Discussion Forum

I am writing a model involving chemical dissolution of a metal by an etchant. In order to do this, I wrote a steady state model (tertiary distribution w/ Nernst Plank, tcdee) that looks at an electrode with two simultaneous reactions. The first is a dissolution reaction (Cu -> Cu2+), and the second is a redox couple (Fe3+ -> Fe2+). I specified all the parameters, including the stoichiometric coefficients.

I tried to look at a zero net current case by enforcing electrical insulation on the boundaries. I did allow for diffusion through an edge (so that I'd get a steady state profile). My problem is that my anion (SO4 2-) is somehow being created at the electrode. The stoichiometric coefficients for SO4 2- are zero in both reactions. I did choose the anion as the specie determined by electroneutrality.

I have a good working knowledge of COMSOL, so I tried to trouble shoot by backtracking through the equations (using equation view), but I got lost because I cannot find where the reaction or flux terms for the chemical species at the electrode are listed. I know it is input at the very bottom of "Electrode Reaction N", under the stiochiometric coefficients. It gives the reaction term there. However, when I switch to equation view, only the stoichiometric coefficients themselves pop up, not the actual reaction or flux terms. They are not under the more generic 'Electrolyte-Electrode Domain Interface" equation view either, which is actually entirely blank.

Does anyone have a suggestion on how to either fix the problem or to at least find the equations?