Electric double layer at interfaces

While the formation of an electrical double layer at interfaces is a general phenomenon, the electrode-electrolyte solution interface will be considered... 

Before going further into the adsorption of surfactants at interfaces, it is advisable to discuss the so-called electrical double layer at interfaces, since this is necessary for an understanding of the electrical aspects of adsorption. 

Electric Double-Layer at Interface of Electrode and Electrolyte Solution... 

On the electrode side of the double layer the excess charges are concentrated in the plane of the surface of the electronic conductor. On the electrolyte side of the double layer the charge distribution is quite complex. The potential drop occurs over several atomic dimensions and depends on the specific reactivity and atomic stmcture of the electrode surface and the electrolyte composition. The electrical double layer strongly influences the rate and pathway of electrode reactions. The reader is referred to several excellent discussions of the electrical double layer at the electrode—solution interface (26-28). 

Pig. 3. Representation of the electrical double layer at a metal electrode—solution interface for the case where anions occupy the inner Helmholtz plane... 

Fig. 7. (a) Simple battery circuit diagram where represents the capacitance of the electrical double layer at the electrode—solution interface, W depicts the Warburg impedance for diffusion processes, and R is internal resistance and (b) the corresponding Argand diagram of the behavior of impedance with frequency, for an idealized battery system, where the characteristic behavior of A, ohmic B, activation and C, diffusion or concentration (Warburg... 

A. Watts, T. J. VanderNoot. The electrical double layer at hquid-hquid interfaces. In A. G. Volkov, D. W. Deamer, eds. Liquid-Liquid Interfaces. Theory and Methods. Boca Raton CRC Press, 1996, pp. 77-102. 

Activation Overpotential that part of an overpotential (polarisation) that exists across the electrical double layer at an electrode/solution interface and thus directly influences the rate of the electrode process by altering its activation energy. 

The electrical double layer at Hg, Tl(Ga), In(Ga), and Ga/aliphatic alcohol (MeOH, EtOH) interfaces has been studied by impedance and streaming electrode methods.360,361 In both solvents the value ofis, was independent of cei (0.01 < cucio4 <0.25 M)and v. The Parsons-Zobel plots were linear, with /pz very close to unity. The differential capacity at metal nature, but at a = 0,C,-rises in the order Tl(Ga) < In(Ga) < Ga. Thus, as for other solvents,120 343 the interaction energy of MeOH and EtOH molecules with the surface increases in the given order of metals. The distance of closest approach of solvent molecules and other fundamental characteristics of Ga, In(Ga), Tl(Ga)/MeOH interfaces have been obtained by Emets etal.m... 

The electrical double layer at a pc-Ag/aqueous solution interface has been discussed by LeiMs et al., Valette and Hamelin, and Beck et al. in many papers.24 63 67146 223 272363-368 Detailed reviews have been given by Hamelin63 and Vorotyntsev74 in this work only a few comments will be added. First, the diffuse-layer minimum in the C,E curve was obtained363... 

The electrical double layer at a pc-Au/H20 interface has been studied mainly by Clavilier and Nguyen Van Huong,213,256,457-464 Hamelin,465 167 Beck et al.,468-470 and others.471 472 Detailed reviews have been given by Frumkin,10 Hamelin,63 and Vorotyntsev.74 Only a few comments will be added here. 

The electrical double layer at pc-Zn/fyO interfaces has been studied in many works,154 190 613-629 but the situation is somewhat ambiguous and complex. The polycrystalline Zn electrode was found to be ideally polarizable for sufficiently wide negative polarizations.622"627 With pc-Zn/H20, the value of Eg was found at -1.15 V (SCE)615 628 (Table 14). The values of nun are in reasonable agreement with the data of Caswell et al.623,624 Practically the same value of Eff was obtained by the scrape method in NaC104 + HjO solution (pH = 7.0).190 Later it was shown154,259,625,628 that the determination of Eo=0 by direct observation of Emin on C,E curves in dilute surface-inactive electrolyte solutions is not possible in the case of Zn because Zn belongs to the group of metals for which E -o is close to the reversible standard potential in aqueous solution. 

