Quaternary Medium-Entropy Alloy Metallene with Strong Charge Polarization for Highly Selective Urea Electrosynthesis from Carbon Dioxide and Nitrate.

Electrochemical urea synthesis via the coreduction of CO₂ and NO₃^- is a sustainable alternative to the traditional Bosch-Meiser process. However, the sluggish reaction kinetics usually result in a low efficiency. Herein, we designed a kind of quaternary PdCuCoZn medium-entropy alloy (MEA) metallene for highly selective urea electrosynthesis. The random occupation of Cu, Co, and Zn with lower electronegativity in the face-centered cubic lattice of Pd-based metallene enables abundant electron donation from transition metals to adjacent Pd atoms, leading to the formation of charge-polarized Pd^δ--Cu/Co/Zn^δ+ sites. Considering that the pivotal C- and N-intermediates, namely, *CO and *NH₂, are electrophilic and nucleophilic, respectively, such strong charge polarization would greatly benefit their respective formation and stabilization. The stable adsorption with *CO bonded to electron-rich Pd-based sites and *NH₂ bonded to electron-deficient Cu/Co/Zn-based sites is demonstrated by the combination of in situ characterizations and theoretical calculations. The proof-of-concept PdCuCoZn MEA metallene achieves a maximum urea yield rate of 1840 μg h^-1 mg^-1 and a high Faradaic efficiency of 70.2%, surpassing most of the reported state-of-the-arts. Our strategy proposed in this work is believed to enlighten the design of an effective catalyst used for multistep reactions.