Boundary Conditions Using Reference Electrode Potentials
The set of boundary conditions defined in a model of an electrochemical cell needs to ensure that no current flows through the reference electrode. A constraint for the potential on the actual reference electrode is not suitable in general since it can create unwanted local sources or sinks of current.
When modeling the control of an electrochemical cell by a potentiostat, which monitors and controls the potential of an electrodes versus a reference electrode, the electric potential conditions should be applied to the boundaries over which the current flows in the cell. One electrode (the counter electrode) is typically grounded, whereas an electric potential condition is set on all other (working) electrode boundaries according to
(3-21)
where s , bnd (SI unit: V) is the applied electric boundary potential on the electrode.