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 Mössbauer 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.

缺乏模型单原子催化剂（SAC）和原子分辨率操作光谱技术极大地限制了我们对催化性质的理解。在此，基于设计模型具有良好控制的微环境的单铁原子催化剂，我们探索了催化中心的确切结构，并提供了利用拉曼操作法研究自旋交叉参与氧还原反应（ORR）的机理的见解， X射线吸收光谱学和发达的⁵⁷ FeMössbauer 光谱学。与理论研究相结合，N-FeN ₄ C ₁₀所述部分被证明是ORR的更活跃位点。而且，无论几何结构和反应性的单-铁-原子部分的电子结构的潜在相关动态循环通过捕获peroxido（*○证明₂ ^-和羟基（* OH）^-下中间体）在原位ORR条件。我们预计，这项工作中操作技术和SAC的集成将为电子层次上对催化中心和潜在反应机理的洞察提供一些启示。