Adsorption of the formate species on copper surfaces: a DFT study

Abstract

The density functional theory and the cluster model approach have been applied to study the interaction of the formate species with the copper (100), (110) and (111) surfaces. The short-bridge, long-bridge and cross-bridge sites of the copper surface have been modelled by Cu 7 and Cu 8 metal clusters after checking the validity of the results against those obtained with much larger clusters. The results show that the formate species is stabilized strongly on the short-bridge site of the surfaces considered and this is in agreement with available experimental data. For adsorption on the short-bridge site, and for the three surfaces considered, the Cu surfO is close to 2.02 Å, the CO bond length is 1.26 Å and the OCO angle is 128°. On this adsorption site, formate is bridge-bonded with the two oxygens almost in a top position on two copper atoms. For the long-bridge site, the oxygen atoms of the adsorbate are not located above the two copper atoms. The two OC bonds are equivalent when formate is adsorbed on these two sites. On the cross-bridge site, the formate species is bonded to the surface in a monodentate conformation. The two OC bonds are different with two clearly different bond lengths. The difference is larger for adsorption on the Cu (100) surface. In this case, the bond lengths are typical of a bond order of one and two. The bonding to the surface is essentially ionic, and the total charge in the adsorbate is 0.75 ±0.05 e, approximately.