Preparation of sulfonated graphene–polyaniline nanofiber composites by oil/water interfacial polymerization and their application for supercapacitors

Abstract

An easy and one-pot method for the preparation of sulfonated graphene–polyaniline nanofiber (SGEPA) composites by oil/water interfacial polymerization was studied in this work. Among the composites were obtained at different mass ratios of graphene and aniline. The chemical structure of the materials was characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The morphology of the material was studied by scanning electron microscope and high resolution transmission electron microscopy. The SGEPA composite electrodes with a mass ratio of 1:10 showed better electrochemical performance than pure polyaniline nanofiber and graphene. A high specific capacitance of 962 F/g was obtained at a potential scan rate of 2 mV/s and the specific capacitance value of SGEPA-110 retained about 78% after 1000 cycles. It also exhibited a high energy density of 68.86 Wh/kg at a power density of 102 W/kg. The extraordinary electrochemical properties of the composites were attributed to the well-designed structural advantages of binary nanocomposites and the good combination and synergistic effects between graphene and polyaniline.

Introduction

The remarkable properties of graphene, such as high specific surface area, good electrical conductivity, outstanding mechanical strength and exceptional thermal stability have attracted great attention for potential application in electronics and sensors [1], [2]. Up to now, graphene can be prepared by mechanical cleavage [1], epitaxial growth on SiC [3], chemical vapor deposition [4] and chemical exfoliation [5]. In electrochemical measurements, graphene is considered as a promising electrode material for supercapacitors and lithium batteries. Recently, great effort has also been devoted to compounding graphene with polymers or inorganic particles. Among the conducting polymers, polyaniline (PANI) is the most investigated conducting polymer due to its low cost, easy synthesis, environmental stability, good electrical conductivity and controllable doping level [6], [7], [8], [9], [10], [11], [12]. However, it is very easy for PANI to be swelling and shrinkage in the charge–discharge process. In order to deal with this problem, it is a good methodology to compound PANI and carbon materials to increase the stability of PANI as well as to maximize the capacitance value [13]. Among them, graphene brings many advantages that make it better than other carbon materials, such as superior chemical stability, large surface-to-volume and a broad electrochemical window [14].

Different methods for the preparation of graphene–PANI composites have been studied. Zhang et al. [15] have reported an in situ polymerization method to prepare chemical modified graphene and PANI nanofiber (PANI-F) composite under acid conditions. The obtained graphene oxide/PANI composites with different mass ratios were reduced to graphene/PANI using hydrazine. A specific capacitance of as high as 480 F/g at a current density of 0.1 A/g was achieved over a PANI-doped graphene composite. Wang et al. [16] have reported an in situ anodic electro polymerization method to prepare freestanding and flexible graphene/PANI composite paper. This graphene-based composite paper electrode, consisting of graphene/PANI composite sheets as building blocks, shows a favorable tensile strength of 12.6 MPa and a stable large electrochemical capacitance (233 F/g and 135 F cm⁻³ for gravimetric and volumetric capacitances). Murugan et al. [17] have reported a rapid and facile microwave-solvothermal method to synthesis graphene nanosheets and their PANI nanocomposites for energy storage. The cyclic voltammetry (CV) plots of graphene–PANI nanocomposite (50:50, wt%) show a behavior characteristic of a combination of both electric double layer capacitance (EDLC) and re-dox capacitance with a significantly enhanced overall specific capacitance of 408 F/g. However, it is a question how the morphology of PANI influence the electrochemical properties of graphene–PANI composites? Therefore, many researchers tried to find a new method to control the morphology of PANI uniformly.

Interfacial polymerization is considered as an easy approach to make bulk quantities of nanofibrous PANI. Wang et al. [18] reported a morphology-controlled strategy to prepare sulfonated graphene/PANI composites by a liquid/liquid interfacial method, using sulfonated graphene (SGE) as both a substrate and a macromolecular acid dopant. Composites obtained with two different ratios of SGE to PANI showed higher specific capacitance of 793 F/g and 931 F/g, but lower capacity retention after 100 cycles of 77% and 76%, respectively. In this work, we report an easy one-step interfacial polymerization method for the preparation of surfactant graphene–PANI-F composites, which exhibit very good performance as supercapacitor electrode. Sodium dodecylbenzene sulfonate (SDBS) stabilized graphene (SDBS-Graphene) materials were prepared by reduction of graphene oxide (GO) solution using hydrazine in the presence of SDBS. The obtained SDBS-Graphene can form a stable aqueous dispersion. Therefore, interfacial polymerization can be achieved. Different mass feed ratios of SDBS-Graphene and aniline in the interfacial polymerization was also investigated to select the SDBS-Graphene–PANI-F (SGEPA) composites by their effect on the supercapacitor performance. It can be found that the composites show high specific capacitance and good cycling stability when mass ratio of PANI-F to SDBS-Graphene is 10.