Abstract
The ubiquity of aqueous solutions in contact with charged surfaces and the realization that the molecular-level details of water-surface interactions often determine interfacial functions and properties relevant in many natural processes have led to intensive research. Even so, many open questions remain regarding the molecular picture of the interfacial organization and preferential alignment of water molecules, as well as the structure of water molecules and ion distributions at different charged interfaces. While water, solutes and charge are present in each of these systems, the substrate can range from living tissues to metals. This diversity in substrates has led to different communities considering each of these types of aqueous interface. In this Review, by considering water in contact with metals, oxides and biomembranes, we show the essential similarity of these disparate systems. While in each case the classical mean-field theories can explain many macroscopic and mesoscopic observations, it soon becomes apparent that such theories fail to explain phenomena for which molecular properties are relevant, such as interfacial chemical conversion. We highlight the current knowledge and limitations in our understanding and end with a view towards future opportunities in the field.
Highlights
Water in contact with charged interfaces is relevant to a plethora of geological, atmospheric and biological processes, as well as technological applications such as in drug design, bioimplants, energy production and storage devices
In oxide-based photocatalytic water splitting, H2 is produced from H2O on the surface of a metal oxide electrode on irradiation, and the photocatalytic activity is strongly affected by surface speciation and solution pH, which, in turn, affect the surface charge[16,17,18,19,20]
Based on the chemistry of the interface, the systems can be divided into three categories: (1) inorganic compounds, characterized by a mechanically stiff interface, with localized surface charges; (2) biomembranes ormolecules that have a deformable interface with localized charges; and (3) metals in which the charge is delocalized
Summary
Abstract | The ubiquity of aqueous solutions in contact with charged surfaces and the realization that the molecular-level details of water–surface interactions often determine interfacial functions and properties relevant in many natural processes have led to intensive research. While several recent reviews have examined the behaviour of water in one of these systems separately[8,29,30,32,33,34,36,37,38,39,40,41], by considering them together, we aim to develop a more unified framework for water at charged interfaces, highlighting the current knowledge and limitations in our understanding Such a unified framework requires understanding elementary processes as well as the characteristic length scales and timescales that span more than ten orders of magnitude. We start by providing a historical overview of the classical mean-field models used to describe charged surfaces in contact with an aqueous electrolyte solution and continue by detailing the different components of the system: the charged interface, water and ions. The description of equilibrium properties of many aqueous solution–charged interfaces becomes challenging, and describing such systems under non-equilibrium conditions makes their
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