Development of efficient and selective electrocatalysts is a key challenge to achieve an industry-relevant electrochemical CO 2 reduction reaction (CO 2 RR) to produce commodity chemicals. Here, we report that Au 25 clusters with Authiolate staple motifs can initiate electrocatalytic reduction of CO 2 to CO with nearly zero energy loss and achieve a high CO 2 RR current density of 540 mA cm −2 in a gas-phase reactor. Electrochemical kinetic investigations revealed that the high CO 2 RR activity of the Au 25 originates from the strong CO 2 binding affinity, leading to high CO 2 electrolysis performance in both concentrated and dilute CO 2 streams. Finally, we demonstrated an 18.0% solar-to-CO conversion efficiency using a Au 25 electrolyzer powered by a Ga 0.5 In 0.5 P/GaAs photovoltaic cell. The electrolyzer also showed 15.9% efficiency and a 5.2% solar-driven single-path CO 2 conversion rate in a 10% CO 2 gas stream, the CO 2 concentration in a typical flue gas.

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