Atomically precise nanoclusters of coinage metals in the 1–3 nm size regime have been intensively pursued in recent years. Such nanoclusters are attractive as they fill the gap between small molecules (<1 nm) and regular nanoparticles (>3 nm). This intermediate identity endows nanoclusters with unique physicochemical properties and provides nanochemists opportunities to understand the fundamental science of nanomaterials. Metal nanoparticles are well known to exhibit plasmon resonances upon interaction with light; however, when the particle size is downscaled to the nanocluster regime, the plasmons fade out and step-like absorption spectra characteristic of cluster sizes are manifested due to strong quantum confinement effects. Recent research has revealed that nanoclusters are commonly composed of a distinctive kernel and a surface-protecting shell (or staple-like metal–ligand motifs). Understanding the kernel configuration and evolution is one of the central topics in nanoscience research. This Review summarizes the recent progress in identifying the growth patterns of atomically precise coinage nanoclusters. Several basic kernel units have been observed, such as the M 4 , M 13 and M 14 polyhedrons (where, M = metal atom). Among them, the tetrahedral M 4 and icosahedral M 13 units are the most common ones, which are adopted as building blocks to construct larger kernel structures via various fusion or aggregation modes, including the vertex- and face-sharing mode, the double-strand and alternate single-strand growth, and cyclic fusion of units, as well as the fcc-based cubic growth pattern. The identification of the kernel growth pathways has led to deeper understanding of the evolution of electronic structure and optic properties.
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Atomic-precision engineering of metal nanoclusters
Ultrasmall metal nanoparticles (below 2.2 nm core diameter) start to show discrete electronic energy levels due to strong quantum confinement effects and thus behave much like molecules. The size and structure dependent quantization induces a plethora of new phenomena, including multi-band optical absorption, enhanced luminescence, single-electron magnetism, and catalytic reactivity. The exploration of such new properties is largely built on the success in unveiling the crystallographic structures of atomically precise nanoclusters (typically protected by ligands, formulated as M n L m q , where M = metal, L = Ligand, and q = charge). Correlation between the atomic structures of nanoclusters and their properties has further enabled atomic-precision engineering toward materials design. In this frontier article, we illustrate several aspects of the precise engineering of gold nanoclusters, such as the single-atom size augmenting, single-atom dislodging and doping, precise surface modification, and single-electron control for magnetism. Such precise engineering involves the nanocluster's geometric structure, surface chemistry, and electronic properties, and future endeavors will lead to new materials design rules for structure–function correlations and largely boost the applications of metal nanoclusters in optics, catalysis, magnetism, and other fields. Following the illustrations of atomic-precision engineering, we have also put forth some perspectives. We hope this frontier article will stimulate research interest in atomic-level engineering of nanoclusters.
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- Award ID(s):
- 1808675
- NSF-PAR ID:
- 10228312
- Date Published:
- Journal Name:
- Dalton Transactions
- Volume:
- 49
- Issue:
- 31
- ISSN:
- 1477-9226
- Page Range / eLocation ID:
- 10701 to 10707
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract With the recent establishment of atomically precise nanochemistry, capabilities toward programmable control over the nanoparticle size and structure are being developed. Advances in the synthesis of atomically precise nanoclusters (NCs, 1–3 nm) have been made in recent years, and more importantly, their total structures (core plus ligands) have been mapped out by X‐ray crystallography. These ultrasmall Au nanoparticles exhibit strong quantum‐confinement effect, manifested in their optical absorption properties. With the advantage of atomic precision, gold‐thiolate nanoclusters (Au
n (SR)m ) are revealed to contain an inner kernel, Au–S interface (motifs), and surface ligand (‐R) shell. Programming the atomic packing into various crystallographic structures of the metal kernel can be achieved, which plays a significant role in determining the optical properties and the energy gap (E g) of NCs. When the size increases, a general trend is observed for NCs with fcc or decahedral kernels, whereas those NCs with icosahedral kernels deviate from the general trend by showing comparably smallerE g. Comparisons are also made to further demonstrate the more decisive role of the kernel structure over surface motifs based on isomeric Au NCs and NC series with evolving kernel or motif structures. Finally, future perspectives are discussed. -
The transition from the discrete, excitonic state to the continuous, metallic state in thiolate-protected gold nanoclusters is of fundamental interest and has attracted significant efforts in recent research. Compared with optical and electronic transition behavior, the transition in magnetism from the atomic gold paramagnetism (Au 6s 1 ) to the band behavior is less studied. In this work, the magnetic properties of 1.7 nm [Au 133 (TBBT) 52 ] 0 nanoclusters (where TBBT = 4- tert -butylbenzenethiolate) with 81 nominal “valence electrons” are investigated by electron paramagnetic resonance (EPR) spectroscopy. Quantitative EPR analysis shows that each cluster possesses one unpaired electron (spin), indicating that the electrons fill into discrete orbitals instead of a continuous band, for that one electron in the band would give a much smaller magnetic moment. Therefore, [Au 133 (TBBT) 52 ] 0 possesses a nonmetallic electronic structure. Furthermore, we demonstrate that the unpaired spin can be removed by oxidizing [Au 133 (TBBT) 52 ] 0 to [Au 133 (TBBT) 52 ] + and the nanocluster transforms from paramagnetism to diamagnetism accordingly. The UV-vis absorption spectra remain the same in the process of single-electron loss or addition. Nuclear magnetic resonance (NMR) is applied to probe the charge and magnetic states of Au 133 (TBBT) 52 , and the chemical shifts of 52 surface TBBT ligands are found to be affected by the spin in the gold core. The NMR spectrum of Au 133 (TBBT) 52 shows a 13-fold splitting with 4-fold degeneracy of 52 TBBT ligands, which are correlated to the quasi- D 2 symmetry of the ligand shell. Overall, this work provides important insights into the electronic structure of Au 133 (TBBT) 52 by combining EPR, optical and NMR studies, which will pave the way for further understanding of the transition behavior in metal nanoclusters.more » « less
