Ag2O-loaded Cu based metal–organic framework material as pre-electrocatalyst for efficient urea synthesis

Abstract

The electrocatalytic synthesis of urea from CO₂ and NO₃⁻ represents a sustainable alternative to traditional energy-intensive processes. Metal–organic frameworks (MOFs), with their tailorable porous structures and atomically dispersed metal sites, provide an ideal platform for multi-step catalytic reactions. Among them, copper-based MOFs exhibit dual catalytic activity in both CO₂ reduction reaction (CO₂RR) and nitrate reduction reaction (NO₃RR), making them promising candidates for urea electrosynthesis. However, single-site Cu catalysts often struggle to effectively promote C–N coupling, a key step in urea formation. To address this limitation, we developed a heterojunction catalyst by incorporating Ag₂O nanoparticles into a Cu-based MOF, creating dual active sites that enhance C–N coupling. This catalyst achieves a maximum urea faradaic efficiency of 16.4% at −0.4 V vs. RHE and a yield of 11.2 mmol h⁻¹ g⁻¹ at −0.5 V vs. RHE, both superior to those of individual Ag₂O or Cu MOF catalysts. Structural analysis reveals that the catalyst consists of Cu MOF nanosheets with uniformly distributed Ag₂O nanoparticles, which undergo in situ reconstruction into a Cu–Ag heterostructure under operating conditions. In situ infrared spectroscopy verifies that urea forms via the coupling of *CO and *NH₂ species. Theoretical calculations highlight the complementary roles of the dual active sites: Ag facilitates *CO formation, while Cu promotes *NH₂ generation. Additionally, the Cu–Ag heterostructure lowers the energy barrier for *CO and *NH₂ coupling, with Cu sites stabilizing *NH₂ and enabling spontaneous migration of *CO from Ag to Cu for efficient CO–NH₂ coupling at the interface. This MOF-derived heterojunction catalyst, featuring dual active sites with distinct functionalities, provides a synergistic strategy to enhance C–N coupling and offers valuable insights for designing high-performance electrocatalysts for sustainable urea synthesis.