MECHANISM OF MASS TRANSFER OF INDICATOR IONS TO AN OXYGEN-EVOLVING AND A HYDROGEN- EVOLVING ELECTRODE IN ALKALINE SOLUTION

Abstract-A new convection-penetration model for mass transfer of indicator ions to a gas-evolving electrode at forced convection of solution is described theoretically. To check this model, the mass transfer coeficients for ferricyanide ions and ferrocyanide ions to, respectively, a hydrogen-evolving and an oxygen-evolving electrode in 1 M KOH and at 298 K and various bulk-solution flow velocities have been determined in the usual way. The average diameter, cross-section and volume of detached bubbles and the eficiency of gas bubble evolution, have been determined photographically, however. It has been found that the mass transfer of indicator ions to a gas-evolving electrode can be described well by the new model. The contribution of an oxygen bubble departing from the electrode surface to the mass transfer is much greater than the contribution of a departing hydrogen bubble. NOMENCLATURE proportional factor average cross-section of detached bubbles; bubble cross-section (m*) surface area of electrode (m2) concentration of species i in bulk of solutio