Direct Formation of Colloidal All-Inorganic Metal Nanocrystals from Magic-Size Clusters

All-inorganic metal nanocrystals (NCs) offer an ideal platform for atomically precise surface design and show improved electrocatalytic activity compared to conventional NCs capped with organic ligands. Here, we show the possibility of obtaining colloidal all-inorganic Au NCs directly from magic-size clusters (MSCs) with the assistance of inorganic molecules, NOBF4 or Na2S2O8. The unique advantages of NOBF4 or Na2S2O8 as both oxidizing agents and stripping ligands are taken to tune the surface state of Au25(PET)18–TOA+ MSCs and assemble them to form either positively or negatively charged all-inorganic Au NCs. We show that positively charged all-inorganic Au NCs can be further modified with different functional groups, which provide the possibility to meet the target requirements. We found that the negatively charged NCs exhibit improved faradaic efficiency (FE = 92%) for the reduction of CO2 to CO at −0.369 V (vs RHE) and a 5-fold increase in current density compared to organic-capped Au NCs (FE = 67%). In addition, we extended this approach to other MSCs and formed all-inorganic metal NCs with different compositions and morphologies. The use of simple inorganic ligands to induce the conversion from MSCs to metal NCs enriches the current solution process of synthesizing all-inorganic NCs and can open up more opportunities for designing colloidal nanocrystal catalysts.