Double-layer properties

When we discussed the double-layer properties of metal electrodes in contact with an electrolyte solution, we introduced the notion of an ideally polarizable interface, which is marked by the absence of charge- 

The capacitances C and C 2 of the two phases can be obtained from the Gouy-Chapman theory treated in Chapter 3. We only have to note that the potentials in the bulk of the two phases are not zero (we could set one of them equal to zero). So we replace / (()) in Eq. (3.11) by pf — (p°°, where i = 1,2, and (f f denotes the potential in phase i at the interface. This gives for a z-z electrolyte  

The inner potentials f have to be calculated by solving the Poisson-Boltzmann equations for the potentials this is done in Appendix A. 

The potentials (f j on the two sides of the interface can differ by an interfacial dipole potential. If this changes with the applied potential it gives an extra contribution to the interfacial capacity, and Eq. (12.9) must be replaced by  

On the whole, the Gouy-Chapman theory seems to work well for ITIES, indicating that any contribution from the dipole potential is small. In particular the interfacial capacity exhibits a minimum at the potential of zero charge for low electrolyte concentrations (see Fig. 12.3). 

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Hamelin, A. Double-Layer Properties at sp and sd Metal Single-Crystal Electrodes 16... 

Lead, electrical double layer properties, tabulated, 96... 

Non-situ and ex situ studies can provide important information for understanding the properties of metal/electrolyte interfaces. The applicability of these methods for fundamental studies of electrochemistry seems to be firmly established. The main differences between common electrochemical and UHV experiments are the temperature gap (ca. 300 vs. 150 K) and the difference in electrolyte concentration (very high concentrations in UHV experiments). In this respect, experimental research on double-layer properties in frozen electrolytes can be treated as a link between in situ experiments. The measurements of the work functions... 

Although it was elear that separation of an interface into surface and bulk components as in Eq, (19) is artifieial and must disappear in a consistent microscopic analysis, electronic effects were initially diseussed in terms of a compact layer and its capacitance C, It was apparent early on that the eleetrons strongly influence double layer properties [28-33],... 

Many of the processes that are familiar from ordinary electrochemistry have an analog at ITIES so these form a wide field of study. We limit ourselves to a brief introduction into a few important topics thermodynamics, double-layer properties, and charge-transfer reactions. Further details can be found in several good review articles... 

Davis, J. A., James, R. O. and Leckie, J. O. (1978). Surface ionization and complexation at the oxide/water interface. I. Computation of electrical double layer properties in simple electrolytes, J. Coll. Inter/. Sci., 63, 480-499. 

Fig. 4.16 provides an illustration of the adsorption of a neutral polymer, polyvinyl alcohol, on a polar surface, and the resulting effects on the double layer properties. Adsorption of anionic polymers on negative surfaces - especially in the presence of Ca2+ or Mg2+ which may act as coordinating links between the surface and functional groups of the polymer - is not uncommon (Tipping and Cooke, 1982). 

Harding, I. H., and T. W. Healy (1985), "Electrical Double Layer Properties of Amphoteric Polymer Latex Colloids", J. Coll. Interf. Sd. 107, 382-397. 

What is the likely future use of MC and MD techniques for studying interfacial systems Several promising approaches are possible. Continued investigation of double layer properties, "hydration forces", "hydrophobic effects", and "structured water" are clearly awaiting the development of improved models for water-water, solute-water, surface-water, and surface-solute potentials. 

From the preceding contributions in this volume it is evident that the techniques of modelling the electrical double layer properties at the oxide/electrolyte interface have been well developed (2, 11). However, the problem still contains a certain amount of " art form in the sense that there is more than one school of thought as to how the various modelling techniques should be applied. 

Since the metal can be treated as a nearly perfect conductor, C is high compared with C, and cannot influence the value of the measured doublelayer capacitance. The role of the metal in the double layer structure was discussed by Rice, who suggested that the distribution of electrons inside the metal decides the properties of the double-layer. This concept was later used to describe double-layer properties at the semiconductor/electrolyte interface. As shown later, the electron density on the metal side of the interface can be changed under the influence of charged solution species (dipoles, ions). ... 

Double-layer properties in aqueous, propylene carbonate and formamide solutions have been studied at room temperature for liquid Ga-Pb alloy (0.06 atom % of Pb) [15], as a model of Pb electrode with renewable surface. The electrode behaves as an ideally polarizable electrode in a wide potential range, and its capacitance is intermediate between that of Ga and Hg electrodes and is independent of the solvent. This electrode is much less lipophilic than Ga. Adsorption of anions on this electrode increases in the sequence -BP4 = S042 < Gl < Br < r. 

Surface and Double-layer Properties An extensive, recent review on electrochemical properties of the (polycrystalline) pc-Ag/solution interface, together... 

Surface and Double-layer Properties Valette [19] has analyzed earlier experimental data on the inner-layer capacity at PZC for Ag(lll), Ag(lOO), and Ag(llO) surfaces in order to estimate the surface area and capacitance contributions of superficial defects for real electrodes, as compared to ideal faces. Considering the application of surface spectroscopy techniques to single-crystal Ag electrodes, one should note that anisotropy of the SHG response for metal electrode allows one to analyze and correlate its pattern with interfacial symmetries and its variations by changing nonlinear susceptibility and the surface structure. Early studies on Ag(lll) single-crystal electrodes have... 

The differences between various Ag surfaces can be distinguished by comparing their surface morphology (generally, the surface of (110) crystal is more folded than that of (111)) and other properties, such as the surface density of atoms, the PZC, and double-layer capacitance. The double-layer properties of single-crystal Ag electrodes have been studied very intensively [3, 22-27]. Selected characteristics of various Ag surfaces are compared in Table 1, which shows that the higher the surface density of atoms, the more positive PZC becomes. Furthermore, Fig. 2 exemplifies differential capacity data of those Ag surfaces. 

Double-layer Properties of Hg/Nonaqueous Media Interface. 961... 

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