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 O-2 (ads), superoxide anion O-2(-)*, and OOH* are monitored with in situ spectroscopy. We propose that the formation of *OOH species from O-2(-)* (O-2(-)*+H2O -> OOH*+OH-) is a possible RDS during the ORR process, whereas the generation of O-2 from OOH* species is the most likely RDS during the OER process.

Automated summary

This study investigates the role of different nitrogen groups in nitrogen-modified carbon catalysts in ORR and OER. By using seven aromatic molecules as models, the research monitors the evolution of active sites and key adsorbed intermediate products such as O-2 and OOH* through in situ spectroscopy.