Concomitant Near-Infrared Photothermy and Photoluminescence of Rod-Shaped Au52(PET)32 and Au66(PET)38 Synthesized Concurrently.

Gold nanoclusters exhibiting concomitant photothermy (PT) and photoluminescence (PL) under near-infrared (NIR) light irradiation are rarely reported, and some fundamental issues remain unresolved for such materials. Herein, we concurrently synthesized two novel rod-shaped Au nanoclusters, Au52(PET)32 and Au66(PET)38 (PET = 2-phenylethanethiol), and precisely revealed that their kernels were 4 × 4 × 6 and 5 × 4 × 6 face-centered cubic (fcc) structures, respectively, based on the numbers of Au layers in the [100], [010], and [001] directions. Following the structural growth mode from Au52(PET)32 to Au66(PET)38, we predicted six more novel nanoclusters. The concurrent synthesis provides rational comparison of the two nanoclusters on the stability, absorption, emission and photothermy, and reveals the aspect ratio-related properties. An interesting finding is that the two nanoclusters exhibit concomitant PT and PL under 785 nm light irradiation, and the PT and PL are in balance, which was explained by the qualitative evaluation of the radiative and non-radiative rates. The ligand effects on PT and PL were also investigated.

Atomically Precise Nanometer-Sized Pt Catalysts with an Additional Photothermy Functionality.

Atomically precise ~1-nm Pt nanoparticles (nanoclusters, NCs) with ambient stability are important in fundamental research and exhibit diverse practical applications (catalysis, biomedicine, etc.). However, synthesizing such materials is challenging. Herein, by employing the mixture ligand protecting strategy, we successfully synthesized the largest organic-ligand-protected (~1-nm) Pt23 NCs precisely characterized with mass spectrometry and single-crystal X-ray diffraction analyses. Interestingly, natural population analysis and Bader charge calculation indicate an alternate, varying charge -layer distribution in the sandwich-like Pt23 NC kernel. Pt23 NCs can catalyze the oxygen reduction reaction under acidic conditions without requiring calcination and other treatments, and the resulting specific and mass activities without further treatment are sevenfold and eightfold higher than those observed for commercial Pt/C catalysts, respectively. Density functional theory and d-band center calculations interpret the high activity. Furthermore, Pt23 NCs exhibit a photothermal conversion efficiency of 68.4 % under 532-nm laser irradiation and can be used at least for six cycles, thus demonstrating great potential for practical applications.

1T'-transition metal dichalcogenide monolayers stabilized on 4H-Au nanowires for ultrasensitive SERS detection.

Unconventional 1T'-phase transition metal dichalcogenides (TMDs) have aroused tremendous research interest due to their unique phase-dependent physicochemical properties and applications. However, due to the metastable nature of 1T'-TMDs, the controlled synthesis of 1T'-TMD monolayers (MLs) with high phase purity and stability still remains a challenge. Here we report that 4H-Au nanowires (NWs), when used as templates, can induce the quasi-epitaxial growth of high-phase-purity and stable 1T'-TMD MLs, including WS2, WSe2, MoS2 and MoSe2, via a facile and rapid wet-chemical method. The as-synthesized 4H-Au@1T'-TMD core-shell NWs can be used for ultrasensitive surface-enhanced Raman scattering (SERS) detection. For instance, the 4H-Au@1T'-WS2 NWs have achieved attomole-level SERS detections of Rhodamine 6G and a variety of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike proteins. This work provides insights into the preparation of high-phase-purity and stable 1T'-TMD MLs on metal substrates or templates, showing great potential in various promising applications.

Pd8 Nanocluster with Nonmetal-to-Metal- Ring Coordination and Promising Photothermal Conversion Efficiency.

