Electroreduction of diluted CO2 to multicarbon products with high carbon utilization at 800 mA cm–2 in strongly acidic media

Acidic CO₂ electroreduction using diluted CO₂ (as in flue gas) as the feedstock can simultaneously circumvent the CO₂ purification step and lower the carbon loss in conventional alkaline or neutral electrolyte, and thus is highly desired but has rarely been achieved thus far. Herein, we report a simple and general strategy using an imidazolium-based anion-exchange ionomer as the coating layer, which could enrich the diluted CO₂ to generate a high local CO₂ concentration, and simultaneously block the proton transport to the cathode surface to suppress the competing hydrogen evolution reaction. As a result, the ionomer-modified Cu catalyst can achieve an efficient electroreduction of diluted CO₂ (15 vol% CO₂) to multicarbon (C₂₊) products in strong acid (pH 0.8), with a high C₂₊ Faradaic efficiency of 70.5% and a high single-pass carbon efficiency of 73.6% at a current density of 800 mA cm^–2, competitive with that obtained with pure CO₂. These findings provide opportunity for the direct electrochemical conversion of flue gas into valuable products with high efficiency.