Double layer structure

In situ Fourier transform infrared and in situ infrared reflection spectroscopies have been used to study the electrical double layer structure and adsorption of various species at low-index single-crystal faces of Au, Pt, and other electrodes.206"210 It has been shown that if the ions in the solution have vibrational bands, it is possible to relate their excess density to the experimentally observed surface. 

The double-layer structure of Ga and its liquid alloys was discussed by Trasatti in a chapter in this series in 19807 and by Bagotskaya in 1986.120 Other discussions can be found in books of the NATO series.25,26... 

The electrical double-layer structure at the liquid Ga/H20 interface has been studied by Frumkin and Bagotskaya et al 10,103,120,333-335 pez ... 

The electrical double-layer structure at Ga/DMF, In(Ga)/DMF, and Tl(Ga)/DMF interfaces upon the addition of various amounts of NaC104 as a surface-inactive electrolyte has been investigated by differential capacitance, as well as by the streaming electrode method.358 The capacitance of all the systems was found to be independent of the ac frequency, v. The potential of the diffuse layer minimum was independent of... 

The electrical double-layer structure and fractal geometry of a pc-Ag electrode have been tested by Se vasty an ov et al.272 They found that the geometrical roughness of electrochemically polished pc-Ag electrodes is not very high (/pz 1.5 to 1.25), but the dependence of Chtr curves on cej, as well as on/pz, is remarkable (C, =30 to 80 fi cm-2 if/pz =1.5 to 1.0). 

K. The electrical double-layer structure at Ag single-crystal faces has been studied extensively.6,10,i5,22,24,32,61,63,75,ss, 149-151,177a, 188,250-... 

The electrical double-layer structure at Au(l 11), Au(110), Au(100), and Au(210) faces and at a pc-Au electrode has been studied in 5 x 10 3 and 1 x 10-2 M LiC104 solutions in DMSO by cyclic voltammetry and impedance methods.477 The electrodes were cleaned by heating in a flame ... 

The pc-Bi/aqueous solution interface has been studied mainly by Palm et a/.666-669 Ea= and other fundamental characteristics were obtained. The electrical double-layer structure at a bismuth solid drop electrode with remelted surface (BiDER/H20) was investigated by Salve... 

Mishuk et a/.675,676 have applied the modified amplitude demodulation method to electrochemically polished pc-Bi in aqueous NaF solution. The curves of the real component of the nonlinear impedance Z" as a function of the electrode potential, unlike pc-Cd and pc-Pb, intersect for various cNaF at E - -0.62 V (SCE),674 i.e., at Ea=0 for pc-Bi, as obtained by impedance.666-672 The different behavior of pc-Bi from pc-Cd and pc-Pb at a > 0 has been explained by the semimetallic nature of pc-Bi electrodes. A comparison of inner-layer nonlinear parameter values for Hg, Cd, and Bi electrodes at a < 0 shows that the electrical double-layer structure at negative charges is independent of the metal.675,676... 

In the region of a very good correspondence has been found between experimental and calculated C,E curves and this has been taken to indicate that the electrical double-layer structure conforms to the GCSG theory. Comparison of the ChE curves for Hg/TMU and Fe/TMU shows that the dependence of Cf on E is less pronounced for an Fe electrode than for Hg/TMU, and the values of Cf for Fe are remarkably lower than for Hg. The same is the case for Fe/DMF, DMAA, MPF, and HMPA interfaces.732-736... 

First attempts to study the electrical double layer at A1 electrodes in aqueous and nonaqueous solutions were made in 1962-1965,182,747,748 but the results were not successful.190 The electrical double-layer structure at a renewed Al/nonaqueous solution of surface-inactive electrolytes such as (CH3)4NBF4) (CH3)4NC104, (CH3>4NPF6, and (C4H9)4NBF4, has been investigated by impedance.749-751 y-butyrolactone (y-BL), DMSO, and DMF have been used as solvents. In a wide region of E [-2.5 [Pg.128]

The electrical double-layer structure of a Pt/DMSO interface has been investigated using the potentiostatic pulse method.805 The value of C at E = const, as well as the potential of the diffuse layer minimum, have been found to depend on time, and this has been explained by the chemisorption of DMSO dipoles on the Pt surface, whose strength depends on time. Eg=Q has been found11 at E = -0.64 V (SCE in H2O). 

The first studies of the electrical double-layer structure at Sn + Pb and Sn + Cd solid drop electrodes in aqueous surface-inactive electrolyte solutions were carried out by Kukk and Piittsepp.808 Alloys with various contents of Pb (from 0.2 to 98%) were investigated by impedance.615,643,667,816 Small amounts of Pb caused dramatic shifts of toward more negative values. For alloys with Pb bulk content 0.2%, was the same as for pc-Pb. The was independent of Crf and frequency. C xt Cjl plots were linear, with/pz very close to unity. Thus the surface of Sn + Pb alloys behaves as if it were geometrically smooth, and Pb appears to be the surface-active component. 

