical properties making it suitable fornanocomposites, sensors and conductive films applications. However, there are still somecritical issues unresolved such as seriously chemical inertness and extremely strong reunion.On the other hand, PANI is anattractive conducting material owing to easy synthesis, low costand distinctive doping mechanism.Unfortunately, there are two major drawbacks that limit thepractical use of PANI: their low solubility in most of organic solvents and the fact that theydegrade before melting.Usually, preparing graphene/PANI composites aiming to combine themerits of both graphene and polyaniline have attracted great research interests. It should benoted here that so weaker noncovalent interaction between two component interfacial in thesecomposites than that of covalent bonding that poor homogeneity along with the phaseseparation generated.In this paper, on the basis of obtain high capacitance ratio and good cycle stabilitysupercapacitor electrode material, we demonstrate a novel soluble and highly dopedN-substituted carboxyl polyaniline (NPAN) grafted secondary amino-functionalized reducedgraphene oxide composite. Covalent connection not only enhances chemical compatibilityamong them, but also reduces interfacial resistance and accelerates the charge transfer atgraphene-PANI interface, hence improve electrochemical properties. In detail, grapheneoxide(GO) was functionalized with aminodiphenylamine (ADPA), aniline andN-phenylglycine (NAN),following by reduce by hydrazine to acquire active secondary amine groups on the surface or edge of graphene denoted as aRGO, bRGO and nRGO, respectively；and then these functionalized graphene was served as nucleation sites for in situ oxidativepolymerization of N-phenylglycine monomer to accomplish covalently bonded N-substitutedcarboxyl polyaniline (NPAN) onto individual graphene surface. The obtained compositeswere designated as aRGO/NPAN, bRGO/NPAN and nRGO/NPAN, respectively. The mainreseach contents and and relevant results are as follows:1. aRGO/NPAN composites with various NPAN contents in composites were obtainedthrough in situ oxidative polymerization of N-phenylglycine monomer using aRGO withnumerous nucleation sites,and then their electrical conductivity, thermal stability as well asdoping extent and the graft ratio of NPAN, were also investigated. It was found that thedoping content and graft ratio of NPAN in composites were26.82%and54%, respectively;conductivity of chemically bonded aRGO/NPAN composites was higher three orders ofmagnitude than that of HCl-NPAN,and five times than conventional non-covalentfunctionalization composites under the same condition. TGA analysis showed that thermalstability of the aRGO/NPAN composites was higher than that of HCl-NPAN.2. The structure, morphology and electrochemical properties of bRGO/NPAN compositeswere characterized by FT-IR, UV-vis, Raman, XPS,XRD spectroscopy and SEM,TEM andCHI660C electrochemical workstation. Results showed that a successful grafting of anilineonto the surface of GO along with reduce GO. bRGO/NPAN composites display a layeredstructure, exhibits a high specific capacitance (662.25F/g), an excellent cycle stability (97%after200times cycle).3. N-phenylglycine-terminated reduced graphene oxide(nRGO) was synthesized byp-aminobenzoic acid diazotization, Schmidt rearrangement reaction, amidation reaction, andthe reduction treatment of hydrazine,respectively. Chemically bonded aRGO/NPAN has beensynthesized as well as its structure and morpho logy were characterized by FTIR, UV-vis,Raman, XRD and XPS spectroscopy as well as SEM and TEM, finally, the relatedpolymerization mechanism was also proposed.Thermal stability was investigated by TGA,illustrating that the thermal stability of the composite material was dual controlled by both thethermal degradation of NPAN and thermal decomposition of chemical bonds between nRGOand NPAN, exhibiting enhanced thermal behavior than individual NPAN. Further graftingratio of NPAN was calculated24.8%. Electrochemical tests reveal that nRGO/NPANcomposite has high capacitance performances of654.25F/g at the current density of1A·g-1compared to those of pristine NPAN and nRGO, and good electrochemical stabilityhighlighting.Additionally,its charge transfer resistance (Rct) is150Ω, less than nRGO (750Ω) and HCl-NPAN (1400Ω). In a word, the structural advantage of chemically bondednRGO/NPAN in supercapacitor applications.