Fe ²⁺ /Fe ³⁺ Redox Modulation in Iron-Based Metal–Organic Frameworks for Efficient C–N Coupling in Electrocatalytic Urea Synthesis

Designing efficient catalysts for the electrocatalytic coreduction of CO₂ and N₂ into urea remains challenging due to the sluggish activation of both molecules and the complex C-N coupling process. Herein, we report an iron-based metal-organic framework (Fe-MOF) system in which the ratio of Fe²⁺/Fe³⁺ active sites is modulated via solvent regulation to promote synergistic catalysis. Structural and spectroscopic analyses confirm that Fe-MOF-1, prepared in ethanol, possesses a higher Fe²⁺/Fe³⁺ ratio (0.91) than Fe-MOF-2 (0.56), leading to enhanced electronic conductivity and charge-transfer efficiency. Fe-MOF-1 exhibits a urea yield rate of 3.02 mmol h^-1 g^-1 with a Faradaic efficiency of 10.4% at -0.71 V (vs RHE), outperforming Fe-MOF-2. In situ FT-IR analysis reveals the generation of *COOH, *NH₂, and C-N intermediates, confirming the occurrence of C-N coupling on Fe-MOF-1. The cooperative function of Fe²⁺ and Fe³⁺ centers facilitates simultaneous CO₂ reduction and N₂ activation, enabling efficient urea synthesis under mild conditions. This work provides mechanistic insights and a rational design strategy for dual-valence metal sites toward sustainable C-N coupling catalysis.