Constructing ambient-stable, single-atom-layered metal-based materials with atomic precision and understanding their underlying stability mechanisms are challenging. Here, stable single-atom-layered nanoclusters of Pd were synthesized and precisely characterized through electrospray ionization mass spectrometry and single-crystal X-ray crystallography. A pseudo-pentalene-like Pd8 unit was found in the nanocluster, interacting with two syn PPh units through nonmetal-to-metal -ring coordination. The unexpected coordination, which is distinctly different from the typical organoring-to-metal coordination in half-sandwich-type organometallic compounds, contributes to the ambient stability of the as-obtained single-atom-layered nanocluster as revealed through theoretical and experimental analyses. Furthermore, quantum chemical calculations revealed dominant electron transition along the horizontal x-direction of the Pd8 plane, indicating high photothermal conversion efficiency (PCE) of the nanocluster, which was verified by the experimental PCE of 73.3 %. Therefore, this study unveils the birth of a novel type of compound and the finding of the unusual nonmetal-to-metal -ring coordination and has important implications for future syntheses, structures, properties, and structure-property correlations of single-atom-layered metal-based materials.

Synthesis of 2H/fcc-Heterophase AuCu Nanostructures for Highly Efficient Electrochemical CO2 Reduction at Industrial Current Densities.

Structural engineering of nanomaterials offers a promising way for developing high-performance catalysts toward catalysis. However, the delicate modulation of thermodynamically unfavorable nanostructures with unconventional phases still remains a challenge. Here, the synthesis of hierarchical AuCu nanostructures is reported with hexagonal close-packed (2H-type)/face-centered cubic (fcc) heterophase, high-index facets, planar defects (e.g., stacking faults, twin boundaries, and grain boundaries), and tunable Cu content. The obtained 2H/fcc Au99 Cu1 hierarchical nanosheets exhibit excellent performance for the electrocatalytic CO2 reduction to produce CO, outperforming the 2H/fcc Au91 Cu9 and fcc Au99 Cu1 . The experimental results, especially those obtained by in-situ differential electrochemical mass spectroscopy and attenuated total reflection Fourier-transform infrared spectroscopy, suggest that the enhanced catalytic performance of 2H/fcc Au99 Cu1 arises from the unconventional 2H/fcc heterophase, high-index facets, planar defects, and appropriate alloying of Cu. Impressively, the 2H/fcc Au99 Cu1 shows CO Faradaic efficiencies of 96.6% and 92.6% at industrial current densities of 300 and 500 mA cm-2 , respectively, as well as good durability, placing it among the best CO2 reduction electrocatalysts for CO production. The atomically structural regulation based on phase engineering of nanomaterials (PEN) provides an avenue for the rational design and preparation of high-performance electrocatalysts for various catalytic applications.

Lattice Compression Revealed at the ≈1†nm Scale.

Lattice tuning at the ≈1 nm scale is fascinating and challenging; for instance, lattice compression at such a minuscule scale has not been observed. The lattice compression might also bring about some unusual properties, which waits to be verified. Through ligand induction, we herein achieve the lattice compression in a ≈1 nm gold nanocluster for the first time, as detected by the single-crystal X-ray crystallography. In a freshly synthesized Au52 (CHT)28 (CHT=S-c-C6 H11 ) nanocluster, the lattice distance of the (110) facet is found to be compressed from 4.51 to 3.58 Šat the near end. However, the lattice distances of the (111) and (100) facets show no change in different positions. The lattice-compressed nanocluster exhibits superior electrocatalytic activity for the CO2 reduction reaction (CO2 RR) compared to that exhibited by the same-sized Au52 (TBBT)32 (TBBT=4-tert-butyl-benzenethiolate) nanocluster and larger Au nanocrystals without lattice variation, indicating that lattice tuning is an efficient method for tailoring the properties of metal nanoclusters. Further theoretical calculations explain the high CO2 RR performance of the lattice-compressed Au52 (CHT)28 and provide a correlation between its structure and catalytic activity.

Atom-stepped surface-regulated Pd nanowires for boosting alcohol oxidation activity.

