Dramatic differences in carbon dioxide adsorption and initial steps of reduction between silver and copper

Converting carbon dioxide (CO₂) into liquid fuels and synthesis gas is a world-wide priority. But there is no experimental information on the initial atomic level events for CO₂ electroreduction on the metal catalysts to provide the basis for developing improved catalysts. Here we combine ambient pressure X-ray photoelectron spectroscopy with quantum mechanics to examine the processes as Ag is exposed to CO₂ both alone and in the presence of H₂O at 298 K. We find that CO₂ reacts with surface O on Ag to form a chemisorbed species (O = CO₂^δ-). Adding H₂O and CO₂ then leads to up to four water attaching on O = CO₂^δ- and two water attaching on chemisorbed (b-)CO₂. On Ag we find a much more favorable mechanism involving the O = CO₂^δ- compared to that involving b-CO₂ on Cu. Each metal surface modifies the gas-catalyst interactions, providing a basis for tuning CO₂ adsorption behavior to facilitate selective product formations.