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 NiPd100–xCux, employing Ni spheres as templates, were deposited onto the support ZnO to form a heterostructured composite catalyst NiPd100–xCux/ZnO. The urea yield rate and Faradaic efficiency (FE) of NiPd50Cu50/ZnO were 194.02 mg h–1 gcat–1 (±8.60 mg h–1 gcat–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.