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The formic acid oxidation reaction (FAOR) represents an important class of small organic molecule oxidation and is central to the practical application of fuel cells. In this study, we report the fabrication of Ir(IV)-doped PdAg alloy nanodendrites with sub-5 nm branches via stepwise synthesis in which the precursors of Pd and Ag were co-reduced, followed by the addition of IrCl3 to conduct an in situ galvanic replacement reaction. When serving as the electrocatalyst for the FAOR in an acidic medium, Ir(IV) doping unambiguously enhanced the activity of PdAg alloy nanodendrites and improved the reaction kinetics and long-term stability. In particular, the carbon-supported PdAgIr nanodendrites exhibited a prominent mass activity with a value of 1.09 A mgPd−1, which is almost 2.0 times and 2.7 times that of their PdAg and Pd counterparts, and far superior to that of commercial Pt/C. As confirmed by the means of the DFT simulations, this improved electrocatalytic performance stems from the reduced overall barrier in the oxidation of formic acid into CO2 during the FAOR and successful d-band tuning, together with the stabilization of Pd atoms. The current study opens a new avenue for engineering Pd-based trimetallic nanocrystals with versatile control over the morphology and composition, shedding light on the design of advanced fuel cell electrocatalysts. [ABSTRACT FROM AUTHOR]

We report the fabrication of PdSm bimetallic nanocrystals with controlled shapes and explore their applications as the electrocatalysts for electroxidation of ethanol (EOR) in alkaline medium. The success of current synthesis relies on the co-reduction of Pd(acac) 2 and Sm(acac) 3 in the presence of N-oleyl-1,3-propanediamine (OPDA) and Mo(CO) 6 at an elevated temperature. For the first time, ultrathin nanostructures composed of Pd-rare earth metal bimetals could be prepared in high purity, in the form of ultrathin porous nanosheets and concave tetrahedra, together with the size/edge length limited to sub-3 nm size range. When serving as electrocatalysts for EOR, the carbon-supported PdSm nanocrystals exhibited in seven-fold increase in mass activity as compared to that of Pt/C, as well as improved reaction kinetics and long-term durability. DFT calculations verify that the PdSm NCs/C catalyst modulate the reaction pathway of ethanol oxidation with lower energy barriers as compared with Pd catalyst, accounting for the improved catalytic performance. The present study provides a feasible strategy to create rare earth metal-doped bimetallic nanocrystals with controlled morphology for rational design over fuel cell catalysts and could be extended to other noble metals or alloys. Ultrathin Sm-doped Pd nanocrystals with two exotic shapes, ultrathin porous nanosheet and concave tetrahedron, are successfully prepared via a one-pot synthesis, exhibiting noticeable enhancement in electrocatalytic activity for ethanol oxidation reaction in alkaline medium. [Display omitted] • Sm-doped Pd nanocrystals were facilely synthesized with ultrathin sizes. • The morphologies of porous nanosheet and concave tetrahedron were obtained. • PdSm NCs/C exhibited enhanced EOR mass activity, reaction kinetics and stability. • DFT calculations suggest the Sm-doping can lower the energy barriers for EOR. [ABSTRACT FROM AUTHOR]

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 the preparation of gold (Au) nanosheets with a quasi‐square morphology and curved edges (Au QSNSs). The atomic packing on the edge, corner, and central part of an individual Au QSNS is carefully observed via spherical aberration corrected high‐resolution transmission electron microscopy, and the atomic‐resolution images confirm the dominant presence of {100} facets on all these regions. Such type of two‐dimensional nanostructure is of great interest, as conventional gold nanoplates/nanoprisms are mainly enclosed with {111} facets on upper/bottom faces. The use of glutathione and octadecyltrimethylammonium chloride as the shape‐directing agent and the capping agent, respectively, at appropriate amounts, together with a dropwise addition of Au precursor at controlled rate, have been validated to be crucial for the formation of such a unique two‐dimensional nanostructure. When acting as electrocatalysts for the methanol oxidation reaction in alkaline medium, the Au QSNSs/C exhibited noticeable enhancement, compared to spherical counterparts, in terms of mass activity, reaction kinetics, and long‐term durability, demonstrating their structural advantage. [ABSTRACT FROM AUTHOR]

