Homoleptic alkynyl-protected Ag32 nanocluster with atomic precision: Probing the ligand effect toward CO2 electroreduction and 4-nitrophenol reduction

We report a superatomic homoleptic alkynyl-protected Ag32L24 (L = 3,5-bis(trifluoromethylbenzene) acetylide, Ag-32 for short) nanocluster with atomic precision, which possesses eight free electrons. Ag 32 is formed by an Ag-17 core with C-3 symmetry and the remaining 15 Ag atoms bond to each other and coordinate with the 24 surface ligands. When applied as electrocatalyst for CO2 reduction reaction (CO2RR), Ag-32 exhibited the highest Faradaic efficiency (FE) of CO up to 96.44% at -0.8 V with hydrogen evolution being significantly suppressed in a wide potential range, meanwhile it has a reaction rate constant of 0.242 min(-1) at room temperature and an activation energy of 45.21 kJ-mol(-1) in catalyzing the reduction of 4-nitrophenol, both markedly superior than the thiolate and phosphine ligand co-protected Ag-32 nanocluster. Such strong ligand effect was further understood by density functional theory (DFT) calculations, as it revealed that, one single ligand stripping off from the intact cluster can create the undercoordinated Ag atom as the catalytically active site for both clusters, but alkynyl-protected Ag-32 nanocluster possesses a smaller energy barrier for forming the key *COOH intermediate in CO2RR, and favors the adsorption of 4-nitrophenol. This study not only discovers a new member of homoleptic alkynyl-protected Ag nanocluster, but also highlights the great potentials of employing alkynyl-protected Ag nanoclusters as bifunctional catalysts toward various reactions.

Automated summary

We report a superatomic homoleptic alkynyl-protected Ag32L24 nanocluster with atomic precision, which exhibits excellent catalytic performance in the CO2 reduction reaction (CO2RR) and the reduction of 4-nitrophenol. Density functional theory calculations further reveal the influence of ligand effect on the catalytic activity of the nanocluster.