Restructuring of a Diamagnetic Diiron-Sulfur Complex to Paramagnetic Ferredoxin-Inspired [Fe4S4] Porous Organic Polymer Stimulates Optimally Coordinated Sites for Oxygen Evolution Catalysis.

Inspired by the electron-transfer function of biological ferredoxins, we report a biomimetic iron-sulfur cluster-functionalized porous organic polymer (FeS-POP) for efficient oxygen evolution reaction (OER). FeS-POP is constructed through polymerization-induced restructuring of a diamagnetic diiron carbonyl precursor (FeS-Com), wherein Fe─Fe bond cleavage and decarbonylation trigger a diamagnetic-to-paramagnetic transformation, generating atomically dispersed cubane [Fe4S4] active centers within a conjugated porous framework. FeS-POP exhibits excellent OER activity in alkaline media, delivering 10 mA cm-2 at an overpotential of 390 mV with a Tafel slope of 68 mV dec-1, ∼89% Faradaic efficiency, and remarkable durability, positioning it among the leading polymer-based OER electrocatalysts reported thus far. Importantly, synchrotron Fe K-edge XAFS establishes a cubane [Fe4S4(OH)4] motif as the catalytically active center and reveals its structural resilience throughout prolonged electrolysis, thereby elucidating the atomic-level structure-activity relationship governing OER. Complementary DFT calculations reveal the thermodynamic driving force for cluster reconstruction and show that cooperative multi-metallic interactions within the [Fe4S4] core facilitate O-O bond formation through a low-barrier redox-isomerization pathway. Our findings principally shed light on the molecular mechanism underlying this remarkable diamagnetic-to-paramagnetic transformation, establishing a synthetic blueprint for engineering biomimetic iron-sulfur active sites in porous electrocatalysts.