Tuning the electrochemical performance of graphene via covalent surface functionalization using silane coupling agent and incorporation of acid-modified multi-walled carbon nanotube for high energy and high power supercapacitor application

Abstract

The covalent functionalization of the graphene surface is successfully employed using a silane coupling agent, 3-aminopropyl trimethoxy silane (APTMS). The silane modification increased the interlayer spacing between the rGO layers. The composite electrode loaded with 1.5 g APTMS displayed 97.3 % pseudocapacitance, implying the successful silylation of the oxygenated functional groups on the graphene structure. The silylation imparts a sheet-like internal morphology with sharp edges to rGO's morphology. Among binary electrodes, Si-rGO with 20 wt% loading of acid-treated multi-walled carbon nanotubes (A-CNT) (PSRC20 binary electrodes) show excellent electrochemical properties and the highest specific capacitance. PSRC20 binary electrode displayed 82.6 % pseudocapacitance. A uniform dispersion of A-CNT in the silane-modified rGO matrix is revealed in the TEM micrographs. A specific capacitance of 225.8 F/g is obtained for the aqueous symmetric supercapacitor assembled using the PSRC20 binary electrode. Cycling performance evaluation over 2000 charge-discharge cycles at a current of 0.03 A showed that the device maintained 95 % of its initial capacitance and achieved a coulombic efficiency of 98 %. The perceived specific energy and specific power are 31.4 Wh/kg and 1714 W/kg at a current of 0.03 A. The fabricated pseudocapacitor is highly efficient in high-current applications, providing high energy density.