Pd4O3 Subsurface Oxide on Pd(111) Formed during Oxygen Adsorption-Induced Surface Reconstruction and Its Activity toward Formate Oxidation Reactions

Surface reconstruction and surface oxide formation on Pd(111) facet are investigated using density functional theory calculations coupled with particle swarm optimization (PSO) algorithms, and a series of surface oxides and isomers are obtained and evaluated for the catalytic activity toward formate oxidation reactions for the first time. A globally stable Pd4O3 subsurface oxide is identified on Pd(111) facet during the oxygen adsorbed-induced surface reconstruction and featured by three subsurface oxygen atoms. The Pd(111) surface during the surface reconstruction undergoes two phase transitions starting from the oxygen-adsorbed surface to the surface oxide with an activation energy barrier of 0.366 eV and then to the Pd4O3 subsurface oxide with an activation energy barrier of 0.231 eV. During the formate oxidation reaction, the limiting potentials for the Pd(111) clean surface, Pd(111) oxygen-adsorbed surface, Pd4O3 surface oxide, and Pd4O3 subsurface oxide are 0.612, 0.232, 0.828, and 0.141 eV, respectively, indicating that the catalytic activity is suppressed when the surface is oxidized to form Pd4O3 surface oxide and then enhanced as Pd4O3 subsurface oxide further forms. The reconstructed Pd4O3 subsurface oxide has the highest activity among various Pd4Ox (x = 1–4) (sub)surface oxides and isomers. Overall, this work identifies a previously unknown surface reconstruction on Pd(111) facet and proposes a mechanism of oxygen-induced surface reconstruction on Pd(111) facet and a new strategy to identify active species for reconstructed electrocatalysts in the formate oxidation reactions.