ABSTRACT

Surfaces of metal oxides undergo hydroxylation in the presence of water molecules. Hydroxyl groups formed during this process may be coordinated by one or a few metal atoms.[1] In electrolyte solution, these groups may associate with hydronium ions but may also expel H+ by dissociation. The acid-base properties of such groups depend on the type of metal atom forming the oxide and on the number of metal atoms coordinating to the hydroxyl group. The acid-base reactions of the surface hydroxyl groups are responsible for the charge formation on the metal oxide surface in electrolyte solutions. In such systems, in addition to acid-base reactions, unbalanced adsorption or dissolution of metal ions constituting the crystal net of metal oxides and their hydroxy complexes may take place.[2-4] Surface charge is compensated in the solution layer adjoining the surface of the solid. In this range, two layers (diffuse and compact) are distinguished. The space at the interface, which consists of the surface charge and both compact and diffuse layers, is called the electrical double layer (edl).