Porous Electrodes
A porous electrode is one in which the three-dimensional structure of the electrode is permeable to electrolyte. The electrode-electrolyte interface then extends over a much larger surface area. This specific surface area (“SSA”, area per unit volume, units 1/m) is a key property of a porous electrode. Additionally, such an electrode can conduct electrical current independently through its electrode and electrolyte domains.
Most electrochemical interfaces in COMSOL Multiphysics include Porous Electrode domain nodes that can be used to model the above situation. In a Porous Electrode, current density is carried in both the electrode and in the pores which are assumed to contain electrolyte. For gas diffusion electrodes where the solid is conducting but the pore phase is not, the Electrode condition should be used.
It is common to combine an electrochemical interface with other physics, in order to model the mass transport, heat transfer and flow properties of a porous medium. For instance, Secondary Current Distribution might be coupled to Transport of Diluted Species in Porous Media, Heat Transfer in Porous Media and Darcy’s Law.
Homogenized transport parameters such as diffusion coefficients are commonly obtained for a bulk solution of the material. In porous media these must be corrected for tortuosity and porosity. Carefully consider such effects when defining your material properties.
Porous Electrode Theory