Macrokinetics of Electrochemical Processes Systems with Distributed Parameters

3 MACROKINETICS OF ELECTROCHEMICAL PROCESSES (SYSTEMS WITH DISTRIBUTED PARAMETERS) 

Electrochemical macrokinetics deals with the combined effects of polarization characteristics and of ohmic and diffusion factors on the current distribution and overall rate of electrochemical reactions in systems with distributed parameters. The term macrokinetics is used (mainly in Russian scientific publications) to distinguish these effects conveniently from effects arising at the molecular level. 

Consider a cell with one positive and two negative electrodes where the latter are at different distances, and I2, from the former (Fig. 18.3). We shall assume for the sake of simplicity that polarization of the electrodes is proportional to current density [i.e., AE = pi (p is the combined polarization resistance of the positive and negative electrodes)]. The voltages of the two halves of the cell, which are in parallel, are identical hence, the snm of ohmic losses and polarization in the two halves shonld also be identical. The ohmic losses in the electrolyte are given by IH 3. Thus, 

FIGURE 18.3 Electrochemical cell with dissimilar distances between electrodes. 

FIGURE 18.4 Concerning the derivation of equations for nonuniform current distribution (a) in a flat electrode (b) in a cylindrical pore. 

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