Revealing the Active Sites of Fe−N/C Oxygen Reduction Electrocatalysts by Mössbauer spectroscopy

Abstract

Iron and nitrogen doped on carbon (Fe−N/C) catalysts have emerged as promising nonprecious metal catalysts (NPMCs) for oxygen reduction reaction (ORR) for fuel cells. In this presentation, we show that Mössbauer spectroscopy, in combined with other spectroscopic and microscopic methods, plays a pivotal role in revealing the nature of active sites in Fe−N/C catalysts. Based on the information on the active sites, we developed a general “silica-protective-layer-assisted” approach that can preferentially generate the catalytically active Fe−Nx sites in Fe−N/C catalysts while suppressing the formation of inactive large Fe-based particles. The preferential formation of Fe−Nx sites in the resulting Fe−N/C catalysts was characterized by Mössbauer spectroscopy, X-ray absorption spectroscopy, X-ray diffraction, and transmission electron microscopy. The developed Fe−N/C catalysts showed very high ORR activity and excellent stability in both alkaline and acidic media.