不同表面结构PdH0.43纳米晶的制备及其甲酸电氧化性能（英文）

制备具有确定形貌和表面结构的纳米晶为研究其构效关系提供了有效途径,且有利于设计开发具有优异催化性能的纳米催化剂.本研究发展了一种制备不同形貌PdH0.43纳米晶的简易方法,其形貌分别为立方体、八面体和菱形十二面体,对应的裸露晶面分别为{100},{111}和{110}晶面.不同形貌PdH0.43纳米晶都非常稳定.其与商业Pd黑和三种纯Pd纳米晶相比,在甲酸电催化氧化反应中显示出更高的催化活性和极低的氧化过电位.立方体PdH0.43纳米晶的催化活性分别高于商业Pd黑的5倍和立方体Pd纳米晶的2倍.不同表面结构PdH0.43纳米晶的催化活性依次为PdH0.43{100}>PdH0.43{111}>PdH0.43{110}.     

Synthesis of spatially uniform metal alloys nanocrystals via a diffusion controlled growth strategy: The case of Au-Pd alloy trisoctahedral nanocrystals with tunable composition

Rational synthesis of bimetallic alloy nanocrystals (NCs) is still a great challenge. Especially, spatially uniform alloy NCs are very difficult to achieve because of the different reduction rates of the individual alloy components. Herein we propose a facile wet chemical synthetic strategy to prepare uniform bimetallic alloy NCs with tunable composition by controlling the growth of alloy NCs under diffusion controlled conditions. Using this strategy, we successfully synthesized trisoctahedral (TOH) Au-Pd alloy NCs enclosed by {hhl} high-index facets with uniform spatial distributions and different compositions. Significantly, using our strategy, the composition of the as-prepared Au-Pd alloy NCs is identical to the ratio of the two metal precursors in the reaction solution over a wide range. Investigation of the composition-dependent electrochemical behavior of the as-prepared TOH Au-Pd alloy NCs showed that the TOH Au-Pd alloy NCs containing 14.1 atom% Pd exhibited the best activity.      

Graphene Oxide‐Assisted Synthesis of Pt–Co Alloy Nanocrystals with High‐Index Facets and Enhanced Electrocatalytic Properties

Metal nanocrystals (NCs) are grown directly on the surface of reduced graphene oxide (rGO), which can maximize the rGO‐NCs contact/interaction to achieve the enhanced catalytic activity. However, it is difficult to control the size and morphology of metal NCs by in situ method due to the effects of functional groups on the surface of GO, and as a result, the metal NCs/rGO hybrids are conventionally synthesized by two‐step method. Herein, one‐pot synthesis of Pt–Co alloy NCs is demonstrated with concave‐polyhedrons and concave‐nanocubes bounded by {hkl} and {hk0} high‐index facets (HIFs) distributed on rGO. GO can affect the geometry and electronic structure of Pt–Co NCs. Thanks to the synergy of the HIFs and the electronic effect of the intimate contact/interaction between Pt–Co alloy and rGO, these as‐prepared Pt–Co NCs/rGO hybrids presents enhanced catalytic properties for the electrooxidation of formic acid, as well as for the oxygen reduction reaction.     

Facile syntheses and enhanced electrocatalytic activities of Pt nanocrystals with {<Emphasis Type="Italic">hkk</Emphasis>} high-index surfaces

