Overall Oxygen Electrocatalysis on Nitrogen‐Modified Carbon Catalysts: Identification of Active Sites and In Situ Observation of Reactive Intermediates

The recent mechanistic understanding of active sites, adsorbed intermediate products, and rate‐determining steps (RDS) of nitrogen (N)‐modified carbon catalysts in electrocatalytic oxygen reduction (ORR) and oxygen evolution reaction (OER) are still rife with controversy because of the inevitable coexistence of diverse N configurations and the technical limitations for the observation of formed intermediates. Herein, seven kinds of aromatic molecules with designated single N species are used as model structures to investigate the explicit role of each common N group in both ORR and OER. Specifically, dynamic evolution of active sites and key adsorbed intermediate products including O₂ (ads), superoxide anion O₂⁻*, and OOH* are monitored with in situ spectroscopy. We propose that the formation of OOH species from O₂⁻ (O₂⁻*+H₂O→OOH*+OH⁻) is a possible RDS during the ORR process, whereas the generation of O₂ from OOH* species is the most likely RDS during the OER process.

Dynamic evolution of active sites and key oxygen intermediate products during the ORR and OER on N-doped carbon catalysts are monitored experimentally with in situ ATR-IR spectra. With the assistance of isotopic labeling, the formation of OOH species from O₂⁻ (O₂⁻*+H₂O→OOH*+OH⁻) is suggested to be a possible RDS during the ORR process, whereas the generation of O₂ from OOH* species is the most possible RDS during the OER process.