Factors Influencing Catalytic Activity of Size-Specific Triphenylphosphine-Ligated Gold Nanoclusters in the Electrocatalytic Hydrogen Evolution Reaction

Hydrogen production via electrocatalytic water splitting has attracted growing attention as an alternative renewable and clean energy source. Size-specific gold nanoclusters and complexes (AuNCs) can serve as models for investigating the catalytic behavior toward the hydrogen evolution reaction (HER) at the atomic level. This work is focused on exploring the factors influencing the catalytic activity of phosphine-ligated AuNCs as electrocatalysts for improving HER performance using Au₁₀₁(PPh₃)₂₁Cl₅, Au₉(PPh₃)₈(NO₃)₃, and Au₁(PPh₃)Cl supported on reduced graphene oxide (rGO). Production of AuNC–rGO nanocomposites without agglomeration of the AuNCs was confirmed by transmission electron microscopy, X-ray photoelectron spectroscopy, and visible light absorbance. The weight loading of gold in the nanocomposite material was confirmed to be ≈5 wt % by thermogravimetric analysis and inductively coupled plasma mass spectrometry. Electrocatalytic performance of the AuNCs was determined through linear sweep voltammograms in 0.5 M sulfuric acid. Greater performance was observed for Au₁₀₁NC–rGO, while Au₉NC–rGO and Au₁NC–rGO showed similar performance. The stability of each AuNC was determined through extended chronoamperometry experiments, and negligible reduction in performance was observed for Au₁₀₁NC–rGO and Au₉NC–rGO, while Au₁NC–rGO was less stable. The variation in performance was attributed to a range of factors including catalyst size, electronic structure, and ligand density. This work provides guidelines to design highly efficient electrocatalysts using ligated metal clusters.