Abstract
Electrochemical CO(2) reduction has the potential to use excess renewable electricity to produce hydrocarbon chemicals and fuels. Gas diffusion electrodes (GDEs) allow overcoming the limitations of CO(2) mass transfer but are sensitive to flooding from (hydrostatic) pressure differences, which inhibits upscaling. We investigate the effect of the flooding behavior on the CO(2) reduction performance. Our study includes six commercial gas diffusion layer materials with different microstructures (carbon cloth and carbon paper) and thicknesses coated with a Ag catalyst and exposed to differential pressures corresponding to different flow regimes (gas breakthrough, flow-by, and liquid breakthrough). We show that physical electrowetting further limits the flow-by regime at commercially relevant current densities (≥200 mA cm(-2)), which reduces the Faradaic efficiency for CO (FE(CO)) for most carbon papers. However, the carbon cloth GDE maintains its high CO(2) reduction performance despite being flooded with the electrolyte due to its bimodal pore structure. Exposed to pressure differences equivalent to 100 cm height, the carbon cloth is able to sustain an average FE(CO) of 69% at 200 mA cm(-2) even when the liquid continuously breaks through. CO(2) electrolyzers with carbon cloth GDEs are therefore promising for scale-up because they enable high CO(2) reduction efficiency while tolerating a broad range of flow regimes.