Nitrogen‐doped Carbon Nanofibers for the Oxygen Reduction Reaction: Importance of the Iron Growth Catalyst Phase

Abstract

AbstractA systematic evaluation of the oxygen reduction reaction (ORR) on nitrogen‐doped carbon nanofibers (N‐CNFs) has been performed by tuning the properties of the N‐CNFs by using chemical vapor deposition. Analysis of the as‐synthesized N‐CNFs shows that the iron used as the growth catalyst consists of iron carbides, including Fe7C3, χ‐Fe5C2, and θ‐Fe3C, depending on the carbon activity of the synthesis feed. Furthermore, a relationship between the growth catalyst phase, the N‐CNF properties, and the electrocatalytic activity for the oxygen reduction in acidic electrolyte is revealed. The best catalytic activity and selectivity was achieved if the N‐CNFs were grown from Hägg carbide, χ‐Fe5C2, suggesting that this carbide phase favors the incorporation of active sites into the N‐CNFs. Controlling the phase of the iron particles used as growth catalysts is therefore essential for obtaining N‐CNFs with a high active site density for the oxygen reduction reaction.