Electrochemical Langmuir-type adsorption

When a prior discharge step producing the adsorbed intermediate, for example, H in the HER, can be considered in quasi-equilibrium when the desorption step is rate controlling (an experimentally encountered situation at a number of metals), 6 is expressed by an electrochemical Langmuir-type adsorption relation ... 

Such a model should be as simple as possible, without however missing any of the underlying thermodynamic and physicochemical factors which cause electrochemical promotion. In particular it will be shown that even the use of Langmuir-type adsorption isotherms, appropriately modified due to the application of potential (or equivalently by the presense of promoters) suffice to describe all the experimentally observed rules G1 to G7 as well as practically all other observations regarding electrochemical promotion including the effect of potential on heats of adsorption as well as on kinetics and reaction orders. 

Using the values of kinetic parameters proposed in the seminal paper by Sepa et al. (1981), gives ac - yh+ = -1 /2, under both Temkin- and Langmuir-type adsorption conditions. This means that the net effect of increasing solution phase potential and decreasing proton concentration on the rate of the ORR and on Teiec is negative. In other words, an increase in proton concentration C + at the pore wall along with a decrease in has a net positive impact on electrochemical performance. It is, thus, of primordial importance to understand the factors that influence the proton affinity of the channel. 

Ferrocene-based Linear Polymers. The first derivative that was studied from the electrochemical point of view was polyvinylferrocene (PVF). As illustrated in Figure 25, it displays a single oxidation process, which in some solvents is affected by problems of adsorption of the oxidation product (though not of the ideal Langmuir isotherm type discussed in Chapter 2, Section 1.6). 

The kinetics of tiiis reaction were also found to follow a Langmuir-Hinshelwood type behavior, with competitive adsorption of C2H4 and oxygen. A comparative kinetic diagram for all the supported Rh catalysts is given in Fig. 4. The dashed lines indicate an abrupt drop in the ethylene combustion rate which is probably due to surface oxide formation. The same behavior was also observed in the electrochemical promotion (NEMCA) experiments, as briefly discussed below and further described elsewhere [22]. 

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