Which dominates CO2 to CO electroreduction from low to industrial current density: Catalyst activity or CO2 availability?

Which dominates CO2 to CO electroreduction from low to industrial current density: Catalyst activity or CO2 availability?

Electrochemical reduction of CO2 (CO2RR) offers a sustainable route for converting renewable electricity into value-added chemicals. However, scaling CO2RR to industrially relevant current densities remains challenging due to intrinsic kinetics barriers, competing side reactions such as the hydrogen evolution reaction (HER), and limitations in CO2 mass transport. To elucidate whether catalyst activity or CO2 availability dominates CO2RR performance across current densities, we engineered flow-through hollow fiber gas diffusion electrodes (HFGDEs) integrated with in-situ grown, defect-rich silver nanosheets. At low current densities, catalytic activity is the primary determinant. The developed HFGDE with defect-rich silver nanosheets yields a high Faradaic efficiency of CO of 93.5 % at −0.8 (V vs. RHE), attributed to enhanced adsorption of *COOH intermediate on silver defect sites, as confirmed by in-situ Raman spectroscopy and density functional theory (DFT) calculations. However, as the system scales to industrially relevant current densities (up to 500 mA/cm2), CO2 availability becomes the dominant limitation due to the intensified fight between CO2 and H2O for electrons. The HFGDE architecture addresses this challenge by continuously supplying convective CO2 flow to the active sites, enabling a CO partial current density of 381.8 mA/cm2 under a total current density of 500 mA/cm2. These findings highlight that while catalyst activity governs CO2RR performance at lower current densities, adequate CO2 supply is essential to maintain high selectivity and suppress HER under industrial conditions.