High-rate and selective conversion of CO from aqueous solutions to hydrocarbons.

Electrochemical carbon dioxide (CO) conversion to hydrocarbon fuels, such as methane (CH), offers a promising solution for the long-term and large-scale storage of renewable electricity. To enable this technology, CO-to-CH conversion must achieve high selectivity and energy efficiency at high currents. Here, we report an electrochemical conversion system that features proton-bicarbonate-CO mass transport management coupled with an in-situ copper (Cu) activation strategy to achieve high CH selectivity at high currents. We find that open matrix Cu electrodes sustain sufficient local CO concentration by combining both dissolved CO and in-situ generated CO from the bicarbonate. In-situ Cu activation through alternating current operation renders and maintains the catalyst highly selective towards CH. The combination of these strategies leads to CH Faradaic efficiencies of over 70% in a wide current density range (100 - 750 mA cm) that is stable for at least 12 h at a current density of 500 mA cm. The system also delivers a CH concentration of 23.5% in the gas product stream.