FeSAC

In this study, we introduce time-of-flight secondary ion mass spectrometry (ToF-SIMS) as a powerful and precise tool to identify the coordination structure of SACs. Using Fe SACs derived from biomass as a model system, we demonstrate that Fe adopts an Fe-N₂C₂ coordination rather than the commonly assumed Fe-N₄ configuration. Electron paramagnetic resonance (EPR) and Mössbauer spectroscopy further confirm the low-spin nature of this Fe-N₂C₂ structure. This unique coordination endows our Fe@CS-8.8 catalyst with outstanding oxygen reduction reaction (ORR) activity, achieving a half-wave potential of 0.91 V vs. RHE, surpassing the benchmark Pt/C catalyst.