Gold–palladium (AuPd) alloy nano-corolla are successfully prepared in high purity, followed by exploration as electrocatalysts for electroxidation of ethanol (EOR) in alkaline medium. Applying kinetics control on the one-pot formation process using a syringe pump is emphasized, where the Au/Pd precursor solution is dropwise titrated into the reaction mixture containing capping agent and reductant at an elevated temperature. We perform systematical investigation towards the morphology evolution pathway and effects of several key parameters. After loading on carbon black, the current AuPd alloy nano-corolla exhibit superb specific activity, reaction kinetics, and operation stability for EOR, showing morphological and structural merit. The present study provides insight into fabrication of bimetallic alloy nanocrystals with open structure, which could find important use in crystal engineering for multimetallic nanocrystals and rational design of fuel cell electrocatalyst. Gold–palladium (AuPd) alloy nanocrystals in the form of corolla are successfully prepared via kinetic-controlled synthesis in high purity, exhibit improved activity and stability as EOR electrocatalysts in KOH solution [ABSTRACT FROM AUTHOR]

We report a niche synthetic strategy to manipulate the shape of gold‐silver (AuAg) nanocrystals based on kinetics control. The success of current work relies on the use of two syringe pumps to add Au and Ag precursor solutions independently at distinct injection rates, which allows the separate control over the feeding rate of Au and Ag atoms, respectively. Such strategy is validated effective in both one‐pot reduction and seeded growth involving spherical and rod‐likes Au seeds. By conducting orthogonal experiments setting two injection rates at three levels, a set of morphologies are obtained. Interestingly, AuAg alloy nanocrystals in the form of multipod, hollow protruded particles, and branched hollow nanoplate, that are rare to obtain via conventional routes, are successfully screened out, exhibiting the unique advantage of this strategy. The current work provides a feasible approach to applying kinetics control over AuAg bimetallic nanocrystals, which could be extended to other noble metals or material combinations. [ABSTRACT FROM AUTHOR]

Wavy gold@palladium-gold (Au@PdAu) core-shell nanoplates are successfully prepared via seeded growth. Starting with the use of plate-like Au nanocrystals with the thickness of ~10 nm as seeds, the preferential deposition of Pd atoms vertical to the upper/bottom surface plane allows the formation of the core-shell structure with tunable thickness, where the shell thickness can be limited to sub-10 nm. As confirmed by X-ray diffraction (XRD) analyses, further atomic diffusion allows the generation of PdAu alloy phase in the products, leading to the formation of Au@PdAu core-shell nanostructure. With the strong absorbance in near-infrared (NIR) region, they could work as efficient catalysts towards reduction of 4-nitrophenol under visible light irritation. In particular, the enhancement factor (the ratio of apparent rate constant in light to that in dark) reaches as high as 6.76 arising from the plasmonic-enhancement effect. The current work provides a feasible strategy to fabricate Pd-based bimetallic nanocrystals with plasmonic properties and validates their promising application in the plasmonic-enhanced catalysis. [ABSTRACT FROM AUTHOR]

We report a niche strategy to fabricate planar trimetallic nanocrystals with in‐plane branches and a unique hybrid structure. The success of current work relies on the use of seeded growth to produce Au@Ag core‐shell nanocubes, followed by the reaction with an excessive third metal precursor (i. e. Pd) via galvanic replacement reaction (GRR) in the presence of controlled reduction. The morphology of resulting products varied in the order of cube, concave cube, hollow cage, yolk‐shell frame, and finally branched nanoplates with Au‐PdAg hybrid structure. The controlled reduction involved in the GRR process, together with the use of Au seed at appropriate amounts and docosyltrimethylammonium chloride as the capping agent, is demonstrated to be crucial for the formation of such unique structure. When loaded on carbon black and working as electrocatalysts for electroxidation of ethanol in alkaline media, the current products exhibit satisfying electrocatalytic activity (e. g. 591 mA mgPd−1 in mass activity and 10.01 A m−2 in specific activity), improved kinetics, and long‐term durability, as compared to commercial Pt/C. The present study offers a feasible route to applying precise spatial control over elemental metals for two‐dimensional dendritic noble metal nanocrystals and could be potentially extended to other metals or alloy. [ABSTRACT FROM AUTHOR]

