Pathways to enhance electrochemical CO₂ reduction identified through direct pore-level modeling

Area of Science:

• Electrochemistry
• Chemical Engineering
• Materials Science

Background:

• Electrochemical conversion of carbon dioxide (CO2) offers a route to reduce emissions and produce valuable products.
• Gas diffusion electrodes (GDEs) enable higher current densities for CO2 electrolysis compared to aqueous phase systems.
• Existing models for GDEs often use volume-averaged approximations, neglecting crucial pore-scale multi-physical transport phenomena.

Purpose of the Study:

• To develop and utilize a direct, non-volume-averaged pore-level transport model for GDEs.
• To investigate the impact of pore-scale phenomena on CO2 reduction within GDEs.
• To identify strategies for enhancing GDE performance and increasing current densities.

Main Methods:

• A 2D pore-level transport model was developed, coupling gaseous and liquid electrolyte domains at the interface.
• Transport was resolved around individual catalyst nanoparticles, including electric double layer and steric effects.
• The model analyzed GDE behavior under various idealized catalyst geometries and wetting conditions.

Main Results:

• Catalyst layer thickness, roughness, and wetting significantly influence CO2 reduction transport.
• Identified pathways suggest potential for an order of magnitude increase in current density.
• Observed that liquid-gas interfaces often form filled fronts, not wetting films.
• Electrochemical reactions occur in a broader zone around triple-phase boundaries, not just at them.
• High electrolyte concentrations reduce CO2 solubility, limiting transport; catalyst utilization is heterogeneous.

Conclusions:

• The pore-level model provides unprecedented visualization of multi-scale transport dynamics within GDEs.
• Findings offer critical insights into enhancing GDE performance for electrochemical CO2 reduction.
• The study highlights the importance of pore-scale phenomena in GDE design and optimization.