Gold electrodes double layers

No adsorption of cytochrome c was evident at gold in a.c. impedance measurements reported by Eddowes et at ". No detectable change in the electrode double layer capacitance was found upon addition of cytochrome c to an electrolyte solution. 

Bjerrum and coworkers have assigned the three rate maxima shown in Figs. 10.7 and 10.8 to (starting from the negative potential) (a) destruction of vanadium polymeric chains (b) electric double layer effect at gold working electrode (c) stabilization of V (V) vs V (IV). These explanations are very plausible. 

Mortari, A., Maaroof A., Martin, D. and Cortie, M.B. (2007) Mesoporous gold electrodes for measurement of electrolytic double layer capacitance. Sensors and Actuators B, 123, 262-268. 

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. 

Fig. 6-96. Change in differential capacity of an interfadal double layer leading or not leading to interfadal lattice transformation in anodic and cathodic potential sweeps for a gold electrode surface (100) in perchloric add solution Ey = critical potential beyond which the interfadal lattice transforms from (5 x 20) to (1 x 1) E = critical potential below which the interfadal lattice transforms from (1 x 1) to (5 x 20) Ejm = potential of zero charge VacE = volt referred to the saturated calomel electrode. [From Kolb-Schneider, 1985.]...

Marinkovic et al. [50] have used in situ IR reflection spectroscopy to study adsorption of nitrate ions on Au(lll) electrodes. The ions were bonded to the gold surface via one of their oxygen atoms. Within the double-layer N03 formed contact ion pairs with hydronium ions. The extent of this process depended on the applied potential. 

Using reflectometry, Barten etal. [259] have investigated adsorption of quater-nized poly-2-vinyl pyridine, of a fixed charge per monomer, on a gold electrode. The total adsorbed amount of the compound decreased linearly with the double-layer potential of gold. Adsorption proceeded up to a relatively high doublelayer potential and was accompanied by a relatively high contribution of nonelectro-static interactions. 

In recent years, Burke and coworkers have found [373] that severe cathodization of pc-Au in acid solution resulted in the appearance of faradaic responses in the double-layer region. Such anomalous behavior may be explained by the presence of active gold atoms on the electrode surface. These active atoms appear as a result of the pretreatment process, when the part of inserted energy into the gold sample is retained mosdy by the surface atoms and atoms of the outer layers, in the form of various types of defects, for example, adatoms, vacancies, grain boundaries, and others. 

Fig. 14.31. Logarithm of the anodic current density-potential curves of the Q/QH2 redox couple on gold electrode covered by (x) three layers of DPPC + gramicidin,(a) five layers of DPPC + gramicidin. (Reprinted from A. Rejou-Michel, M. A. Habib, and J. O M. Bockris, Electron Transfer at Biological Interfaces, in Electrical Double Layers in Biology, M. Blank, ed., Fig. 9, p. 175, Plenum, 1986.)...

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