Etching and regrowth are two typical processes involved during wet-chemical synthesis of noble-metal nanocrystals. In the present study, we demonstrate that by rationally manipulating the two processes, trimetallic nanocrystals with a unique multilayered structure can be successfully prepared in high purity, as well as with tunable sizes. In particular, by conducting co-reduction of Pd and Pt precursors in the presence of spherical Au seeds, the continuous etching of Pt(IV) ions as enabled by insufficient reducing power, together with the regrowth of Au and Pd atoms during the growth stage, allows the resultant products to exhibit a multi-layered elemental distribution, where Pd and Pt are in the inner shell while Au and Pt are dominant in the outer shell. When supported on carbon and used as electrocatalysts, these AuPdPt multilayered nanodendrites with controlled sizes in the range of 32–88 nm show an improved electrocatalytic activity and long-term durability for formic acid oxidation, as compared to commercial Pt/C. The present study offers a facile method to prepare tri-metallic nanocrystals with a controlled shape and spatial elemental distribution, which could be further extended to other noble metals or alloys. [ABSTRACT FROM AUTHOR]

We report the fabrication of gold@palladium–gold (Au@PdAu) nanocrystals with a highly branched shape via seeded growth. The success of the current work relies on the use of a syringe pump for dropwise addition of a bimetallic precursor to apply control over the reaction kinetics and an elevated reaction temperature to promote island growth mode as enabled by the coupling between surface diffusion and lattice mismatch. In particular, the one-shot injection of the bimetallic precursor at 60 °C and room temperature, respectively, resulted in the production of Au@PdAu nanocrystals with the shape of a concave cube and segmented branches, respectively, while dropwise addition of the bimetallic precursor at 60 °C led to the formation of a dendritic Pd–Au shell over the spherical Au seeds. When working as electrocatalysts, as compared to solid counterparts, the Au@PdAu core–shell nanodendrites exhibit an improved operation stability for electrooxidation of ethanol in alkaline media, demonstrating the advantage in morphology and structure. [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]

• A facile method for fabrication of AuAg alloy nanoplates with controlled elemental compositions was developed. • They were characterized with a unique morphology of wavy nanoplate, together with sub-15 nm in thickness. • Tunable LSPR properties and satisfying photothermal performance were demonstrated. Gold-silver alloy wavy nanoplates with tunable elemental compositions are successfully prepared, exhibiting strong NIR absorbance and excellent photothermal properties. [Display omitted] We report a facile synthesis of AuAg alloy nanoplates in high purity, together with tunable elemental compositions and uniformity in size and morphology. The success of current work relies on the one-pot co-reduction of Au and Ag precursor in an ice-water bath with the presence of octadecyltrimethylammonium chloride (OTAC) as a capping agent. With the increase in Ag content, the localized surface plasmon resonance (LSPR) of AuAg alloy nanoplates exhibited a noticeable blue-shift from near-infrared (NIR) to visible region. Thanks to the well-defined NIR LSPR properties and broad spectral range, the current products exhibit a remarkably integrated high-quality photothermal feature as well as the efficient photothermal conversion. Meanwhile, the current AuAg alloy nanoplates demonstrate satisfying photothermal stability verified via continuous exposure and cyclic irradiation by an 808-nm laser. The present study offers a facile route to the preparation of two-dimensional AuAg alloy nanocrystals with tunable elemental compositions and validates their excellent responses towards photothermal measurements, which could find promising use in photothermy-based diagnosis and therapy. [ABSTRACT FROM AUTHOR]