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We report a silver‐free synthesis of gold (Au) concave nanocubes (CNCs) that involves the direct deposition of Au atoms over spherical Au seeds under well‐controlled reaction kinetics and surface capping. The elementally‐pure composition makes them ideal research candidate towards validating structural advantage of concave surface in electrocatalytic oxidation of ethanol. In particular, the as‐obtained Au CNCs exhibited an enhanced specific activity and reaction kinetics, but weakened long‐term stability, as compared to quasi‐spherical counterparts. Theoretical simulations suggest that the high‐index planes represent a high catalytic performance for ethanol oxidation. The current work offers an effective synthetic strategy that successfully excludes the necessary and wide use of Ag+ ions in controlled synthesis of pure Au nanocrystals with a concave cubic shape, shedding light on the rational design of fuel cell electrocatalyst from the perspective of crystal facet effect. [ABSTRACT FROM AUTHOR]

We report a seeded growth of gold (Au) nanoplates with two distinct morphologies, which are similar to a lotus leaf and a donut, respectively. The success of this synthesis relies on the use of flat Au nanoplates in high purity as seeds, followed by a controlled deposition. In particular, the presence of Ag+ led to the deposition of Au atoms preferentially occurred at the central part of one face of the nanoplate and thus the formation of lotus leaf‐like shape. In contrast, when Ag+ was absent, the growth mainly occurred to the edge region. Then, cold‐welding of newly‐formed branches and further diffusion of Au atoms created holes in the nanoplate, resulting in the formation of donut‐like shape. The Au nano‐lotus leaves with tunable sizes exhibited absorbance in near‐infrared region and enhanced chemical activities in electrochemical measurements. The current strategy is extended to fabricate Au−Ag nanoplates with a similar lotus leaf‐like morphology, which also exhibited strong absorbance in near‐infrared region in UV‐vis extinction spectra. The current work allows the fabrication of two‐dimensional Au‐based nanomaterials with concave shape and three‐dimensional architecture and could be potentially extended to other noble metals and alloys. [ABSTRACT FROM AUTHOR]

We report an ultrafast synthesis of wavy gold‐silver (AuAg) nanowires with tunable diameters via a seed‐mediated co‐reduction. The success of current strategy relies on the use of an elevated reaction temperature to accelerate the synthesis to be completed within several minutes and the use of Au seeds with controlled sizes to enable the manipulation over their diameters in the range of 2–10 nm. The presence of chloride‐contained quaternary ammonium surfactant and excessive reductant have been demonstrated to be critical for the high‐yield formation of AuAg products with the unique morphology of wavy nanowire. Due to the advantage in size control, the size effect on the plasmonic behavior of AuAg alloy wavy nanowires is investigated, where the products with sub‐5 nm diameter exhibit a broad shoulder absorbance peak in their spectrum. [ABSTRACT FROM AUTHOR]

We report a facile synthesis of Au@PdAg alloy core‐shell nanocrystals in dendrite form, having tunable size and composition. In particular, using spherical Au nanoparticles as seeds, the co‐reduction of Pd and Ag precursor in growth stage results in the formation of PdAg alloy shells with a dendrite shape. Their size and elemental composition can be tuned by varying the seed amount and feeding ratio in Pd and Ag precursor, respectively, illustrating the versatility of the current synthetic strategy. The size, morphology, and elemental composition of the products have been characterized using a set of techniques, including SEM, TEM, XRD, XPS, HAADF‐STEM, and EDX‐STEM mapping. When working as electrocatalysts, the current Au@PdAg alloy core‐shell nanocrystals supported by carbon black exhibit enhanced activity and excellent operation stability for electroxidation of ethanol as compared to commercial Pd/C. The current work offers a feasible strategy to preparation of multi‐metallic core‐shell dendritic nanocrystals with controllable size and composition and could find important use in fuel cells and related fields. [ABSTRACT FROM AUTHOR]

We report the seeded growth of gold@silver (Au@Ag) core‐shell nanocrystals with the shape of truncated right bipyramids (TRB) and their hollow derivatives obtained via a galvanic replacement reaction. In particular, by depositing Ag on single‐crystal Au seeds under kinetic control, the resultant Au@Ag core‐shell products exhibit planar defects. Morphology and structure characterization is performed to confirm the crystallinity variation and the resultant TRB shape. Considering that elemental Au and Ag have similar lattice constants and negligible lattice mismatch, this phenomenon is quite unique, as the crystallinity of product is typically governed by the seed. The size of final product can be controlled in the range of 37–85 nm by varying the volume of the Au seed solution. In addition, by reacting with gold precursor, the as‐prepared Au@Ag TRBs can be converted into Au‐based nanostructures with hollow interiors, showing absorbance properties continuously tuned in the visible range, which could find important use in photocatalysis, sensing, and fluorescence enhancement, among others. [ABSTRACT FROM AUTHOR]

