A microchanneled solid electrolyte for carbon-efficient CO₂ electrolysis

The electrochemical reduction of CO₂ is a promising route to convert carbon emissions into valuable chemicals and fuels. In electrolyzers producing multi-carbon products, 70%–95% of the supplied CO₂ is converted to (bi)carbonates, limiting the carbon efficiency of electrochemical CO₂ conversion. These (bi)carbonate anions can be lost to the aqueous electrolyte, converted back to gaseous CO₂ and diluted in the anode tail gas, and/or combined with alkali metal cations from the electrolyte to form solid salt precipitates. Here, we report a microchanneled solid electrolyte that allows for the recapture and recycling of (bi)carbonate ions before reaching the anode, reducing CO₂ loss to ∼3%. We demonstrate CO₂ electroreduction to multi-carbon products with 77% selectivity without the use of alkali metal cations, by incorporating fixed quaternary ammonium cations. This system simultaneously achieves near-zero CO₂ loss, high selectivity toward multi-carbon products, and stable operation at an industrially relevant current density over 200 h.