Eliminating the need for anodic gas separation in CO 2 electroreduction systems via liquid-to-liquid anodic upgrading.

Electrochemical reduction of CO 2 to multi-carbon products (C 2+ ), when powered using renewable electricity, offers a route to valuable chemicals and fuels. In conventional neutral-media CO 2 -to-C 2+ devices, as much as 70% of input CO 2 crosses the cell and mixes with oxygen produced at the anode. Recovering CO 2 from this stream adds a significant energy penalty. Here we demonstrate that using a liquid-to-liquid anodic process enables the recovery of crossed-over CO 2 via facile gas-liquid separation without additional energy input: the anode tail gas is directly fed into the cathodic input, along with fresh CO 2 feedstock. We report a system exhibiting a low full-cell voltage of 1.9 V and total carbon efficiency of 48%, enabling 262 GJ/ton ethylene, a 46% reduction in energy intensity compared to state-of-art single-stage CO 2 -to-C 2+ devices. The strategy is compatible with today's highest-efficiency electrolyzers and CO 2 catalysts that function optimally in neutral and alkaline electrolytes.