The Primary Current Distribution (cd) interface () and the Secondary Current Distribution (cd) interface () are 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, except that it also 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.

The selection between Primary or Secondary governs how electrode reactions are modeled on interfaces between electrodes and electrolytes.

The Physics vs. Materials Reference Electrode Potential setting on the physics interface node can be used to combine material library data for current densities and equilibrium potentials with an arbitrary reference electrode scale in the physics. The setting affects the electrode potentials used for model input into the materials node, as well as all equilibrium potential values output from the materials node.

Note that the setting will only impact how potentials are interpreted in communication between the physics and the Materials node. If the From material option is not in use for equilibrium potentials or electrode kinetics, the setting has no impact.

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.

The interface uses Linear elements by default and this setting is recommended for most problems. Certain types of problems, such as models using porous electrodes, or current distribution problems in two dimensions or higher, may benefit in terms of solution accuracy from using Quadratic elements.

To see all settings in this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box.