Ideal polarizable electrode description

The thermodynamic description of the boundary layer between electrode and electrolyte is usually based on the application of Gibbs s fundamental equation to the double layer. For this application the surface region is considered as a separate phase called the interphase (Figure 4.3). In the following description it is assumed that no Faradaic current between the electrode and the electrolyte is possible, which means no reduction or oxidation can occur. This is called an ideally polarizable electrode. ... 

Two limiting cases for the description of an electrode are the ideally polarizable electrode and the ideally nonpolarizable electrode [8, 9, 14], The ideally polarizable electrode corresponds to an electrode for which the Zfaiadaic element has infinite resistance (i.e., this element is absent). Such an electrode is modeled as a pure capacitor, with Cdi = Aq 6V (equation 26), in series with the solution resistance. In an ideally polarizable electrode, no electron transfer occurs across the electrode/electrolyte interface at any potential when current is passed rather all current is through capacitive action. No sustained current flow is required to support a large voltage change across the electrode interface. An ideally polarizable electrode is not used as a reference electrode, since the electrode potential is easily perturbed... 

Although this description is frequently given of the semiconductor-solution junction, in fact, such reversible behavior of a semiconductor electrode is rarely found, especially for aqueous solutions. This lack of equilibration can be ascribed to corrosion of the semiconductor, to surface film (e.g., oxide) formation, or to inherently slow electron transfer across the interface. Under such conditions, the behavior of the semiconductor electrode approaches ideal polarizability (see Section 1.2). 

A subsequent description by Bockris and associates drew attention to further complexities as shown in Figure 15. The metal surface now is covered by combinations of oriented structured water dipoles, specifically adsorbed anions, followed by secondary water dipoles along with the hydrated cation structures. This model serves to bring attention to the dynamic situation in which changes in potential involve sequential as well as simultaneous responses of molecular and atomic systems at and near an electrode surface. Changes in potential distribution involve interactions extending from atom polarizability, through dipole orientation, to ion movements. The electrical field effects are complex in this ideal polarized electrode model. 

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