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Metal-ion batteries (e.g., lithium and sodium ion batteries) are the promising power sources for portable electronics, electric vehicles, and smart grids. Recent metal-ion batteries with organic liquid electrolytes still suffer from safety issues regarding inflammability and insufficient lifetime.1 As the next generation energy storage devices, all-solid-state batteries (ASSBs) have promising potentials for the improved safety, higher energy density, and longer cycle life than conventional Li-ion batteries.2 The nonflammable solid electrolytes (SEs), where only Li ions are mobile, could prevent battery combustion and explosion since the side reactions that cause safety issues as well as degradation of the battery performance are largely suppressed. However, their practical application is hampered by the high resistance arising at the solid–solid electrode–electrolyte interface (including cathode-electrolyte interface and anode-electrolyte interface).3 Several methods have been introduced to optimize the contact capability as well as the electrochemical/chemical stability between the metal anodes (i.e.: Li and Na) and the SEs, which exhibited decent results in decreasing the charge transfer resistance and broadening the range of the stable energy window (i.e., lowing the chemical potential of metal anode below the highest occupied molecular orbital of the SEs).4 Nevertheless, mitigation for the cathode in ASSB is tardily developed because: (1) the porous structure of the cathode is hard to be infiltrated by SEs;5 (2) SEs would be oxidized and decomposed by the high valence state elements at the surface of the cathode at high state of charge.5 Herein, we demonstrate a universal cathode design strategy to achieve superior contact capability and high electrochemical/chemical stability with SEs. Stereolithography is adopted as a manufacturing technique to realize a hierarchical three-dimensional (HTD) electrode architecture with micro-size channels, which is expected to provide larger contact areas with SEs. Then, the manufactured cathode is sintered at 700 °C in a reducing atmosphere (e.g.: H2) to accomplish the carbonization of the resin, delivering sufficiently high electronic conductivity for the cathode. To avoid the direct exposure of the cathode active materials to the SEs, oxidative chemical vapor deposition technique (oCVD) is leveraged to build conformal and highly conducting poly(3,4-ethylenedioxythiophene) (PEDOT) on the surface of the HTD cathode.6 To demonstrate our design strategy, both NCM811 and Na3V2(PO4)3 is selected as active materials in the HTD cathode, then each cathode is paired with organic (polyacrylonitrile-based) and inorganic (sulfur-based) SEs assembled into two batteries (total four batteries). SEM and TEM reveal the micro-size HTD structure with built-in channels. Featured by the HTD architecture, the intrinsic kinetic and thermodynamic conditions will be enhanced by larger surface contact areas, more active sites, improved infusion and electrolyte ion accessibility, and larger volume expansion capability. Disclosed by X-ray computed tomography, the interface between cathode and SEs in the four modified samples demonstrates higher homogeneity at the interface between the cathode and SEs than that of all other pristine samples. Atomic force microscopy is employed to measure the potential image of the cross-sectional interface by the peak force tapping mode. The average potential of modified samples is lower than that of pristine samples, which confirms a weakened space charge layer by the enhanced contact capability. In addition, through Electron Energy Loss Spectroscopy coupled with Scanning Transmission Electron Microscopy, the preserved interface between HTD cathode and SE is identified; however, the decomposing of the pristine cathode is clearly observed. In addition, Finite element method simulations validate that the diffusion dynamics of lithium ions is favored by HTD structure. Such a demonstrated universal strategy provides a new guideline to engineer cathode electrolyte interface by reconstructing electrode structures that can be applicable to all solid-state batteries in a wide range of chemical conditions.more » « less
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Abstract The electrochemical CO2reduction reaction (CO2RR) is a promising approach to achieving sustainable electrical‐to‐chemical energy conversion and storage while decarbonizing the emission‐heavy industry. The carbon‐supported, nitrogen‐coordinated, and atomically dispersed metal sites are effective catalysts for CO generation due to their high activity, selectivity, and earth abundance. Here, we discuss progress, challenges, and opportunities for designing and engineering atomic metal catalysts from single to dual metal sites. Engineering single metal sites using a nitrogen‐doped carbon model was highlighted to exclusively study the effect of carbon particle sizes, metal contents, and M−N bond structures in the form of MN4moieties on catalytic activity and selectivity. The structure‐property correlation was analyzed by combining experimental results with theoretical calculations to uncover the CO2to CO conversion mechanisms. Furthermore, dual‐metal site catalysts, inheriting the merits of single‐metal sites, have emerged as a new frontier due to their potentially enhanced catalytic properties. Designing optimal dual metal site catalysts could offer additional sites to alter the surface adsorption to CO2and various intermediates, thus breaking the scaling relationship limitation and activity‐stability trade‐off. The CO2RR electrolysis in flow reactors was discussed to provide insights into the electrolyzer design with improved CO2utilization, reaction kinetics, and mass transport.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d0dt01853h
