Modulating the Spin State of Fe–N–C Single-Atom Catalysts via MoC Clusters for Enhanced Oxygen Reduction Electrocatalysis

The rational design of high-performance, nonprecious-metal oxygen reduction reaction (ORR) catalysts remains a central challenge in advancing metal-air batteries. Herein, we report a heterocluster-single-atom cooperative architecture, where atomically dispersed FeN4 sites are electronically coupled with adjacent MoC(111) nanoclusters embedded in a hierarchical N-doped carbon (NC) matrix. This configuration enables long-range electronic modulation of the Fe center while preserving its structural integrity, thereby driving a spin-state transition from high-spin (S = 2) to intermediate-spin Fe(II). Comprehensive spectroscopic analyses─including HAADF-STEM, XAS, EPR, and SQUID─provide direct experimental validation of this remote spin-state engineering. The resultant MoCC/FeN4 catalyst delivers enhanced ORR activity (E1/2 = 0.880 V vs RHE) and stability (>85% current retention after 200 h) in alkaline media, surpassing commercial Pt/C. Furthermore, zinc-air batteries assembled with this catalyst achieve a high open-circuit voltage (1.51 V) and stable cycling over 120 h. This work establishes a generalizable strategy for spin-controlled electrocatalysis mediated by long-range interactions, distinct from conventional ligand-field engineering.