PVP-assisted synthesis of nitrogen-doped hollow carbon spheres for supercapacitors

Nitrogen-doped hollow carbon spheres (N-HCS) show advantages of regular hollow structure, large surface area, and nitrogen functionality, which make them widely applied in many fields, especially as electrode materials for supercapacitors. Herein, we demonstrated a facile way to prepare N-HCS by using SiO2 spheres as hard template, resorcinol-formaldehyde resin as carbon precursor. Polyvinyl pyrrolidone (PVP) was specially applied to introduce nitrogen and concurrently help resin coat on the surface of SiO2. With assistance of PVP, the resin uniformly coated on the surface of SiO2 by electrostatic adsorption and hydrogen bonding force and agglomeration of SiO2 spheres was prevented, resulting in improved dispersity of carbon spheres. The obtained N-HCS duplicated the morphology of the silica spheres faithfully with regular hollow structure and smooth surface, showing high surface areas and large pore volumes. As electrode material for supercapacitors, N-HCS exhibited good electrochemical performances with capacitance of 173 F g−1 at the current of 0.5 A g−1 and favorable cycling stability of 96.4% after 5000 cycles at current density of 5 A g−1, which make N-HCS become promising electrode material for high-performance supercapacitors.