The evolution from the metallic (or plasmonic) to molecular state in metal nanoparticles constitutes a central question in nanoscience research because of its importance in revealing the origin of metallic bonding and offering fundamental insights into the birth of surface plasmon resonance. Previous research has not been able to probe the transition due to the unavailability of atomically precise nanoparticles in the 1–3 nm size regime. Herein, we investigate the transition by performing ultrafast spectroscopic studies on atomically precise thiolate-protected Au25, Au38, Au144, Au333, Au∼520 and Au∼940 nanoparticles. Our results clearly map out three distinct states: metallic (size larger than Au333, that is, larger than 2.3 nm), transition regime (between Au333 and Au144, that is, 2.3–1.7 nm) and non-metallic or excitonic state (smaller than Au144, that is, smaller than 1.7 nm). The transition also impacts the catalytic properties as demonstrated in both carbon monoxide oxidation and electrocatalytic oxidation of alcohol.

Unravelling the atomic structures of small gold clusters is the key to understanding the origin of metallic bonds and the nucleation of clusters from organometallic precursors. Herein we report the X-ray crystal structure of a charge-neutral [Au18(SC6H11)14] cluster. This structure exhibits an unprecedented bi-octahedral (or hexagonal close packing) Au9 kernel protected by staple-like motifs including one tetramer, one dimer, and three monomers. Until the present, the [Au18(SC6H11)14] cluster is the smallest crystallographically characterized gold cluster protected by thiolates and provides important insight into the structural evolution with size. Theoretical calculations indicate charge transfer from surface to kernel for the HOMO-LUMO transition.

To tackle the excessive emission of greenhouse gas CO 2 , electrocatalytic reduction has been recognized as a promising way. Given the multielectron, multiproduct nature of the CO 2 reduction process, an ideal catalyst should be capable of converting CO 2 with high rates as well as high selectivity to either gas-phase (e.g., CO, CH 4 ) or liquid-phase products (e.g., HCOOH, CH 3 OH, etc.). Gold-and silver-based materials have been extensively investigated as CO 2 reduction catalysts for the formation of CO. This Perspective focuses on the advances of gold-and silver-based electrocatalysts for CO 2 reduction in terms of catalyst design as well as some insights from theoretical investigations. In particular, a special emphasis is placed on the newly emerging, atomically precise metal nanoclusters for CO 2 electroreduction. The strong quantum confinement effect and molecular purity as well as the crystallographically solved atomic structures of nanoclusters make this new class of catalysts quite promising in fundamental studies, and valuable mechanistic insights for CO 2 electroreduction at the atomic scale can be obtained. We hope that this Perspective highlights the opportunities and challenges in the exploration of emerging nanomaterials.

Electrocatalytic water splitting to produce hydrogen comprises the hydrogen and oxygen evolution half reactions (HER and OER), with the latter as the bottleneck process. Thus, enhancing the OER performance and understanding the mechanism are critically important. Herein, we report a strategy for OER enhancement by utilizing gold nanoclusters to form cluster/CoSe composites; the latter exhibit largely enhanced OER activity in alkaline solutions. The Au/CoSe composite affords a current density of 10 mA cm at small overpotential of ∼0.43 V (cf. CoSe: ∼0.52 V). The ligand and gold cluster size can also tune the catalytic performance of the composites. Based upon XPS analysis and DFT simulations, we attribute the activity enhancement to electronic interactions between nanocluster and CoSe, which favors the formation of the important intermediate (OOH) as well as the desorption of oxygen molecules over Au/CoSe composites in the process of water oxidation. Such an atomic level understanding may provide some guidelines for design of OER catalysts.

Recent advances in the synthetic chemistry of atomically precise metal nanoclusters (NCs) have significantly broadened the accessible sizes and structures. Such particles are well defined and have intriguing properties, thus, they are attractive for catalysis. Especially, those NCs with identical size but different core (or surface) structure provide unique opportunities that allow the specific role of the core and the surface to be mapped out without complication by the size effect. Herein, we summarize recent work with isomeric Aun NCs protected by ligands and isostructural NCs but with different surface ligands. The highlighted work includes catalysis by spherical and rod‐shaped Au25 (with different ligands), quasi‐isomeric Au28(SR)20 with different R groups, structural isomers of Au38(SR)24 (with identical R) and Au38S2(SR)20 with body‐centred cubic (bcc) structure, and isostructural [Au38L20(PPh3)4]2+ (different L). These isomeric and/or isostructural NCs have provided valuable insights into the respective roles of the kernel, surface staples, and the type of ligands on catalysis. Future studies will lead to fundamental advances and development of tailor‐made catalysts.