Quantifying mass transport limitations in a microfluidic CO₂ electrolyzer with a gas diffusion cathode

A gas diffusion electrode (GDE) based CO₂ electrolyzer shows enhanced CO₂ transport to the catalyst surface, significantly increasing current density compared to traditional planar immersed electrodes. A two-dimensional model for the cathode side of a microfluidic CO₂ to CO electrolysis device with a GDE is developed. The model, validated against experimental data, examines key operational parameters and electrode materials. It predicts an initial rise in CO partial current density (PCD), peaking at 75 mA cm^-2 at -1.3 V vs RHE for a fully flooded catalyst layer, then declining due to continuous decrease in CO₂ availability near the catalyst surface. Factors like electrolyte flow rate and CO₂ gas mass flow rate influence PCD, with a trade-off between high CO PCD and CO₂ conversion efficiency observed with increased CO₂ gas flow. We observe that a significant portion of the catalyst layer remains underutilized, and suggest improvements like varying electrode porosity and anisotropic layers to enhance mass transport and CO PCD. This research offers insights into optimizing CO₂ electrolysis device performance.