Nemstian diffusion layer

The mass transport coefficient is, in general, a complex time and potential-dependent function through the linear diffusion layer thickness, <% ,. Only under certain conditions does this dependence disappear (as, for example, for nemstian... 

It is important to note that Eq. (3.38) obtained with this treatment (based on the consideration that the diffusion layer corresponding to a non-nemstian electrode process coincides with that corresponding to a reversible one) can also be directly deduced from Eq. (3.17) if Fix) is replaced by its simplified form given by Eq. (E.10) (which is valid for x < 0.185 and x > 19.7 with an error smaller than 5 % see Appendix E) ... 

This approximate treatment predicts a diffusion layer that grows with and a current that decays with In the absence of convection, the current continues to decay, but in a convective system, it ultimately approaches the steady-state value characterized by (0 = (Figure 1.4.6). Even this simplified approach approximates reality quite closely equation 1.4.34 differs only by a factor of 2/7t from the rigorous description of current arising from a nemstian system during a potential step (see Section 5.2.1). 

Recall that Nemstian behavior of diffusing species yields a r1 /2 dependence, hi practice, the ideal behavior is approached for relatively slow scan rates, and for an adsorbed layer that shows no intermolecular interactions and fast electron transfers. 

The peak current, and indeed the current at each point on the wave, is proportional to V, in contrast to the dependence observed for nemstian waves of diffusing species. The proportionality between i and v is the same as that observed for a purely capacitive current [see (6.2.25)], and this fact has led to some treatments of adsorption in terms of pseudocapacitances (32, 34). The area under the reduction wave, corrected for any residual current, represents the charge required for the full reduction of the layer, that is, nFATQ. The anodic wave on scan reversal is the mirror image of the cathodic wave reflected across the potential axis. For an ideal nemstian reaction under Langmuir isotherm conditions, and the total width at half-height of either the cathodic or anodic... 

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