Platinum (Pt) is an outstanding catalyst for many important industrial products. Because of its high cost and scarce reserves, it is very important to improve the performance of Pt catalysts. As the metal nanocrystals (NCs) with high-index surfaces usually show very good catalytic activity because of their high density of atomic steps and kinks, the preparation of Pt NCs with high-index facets has become a very important and hot research topic recently. In this article, we report a facile synthesis of high-yield Pt NCs with a series of {hkk} high-index facets including {211} and {411} via a solvothermal method using Pt(II) acetylacetonate as the Pt source, 1-octylamine as the solvent and capping agent, and formaldehyde as an additional surface structure regulator. Multipod Pt NCs with dominant {211} side surfaces were produced without formaldehyde, while concave Pt NCs with dominant {411} surfaces formed under the influence of formaldehyde. By analyzing the products by IR spectroscopy, we found the presence of CO on the surface of concave Pt NCs with {411} surfaces prepared from the solution containing formaldehyde. It was concluded that amine mainly stabilized the monoatomic step edges, resulting in the {211} exposed surface; with addition of formaldehyde, it decomposed into CO, leading to the formation of {411} surfaces by the additional adsorption of the CO on the {100} terraces. In addition, it was found that the as-prepared Pt NCs with high-index {211} and {411} surfaces exhibited much better catalytic activity in the electro-oxidation of ethanol than a commercial Pt/C catalyst or Pt nanocubes with low-index {100} surfaces, and the catalytic activities of Pt crystal facets decreased in the sequence {411}>{211}>{100}.      

Tuning Surface Structure of 3D Nanoporous Gold by Surfactant‐Free Electrochemical Potential Cycling

3D dealloyed nanoporous metals have emerged as a new class of catalysts for various chemical and electrochemical reactions. Similar to other heterogeneous catalysts, the surface atomic structure of the nanoporous metal catalysts plays a crucial role in catalytic activity and selectivity. Through surfactant‐assisted bottom‐up synthesis, the surface‐structure modification has been successfully realized in low‐dimensional particulate catalysts. However, the surface modification by top‐down dealloying has not been well explored for nanoporous metal catalysts. Here, a surfactant‐free approach to tailor the surface structure of nanoporous gold by surface relaxation via electrochemical redox cycling is reported. By controlling the scan rates, nanoporous gold with abundant {111} facets or {100} facets can be designed and fabricated with dramatically improved electrocatalysis toward the ethanol oxidation reaction.     

Shape‐Dependent Activity of Ceria for Hydrogen Electro‐Oxidation in Reduced‐Temperature Solid Oxide Fuel Cells

Single crystalline ceria nanooctahedra, nanocubes, and nanorods are hydrothermally synthesized, colloidally impregnated into the porous La_0.9Sr_0.1Ga_0.8Mg_0.2O_3‐δ (LSGM) scaffolds, and electrochemically evaluated as the anode catalysts for reduced temperature solid oxide fuel cells (SOFCs). Well‐defined surface terminations are confirmed by the high‐resolution transmission electron microscopy — (111) for nanooctahedra, (100) for nanocubes, and both (110) and (100) for nanorods. Temperature‐programmed reduction in H₂ shows the highest reducibility for nanorods, followed sequentially by nanocubes and nanooctahedra. Measurements of the anode polarization resistances and the fuel cell power densities reveal different orders of activity of ceria nanocrystals at high and low temperatures for hydrogen electro‐oxidation, i.e., nanorods > nanocubes > nanooctahedra at T ≤ 450 °C and nanooctahedra > nanorods > nanocubes at T ≥ 500 °C. Such shape‐dependent activities of these ceria nanocrystals have been correlated to their difference in the local structure distortions and thus in the reducibility. These findings will open up a new strategy for design of advanced catalysts for reduced‐temperature SOFCs by elaborately engineering the shape of nanocrystals and thus selectively exposing the crystal facets.     

Enhanced Photocarrier Generation with Selectable Wavelengths by M‐Decorated‐CuInS2 Nanocrystals (M = Au and Pt) Synthesized in a Single Surfactant Process on MoS2 Bilayers

