H 2 Dissociation on Noble Metal Single Atom Catalysts Adsorbed on and Doped into CeO 2 (111)

We used density functional theory (DFT) calculations to investigate the dissociation of H2 on an Ag single atom catalyst adsorbed on the pristine CeO2 (111) surface (Ag/CeO2), or substituting a surface Ce atom on the reduced (Ag:CeO2-x) and partially hydrogenated (Ag:H-CeO2) surfaces. The initial state of the H2 dissociation reaction in the different investigated models corresponds to distinct oxidation states, +1, +2, or +3, of the Ag atom, thus allowing us to examine the influence of the charge transfers between the noble metal, the oxide, and the hydrogen atoms on the reaction pathway and activation energy. In all investigated models, the computed barrier of H2 dissociation is lowered by about 0.6 eV in comparison to that on metal-free CeO2. On Ag/CeO2 and Ag:CeO2-x, also the energy of H2 dissociative adsorption is smaller than that on metal-free ceria. These results suggest that CeO2 modified with dispersed Ag atoms is a promising anode material for proton exchange membrane fuel cells. Further comparison of our results for Ag to analogous calculations for Cu and Au single atom catalysts reveals trends in the computed barriers that can be related to the change of the metal oxidation state in the reaction.