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

Abstract

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.

A Review of State of the Art in Phosphine Ligated Gold Clusters and Application in Catalysis

“…[ 251e ] Further reports of XPS studies performed to examine the electronic structure of gold–phosphine clusters by different groups are available here. [ 28 , 251 , 252 , 258 , 267 ]…”

“…Strategies to prevent aggregation such as the use of large surface areas, highly porous supports, creation of defects, ultralow gold loading and introduction of functionalized sites have been reported. [ 250 , 258 , 406 ] Alotabi et al. recently demonstrated that deposition of a thin (1.1 nm) layer of Cr 2 O 3 onto Au 9 /TiO 2 inhibits agglomeration of gold clusters after ligand removal by heating.…”

Methanol Tolerant Oxygen Reduction Reaction Electrocatalysis using Size‐Specific Triphenylphosphine‐Ligated Gold Nanoclusters

“…Two of our previous publications were dedicated to the formation of AuNCs-rGO nanocomposites without AuNCs agglomeration. [25,42] The AuNCs-rGO were synthesised via mixing a methanol dispersion of AuNCs and rGO for 1 h at RT in the dark. We discovered that the GO reduction method under acidic pH (pH � 2) is crucial to avoid the agglomeration of AuNCs.…”

“…We have previously reported greater HER performance for Au 101 NC-rGO compared to Au 1 NC-rGO and Au 9 NC-rGO. [42] In order to compare our reported data to literature value, we must consider some limitations in doing so. Electrocatalysis is highly dependent on the geometry of the electrode and the loading of the catalyst.…”

“…In our previous work, we showed that decreasing the AuNCs size results in easy agglomeration due to weak AuNCs-support interaction and high surface energy evidenced by XPS. [42] Therefore, Au 1 and Au 9 are readily agglomerated during chronoamperometry measurements. This result suggests high stability and agglom- eration resistance of Au 101 NC-rGO caused by the larger size and stronger metal-support interaction over Au 1 NC-rGO and Au 9 NC-rGO.…”