Discussion Forum

Hi all,

I am trying to model a H2/Br2 redox flow battery and presently having some problems regarding the boundary condition at the interface between the electrolyte in the model (membrane) and the porous electrode. Since two different physics are used at the 2 domains, I am trying to apply a boundary condition similar to as seen in the 'v battery' model in the applications library but without the Donnan potential jump. At the interface between the membrane and cathode(electrolyte) I have given a point-wise constraint with an expression:

phil_neg - phil_pos ( which eliminates the Donnan potential jump as used in the v flow battery and results in a continuous electrolyte potential profile across the interface)

Also, similar to the constraint force expression in v flow battery, I have added the force expression to implement the conditions of electrolyte current equity in the membrane and electrode. Everything runs smoothly, but the results do not make sense. Especially the H+ concentration profile. I would expect a larger concentration at the membrane interface as this is the source of the current and reduce along the domain. It seems like at the boundary it considers that the anion Br- (In my model) transfers the current through the membrane whereas it is the H+ cation which carries the current and that needs to be equated at the boundary.

Hope somebody can help me get this boundary condition fixed.