Metal nanodendrites composed of highly branched arms have received great attention as electrocatalysts owing to their reasonably large surface area and the potential existence of low-coordinated sites in high densities. Although significant progress has been made in the synthesis of bimetallic nanodendrites, few works involve a system consisting of Pd and Cu, particularly in the case of alloyed nanodendrites. Here, we report a facile and powerful approach for the synthesis of PdCu alloy nanodendrites with tunable composition through varying the molar ratio of the Pd and Cu salt precursors. The key to achieving PdCu alloy nanodendrites is the use of W(CO)6, which serves as a strong reducing agent. In addition, variation in the molar ratio of the precursors, from Pd rich to Cu rich, leads to shape evolution of the PdCu alloy, moving from a polyhedral to a dendritic nanostructure. This result indicates that galvanic replacement between a Cu rich alloy and a Pd precursor also plays an important role in the formation of PdCu alloy nanodendrites. When used as electrocatalysts for the methanol oxidation reaction (MOR), PdCu alloy nanodendrites exhibit remarkably enhanced catalytic properties relative to commercial Pd/C. Specifically, Pd35Cu65 alloy nanodendrites show the highest specific activity and mass activity for the MOR, 9.3 and 7.6 times higher than that of commercial Pd/C, respectively. This enhancement can be attributed to their dendritic structure and a possible bifunctional mechanism between Pd and Cu.

Bimetallic nanocrystals with a branched shape have received great interest as catalysts due to their unique structures and fascinating properties. However, the conventional synthetic approaches based on the island growth mode often lead to the dendritic nanostructures with inhomogeneous and uncontrolled branches. Here precise control over the number of branches has been realized in the deposition of Pt on Pd seeds through the Stranski–Krastanov growth mechanism. Based on such a growth mode, Pd@Pt core–shell hexapods and octapods have been generated by a seeded growth with Pd octahedra and cubes as the seeds, respectively. We found that Pt atoms are initially deposited on the side faces of Pd seeds through a layer-by-layer epitaxial growth in the presence of oleylamine (OAm), leading to a local strain focused at their corners. These strain-concentrated sites promote the subsequent island growth of Pt atoms at the corners of the Pd seeds, resulting in the Pd@Pt core–shell hexapods or octapods. Both the Pd@Pt core–shell hexapods and octapods exhibit the substantially enhanced catalytic properties in terms of activity and stability towards a methanol oxidation reaction (MOR) relative to the commercial Pt/C. Specifically, the Pd@Pt core–shell hexapods show the highest specific (1.97 mA cm−2) activity and mass activity (0.52 mA μgPt−1) for the MOR, which are 5.8 and 2.6 times higher than those of the commercial Pt/C, respectively. This enhancement can probably be attributed to their unique structures and the synergistic effect between Pt and Pd.

Bimetallic nanocrystals with a branched shape have received great interest as catalysts due to their unique structures and fascinating properties. However, the conventional synthetic approaches based on the island growth mode often lead to the dendritic nanostructures with inhomogeneous and uncontrolled branches. Here precise control over the number of branches has been realized in the deposition of Pt on Pd seeds through the Stranski–Krastanov growth mechanism. Based on such a growth mode, Pd@Pt core–shell hexapods and octapods have been generated by a seeded growth with Pd octahedra and cubes as the seeds, respectively. We found that Pt atoms are initially deposited on the side faces of Pd seeds through a layer-by-layer epitaxial growth in the presence of oleylamine (OAm), leading to a local strain focused at their corners. These strain-concentrated sites promote the subsequent island growth of Pt atoms at the corners of the Pd seeds, resulting in the Pd@Pt core–shell hexapods or octapods. Both the Pd@Pt core–shell hexapods and octapods exhibit the substantially enhanced catalytic properties in terms of activity and stability towards a methanol oxidation reaction (MOR) relative to the commercial Pt/C. Specifically, the Pd@Pt core–shell hexapods show the highest specific (1.97 mA cm−2) activity and mass activity (0.52 mA μgPt−1) for the MOR, which are 5.8 and 2.6 times higher than those of the commercial Pt/C, respectively. This enhancement can probably be attributed to their unique structures and the synergistic effect between Pt and Pd.

