Theoretical Insight into the Trends that Guide the Electrochemical Reduction of Carbon Dioxide to Formic Acid.

The electrochemical reduction (electroreduction) of CO2 to formic acid (HCOOH) and its competing reactions, that is, the electroreduction of CO2 to CO and the hydrogen evolution reaction (HER), on twenty-seven different metal surfaces have been investigated using density functional theory (DFT) calculations. Owing to a strong linear correlation between the free energies of COOH* and H*, it seems highly unlikely that the electroreduction of CO2 to HCOOH via the COOH* intermediate occurs without a large fraction of the current going to HER. On the other hand, the selective electroreduction of CO2 to HCOOH seems plausible if the reaction occurs via the HCOO* intermediate, as there is little correlation between the free energies of HCOO* and H*. Lead and silver surfaces are found to be the most promising monometallic catalysts showing high faradaic efficiencies for the electroreduction of CO2 to HCOOH with small overpotentials. Our methodology is widely applicable, not only to metal surfaces, but also to other classes of materials enabling the computational search for electrocatalysts for CO2 reduction to HCOOH.