Synthesis Of Metal Nanocrystals Research Articles

Bridging colloidal and electrochemical syntheses of metal nanocrystals with seeded electrodeposition for tracking single nanocrystal growth.

Metal nanocrystals (NCs) produced by colloidal synthesis have a variety of structural features, such as different planes, edges, and defects. Even from the best colloidal syntheses, these characteristics are distributed differently in each NC. This inherent heterogeneity can play a significant role in the properties displayed by NCs. This manuscript reports the use of electrochemistry to synthesize Au NCs in a system evaluated to track individual NC growth trajectories as a first step toward rapid identification of NCs with different structural features. Au nanocubes were prepared colloidally and deposited onto a glassy carbon electrode using either electrospray or an airbrush, resulting in well-spaced Au nanocubes. The Au nanocubes then served as seeds as gold salt was reduced to deposit metal at constant potential. Deposition at constant potential facilitates overgrowth on the Au nanocubes to achieve new NC shapes. The effects of applied potential, deposition time, precursor concentration, and capping agents on NC shape evolution were studied. The outcomes are correlated to results from traditional colloidal syntheses, providing a bridge between the two synthetic strategies. Moreover, scanning electron microscopy was used to image the same NCs before and after deposition, linking individual seed features to differences in deposition. This ability is anticipated to enable tracking of individual growth trajectories of NCs to elucidate sources of heterogeneity in NC syntheses.

Electrodeposition of Cu Nanocubes in the Presence of Cl- and Br-

Electrodeposition is one of the simple methods for fabricating metal and alloy thin films. Electrodeposition is performed by applying external electrical energy to conductive substrates immersing in electrolytes containing metal precursors. Metal ions or complexes are reduced on a substrate surface and form metal films. The properties of metal thin films and surface morphology of the electrodeposit can be modulated by the parameters of electrodeposition, the composition of electrolytes, i.e., the concentrations of metal precursors and additives. Furthermore, the atomic composition of alloy films can also be easily controlled by electrochemical parameters in the electrodeposition process.1 As explained, the electrodeposition process has various advantages in producing metal thin films with desired properties. However, creating nanostructures with precisely controlling their shapes in the nm scale is relatively difficult. In colloidal syntheses, various nanocrystals, including nanowires, nanospheres, octahedrons, nanocubes, and nanoplates, can be obtained by introducing shape-directing agents.2-4 In the case of electrodeposition, the template-assisted electrodeposition method is the most common to form nanostructures,5,6 and relatively few examples of shape controlling by additives have been reported. Although the formation of metal nanowires in the presence of 3,5-diamino-1,2,4-triazole (DAT) has been recently reported,7 shape control of metal deposits by additives during the electrodeposition process is still limited to few nanostructures. Electrodeposition induces metal growth relatively faster than colloidal synthesis, and a precise nucleation step is not involved in the electrodeposition, which is critical in colloidal syntheses. In this study, we have adopted pulse-reverse electrodeposition to modulate metal nucleation at the initial stage of electrodeposition and also maximize the effects of additives. Pulse-reverse electrodeposition has been researched for controlling the properties of metal thin films and changing the adsorption of additives.8,9 Therefore, pulse-reverse electrodeposition can catch up with the shape control in colloidal syntheses. This presentation will introduce how the parameters in pulse-reverse electrodeposition and additives (halide ions) affect the shape of Cu nanocrystals. References 1) T. P. Moffat, J. J. Mallett, and S. M. Hwang, “Oxygen Reduction Kinetics on Electrodeposited Pt, Pt100− x Nix , and Pt100−xCox” J. Electrochem. Soc. 156, B238 (2009)2) Y. Xia, Y. Xiong, B. Lim, and S. E. Skrabalak, “Shape-Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?” Angew. Chem. Int. Ed. 48, 60 (2009)3) K. A. Fichthorn, Z. Chen, Z. Chen, R. M. Rioux, M. J. Kim, and B. J. Wiley, “Understanding the Solution-Phase Growth of Cu and Ag Nanowires and Nanocubes from First Principles” Langmuir 37, 4419 (2021)4) D. Huo, M. J. Kim, Z. Lyu, Y. Shi, B. J. Wiley, and Y. Xia, “One-Dimensional Metal Nanostructures: From Colloidal Syntheses to Applications” Chem. Rev. 119, 8972 (2019)5) K. R. Yeo, J. Y. Eo, M. J. Kim and S.-K. Kim, “Shape Control of Metal Nanostructures by Electrodeposition and their Applications in Electrocatalysis” J. Electrochem. Soc. 169, 112502 (2022)6) C. Liu, Z. Li, P. Yu, H. W. Wong, and Z. Gu, “Vertically Aligned and Surface Roughed Pt Nanostructured Wire Array as High Performance Electrocatalysts for Methanol Oxidation” ACS Appl. Energy Mater. 1, 3973 (2018)7) T. T. H. Hoang, S. Ma, J. I. Gold, P. J. A. Kenis, and A. A. Gewirth “Nanoporous Copper Films by Additive-Controlled Electrodeposition: CO2 Reduction Catalysis” ACS Catal. 7, 3313 (2017)8) M. J. Kim, T. Lim, K. J. Park, S. K. Cho, S.-K. Kim, and J. J. Kim “Characteristics of Pulse-Reverse Electrodeposited Cu Thin Films: I. Effects of the Anodic Step in the Absence of an Organic Additive” J. Electrochem. Soc. 159, D538 (2012)9) M. J. Kim, T. Lim, K. J. Park, O. J. Kwon, S.-K. Kim, and J. J. Kim “Characteristics of Pulse-Reverse Electrodeposited Cu Thin Film: II. Effects of Organic Additives” J. Electrochem. Soc. 159, D544 (2012) Figure 1

