Vaporized-salt-induced sp(3)-hybridized defects on nitrogen-doped carbon surface towards oxygen reduction reaction

The intrinsic carbon defects including pentagons, vacancies and sp(3)-hybridized carbon have recently been proposed as efficient reactive sites for oxygen reduction reaction (ORR). Nevertheless, it is still a great challenge to controllably introduce the intrinsic defects into carbon materials. Herein, a universal defect-engineering method via vaporized salt is reported to modify the N-doped carbon surface with abundant sp(3)-hybridized carbon defects. At an elevated temperature, the vaporized sodium chloride is found to selectively modulate the surface structure of carbon material. The obtained carbon-based electrocatalyst delivers an outstanding electrocatalytic ORR property with a half-wave potential (E-1/2) of 0.85 V vs. RHE and an excellent performance in zinc air battery (ZAB) test. The analysis of components and structures of surface elements via XANES and XPS reveals that the increasing sp(3)-hybridized carbon defects, induced by the vaporized-salt modification, are responsible for the enhancement of ORR performance. The theoretical calculations further suggest the sp(3) component hybridizes with original sp(2) carbon, forming efficient sp(2)/sp(3) hybridized carbon sites towards ORR. Additionally, other halide salts are proved to have the similar effect on promoting ORR activity and this method can expand to other carbon-based materials, suggesting its universality and significance in synthesis of defect-rich carbon-based materials. (C) 2021 Elsevier Ltd. All rights reserved.