Water adsorption and the wetting of metal surfaces

Water adsorption at metal surfaces is governed by a subtle balance between water–water hydrogen bonding and water–metal interactions, which together determine the stability of the water structures formed. This review describes recent experimental and theoretical studies of water and OH/water coadsorption on well-defined single crystal metal surfaces, systems that have seen an upsurge in interest as new results modify our picture of how water adsorbs on metal surfaces. These results reveal that the simple, conventional ice ‘bilayer’ description of water adsorption, in which water is only marginally distorted from its bulk ice arrangement, is inadequate to describe wetting. Instead, optimisation of the water–metal interaction distorts the local hydrogen bonding geometry of water monolayers significantly from that of bulk ice, with consequent effects on the lateral size and geometry of ice clusters, on the structure of water monolayers and on the wetting of first layer water and growth of ice multilayers. Here we compare adsorption across different metal surfaces, review evidence for the formation of mixed OH/H2O co-adsorption structures and highlight issues that remain uncertain.