Ligand effect on the catalytic activity of porphyrin-protected gold clusters in the electrochemical hydrogen evolution reaction

The "ligand effect" can be used as a novel strategy for enhancing the catalytic properties of metal clusters. Herein, we report the ligand effect of porphyrin derivatives on gold clusters (AuCs, size 2 nm) in the electrochemical hydrogen evolution reaction (HER) at pH 6.7. The current density of porphyrin face-coordinated AuCs at −0.4 V vs. reversible hydrogen electrode (RHE) was 460% higher than that of phenylethanethiol-protected AuCs. X-ray photoemission spectroscopy indicated that the approach of porphyrin to the Au surface induced charge migration from the porphyrin to the Au core, leading to a shift in the 5d state of AuCs that resulted in enhanced HER activities. This ligand effect is pronounced in the cluster region due to the large surface-to-volume ratio. These results pave the way for enhancing catalytic activity of metal clusters using ligand design. Ligand effect on the catalytic activity of gold clusters in the electrochemical hydrogen evolution reaction.