Volta potentials transfer

Knowledge of the Volta potential of a metal/solution interface is relevant to the interpretation of the absolute electrode potential. According to the modem view, the relative electrode potential (i.e., the emf of a galvanic cell) measures the value of the energy of the electrons at the Fermi level of the given metal electrode relative to the metal of the reference electrode. On the other hand, considered separately, the absolute value of the electrode potential measures the work done in transferring an electron from a metal surrounded by a macroscopic layer of solution to a point in a vacuum outside the solotion. ... 

Constant A in Eqs. (29.5) and (29.6) is about 4.4 eV when the standard hydrogen electrode is used as the reference electrode. This value has been determined from experimental values for the electron work function of mercury in vacuum, which is 4.48 eV, and for the Volta potential, between the solution and a mercury electrode polarized to = 0 V (SHE), which is -0.07 V (the work of electron transfer is 0.07 eV). The sum of these two values, according to Eq. (9.8), corresponds to the solution s electron work function at this potential (i.e., to the value of constant A with an inverted sign). 

Vii ial equation of state in two dimensions, 931 Virial isotherm, 936 Visible radiation, 797 Volcanoes, in electrocatalysis, 1284 Volmcr, Max, 1048,1474 Volmer. Weber, electrodeposition. 1303. 1306 Volta, 1423, 1455 Volta potential difference, 822 Voltammetry. 1432 1434 cyclic, 1422 1423 diffusion control reactions, 1426 electron transfer reaction, 1424... 

The crucial point is that the difference of potential available to effect electrode reactions and surmount activation barriers is not simply the difference between the Galvani potential (i.e. the Fermi energy) and the potential in solution. On the side of the solid it is the Volta potential and on the side of the solution it is the potential at the inner Helmholtz plane, where species have to reach to in order for electron transfer to be possible. Corrections to rate constants for the latter are commonly carried out using the Gouy-Chapman model of the electrolyte double layer and will be described in Section 6.9. 

Volta potentials are potentials Just beyond the range of chemical forces so that the work of transfer of a charge from a reference at infinite distance, but in the same phase, to the point where yf is measured, is purely electrostatic. For a phase a in contact with air, y/ is obtainable by bringing an electrode just outside the surface, making the gap conducting by adding a radioactive ionic substance. See flg. 3.38, point A and fig. 3.75. Similarly, y/ is the Volta potential in B, and y/ - y/ = v (B)- v/(A). Further, is the Volta potential at E, etc. 

The corrosion potential, defined by the rate of the electrochemical reactions, is a relevant property of corrosion reactions at the metal/adhesive interface as it reflects the kinetics of the electron-transfer and ion-transfer reactions. Depending on the system being observed, correlations exist between the measurable Volta potential difference and the corrosion potential. 

Case and Parsons used the volta potential measurements directly to measure real free energies of transfer of an ion from water to a given solvent, i.e. 

Fig. 1.2.2 (a) Schematic situation at the border of a phase with vacuum. is the outer electric potential of phase a, i.e., the work that must be done when a unit charge is transferred from infinity (in the vacuum) to the surface of phase a. (The difference in the two outer electric potentials of two different phases is called the Volta potential difference.) x is the surface electric potential of phase a, i.e., the work to be done when a unit charge is transferred from the surface into phase a, and is the inner electric potential of phase a, i.e., the work to be done when a unit charge is transferred from infinity (in vacuum) into the inner of phase a. is a nonmeasurable quantity, whereas 1 can be calculated and measured. The three potentials are interrelated as follows (j> = + x -... 

The observed Volta potential does not change at a sufficiently large buffer capacity of the solution (from 5 to 100 mM Tris-HCI) [47,48]. This indicates that the potential shift at the octane/water interface results from electron transfer across the interface and not from the pH change in the boundary layer. During a redox reaction on BLM containing chlorophyll, a layer adjacent to the membrane is formed with a proton concentration different from that in the bulk phase [7, 38]. Boguslavsky et al. [47,48]... 

The aim of this chapter is to provide a short review covering the present state of research and knowledge, as well as the problems concerning electrochemistry of liquid interfaces at equihbrium. These systems are best described by mutually related chemical parameters, such as ion transfer energy, A%Gi, and electrical parameters, such as Galvani and Volta potentials, A cp and A%,xp, where s and w refer to the system consisting of organic and aqueous phases mutually saturated. It is well known that both these potentials can be correlated with the difference of surface potentials of the s... 

The phenomenological theory of catalytic charge transfer across the interface between two immiscible hquids [23-25] implies that in the absence of side reactions, the Volta potential shift in chain (13) in the case of catalytic charge transfer across the interface is expressed by the formula ... 

During the water photooxidation reaction by chlorophyll involving proton transfer across the interface, a boundary unstirred layer is formed, enriched in products. The dependence of the Volta potential on the pH of the incubation medium was measured. It proved that A

on the incubation time at different buffer concentrations measured at the initial pH 5.9. If during the reaction of Eq. (20) a boundary unstirred proton-enriched layer is formed, then with decreasing buffer capacity, the photopotential value decreases due to pheophytinization of chlorophyll [67]. 

The use of the phrase just outside the sample for the definition of the work function is unimportant for the case of an uncharged sample, where the energetic position just outside the sample is the same as far away from it, i.e. it is equivalent with the vacuum level. But usually the sample is charged and then an additional work component is required to transfer the electrrai from just outside the surface to a position infinitely far away e ff, where xjr is the Volta potential, which is equivalent for the potential drop from the infinity to a position just outside the surface. The Volta potential is due to surface charges see Fig. 15.1. 

---