Gas Diffusion Electrode
The H2 Gas Diffusion Electrode and O2 Gas Diffusion Electrode nodes specify three phase domains where an Electronic Conducting Phase, an Electrolyte Phase, and a Gas Phase node are all active.
Electrode Charge Transport
The effective electronic conductivity, Effective electric conductivity, σs (SI unit: S/m) parameter will define how the electric current in the corresponding Electronic Conducting Phase domain depends on the gradient of the potential.
Effective Electrolyte Charge Transport
The bulk electrolyte conductivity defined in the Electrolyte Phase node will be multiplied by a correction factor to compensate for the effect of the Electrolyte volume fraction being less than 1. This can be done by either using a Bruggeman, Tortuosity, or User defined correlation. For Tortuosity, select either Isotropic to define a scalar value, or Diagonal or Symmetric to define anisotropic tensor values. This feature is unavailable if Solve for electrolyte phase potential is cleared in the interface top node.
Gas Transport
This section is only visible if the Include gas phase diffusion checkbox or the Use Darcy’s law for momentum transport checkbox has been selected in the corresponding Gas Mixture section on the interface top node.
If the Include gas phase diffusion checkbox has been selected, the gas diffusivity defined in the Gas Phase node will be multiplied by a correction factor to compensate for the effect of the Gas pore volume fraction being less than 1. This can be done by either using a Bruggeman, Tortuosity, or User defined correlation. For Tortuosity, select either Isotropic to define a scalar value, or Diagonal or Symmetric to define anisotropic tensor values.
If the Use Darcy’s law for momentum transport checkbox has been selected, the Gas permeability is defined in this node.
By checking Include pore-wall interaction, additional friction forces between the individual gas molecules and the walls are accounted for when computing the gas fluxes (given that Include gas phase diffusion is active). The pore-wall friction forces make use of a Wall diffusivity, which is set to Knudsen by default. The Knudsen diffusivity can be derived from kinetic gas theory by relating the mean-free path of the gas molecules to the Pore diameter of the pores.