Fabrication of graphene and core-shell activated porous carbon-coated carbon nanotube hybrids with excellent electrochemical performance for supercapacitors

Many works have demonstrated that the graphene and carbon nano-tube hybrid (RGO/CNT), synthesized by introducing CNT among graphene sheets, can exhibit improved supercapacitive performance. However, due to its relatively low specific surface area (SSA) and undeveloped pores, the introduced CNT has limited contribution to the electrochemical performance. To solve the problem, we have synthesized a hybrid (RGO/CNT@AC) of graphene and core-shell CNT@AC by introducing activated porous carbon-coated carbon nanotube (CNT@AC) among the graphene sheets. The SSA and micropore volume of RGO/CNT@AC are greatly higher than those of RGO/CNT. Moreover, RGO/CNT@AC shows superior supercapacitive performance compared with RGO/CNT in 6 M KOH electrolyte. The highest specific capacitance is up to 193 F g−1 at a scan rate of 10 mV s−1, much higher than that (91 F g−1) of RGO/CNT. Furthermore, RGO/CNT@AC also shows obviously better rate capability (138 F g−1 retention at a high scan rate of 5000 mV s−1) and excellent cycling stability (almost 100% capacitance maintaining in cycling stability test). The significant improvement in supercapacitive performance of the RGO/CNT@AC hybrid should be ascribed to the abundant micropores contributed by the AC coated on the CNT surface and more diffusion paths existing between RGO sheets.