Chemical Vapor Deposition of Pyridinic-Nitrogen-Dominated Graphene Model Electrocatalysts and in Situ Raman Spectroscopic Evidence on Their Active Sites for Oxygen Reduction Reaction

Probing the reaction intermediates on the electrocatalytic surface is crucial for understanding the catalytically active sites and reaction mechanisms. Although pyridinic nitrogen-doped carbon has been proposed as a highly active site for the technologically important oxygen reduction reaction (ORR) in fuel cells and metal air batteries, direct in situ spectroscopic evidence on the active center (nitrogen or carbon next to nitrogen) and ORR pathways remain lacking. We report the chemical vapor deposition of pyridinic-N-dominated and nondoped graphene domains (GDs) as well-defined ORR model electrocatalysts. By using in situ electrochemical Raman spectroscopy, we reveal that both nondoped and pyridinic N-dominated GDs generate common ORR intermediates (*O2– and *OOH) adsorbed on carbon atoms at the edges or those neighboring pyridinic N, respectively, except higher intensities of the intermediates corresponding to higher ORR activities on the latter. Spatially resolved line profile Raman spectroscopy further evidence that the pyridinic N at the edges is more active than the in-plane sites containing graphitic N. This study provides a general methodology for establishing the structure–activity relationships on well-defined two-dimensional model electrocatalysts using (spatially resolved) in situ Raman spectroscopy.