The Primary Current Distribution and Secondary Current Distribution Interfaces
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.
Primary Current Distribution 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.
Use this physics interface to estimate the ohmic losses in simplified models of electrochemical cells, where the overpotentials of the electrode reactions are small compared to the ohmic voltage drops in the electrolyte and electrodes.
Secondary Current Distribution Interface
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 this physics interface for generic modeling of electrochemical cells. It can be combined with interfaces modeling mass transport to describe concentration dependent (tertiary) current distributions.
Ohm’s law is used in combination with a charge balance to describe the conduction of currents in the electrodes and electrolytes.
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.
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Introduction to Electrochemistry Modeling
Settings
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.
Domain Selection
Domains that do not conduct current should be omitted from the Domain Selection: for example, the gas channels in a fuel cell.
Out-of-Plane Thickness
For 2D components, enter a value or expression for the out-of-plane Thickness d (SI unit: m). The value of d determines the size of the domain perpendicular to the modeled 2D cross section. This value yields, for example, the correct total current when the current density is obtained from a 2D simulation.
Cross Sectional Area
For 1D components, enter a Cross sectional area Ac (SI unit: m2) to define a parameter for the area of the geometry perpendicular to the 1D component. The value of this parameter is used, among other things, to automatically calculate the total current from the current density vector. The analogy is valid for other fluxes. The default is 1 m2.
Current Distribution Type
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 from this list also governs how electrode reactions are modeled on interfaces between electrodes and electrolytes.
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Models using a Primary current distribution type use potential constraints (Dirichlet boundary conditions), according to the equilibrium potential setting.
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Secondary current distribution models use current flux conditions (Neumann boundary conditions) according to the sum of all electrode reaction current densities.
Dependent Variables
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.
Discretization
To see all settings in this section, click the Show button () and select Advanced Physics Options.
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Electrochemical Reactions and the Difference Between a Primary and a Secondary Current Distribution
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Domain Equations for Primary and Secondary Current Distributions
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Shared Physics Features in the Current Distribution Interfaces
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Theory for the Current Distribution Interfaces
Secondary Current Distribution: Mass Transport Analysis of a High Temperature PEM Fuel Cell: Application Library path Batteries_and_Fuel_Cells_Module/Fuel_Cells/ht_pem