Urea electrosynthesis under mild conditions shows great potential to conquer the conventional manufacturing industry with huge energy consumption. Here, self-supported oxygen vacancy-rich ZnO (ZnO-V) porous nanosheets are prepared using the electroreduction method and adopted as an efficient catalyst for aqueous urea electrosynthesis by using CO2 and nitrite contaminants as feedstocks. The urea Faradaic efficiency of ZnO-V achieves 23.26% at −0.79 V versus the reversible hydrogen electrode (RHE), which is almost 3 times as high as that of ZnO (8.10%). Liquid chromatography is developed for quantitative analysis of urea. The combined results of online differential electrochemical mass spectrometry (DEMS) and in situ attenuated total internal reflectance Fourier Transform infrared spectroscopy unveil a possible coupling pathway of NH2∗ and COOH∗ intermediates for urea formation. Our work opens an avenue for rational construction of efficient electrocatalysts for urea electrosynthesis and broadens the scope of products available from nitrite and CO2 reduction. Display omitted ZnO-V is prepared using the electroreduction methodZnO-V delivers efficient urea electrosynthesis using CO2 and nitrite as feedstocksA coupling pathway of NH2∗ and COOH∗ intermediates for urea formation is unveiled Using CO2 and inorganic feedstocks to construct the C-N bond is significant for CO2 conversion and synthetic chemistry. Meng et al. demonstrate that self-supported oxygen vacancy-rich ZnO porous nanosheets can be adopted as efficient catalysts for urea electrosynthesis by co-feeding CO2 and nitrite ions.