A facile approach for the synthesis of Au‐ and Pt‐decorated CuInS₂ nanocrystals (CIS NCs) as sensitizer materials on the top of MoS₂ bilayers is demonstrated. A single surfactant (oleylamine) is used to prepare such heterostructured noble metal decorated CIS NCs from the pristine CIS. Such a feasible way to synthesize heterostructured noble metal decorated CIS NCs from the single surfactant can stimulate the development of the functionalized heterostructured NCs in large scale for practical applications such as solar cells and photodetectors. Photodetectors based on MoS₂ bilayers with the synthesized nanocrystals display enhanced photocurrent, almost 20–40 times higher responsivity and the On/Off ratio is enlarged one order of magnitude compared with the pristine MoS₂ bilayers‐based photodetectors. Remarkably, by using Pt‐ or Au‐decorated CIS NCs, the photocurrent enhancement of MoS₂ photodetectors can be tuned between blue (405 nm) to green (532 nm). The strategy described here acts as a perspective to significantly improve the performance of MoS₂‐based photodetectors with the controllable absorption wavelengths in the visible light range, showing the feasibility of the possible color detection.     

Chemical Design of Palladium‐Based Nanoarchitectures for Catalytic Applications

Palladium (Pd) plays an important role in numerous catalytic reactions, such as methanol and ethanol oxidation, oxygen reduction, hydrogenation, coupling reactions, and carbon monoxide oxidation. Creating Pd‐based nanoarchitectures with increased active surface sites, higher density of low‐coordinated atoms, and maximized surface coverage for the reactants is important. To address the limitations of pure Pd, various Pd‐based nanoarchitectures, including alloys, intermetallics, and supported Pd nanomaterials, have been fabricated by combining Pd with other elements with similar or higher catalytic activity for many catalytic reactions. Herein, recent advances in the preparation of Pd‐based nanoarchitectures through solution‐phase chemical reduction and electrochemical deposition methods are summarized. Finally, the trend and future outlook in the development of Pd nanocatalysts toward practical catalytic applications are discussed.     

Colloid‐Interface‐Assisted Laser Irradiation of Nanocrystals Superlattices to be Scalable Plasmonic Superstructures with Novel Activities

High‐efficient charge and energy transfer between nanocrystals (NCs) in a bottom‐up assembly are hard to achieve, resulting in an obstacle in application. Instead of the ligands exchange strategies, the advantage of a continuous laser is taken with optimal wavelength and power to irradiate the film‐scale NCs superlattices at solid–liquid interfaces. Owing to the Au‐based NCs' surface plasmon resonance (SPR) effect, the gentle laser irradiation leads the Au NCs or Au@CdS core/shell NCs to attach each other with controlled pattern at the interfaces between solid NCs phase and liquid ethanol/ethylene glycol. A continuous wave 532 nm laser (6.68–13.37 W cm^?2), to control Au‐based superlattices, is used to form the monolayer with uniformly reduced interparticle distance followed by welded superstructures. Considering the size effect to Au NCs' melting, when decreasing the Au NCs size to ≈5 nm, stronger welding nanostructures are obtained with diverse unprecedented shapes which cannot be achieved by normal colloidal synthesis. With the help of facile scale‐up and formation at solid–liquid interfaces, and a good connection of crystalline between NCs, the obtained plasmonic superstructured films that could be facilely transferred onto different substrates exhibit broad SPR absorption in the visible and near‐infrared regime, enhanced electric conductivities, and wide applications as surface enhanced Raman scattering (SERS)‐active substrates.     

Nanoporous Gold Bowls: A Kinetic Approach to Control Open Shell Structures and Size‐Tunable Lattice Strain for Electrocatalytic Applications

