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Elucidating Oxygen Reduction Active Sites in Pyrolyzed Metal–Nitrogen Coordinated Non-Precious-Metal Electrocatalyst Systems

2014; American Chemical Society; Volume: 118; Issue: 17 Linguagem: Inglês

10.1021/jp500781v

1932-7455

Urszula Tylus, Qingying Jia, Kara Strickland, Nagappan Ramaswamy, Alexey Serov, Plamen Atanassov, Sanjeev Mukerjee,

CO2 Reduction Techniques and Catalysts

Detailed understanding of the nature of the active centers in non-precious-metal-based electrocatalyst, and their role in oxygen reduction reaction (ORR) mechanistic pathways will have a profound effect on successful commercialization of emission-free energy devices such as fuel cells. Recently, using pyrolyzed model structures of iron porphyrins, we have demonstrated that a covalent integration of the Fe-N x sites into π-conjugated carbon basal plane modifies electron donating/withdrawing capability of the carbonaceous ligand, consequently improving ORR activity. Here, we employ a combination of in situ X-ray spectroscopy and electrochemical methods to identify the various structural and functional forms of the active centers in non-heme Fe/N/C catalysts. Both methods corroboratively confirm the single site 2e- × 2e- mechanism in alkaline media on the primary Fe2+-N4 centers and the dual-site 2e- × 2e- mechanism in acid media with the significant role of the surface bound coexisting Fe/Fe x O y nanoparticles (NPs) as the secondary active sites.