Activation of photocatalytic CO₂ reduction by loading hydrophobic thiolate-protected Au₂₅ nanocluster cocatalyst

The photocatalytic carbon dioxide (CO₂) reduction reaction (CO₂RR), which reduces CO₂ to various useful chemical compounds by light, has attracted attention to achieve carbon neutrality. In photocatalytic CO₂RR, it is effective to load metal nanoparticles (NP) as cocatalysts on the surface of semiconductor photocatalysts to improve their activity and selectivity. In this study, we used ultrafine metal nanoclusters (NC) with a particle size of about 1 nm as cocatalysts to clarify the effect of surface ligands on the activity and selectivity of the photocatalytic CO₂RR. As a result, it was shown that the introduction of hydrophobic ligands to the Au₂₅ NC cocatalyst suppresses the competing hydrogen evolution reaction, thereby increasing the selectivity of CO₂RR. In addition, the hydrophobic ligand-protected Au₂₅ NC cocatalysts exhibited 66 times higher CO evolution rates per Au-loading weights than the Au NP cocatalysts with a particle size of about 7 nm. These results provide crucial insights into the creation of highly active metal NC cocatalysts for photocatalytic CO₂RR.