N,N′-Bis(salicylidene)ethylenediamine as a nitrogen-rich precursor to synthesize electrocatalysts with high methanol-tolerance for polymer electrolyte membrane fuel cell oxygen reduction reaction

•Co–N–S/C catalysts for ORR are synthesized using salen as N-ligand by pyrolyzing process.•The overall electron transfer numbers for the catalyzed ORR are 3.6–3.9 with 3.7–19.9% %H2O2 yield.•The graphitic-N groups are found to be the most active sites for ORR activity.•These Co–N–S/C catalysts exhibit the superior methanol tolerance to commercial 40% Pt/C.

A cost-effective chemical, N,N′-bis(salicylidene)ethylenediamine (salen), is used as a ligand to form a carbon-supported Co-salen complex (Co-salen/C) by a simple solid-sate reaction. The Co-salen/C is then pyrolyzed at 600, 700, 800, 900, and 1000 °C to form carbon-supported Co–N–S/C catalysts for the oxygen reduction reaction (ORR). XRD, EDX, TEM, and XPS are used to characterize the catalysts' composition, crystalline nature, morphology, and possible surface groups induced by heat-treatment. Investigation of the catalytic activity and the ORR mechanisms using rotating disk electrode and rotating ring-disk electrode techniques demonstrates that all of these Co–N–S/C catalysts are highly active for the ORR in an O2-saturated 0.1 M KOH solution, but the catalyst heat treated at 700 °C gives the best ORR activity. The overall electron transfer number for the catalyzed ORR was determined to be 3.6–3.9, with 3.7–19.9% H2O2 production over the potential range of −0.05 to −0.60 V, suggesting that the ORR catalyzed by Co–N–S/C catalysts is dominated by a 4-electron transfer pathway from O2 to H2O. In addition, these catalysts exhibit superior methanol tolerance to commercial 40% Pt/C catalyst, thus the Co–N–S/C catalysts are promising for use as electrocatalysts in alkaline polymer electrolyte membrane fuel cells.