Carbon-supported Au cluster catalysts partially decorated with dendron thiolates: enhanced loading weight and durability for hydrogen evolution reaction

In order to establish a design principle for efficient Au electrocatalysis, it is desirable to synthesize a highly loaded, robust, and atomically precise Au cluster catalyst on a conductive carbon support. In this work, heterogeneous Au 25 catalysts were prepared by calcining 5.0 wt% of mixed ligated [Au 25 (D2S) x (PET) 18− x ] 0 (D2S = second generation Fréchet-type dendron thiolate, PET = 2-phenylethanethiolate) on a carbon support. X-ray absorption fine structure analysis, powder X-ray diffraction, and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) revealed the successful synthesis of carbon-supported partially thiolated Au 25 clusters by calcining [Au 25 (D2S) 10.7 (PET) 7.3 ] 0 at 425 °C for ≥12 h, whereas calcination of [Au 25 (PET) 18 ] 0 under the same conditions resulted in thermally induced aggregation into larger Au nanoparticles. The D2S-modified Au 25 catalyst showed better durability than PET-modified Au 25 in electrocatalytic hydrogen evolution reaction. The higher durability was attributed to the suppression of aggregation of Au 25 clusters during the reaction, as confirmed by AC-HAADF-STEM. These results indicate that the residual D2S ligands on Au 25 enhance the stability against aggregation more than the residual PET due to stronger non-covalent interactions with carbon supports and/or greater steric hindrance of dendritic structure. This work demonstrates that the stability of Au catalysts can be improved by partial decoration with designed ligands. The loading amount and durability of the carbon-supported Au 25 cluster catalyst were successfully enhanced by introducing bulky, dendron thiolates, due to (1) strong non-covalent interactions between ligands and support, and (2) steric repulsion.