Atomic and Molecular Adsorption on the Bi(111) Surface: Insights into Catalytic CO2 Reduction

Bismuth is known to exhibit high selectivity toward production of HCOOH when used as an electrocatalyst for reduction of CO2. However, the current deficiency of knowledge on the surface chemical properties of Bi hinders mechanistic understanding and efficient development of Bi catalysts. In this study, molecular adsorption phenomena on the Bi(111) surface related to the electrocatalytic reduction of CO2 (ERC) are studied using dispersion-corrected density functional theory calculations. It is shown that the Bi(111) surface is inert toward adsorption of molecular species other than O-2, such as CO2 CO2, and HCOOH, confirming the low chemical reactivity of the surface. The adsorbates with O-Bi bonds are systematically more stable than those with C Bi bonds. As a result, *OCHO (formate) is significantly preferred over *COOH (carboxyl), leading to selective formation of HCOOH over CO as ERC product. Direct formation of *OCHO by proton-coupled electron transfer to CO2 is suggested as the reaction mechanism for ERC. Structural, vibrational, and electronic details of these two adsorbates are provided to guide future experimental mechanistic studies.