The production of cyclohexanone oxime was further confirmed by mass spectroscopy (MS, Figure ). The reaction mixture was also analyzed by high-performance liquid chromatography (HPLC) to quantify cyclohexanone and cyclohexanone oxime (Figure ), as well as ion chromatography (IC) to detect and quantify different nitrogen species in solution, namely NO3 -, NO2 -and NH3 (Figure ). In addition, the gas sample in the headspace of the H-cell was analyzed by gas chromatography (GC). Details of products characterization can be found in Supplementary Information. The FE and steady-state potential for the electrochemical NO3R were measured at constant current densities of 5 mA/cm 2 , 25 mA/cm 2 , 50 mA/cm 2 , 100 mA/cm 2 and 150 mA/cm 2 , the results of which are summarized in Figure . At 5 mA/cm 2 , a small amount of cyclohexanone oxime was detected (FE = 6±2%), while the major products were NH3 and H2. The FE for cyclohexanone oxime increased to 27±2% at 100 mA/cm 2 and -0.82 V vs reversible hydrogen electrode (VRHE), and then decreased to 21±2% when the current density further increased to 150 mA/cm 2 . At the different current densities investigated in this work, NH3 was generated as the major product with FEs between 30-50%; other detected products included NO2 -, N2 and H2.