Adsorption, at electrodes

Adsorption at electrodes is universally considered to be a solvent replacement reaction90,906,907 ... 

Bauer, H. H. Critical Observations on the Measurement of Adsorption at Electrodes 7... 

Elving, P. J. Enyo, M. Critical Observations on the Measurement of Adsorption at Electrodes Mechanism of the Hydrogen Electrode Reaction as Studied by Means of Deuterium as a Tracer 7... 

Since the electrolyte is a condensed phase, adsorption at electrodes, unlike at the solid—gas phase interface, is a process of replacement of specifically adsorbed solvent molecules or ions at the interface. 

Parsons distinguishes four limiting cases of adsorption at electrodes with the real situations often crossing the classification boundaries [94] (a) purely electrostatic adsorption, (b) specific ionic adsorption, (c) adsorption of uncharged species (but including dipoles) and (d) chemisorption. 

For a detailled discussion on adsorption at electrodes the reader is referred to refs. 96—98. 

A number of related non-ideal adsorption isotherms have been proposed in order to fit experimental data of adsorption at electrodes and a review is presented in ref. 107. Recently, a simplified molecular theory of solute adsorption at polarizable electrode interface has been presented by Fawcet and Nobriga [108]. 

Fawcet has recently applied a simple molecular theory of solute adsorption at electrodes to the kinetics of electrode reactions under the effect of SAS [125]. 

We conclude that changing anion adsorption at electrodes with temperature can, in some cases, lead to unconventional behavior of Tafel s b coefficient but this is not the only reason for such anomalies, especially in cathodic reactions where potential ranges for appreciable currents are negative to the pzc of the electrode material concerned. 

Application of the foregoing relations to the study of adsorption at electrode surfaces requires an understanding of the electrochemical processes at electrode-solution interfaces. Consider an electrode in contact with a solution containing electroactive species along with supporting electrolytes. Two important processes occur at the electrode surface a faradaic process in which electrons are transferred across the electrodesolution interface (oxidation-reduction reaction). As a result of these reactions current flows through the medium. Adsorption-desorption is... 

According to the Ref. [42, acid anions, such as Cl, CIO, HSO participate directly in the process platinum nanocluster dissolution in electrolytes and change their rates. The ability to dissolution depends not only on the strength of chemical bond of surface atom and adsorption complex but also on the degree of adsorption weakening of bonds between surface atom and its nearest surroundings. In other words, a metal cation departure from the surface follows after specific ion adsorptions at electrodes. Metal surface atom, which interacts with an ion, chemisorbed from solution, do not belongs to the crystal lattice, but still has no stable bond with complex, more or less soluble. 

Adsorption at electrodes is considered to be a solvent replacement reaction B(sol) -H H20(ad) -e- B(ad) - - H20(sol), where B is an adsorbing substance replacing n water molecules on the electrode surface [1, 4, 5, 71, 72]. Adsorption will affect the PZC since water dipoles are replaced by adsorbate dipoles. On the other hand, the Gibbs energy of adsorption for a given adsorbate B can be divided into several contributions AG = Gm-b-Gb-s-Gm-s. where S stands for solvent and G is the bond strength. If the same adsorbate is studied on different metals in the same solvent, then Gb-s const. Furthermore, if only physical adsorption occurs, Gm-b ... 

The practical aspects of electrocatalysis (fuel cell-oriented research) required data on the specific adsorption at electrodes with high real-surface area, while for theoretical considerations, results obtained with well-defined electrode surfaces (single-crystal surfaces) were of great importance. 

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