Decisive role of the energetics of dissociation products in the adsorption of water on O/Ru(0001)

Using density-functional theory we found that, depending on coverage, coadsorbed oxygen can act both as a promoter and as an inhibitor of the dissociation of water on Ru(0001), the transition between these two behaviors occurring at ∼0.2 ML. The key factor that determines this transition is the adsorption energy of the reaction products, OH in particular. The chemistry of this coadsorbed system is dictated by the effective coordination of the Ru atoms that participate in the bonding of the different species. In particular, we observed that a low coverage of oxygen increases the adsorption energy of the OH fraction on the Ru surface. This surprising extra stabilization of the OH with the coadsorption of oxygen can be understood in the context of the metallic bonding and could well correspond to a general trend for the coadsorption of electronegative species on metallic surfaces.
We acknowledge support from the Basque Departamento de Educación, UPV/EHU Grant No. IT-366-07, the Spanish Ministerio de Educación y Ciencia Grant No. FIS2007-66711-C02-02, and ETORTEK research contracts funded by the Basque Departamento de Industria and the Diputación Foral de Guipuzcoa. The work at the Berkeley Lab was supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The work of A.M. was financed by the Marie Curie Outgoing International Fellowship, Project No. 514412.