Direct Observation on Reaction Intermediates and the Role of Bicarbonate Anions in CO2 Electrochemical Reduction Reaction on Cu Surfaces

Cu is the only monometallic catalyst that produces a large amount of hydrocarbon fuels during the CO₂ electrochemical reduction reaction (CO₂RR). However, the CO₂RR mechanism and the impact of electrolyte are unclear. In this communication, two important issues regarding the CO₂RR on Cu surfaces are studied: (1) the direct observation on reaction intermediates and (2) the role of the electrolyte (KHCO₃) in the reaction. Surface-enhanced infrared absorption spectroscopy allows direct observation of several reaction intermediates that have never been detected before, except for the commonly detected CO. Another important finding is that CO₂ molecules are mediated to the Cu surface via their equilibrium with bicarbonate anions instead of direct adsorption from the solution. These results shed light on the full understanding of the CO₂RR on Cu surfaces and developing more advanced catalysts.