A synthetic case is reported that demonstrates the cationic additive, Ag+, can influence the crystallinity and thus shape of final product during seeded growth of Au nanocrystals. Using single‐crystal Au seeds as reference, the crystallinity difference between seed and final product could be directly compared. In particular, three different types of crystallinity/morphology can be obtained by varying the concentration of Ag+ in the particle growth solutions: single‐crystal quasi‐spheres, multiply twinned particles (MTPs), and protruded MTPs, with no Ag+ added and solution Ag+ /Au3+ ratios of 1 : 20 and 1 : 5, respectively. The reaction kinetics are investigated using extinction spectroscopy, indicating the presence of Ag+ leads to a dampened growth of Au nanocrystals. This principle is validated using single‐crystal Au seeds with different morphology and amounts. We also test the anti‐corrosion performance of as‐prepared Au nanocrystals with different crystallinity by treating them with sodium thiosulfate. Interestingly, in addition to reduction in size, the morphology of single‐crystal ones varies from quasi‐sphere to cube, indicating the anisotropy in oxidative etching of Au nanocrystals. [ABSTRACT FROM AUTHOR]

A synthetic case is reported that demonstrates the cationic additive, Ag+, can influence the crystallinity and thus shape of final product during seeded growth of Au nanocrystals. Using single‐crystal Au seeds as reference, the crystallinity difference between seed and final product could be directly compared. In particular, three different types of crystallinity/morphology can be obtained by varying the concentration of Ag+ in the particle growth solutions: single‐crystal quasi‐spheres, multiply twinned particles (MTPs), and protruded MTPs, with no Ag+ added and solution Ag+ /Au3+ ratios of 1 : 20 and 1 : 5, respectively. The reaction kinetics are investigated using extinction spectroscopy, indicating the presence of Ag+ leads to a dampened growth of Au nanocrystals. This principle is validated using single‐crystal Au seeds with different morphology and amounts. We also test the anti‐corrosion performance of as‐prepared Au nanocrystals with different crystallinity by treating them with sodium thiosulfate. Interestingly, in addition to reduction in size, the morphology of single‐crystal ones varies from quasi‐sphere to cube, indicating the anisotropy in oxidative etching of Au nanocrystals. [ABSTRACT FROM AUTHOR]

We report the fabrication of "Pt-on-PdAg" heterogeneous nanocrystals in the form of trigonal/hexagonal plate (THNPs) and explored their applications in electroxidation of methanol (MOR) in alkaline medium. In particular, PdAg polyhedral nanoparticles are prepared in advance, followed by the addition of Pt salts to allow in situ galvanic replacement reaction (GRR) between them, leading to the formation of Pt nano-islands on PdAg particle surface and the transformation of the overall morphology into trigon/hexagon. The deliberately designed Pt-"PdAg alloy" interface arising from the hybrid structure greatly enriches the absorption sites, showing noticeable structural advantages in MOR electrocatalysis. Particularly, the carbon-supported Pt-on-PdAg THNPs exhibit nearly 30-fold increase in specific activity as compared to that of commercial Pt/C, as well as enhanced reaction kinetics and long-term durability. DFT calculations suggest that the reaction of CH 3 OH oxidation mediated by PtAgPd is energetically more favorable compared to the similar reaction promoted by Pt, which rationalizes the experimental observation that PtAgPd shows the improved catalytic performance. The present study offers a feasible route to construct trimetallic nanocrystals with successful interface engineering, and validates their promising use as fuel cell electrocatalyst from both experimental validation and fundamental insights. It may help enlighten the rational design of heterostructured electrocatalysts with regulated multiple active sites. • Stepwise synthesis of trigonal/hexagonal plate-like Pt-on-PdAg hybrid nanostructures is proved. • The density of Pt nano-islands and the overall elemental composition can be tuned. • Interface engineering, tensile strain and multimetallic synergy, contribute to enhanced MOR. • DFT calculations show that MOR mediated by PtAgPd is energetically more favorable. [ABSTRACT FROM AUTHOR]

• Silver nanorods/nanowires were prepared within the range of sub-20 nm diameter. • The diameter can be controlled, as small as 12 nm, using 5-nm spherical Au seeds. • One-dimensional trimetallic (Au@Pd-Ag) hollow products were prepared via GRR. We report a facile synthesis of silver nanorods/nanowires with the diameter in the range of sub-20 nm via seeded growth. The key to the success of this work relies on the use of tiny Au seeds and manipulation over reaction kinetics. In particular, their diameter could be controlled to as small as 12 nm using 5-nm spherical Au seeds. They can be further converted to trimetallic (Au@Ag-Pd) hollow derivatives with tunable hollow degree and elemental compositions by galvanic replacement reaction. [ABSTRACT FROM AUTHOR]