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

The lack of model single-atom catalysts (SACs) and atomic-resolution operando spectroscopic techniques greatly limits our comprehension of the nature of catalysis. Herein, based on the designed model single-Fe-atom catalysts with well-controlled microenvironments, we have explored the exact structure of catalytic centers and provided insights into a spin-crossover-involved mechanism for oxygen reduction reaction (ORR) using operando Raman, X-ray absorption spectroscopies, and the developed operando 57Fe M?ssbauer spectroscopy. In combination with theoretical studies, the N-FeN4C10 moiety is evidenced as a more active site for ORR. Moreover, the potential-relevant dynamic cycles of both geometric structure and electronic configuration of reactive single-Fe-atom moieties are evidenced via capturing the peroxido (?O2?) and hydroxyl (?OH?) intermediates under in situ ORR conditions. We anticipate that the integration of operando techniques and SACs in this work shall shed some light on the electronic-level insight into the catalytic centers and underlying reaction mechanism. ? 2020 Elsevier Inc.Single-atom catalysts (SACs) build a conceptual bridge between homo- and heterogeneous catalysis. 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 catalysts, we explored the exact structure of catalytic centers and provided a spin-crossover-involved mechanism for oxygen reduction reaction (ORR) using operando Raman, X-ray absorption spectroscopies, and the newly developed operando 57Fe M?ssbauer spectroscopy. The potential-relevant electronic and structural dynamic cycles of active single-Fe-atom moieties were evidenced via capturing the ?O2? and ?OH? intermediates and further supported by theoretical calculations. These results provide a proof of concept for the integration of operando techniques and SACs, which may direct the way toward the electronic-level insight into the catalytic centers and reaction mechanism. ? 2020 Elsevier Inc.Operando M?ssbauer spectroscopy was developed for in situ monitoring the evolution of catalytic centers in single-Fe-atom catalyst under practical oxygen reduction reaction conditions. Combining with operando Raman and X-ray absorption spectroscopies, the potential-relevant electronic and structural dynamic cycles of active single-Fe-atom moieties were evidenced via capturing the ?O2? and ?OH? intermediates and further supported by theoretical calculations. ? 2020 Elsevier Inc.