Adsorbed charge-transfer process with

Note that the resistance R,j> is an integral part of the physical phenomenon that gives rise to the formation of the adsorption pseudocapacitance. It is a Faradaic resistance, since C< > is due to a charge-transfer process. The association of this charge-transfer process with the formation of an adsorbed intermediate, which can proceed only xmtil the appropriate coverage has been reached, is manifested by placing the resistor in series with the capacitor. It should also be borne in mind that both Cequivalent circuits representing the electrochemical interface... 

Sluyters and coworkers [38] have studied the catalytic influence of adsorbed iodide ions on the electroreduction of Zn(II) on the mercury electrode. It was found that the charge-transfer process proceeds through two consecutive one-electron transfer steps. Logarithms of the rate constant of both steps are linearly dependent on the amount of adsorbed iodides (Fig. 2). The experimental data were compared with the existing theoretical anion-binding model used to describe the observed results. 

Chemisorption of hydrogen — Process leading to the formation of strongly bound (chemisorbed) hydrogen atoms on an adsorbent (mostly on metal) either via the dissociative adsorption of molecular hydrogen (H2) or, in the case of electrified interfaces, by charge transfer process occurring, for instance, with H+(H30+) or H20 species... 

A relatively constant Tafel slope for reactions not involving adsorption, and those involving adsorption with complete charge transfer across the double layer, distorted by second order effects, may also be explained in terms of a non-Franck-Condon process. Since adsorbed intermediates in charge transfer processes also show adsorption energies depending on potential in the same way as the potential energy barrier maxima, these should also follow the same phenomena. 

The equivalent circuit must usually include a solution resistance, / , in series with the combination of Qi and Rp. For the case of a charge-transfer process producing an adsorbed intermediate which can be desorbed (D) in a following step whose rate is characterized by a second reciprocal resistance Rd the equivalent circuit is written as... 

Reactions of hydrocarbons or the gases H2 and NH3 when adsorbed and illuminated on these high surface catalysts have been interpreted [74b] in terms of reaction with the O (cus) species produced by the intramolecular charge-transfer process indicated in eqn. (15). 

To summarize, in situ IR spectroscopy allows the adsorption of organic molecules at semiconductor electrodes to be studied with a sensitivity on the order of 0.1 ML and provides information not only on the chemical identity of the surface species and their orientation but also on the nature of the charge transfer processes at the interface and the surface hydrophobicity/hydrophilicity. Because of the instability of adsorbed xanthate, the surface composition of the electrode after decoupling from the electrochemical system differs from that existing under an applied potential. 

FIGURE 4.3.19. Equivalent circuit representation of an electrode-solution interface for a simple charge-transfer process. (A) Without adsorbed intermediates, and (B) with adsorbed intermediates. 

Thus, the equivalent circuit consists of a solution resistance, / s. in series with the double layer capacitance, Qi, and /fp, the Faradaic resistance associated with the charge-transfer process. However, if an adsorbed intermediate is involved in the charge-transfer process, such as ... 

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