Towards high purity graphene/single-walled carbon nanotube hybrids with improved electrochemical capacitive performance

CoMgAl layered double hydroxides were prepared as catalysts for the in situ synchronous growth of graphene and single-walled carbon nanotubes (SWCNTs) from methane by chemical vapor deposition. The as-calcined CoMgAl layered double oxide (LDO) flakes served as the template for the deposition of graphene, and Co nanoparticles (NPs) embedded on the LDOs catalyzed the growth of SWCNTs. After the removal of CoMgAl LDO flakes, graphene (G)/SWCNT/Co3O4 hybrids with SWCNTs directly grown on the surface of graphene and 27.3 wt.% Co3O4 NPs encapsulated in graphene layers were available. Further removal of the Co3O4 NPs by a CO2-oxidation assistant purification method induced the formation of G/SWCNT hybrids with a high carbon purity of 98.4 wt.% and a high specific surface area of 807.0 m(2)/g. The G/SWCNT/Co3O4 hybrids exhibited good electrochemical performance for pseudo-capacitors due to their high Co3O4 concentration and the high electrical conductivity of SWCNTs and graphene. In another aspect, the G/SWCNT hybrids can be used as excellent electrode materials for double-layer capacitors. A high capacity of 98.5 F/g(electrode) was obtained at a scan rate of 10 mV/s, 78.2% of which was retained even when the scan rate increased to 500 mV/s. (C) 2012 Elsevier Ltd. All rights reserved.