Interfacial high-spin sites cooperated with contaminant-electron-supply in nonplanar N1-Fe-C2 for boosted radical generation

Overcoming the symmetric electronic structure of single-atom catalysts (SACs) to promote the cleavage of O-O bond remains critical for efficient H 2 O 2 activation. Herein, the high-loading Fe SACs (FeN 1 C 2 /C 2 N, 7.2   wt%) is designed via in-situ carbon defect engineering, which breaks the symmetric electronic structure through the nonplanar asymmetric coordination of Fe. DFT calculations and characterizations reveal that compared to the planar symmetric Fe-N 2 structure, N 1 -Fe-C 2 coordination modifies d-p orbital hybridization, inducing the spin state of Fe from low-spin (LS, t 2g : ↑↓ , ↑↓ , ↑↓ ; e g : _, _, _) to high-spin (HS, t 2g : ↑↓ , ↑ , ↑ ; e g : ↑ , ↑ ; _). The HS state weakens the coupling between *H 2 O 2 and Fe 3 d orbitals, promoting H 2 O 2 decomposition into abundant •OH, further achieving electron-rich pollutant Sulfamerazine (SMR) degradation with the rate constant of k obs =0.3308   min -1 . Additionally, such nonplanar asymmetric coordination releases the N atoms adjacent to the Fe sites, allowing them to form electron-transfer channel with SMR, which establishes nonradical electron transfer pathway (ETP). Pollutant pre-adsorption enables •OH to attack the target in situ along an ultrashort pathway, resulting in an efficient ETP-assisted radical oxidation mechanism. Overall, this work provides new insights into SACs design and a novel perspective for Fenton-like systems application.