Electrocatalytic hydrogen evolution reaction (HER) holds promise in the renewable clean energy scheme. Crystalline Au and Ag are, however, poor in catalyzing HER, and the ligands on colloidal nanoparticles are generally another disadvantage. Herein, we report a thiolate (SR)-protected Au 36 Ag 2 (SR) 18 nanocluster with low coverage of ligands and a core composed of three icosahedral (I h ) units for catalyzing HER efficiently. This trimeric structure, together with the monomeric I h Au 25 (SR) 18− and dimeric I h Au 38 (SR) 24 , constitutes a unique series, providing an opportunity for revealing the correlation between the catalytic properties and the catalyst's structure. The Au 36 Ag 2 (SR) 18 surprisingly exhibits high catalytic activity at lower overpotentials for HER due to its low ligand-to-metal ratio, low-coordinated Au atoms and unfilled superatomic orbitals. The current density of Au 36 Ag 2 (SR) 18 at −0.3 V vs RHE is 3.8 and 5.1 times that of Au 25 (SR) 18 − and Au 38 (SR) 24 , respectively. Density functional theory (DFT) calculations reveal lower hydrogen binding energy and higher electron affinity of Au 36 Ag 2 (SR) 18 for an energetically feasible HER pathway. Our findings provide a new strategy for constructing highly active catalysts from inert metals by pursuing atomically precise nanoclusters and controlling their geometrical and electronic structures.

Temperature-dependent optical properties are of paramount importance for fundamentally understanding the electron−phonon interactions and phonon modes in atomically precise nanocluster materials. In this work, low-temperature optical absorption spectra of the icosahedral [Au 25 (SR) 18 ] − nanocluster are measured from room temperature down to liquid helium temperature by adopting a thin-film-based technique. The thin-film measurement is further compared with results from the previous solution-based method. Interestingly, the previously missing core phonon is revealed by a quantitative analysis of the film data through peak deconvolution and fitting of the temperature trend with a theoretical model. The two lowest-energy absorption peaks (at 1.6 and 1.8 eV) of Au 25 are determined to couple with the staple-shell phonon (average energy ∼350 cm −1 ) in the solution state, but in the solid state these electronic transitions couple with the core phonon (average energy ∼180 cm −1 ). The suppression of the staple-shell phonon in the solid state is attributed to the intracluster and cluster−matrix interactions.

This work presents the synthesis and intriguing photoluminescence of the Au 42 (PET) 32 (PET = 2-phenylethanethiolate) nanocluster (NC). The Au 42 (PET) 32 NC exhibits dual emission at 875 and 1040 nm, which are revealed to be fluorescence and phosphorescence, respectively. The emission quantum yield (QY) of Au 42 (PET) 32 in dichloromethane is 11.9% at room temperature in air, which is quite rare for thiolate-protected Au NCs. When Au 42 (PET) 32 NCs are embedded in polystyrene films (solid state), the fluorescence was dramatically suppressed while the phosphorescence was significantly enhanced. This divergent behavior is explained by dipolar interaction-induced enhancement of intersystem crossing from singlet to triplet excited state.

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Understanding the electron–phonon interaction in Au nanoclusters (NCs) is essential for enhancing and tuning their photoluminescence (PL) properties. Among all the methods, ligand engineering is the most straightforward and facile one to design Au NCs with the desired PL properties. However, a systematic understanding of the ligand effects toward electron–phonon interactions in Au NCs is still missing. Herein, we synthesized four Au25(SR)18 – NCs protected by different −SR ligands and carefully examined their temperature-dependent band-gap renormalization behavior. Data analysis by a Bose–Einstein two-oscillator model revealed a suppression of high-frequency optical phonons in aromatic-ligand-protected Au25 NCs. Meanwhile, a low-frequency breathing mode and a quadrupolar mode are attributed as the main contributors to the phonon-assisted nonradiative relaxation pathway in aromatic-ligand-protected Au25 NCs, which is in contrast with non-aromatic-ligand-protected Au25 NCs, in which tangential and radial modes play the key roles. The PL measurements of the four Au25 NCs showed that the suppression of optical phonons led to higher quantum yields in aromatic-ligand-protected Au25 NCs. Cryogenic PL measurements provide insights into the nonradiative energy relaxation, which should be further investigated for a full understanding of the PL mechanism in Au25 NCs.

Photoluminescence of ultrasmall, atomically precise gold nanoclusters constitutes an area of significant interest in recent years for both fundamental research and biological applications. However, the exploration of near-infrared photoluminescence of gold nanoclusters is still in its infancy due to the limitations of synthetic methods and characterization techniques. Herein, the photoluminescence properties of an Au38(PET)26 (PET = 2-phenylethanethiolate) nanocluster are investigated in detail. The Au38(PET)26 exhibits an emission peak at 865 nm, which is revealed to be a mix of fluorescence, thermally activated delayed fluorescence, and phosphorescence via the combined analyses of time-resolved and temperature-dependent photoluminescence measurements. The quantum yield of Au38(PET)26 is determined to be 1.8% at room temperature under ambient conditions, which increases to above 90% by suppressing the non-radiative relaxation pathway at a cryogenic temperature (80 K). Overall, the results of this work discover the coexistence of three radiative processes in thiolate-protected Au nanoclusters and will pave the way for understanding the intriguing photoluminescence properties of gold nanoclusters in future studies.

The development of renewable energy technologies is critical for reducing global carbon emissions. Water splitting offers a promising renewable energy mechanism by converting water into H2 and O2 gas, which can directly power fuel cells or be utilized as chemical feedstocks. To increase the efficiency of water splitting, catalysts must be developed for the water reduction and water oxidation half-reactions. To promote rational catalyst design, atomically precise metal clusters (APMCs) with earth-abundant metals provide a framework for developing both structure–activity relationships and cost-effective catalysts. Previous reports on the water oxidation activity of nickel-thiolate clusters [Ni n (SR)2n ] have not developed a systematic description of a possible size–activity relationship. Utilizing recent advancements in preparative chromatography for isolating APMCs, we have synthesized a series of Ni n (SR)2n (n = 4, 5, or 6) clusters as electrocatalysts for the oxygen evolution reaction. We discovered a clear size–activity and size–stability trend, with intrinsic activity and stability increasing with cluster size. Using density functional theory, we found that intrinsic activity is inversely correlated to intermediate binding energy, and by extension the oxidation potential of each cluster. Our work demonstrates the ability of APMCs to uncover previously unknown structure–activity relationships that can guide future catalyst design.

The emergence of ligand-protected, atomically precise gold nanoclusters (NCs) in recent years has attracted broad interest in catalysis due to their well-defined atomic structures and intriguing properties. Especially, the precise formulas of NCs provide an opportunity to study the size effects at the atomic level without complications by the polydispersity in conventional nanoparticles that obscures the relationship between the size/structure and properties. Herein, we summarize the catalytic size effects of atomically precise, thioate-protected gold NCs in the range of tens to hundreds of metal atoms. The catalytic reactions include electrochemical catalysis, photocatalysis, and thermocatalysis. With the precise sizes and structures, the fundamentals underlying the size effects are analyzed, such as the surface area, electronic properties, and active sites. In the catalytic reactions, one or more factors may exert catalytic effects simultaneously, hence leading to different catalytic-activity trends with the size change of NCs. The summary of literature work disentangles the underlying fundamental mechanisms and provides insights into the size effects. Future studies will lead to further understanding of the size effects and shed light on the catalytic active sites and ultimately promote catalyst design at the atomic level.