A highly active surface can endow the electrocatalysts with extraordinary catalytic performances. However, it remains challenging to tailor the atomic packing characteristics and thus the physical and chemical characteristics of the electrocatalysts. Herein, penta-twinned Pd nanowires (NWs) with abundant high-energy atomic steps (i.e., stepped Pd) are synthesized by seeded synthesis on Pd NWs enclosed by (100) facets. Benefiting from the catalytically active atomic steps, such as [n(100) × m(111)] on the surface, the resultant stepped Pd NWs can work as an effective electrocatalyst for the ethanol oxidation reaction (EOR) and ethylene glycol oxidation reaction (EGOR), which are essential anode reactions in direct alcohol fuel cells (DAFCs). Compared with commercial Pd/C, the Pd nanowires bound by (100) facets and atomic steps both display enhanced catalytic activity and stability towards the EOR and EGOR. Importantly, the mass activities of the stepped Pd NWs toward the EOR and EGOR are 6.38 and 7.98 A mgPd-1, which are 3.1 and 2.6 times those of Pd NWs enclosed by (100) facets, respectively. Besides, our synthetic strategy also enables the formation of bimetallic Pd-Cu nanowires with abundant atomic steps. This work not only demonstrates a simple yet effective strategy to obtain mono- or bi-metallic nanowires with abundant atomic steps, but also highlights the significant role of atomic steps for boosting the activity of electrocatalysts.

Sandwich-Kernelled AgCu Nanoclusters with Golden Ratio Geometry and Promising Photothermal Efficiency.

Metal nanoclusters have recently attracted extensive interest from the scientific community. However, unlike carbon-based materials and metal nanocrystals, they rarely exhibit a sheet kernel structure, probably owing to the instability caused by the high exposure of metal atoms (particularly in the relatively less noble Ag or Cu nanoclusters) in such a structure. Herein, we synthesized a novel AgCu nanocluster with a sandwich-like kernel (diameter≈0.9 nm and length≈0.25 nm) by introducing the furfuryl mercaptan ligand (FUR) and the alloying strategy. Interestingly, the kernel consists of a centered silver atom and two planar Ag10 pentacle units with completely mirrored symmetry after a rotation of 36 degrees. The two Ag10 pentacles and some extended structures show an unreported golden ratio geometry, and the two inner five-membered rings and the centered Ag atom form an unanticipated full-metal ferrocene-like structure. The featured kernel structure causes the dominant radial direction transition of excitation electrons, as determined via time-dependent density functional theory calculations, which affords the protruding absorption at 612 nm and contributes to the promising photothermal conversion efficiency of 67.6 % of the as-obtained nanocluster, having important implications for structure-property correlation and the development of nanocluser-based photothermal materials.

Boosting the reaction kinetics in aprotic lithium-carbon dioxide batteries with unconventional phase metal nanomaterials.

Given the high energy density and eco-friendly characteristics, lithium-carbon dioxide (Li-CO2) batteries have been considered to be a next-generation energy technology to promote carbon neutral and space exploration. However, Li-CO2 batteries suffer from sluggish reaction kinetics, causing large overpotential and poor energy efficiency. Here, we observe enhanced reaction kinetics in aprotic Li-CO2 batteries with unconventional phase 4H/face-centered cubic (fcc) iridium (Ir) nanostructures grown on gold template. Significantly, 4H/fcc Ir exhibits superior electrochemical performance over fcc Ir in facilitating the round-trip reaction kinetics of Li+-mediated CO2 reduction and evolution, achieving a low charge plateau below 3.61 V and high energy efficiency of 83.8%. Ex situ/in situ studies and theoretical calculations reveal that the boosted reaction kinetics arises from the highly reversible generation of amorphous/low-crystalline discharge products on 4H/fcc Ir via the Ir-O coupling. The demonstration of flexible Li-CO2 pouch cells with 4H/fcc Ir suggests the feasibility of using unconventional phase nanomaterials in practical scenarios.

Single-Atom-Kernelled Nanocluster Catalyst.

To propose the concept of single-atom-kernelled nanocluster, we synthesized a Pd-based trimetal nanocluster with a single-Ag atom-kernel for the first time by introducing some steric hindrance factors and employing a joint alloying strategy that combines the coreduction with an antigalvanic reduction (AGR). Although the AGR-derived Pd-based trimetal nanoclusters with single-silver atom kernels have low contents of gold, they show higher activity and selectivity than those of the bimetal precursor nanocluster in the electrocatalytical reduction of CO2 to CO. Furthermore, it is revealed that the kernel single atoms from both Au4Pd6(TBBT)12 and Au3AgPd6(TBBT)12 are not the active sites for catalysis, but greatly influence the catalytical performance by effecting the electronic configuration. Thus, it is demonstrated that the single-atom-kernelled nanocluster can not only improve the precious metal utilization (even to 100%) but also better the properties and provide insight into the structure-property correlation for metal nanoclusters.