Colloidal Synthesis of Metal Nanocrystals: From Asymmetrical Growth to Symmetry Breaking.

Nanocrystals offer a unique platform for tailoring the physicochemical properties of solid materials to enhance their performances in various applications. While most work on controlling their shapes revolves around symmetrical growth, the introduction of asymmetrical growth and thus symmetry breaking has also emerged as a powerful route to enrich metal nanocrystals with new shapes and complex morphologies as well as unprecedented properties and functionalities. The success of this route critically relies on our ability to lift the confinement on symmetry by the underlying unit cell of the crystal structure and/or the initial seed in a systematic manner. This Review aims to provide an account of recent progress in understanding and controlling asymmetrical growth and symmetry breaking in a colloidal synthesis of noble-metal nanocrystals. With a touch on both the nucleation and growth steps, we discuss a number of methods capable of generating seeds with diverse symmetry while achieving asymmetrical growth for mono-, bi-, and multimetallic systems. We then showcase a variety of symmetry-broken nanocrystals that have been reported, together with insights into their growth mechanisms. We also highlight their properties and applications and conclude with perspectives on future directions in developing this class of nanomaterials. It is hoped that the concepts and existing challenges outlined in this Review will drive further research into understanding and controlling the symmetry breaking process.

Unusual Role of the Surfactant in the Self-Assembly of Pt Alloy in Ordered Mesoporous Carbon: Tuning the Nanocluster Size

In the one-step self-assembly synthesis of metallic nanocrystals in ordered mesoporous carbon (OMC), the surfactant functionalizes well as the structure directing agent and mesopore template. Interestingly, this work demonstrates another unusual role the surfactant plays: tuning the size of the nanocrystals. Our investigation shows that the decreasing molecular weight of the PS segment of PEO-b-PS leads to sequentially reduced PtRu particle sizes of 4.4, 3.9, and 2.9 nm, while F127 which has a distinctly smaller hydrophobic PO domain with a bending structure in the micelles successfully results in sub-2 nm PtM (M = Ru, Ir, Rh, Pd) nanoclusters in OMC. This well indicates that the nanocluster size is largely decided by the volume of the hydrophobic segment of the surfactant to which the metallic precursor is linked. The smaller the volume, the fewer the precursor molecules are adsorbed, and the smaller the alloy nanoclusters. In the electrocatalytic methanol oxidation reaction, the mass activity of PtRu-1.6/OMC with 1.6 nm PtRu clusters at 0.87 V reaches 1.07 A mgPt-1, which is 2.9 times that of commercial PtRu/C with an average alloy size of 2.7 nm. In principle, a wide range of ultrafine metallic clusters embedded in OMC can be prepared via this route for various applications.

