Polypyrrole-decorated 2D carbon nanosheet electrodes for supercapacitors with high areal capacitance

Abstract

Nanocarbon electrodes such as carbon nanotubes, graphene, graphene oxide, etc. are costly materials and hence it is necessary to develop new carbonaceous materials for application as electrodes for low cost supercapacitors (SCs) with high performance. Highly capacitive cost-free electrodes are synthesized with hierarchically mesoporous 2D exfoliated graphite nanosheet (EGN)/polypyrrole (PPY) (EGN/PPY) nanocomposites for supercapacitors (SCs). Initially, EGN is synthesized by a microwave irradiation technique from natural flake graphite with the help of perchloric acid–sulphuric acid–potassium dichromate–acetic acid anhydride based graphite intercalation system and EGN/PPY nanocomposites are prepared by in situ oxidative chemical polymerization thereafter. The EGN exhibits a Brunauer–Emmett–Teller surface area of 620 m² g⁻¹ with a mesoporous structure (average pore diameter ∼ 11 nm). The electron probe-microanalysis reveals that the PPY is uniformly coated over the surface of EGN. The surface topographies of the nanocomposites are examined by scanning electron microscopy and transmission electron microscopy. The structure and chemical bonding of the nanocomposites are determined by X-ray diffraction, Raman spectroscopy and Fourier-transform infrared spectroscopy. XPS analysis shows that various chemical species are attached on the surface of the EGN/PPY nanocomposites. The electrochemical properties of the symmetric type EGN/PPY SC cells are examined by electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge/discharge measurements. The galvanostatic charge/discharge measurement shows that the EGN/PPY SC cell exhibits a maximum area specific capacitance of 376.9 mF cm⁻² with an area specific energy density of 0.052 mW h cm⁻² at a current density of 0.25 mA cm⁻² and it has a good cycle life too.