Electrocatalytic Synthesis of Urea from Carbon Dioxide and Nitrate over ZnO-Based Supported Palladium–Copper Alloy Catalysts

The catalytic coreduction of CO₂ and NO₃^– to urea is regarded as one of the most promising green technologies. Nevertheless, the C–N coupling reaction, which demands a high reaction selectivity, restricts its catalytic efficiency. Hollow nanoalloy spheres NiPd_100–xCu_x, employing Ni spheres as templates, were deposited onto the support ZnO to form a heterostructured composite catalyst NiPd_100–xCu_x/ZnO. The urea yield rate and Faradaic efficiency (FE) of NiPd₅₀Cu₅₀/ZnO were 194.02 mg h^–1 g_cat^–1 (±8.60 mg h^–1 g_cat^–1) and 29.38% (±1.43%) at −0.6 V (vs RHE), respectively, which were 5.43-fold and 4.58-fold higher than those of pristine ZnO, and the current density showed hardly any decay during the 12 h stability test. The results show that the loading of the NiPdCu alloy can effectively enhance the catalytic performance. Based on the above results, it can be determined that the intermediate *CO of the CO₂ reduction reaction (CO₂RR) and the intermediate *NH₂ of the NO₃^– reduction reaction (NO₃RR) undergo C–N coupling to form urea. Furthermore, the composite catalyst NiPd₅₀Cu₅₀/ZnO shows a synergistic catalytic effect between alloy NiPd₅₀Cu₅₀ and oxide support ZnO for urea synthesis. This work offers a novel design concept for the efficient electrocatalytic C–N coupling of NO₃^– and CO₂.