When Graphitic Nitrogen Meets Pentagons: Selective Construction and Spectroscopic Evidence for Improved Four-Electron Oxygen Reduction Electrocatalysis

Abstract

Nitrogen-doped carbon materials have emerged as promising metal-free electrocatalysts for oxygen reduction reaction (ORR) in fuel cells and metal-air batteries. However, the structural inhomogeneity, particularly the coexistence of four nitrogen doping structures–pyridinic, graphitic, pyrrolic, and oxidized nitrogen–makes assessing their respective contributions challenging and controversial. The current understanding of the four nitrogen doping structures may be also oversimplified and even problematic. The development of a distinctive graphitic-N-doped carbon electrocatalyst is presented in which graphitic nitrogen coordinated with pentagon defects is selectively constructed. Contrary to the previously held belief that graphitic nitrogen has little effect on ORR electrocatalysis, the unique graphitic N configuration exhibited significantly enhanced four-electron ORR activity in both alkaline and acidic media. In situ electrochemical Raman spectroscopy combined with density functional theory calculations further revealed that graphitic nitrogen, when coordinated with pentagon defects, optimized the density of states near the Fermi level, leading to optimized binding energies with oxygen-containing intermediates. The results rationalize the long-standing controversy over the role of different nitrogen dopants in ORR electrocatalysis and suggest that there is considerable potential to precisely construct new nitrogen doping configurations to achieve superior electrocatalytic performance.