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

Abstract

Electrochemical conversion of CO₂ to hydrocarbons is limited by the low solubility and slow transport of CO₂ in aqueous systems. We demonstrate that we can reach partial current densities for CO₂-to-CO of 40 mA/cm² 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 CO₂ 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 CO₂ 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 CO₂ 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 CO₂ conversion in aqueous systems can be enhanced considerably by exploiting larger electrolyte volumes via smart electrode designs, such as a flow-through principle.