Surfaceenhanced Raman scattering (SERS) spectroscopy was used to explore the electrochemical reduction of CO, at a polycrystalline Ag electrode in KHCO, aqueous solution saturated with CO, at room temperature. Raman scattering from the oxidatioweduction cycled Ag electrode suggests the formation of CO and HCOOH by CO, 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-'. 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-' at -0.8 V). The O -C a antisymmetric and symmetric stretch modes of HCOO-observed at near 1550 and 1350 cm-' decrease in intensity with increasing negative potential, presenting a striking contrast to the C-H stretch mode. The SERS experiment with a C0,-saturated KHC0,-D,O solution is also described and discussed.
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