Synthesis Of Polypyrrole/Graphene Composite And Their Application In Electrode Materials Of Supercapacitors

Supercapacitors, the new energy storage devices between secondary batteries and traditional capacitors, have attracted considerable attention for the fast charge and discharge, higher energy density, longer cycle life, and wide temperature range. Nowadays, due to the energy shortage, peoples begin to search the development of renewable energy sources. Supercapacitors are deserved extensive investigation. Because the electrode materials are the key for the supercapacitors’performance, they have become one of current hot research topic.Graphene (GNS), with two-dimensional structure, its large surface area and high conductivity, has become an attractive material for supercapacitors. Polypyrrole (PPy), as a typical conductive polymer, has been considered as one of the most promising electrode materials for supercapacitors owing to its relatively high electrical conductivity, better environmental friendliness and good capacitive performance. However, its poor cyclic stability and processability limit the applications of PPy. To enhance the properties of PPy electrodes, the attempts by introducing some effective materials such as graphene sheet have been made. Meanwhile, the capacitance of graphene has been optimized.In this paper, it was investigated the electrochemical performance of GNS, PPy and PPy/GNS composites. The work is summarized as follows.1. GNS was synthesized by chemical oxidation-reduction method, the electrochemical properties of GNS were measured in1mol/L H2SO4electrolyte. Using galvanostatic charging and discharging at a current density of0.5A/g, the result shows that the first discharge specific capacitance of GNS is97.3F/g. After1000cycles, the specific capacitance of GNS decreases to91.1F/g, and the retention of the specific capacitance is more than97.6%, indicating that GNS has excellent cyclic performance. The cyclic voltammetry (CV) curves of GNS was tested in the three-electrode cell configuration. GNS reached about150.4F/g of specific capacitance at a scan rate of10mV/s; when increasing to50mV/s of scan rate, it has119.3F/g specific capacitance.2. Conductive PPy was prepared by chemical oxidation with FeCl3·6H2O as an oxidant. The electrochemical performances of PPy were tested as the same methods above. The result shows that the first discharge specific capacitance of PPy is400.0F/g at a current density of0.5A/g. After1000cycles, the specific capacitance of PPy decreases to344.4F/g. The retention of the specific capacitance is86.1%, indicating that pure PPy has a poor cycleability. PPy reached about384.0F/g of specific capacitance at a scan rate of10mV/s. At the scan rate of50mV/s, PPy has162.9F/g of specific capacity.3. Graphene and polypyrrole composites (PPy/GNS) were synthesized by in situ chemical oxidative polymerization of pyrrole monomer in the presence of graphene nanosheets under acidic conditions, using FeCl3·6H2O as an oxidant. The structure and morphology of the composites are characterized by X-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR) and Field-emission scanning electron microscope (FE-SEM). It is found that a uniform composite is consisted of GNS covered with PPy homogeneously. We prepared different mass ratios of PPy/GNS composites: PG9:1、PG7:3、PG6:4. Their electrochemical performances are evaluated by galvanostatic charge-discharge and CV in1mol/L H2SO4electrolyte. The result shows that, when the mass ratio of pyrrole monomer and graphene is9:1, the composite displays excellent electrochemical performances. We choose PG9:1to investigate the composite electrochemical performance. The first discharge specific capacitance of PG9:1is402.0F/g at a current density of0.5A/g. After1000cycles, the specific capacitance of PG9:1decrease to380.0F/g, with more than95.0%of capacitance retention. The CV of PG9:1was tested in the three-electrode cell configuration, PG9:1reached about466.0F/g specific capacitance at a scan rate of10mV/s. When the scan rate increased to50mV/s, the PG9:1has332.7F/g. The result shows that the PG9:1composite has excellent cyclic stability and better specific capacitance.