The Primary Current Distribution (cd) interface (
) and the
Secondary Current Distribution (cd) interface (
) are both found under the
Electrochemistry branch (
) when adding a physics interface.
The Primary Current Distribution interface defines the transport of charged ions in an electrolyte of uniform composition as well as current conduction in electrodes using Ohm’s law in combination with a charge balance. The physics interface neglects activation overpotentials due to charge transfer reactions.
The Secondary Current Distribution interface is similar to the Primary Current Distribution interface with the difference that it accounts for activation overpotentials. The relation between charge transfer and overpotential can be described using arbitrary kinetic expressions, such as Butler-Volmer and Tafel equations.
Use the Current Distribution Type setting on the physics interface node, described below, to switch between a Primary Current Distribution and a Secondary Current Distribution interface.
The Label is the default physics interface name.
The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern
<name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the
name string must be unique. Only letters, numbers, and underscores (_) are permitted in the
Name field. The first character must be a letter.
The default Name (for the first physics interface in the model) is
cd.
The Current Distribution Type selected in the list is based on the choice made when adding a physics interface —
Primary or
Secondary. The Primary Current Distribution interface changes to a Secondary Current Distribution interface if the choice is changed to
Secondary, and vice versa.
This physics interface defines dependent variables (fields) for the Electrolyte potential and
Electric potential. The names can be changed but the names of fields and dependent variables must be unique within a model.
) and select Advanced Physics Options in the Show More Options dialog box. 
