Nitrogen-doped hollow carbon spheres functionalized by 9,10-phenanthrenequinone molecules as a high-performance electrode for asymmetric supercapacitors

In this study, uniform nitrogen-doped hollow carbon spheres (NHCSs) have been synthesized using sphere-like SiO2 as a template and polydopamine as a carbon source. It is found that NHCSs have an ultrahigh specific surface area of 870.1 m(2) g(-1) and high porosity. 9,10-Phenanthrenequinone (PQ) molecules are selected to decorate NHCSs to obtain electrode materials (NHCSs/PQ) for supercapacitors, which show a clear capacitance increase in comparison with pure NHCSs when tested in 1 M H2SO4 aqueous solution. In a three-electrode system, the NHCSs/PQ (mass ratio 4:2) electrodes exhibit larger specific capacitance (as high as 252 F g(-1) at 1 A g(-1)) and an ultrahigh rate capability (80.8% capacitance retention at 30 A g(-1)). Furthermore, the asymmetric supercapacitor is assembled using NHCSs/PQ as a positive electrode material and nitrogen-doped porous carbon (NPCs) that has adsorbed anthraquinone as a negative electrode material, respectively. The device exhibits a high energy density of 8.34 W h kg(-1) along with a power density of 600 W kg(-1).