Unraveling the roles of atomically-dispersed Au in boosting photocatalytic CO2 reduction and aryl alcohol oxidation

Atomically-dispersed metal-based materials represent an emerging class of photocatalysts attributed to their high catalytic activity, abundant surface active sites, and efficient charge separation. Nevertheless, the roles of different forms of atomically-dispersed metals (i.e., single-atoms and atomic clusters) in photocatalytic reactions remain ambiguous. Herein, we developed an ethylenediamine (EDA)-assisted reduction method to controllably synthesize atomically dispersed Au in the forms of Au single atoms (Au_SA), Au clusters (Au_C), and a mixed-phase of Au_SA and Au_C (Au_SA+C) on CdS. In addition, we elucidate the synergistic effect of Au_SA and Au_C in enhancing the photocatalytic performance of CdS substrates for simultaneous CO₂ reduction and aryl alcohol oxidation. Specifically, Au_SA can effectively lower the energy barrier for the CO₂→*COOH conversion, while Au_C can enhance the adsorption of alcohols and reduce the energy barrier for dehydrogenation. As a result, the Au_SA and Au_C co-loaded CdS show impressive overall photocatalytic CO₂ conversion performance, achieving remarkable CO and BAD production rates of 4.43 and 4.71 mmol g⁻¹ h⁻¹, with the selectivities of 93% and 99%, respectively. More importantly, the solar-to-chemical conversion efficiency of Au_SA+C/CdS reaches 0.57%, which is over fivefold higher than the typical solar-to-biomass conversion efficiency found in nature (ca. 0.1%). This study comprehensively describes the roles of different forms of atomically-dispersed metals and their synergistic effects in photocatalytic reactions, which is anticipated to pave a new avenue in energy and environmental applications.