Confined Growth of Silver-Copper Janus Nanostructures with {100} Facets for Highly Selective Tandem Electrocatalytic Carbon Dioxide Reduction.

Electrocatalytic carbon dioxide reduction reaction (CO2 RR) holds significant potential to promote carbon neutrality. However, the selectivity toward multicarbon products in CO2 RR is still too low to meet practical applications. Here the authors report the delicate synthesis of three kinds of Ag-Cu Janus nanostructures with {100} facets (JNS-100) for highly selective tandem electrocatalytic reduction of CO2 to multicarbon products. By controlling the surfactant and reduction kinetics of Cu precursor, the confined growth of Cu with {100} facets on one of the six equal faces of Ag nanocubes is realized. Compared with Cu nanocubes, Ag65 -Cu35 JNS-100 demonstrates much superior selectivity for both ethylene and multicarbon products in CO2 RR at less negative potentials. Density functional theory calculations reveal that the compensating electronic structure and carbon monoxide spillover in Ag65 -Cu35 JNS-100 contribute to the enhanced CO2 RR performance. This study provides an effective strategy to design advanced tandem catalysts toward the extensive application of CO2 RR.

Surface Molecular Functionalization of Unusual Phase Metal Nanomaterials for Highly Efficient Electrochemical Carbon Dioxide Reduction under Industry-Relevant Current Density.

The electrochemical carbon dioxide reduction reaction (CO2 RR) provides a sustainable strategy to relieve global warming and achieve carbon neutrality. However, the practical application of CO2 RR is still limited by the poor selectivity and low current density. Here, the surface molecular functionalization of unusual phase metal nanomaterials for high-performance CO2 RR under industry-relevant current density is reported. It is observed that 5-mercapto-1-methyltetrazole (MMT)-modified 4H/face-centered cubic (fcc) gold (Au) nanorods demonstrate greatly enhanced CO2 RR performance than original oleylamine (OAm)-capped 4H/fcc Au nanorods in both an H-type cell and flow cell. Significantly, MMT-modified 4H/fcc Au nanorods deliver an excellent carbon monoxide selectivity of 95.6% under the industry-relevant current density of 200 mA cm-2 . Density functional theory calculations reveal distinct electronic modulations by surface ligands, in which MMT improves while OAm suppresses the surface electroactivity of 4H/fcc Au nanorods. Furthermore, this method can be extended to various MMT derivatives and conventional fcc Au nanostructures in boosting CO2 RR performance.

Preparation of Au@Pd Core-Shell Nanorods with fcc-2H-fcc Heterophase for Highly Efficient Electrocatalytic Alcohol Oxidation.

Controlled construction of bimetallic nanostructures with a well-defined heterophase is of great significance for developing highly efficient nanocatalysts and investigating the structure-dependent catalytic performance. Here, a wet-chemical synthesis method is used to prepare Au@Pd core-shell nanorods with a unique fcc-2H-fcc heterophase (fcc: face-centered cubic; 2H: hexagonal close-packed with a stacking sequence of "AB"). The obtained fcc-2H-fcc heterophase Au@Pd core-shell nanorods exhibit superior electrocatalytic ethanol oxidation performance with a mass activity as high as 6.82 A mgPd-1, which is 2.44, 6.96, and 6.43 times those of 2H-Pd nanoparticles, fcc-Pd nanoparticles, and commercial Pd/C, respectively. The operando infrared reflection absorption spectroscopy reveals a C2 pathway with fast reaction kinetics for the ethanol oxidation on the prepared heterophase Au@Pd nanorods. Our experimental results together with density functional theory calculations indicate that the enhanced performance of heterophase Au@Pd nanorods can be attributed to the unconventional 2H phase, the 2H/fcc phase boundary, and the lattice expansion of the Pd shell. Moreover, the heterophase Au@Pd nanorods can also serve as an efficient catalyst for the electrochemical oxidation of methanol, ethylene glycol, and glycerol. Our work in the area of phase engineering of nanomaterials (PENs) opens the way for developing high-performance electrocatalysts toward future practical applications.

