Facile synthesis of mesoporous carbon microspheres/graphene composites in situ for application in supercapacitors

Mesoporous carbon/graphene composites (MCG) have exhibited good electrochemical performances; however, the fixed mesoporous carbon, the low specific surface area, and porosity are the main obstacles in their application in supercapacitors. In this paper, mesoporous carbon microspheres/graphene composites (MCMG) were synthesized in situ via a soft template method and subsequent thermal reduction by using cetyltrimethylammonium bromide (CTAB) as the structure-directing agent, and aqueous mesophase pitch (AMP) and graphene oxide (GO) as the carbon sources. The strong electrostatic interaction between GO/CTAB and AMP promoted the self-assembly of CTAB and AMP to form the MCMG precursor. The results showed that the CTAB concentration and aging temperature have an important effect on the morphology and pore structure of the synthesized MCMG. The high aging temperature promoted the formation of mesoporous carbon spheres and its diameter increased with the increase in the concentration of CTAB. The as-prepared MCMG at the aging temperature of 140 °C had obvious spherical and layered carbon materials after carbonization at 900 °C. When the concentration of CTAB was 10.6 g L^-1, the formed mesoporous carbon spheres with the diameter of 30-40 nm were uniformly dispersed among the layered graphenes in MCMG-140-0.2 (the aging temperature of 140 °C and the CTAB content of 0.2 g). In addition, its specific surface area was 1150.5 m² g^-1 and the mesopore size was centered at 4.3 nm, 7.9 nm, and 17.1 nm. Compared with the MCMG precursor, the ordered degree of the mesopores for MCMG was reduced due to the high temperature carbonization. Importantly, the specific capacitance of MCMG-140-0.2 at the current density of 0.1 A g^-1 was as high as 356.3 F g^-1. Moreover, the specific capacitance of MCMG-140-0.2 at 1 A g^-1 remained at 278.5 F g^-1, the capacitance retention was 92.1% after 6000 cycles, and the coulombic efficiency was over 98% at a high current density of 2 A g^-1. Therefore, the as-prepared MCMG can be an excellent candidate for electrode materials in supercapacitors.