Specific adsorption, of anions

The effect of surface deformation in the Helmholtz layer should also be involved in Eq. (35). In consideration of specific adsorption of anions, such effects can be expressed by the potential gradient Lj y, z, as follows,... 

Teliska M, Murthi VS, Mukeqee S, Ramaker DE. 2007. Site-specific vs specific adsorption of anions on Pt and Pt-based alloys. J Phys Chem C 111 9267-9274. 

Uchida H, Ikeda N, Watanahe M. 1997. Electrochemical quartz crystal microhalance study of copper ad-atoms on gold electrodes. Part II. Further discussion on the specific adsorption of anions from the solutions. J Electroanal Chem 424 5-12. 

These experimental results demonstrate that the specific adsorption of anions leads to a significant decrease in junction stability, as illustrated in particular in the potential regions of disordered anion adsorption, as well as in the fluctuations in the plateau currents at potentials of the 2D-ordered anion adlayers. The instability of the conductance plateaus were statistically analyzed, by determining the standard... 

With this in aind the species which fits the best with the experiaental data for the anoaalous adsorption states would be a fully reversibly discharged species including transfer of one electron. It could be an adsorbed hydrogen-like species under full control of the specific adsorption of anions of the base electrolyte... 

The cyclic voitammogram for Pt (111) in 5 M sulfuric acid is shown in Fig. 2-21. Compared with that in 0.5 M sulfuric acid (Fig. 2-15), the anodic part of the two split hydrogen adsorption-desorption areas was compressed in the cathodic direction and became two sharp peaks while the cathodic part did not change its shape very much. The asymmetric peak at 700 mV shifted cathodicly and became more symmetric and sharp. The oxidation of platinum shifted about 100 mV in the anodic direction. All these changes could be attributed to the increase in specific adsorption of anions or the decrease of the activity of water as well as the pH change. 

Let us consider the case that underpotential deposition takes place at potentials where specifically adsorbed anions depart from the surface, or the removal of underpotential deposition species induces specific adsorption of anions. Then the underpotential deposition process is taken to consist of three consecutive steps (1) desorption of specifically adsorbed anions from substrate M, (2) adsorption and electron transfer of metal ions M"" to form an underpotential deposition metal layer on the substrate metal M, and (3) readsorption of the anions on the underpotential deposition metal M on M, i.e.. 

Quirk, J.P. (1968) Specific adsorption of anions on goethite. Int. Congr. Soil Sci. Trans. 

This effect is explained by the role of the specific adsorption of anions. It is assumed that the specific adsorption of C104 ions is negligible [45, 46], and no chemical changes occur in the course of the electrochemical study of anodic dissolution and corrosion of nickel [47]. 

The capacitance-potential dependences of Cd(OOOl) in dilute solutions of Cl04, N02, and NOs" were also studied [6]. A weak specific adsorption of anions increasing in the order Cl04 < N02 < N03 was observed. The adsorption of halides on the Cd(OOOl) single crystal electrode was studied [7], and was found to increase in the sequence Cl < Br < 1 [8]. Analysis of the impedance data does not point to the specific adsorption of Cl ions, and shows that the surface excess (T) of halide ions changes with potential and increases from Br to 1 (Fig. 1) [7]... 

Since specific adsorption of anions is harmful for the reconstructed surfaces, the immersion potential of the electrode should be negative to keep the surface free from the specifically adsorbed anions. In practice, it should be 0.5 to 0.6 V more negative than the zero charge potential. The influence of the anion adsorption on the potential of the reversed transition is shown in Fig. 10. 

There are a number of factors that determine crystal size. Probably the two most important are the deposition mechanism (ion-by-ion growth, in general, will result in larger crystal size than the hydroxide mechanism, discussed in detail in Chap. 3) and specific adsorption of anions onto the growing crystal (this can affect both crystal structure and size). 

In the absence of specific adsorption of anions, the GCSG model regards the electrical double layer as two plate capacitors in series that correspond respectively, to two regions of the electrolyte adjacent to the electrode, (a) An inner compact layer of solvent molecules (one or two layers) and immobile ions attracted by Coulombic forces (Helmholtz inner plane in Fig. 2). Specific adsorption of anions at the electrode surface may occur in this region by electronic orbital coupling with the metal, (b) An outer diffuse region of coulombically attracted ions in thermal motion that complete the countercharge of the electrode. 

In the presence of specific adsorption of anions other than the reactant species, the double layer correction outlined above can be extended assuming that the pre-electrode layer is still the OHP and taking into account the total electrode charge [46]. 

Studies of specific adsorption of a series of anions to be discussed in detail elsewhere (5), have shown that the maximum specific adsorption at any pH, r0(1)H>, is related to the pKD of the anion acid and the charge on the adsorbing species. From these studies essential requirements for specific adsorption of anions, or exchange of specifically adsorbed ions, seem to be as follows ... 

Adsorption processes can also lead to the development of a negatively charged particle surface. One example is the specific adsorption of anionic organic compounds onto the surfaces of particles. Another... 

The specific adsorption of anions into germanium may be represented as follows (2) ... 

Specific adsorption of anions leads to a shift of the electrode potential of germanium towards more anodic values apparently because the surface becomes less p-type. Accordingly, the effect of illumination on the potential of electrodes other than strongly p-type is decreased in the presence of anions (7). As shown in Fig. 6, a given photoeffect in the presence of 0. IN KC1 corresponds to the photoeffect exhibited by a more p-type... 

Fig. 6G Schematic representation of the structure of the double layer, (a) At very negative potentials with respect to the PZC) (b) At positive potentials, where specific adsorption of anions occurs. The Outer Helmholtz Plane is shown at a distance of...

A variant of [3.6.36] applies to the case where, say positive, charges on the surface act as the sites where specific adsorption of anions may occur, i.e. when the specific adsorption is of the second kind. Then ion pairs are formed, held together by electrostatic and non-electrostatic interactions. Defining 0 as the fraction of [Pg.309]

Situation b of fig. 3.34 is more common and is indicative of specific adsorption of cations. (For specific adsorption of anions the intersection points... 

The specific adsorption of anions at titanium dioxide (discussed in the following part of this chapter) seems to occur via the replacement of the basic OH groups. It appears difficult, at the first sight, to find a common point among the anions known to give rise to the super-equivalent adsorption on the surface of Ti02. 

The effect of anions was pronounced both on Au and on Ag. The fact that r (CO) on Au and Ag increases when halogen ions are added implies that the amount of adsorbed hydrogen may be decreased by a specific adsorption of anions to the metal electrodes. This may be the reason why t] CO) on Au and Ag depends on anions. 

---