Anion metal-solution interphase

Figure 1. Schematic picture of the metal/solution interphase in the case of nonspecific (a) and specific (b) anionic adsorption, x = 0, x = P and x = d are die electrode surface plane, the plane of closest approach for the specifically adsorbed anions, and that for the nonspecifically adsorbed ions. Curve 1 represents the potential-distance profile. In (b), curve 1 results from the combination of curve 2, expressing die contribution from the charge density as of the specifically adsorbed anions, and curve 3, expressing die contribution from die charge density Om on the metal. The potential difference, ft1 — d> across die inner layer is the same in (a) and (b). (Reprinted from Ref.7 with permission from the Am. Chem. Soc.)...

In the case of a metal/solution interface, the charge on the metal is one of the signals that can be picked up. This electrode charge is mirrored on the solution side by an equal and opposite net charge constituted of separate contributions of the positive and negative charges, i.e., the relative concentrations of cations and anions in the interphase. However, are these ions on the metal or near the metal ... 

Thus, according to these theories, all univalent (1 1) electrolytes should behave the same way. However, this is not what was observed experimentally. Solutions of different 1 1 electrolytes (e.g., NaCl, NaBr, Nal, KI) show species-specific behavior. In order to interpret this specific behavior, Grahame (5) proposed a new model of the interphase the triple-layer model. The basic idea in the interpretation of the ion-specific behavior is that anions, when attracted into the interphase, may become dehydrated and thus get closer to the electrode. Each anion undergoes this to a different extent. This difference in the degree of dehydration and the difference in the size of ions results in the specific behavior of the anions. Ions that are partially or fully dehydrated are in contact with the electrode. This contact adsorption of ions allows short-range forces (e.g., electric image forces) to act between the metal elec-... 

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