Toward a Realistic Surface State of Ru in Aqueous and Gaseous Environments

Identifying the surface species is critical in developing a realistic understanding of supported metal catalysts working in water. To this end, we have characterized the surface species present at a Ru/water interface by employing a hybrid computational approach involving an explicit description of the liquid water and a possible pressure of H₂. On the close-packed, most stable Ru(0001) facet, the solvation tends to favor the full dissociation of water into atomic O and H in contrast with the partially dissociated water layer reported for ultra-high-vacuum conditions. The solvation stabilization was found to reach -0.279 J m², which results in stable O and H species on Ru(0001) in the presence of liquid water even at room temperature. Conversely, introducing even a small H₂ pressure (10^-2 bar) results in a monolayer of chemisorbed H at the interface, a general trend found on the three most exposed facets of Ru nanoparticles. While hydroxyls were often hypothesized as possible surface species at the Ru/water interface, this computational study clearly demonstrates that they are not stabilized by liquid water and are not found under realistic reductive catalytic conditions.