LAUSR

Achieving high product selectivities is one challenge that limits viability of electrochemical CO 2 reduction (CO 2 R) to chemical feedstocks. We demonstrate how interactions between Ag foil cathodes and reline (choline chloride + urea) lead to highly selective CO 2 R to CO with a faradaic efficiency of 96 ± 8% in 50 wt% aqueous reline at - 0.884 V vs RHE, which is a 1.5-fold improvement over CO 2 R in KHCO 3 . In reline the Ag foil was roughened by (i) dissolution of oxide layers followed by (ii) electrodeposition of Ag nanoparticles back on cathode. This surface restructuring exposes low-coordinated Ag atoms, and subsequent adsorption of choline ions and urea at the catalyst surface limits proton availability in the double layer, and stabilizes key intermediates such as *COOH. These approaches could potentially be extended to other electro-catalytic metals, and to lower viscosity deep eutectic solvents to achieve higher current density CO 2 R in continuous flow cell electrolysers.