To add an Electrode Reaction node () either right-click the Chemistry node or on the Chemistry toolbar click Electrode Reaction.

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.

Enter an electrode reaction Formula, as a reduction reaction. Use the single letter “e” to symbolize an electron. The delimiter between reactants and products has to be written as “<=>” (without quotation marks). The phase of the species, that is (aq) for aqueous dilute ions, (s) for solids, and (g) for gases can be indicated in the name. The phase is used to select an automatic reference state (see Reference Concentrations) for computing the equilibrium potential using the Nernst equation. Click Apply to make the interface examine the species taking part in the model’s reactions and automatically add the associated Species features to the Model Builder.

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

After providing the reference electrode potential, the equilibrium potential is calculated using the Nernst equation. The concentrations entered in the Species Matching section of the Chemistry interface will be used to calculate the equilibrium potential. The reference concentrations, defined in the Reference Concentrations section, will be used to compute the activities in the reaction quotient expression, Qr.

This option is only available if the Calculate Transport Properties option is checked.

The Species enthalpies and entropies are used to calculate the equilibrium potential of the electrode reaction at the temperature and composition of the system.

If only species enthalpies and entropies at standard state are available, use the Nernst Equation option instead.

For aqueous dilute species, denoted by (aq) in their names, the activity is calculated as their concentration divided by 1 M. For gaseous species, denoted by (g) in their names, the activity is calculated as their concentration divided by the standard reference pressure of 1 atm, converted into concentration using the ideal gas law. For solid species, denoted by (s) in their names, the reference concentration 1. For surface species, denoted by (ads) in their names, the reference surface concentration will be set to the site density configured in the Species Matching section. Any species not containing a phase in their name, will use a reference state depending on the phase selected under Mixture Properties. If the phase is Gas, the gaseous species reference concentration described above will be used, while if the phase is Liquid, the aqueous species 1 M reference concentration will be used.

See the Electrode Reaction node in Shared Physics Features in the Current Distribution Interfaces for a general description of the Electrode Kinetics section.

Electrode reactions in the Chemistry interface support User-defined, Butler-Volmer and Linearized Butler-Volmer kinetics. For the latter two options, User-defined exchange current densities and exchange current densities according to the Mass Action Law are supported.

If the equilibrium potential is calculated using Nernst Equation, the exponents in the local current density expression are evaluated using the reference overpotential. If instead the equilibrium potential is calculated using the Automatic option, the exponents are evaluated using the overpotential.

See the Electrode Reaction node in Shared Physics Features in the Current Distribution Interfaces for a general description of the Heat of Reaction section. Electrode Reactions in Chemistry do not support the Temperature Derivative option.

By choosing Automatic, the Thermoneutral voltage parameter, Etherm (SI unit: V), will be calculated according to

using the Species enthalpies.