A gram-scale reaction experiment for 29 h was carried out to investigate the change in the molar concentration of each substance (detected by GC) (Figure ). The concentration of each component is normalized to the corresponding concentration of nitrobenzene (see Supplementary information). The concentration of nitrobenzene dramatically drops within 15 h while aniline increases steadily after 4 h until 29 h. It implies that aniline is not converted directly by nitrobenzene. After electrolysis for a period, azoxybenzene appears and increases followed by azobenzene. Azobenzene converts from azoxybenzene according to the previous study and can be supported by the order they appear in the reaction process. Azoxybenzene comes from the reaction between nitrosobenzene and phenylhydroxylamine . The rate of this reaction is relatively fast which is proved by the low concentration level of nitrosobenzene. It is assumed that aniline is from the decomposition of azobenzene because azobenzene gradually abates and finally disappears. Two validation experiments confirm that azobenzene or azoxybenzene can indeed be converted into aniline (Supplementary information, Table S 9, Entry 5,6) which is consistent with the speculation. This route is consistent with the descriptions that exist the coupling intermediates in the Haber mechanism and Jackson mechanism . The conversion of azoxybenzene to azobenzene, along with the conversion of azobenzene to aniline, are two rate-determining steps because of their relatively high concentration during the reaction. Moreover, it is evidenced that aniline, nitrosobenzene, azoxybenzene, and azobenzene are all not oxidated at the anode. All reactions of nitrobenzene and its derivatives happen at the cathode. The fluctuation of voltage over time offers another way to insight into the process. The voltage increases in the initial 3 hours, which represents an increase in internal resistance. It should be attributed to the SEI growing on the cathode which inhibits the charge transfer . The decrease in voltage after the 3rd hour implies massive charge transfer caused by a hydrogenation process. The reduction of nitrobenzene and nitrosobenzene are the reasons for the resistance drop. Internal resistance increases after the 8th hour because of the coupling of nitrosobenzene and phenylhydroxylamine which requires no extra additional redox agents and charge transfer. Afterward, the resistance drops for the dominance of hydrogenolysis and aniline production. Resistance reaches a minimum at the 26 th hour at the depletion of azoxybenzene and returns to a high level until the aniline fully forms.