Template-free synthesis of ultrathin porous carbon shell with excellent conductivity for high-rate supercapacitors

The ultrathin porous carbon shell with the thickness of about 10 nm has been fabricated by a facile method using sodium citrate as carbon precursor without any activation. The electric conductivity of the material is as high as 7.12 S/cm, which contributes to a good rate performance for supercapacitor electrode without any conductive additive. When tested in 6 M KOH by three-electrode system, the C-700 sample exhibits specific capacitance of 251 F g−1 at 1 A g−1, high rate capability with the specific capacitance of 228 F g−1 at 20 A g−1, only a loss of 3% after 10000 cycles at a current density of 3 A g−1. Non aqueous performance was tested in 1 M TEA-BF4/acetonitrile, the material can deliver an energy density of 12-17 Wh kg−1 in a two-electrode system. Apparently, the porous carbon with ultrathin structure can provide low-resistant pathways and short ion diffusion channels for energy storage. Therefore, the ultrathin porous carbon shell would be a promising material particularly for applications where high power output performances are required.