Secondary current distribution in a two-dimensional model cell composed of an electrode with an open part

On the assumption that the relation between the overpotential and the current density is expressed by linear and Butler-Volmer equations, secondary current distributions were obtained in a two-dimensional model cell in which a working electrode with an open part serving to release gas bubbles to the back side of the electrode is located parallel to a counter electrode or a separator. Cell resistances or cell voltage in the model cell were evaluated for various combinations of geometrical parameters and heterogeneous kinetic parameters by means of the finite element method. As a result, when the kinetic equation was the linear approximation, the cell resistance or cell voltage varied mainly with two geometrical parameters (the interelectrode distance and the electrode surface ratio) and the kinetic parameters. On the other hand, when the kinetic equation was of the Butler-Volmer type the cell voltage varied with the kinetic parameters and the percentage of open area instead of the electrode surface ratio. In order to facilitate estimation of cell voltage for an industrial productiontype cell composed of electrodes with voids or holes, the computed cell voltages were expressed as functions of these parameters in simple approximate equations. A criterion for estimating whether the cell voltage is controlled by the overpotential or the ohmic drop is presented.