First-principles Investigation Of Cu, Ag, Au Atom Adsorption On CeO₂ (111) And (110) Surfaces

Cubic fluorite type CeO₂ is a kind of industrially important rare-earth metail oxide material with low price, good thermal stability, non-toxic and environmentally friendly features. It can be used as the main component of the anode materials for solid state oxide fuel cell. The excellent catalytic activity and electrochemical performance of CeO₂ is closely related to its surface properties.We have investigated the the adsorption behaviors of metal (Cu, Ag, Au) atoms on the CeO₂(111) and (110) surfaces using using the first-principels calculations and made the systematical comparison with the available experimental results. Atomic and electronic structures of M/CeO₂ interfaces have been in detail analyzed. Conclusions are summarized as follows:1. Detailed studies of metal (Cu, Ag, Au) atoms adsorption on the CeO₂(111) surface have been carried out. The most stable adsorption configuration for Cu and Ag atoms is at the three-fold Od site, whereas the two-fold Ou-Ou site is true for the case of Au atom adsorption. Cu atom exhibits the largest adsorption energy followed by Ag and Au. Metal atom is oxidized to +1 valence state with its adsorption on the CeO₂(111) surface. Analysis of net magneti moment and electronic density of states indicates that for the same adsorption site, excess electron due to metal oxidization can localize on the different Ce ions. Generally speaking, the adsorption configuration, in which excess electron localizes on the surface Ce ion far from the metal, is energetically favorable. This can be understood from the occurrence of M-Ce-O bonds upon the adsorption, which in turn reasonably explains the experimental phenomenon.2. Detailed studies of metal (Cu, Ag, Au) atoms adsorption on the CeO₂(110) surface have been performed. The most stable adsorption configuration for Cu and Au atoms is two-fold O bridge (Ou-Ou) site, whereas the two-fold Ce bridge (Ce-Ce) is true for the case of Ag atom adsorption. Cu and Ag exhibit the largest and smallest adsorption energies, respectively. Metal atom adsorption on the the CeO₂(110) surface can cause its oxidization. It should be emphasized that the occurrence of Cu2+ ion on the CeO₂(110) surface is theoretically observed for the first time, thus explaining the experimental phenomenon very well. Similarly to the case of M(Cu, Ag, Au) adsorption on the CeO₂(111) surface, there exist the several electron localization configurations for the same adsorption site.