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

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.