Multiple Adsorption of CO Molecules on Transition Metal Substitutional Impurities in Copper Surfaces

Copper-based catalysts are of particular interest for electrochemical reduction of $$ (CO2RR) as products beyond CO can form. To improve activity and selectivity, several studies have focused on the addition of other elements as substitutional impurities. Although the adsorption of a single CO molecule has often been used as a descriptor for CO2RR activity, our recent calculations using the RPBE functional showed that multiple CO molecules can bind to first-row transition metal impurities. Here, we extend the study to second-row transition metals and also to a functional that explicitly includes dispersion interaction, BEEF-vdW. The binding energy of the first CO molecule on the impurity atom is found to be significantly larger than on the clean Cu(111) and Cu(100) surfaces, but the differential binding energy generally drops as more CO molecules adsorb. The dispersion interaction is found to make a significant contribution to the binding energy, in particular for the last and weakest bound CO molecule, the one that is most likely to participate in CO2RR. In some cases, four CO admolecules can bind more strongly on the impurity atom than on the clean copper surface. The adsorption of CO causes the position of the impurity atom to shift outwards and in some cases, even escape from the surface layer. The C─O stretch frequencies are calculated in order to identify possible experimental signatures of multiple CO adsorption.