Single-Crystal Electrochemistry Uncovers the Role of Citrate in the Anisotropic Growth of Ag Nanostructures

Shape-controlled synthesis of metal nanocrystals is usually achieved by the addition of capping agents and serves an important approach to endowing metal nanomaterials with desired properties.1 A widely accepted hypothesis in the role of capping agents is they suppress the atomic deposition on the facets they selectively adsorb to, which leads to anisotropic growth.2 However, the roles of capping agents are often qualitatively deduced from the shape of metal nanocrystals formed, making it difficult to rationally design a synthetic condition for a certain shape or aspect ratio. Single-crystal electrochemical measurements have been used to uncover the facet-selective roles of a wide range of capping agents, such as chloride in the synthesis of Cu nanowires, bromide in the synthesis of Au nanorods, and iodide in the synthesis of Cu microplates.3-6 However, the anisotropic growth revealed by the growth of these nanocrystals is 10 times higher than that predicted by the single-crystal electrochemical measurements, indicating planar defects, such as twin planes and stacking faults, can also cause anisotropic growth.To elucidate the effects surface capping and defects in the anisotropic growth of metal nanocrystals, the work presented here combines synthetic methods and electrochemical measurements to reveal the roles of citrate in the growth of seeds with different structures.7 The single-crystal Ag seeds (Figure 1A) grow into cuboctahedra in the absence of citrate (Figure 1B) and octahedra in the presence of citrate (Figure 1C), which closely matches the shape prediction from the electrochemical measurements. Linear sweep voltammetry (LSV) measurements under the synthetic conditions demonstrate the anisotropic growth with citrate is a result of citrate selectively suppressing the oxidation of a reducing agent, ascorbic acid, and citrate does not affect silver ion reduction. The Ag nanoplate seeds with planar defects (Figure 1D) undergo isotropic growth in the absence of citrate (Figure 1E), but exhibit 30~100 times more anisotropic growth in the presence of citrate than the single-crystal seeds and electrochemical prediction (Figure 1F). Further investigation suggests planar defects can catalyze silver atom deposition to the nanoplate side planes and citrate suppresses surface diffusion to the nanoplate basal planes.(1) Yang, T.-H.; Shi, Y.; Janssen, A.; Xia, Y., Surface Capping Agents and Their Roles in Shape-Controlled Synthesis of Colloidal Metal Nanocrystals. Angew. Chem., Int. Ed. 2020, 59, 15378-15401.(2) Xia, Y.; Xiong, Y.; Lim, B.; Skrabalak, S. E., Shape-Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics? Angew. Chem., Int. Ed. 2009, 48, 60-103.(3) Kim, M. J.; Brown, M.; Wiley, B. J., Electrochemical investigations of metal nanostructure growth with single crystals. Nanoscale 2019, 11, 21709-21723.(4) Kim, M. J.; Alvarez, S.; Chen, Z.; Fichthorn, K. A.; Wiley, B. J., Single-Crystal Electrochemistry Reveals Why Metal Nanowires Grow. J. Am. Chem. Soc. 2018, 140, 14740-14746.(5) Brown, M.; Wiley, B. J., Bromide Causes Facet-Selective Atomic Addition in Gold Nanorod Syntheses. Chem. Mater. 2020, 32, 6410-6415.(6) Kim, M. J.; Cruz, M. A.; Chen, Z.; Xu, H.; Brown, M.; Fichthorn, K. A.; Wiley, B. J., Isotropic Iodide Adsorption Causes Anisotropic Growth of Copper Microplates. Chem. Mater. 2021, 33, 881-891.(7) Xu, H.; Wiley, B. J., The Roles of Citrate and Defects in the Anisotropic Growth of Ag Nanostructures. Chem. Mater. 2021, 33, 8301-8311. Figure 1

Copper Phosphonate Lamella Intermediates Control the Shape of Colloidal Copper Nanocrystals.

