Phosphorus, nitrogen and oxygen co-doped polymer-based core-shell carbon sphere for high-performance hybrid supercapacitors

Highlights: • A series of oxygen, nitrogen and phosphorus co-doped core-shell carbon sphere were developed. • The suspension polymerization method and H₃PO₄ activation process was used to prepare the carbons. • The sample prepared at 800 °C with H₃PO₄ activation showed the highest capacity and energy density. • The co-doped carbon can be used as promising materials for supercapacitors especially with high power density demand. Co-doping heteroatoms of the carbon lattice has been proven as an efficient strategy that can improve the capacitive performance, due to the synergetic effect of several dopants. Herein, a series of phosphorus, nitrogen and oxygen, co-doped polymer-based carbon spheres were prepared by the suspension polymerization method and chemical activation with phosphoric acid at different temperatures. The presence of heteroatoms was confirmed by X-ray photoelectron spectroscopy and elemental analysis. The structure of the carbons was characterized by scanning electron microscopy, Raman spectroscopy and nitrogen adsorption. Carbon obtained at 800 °C with a P, N and O doping level of 11.17 at%, 2.79 at% and 11.77 at% respectively, shows a capacitance of 157 F g⁻¹ at the current density of 0.05 A g⁻¹. Moreover, the electrode can survive at a wide potential window of 1.5 V with only 15% decrease in capacity after 10000 cycles at a current density of 5 A g⁻¹, providing a high energy density of 10 Wh kg⁻¹ and a high power density of 750 W kg⁻¹. For the outstanding features, it is expected that the phosphorus, nitrogen and oxygen co-doped carbons will be a very suitable material not only for supercapacitors, but also for lithium batteries and oxygen reduction reaction. In addition, the co-doping method described here might be extended to the preparation of other kinds of porous carbon materials.