Seeded Synthesis of Unconventional 2H-Phase Pd Alloy Nanomaterials for Highly Efficient Oxygen Reduction.

Crystal phase engineering of noble-metal-based alloy nanomaterials paves a new way to the rational synthesis of high-performance catalysts for various applications. However, the controlled preparation of noble-metal-based alloy nanomaterials with unconventional crystal phases still remains a great challenge due to their thermodynamically unstable nature. Herein, we develop a robust and general seeded method to synthesize PdCu alloy nanomaterials with unconventional hexagonal close-packed (hcp, 2H type) phase and also tunable Cu contents. Moreover, galvanic replacement of Cu by Pt can be further conducted to prepare unconventional trimetallic 2H-PdCuPt nanomaterials. Impressively, 2H-Pd67Cu33 nanoparticles possess a high mass activity of 0.87 A mg-1Pd at 0.9 V (vs reversible hydrogen electrode (RHE)) in electrochemical oxygen reduction reaction (ORR) under alkaline condition, which is 2.5 times that of the conventional face-centered cubic (fcc) Pd69Cu31 counterpart, revealing the important role of crystal phase on determining the ORR performance. After the incorporation of Pt, the obtained 2H-Pd71Cu22Pt7 catalyst shows a significantly enhanced mass activity of 1.92 A mg-1Pd+Pt at 0.9 V (vs RHE), which is 19.2 and 8.7 times those of commercial Pt/C and Pd/C, placing it among the best reported Pd-based ORR electrocatalysts under alkaline conditions.

Traceless Removal of Two Kernel Atoms in a Gold Nanocluster and Its Impact on Photoluminescence.

Removing or adding kernel atoms of metal nanoclusters (NCs) without leaving a trace is a substantial challenge because the kernel atoms are inside and covered by the outer staples. However, such kernel tuning is very important for improving the properties and acquiring an in-depth understanding of the kernel-property correlation. Photoluminescence (PL) is one of the most intriguing characteristics of metal NCs but has not been well understood until now. Inspired by these challenges/questions, we conducted this study and, for the first time, achieved the traceless removal of two kernel atoms in a gold nanocluster by applying a simple thermal treatment and revealed its impact on PL. Further, we demonstrated that the kernel Au-Au bond length can be an indicator for a comparison of the PL or kernel charge state between nanoclusters with similar kernel structures and sizes.

Structural Oscillation Revealed in Gold Nanoparticles.

Oscillation is an intriguing phenomenon in nature. However, structural oscillation has not yet been found in semiconducting nanoparticles, primarily due to the difficulty of structural resolution at the atomic level. The emergence of gold nanoclusters (ultrasmall nanoparticles) has provided an excellent opportunity to address some challenging issues in the nanoparticle field. Herein, two Au28(CHT)20 (CHT: cyclohexanethiolate) structural isomers (Au28i and Au28ii for short) were concurrently synthesized by employing a quasi-antigalvanic method, and they could be reversibly transformed into each other for at least 10 cycles, driven by dissolution and crystallization processes. The transformation from Au28ii to Au28i is solvent-dielectric-constant-dependent, with a notable deuteration effect from dichloromethane. The markedly different photoluminescence values of these two isomers not only have important implications for the structure-property correlations but also have potential applications in converting, sensing, etc.

An Unprecedented Kernel Growth Mode and Layer-Number-Odevity-Dependent Properties in Gold Nanoclusters.

