Local Variations in Current Density and Selectivity in CO ₂ Electrolyzers

As CO₂ electrolysis emerges as a key technology for industrial decarbonization, scaling from lab to industrial systems introduces challenges beyond increasing the active area or the CO₂ feed rate. Larger reactors often exhibit spatial inhomogeneities in selectivity and current density, issues overlooked in conventional performance studies. To address this, we designed, built, and tested a zero-gap flow cell for CO₂ electrolysis that enables local monitoring of the product selectivity and current density. Gas composition is sampled at multiple points along the flow path, while current density is tracked across the cell. This approach reveals where and under what conditions parasitic hydrogen evolution occurs. In this work we present how operating parameters influence localized product formation and current density profiles in a CO₂-to-CO electrolyzer. Our findings emphasize the importance of moving beyond averaged metrics to achieve efficient, uniform operation across the cell, an essential step for successful scale-up.