CO adsorption on electrochemically facetted (Clavilier), 135 Hamm etal, 134 surfaces (Hamm etal), 134 Platinum group metals in aqueous solutions, 132 and Frumkin s work on the potential of zero charge thereon, 129 Iwasita and Xia, 133 and non-aqueous solutions, 137 potentials of zero charge, 132, 137 preparation of platinum single crystals (Iwasita and Xia), 133 Platinum-DMSO interfaces, double layer structure, 141 Polarization time, 328 Polarons, 310... 

Photoemission phenomena are of great value for a number of areas in electrochemistry. In particnlar, they can be used to study the kinetics and mechanism of electrochemical processes involving free radicals as intermediates. Photoemission measurements can be also used to study electric double-layer structure at electrode surfaces. For instance by measuring the photoemission current in dilute solution and under identical conditions in concentrated solutions (where we know that / = 0), we can find the value of / in the dilute solution by simple calculations using Eq. (29.9). 

A detailed analysis of this behavior, as well as its analogy to the mercury-KF solution system, can be found in several papers [1-3,8,14]. The ions of both electrolytes, existing in the system of Scheme 13, are practically present only in one of the phases, respectively. This allows them to function as supporting electrolytes in both solvents. Hence, the above system is necessary to study electrical double layer structure, zero-charge potentials and the kinetics of ion and electron reactions at interface between immiscible electrolyte solutions. 

The effect of the phospholipids on the rate of ion transfer has been controversial over the last years. While the early studies found a retardation effect [6-8], more recent ones reported that the rate of ion transfer is either not retarded [9,10] or even enhanced due to the presence of the monolayer [11 14]. Furthermore, the theoretical efforts to explain this effect were unsatisfactory. The retardation observed in the early studies was explained in terms of the blocking of the interfacial area by the phospholipids, and therefore was related to the size of the transferring ion and the state of the monolayer [8,15]. The enhancement observed in the following years was attributed to electrical double layer effects, but a Frumkin-type correction to the Butler Volmer (BV) equation was found unsuitable to explain the observations [11,16]. Recently, Manzanares et al. showed that the enhancement can be described by an electrical double layer correction provided that an accurate picture of the electrical double layer structure is used [17]. This theoretical approach will be the subject of Section III.C. 

The effect of the electrical double-layer structure on the rate of the electrode reaction... 

An analogous expression assuming space charge effects and the double layer structure of the anodic oxide has been obtained by Goruk et al.5 and Bray.57... 

Emersion has been shown to result in the retention of the double layer structure i.e, the structure including the outer Helmholtz layer. Thus, the electric double layer is characterised by the electrode potential, the surface charge on the metal and the chemical composition of the double layer itself. Surface resistivity measurements have shown that the surface charge is retained on emersion. In addition, the potential of the emersed electrode, , can be determined in the form of its work function, , since and represent the same quantity the electrochemical potential of the electrons in the metal. Figure 2.116 is from the work of Kotz et al. (1986) and shows the work function of a gold electrode emersed at various potentials from a perchloric acid solution the work function was determined from UVPES measurements. The linear plot, and the unit slope, are clear evidence that the potential drop across the double layer is retained before and after emersion. The chemical composition of the double layer can also be determined, using AES, and is consistent with the expected solvent and electrolyte. In practice, the double layer collapses unless (i) potentiostatic control is maintained up to the instant of emersion and (ii) no faradaic processes, such as 02 reduction, are allowed to occur after emersion. 

Figure 4. a) Model for the double-layer structure on Pt(lll) as viewed both normal to (111) plane and parallel to the (111) plane at the potential 0TOin. The potential 0ro n is defined in the voltammetry curve in b). 

Double layer emersion continues to allow new ways of studying the electrochemical interphase. In some cases at least, the outer potential of the emersed electrode is nearly equal to the inner potential of the electrolyte. There is an intimate relation between the work function of emersed electrodes and absolute half-cell potentials. Emersion into UHV offers special insight into the emersion process and into double layer structure, partly because absolute work functions can be determined and are found to track the emersion potential with at most a constant shift. The data clearly call for answers to questions involving the most basic aspects of double layer theory, such as the role water plays in the structure and the change in of the electrode surface as the electrode goes frcm vacuum or air to solution. 

The processes classified in the third group are of primary importance in elucidating the significance of electric variables in electrosorption and in the double layer structure at solid electrodes. These processes encompass interactions of ionic components of supporting electrolytes with electrode surfaces and adsorption of some organic molecules such as saturated carboxylic acids and their derivatives (except for formic acid). The species that are concerned here are weakly adsorbed on platinum and rhodium electrodes and their heat of adsorption is well below 20 kcal/mole (25). Due to the reversibility and significant mobility of such weakly adsorbed ions or molecules, the application of the i n situ methods for the surface concentration measurements is more appropriate than that of the vacuum... 

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