Surface transport processes in charged porous media.

Area of Science:

• Surface Science
• Colloidal Science
• Geophysics
• Chemical Engineering
• Biophysics

Background:

• Surface transport processes are crucial across multiple scientific disciplines.
• Electrical double layers (EDLs) form at solid-liquid interfaces due to surface charges, influencing ion transport.
• Existing models often simplify or overlook the complexities of ion transport within charged porous media.

Purpose of the Study:

• To develop and present a model for simulating bulk and surface ion transport in homogeneous porous media with large pores.
• To investigate the impact of electrical double layers on transport phenomena in charged porous systems.
• To derive averaged transport equations incorporating surface transport effects.

Main Methods:

• A theoretical model based on capacitive charging of ideally polarizable porous electrodes was employed.
• Volume averaging techniques were utilized to derive averaged transport equations in the thin EDL limit.
• The Gouy-Chapman-Stern (GCS) model described the electrical double layer structure.
• Boundary conditions for diffuse interfaces introduced surface transport terms into the averaged equations.

Main Results:

• The derived averaged equations include two additional surface transport terms.
• A surface diffusion term, analogous to transport in non-charged media, was identified.
• A novel migration term, specific to charged porous media, was discovered.
• Effective bulk and transport parameters were calculated by solving closure problems for isotropic media.

Conclusions:

• The model successfully captures the complexities of ion transport in charged porous media.
• The identified surface migration term is a key characteristic of transport in these systems.
• The findings provide a more accurate framework for understanding surface transport phenomena in diverse applications.