Controlling sub‐10 nm ligament sizes and open‐shell structure in nanoporous gold (NPG) to achieve strained lattice is critical in enhancing catalytic activity, but it remains a challenge due to poor control of reaction kinetics in conventional dealloying approach. Herein, a ligament size‐controlled synthesis of open‐shell NPG bowls (NPGB) through hetero‐epitaxial growth of NPGB on AgCl is reported. The ligament size in NPGB is controlled from 6 to 46 nm by varying the hydroquinone to HAuCl₄ ratio. The Williamson–Hall analysis demonstrates a higher lattice strain in smaller ligament size. In particular, NPGB with 6 nm (NPGB 6) ligament size possess the highest strain of 15.4 × 10^?3, which is nearly twice of conventional 2D NPG sheets (≈8.8 × 10^?3). The presence of high surface energy facets in NPGBs is also envisaged. The best electrocatalytic activity toward methanol oxidation is observed in NPGB 6 (27.8 μA μg^?1), which is ≈9‐fold and 3‐fold higher than 8 nm solid Au nanoparticles, and conventional NPG sheets. The excellent catalytic activity in NPGB 6 is attributed to the open‐shell structure, lattice strain, and higher electro‐active surface area, allowing efficient exposure of catalytic active sites to facilitate the methanol oxidation. The results offer a potential strategy for designing next generation electrocatalysts.     

Transition‐Metal‐Ions‐Induced Coalescence: Stitching Au Nanoclusters into Tubular Au‐Based Nanocomposites

Rod‐shaped assemblages of Au nanoclusters (AuNCs) can serve as self‐templating solid precursors to produce tubular Au‐based nanocomposites via the coalescence induced by transition metal ions. Specifically, when the AuNC assemblages react with transition metal ions with relatively high standard oxidation potentials such as Cu(II), Ag(I), Pd(II), and Au(III), a series of polycrystalline and ultrathin Au and Au_xM_y (where M = Cu, Ag, and Pd) alloy hollow nanorods (HNRs) can be obtained with further reduction; these metallic products are evaluated for electrooxidation of methanol. Alternatively, the above transition metal ions‐induced transformations can also be carried out after coating the AuNC assemblages with a layer of mesoporous SiO₂ (mSiO₂), giving rise to many mSiO₂‐coated Au‐based HNRs. Onto the formed AuPd_0.18 alloy HNRs, furthermore, a range of transition metal oxides such as TiO₂, Co₃O_4, and Cu₂O nanocrystals can be deposited easily to prepare metal oxide–AuPd_0.18 HNRs nanocomposites, which can be used as photocatalysts. Compared with those conventional galvanic replacement reactions, the controlled coalescence of AuNCs induced by transition metal ions provides a novel and efficient chemical approach with improved element efficiency to tubular Au‐based nanocomposites.     

Selective Etching Induced Synthesis of Hollow Rh Nanospheres Electrocatalyst for Alcohol Oxidation Reactions

The hollow noble metal nanostructures have attracted wide attention in catalysis/electrocatalysis. Here a two‐step procedure for constructing hollow Rh nanospheres (Rh H‐NSs) with clean surface is described. By selectively removing the surfactant and Au core of Au‐core@Rh‐shell nanostructures (Au@Rh NSs), the surface‐cleaned Rh H‐NSs are obtained, which contain abundant porous channels and large specific surface area. The as‐prepared Rh H‐NSs exhibit enhanced inherent activity for the methanol oxidation reaction (MOR) compared to state‐of‐the‐art Pt nanoparticles in alkaline media. Further electrochemical experiments show that Rh H‐NSs also have high activity for the electrooxidation of formaldehyde and formate (intermediate species in the course of the MOR) in alkaline media. Unfortunately, Rh H‐NSs have low electrocatalytic activity for the ethanol and 1‐propanol oxidation reactions in alkaline media. All electrochemical results indicate that the order of electrocatalytic activity of Rh H‐NSs for alcohol oxidation reaction is methanol (C₁) > ethanol (C₂) > 1‐propanol (C₃). This work highlights the synthesis route of Rh hollow nanostructures, and indicates the promising application of Rh nanostructures in alkaline direct methanol fuel cells.     

