The Electrode Reaction subnode defines the electrode kinetics for a charge transfer reaction that occurs on an electrolyte-electrode interface boundary. Use multiple nodes to model multiple reactions, for instance in mixed potential problems.

The parent node may be either an Internal Electrode Surface or an Electrode Surface.

The Equilibrium potential, Eeq (SI unit: V), is used in the electrode kinetics expressions in the following section (via the definition of the over potential), or for setting up primary current distribution potential constraints.

The Temperature derivative of equilibrium potential parameter, dEeq/dT (SI unit: V/K), is used when calculating the reversible heat source of the electrode reaction, which in turn can be used for coupling to heat transfer physics. Note that dEeq/dT parameter value has no impact on the equilibrium potential variable.

The settings of this section will define the Local current density, iloc (SI unit: A/m2), at the interface between the electrolyte and the electrode. Note that iloc for all built-in kinetics expression types will depend on the overpotential, which in turn depend on the Equilibrium potential defined in the previous section..

For all expressions the Exchange current density i0 (SI unit: A/m2) is a measure of the kinetic activity.

The Linearized Butler-Volmer is valid when the overpotentials of the reactions are small (<<25 mV). The linearized version can also be used to troubleshoot a model with convergence problems.

The Anodic transfer coefficient, αa (dimensionless), and Cathodic transfer coefficient, αc (dimensionless), parameters will impact how much iloc will change upon changes in the overpotential.

The Anodic Tafel slope, Αa (SI unit: V), defines the required increase in overpotential to result in a tenfold increase in the current density.

The Cathodic Tafel slope, Αc (SI unit: V), describes the required decrease in overpotential to result in a tenfold increase in the current density magnitude. Αc should be a negative value.

This kinetics expression type is typically used in tertiary current distribution problems. One or both of the Oxidizing species expression CO (dimensionless) and Reducing species expression CR (dimensionless) parameters may be concentration dependent, and should typically be defined so that CO = CR at equilibrium.

Use the Limiting Current Density to impose an upper limit on the local current density magnitude. The feature can be used to model additional mass transport limitations that are not already included in the local current density expression.

For Limiting Current Density enter a value for ilim (SI unit: A/m2).

Specify the Number of participating electrons nm in the electrode reaction and the Stoichiometric coefficient (vc1, vc2, and so forth) for each of the involved species according to the following generic electrochemical reaction:

Set νi as positive (νred) for the reduced species and negative (νox) for the oxidized species in an electrochemical reaction. The number of participating electrons, n, should be positive.