Atomically Thin PdIn Bimetallene with Surface-Ordered Palladium Trimers for Efficient Urea Electrosynthesis from N2 and CO2

Urea synthesis via N₂ and CO₂ electrocatalysis has attracted significant interest but is hindered by unclear conversion mechanisms and low catalytic efficiency. Here, we report three atomically thin PdIn bimetallene catalysts, from surface-ordered Pd₄ tetramers to linearly arranged Pd atoms, where the Pd–In dual-site atomic geometric configuration is tuned by introducing polyamine ligands to induce a steric hindrance effect. Experimental data and simulations show that the atomically thin structure enhances the exposure of internal sites, where Pd and In act as activation centers for N₂ and CO₂, respectively. Notably, on the orthorhombic Pd₂In surface, an ordered Pd₃ trimers nitrogen activation region exists, enabling the transformation of nitrogen from initial end-on to more favorable side-on adsorption in the C–N coupling intermediate. This transformation highly activates the N–N group in the *NCON intermediate, promoting proton hydrogenation. Consequently, Pd₂In with ordered Pd₃ trimers achieves a high urea yield of 5.69 ± 0.12 mmol g^–1 h^–1 and a Faradaic efficiency of 31.8 ± 0.3% at an ultralow potential of −0.1 V vs the reversible hydrogen electrode, marking one of the highest values in N₂ and CO₂ coreduction systems.