Electrical Effects of Bubbles on Electrodes

Just as bubbles dispersed in the bulk electrolyte increase ohmic losses and alter the macroscopic current distribution within elec- 

The first term on the right-hand side of Eq. (16) is the ohmic potential difference between any point on the electrode and the reference electrode, the second term is the local surface overpotential for the reaction, and the third term is the local concentration overpotential. These three terms may vary from point to point on the electrode, but their sum must always be A X T. Distinguishing among the three components of the experimentally measured voltage of the electrode is a complicated problem, but necessary if one wishes, for example, to obtain fundamentally meaningful values for the surface overpotential as a function of current density for a gas-evolving electrode. Consider the following cases. 

If the electrode reaction is reversible and product gas does not supersaturate the electrolyte near the electrode, Eq. (16) simplifies to 

The potential drop between the working and reference electrodes is thus entirely ohmic. As in bulk dispersions, bubbles on the electrode force the current to take longer paths and flow through constricted areas. Calculation of the potential drop requires knowledge of the electrical conductivity of the bubble layer either from theory or experiment. Theoretical treatments of the bubble layer are few because solving Laplace s equation in the complicated asymmetric environment is difficult nevertheless, solution of the 

The current distribution around a single bubble attached to an electrode appears in Fig. 10. The abscissa is normalized distance from the contact point while the ordinate is normalized current 

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