Effect of Doping Order on Metal-Free Heteroatoms Dual-Doped Carbon As Oxygen Reduction Electrocatalyst

Metal-free heteroatoms dual-doped carbon has been recognized as one of the most promising Pt/C-substitutes for oxygen reduction reaction (ORR). Herein, we optimize the preparation process by doping order of metal-free heteroatoms to obtain the best electrocatalytic performance through three types of dual-doped carbon, including XC-N (first X doping then N doping), NC-X (first N doping then X doping) and NXC (N and X doping) (X = P, S and F). XC-N has more defect than the other two indicated by Raman spectra. X-ray photoelectron spectrom (XPS) measurements indicate that N and X have been dual-doped into the carbon matrix with different doping contents and modes. Electrocatalytic results, including the potential of ORR peak (E-p), the half-wave potential, the diffusion-limiting current density mainly follows the order of XC-N > NC-X > NXC. Furthermore, the synergistic effect of second atom doping are also compared with the single doped carbon (NC, PC, SC and FC). The differences in electronegativity and atomic radius of these metal-free heteroatoms can affect the defect degree, the doping content and mode of heteroatoms on carbon matrix, induce polarization effect and space effect to affect O-2 adsorption and product desorption, ultimately to the ORR electrocatalytic performance. (C) 2020 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.