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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 a niche route to the fabrication of Au-based hybrid nanostructures in the form of homojunction via seeded growth mediated with etching regrowth. In particular, the trioctahedral Au nanoparticles are initially doped with limited amounts of Pt/Ag atoms on the surface, followed by oxidative etching using HAuCl4. Instead of truncation on sharp corners/edges, the resulting products maintain the trioctahedral morphology but with an extra segment anchored on one side of the particle. Due to the structural advantages in metal–metal interface engineering and elemental doping, the current Au-based nanoscale homojunctions exhibit improved specific activity, reaction kinetics, and long-term durability in electrooxidation of methanol, as compared to pure Au trioctahedral counterparts. As verified by DFT simulation, such high catalytic performance can be ascribed to the favorable adsorption of the reactive species and low energy barrier for the rate determining step of Pt/Ag doping on the Au-Au interface. The present study introduces a niche synthetic strategy to create noble metal hybrid nanostructures based on oxidative etching and validates their promising use in electrocatalysis, which could be beneficial for the rational design of advanced fuel cell catalysts with versatile interface engineering. [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 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]

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]