Schiff-base polymer derived nitrogen-rich microporous carbon spheres synthesized by molten-salt route for high-performance supercapacitors

Abstract

Nitrogen-rich microporous carbon spheres (NMCSs) have been prepared via thermal treatment of Schiff-base polymer monomers of melamine and terephthalaldehyde in the presence of a molten-salt ZnCl₂/KCl system. The use of ZnCl₂ and KCl in the reaction allows for NMCSs with a high specific surface area of 1929 m² g⁻¹ and pore volume of 0.85 cm³ g⁻¹. More importantly, most of the pore volume is contributed to micropores, making it an ideal electrode material for high-performance supercapacitors. When tested as supercapacitor electrodes, NMCSs delivered an excellent specific capacitance of 365 F g⁻¹ at a current density of 0.5 A g⁻¹ and still maintained 230 F g⁻¹ even at 10 A g⁻¹. Moreover, a very stable cycle life with 94% capacitance retention was observed after 10 000 charge–discharge cycles at a current density of 3 A g⁻¹. With regard to the inexpensive precursors, simple and environmentally-friendly synthetic route, this novel molten salt strategy holds great potential for the industrial manufacture of NMCSs for use in energy storage and conversion.