Tuning intermediate binding enables selective electroreduction of carbon dioxide to carbon monoxide on a copper-indium catalyst.

Electrosynthesis of carbon monoxide (CO) from carbon dioxide (CO2) and water driven by renewable electricity represents a sustainable route to carbon upgrading, but the lack of cost-effective catalysts hinders its scaling-up. Here, we judiciously designed a bimetallic Cu-In catalyst via in situ electroreduction of In-coated CuO nanowires. This facilely-prepared Cu-In catalyst delivers an excellent performance towards CO production in a flow cell, with a faradaic efficiency of CO of up to 91% at a geometric current density of -69 mA cm-2. Different from previous studies suggesting that In-modified Cu strengthens the adsorption of *COOH and/or weakens the binding of *H, we discovered that In acts as the active site. The modification of In by Cu weakens the adsorption of *CO. This facilitates a faster desorption of *CO, thus inhibiting the C-C coupling process. As a result, the formation of multi-carbon products is suppressed. This conclusion was drawn through a rigorous analysis of the electrochemical reduction of CO, the electrochemical adsorption of *CO and in situ Raman spectroscopy. Finally, we wired our CuIn-based electrolyzer to an efficient triple-junction solar cell for the demonstration of solar-driven CO2 conversion and achieved a solar-to-chemical energy conversion efficiency of greater than 10% for CO.