A novel Si/SiOx porous structure with a SiOx coating layer of varying thicknesses was prepared via a simple annealing and acid washing process. When used as an anode material for lithium-ion batteries, the Si/SiOx porous structure with an ∼9 nm SiOx coating layer demonstrates significantly improved electrochemical performance with a high reversible discharge capacity of over 915 mA h g−1 after 500 long cycles at 1 A g−1. The lithiation mechanism of a SiOx layer of different thicknesses has also been investigated.

PdAu bimetallic nanoplates are synthesized by titrating HAuCl4 into an aqueous solution containing in situ generated Pd square nanoplates (PdSPs) on reduced graphene oxide (rGO) in the presence of ascorbic acid (AA), serving as a reducing agent, at different injection rates. At a high injection rate (e.g., 45 mL min−1), PdAu core–shell nanoplates on rGO are generated by strong galvanic replacement between PdSPs and the Au precursor, followed by reduction of the Pd precursor. In contrast, PdAu nanoplates with a core–shell and alloy integrating structure are obtained on rGO by co-reduction of the Au and Pd precursors by AA due to the inhibition of the abovementioned galvanic replacement at a slow injection rate (e.g., 0.5 mL min−1). The PdAu nanoplates with a core–shell and alloy integrating structure on rGO exhibit a substantially enhanced catalytic activity towards the hydrogen evolution reaction (HER) relative to the PdAu core–shell nanoplates and PdSPs on rGO, and is comparable to the commercial Pt/C. Significantly, these core–shell and alloy integrating nanoplates on rGO have much superior durability over Pt/C for catalyzing the HER under acidic conditions. The remarkable enhancement in activity and durability can be attributed to the cooperative function of the PdAu alloy and electron coupling between nanoplates and graphene.

Au nanorings are of particular interest in catalysis owing to their fascinating properties, however, it still remains a tremendous challenge to generate such hollow nanostructures with small size. Here, we report the synthesis of Au nanorings with an outer diameter of less than 20 nm by a seed-mediated approach with Pd nanoplates as seeds in the presence of Ag+ ions. The incorporation of Ag+ ions substantially slows down the reduction rate of the Au precursor through an underpotential deposition (UPD) process, leading to the formation of small Au nanoparticles. These small Au nanoparticles then coalesced into nanorings on small Pd nanoplates. The outer diameter of the Au nanorings is tuned by varying the size of the Pd nanoplates. The smallest Au nanorings are evaluated as catalysts towards the hydrogenation of 4-nitrophenol, showing substantially enhanced catalytic activity relative to the Au nanoparticles with the same size. This enhancement in the catalytic activity can be attributed to the unique structural features including the large specific surface areas, convenient accessibility of both interior and exterior surfaces for the reactants, and existence of highly active sites in the interior part.

Pt-based multimetallic core–shell nanoplates have received great attention as advanced catalysts, but the synthesis is still challenging. Here we report the synthesis of multimetallic Pd@PtM (M = Ni, Rh, Ru) nanoplates including Pd@Pt nanoplates, in which Pt or Pt alloy shells with controlled thickness epitaxially grow on plate-like Pd seeds. The key to achieve high-quality Pt-based multimetallic nanoplates is in situ generation of CO through interfacial catalytic reactions associated with Pd nanoplates and benzyl alcohol. In addition, the accurate control in a trace amount of CO is also of great importance for conformal growth of multimetallic core–shell nanoplates. The Pd@PtNi nanoplates exhibit substantially improved activity and stability for methanol oxidation reaction (MOR) compared to the Pd@Pt nanoplates and commercial Pt catalysts due to the advantages arising from plate-like, core–shell, and alloy structures.Keywords: electrocatalysis; epitaxial growth; interfacial catalytic reactions; Multimetallic core−shell nanocrystals; nanoplates;

