Diversity at the Water–Metal Interface: MetalWater Thickness and Confinement Effects

摘要

The structure and properties of water films in contact with metal surfaces are crucial to understand the chemical and electrochemical processes involved in energy-related technologies. The nature of thin water films on Pd, Pt, and Ru has been investigated by first-principles molecular dynamics to assess how the chemistry at the water–metal surface is responsible for the diversity in the behavior of the water layers closer to the metal. The characteristics of liquid water: the radial distribution functions, coordination, and fragment speciation appear only for unconfined water layers of a minimum of 1.4 nm thick. In addition, the water layer is denser in the region closest to the metal for Pd and Pt, where seven- and five-membered ring motifs appear. These patterns are identical to those identified by scanning tunneling microscopy for isolated water bilayers. On Ru densification at the interface is not observed, water dissociates, and protons and hydroxyl groups are locked at the surface. Therefore, the acid–base properties in the area close to the metal are not perturbed, in agreement withexperiments, and the bulk water resembles an electric double layer.Confinement affects water making it closer to ice for both structuraland dynamic properties, thus being responsible for the higher viscosityexperimentally found at the nanoscale. All these contributions modifythe solvation of reactants and products at the water–metalinterface and will affect the catalytic and electrocatalytic propertiesof the surface.