Electrochemical reduction of CO 2 on silver as probed by surface‐enhanced Raman scattering

Surface‐enhanced Raman scattering (SERS) spectroscopy was used to explore the electrochemical reduction of CO 2 at a polycrystalline Ag electrode in KHCO 3 aqueous solution saturated with CO 2 at room temperature. Raman scattering from the oxidation‐reduction cycled Ag electrode suggests the formation of CO and HCOOH by CO 2 reduction. At an electrode potential of 0.08 V ( vs. Ag/AgCl), adsorbed CO gives rise to a C‐O stretch band at 2128 cm −1 . This band decreases in intensity and shifts to higher wavenumber with an increase of negative potential in the range from 0.0 to − 0.24 V. A different potential dependence is observed for the C‐H stretch mode of adsorbed HCOO − (2870 cm −1 at − 0.8 V). The O‐C‐O antisymmetric and symmetric stretch modes of HCOO − observed at near 1550 and 1350 cm −1 decrease in intensity with increasing negative potential, presenting a striking contrast to the C‐H stretch mode. The SERS experiment with a CO 2 ‐saturated KHCO 3 D 2 O solution is also described and discussed.