Adsorption-desorption peaks

Figure Bl.26.8. Adsorption/desorption peaks for nitrogen obtained with the continuous flow metiiod (Nelsen F M and Eggertsen F T 1958 Anal. Chem. 30 1387-90).

Parsons-Zobel plot for NaF solutions was linear (Table 12). The value of Cf"0,determined by the extrapolation of the Cl, Q1 curve to Cjl = 0 and corrected by the value of /pz, has been obtained (Cf 0 - 0.32 F m 2). Adsorption studies of (C l at a polished pc-Pb show splitting of the adsorption-desorption peaks, which can be explained by the energetic inhomogeneity of the surface. The difference between Ea=Q values of various Pb faces has been estimated to be on the order of50-60 mV.604... 

Studies in surface-inactive electrolyte solutions with various organic compounds (cyclohexanol, 1-pentanol, 2-butanol, camphor, tetra-buthyl ammonium ion, TBN+) show that the adsorption-desorption peak shifts to more negative potentials in the order (0001) < (1010) < (1120) this was explained by the increasing negative value of Eff=0 in the same direction.259 629-635... 

The R of electropolished Zn single-crystal face electrodes has been obtained from the shape of the adsorption-desorption peak of cyclohex-anol at various Zn and Hg surfaces.154 The roughness factor of Zn electrodes has been found to increase in the order Zn(0001) < Zn(lOlO) < Zn(llZO) with values in the range 1.1 to 1.25. 

Adsorption of aliphatic alcohols and tetra-alkylammonium cations from Na2S04 + HjO solutions on Sb electrodes has been investi-gated.721 724 Splitting of the adsorption-desorption peak into two independent maxima has been found725,726 for cyclohexanol adsorption at an electrochemically polished pc-Sb electrode accordingly, the difference between the [Pg.120]

Renewed Sn + Cd alloy surfaces have been studied by Safonov and Choba821 by impedance. The has been found to shift toward more negative E with time, suggesting that the content of Cd at the Sn + Cd alloy surface increases with time. For the alloy with 10% Cd, the time dependence of C for adsorption of organic substances is significantly different from that for Sn + Pb alloys. At relatively short times, E"1 shifts in the negative direction, which shows the increase of the Cd content in the Sn + Cd alloy surface layer. At longer times, an additional adsorption-desorption peak (step) has been observed, which has been explained by the formation of rather wide two-dimensional areas of Cd microcrystals at the alloy surface.824... 

Figure 12.5 CO stripping voltammogram with a CO- tee 0.1 M H2SO4 electrolyte. Compare the data in Fig. 12.4 the CO oxidation region begins at V = 0.43 V. After CO stripping, hydrogen adsorption/desorption peaks and the beginning of the Pt oxidation range are shown.

The dotted line represents the base current of the supporting electrolyte only adsorption at the dme of any other component (e.g., a detergent) than the solvent or ions of that electrolyte causes a lowering of the capacitance specific adsorption occurs within the lower capacity region delimited by the anodic ( t + ) and the cathodic (ET ) adsorption/desorption peaks. A more specific... 

Within the low-capacity region between the adsorption/desorption peaks around the electrocapillary maximum (ecm see Fig. 3.18), the depression of the base current is greatest because of maximum adsorption of the surfactant in that area. 

The second most widely used noble metal for preparation of electrodes is gold. Similar to Pt, the gold electrode, contacted with aqueous electrolyte, is covered in a broad range of anodic potentials with an oxide film. On the other hand, the hydrogen adsorption/desorption peaks are absent on the cyclic voltammogram of a gold electrode in aqueous electrolytes, and the electrocatalytic activity for most charge transfer reactions is considerably lower in comparison with that of platinum. 

Each of the low index Ag single crystals displayed mutually unique voltammetry curves with multiple adsorption/desorption peaks (Figure 2). The nominal features of these curves are similar to those obtained by other authors for Ag single crystal surfaces in HF or HCIO4 using both UHV and non-UHV methods (4-7). 

However the aore iaportant question which can be solved with such saaples is related to characterization of surface sites because each basal orientation shows well-characterized hydrogen adsorption-desorption peaks which eight be helpfully used for this purpose. 

