Chemical Vapor\nDeposition of Pyridinic-Nitrogen-Dominated\nGraphene Model Electrocatalysts and in Situ Raman Spectroscopic Evidence\non Their Active Sites for Oxygen Reduction Reaction

Probing\nthe reaction intermediates on the electrocatalytic\nsurface\nis crucial for understanding the catalytically active sites and reaction\nmechanisms. Although pyridinic nitrogen-doped carbon has been proposed\nas a highly active site for the technologically important oxygen reduction\nreaction (ORR) in fuel cells and metal air batteries, direct in situ\nspectroscopic evidence on the active center (nitrogen or carbon next\nto nitrogen) and ORR pathways remain lacking. We report the chemical\nvapor deposition of pyridinic-N-dominated and nondoped graphene domains\n(GDs) as well-defined ORR model electrocatalysts. By using in situ\nelectrochemical Raman spectroscopy, we reveal that both nondoped and\npyridinic N-dominated GDs generate common ORR intermediates (*O<sub>2</sub><sup>–</sup> and *OOH) adsorbed on carbon atoms at\nthe edges or those neighboring pyridinic N, respectively, except higher\nintensities of the intermediates corresponding to higher ORR activities\non the latter. Spatially resolved line profile Raman spectroscopy\nfurther evidence that the pyridinic N at the edges is more active\nthan the in-plane sites containing graphitic N. This study provides\na general methodology for establishing the structure–activity\nrelationships on well-defined two-dimensional model electrocatalysts\nusing (spatially resolved) in situ Raman spectroscopy.