The electrical double layer at BiDER/PrOH and BiDER/2-PrOH interfaces with the addition of various electrolytes (LiC104> Lil, LiSCN, KSCN) has been studied using impedance.691-693 The Emj was independent of cei and v. A weak dependence of C on v has been found at cucio4 < 0- 1 M and at a > -0.03 C m 2, and the equilibrium differential capacitance C o has been obtained by linear extrapolation of C vs. tu,/2 to co1/2 = 0. Parsons-Zobel plots at a = 0 are linear, with/pz = 1.01 0.01. The values of cf have been obtained according to Grahame and Soder-... 

Potential differences at the interface between two immiscible electrolyte solutions (ITIES) are typical Galvani potential differences and cannot be measured directly. However, their existence follows from the properties of the electrical double layer at the ITIES (Section 4.5.3) and from the kinetics of charge transfer across the ITIES (Section 5.3.2). By means of potential differences at the ITIES or at the aqueous electrolyte-solid electrolyte phase boundary (Eq. 3.1.23), the phenomena occurring at the membranes of ion-selective electrodes (Section 6.3) can be explained. 

Marynov, G. A., and R. R. Salem, Electrical Double Layer at Metal-Dilute Solution Interface, Lecture Notes in Chemistry, Vol. 33, Springer-Verlag, Berlin, 1983. 

The Electrical Double Layer at the Electrolyte-Non-metallic Phase Interface... 

The basic difference between metal-electrolyte and semiconductor-electrolyte interfaces lies primarily in the fact that the concentration of charge carriers is very low in semiconductors (see Section 2.4.1). For this reason and also because the permittivity of a semiconductor is limited, the semiconductor part of the electrical double layer at the semiconductor-electrolyte interface has a marked diffuse character with Debye lengths of the order of 10 4-10 6cm. This layer is termed the space charge region in solid-state physics. 

The situation of the electric double layer at a semiconductor/electrolyte solution interface affected by light radiation will be dealt with in Section 5.10. 

It should, however, be noted that the electrical double layer at the metal-fused electrolyte interface does not have this character, in spite of the ion concentration being high. In this system, the space charge includes several ion layers at the interface. 

Samec, Z., The electrical double layer at the interface of two immiscible electrolyte solutions, Chem. Revs, 88, 617 (1988). 

The formation of a membrane potential is connected with the presence of an electrical double layer at the surface of the membrane. For a thick, compact membrane, an electrical double layer is formed at both interfaces. The electrical double layer at a porous membrane is formed primarily in the membrane pores (see Section 6.2). The electrical double layer at thin membranes is formed on both membrane surfaces. It is formed by fixed ions on the surface of the membrane and the diffuse layer in the electrolyte. 

Another point of importance about the film structure is the degree to which it can be permeated by various ions and molecules. It is of course essential that supporting electrolyte ions be able to penetrate the film, else the electrical double layer at the electrode/polymer interface could not be charged to potentials that drive electron transfers between the polymer and the electrode. The electroneutrality requirements of porphyrin sites as their electrical charges are changed by oxidation or reduction also could not be satisfied without electrolyte permeation. With the possible exception of the phenolic structure in Fig. 1, this level of permeability seems to be met by the ECP porphyrins. 

Parsons, R. (1987), "The Electric Double Layer at the Solid-Solution Interface", in W. Stumm, Ed., Aquatic Surface Chemistry, John Wiley and Sons, New York, 33-47. 

Yates, D. E., S. Levine, and T. W. Healy (1974), "Site-binding Model of the Electrical Double Layer at the Oxide/Water Interface", J. Chem. Soc. Faraday Trans. 70,1807. 

Free Energies of Electrical Double Layers at the Oxide-Solution Interface... 

The aim of this paper is not to add to the current debate but to present a simple graphical method of analysing the free energy of formation of the electrical double layer at the oxide/solution interface ( 1). This will provide a simple way of visualizing the complementary roles of chemical reactions or surface properties of... 

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