In the hydrogen region (50 - 350 mV) in the first cycle, the hydrogen adsorption-desorption ciirrents were depressed because the surface was covered with COad COad oxidized to CO2 in the anodic peak between 700 mV and 1000 mV. This peak overlapped with the platiniim oxidation whose voltammogram is shown as the dashed line. After this peak the voltammogram became identical with the voltammogram without CO. The h rdrogen adsorption-desorption peaks were fully recovered. This shows the COad completely oxidized and there was no CO in the liquid phase. 

In the presence of tetrabutylammonium iodide (TBAI) in its adsorption region on the pc-Zn electrode, the edl capacitance decreased with increasing TBAI concentration and the capacity minimum shifted to more negative potentials [13]. At still more negative potentials, a well-defined adsorption- desorption peak was observed. Splitting of this peak was explained by the presence of different faces on the surface of pc-Zn electrode. 

The adsorption-desorption peaks on the single-crystal faces were narrower and higher than the peaks on the polycrystalline electrodes. 

The potential cycling illustrated by Figure 5.20 is a commonly used pre-treatment procedure for attainment of a reproducible active surface. Less widely known is the fact that in aqueous solution this cycling procedure causes the dissolution of appreciable quantities of metal. The discrepancy between the integrated anodic and cathodic oxygen adsorption-desorption peaks has been shown to be due to dissolution of the metal. Typical values are given in Ref. 68 and indicate that platinum and gold dissolve to a much lesser extent than do palladium and rhodium. 

When there are organic neutral substances on the metal side of the oHp, there is also substitution of solvent molecules by neutral molecules and metal-neutral substances interactions are observed, they could also alter the metal-solvent interactions in some cases the adsorption-desorption peaks can be observed [see Section... 

For cyclohexanol adsorption on the three faces of lowest indices of zinc (in 100 mM KCl + 0.1 mM H2SO4), C(E) curves are given in Fig. 50. Obviously, only one of the adsorption-desorption peaks is observable in the dl region. These results were shown to fit the two-parallel-capacitors model (dashed lines). For a given concentration of adsorbate, the potentials of the peak and of the maximum of adsorption shift in the same order as the pzc s in base electrolyte. From the complete analysis of the curves, all adsorption parameters were found to be co dependent.f... 

The formation of a Pb monolayer occms in three distinct potential ranges associated with the voltammetric adsorption/desorption peaks Al/Dl, A2/D2, and A3/D3. The local progress of adsorbate formation at the morphologically different domains of the non-ideal Ag(l 11) substrate can be described as follows ... 

The adsorption is accompanied by a decrease in the differential capacity C in the region of E x, the potential of maximum in adsorption. At potentials more positive or more negative than Emwc the organic adsorbate is desorbed giving rise to typical adsorption-desorption peaks. 

Deviations from the above properties have been observed attributed to various factors. For example, the reorientation of the solute molecules on the electrode surface is a factor that may disturb seriously the above picture, especially when the area covered by a solute molecule on the electrode surface changes upon reorientation. " In this case the maximum in adsorption is concentration dependent and for this reason the plots of a v.y.. E do not exhibit a common intersection point, the capacitance plots show characteristic humps in the region between the adsorption-desorption peaks, and the validity of the Frumkin isotherm is questionable. 

Cu crystallizes in the fee system. The experimental data for single-crystal CUIH2O and for PC Cu are controversial [2-5,7,44,45[. The first studies with Cu(lll), Cu(lOO), Cu(llO), and PC Cu in surface-inactive electrolyte solutions show a capacitance minimum at E less negative than the positive limit of ideal polarizability of Cu electrodes. More reliable values of cr=o for Cu single-crystal faces have been obtained by Lecoeur and Bellier [44] with EP Cu(l 11) and Cu(lOO) (Table 1). Eoresti etal. [46] have found =o = -0.93 0.01 V (SCE) for the Cu(l 10)-aqueous solution interface, and the validity of the GCSG model has been verified. As for Zn single-crystal electrodes, reliable values of cr=o have been obtained indirectly from the dependence of the adsorption-desorption peak... 

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