Accurate identification of active sites is critical for elucidating catalytic reaction mechanisms and developing highly efficient and selective electrocatalysts. Herein, we report the atomic‐level identification of active sites using atomically well‐defined gold nanoclusters (Au NCs) Au25, Au38, and Au144 as model catalysts in the electrochemical CO2 reduction reaction (CO2RR). The studied Au NCs exhibited remarkably high CO2RR activity, which increased with increasing NC size. Electrochemical and X‐ray photoelectron spectroscopy analyses revealed that the Au NCs were activated by removing one thiolate group from each staple motif at the beginning of CO2RR. In addition, density functional theory calculations revealed higher charge densities and upshifts of d‐states for dethiolated Au sites. The structure–activity properties of the studied Au NCs confirmed that dethiolated Au sites were the active sites and that CO2RR activity was determined by the number of active sites on the cluster surface.

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.

Electrocatalytic CO 2 reduction reaction (CO 2 RR) is greatly facilitated by Au surfaces. However, large fractions of underlying Au atoms are generally unused during the catalytic reaction, which limits mass activity. Herein, we report a strategy for preparing efficient electrocatalysts with high mass activities by the atomic-level transplantation of Au active sites into a Ni 4 nanocluster (NC). While the Ni 4 NC exclusively produces H 2 , the Au-transplanted NC selectively produces CO over H 2 . The origin of the contrasting selectivity observed for this NC is investigated by combining operando and theoretical studies, which reveal that while the Ni sites are almost completely blocked by the CO intermediate in both NCs, the Au sites act as active sites for CO 2 -to-CO electroreduction. The Au-transplanted NC exhibits a remarkable turnover frequency and mass activity for CO production (206 mol CO /mol NC /s and 25,228 A/g Au , respectively, at an overpotential of 0.32 V) and high durability toward the CO 2 RR over 25 h.

Atomically precise metal nanoclusters (NCs) are promising catalysts for the electrochemical CO 2 reduction reaction (CO 2 RR) and are effective model catalysts for the identification of active sites. We report the metal-dependent CO 2 RR activities of Au 25 (SR) 18 and Ag 25 (SR) 18 (SR = thiolate). While both NCs produced CO as a main CO 2 RR product, the Au 25 NC exhibited a significantly higher CO 2 RR activity than the Ag 25 NC. Theoretical and operando studies revealed that the CO 2 RR limiting potential for the Au 25 NC was significantly smaller than that for the Ag 25 NC, while both NCs contained the partially dethiolated metal sites as the active sites. Active-site engineering was performed by replacing the Ag 12 (SR) 18 shell of the Ag 25 (SR) 18 NC with the Au 12 (SR) 18 shell to generate a core−shell AuAg 12 @Au 12 (SR) 18 NC, which exhibited dramatically enhanced CO 2 RR activity compared with the Ag 25 (SR) 18 NC. The AuAg 12 @Au 12 NCs exhibited stable CO 2 -to-CO electroreduction at a commercially relevant current density of 200 mA/cm 2 and a full-cell potential of 2.1 V in a zero-gap CO 2 electrolyzer.

Syngas, a gaseous mixture of CO and H2, is a critical industrial feedstock for producing bulk chemicals and synthetic fuels, and its production via direct CO2 electroreduction in aqueous media constitutes an important step toward carbon-negative technologies. Herein, we report controlled syngas production with various H2/CO ratios via the electrochemical CO2 reduction reaction (CO2RR) on specifically formulated Au25 and PtAu24 nanoclusters (NCs) with core-atom-controlled selectivities. While CO was predominantly produced from the CO2RR on the Au NCs, H2 production was favored on the PtAu24 NCs. Density functional theory calculations of the free energy profiles for the CO2RR and hydrogen evolution reaction (HER) indicated that the reaction energy for the conversion of CO2 to CO was much lower than that for the HER on the Au25 NC. In contrast, the energy profiles calculated for the HER indicated that the PtAu24 NCs have nearly thermoneutral binding properties; thus, H2 production is favored over CO formation. Based on the distinctly different catalytic selectivities of Au25 and PtAu24 NCs, controlled syngas production with H2/CO ratios of 1 to 4 was demonstrated at a constant applied potential by simply mixing the Au25 and PtAu24 NCs based on their intrinsic catalytic activities for the production of CO and H2.