Abstract
We demonstrate by Raman Spectroscopy that simultaneous reduction of NO_3~- and CO2 on Cu surfaces leads to formation of Cu-C≡N-like species, showing Raman bands at 2080 and 2150 cm~(-1) when associated with reduced or oxidized Cu surfaces, respectively. Furthermore Cu-C≡N-like species are soluble, explaining vast restructuring of the Cu surface observed after co-electrolysis of CO2 and nitrate. Oxidation of deposited Cu-C≡N-like species results in the formation of NO. Cu-C≡N-like species do not form in electrolytes containing i) NH_4~+ and CO2, or ii) NO_3~- and HCOO~-, suggesting these likely originate from Cu-CO, the commonly accepted intermediate in electrochemical reduction of CO2, and Cu-NH_x species, previously identified in the literature as intermediate towards C-N bond formation. The implications of the previously unresolved formation of Cu-C≡N-like species for the development of electrodes and processes for electrochemical formation of carbon-nitrogen bonds, including urea, amines or amides, are briefly discussed.
NSTL