Nanorings made of noble metals such as Au and Ag have attracted particular interest in plasmonic properties since they allow remarkable tunability of plasmon resonance wavelengths associated with their unique structural features. Unfortunately, most of the syntheses for Au nanorings involve complex procedures and/or require highly specialized and expensive facilities. Here, we report a seed-mediated approach for selective deposition of Au nanorings on the periphery of Pd seeds with the structure of an ultrathin nanosheet through the island growth mode. In combination with selective etching of Pd nanosheets, Au nanorings are eventually produced. We can control the outer diameter and wall thickness of the nanorings by simply varying the size of the Pd nanosheets and reaction time. By taking the advantage of this size controllability, the nanorings show tunable surface plasmonic properties in the near infrared (NIR) region arising from both the in-plane dipole and face resonance modes. Owing to their good surface plasmonic properties, the nanorings show substantially enhanced surface-enhanced Raman spectroscopy (SERS) performance for rhodamine 6G, and are therefore confirmed as good SERS substrates to detect trace amounts of molecules.

PtRu bimetallic particles are well-known commercial catalysts with promising performance for methanol oxidation. However, shape-controlled synthesis of PtRu bimetallic nanocrystals, especially for the platonic structures with {100} (e.g., cubes) or {111} facets (e.g., icosahedra) exposed towards catalysis, has met only limited success due to the different crystal structures of Pt and Ru. Here we report a facile approach to the synthesis of Ru decorated Pt bimetallic cubes and icosahedra in a mixed solvent. We found that the cubes were formed in the solvent containing N,N-dimethylmethanamide (DMF) and oleylamine (OAm) possibly due to the selective adsorption of CO on Pt{100} arising from the decomposition of DMF catalyzed by a Ru salt precursor. When hexadecane was added into the aforementioned solvent, the synthesis became a two-phase interfacial reaction due to the large difference in solvent polarity, thereby retarding the reaction kinetics and promoting the formation of the icosahedra with the composition similar to the cubes. When evaluated as catalysts towards methanol oxidation, the Ru decorated Pt icosahedra showed much better performance in terms of specific and mass activity relative to the corresponding cubes. Specifically, the Ru decorated Pt bimetallic icosahedra achieved a specific activity of 0.76 mA cm−2 and mass activity of 74.43 mA mgPt−1, which is ∼6.7 and 2.2 times as high as those of the carbon supported Pt7Ru nanoparticles, respectively. This enhancement can be attributed to a combination of twin-induced strain and facet effects.

Pt epitaxial layer on a nanoparticle with twinned structure and well-defined shape is highly desirable in order to achieve high performance in both catalytic activity and durability toward oxygen reduction reaction (ORR). However, it remains tremendously challenging to produce conformal, heterogeneous, twinned nanostructures due to the high internal strain and surface energy of Pt. In addition, these twinned nanostructures may be subject to degradation in highly corrosive ORR environments due to the high energy of twin boundary. Here we report the synthesis of Au–Pt core–shell star-shaped decahedra bounded mainly by {111} facets, in which Pt shells with controlled thickness epitaxially grew on Au cores with a 5-fold twinned structure. The incorporation of the amine group decreases the surface energy of Pt by strong adsorption and thus facilitates the epitaxial growth of Pt on Au core instead of the dendritic growth. In addition, Br– ion could largely stabilize the {111} facets of Pt, which prevent the formation of spherical nanoparticles. The Au–Pt core–shell decahedra with thicker Pt shell exhibited enhanced ORR properties in terms of activity and durability. Specifically, AuPt1.03 star-shaped decahedra achieved the highest mass activity (0.94 mA/μgPt) and area activity (1.09 mA/cm2Pt), which is ∼6.7 and 5 times, respectively, as high as those of the commercial Pt/C (ETEK). Significantly, such star-shaped decahedra were highly stable with ∼10% loss in area activity and ∼20% loss in mass activity after 30 000 CV cycles in O2 saturated acid solution.

