Bubble bulk region resistances

The bubbles in the inter-electrode gap (bubble diffusion region and bulk region) increase the inter-electrode resistance, as they affect the electrical conductivity of the electrolyte. The parameter describing this increase is the gas void fraction e, defined as the fraction between the volume of gas and the total volume of liquid and gas. Several relations are used in the electrochemical literature to quantify this effect. The most widely used are the relations from Bruggeman [16] ... 

The expression for R(9) contains three contributions. The first is the resistance of the bulk electrolyte. The second is due to the bubble diffusion region. As discussed in Section 3.4, this contribution is almost constant. The third comes from the shielding effect of the bubbles growing on the electrode surface. This contribution is a function of 0. A possible ansatz for R(9) is (see also Fig. 3.11 and the corresponding discussion) ... 

Electrolytically evolved gas bubbles affect three components of the cell voltage and change the macro- and microscopic current distributions in electrolyzers. Dispersed in the bulk electrolyte, they increase ohmic losses in the cell and, if nonuniformly distributed in the direction parallel to the electrode, they deflect current from regions where they are more concentrated to regions of lower void fraction. Bubbles attached to or located very near the electrodes likewise present ohmic resistance, and also, by making the microscopic current distribution nonuniform, increase the effective current density on the electrode, which adds to the electrode kinetic polarization. Evolution of gas bubbles stirs the electrolyte and thus reduces the supersaturation of product gas at the electrode, thereby lowering the concentration polarization of the electrode. Thus electrolytically evolved gas bubbles affect the electrolyte conductivity, electrode current distribution, and concentration overpotential and the effects depend on the location of the bubbles in the cell. Discussed in this section are the conductivity of bulk dispersions and the electrical effects of bubbles attached to or very near the electrode. Readers interested in the effect of bubbles dispersed in the bulk on the macroscopic current distribution in electrolyzers should see a recent review of Vogt.31... 

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