Ligand-induced surface functionalization in Ag₂S nanocrystals for efficient hydrogen evolution reaction in acidic media

Colloidal nanocrystals (NCs) have gained attention as electrocatalysts due to their tunable surfaces and compositions. However, the presence of surface ligands on NCs has been considered detrimental to their electrocatalytic performance. Here we demonstrate that ligand-derived surface functionalization in Ag₂S NCs can significantly enhance the hydrogen evolution reaction (HER) activity. We synthesized Ag₂S NCs capped with either 3-mercaptopropionic acid (MPA) or oleylamine (OLA) as surface ligands. The MPA-functionalized NCs exhibited strong hydrophilicity and higher HER activity. In contrast, the OLA-functionalized NCs showed hydrophobicity with lower HER activity. Density functional theory calculations supported the favorable HER activity of the MPA-functionalized NCs due to their relatively lower Gibbs free energy. Proton exchange membrane electrolysis cells employing the MPA-functionalized Ag₂S NCs exhibited stable operation for 24 h at −200 mA/cm² with >95 % Faradaic efficiency. This suggests the importance of surface functionalization in catalytic performance of nanocatalysts.