Fabrication of hollow carbon spheres with robust and significantly enhanced capacitance behaviors

Hierarchical porous structure and high utilization of surface area are critical to the high-specific capacitance, great rate performance ,and super cycling stability of porous carbon materials for supercapacitive energy storage. In the present work, hollow carbon spheres (HCS) with unique hierarchical porous architecture were fabricated by a template method combined with polymer blend carbonization. As-prepared HCS possesses a monodisperse spherical morphology with uniform diameters between 200 and 280 nm and cavity size of ~ 45 nm. It exhibits a BET surface area of 399.6 m² g⁻¹, a t-Plot micropore area of 318.5 m² g⁻¹ and large micropores diameter of ~ 1.70 nm. As a supercapacitor electrode material, as-prepared HCS shows a superb cycle performance where the capacitance value after 8000 charge–discharge cycles still surpasses its initial value (117.1% retention after 8000 cycles). After a thorough investigation of the electrochemical capacitance on HCS electrode tested after 3000 cycles, it is found that the cycled sample exhibits a small charge transfer resistance (0.07 Ω), an ideal EDLC behavior and an significantly improved capacitance performance in terms of enhanced specific capacitance (172.5  F g⁻¹ at 5 A g⁻¹) and outstanding rate capability (71.3% retention from 1 to 20 A g⁻¹) when compared with fresh HCS electrode, which is attributable to the electrochemical enlargement of utilized surface areas via repetitive cycling treatment. This finding would inspire the structural design of nanoporous carbon materials for advanced supercapacitors especially with superb cycle stability and outstanding rate performances.