Ligand-to-Metal Charge Transfer Controls the Photophysical Properties and HER Activity of Ag13 Nanoclusters Depends on the Hydrogen Adsorption Energy

The hydrogen evolution reaction (HER) activity of ligand-protected metal nanoclusters (NCs) has been emphasized, where the ligands influence the electronic properties and hydrogen adsorption energy during the catalytic process. Here, we highlight the influence of the ligand-to-metal charge transfer (LMCT) on the photoluminescence (PL) properties and the adsorption free energy on the HER activity of Ag₁₃ NCs. MALDI-MS analysis confirms the composition of the NCs as [Ag₁₃(L)₉] NCs [L = D-penicillamine (DPA), cysteine (CYS), and mercaptopropionyl glycine (MPG)]. XPS study and DFT calculations reveal that electron-donating ligands modulate the electron density of the Ag(I) core and cause a change in the HOMO–LUMO gap and PL properties due to LMCT. Partial density of states (PDOS) calculation shows that H 1s–Ag bonding occurs below the Fermi level, causing a substantial contribution of hydrogen to the valence band region in [Ag₁₃(CYS)₉] NCs. The optimal hydrogen adsorption energy and efficient charge transfer kinetics are the reasons for the superior HER activity in [Ag₁₃(CYS)₉] NCs.