Postprocessing Your Solution
Potential Variables
Several different potential variables are available for postprocessing and during computation. The most common ones are described in Table 2-1.
The unit is V for all the above variables.
xxx denotes the tag of the physics interface. For instance, cd for the Secondary Current Distribution interface.
yy denotes the tag of the (Porous) Electrode Reaction node, for instance, er1 for an Electrode Reaction node.
Current Variables and Calculating the Total Cell Current
The current density may vary between locations on an electrode surface. This effect is very important to understand through modeling because it cannot be directly measured. Experimental measurement can only return the total current drawn at an electrode, although the variation in current density can be inferred by other means.
To calculate the total current in COMSOL Multiphysics, it is necessary to integrate the total drawn current density along the boundary or over the domain of the electrode. Some common current density variables are shown in Table 2-2.
xxx denotes the tag of the physics interface. For instance cd for the Secondary Current Distribution interface.
yy denotes the tag of the (Porous) Electrode Reaction node, For instance er1 for an Electrode Reaction node.
 
In 1D or 1D axisymmetric, the electrode is implicitly uniform so you can just multiply by the area of the electrode. In 2D or 2D axisymmetric, compute the appropriate line integral. In 3D, compute the surface integral.
You can also define your own total current variable by using an Integration component coupling across the electroactive boundaries. This variable can also be used during the computation. In 1D axisymmetric and 2D axisymmetric components, make sure to select the Compute integral in revolved geometry check box.
In the COMSOL Multiphysics Reference Manual:
Avoid evaluating the xxx.IlMag/xxx.IsMag variables on boundaries. These are generally less accurate than the xxx.nIl/xxx.nIs variables.