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.