Spectroscopic analysis reveals dominant 14- and 16-membered ring FeN4 active sites in Fe-N-C electrocatalysts, indicating key structural determinants for oxygen reduction reaction activity.
To gain insights into single‐atom active sites of iron, nitrogen‐doped carbon (Fe‐N‐C), we performed comprehensive element‐specific spectroscopies including Fe K ‐edge X‐ray absorption, 57 Fe Mössbauer, and Fe Kβ 1,3 and valence‐to‐core (VtC) X‐ray emission spectroscopy for two Fe‐N‐C electrocatalysts that exclusively have atomically dispersed FeN 4 active sites for the oxygen reduction reaction. Experimental VtC X‐ray emission spectra (VtC‐XES) coupled with spectral simulation of FeN 4 active site models allowed us to determine the dominant active site in each catalyst: FeN 4 active sites with 14‐membered or 16‐membered rings. Our study will open up possibilities to understand more details on active site structure–activity relationships not only for Fe‐N‐C electrocatalysts but also the other single‐atom (electro)catalysts.
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Kato et al. (2026) studied this question.
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