Graphitized hierarchical porous carbon nanospheres: simultaneous activation/graphitization and superior supercapacitance performance

Abstract

A novel graphitized porous carbon nanosphere (GPCNS) material obtained by a convenient simultaneous activation and graphitization route, which was realized by heating resorcinol–formaldehyde (RF) resin nanospheres immersed with ZnCl₂ and FeCl₃ in an inert atmosphere, has been reported. A high graphitization level was achieved through the catalytic graphitization by reduced Fe metal, and the hierarchically micro/mesoporous structure was produced in a controlled fashion by tuning the mass ratio of the activating agent ZnCl₂ and a carbon precursor. An optimal sample of GPCNS-2 was prepared with a FeCl₃/ZnCl₂/RF mass ratio of 0.5 : 2 : 1, exhibiting a highly graphitized framework and uniform spherical morphology with an average diameter of ∼500 nm, as well as well-interconnected micro/mesoporous structure with a large surface area of 1664.8 m² g⁻¹. Acting as an electrode material for a supercapacitor application in 6 M KOH electrolyte, GPCNS-2 displayed excellent electrochemical performance with a high specific capacitance of 402.5 F g⁻¹ at a current density of 1 A g⁻¹. Moreover, an electrochemical impedance spectroscopy test demonstrated that the low internal electrical resistance of GPCNS-2 contributed a superior rate capability of above 75% retention rate even at 50 A g⁻¹. Furthermore, the GPCNS-2 electrode possessed an outstanding cycling stability, and about 96% of its initial specific capacitance at 5 A g⁻¹ was maintained after 5000 cycles.