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 CO 2 and N 2 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 Fe 2+ /Fe 3+ 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 Fe 2+ /Fe 3+ 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, *NH 2, and C–N intermediates, confirming the occurrence of C–N coupling on Fe-MOF-1. The cooperative function of Fe 2+ and Fe 3+ centers facilitates simultaneous CO 2 reduction and N 2 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.