Atomically Precise Thiolate-Protected Hexanuclear Silver Nanocluster [Ag₆(PMBI)₆] as Efficient Catalyst for Hydrogen Evolution Reactions

Metal nanoclusters (MNCs) with atomic precision and well-defined structures are gaining attention for various applications. In this work, we present the synthesis and structure of a novel thiolate-protected silver nanocluster with the molecular formula Ag6(PMBI)6, where PMBI denotes 9-propyl-2-mercaptobenzimidazole. The nanocluster was synthesized using a one-pot approach, and its structure was determined using single-crystal X-ray diffraction (SC-XRD). SC-XRD analysis further revealed a well-defined Ag6 core coordinated by six thiolate ligand units, forming a discrete and symmetric molecular cluster. Ligand engineering of silver nanoclusters enhances stability, modulates the physical and chemical properties of clusters, transforming them into efficient electrocatalysts for the hydrogen evolution reaction (HER). We investigated the nanoclusters' electrocatalytic HER activity in alkaline conditions. It exhibited an overpotential of 197 mV at 10 mA cm-2 and a Tafel slope of 125.3 mV dec-1. In addition, AgNCs@PMBI shows negligible toxicity, indicating its environmental and biological safety. This study showcases the potential of discrete, bare silver nanoclusters as a cost-effective and scalable HER electrocatalyst, providing an alternative to classical platinum-based electrocatalysts.