Achieving CO₂reduction with H₂O on metal photocatalysts and understanding the corresponding mechanisms at the molecular level are challenging. Herein, we report that quantum-sized Au nanoparticles can photocatalytically reduce CO₂to CO with the help of H₂O by electron-hole pairs mainly originating from interband transitions. Notably, the Au photocatalyst shows a CO production rate of 4.73 mmol g⁻¹h⁻¹(~100% selectivity), ~2.5 times the rate during CO₂reduction with H₂under the same experimental conditions, under low-intensity irradiation at 420 nm. Theoretical and experimental studies reveal that the increased activity is induced by surface Au–O species formed from H₂O decomposition, which synchronously optimizes the rate-determining steps in the CO₂reduction and H₂O oxidation reactions, lowers the energy barriers for the *CO desorption and *OOH formation, and facilitates CO and O₂production. Our findings provide an in-depth mechanistic understanding for designing active metal photocatalysts for efficient CO₂reduction with H₂O.

Copper-based catalysts are widely applied in catalytic CO conversion. Despite their importance in determining catalytic performance, the interaction of CO with different copper states has often been the subject of debate. Herein, we discuss the preparation of four different CuO_x states (namely, fully oxidized and reduced (O-573 and R-573, respectively) and 800 and 1000 K annealed (A-800 and A-1000, respectively)) through in situ treatments, comparing CO adsorption behaviors with vacuum-transmission IR spectroscopy. CO only weakly adsorbed on the A-1000 and R-573 surfaces, whereas it led to the creation of trace amounts of surface oxygen vacancies over the O-573 surface, providing adsorption sites for the subsequent CO. Meanwhile, the produced CO₂ re-adsorbed on the catalyst to form carbonate species. The reduction process was notably promoted over A-800 due to the presence of abundant surface oxygen vacancies, demonstrating the key role of Cu^δ+ in oxygen vacancies, rather than merely its chemical state, in dominating the interaction of CO with CuO_x.

Single atom alloys (SAAs) often bring new chemistry in heterogeneous catalysis and well-defined structure for the study of structure–activity relationship (SAR). However, the existing pressure gap causes the reported SARs quite divergent. Herein, we have studied CO activation over Ni/Cu(100) SAAs in ultrahigh vacuum (UHV) and millibar range. While the Ni SAAs formed on Cu(100) significantly enhance the CO adsorption strength under UHV conditions, the CO treatment at elevated pressure leads to notable surface carbon and oxygen deposition through surface reaction. Density functional theory calculations revealed that either dissociation or disproportionation is thermodynamically forbidden for the coverage of CO less than 5/16 ML. However, these two reaction pathways can be opened at higher CO coverages due to the elevated energy state involving repulsion between adsorbed CO. This work uncovers the initial activation process of CO and demonstrates one typical cause for the pressure gap in surface science study as well.

Strain commonly exists in nanomaterials and may significantly influence the physico-chemical properties and local reactivities. Enhanced oxygen adsorption was reported to be induced by subsurface Ar bubbles [Gsell et al., Science 280, 717–720 (1998)] due to the alteration of local surface strain. In this work, we show a reverse effect wherein post-oxygen exposure induces the desorption of Ar from the subsurface of sputter-annealed Cu(100). The multiple desorption peaks, by the combined analysis of multiple techniques, are ascribed to the structural evolution (surface roughening and recrystallization) and strain release during oxygen exposure and subsequent annealing. Notably, the quantity of desorbed subsurface Ar exhibits a correlation with oxygen exposure. The thermal behaviors of subsurface Ar as well as the surface reactivities can thus be rationally regulated by the modification of the surface, demonstrating a new strategy to tune the physico-chemical properties of subsurface species.

Modification of copper-based catalysts by incorporating a second metal is prevailing in developing high-performance catalysts for CO2 hydrogenation. In particular, the insight into how the reaction is influenced is key to understanding the nature of the strategy. Herein, we show that both intermediates and reaction pathways of CO2 over Cu(100) are conspicuously regulated by Ni deposition and CO2 pressure. CO2 exposure to Cu(100) at room temperature mainly yields surface oxygen and gas phase CO, whereas the deposited Ni functions in two ways: either to stabilize the surface carbonate species or to dissociate CO, leading to surface carbon and oxygen deposition. Interestingly, the pathways depend strongly on the pressure of CO2, which essentially induces surface roughening and alters the competition of CO/CO2 to react with Ni. Density functional theory simulations reveal that both factors have a notable influence on the adsorption/desorption kinetics and the stability of intermediates, hence leading to varied pathways.