Mechanistic analysis of highly active nitrogen-doped carbon nanotubes for the oxygen reduction reaction

The kinetics of the oxygen reduction reaction (ORR) occurring on nitrogen-doped carbon nanotubes (NCNT) and carbon supported platinum (Pt/C) catalysts in alkaline conditions is analyzed through rotating ring disk electrode (RRDE) measurements and modeled based on typical mechanisms reported in the literature. The purely chemical intermediate reactions are found to be insensitive in the modeling of this mechanism, whereby the models can be simplified to the occurrence of parallel two and four electrochemical electron pathways. Rotating ring disk measurements are shown to be an alternative technique to split the total current density into partial currents that could be associated with the respective reaction pathways. Experimental comparisons of the NCNT and Pt/C catalysts revealed that the ORR kinetics on these materials proceeds similarly throughout two and four electron pathways. The four-electron pathway is found to be the most dominant in both catalysts. Kinetic improvements for the NCNT catalysts are observed, positioning them as promising materials for the ORR catalysis in fuel cells.