Trends in the Adsorption and Dissociation of Water Clusters on Flat and Stepped Metallic Surfaces

Understanding the structure and chemical reactivity of water adsorbed at metallic surfaces is very important in many processes such as catalysis, corrosion, and electrochemistry. Using density functional theory calculations, we investigate the adsorption and dissociation of water clusters on flat and stepped surfaces of several transition metals: Rh, Ir, Pd, and Pt. We find that water binds preferentially to the step edges than to terrace sites, thus linear clusters or one-dimensional water wires can be isolated by differential desorption. The clusters formed at the step are stabilized by the cooperative effect of chemical bonds with the metal and hydrogen bonding. The enhanced reactivity of the step edges and the cooperative effect of hydrogen bonding improve the chances of partial dissociation of water clusters. We assess the correlations between adsorption and dissociation energies, observing that they are increased on stepped surfaces. We present a detailed interpretation of water dissociation by analyzing changes in the electronic structure of both water and metals. The identification of trends in the energetics of water dissociation at transition metals is expected to aid the design of better materials for catalysis and fuel cells, where the density of steps at surfaces would be a relevant additional parameter.