Properties of Electrodes and Biological Membranes

The interfacial properties of metal electrodes in contact with aqueous solutions, usually containing electrolytes, have been the focus of considerable attention. The majority of this work has used mercury for the electrode phase but recent attention has been increasingly focused on solid 

Nonspecifically adsorbed ions are those ions which retain their primary solvation shells and which are concentrated adjacent to the electrode surface due to electrostatic forces only. However, because of thermal motion, the nonspecifically adsorbed ions are actually distributed in a layer extending some distance from the electrode surface. This layer is called the diffuse layer, and 

Another very important property of a given electrode/solution interface with regard to its structure and functioning is its potential of zero charge (pzc). This is the unique value of electrode potential at which the excess charge on the electrode is zero. Acquisition of pzc data for solid electrodes is dependent on the chemical nature of the electrode surface, and wide variations in pzc values for electrodes of the same metal in identical solutions have been reported. 

Brief consideration is now given to the solvent structure at metal/aqueous electrolyte interfaces.Several molecular models have been proposed which treat a single layer of water molecules at the metal surface. Within the layer, the individual water molecules (or clusters of molecules) are allowed to have certain orientations. In the earliest and simplest molecular model, an inner-layer water molecule is oriented as a result of its dipole interaction with the charge on the metal electrode. Orientation is limited to either of the two positions in which the molecular dipole is perpendicular to the electrode surface. More realistic treatments have since been described which variously 

The interfacial water structure at a metal electrode has also been considered in terms of the hydrophobic/hydrophilic nature of the metal as commonly determined through contact angle measurements. Hydrophilic electrodes that are readily wetted by water result in water structuring at the electrode surface that is believed to be different from that which occurs at more hydrophobic electrodes. The history of an electrode can result in divergent results with respect to the hydrophilic properties of its surface. Gold has recently been shown to be hydrophilic when the surface is clean.Exposure to ambient laboratory atmosphere alters this property and this may account for conflicting reports which have addressed this question. 

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