Carbon Dioxide Electroreduction on Gold without Metal or Organic Cations.

Extensive research efforts have been concentrated into the conversion of CO2 into value-added chemicals as it provides a route to a circular carbon economy. Electroreduction of CO2 on Au surfaces allows for the selective transformation of CO2 into CO via carbon dioxide reduction reaction (CO2RR), and the catalytic activity depends on the concentration and identity of cations present at the electrode-electrolyte interface. Experimental reports performed under typical CO2RR-operating conditions have widely shown that the CO2RR is enabled by the presence of metal or organic cations in the cathodic interfacial microenvironment. A remaining question is to address if CO2RR can occur in the absence of metal or organic cations and, if so, what the mechanism may be. Here, we show that CO2 can be electrochemically reduced to CO on Au in acidic electrolytes rigorously controlled to avoid the presence of metal and organic cations and systematically suggest the important contributions allowing this reaction to proceed. The formation of CO is confirmed by both qualitative and quantitative methods using potentiodynamic CO-stripping scans and chromatography-assisted constant potential electrolysis. Calculations indicate that H3O+ is able to stabilize the formation of *CO2 -, albeit at more negative potentials than when an alkali metal cation is present. Spectroelectrochemical experiments show that the electric field at the interface is reduced when metal cations are not added, indicating that the decreased field stabilization of intermediates could play an important role in increased overpotential required for the CO2RR to occur.