Flow-through electrodes enable order of magnitude higher partial current densities in aqueous CO2 electrolysis

Electrochemical conversion of CO 2 to hydrocarbons is limited by the low solubility and slow transport of CO 2 in aqueous systems. We demonstrate that we can reach partial current densities for CO 2 -to-CO of 40 mA/cm 2 in fully aqueous systems, without the use of gas diffusion electrodes. We alleviate the mass transfer limitation by combining a suspension of catalytically active silver nanoparticles (Ag NPs) with a flow-through current collector. This extends the reactive area into the electrolyzer channel and improves the accessibility of dissolved CO 2 in a larger volume of electrolyte. The flow-through electrode system also outperforms a fully suspended electrode (based on carbon black particles), due to enhanced electric conductivity and smaller carbon area to minimize parasitic side-reactions. Additionally, we show that the distribution of the Ag NPs is pivotal for high CO 2 conversion rates, demonstrated by the highest CO current density obtained when a suspension of Ag NPs and SDS as surfactant is flowing through the 3D electrodes as pre-treatment. A stable CO current density can be sustained for more than 4 h. Although the conversion rate is still moderate compared to gas-fed CO 2 electrolzyers, the partial current density for flow-through electrodes is more than an order of magnitude larger than for planar flow systems. This work shows that CO 2 conversion in aqueous systems can be enhanced considerably by exploiting larger electrolyte volumes via smart electrode designs, such as a flow-through principle. • An Ag suspension flowing through 3D electrodes enhances the CO 2 -to-CO conversion. • Partial current densities in 3D electrodes are > 10x higher than at planar electrode. • Foams outperform carbon slurries due to disturbed flow and conductive networks. • Surfactants promote the stability of the Ag nanoparticle suspension.