Spin-State-Modulated Interfacial Fe²⁺ in Solid-Solution Heterostructures Promotes H₂O₂ Selectivity and Electro-Fenton...

In heterogeneous electro-Fenton (EF) catalysis, achieving selective H₂O₂ generation with efficient ^•OH production remains challenging due to poor oxygen reduction reaction (ORR) selectivity and cycling stability. This study employs an interfacial spin-state engineering strategy to construct CoFe solid solutions/Fe₃O₄ heterostructures (CoFe_ss/Fe₃O₄) through controlled Co doping. Co incorporation induces Fe⁰ lattice expansion, forming CoFe_ss phases that creates oxygen-bridged heterointerfaces with Fe₃O₄ (CoFe_ss-O-Fe²⁺), altering the coordination environment and facilitating the Fe²⁺ spin-state transition from high-spin (t_2g⁴e_g² S = 2) to intermediate-spin (t_2g⁵e_g¹ S = 1) configuration at the interface. This modulation optimizes electron transfer dynamics, steering ORR toward the 2-electron ORR pathway with H₂O₂ selectivity of 75.9%. Co_0.1Fe_ss/Fe₃O₄ (with a 0.1 Co/Fe molar ratio) exhibits exceptional tetracycline degradation performance, achieving 95.0% removal within 60 min, outperforming the undoped catalyst. The degradation involves ^•OH as the dominant reactive species, with ^•O₂^- and ¹O₂ contributing synergistically to drive tetracycline degradation through hydroxylation, demethylation, and ring-opening pathways. The catalyst demonstrates broad-spectrum pollutant removal and excellent cycling stability, with negligible metal ion leaching. Ecotoxicity assessments confirm that degradation intermediates exhibit low toxicity to aquatic organisms, ensuring high environmental safety. This work elucidates heterometallic doping as an effective spin-state engineering strategy through interfacial electronic reconstruction, providing insights for efficient EF catalysts in antibiotic wastewater treatment.