Structural Evolution of Atomically Dispersed Fe Species in Fe–N/C Catalysts Probed by X-ray Absorption and 57 Fe Mössbauer Spectroscopies

Iron and nitrogen codoped carbon (Fe–N/C) catalysts are considered the most promising nonprecious metal catalysts for the oxygen reduction reaction (ORR), with their activities approaching those of Pt-based catalysts. Recently, silica-based protective-layer or intermediate layer-assisted synthesis strategies have been developed to preferentially generate catalytically active Fe–N x sites while suppressing inactive Fe clusters. However, the role of the silica layer in the formation of Fe–N x sites remains elusive. In this study, we used X-ray absorption and 57 Fe Mössbauer spectroscopies to determine the evolution of the structure of Fe-based species during the silica-coating-mediated synthesis. Through X-ray absorption near-edge structure and 57 Fe Mössbauer spectroscopy analyses, the formation of iron silicide (Fe–Si) species after silica coating was identified. Peak parameter analyses …