Understanding the structure and behavior of intermediates in chemical reactions is the key to developing greater control over the reaction outcome. This principle is particularly important in the synthesis of metal nanocrystals (NCs), where the reduction, nucleation, and growth of the reaction intermediates will determine the final size and shape of the product. The shape of metal NCs plays a major role in determining their catalytic, photochemical, and electronic properties and, thus, the potential applications of the material. In this work, we demonstrate that layered coordination polymers, called lamellae, are reaction intermediates in Cu NC synthesis. Importantly, we discover that the lamella structure can be fine-tuned using organic ligands of different lengths and that these structural changes control the shape of the final NC. Specifically, we show that short-chain phosphonate ligands generate lamellae that are stable enough at the reaction temperature to facilitate the growth of Cu nuclei into anisotropic Cu NCs, being primarily triangular plates. In contrast, lamellae formed from long-chain ligands lose their structure and form spherical Cu NCs. The synthetic approach presented here provides a versatile tool for the future development of metal NCs, including other anisotropic structures.

Shape Control Beyond the Seeds in Gold Nanoparticles

In typical seed-mediated syntheses of metal nanocrystals, the shape of the nanocrystal is determined largely by the seed nucleation environment and subsequent growth environment (where “environment” refers to the chemical environment, including the surfactant and additives). In this approach, crystallinity is typically determined by the seeds, and surfaces are controlled by the environment(s). However, surface energies, and crystallinity, are both influenced by the choice of environment(s). This limits the permutations of crystallinity and surface facets that can be mixed and matched to generate new nanocrystal morphologies. Here, we control post-seed growth to deliberately incorporate twin planes during the growth stage to deliver new final morphologies, including twinned cubes and bipyramids from single-crystal seeds. The nature and number of twin planes, together with surfactant control of facet growth, define the final nanoparticle morphology. Moreover, by breaking symmetry, the twin planes introduce new facet orientations. This additional mechanism opens new routes for the synthesis of different morphologies and facet orientations.

Facile Synthesis of Platinum Right Bipyramids by Separating and Controlling the Nucleation Step in a Continuous Flow System.

Colloidal synthesis of metal nanocrystals with controlled shapes and internal structures calls for a tight control over both the nucleation and growth processes. Here we report a method for the facile synthesis of Pt right bipyramids (RBPs) by separating nucleation from growth and controlling the nucleation step in a continuous flow reactor. Specifically, homogeneous nucleation was thermally triggered by introducing the reaction solution into a tubular flow reactor held at an elevated temperature to generate singly-twinned seeds. At a lower temperature, the singly-twinned seeds were protected from oxidative etching to allow their slow growth and evolution into RBPs while additional nucleation of undesired seeds could be largely suppressed to ensure RBPs as the main product. Further investigation indicated that the internal structure and growth pattern of the seeds were determined by the temperatures used for the nucleation and growth steps, respectively. The Br- ions involved in the synthesis also played a critical role in the generation of RBPs by serving as a capping agent for the Pt{100} facets while regulating the reduction kinetics through coordination with the Pt(IV) ions.

Reversible isomerization of metal nanoclusters induced by intermolecular interaction

Reversible isomerization of metal nanoclusters induced by intermolecular interaction

Synthesis of silver nanocrystal with an excellent oxidase-like activity and its application in colorimetric detection of D-penicillamine

High-index facets of metal nanocrystal have often a higher catalytic activity compared with the low-index facets. However, the shape-controlled synthesis of silver nanocrystal still faces great challenges. In the study, we reported synthesis of silver nanocrystals using histidine-functionalized graphene quantum dots (His-GQDs) as a chelating agent and shape inducer. Silver ions were coordinated with His-GQDs to form stable complex and then heated at 180 °C for 3 h. The resulting Ag/His-GQD nanohybrid offers polygonal nanostructure. The architecture improves the exposure of high-index facets, leading to an improved oxidase-like activity. Ag/His-GQD was used as the mimetic enzyme for colorimetric detection of D-penicillamine. In the detection Ag/His-GQD catalyzes the oxidization of 3,3′,5,5′-tetramethylbenzidine into blue product. D-penicillamine can inhibit the catalytic activity of Ag/His-GQD and leads to a reduced oxidization rate, because sulfhydryl in D-penicillamine was combined with silver in the Ag/His-GQD to form Ag-S bond. The absorbance at 652 nm linearly decreases with increasing D-penicillamine concentration in the range from 0.1 to 1.25 μM with detection limit of 0.034 μM (S/N = 3). The proposed method exhibits a better sensitivity, selectivity and stability and was successfully applied in colorimetric detection of D-penicillamine. The study also provides a promising approach for synthesis of metal nanocrystals with excellent catalytic activity.

