The impact of ligand chain length on the HER performance of atomically precise Pt₆(SR)₁₂ nanoclusters

Atomically precise metal cluster-based electrocatalysts have been paid significant attention for an efficient hydrogen evolution reaction (HER). Herein, we have synthesized atomically precise Pt₆(SR)₁₂ nanoclusters using 3-mercaptopropionic acid (MPA), 6-mercaptohexanoic acid (MHA), 8-mercaptooctanoic acid (MOA), and 11-mercaptoundecanoic acid (MUA) thiol ligands in aqueous media at room temperature to understand the impact of ligand chain length on the HER performance. The composition of Pt₆(SR)₁₂ metal clusters was confirmed by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. Electrochemical studies confirmed that the HER performance of Pt₆(SR)₁₂ NCs is notably affected by the ligand chain length, and Pt₆(MPA)₁₂ exhibits an overpotential of 19 mV at a current density of 10 mA cm^-2, which is several-fold higher than the Pt NCs developed in the recent past. The interfacial charge transfer kinetics and the HER performance decrease with the increase in the chain length of the thiol ligands. Density functional theory calculations showed that the Gibbs free energy for hydrogen adsorption decreases with decreasing chain length of the thiol ligand. The ligands used to synthesize Precise metal clusters for electrocatalysis play an essential role in their efficiency.