Desorption charge transfer coefficient

For desorption (an anodic process with the charge transfer coefficient aj... 

The first equation describes the reproduction of the kink site position in the process of separation of an atom from the kink site position and formation of an ad-atom. The second step represents desorption of the ad-atom. The charge transfer is split. Following the description of partial charge transfer in Section 4.3 with the introduction of a partial charge transfer coefficient A the charge transfer in the first step is = Xz, and the charge transfer in the second step Az j = (1 — A )z. The intermediate ad-atom can be a lower valent oxidation state stabilized as an anion complex. 

II.2). In various places in the text, where generality is implied and the process concerned is not necessarily ale, single-step reaction, the transfer coefficient a is written. In the latter case, e.g., when charge transfer is involved in a rate-controlling desorption step, a factor is included in the relevant value of a (see p. 115). t Introduction of the stoichiometric number p, with a and n, in b is sometimes confusing. Some discussion of this matter is to be found in Ref. 13 and in Gileadi s contribution in Chapter 8 of the present author s monograph, Theory and Principles of Electrode Processes, Ref. 25. 

For more complex processes, e.g. in the case of the desorption steps II or III in the H2 evolution reaction, b can take limiting values of RT/(1+3)F or RT/2F, depending on the mechanism. The evaluation and interpretation of the Tafel b coefficient has played an important role in elucidation of mechanisms of multi-step electrode processes involving coupled charge-transfer and surface-chemical steps, and many cases have been worked out (26). 

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