Surface engineering of Rh-modified Pd nanocrystals by colloidal underpotential deposition for electrocatalytic methanol oxidation.

The development of methods to control the surface structures of metallic nanocatalysts is of vital importance for their application as heterogeneous catalysts in chemical conversions of energy and environmental and chemical engineering. The underpotential deposition (UPD) phenomenon has received considerable interest as a tool for the controllable synthesis of metal nanocrystals and engineering their catalytic performances. Herein, the discovery of UPD of Rh on Pd nanocrystals is reported. More importantly, the UPD of Rh is explored as a strategy to direct the synthesis of Rh-modified Pd nanocrystals with controllable shapes and surface structures. The mechanism of the UPD of Rh on Pd is elucidated in terms of electronegativity difference considerations. Compared with pristine Pd octahedral nanocrystals and commercial carbon-supported Pd catalysts, the Rh-modified Pd octahedral nanocrystals exhibit remarkable electrocatalytic performances during the methanol oxidation reaction in alkaline media. Our discovery heralds a new paradigm for UPD-mediated growth of metal nanocrystals and may provide a mechanistic understanding for the guided design of other colloidal UPD systems in the synthesis and surface engineering of metal nanocrystals.

Completely green synthesis of rose-shaped Au nanostructures and their catalytic applications.

The importance of and demand for eco-friendly syntheses of metal nanocrystals are increasing. In this study, a novel protocol for the one-pot, template/seed-free, and completely green synthesis of rose-shaped Au nanostructures with unique three-dimensional hierarchical structures was developed. The synthesis of the nanostructures was carried out at room temperature using water as a reaction medium and an eco-friendly biopolymer (sodium salt of alginic acid (Na-alginate)) as a reducing agent. The morphologies of the Au nanostructures were controlled by adjusting the amount of capping ligand (polyvinylpyrrolidone (PVP)) in the reaction mixture, and a limited ligand protection (LLP) strategy was used to induce the formation of rose-shaped Au nanostructures. A formation mechanism for the rose-shaped Au nanostructures was proposed on the basis of structural characterizations and the shape evolution of the nanostructures. The unique structural features of the rose-shaped nanostructures, which include a high surface roughness, a large surface area-to-volume ratio, and abundant edges and sharp tips, motivated us to use them as a high-performance catalyst. They were used as an environmentally benign catalyst in an organic reaction to remove a hazardous chemical from an aqueous medium: specifically, the hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride. Without an additional supporting material, the rose-shaped Au nanostructures showed outstanding catalytic activity that was maintained when the catalyst was recycled and used a total of five times.

Facile engineering of silk fibroin capped AuPt bimetallic nanozyme responsive to tumor microenvironmental factors for enhanced nanocatalytic therapy.

Background: Reactive oxygen species (ROS), as a category of highly reactive molecules, are attractive for eliminating tumor cells in situ. However, the intrinsic tumor microenvironment (TME) always compromises treatment efficacy. In another aspect, silk fibroin (SF), as a category of natural biomacromolecules, is highly promising for synthesis of metallic nanocrystals via biomineralization.Methods: As a proof-of-concept study, AuPt bimetallic nanozyme derived from bioinspired crystallization of chloroauric acid and chloroplatinic acid was facilely developed in the presence of silk fibroin (SF). Antitumor effects caused by the as-synthesized AuPt@SF (APS) nanozyme were demonstrated in 4T1 tumor cells in vitro and xenograft tumor models in vivo.Results: APS nanozyme can decompose glucose to constantly supply H2O2 and deplete intracellular glutathione (GSH). APS nanozyme can simultaneously convert adsorbed O2 and endogenic H2O2 into superoxide radicals (•O2-) and hydroxyl radical (•OH), respectively, upon highly efficient catalytic reaction. Subsequently, these cytotoxic ROS cause irreversible damage to the cell membrane, nucleic acid and mitochondria of tumors. Upon fluorescence/photoacoustic (FL/PA)-imaging guidance, remarkable tumor damage based on the current nanoplatform was confirmed in vivo.Conclusion: The objective of our investigation is to supply more useful insights on the development of SF-based nanocatalysts, which are specifically responsive to TME for extremely efficient tumor theranostics.

