Controllably fabricating carbon microspheres with hierarchical porous structure for supercapacitors

The porous carbon microspheres (PCS) with hierarchical pore structure were fabricated by annealing the mixtures of aluminum potassium sulfate, calcium carbonate, and corn starch in a tube furnace in N₂ atmospheres. The mechanisms of forming carbon microspheres and producing the hierarchical pore structures were explored. The result shows that formation of carbon spheres depends on the pretreated starch by KAl (SO₄)₂, and CaCO₃ can promote more mesoporous structure produced. The resulting PCS-Ca1 electrode exhibits a high capacitance of 300 F g⁻¹ at a current density of 0.5 A g⁻¹, a superior rate capability of 228 F g⁻¹ at 20 A g⁻¹, and almost no capacitance fading (only 0.6% loss after 10,000 cycles) in 6 mol L⁻¹ KOH electrolyte. The symmetric supercapacitor fabricated with PCS-Ca1 electrodes displays a high energy density of 8.54 Wh kg⁻¹ at a power density of 125 W kg⁻¹ in 6 mol L⁻¹ KOH electrolyte.