where a represents the specific (CAM-SE) interfacial area and f(|φAM -φEl|) is any suitable function to describe the polarization at the interface as a function of the potential difference |φAM -φEl|. The function can take the general form of the Butler-Volmer equation, a linearized approximation for low overpotentials and a Tafel approximation for high overpotentials of charge transfer. Newman and Tobias showed that this set of equations can be cast into a differential equation to describe the reaction current density distribution. The differential equation can be solved numerically using appropriate boundary conditions. From this assessment, dimensionless descriptors were identified that scale with and give a measure of the uniformity of the reaction current density distribution. For Tafel polarization and considering symmetric charge transfer coefficients in the polarization equation, the uniformity of the reaction current density distribution is proportional to a dimensionless current density δ: