Development of efficient and selective electrocatalysts is a key challenge to achieve an industry-relevant electrochemical CO2 reduction reaction (CO2RR) to produce commodity chemicals. Here, we report that Au25 clusters with Au-thiolate staple motifs can initiate electrocatalytic reduction of CO2 to CO with nearly zero energy loss and achieve a high CO2RR current density of 540 mA cm-2 in a gas-phase reactor. Electrochemical kinetic investigations revealed that the high CO2RR activity of the Au25 originates from the strong CO2 binding affinity, leading to high CO2 electrolysis performance in both concentrated and dilute CO2 streams. Finally, we demonstrated an 18.0% solar-to-CO conversion efficiency using a Au25 electrolyzer powered by a Ga0.5In0.5P/GaAs photovoltaic cell. The electrolyzer also showed 15.9% efficiency and a 5.2% solar-driven single-path CO2 conversion rate in a 10% CO2 gas stream, the CO2 concentration in a typical flue gas.
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