Water--From Interfaces to the Bulk. Concluding remarks

Orientational Water Bonding on Pt(111): Beyond the Frontier Orbital Principle

For decades, our understanding of water-metal bonding has been dominated by the frontier orbital principle in which globally stable water-metal interactions are ruled by HOMO interacting with metal surfaces. Using density functional theory calculations, herein, we have revealed that the frontier orbital principle cannot be applied to metastable water bonding on Pt(111), where the decisive role of HOMO is replaced by HOMO-1 in terms of the greatest orbital shifts and depopulations as the two different bonding indicators. Unlike the stable water configuration in which both HOMO-1 and HOMO prefer to overlap with metal states through σ-like orbital interactions, metastable configurations exhibit delicate competition or balance between σ-like and π-like orbital interactions exerted by HOMO-1 and HOMO, respectively. These findings have significantly deepened our understanding of orbital roles in water-metal bonding interactions and bridged the gap between theoretical understanding of electrified waters at electrochemical interfaces and water science on metal surfaces.

Coexistence of ice clusters and liquid-like water clusters on the Ru(0001) surface

Detailed RAIRS spectra reveal rich and varied local hydrogen bonding structures inside the two types of water clusters found on the Ru(0001) surface.

Structure and energetics of hydrogen-bonded networks of methanol on close packed transition metal surfaces

Methanol is a versatile chemical feedstock, fuel source, and energy storage material. Many reactions involving methanol are catalyzed by transition metal surfaces, on which hydrogen-bonded methanol overlayers form. As with water, the structure of these overlayers is expected to depend on a delicate balance of hydrogen bonding and adsorbate-substrate bonding. In contrast to water, however, relatively little is known about the structures methanol overlayers form and how these vary from one substrate to another. To address this issue, herein we analyze the hydrogen bonded networks that methanol forms as a function of coverage on three catalytically important surfaces, Au(111), Cu(111), and Pt(111), using a combination of scanning tunneling microscopy and density functional theory. We investigate the effect of intermolecular interactions, surface coverage, and adsorption energies on molecular assembly and compare the results to more widely studied water networks on the same surfaces. Two main factors are shown to direct the structure of methanol on the surfaces studied: the surface coverage and the competition between the methanol-methanol and methanol-surface interactions. Additionally, we report a new chiral form of buckled hexamer formed by surface bound methanol that maximizes the interactions between methanol monomers by sacrificing interactions with the surface. These results serve as a direct comparison of interaction strength, assembly, and chirality of methanol networks on Au(111), Cu(111), and Pt(111) which are catalytically relevant for methanol oxidation, steam reforming, and direct methanol fuel cells.

A molecular perspective of water at metal interfaces

Water/solid interfaces are relevant to a broad range of physicochemical phenomena and technological processes such as corrosion, lubrication, heterogeneous catalysis and electrochemistry. Although many fields have contributed to rapid progress in the fundamental knowledge of water at interfaces, detailed molecular-level understanding of water/solid interfaces comes mainly from studies on flat metal substrates. These studies have recently shown that a remarkably rich variety of structures form at the interface between water and even seemingly simple flat surfaces. In this Review we discuss the most exciting work in this area, in particular the emerging physical insight and general concepts about how water binds to metal surfaces. We also provide a perspective on outstanding problems, challenges and open questions.