Nitrogen-doped hollow carbon spheres for supercapacitors

We present high nitrogen-doped hollow carbon spheres (HNHCSs) via cooperative template-directed coating method. The SiO2 spheres serve as hard template; ionic liquids, such as 1-hexadecyl-3-methylimidazolium bromide (CMMB), serve as cationic surfactant; resorcinol formaldehyde (RF) resins as carbon source; and melamine as nitrogen source. The CMMB used in the coating procedure improves the SiO2 spheres dispersion in the reaction media and introduces nitrogen atom into carbon skeleton. The CMMB, SiO2 spheres, and RF resins self-assemble into inorganic-organic core-shell structures through electrostatic interaction. After being treated with melamine, the nitrogen content of the sample further improved, which can enhance the performance of supercapacitor. Due to high nitrogen content, specific surface area, and unique hollow structure, the HNHCSs exhibit a reversible specific capacitance of 368 F g(-1) at 0.2 A g(-1) in 6 M KOH, and maintains a good high-class capacitance retention capability (85.1%) at 5.0 A g(-1) for up to 5000 cycles. These results show that the HNHCSs with high nitrogen content, specific surface area, and hollow structure represent a promising alternative of efficient electrode material for supercapacitor.