Commensurate water monolayer at the RuO2(110)/water interface

We demonstrate the presence of two types of commensurate, registered water monolayers with different densities at the RuO2(110)/bulk-water (0.1 M NaOH solution) interface with off-specular, oxygen crystal truncation rods. At anodic potentials (close to oxygen evolution), the extraneous water layer and the surface hydroxide layer form a bilayer with O-H-O bond distances similar to that of ice X. At cathodic potentials, the water molecules converted from the bridging OH molecules form a low-density water layer.