Quantitative Analysis of DNA-Mediated Formation of Metal Nanocrystals.

The predictive synthesis of metal nanocrystals with desired structures relies on the precise control of the crystal formation process. Using a capping ligand is an effective method to affect the reduction of metal ions and the formation of nanocrystals. However, predictively synthesizing nanostructures has been difficult to achieve using conventional capping ligands. DNA, as a class of the promising biomolecular capping ligands, has been used to generate sequence-specific morphologies in various metal nanocrystals. However, mechanistic insight into the DNA-mediated nanocrystal formation remains elusive due to the lack of quantitative experimental evidence. Herein, we quantitatively analyzed the precise control of DNA over Ag+ reduction and the structures of resulting Au-Ag core-shell nanocrystals. We derived the equilibrium binding constants between DNA and Ag+, the kinetic rate constants of sequence-specific Ag+ reduction pathways, and the percentage of active surface sites remaining on the nanocrystals after DNA passivation. These three synergistic factors influence the nucleation and growth process both thermodynamically and kinetically, which contributed to the morphological evolution of Au-Ag nanocrystals synthesized with different DNA sequences. This study demonstrates the potential of using functional DNA sequences as a versatile and tunable capping ligand system for the predictable synthesis of metal nanostructures.

Applications of Metal Nanocrystals with Twin Defects in Electrocatalysis.

Electrocatalytic energy conversion is one of the most promising pathways to develop clean and renewable energy technologies, and the development of high-performance electrocatalysts to improve the energy conversion efficiency is of paramount importance. Metal nanocrystals with twin defects possess unique features, including lattice strain and high density of low-coordinated atoms at the twin boundary, endowing them with excellent catalytic performance in various electrocatalytic reactions. Herein, we briefly summarize recent advances in the synthesis of metal nanocrystals with various twin structures, recent breakthroughs related to electrocatalytic applications of twin metal nanocrystals are also overviewed. Finally, the major challenges and perspectives for future development of twin metal nanocrystals in electrochemical applications are proposed.

Surface Capping Agents and Their Roles in Shape-Controlled Synthesis of Colloidal Metal Nanocrystals.

Surface capping agents have been extensively used to control the evolution of seeds into nanocrystals with diverse but well-controlled shapes. Here we offer a comprehensive review of these agents, with a focus on the mechanistic understanding of their roles in guiding the shape evolution of metal nanocrystals. We begin with a brief introduction to the early history of capping agents in electroplating and bulk crystal growth, followed by discussion of how they affect the thermodynamics and kinetics involved in a synthesis of metal nanocrystals. We then present representative examples to highlight the various capping agents, including their binding selectivity, molecular-level interaction with a metal surface, and impacts on the growth of metal nanocrystals. We also showcase progress in leveraging capping agents to generate nanocrystals with complex structures and/or enhance their catalytic properties. Finally, we discuss various strategies for the exchange or removal of capping agents, together with perspectives on future directions.

Disk-Shaped Cobalt Nanocrystals as Fischer\u2013Tropsch Synthesis Catalysts Under Industrially Relevant Conditions

Colloidal synthesis of metal nanocrystals (NC) offers control over size, crystal structure and shape of nanoparticles, making it a promising method to synthesize model catalysts to investigate structure-performance relationships. Here, we investigated the synthesis of disk-shaped Co-NC, their deposition on a support and performance in the Fischer–Tropsch (FT) synthesis under industrially relevant conditions. From the NC synthesis, either spheres only or a mixture of disk-shaped and spherical Co-NC was obtained. The disks had an average diameter of 15 nm, a thickness of 4 nm and consisted of hcp Co exposing (0001) on the base planes. The spheres were 11 nm on average and consisted of ε-Co. After mild oxidation, the CoO-NC were deposited on SiO2 with numerically 66% of the NC being disk-shaped. After reduction, the catalyst with spherical plus disk-shaped Co-NC had 50% lower intrinsic activity for FT synthesis (20 bar, 220 °C, H2/CO = 2 v/v) than the catalyst with spherical NC only, while C5+-selectivity was similar. Surprisingly, the Co-NC morphology was unchanged after catalysis. Using XPS it was established that nitrogen-containing ligands were largely removed and in situ XRD revealed that both catalysts consisted of 65% hcp Co and 21 or 32% fcc Co during FT. Furthermore, 3–5 nm polycrystalline domains were observed. Through exclusion of several phenomena, we tentatively conclude that the high fraction of (0001) facets in disk-shaped Co-NC decrease FT activity and, although very challenging to pursue, that metal nanoparticle shape effects can be studied at industrially relevant conditions.

