Efficient Electrocatalytic Semi-Hydrogenation of Alkynes by Interfacial Engineering of Atomically Precise Silver Nanoclusters.

Owing to its green energy and hydrogen sources, electrocatalytic semi-hydrogenation of alkynes is an attractive alternative for industrial alkene production. However, its broad application is hindered by low selectivity and low Faradaic efficiency (FE) due to side reactions like over-hydrogenation to alkanes. Here, we demonstrate that atomically precise Ag25(MHA)18 nanoclusters (NCs) can electrocatalyze alkyne semi-hydrogenation with 98% conversion, 99% selectivity, and 85% FE, in a broad substrate pool. This is achieved by engineering the local environment at the catalytically active sites. We leverage amphiphilic MHA (6-mercaptohexanoic acid) ligands to pre-concentrate water molecules and alkynes near the ligand-layer/Ag25 interface. Long-chain ligands can disrupt the hydrogen-bond network at the interface, the high negative charge of Ag25 can attract weakly hydrogen-bonded water through counterions and promote the generation of active hydrogen (H*), while the enzyme-like catalytic pockets on the surface of Ag25 NCs facilitate adsorption of terminal alkynes via σ-bonding to the surface Ag atoms. Density functional theory calculations confirmed the preference of the σ-bonding model of alkyne and further revealed the facile release of product alkene. This work exemplifies an atomically precise interface engineering strategy to control the local environment of active sites for optimized activity and selectivity.