Rh is a promising candidate as an indispensible component in bimetallic catalysts due to its unique capability to resist against the aggressive corrosion from the reaction medium. However, Rh has a very strong oxygen binding ability and is generally not suitable for the oxygen reduction reaction (ORR). Here, we have demonstrated shape-controlled synthesis of Rh–Pd alloy nanocrystals with high activity and durability for ORR by retarding the reaction kinetics at an ultra-slow injection rate of metal salts using a syringe pump. Under precise control of sluggish reaction kinetics, Pd followed a preferential overgrowth along the <100> direction, whereas the growth behavior of Rh was dominant along the <111> direction. These different kinetically-controlled growth behaviors associated with Rh and Pd were essential for achieving the shape transition between the cube and the octahedron of their alloys. The Rh8Pd92 alloy octahedra exhibited the highest mass activity with a value of 0.18 mA μg−1 in terms of the equivalent Pt cost, and were two-fold higher than that of commercial Pt/C. Significantly, all Rh–Pd alloy nanocrystals were highly stable with only less than 25% loss in mass activity after 30000 CV cycles in O2 saturated acid solution compared to ∼56% loss of the commercial Pt/C (E-TEK). Indeed, the mass activity of Rh8Pd92 was 3.3 times higher than that of commercial Pt/C after the accelerated stability test (ADT). This improvement in activity and durability may arise possibly from synergistic effects between the facet and the surface composition.

In this work, we reported our experimental approach to reveal the detailed growth behavior of platinum (Pt)–copper (Cu) bimetallic multipod nanostructures in a one-pot synthesis by analyzing the intermediate products from different stages by using aberration-corrected scanning transmission electron microscopy and associated energy-dispersive X-ray spectroscopy. An element-specific growth trajectory of Pt–Cu multipod nanostructures with compositional variation couples to geometric morphologies was observed: Ptx–Cu1−x multipods start from Pt-rich seeds (x > 0.6), evolve into a Pt–Cu alloy phase (x ≈ 0.5), and then form Pt-rich branches (with x > 0.8). This could be further explained on considering the different redox potentials of two metals and their interactions through underpotential deposition, galvanic replacement, and phase segregation. The observed combination of geometric morphologies and compositional variations may provide new strategies to potentially aid rational synthesis of alloy catalysts.

Anisotropic Au nanoparticles show unique localized surface plasmon resonance (LSPR) properties, which make them attractive in optical, sensing, and biomedical applications. In this contribution, we report a general and facile strategy towards aqueous synthesis of Au and M@Au (M = Pd, CuPt) hybrid nanostars by reducing HAuCl4 with ethanolamine in the presence of cetyltrimethylammonium bromide (CTAB). According to electron microscopic observations and spectral monitoring, we found that the layered epitaxial growth mode (i.e., the Frank-van der Merwe mechanism) contributes to the enlargement of the core, while the random attachment of Au nanoclusters onto the cores accounts for the formation of the branches. Both of them are indispensable to the formation of the nanostars. The LSPR properties of the Au nanoparticles have been well investigated with morphology control via the precursor amount and growth temperature. The Au nanostars showed improved surface-enhanced Raman spectroscopy (SERS) performance for rhodamine 6G due to their sharp edges and tips, which were therefore confirmed as good SERS substrates to detect trace amounts of molecules.

Oxidative etching has widely prevailed in the synthesis of a crystal and played a critical role in determining the final growth behavior. In this Letter, we report an in situ microscopic study on the oxidative etching of palladium cubic nanocrystals by liquid cell scanning transmission electron microscopy. The etching was realized with oxidative radiation reactants from electron–water interaction in the presence of Br– ions. Dissolution dynamics of monodispersed and aggregated nanocrystals were both investigated and compared. Analyses on the dissolution kinetics of nanocrystals and the diffusion kinetics of the dissolved agents were carried out based on the scanning transmission electron microscopy characterizations. The results presented here pave a way toward the quantitative understanding of the oxidative etching reaction and its application in the functionally orientated fabrication of nanocrystals with certain sizes, structures, and morphologies.

