Bimetallic Phase Transition Induced Asymmetric Spin‐State Modulation for Controllable Radical‐Nonradical Pathways

Abstract Rational spin‐states modulation in bimetallic catalysts presents a promising strategy to enhance both the activity and selectivity of advanced oxidation processes. However, the underlying spin‐electronic mechanisms, particularly in structurally complex, multiphase systems, remain insufficiently understood. In this study, a sulfur‐assisted phase engineering strategy is employed to tune the structure of cobalt‐iron catalysts between spinels (CoFe 2 O 4 and CoFe 2 S 4 ) and heterojunctions (CoS@Fe 3 S 4 and Co 3 S 4 @Fe 3 S 4 ). Integrated experimental and density functional theory (DFT) analysis reveal that sulfur incorporation triggers asymmetric spin‐state modulation, characterized by enhanced electron localization in low‐spin‐state Co sites and significant spin polarization on S atoms. Such electronic configuration opens a directional Co─S─Fe electron spin channel in bimetallic sulfides, which promotes interfacial electron transfer and initiates the proton‐coupled electron transfer (PCET) process, thereby enabling efficient activation of peroxymonosulfate (PMS) and selective generation of nonradical 1 O 2 species. The resulting CoS@Fe 3 S 4 catalytic system demonstrates ≈14‐fold increase in reaction kinetics compared to CoFe 2 O 4 spinels, alongside high environmental applicability (Life Cycle Assessment) and minimal ecotoxicity of degradation intermediates. These findings highlight the critical role of asymmetric spin‐state modulation in governing reactive oxygen species (ROS) pathways, providing a rational design strategy for tunable advanced oxidation processes.