Identification of the Electronic and Structural Dynamics of Catalytic Centers in Single-Fe-Atom Material

Abstract

Single-atom catalysts (SACs) offer us new opportunities for capturing the reaction intermediates, identifying the active sites, and even monitoring the structural and electronic evolution of catalytic centers. However, the lack of model SACs and atomic-resolution operando spectroscopic techniques greatly limits our comprehension of the nature of catalysis. Herein, based on the newly designed model single-Fe-atom catalyst with well-controlled site density and coordination environment, we have explored the exact structure of catalytic centers and provided insights into a novel spin-crossover-involved mechanism for oxygen reduction reaction (ORR) using operando Raman, X-ray absorption spectroscopies, as well as the newly developed operando 57Fe Mossbauer technique. Combining with theoretical studies, the single-Fe-atom site of N-FeN4C10 moiety, with preferential reaction to O2 near the onset potential, is shown as a more active site for ORR. Moreover, the potential-relevant dynamic cycles of both the geometric structure and electronic configuration of reactive single-Fe-atom moieties are evidenced via directly capturing the peroxido (*O2-) and hydroxyl (*OH-) intermediates under in-situ ORR conditions. Our results provide proof-of-concept for the integration of operando techniques and SACs, which directs the way towards the electronic-level insight into catalytic centers and underlying reaction mechanism.