In addition to activity, durability of Pd-based catalysts in a highly corrosive medium has become one of the most important barriers to limit their industrial applications such as low-temperature fuel cell technologies. Here, Rh with a unique capability to resist against oxidation etching was incorporated into Pd-based catalysts to enhance both their activity and durability for oxygen reduction reaction (ORR). This idea was achieved through the synthesis of the Rh–Pd alloy nanodendrites by co-reducing Rh and Pd salt precursors in oleylamine (OAm) containing cetyltrimethylammonium bromide (CTAB). In this synthesis, Rh–Pd alloy nanostructures with Rh–Pd atomic ratios from 19:1 to 1:4 were generated by varying the molar ratios of Rh and Pd salt precursors. Interestingly, this variation of the molar ratios of the precursors from Rh rich to Pd rich would lead to the shape evolution of Rh–Pd alloy from dendritic nanostructures to spherical aggregations. We found that Br− ions derived from CTAB were also indispensible to the production of Rh–Pd alloy nanodendrites. Owing to the addition of highly stable Rh as well as the radical structure with a large number of low-coordinated sites on the arms, Rh–Pd alloy nanodendrites with a Rh–Pd atomic ratio of 4:1 (Rh80Pd20) exhibited a substantially enhanced electrocatalytic performance towards ORR with a 5% loss of mass activity during the accelerated stability test for 10000 cycles compared to ∼50% loss of the commercial Pt/C (E-TEK).

We investigated the growth of two-dimensional (2D) palladium dendritic nanostructures (DNSs) using in situ liquid-cell transmission electron microscopy (TEM). Detailed in situ and ex situ high-resolution scanning TEM (S/TEM) characterization and fractal dimension analyses reveal that the diffusion-limited aggregation and direct atomic deposition are responsible for the growth of palladium dendritic nanostructures.

This paper describes a facile chemical vapor deposition (CVD) and subsequent radio-frequency (RF)-sputtering approach for the synthesis of CoO/NiSix core–shell nanowire (NW) arrays on Ni foams. The metallic core (i.e., NiSix) with high conductivity acts as a nanostructured current collector. The as-synthesized CoO/NiSix core–shell NW arrays have been applied as anode materials for lithium-ion batteries, which deliver high cycle life and enhanced power performance compared to planar CoO electrodes on Ni foams. The high surface-to-volume ratio and improved electronic/ionic conductivity of the nanostructured electrodes may be responsible for the improved performance.

In this paper, we have reported a novel hierarchical nanostructure made of vertically ordered Ni3Si2/Si nanorod arrays to moderate the notorious pulverization and capacity decay usually occurring in the silicon used as the anode materials in Li-ion batteries. During the lithiation and delithiation process, the amorphous Si (a-Si) layer acts as an active material and participates in the processes, whereas the Ni3Si2 nanorod arrays work as a mechanically stable supporter and fast charge transport pathway. In addition, they can afford sufficient interspace for expansion/contraction upon lithium insertion/extraction. These Ni3Si2/Si nanorod arrays anodes exhibit excellent cycling performance at high current rates of 1 C (4.2 A g−1), 2 C (8.4 A g−1), and 4 C (16.8 A g−1), respectively. A high and steady discharge capacity of over 2184 mA h g−1 can be achieved after 50 cycles with a high initial coulombic efficiency of 86.7%. The synthesis approach is simple, efficient and rich-yielding, probably providing a new strategy for the application of silicon-based anode materials with enhanced performance.

A novel and versatile layer-by-layer approach has been developed to synthesize composite metal oxide nanotubes on carbon-nanotube (CNT) templates. We demonstrate this approach by the preparation of CeO2−SnO2 and Ag−NiO composite nanotubes. The electrostatic attraction between the CNTs and metal ions play the most important role in the formation of CNT-based core−shell nanotubes, from which the composite metal oxide nanotubes are subsequently synthesized. It is found that the CeO2−SnO2 and Ag−NiO composite nanotubes lead to excellent device performance when they are used in gas sensors and Li-ion batteries, respectively.

