Carbon-nitrogen bond formation on Cu electrodes during CO2 reduction in NO3- solution

We demonstrate by Raman Spectroscopy that simultaneous reduction of NO3- and CO2 on Cu surfaces leads to formation of Cu-CN–like species, showing Raman bands at 2080 and 2150 cm−1 when associated with reduced or oxidized Cu surfaces, respectively. Furthermore Cu-CN–like species are soluble, explaining vast restructuring of the Cu surface observed after co-electrolysis of CO2 and nitrate. Oxidation of deposited Cu-CN–like species results in the formation of NO. Cu-CN–like species do not form in electrolytes containing i) NH4+ and CO2, or ii) NO3- and HCOO-, suggesting these likely originate from Cu-CO, the commonly accepted intermediate in electrochemical reduction of CO2, and Cu-NHx species, previously identified in the literature as intermediate towards C-N bond formation. The implications of the previously unresolved formation of Cu-CN–like species for the development of electrodes and processes for electrochemical formation of carbon-nitrogen bonds, including urea, amines or amides, are briefly discussed.