Fe2+/Fe3+ 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.