Role of Pyridinic Nitrogen in the Mechanism of the Oxygen Reduction Reaction on Carbon Electrocatalysts
Abstract
The introduction of pyridinic nitrogen (pyri‐N) into carbon‐based electrocatalysts for the oxygen reduction reaction is considered to create new active sites. Herein, the role of pyri‐N in such catalysts was investigated from a mechanistic viewpoint using carbon black (CB)‐supported pyri‐N‐containing molecules as model catalysts; the highest activity was observed for 1,10‐phenanthroline/CB. X‐ray photoemission spectroscopy showed that in acidic electrolytes, both pyri‐N atoms of 1,10‐phenanthroline could be protonated to form pyridinium ions (pyri‐NH+). In O2‐saturated electrolytes, one of the pyri‐NH+ species was reduced to pyri‐NH upon the application of a potential; no such reduction was observed in N2‐saturated electrolytes. This behavior was ascribed to electrochemical reduction of pyri‐NH+ occurring simultaneously with the thermal adsorption of O2, as supported by DFT calculations. According to these calculations, the coupled reduction was promoted by hydrophobic environments.
