N, P dual-doped hollow carbon spheres for high-performance supercapacitors

A series of nitrogen (N) and phosphorus (P) dual-doped hollow carbon spheres (NPHCSs) with different contents of N and P were synthesized by Stöber method with a subsequent pyrolysis process in N₂ atmosphere. The morphology, structure, and electrochemical performance were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and nitrogen adsorption-desorption, cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectra. The results show that the specific capacitance and cycling stability of the hollow carbon spheres (HCSs) electrodes are improved after N, P dual-doping. When the doping ratio reaches up to 7.56 at.% for N and 4.31 at.% for P, the obtained NPHCSs-2 exhibits the maximum specific capacitance (355 F g⁻¹ at 1 A g⁻¹) and excellent capacitance retention (97.1% after 10,000 cycles at 10 A g⁻¹) in 1 M H₂SO₄ aqueous solution due to its high specific surface area and good electrical conductivity. The NPHCSs-2 electrode should be a promising candidate for highly efficient electrode materials of supercapacitors.