Crystal-phase and surface-structure engineering of ruthenium nanocrystals

Metal nanocrystals with controlled shapes or surface structures have received increasing attention, owing to their desirable properties for applications ranging from catalysis to photonics, energy and biomedicine. Most studies, however, have been limited to nanocrystals with the same crystal phase as the bulk material. Engineering the phase of metal nanocrystals while simultaneously attaining shape-controlled synthesis has recently emerged as a new frontier of research. Here, we use Ru as an example to evaluate recent progress in the synthesis of metal nanocrystals featuring different crystal phases and well-controlled shapes. We first discuss synthetic strategies for controlling the crystal phase and shape of Ru nanocrystals, with a focus on new mechanistic insights. We then highlight the major factors that affect the packing of Ru atoms and, thus, the crystal phase, followed by an examination of the thermal stability of Ru nanocrystals in terms of both crystal phase and shape. Next, we showcase the successful implementation of these Ru nanocrystals in various catalytic applications. Finally, we end with a discussion of the challenges and opportunities in the field, including leveraging the lessons learned from Ru to engineer the crystal phase and surface structure of other metals. Engineering the phase of metal nanocrystals while simultaneously achieving shape-controlled synthesis can enable new and desirable properties. This Review highlights the synthetic strategies for generating Ru nanocrystals with different crystal phases and surface structures, and outlines their implementation in catalytic applications.

(Electrodeposition Division Early Career Investigator Award) Additives in Cu Electrodeposition for Through-Silicon Via Filling and the Growth of Cu Nanocrystals

