Electrochemically Partial Exfoliation Of Graphene And Its Composites With Dual Doping Polypyrrole For High-performance Supercapacitor Electrodes

Partial exfoliation of graphene from graphite foil (GF) was achieved for the first time by a convenient one-step electrochemical exfoliation method. The obtained graphene sheets are anchored standing on top of the graphite surface to afford Ex-GF. Ex-GF was characterized by X-ray photoelectron spectroscopy (XPS), Raman and scanning electron microscope (SEM).Subsequently, electropolymerization of pyrrole was carried out on Ex-GF with 1,5-naphthalene disulfonate (NDS) and 2-naphthalene sulfonate (NMS) as the ’permanent’ doping anions, in order to prepare partially exfoliated graphene/polypyrrole composites Ex-GF/PPy-NDS and Ex-GF/PPy-NMS, respectively. The polymer in the composites was anionic and cationic dual doped due to the ’permanent’ doping by NDS or NMS. The composites were characterized by SEM, XPS and fourier transform infrared spectroscopy (FT-IR). Electrochemical activities of the composites were studied by cyclic voltammetry, and their pseudocapacitive properties were further studied by galvanostatic charge/discharge experiments and electrochemical impedance spectroscopy (EIS). The electrodeposited PPy displayed an opened structure due to its facilitated homogeneous nucleation over the heterogeneous growth on the initially-formed polymer nanoparticles, which helped with fast ion transportation between the polymer and the electrolyte. The Ex-GF/PPy-NDS and Ex-GF/PPy-NMS composites exhibited an improved specific capacitance (351 F/g and 322 F/g, respectively at 1 A/g) compared to the polymers deposited on GF, GF/PPy-NDS and GF/PPy-NMS (240 F/g and 148 F/g, respectively). In addition, discharge potential window of the polymer was enlarged to 1.3 V (from -0.8 V to 0.5 V vs SCE) due to the dual doping. Specifically, Ex-GF/PPy-NDS maintained 79% of its specific capacitance when the discharge current increased 20 times from 1 A/g to 20 A/g, GF/PPy-NDS displayed a high energy density of 82.4 W·h/kg at the power density of 650 W/kg and 65.1 W·h/kg at the power density of 13 kW/kg. The cyclic charge/discharge stability of the polymers was also modified when composited with partially exfoliated graphene.