Comprehensive Spectroscopic Elucidation of Atomically Dispersed FeN 4 Active Sites of Fe‐N‐C Electrocatalysts
Masaru Kato, Hiroyuki Asakura, Siqi Xie, Koki Matsumoto, Akira Onoda, Shun Saito, Kenji Ishii, Takaya Mitsui, Kosuke Fujiwara, Ichizo YagiABSTRACT
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.