Tandem Catalysis on Phase-Separating Alloys for Electrochemical Urea Synthesis

In this work, density functional theory calculations combined with a constant-potential model are used to examine urea formation by co-reduction of CO₂ and NO₃⁻ on Co(111), Ni(111), Cu(111), and Zn(0001) surfaces, representing metals with distinct N and O adsorption characteristics. While Cu and Zn both promote C-N coupling, each surface exhibits thermodynamic limitations in different elementary steps. These complementary roles motivate a phase-separating Cu-Zn tandem catalyst in which NO₃⁻ adsorption and the first C-N coupling occur on Zn to form *NH₂COOH, followed by spillover to Cu for subsequent hydrogenation and the final C-N coupling. Guided by the resulting empirical criterion that metals with higher O-affinity than N-affinity and moderate N adsorption favor C-N coupling, the screening is extended to the full transition-metal series, identifying Cu, Zn, Ag, and Cd as viable components and yielding six candidate tandem combinations. This work establishes a phase-separating tandem catalysis framework and offers transferable guidance for catalyst design in electrochemical urea synthesis.