Elucidating the stability of ligand-protected Au nanoclusters under electrochemical reduction of CO2

Abstract

Ligand-protected gold nanoclusters are a novel class of particles that have attracted great interest in the field of catalysis due to their atomically-precise structure, high surface-to-volume ratio, and unique electronic properties. In particular, the anionic thiolate-protected Au 25 nanocluster (NC), [Au 25 (SR) 18 ] 1− , with partially lost ligands, has been demonstrated to act as an active catalyst for the electrochemical reduction of CO 2. However, the stability of this and other thiolate-protected NCs after partial ligand removal remains elusive. Using density functional theory (DFT) calculations and the recently developed thermodynamic stability model, we investigate the stability of [Au 25 (SR) 18 ] 1− , [Au 18 (SR) 14 ] 0 , [Au 23 (SR) 16 ] 1− , and [Au 28 (SR) 20 ] 0 with ligand loss. Additionally, we examine the stability of the partially protected NCs upon adsorption of CO 2 reduction reaction intermediates (i.e. H, CO, and COOH) on the different active sites generated after ligand removal. Our results reveal that the partially protected Au 25 NC shows the highest stability compared to the other partially protected NCs in the presence of electrochemical reduction intermediates. We find that the presence of the COOH intermediate on the generated active sites stabilizes the Au 25 NC almost as well as the removed ligands. Moreover, time-dependent DFT calculations and UV-Vis/Raman experiments suggest that the most probable ligand removal mode under electrochemical conditions is the one that generates S active sites, in agreement with the DFT ligand removal thermodynamic analysis. Importantly, this study demonstrates the robustness of the Au 25 NC and offers a novel way to address stability of ligand protected NCs during electrocatalytic reaction conditions.

Boosting CO2 Electrochemical Reduction with Atomically Precise Surface Modification on Gold Nanoclusters

“…We observed that it is more thermodynamically feasible to remove the ‐R group as compared to the ‐SR group from both NCs. This is consistent with previous work that reported the ease of exposing a sulfur atom (‐R group removal, R=CH 3 ) as an active site compared to gold (‐SR removal) from the [Au 25 (SCH 3 ) 18 ] 1− nanocluster [26c] . Cleaving a ‐R group from either nanocluster was nearly thermoneutral, implying that the thermodynamics of formation of the S active site is similar on both NCs.…”

Understanding the Single Atom Doping Effects in Oxygen Reduction with Atomically Precise Metal Nanoclusters

“…The relaxed structures of the NCs obtained from DFT are similar to the experimentally obtained structures (Figure S3). A common approach to reduce the computational expense while still accurately capturing the catalytic activity trends of NCs is to replace the experimental bulky ligands such as SPhMe 2 with SCH 3 groups. ,, Here we use the same approach for DFT calculations. Previous studies have shown that removing a ligand under reaction conditions is feasible and can lead to the creation of active sites for catalysis. , Using the fully relaxed structures, we calculate the Gibbs free energy (Δ G ) of removing either the −R (−CH 3 ) group or the −SR (−SCH 3 ) group, which leads to the exposure of a sulfur or metal atom, respectively, as an active site.…”

“…A common approach to reduce the computational expense while still accurately capturing the catalytic activity trends of NCs is to replace the experimental bulky ligands such as SPhMe 2 with SCH 3 groups. 22,29,30 Here we use the same approach for DFT calculations. Previous studies have shown that removing a ligand under reaction conditions is feasible and can lead to the creation of active sites for catalysis.…”

Toward the creation of high-performance heterogeneous catalysts by controlled ligand desorption from atomically precise metal nanoclusters

“…Several recent DFT calculations have predicted that higher activity can be achieved through the elimination of ligands also in the application of metal NCs as electrocatalysts. [337][338][339][340][341][342] However, there are also reactions in which the presence of ligands leads to an improvement of the conversion efficiency. In addition, the presence of ligands has advantages in changing the reaction selectivity and suppressing aggregation of metal NCs, thereby improving the catalyst durability.…”

“…For such heterogeneous catalysts composed of atomically precise metal NCs, DFT calculations may be able to predict highly functional catalyst systems. [337][338][339][340][341][342]348 Thus, in the future, it is expected that studies for improving the functionality of heterogeneous catalysts will shift from searching for the optimum system based on trial-and-error experiments to prediction by DFT calculation.…”