The H2 Gas Diffusion Layer and O2 Gas Diffusion Layer nodes specify domains where both an Electronic Conducting Phase and a Gas Phase node are active.

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.

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 a User defined correlation.

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.