Eliminating the need for anodic gas separation in CO2 electroreduction systems via liquid-to-liquid anodic upgrading

Electrochemical reduction of CO2 to multi-carbon products (C2+), when powered using renewable electricity, offers a route to valuable chemicals and fuels. In conventional neutral-media CO2-to-C2+ devices, as much as 70% of input CO2 crosses the cell and mixes with oxygen produced at the anode. Recovering CO2 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 CO2 via facile gas-liquid separation without additional energy input: the anode tail gas is directly fed into the cathodic input, along with fresh CO2 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 CO2-to-C2+ devices. The strategy is compatible with today's highest-efficiency electrolyzers and CO2 catalysts that function optimally in neutral and alkaline electrolytes. In the electrified conversion of CO2 to multicarbon products, CO2 crossover to the O2-rich anodic stream adds a further, energy-intensive, chemical separation step. Here, the authors demonstrate a strategy that eliminates the separation requirement.