Constructing Active Sites in an Atomically Precise Silver Nanocluster toward Electrochemical Hydrogenation of 5-Hydroxymethylfurfural

Tailoring the electrocatalytic hydrogenation (ECH) performance of silver nanoclusters at the atomic level remains challenging. A mixed-ligand-protected superatomic silver nanocluster, Ag28(PNP)3(p-TBBT)20 (Ag28) (PNP= 2,6-bis(diphenylphosphino)pyridine; p-TBBT = 4-tert-butylthiophenol), was synthesized, and its structure was determined by single-crystal X-ray diffraction (SCXRD). Ag28 consisted of a capped icosahedral Ag18 kernel and accessible Ag(RS)3 and Ag(RS)2 motifs. Density functional theory calculations revealed that Ag28 can be rationalized as a closed-shell 8-electron superatom with a jellium configuration of 1S21P6. Remarkably, in comparison to other previously reported Ag19/21/25/29 nanoclusters that possess similar metal kernels but disparate surface ligands or coordination structures, Ag28 exhibited a significantly improved ECH performance for the conversion of 5-hydroxymethylfurfural (HMF) to 2,5-bishydroxymethylfuran (BHMF), with excellent selectivity and faradaic efficiency toward BHMF reaching 100% and 91.1%, respectively. It has been demonstrated through experimental and theoretical calculations that the more accessible Ag(RS)3 site, which is constructed using the steric hindrance effect of PNP on the surface of Ag28, plays a crucial role in the improved catalytic performance. This work represents the inaugural application of atomically precise Ag nanoclusters to the ECH of HMF and paves a new avenue for the rational design and application of cluster catalysts for electrocatalytic hydrogenation.