Additives play a key role in modulating the kinetics of electrochemical reactions. They adsorb onto metal surfaces and their surface coverage changes the charge transfer resistance of electrochemical reactions. This phenomenon is critical in a variety of electrochemical processes such as corrosion, electrochemical deposition, electrocatalysis, and colloidal synthesis of metal nanocrystals. The use of additives in Cu electrodeposition is key to achieving defect-free interconnections for semiconductor devices. Controlling the surface coverage of additives enables Cu to selectively grow from the bottom of filling features, while Cu deposition outside of the features is effectively inhibited.1 This filling process is referred to as superfilling, superconformal deposition, or bottom-up filling. As a result of tremendous efforts to advance electrodeposition processes, nanometer-scaled Damascene features can be easily filled with Cu in the presence of polyether suppressors and accelerators.1,2 Furthermore, micrometer-scaled features including through-silicon vias (TSVs), microvias, and through-holes can also be successfully filled by adopting additional levelers.3,4 To further advance the metallization process, various experimental and theoretical studies are still on-going to develop new additives,5,6 to improve properties of Cu interconnections,7 and to gain a better understanding of the additives.8,9 Inorganic/organic additives, referred to as shape-directing agents or capping agents, are also essential in the colloidal syntheses of various nanocrystals.10 With the aid of additives, the shape of nanocrystals can be modulated from spherical nanoparticles to one-dimensional nanowires or to two-dimensional nanoplates. The growth of nanocrystals in colloidal syntheses is similar to metal electroless deposition because both processes are based on spontaneous redox reactions, i.e. the reduction of metal ions and the oxidation of reducing agents. However, in colloidal synthesis, the behavior of shape-directing agents is crystal facet-dependent, determining the final shape of nanocrystals by facilitating or inhibiting metal growth on certain crystal surfaces. Recently, electrochemical techniques using single-crystal electrodes have proven to be a powerful analytical tool that can clarify the growth mechanism of anisotropic nanocrystals by providing the metal growth rates on each single-crystal electrode.11,12 Successive research is still on-going to fully understand the facet-selective chemistry that occurs during nanocrystal growth. This presentation summarizes my recent progress in TSV filling and the mechanistic study of Cu nanowire growth. The first part of this presentation will mainly focus on bromide and iodide ions that act as a leveler for TSV filling,13,14 and the second part will introduce how electrochemical analyses using single-crystal electrodes reveal the growth mechanism of Cu nanowires and how halide ions change the shape of Cu nanocrystals.11,12,15 References T.P. Moffat, J.E. Bonevich, W.H. Huber, A. Stanishevsky, D.R. Kelly, G.R. Stafford, and D. Josell, J. Electrochem. Soc., 147, 4524–4535 (2000).P. Broekmann, A. Fluegel, C. Emnet, M. Arnold, C. Roeger-Goepfert, A. Wagner, N.T.M. Hai, and D. Mayer, Electrochim. Acta, 56, 4724–4734 (2011).V.-H. Hoang and K. Kondo, J. Electrochem. Soc., 164, D795–D797 (2017).J. Luo, Z. Li, M. Shi, J. Chen, Z. Hao, and J. He, J. Electrochem. Soc., 166, D104–D112 (2019).M.J. Kim, Y. Seo, H.C. Kim, Y. Lee, S. Choe, Y.G. Kim, S.K. Cho, and J.J. Kim, Electrochim. Acta, 163, 174–181 (2015).H.C. Kim, S. Choe, J.Y. Cho, D. Lee, I. Jung, W.-S. Cho, M.J. Kim, and J.J. Kim, J. Electrochem. Soc., 162, D109–D114 (2015).Q. Zhu, X. Zhang, S. Li, C. Liu, and C.-F. Li, J. Electrochem. Soc., 166, D3097–D3099 (2019).G.-K. Liu, S. Zou, D. Josell, L.J. Richter, and T.P. Moffat, J. Phys. Chem. C, 122, 21933–21951 (2018).T. Akita, M. Tomie, R. Ikuta, H. Egoshi, and M. Hayase, J. Electrochem. Soc., 166, D3058–D3065 (2019).D. Huo, M.J. Kim, Z. Lyu, Y. Shi, B.J. Wiley, and Y. Xia, Chem. Rev., in press, doi:10.1021/acs.chemrev.8b00745 (2019).M.J. Kim, P.F. Flowers, I.E. Stewart, S. Ye, S. Baek, J.J. Kim, and B.J. Wiley, J. Am. Chem. Soc., 139, 277–284 (2017).M.J. Kim, S. Alvarez, Z. Chen, K.A. Fichthorn, and B.J. Wiley, J. Am. Chem. Soc., 140, 14740–14746 (2018).M.J. Kim, H.C. Kim, and J.J. Kim, J. Electrochem. Soc., 163, D434–D441 (2016).H.C. Kim, M.J. Kim, and J.J. Kim, J. Electrochem. Soc., 165, D91–D93 (2018).M. J. Kim, S. Alvarez, T. Yan, V. Tadepalli, K.A. Fichthorn, and B.J. Wiley, Chem. Mater., 30, 2809–2818 (2018).

Nanosilica-Confined Synthesis of Orthogonally Active Catalytic Metal Nanocrystals in the Compartmentalized Carbon Framework.

Multifunctionalized porous catalytic nanoarchitectures are highly desirable for a variety of chemical transformations; however, selective installation of different catalysts with spatial and functional precision working synergistically and predictably, is highly challenging. Here, a synthetic strategy is developed toward the customizable combination of orthogonally reactive metal nanocrystals within interconnected carbon-cavities as a compartmentalized framework by employing aminated-silica-directed thermal solid-state nanoconfined synthesis of metal nanocrystals and endotemplating concomitant carbonization-mediated interlocking, as key processes. The main advantage of the strategy is the facility to choose any combination of metals, which can be further employed according to the desired application. The strategically synthesized compartmentalized multifunctional catalytic architectures of Pd-Pt@Com-CF regulate the O2 -mediated selective cascade oxidation reaction converting alcohol to acid with high yield and selectivity; and another Pt-Ir@Com-CF platform is demonstrated as a bifunctional electrocatalyst for oxygen reduction/evolution reactions.