A layer-by-layer (LBL) assembly approach has been developed to synthesize ZnO nanorod-based hybrid nanomaterials such as ZnO/CeO2, ZnO/CdS, and ZnO/Ag on ZnO nanorod templates at room temperature. The morphology, structure, and composition of the ZnO nanorod-based hybrid nanomaterials have been characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis. It is indicated that a uniform coating layer consisting of homogeneous nanoparticles is deposited on the surface of ZnO nanorods due to the strong electrostatic attraction between metal ions and polyelectrolyte modified ZnO nanorods. The general approach presented here can be extended to the synthesize other one-dimensional (1D) nanostructure-based hybrid nanomaterials.

Anisotropic Au nanoparticles show unique localized surface plasmon resonance (LSPR) properties, which make them attractive in optical, sensing, and biomedical applications. In this contribution, we report a general and facile strategy towards aqueous synthesis of Au and M@Au (M = Pd, CuPt) hybrid nanostars by reducing HAuCl4 with ethanolamine in the presence of cetyltrimethylammonium bromide (CTAB). According to electron microscopic observations and spectral monitoring, we found that the layered epitaxial growth mode (i.e., the Frank-van der Merwe mechanism) contributes to the enlargement of the core, while the random attachment of Au nanoclusters onto the cores accounts for the formation of the branches. Both of them are indispensable to the formation of the nanostars. The LSPR properties of the Au nanoparticles have been well investigated with morphology control via the precursor amount and growth temperature. The Au nanostars showed improved surface-enhanced Raman spectroscopy (SERS) performance for rhodamine 6G due to their sharp edges and tips, which were therefore confirmed as good SERS substrates to detect trace amounts of molecules.

We investigated the growth of two-dimensional (2D) palladium dendritic nanostructures (DNSs) using in situ liquid-cell transmission electron microscopy (TEM). Detailed in situ and ex situ high-resolution scanning TEM (S/TEM) characterization and fractal dimension analyses reveal that the diffusion-limited aggregation and direct atomic deposition are responsible for the growth of palladium dendritic nanostructures.

A novel Si/SiOx porous structure with a SiOx coating layer of varying thicknesses was prepared via a simple annealing and acid washing process. When used as an anode material for lithium-ion batteries, the Si/SiOx porous structure with an ∼9 nm SiOx coating layer demonstrates significantly improved electrochemical performance with a high reversible discharge capacity of over 915 mA h g−1 after 500 long cycles at 1 A g−1. The lithiation mechanism of a SiOx layer of different thicknesses has also been investigated.

Single-crystalline Pd square nanoplates enclosed by {100} facets were generated on reduced graphene oxide and exhibited the substantially enhanced properties for the formic acid oxidation reaction. The combination of carbonyl groups formed on the surface of annealed graphene oxide and Br− ions played important roles in this synthesis.

In this work, we reported our experimental approach to reveal the detailed growth behavior of platinum (Pt)–copper (Cu) bimetallic multipod nanostructures in a one-pot synthesis by analyzing the intermediate products from different stages by using aberration-corrected scanning transmission electron microscopy and associated energy-dispersive X-ray spectroscopy. An element-specific growth trajectory of Pt–Cu multipod nanostructures with compositional variation couples to geometric morphologies was observed: Ptx–Cu1−x multipods start from Pt-rich seeds (x > 0.6), evolve into a Pt–Cu alloy phase (x ≈ 0.5), and then form Pt-rich branches (with x > 0.8). This could be further explained on considering the different redox potentials of two metals and their interactions through underpotential deposition, galvanic replacement, and phase segregation. The observed combination of geometric morphologies and compositional variations may provide new strategies to potentially aid rational synthesis of alloy catalysts.