Kernel atoms of Au nanoclusters are packed layer-by-layer along the [001] direction with every full (001) monolayer composed of 8 Au atoms (Au8 unit) in nanoclusters with formula of Au8n+4 (TBBT)4n+8 (n is the number of Au8 units; TBBTH=4-tert-butylbenzenelthiol). It is unclear whether the kernel atoms can be stacked in a defective-layer way along the [001] direction during growth of the series of nanoclusters and how the kernel layer number affects properties. Now, a nanocluster is synthesized that is precisely characterized by mass spectrometry and single-crystal X-ray crystallography, revealing a layer stacking mode in which a half monolayer composed of 4 atoms (Au4 unit) is stacked on the full monolayer along the [001] direction. The size and the odevity of the kernel layer number influence the properties (polarity, photoluminescence) of gold nanoclusters. The obtained nanocluster extends the previous formula from Au8n+4 (TBBT)4n+8 to Au4n+4 (TBBT)2n+8 (n is the number of Au4 units).

A Dual Purpose Strategy to Endow Gold Nanoclusters with Both Catalysis Activity and Water Solubility.

Gold nanoclusters have attracted extensive interest for catalysis applications in recent years due to their ultrasmall sizes and well-defined compositions and structures. However, at least two challenges exist in this emerging field. First, the steric hindrance of the ligands inhibits the catalysis activity, and second, the mechanism underlying water-phase catalysis using gold nanoclusters is often ambiguous. Herein, we introduce a "kill two birds with one stone" strategy to address these two challenges via the use of host-guest chemistry. As an illustration, a novel adamantanethiolate-protected Au40(S-Adm)22 nanocluster was synthesized, bound with γ-CD-MOF, and then transferred to the HRP-mimicking reaction system. The as-obtained catalyst exhibits excellent water solubility and catalytical activity, totally different from the virgin Au40(S-Adm)22 nanoclusters. Further, the detailed HRP-mimicking catalysis mechanism was proposed and supported by DFT calculation. Another interesting finding is the unique structure of Au40(S-Adm)22, which can be regarded as an Au13 icosahedron unit derived structure but different from the widely reported icosahedron contained nanocluster where the Au13 icosahedrons are often centered. These novel, intriguing results have important implication for the property tuning and practical application of metal nanoclusters in the future.

Hard-Sphere Random Close-Packed Au47 Cd2 (TBBT)31 Nanoclusters with a Faradaic Efficiency of Up to 96 % for Electrocatalytic CO2 Reduction to CO.

Metal nanoclusters have recently attracted considerable attention, not only because of their special size range but also because of their well-defined compositions and structures. However, subtly tailoring the compositions and structures of metal nanoclusters for potential applications remains challenging. Now, a two-phase anti-galvanic reduction (AGR) method is presented for precisely tailoring Au44 (TBBT)28 to produce Au47 Cd2 (TBBT)31 nanoclusters with a hard-sphere random close-packed structure, exhibiting Faradaic efficiencies of up to 96 % at -0.57 V for the electrocatalytic reduction of CO2 to CO.

Alternating Array Stacking of Ag26 Au and Ag24 Au Nanoclusters.

An assembly strategy for metal nanoclusters using electrostatic interactions with weak interactions, such as C-H⋅⋅⋅π and π⋅⋅⋅π interactions in which cationic [Ag26 Au(2-EBT)18 (PPh3 )6 ]+ and anionic [Ag24 Au(2-EBT)18 ]- nanoclusters gather and assemble in an unusual alternating array stacking structure is presented. [Ag26 Au(2-EBT)18 (PPh3 )6 ]+ [Ag24 Au(2-EBT)18 ]- is a new compound type, a double nanocluster ion compound (DNIC). A single nanocluster ion compound (SNIC) [PPh4 ]+ [Ag24 Au(2-EBT)18 ]- was also synthesized, having a k-vector-differential crystallographic arrangement. [PPh4 ]+ [Ag24 Au(2,4-DMBT)18 ]- adopts a different assembly mode from both [Ag26 Au(2-EBT)18 (PPh3 )6 ]+ [Ag24 Au(2-EBT)18 ]- and [PPh4 ]+ [Ag24 Au(2-EBT)18 ]- . Thus, the striking packing differences of [Ag26 Au(2-EBT)18 (PPh3 )6 ]+ [Ag24 Au(2-EBT)18 ]- , [PPh4 ]+ [Ag24 Au(2-EBT)18 ]- and the existing [PPh4 ]+ [Ag24 Au(2,4-DMBT)18 ]- from each other indicate the notable influence of ligands and counterions on the self-assembly of nanoclusters.