Using pyridine as nitrogen-rich precursor to synthesize Co-N-S/C non-noble metal electrocatalysts for oxygen reduction reaction

Abstract

The development of non-noble metal catalysts is of great interest due to their significant potential application in both fuel cell systems and metal–air batteries, particularly when considering long term commercial deployment. In this regard, novel Co-N-S/C non-noble metal catalysts supported on carbon, are synthesized in this study using a solvent-milling method followed by heat-treatment at elevated temperatures. Pyridine is used as the nitrogen-rich ligand for Co-Nx precursor complex formation. The morphology and composition of the catalyst are characterized by X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM) as well as X-ray photoelectron spectroscopy (XPS). Several catalysts containing different amounts of Co are also synthesized. The optimal Co content is found to be in the range of 10–15wt% nominal, in terms of catalytic oxygen reduction reaction (ORR) activity. This catalyst shows high electroactivity for the ORR with a high stability in alkaline media. Using rotating disk electrode measurements, and Koutechy–Levich analysis, the overall electron transfer number in the catalyzed ORR is found to be 3.8–4.0, suggesting the catalyzed ORR is a four-electron transfer process from O2 to H2O.