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

Converting carbon dioxide (CO_2) into liquid fuels and synthesis gas is a world-wide priority. But there is no experimental information on the initial atomic level events for CO_2 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 CO_2 both alone and in the presence of H_2O at 298 K. We find that CO_2 reacts with surface O on Ag to form a chemisorbed species (O = CO_2^(δ−)). Adding H_2O and CO_2 then leads to up to four water attaching on O = CO_2^(δ−) and two water attaching on chemisorbed (b-)CO_2. On Ag we find a much more favorable mechanism involving the O = CO_2^(δ−) compared to that involving b-CO_2 on Cu. Each metal surface modifies the gas-catalyst interactions, providing a basis for tuning CO_2 adsorption behavior to facilitate selective product formations