A General Strategy Assisted with Dual Reductants and Dual Protecting Agents for Preparing Pt‐Based Alloys with High‐Index Facets and Excellent Electrocatalytic Performance

Synthesizing noble metallic nanoparticles (NPs) enclosed by high‐index facets (HIFs) is challenged as it involves the tuning of growth kinetics, the selective adsorption of certain chemical species, and the epitaxial growth from HIF enclosed seeds. Herein, a simple and general strategy is reported by using dual reduction agents and dual capping agents to prepare Pt‐based alloy NPs with HIFs, in which both glycine and poly(vinylpyrrolidone) serve as the reductants and capping agents. Due to the facilely tunable growth/nucleation rates and protecting abilities of the reductants and capping agents, Pt concave nanocube (CNC), binary Pt–Ni CNC, ternary Pt–Mn–Cu CNC, and Pt–Mn–Cu ramiform polyhedron alloy NPs terminated by HIFs as well as other NPs with well‐defined morphologies such as Pt–Mn–Cu nanocube and Pt–Mn–Cu nanoflower are obtained with this approach. Owing to the high density of low‐coordinated Pt sites (HIF structure) and the unique electronic effect of Pt–Mn–Cu ternary alloys, the as‐prepared Pt–Mn–Cu NPs show enhanced catalytic activity toward methanol and formic acid electro‐oxidation reactions with excellent stability. This work provides a promising methodology for designing and fabricating Pt‐based alloy NPs as efficient fuel cell catalyst.     

Maneuvering the Peroxidase-Like Activity of Palladium-Based Nanozymes by Alloying with Oxophilic Bismuth for Biosensing

Engineering the catalytic performance of nanozymes is of vital importance for their broad applications in biological analysis, cancer treatment, and environmental management. Herein, a strategy to boost the peroxidase-like activity of Pd-based nanozymes with oxophilic metallic bismuth (Bi) is demonstrated, which is based on the incorporation of oxophilic Bi in the Pd-based alloy nanocrystals (NCs). To synthesize PdBi alloy NCs, a seed-mediated method is employed with the assistance of underpotential deposition (UPD) of Bi on Pd. The strong interaction of Bi atoms with Pd surfaces favors the formation of alloy structures with controllable shapes and excellent monodispersity. More importantly, the PdBi NCs show excellent peroxidase-like activities compared with pristine Pd NCs. The structure–function correlations for the PdBi nanozymes are elucidated, and an indirect colorimetric method based on cascade reactions to determine alkaline phosphatase (ALP) is established. This method has good linear range, low detection limit, excellent selectivity, and anti-interference. Collectively, this work not only provides new insights for the design of high-efficiency nanozymes, expands the colorimetric sensing platform based on enzyme cascade reactions, but also represents a new example for UPD-directed synthesis of alloy NCs.     

Self‐Supported PtAuP Alloy Nanotube Arrays with Enhanced Activity and Stability for Methanol Electro‐Oxidation

Inhibiting CO formation can more directly address the problem of CO poisoning during methanol electro‐oxidation. In this study, 1D self‐supported porous PtAuP alloy nanotube arrays (ANTAs) are synthesized via a facile electro‐codeposition approach and present enhanced activity and improved resistance to CO poisoning through inhibiting CO formation (non‐CO pathway) during the methanol oxidation reaction in acidic medium. This well‐controlled Pt‐/transition metal‐/nonmetal ternary nanostructure exhibits a specific electroactivity twice as great as that of PtAu alloy nanotube arrays and Pt/C. At the same time, PtAuP ANTAs show a higher ratio of forward peak current density (I_f) to backward peak current density (I_b) (2.34) than PtAu ANTAs (1.27) and Pt/C (0.78). The prominent I_f/I_b value of PtAuP ANTAs indicates that most of the intermediate species are electro‐oxidized to carbon dioxide in the forward scan, which highlights the high electroactivity for methanol electro‐oxidation.     

High‐Yield Synthesis of Crystal‐Phase‐Heterostructured 4H/fcc Au@Pd Core–Shell Nanorods for Electrocatalytic Ethanol Oxidation

Noble‐metal nanomaterials are attracting increasing research interest due to their promising applications in electrochemical catalysis, for example. Although great efforts have been devoted to the size‐, shape‐, and architecture‐controlled synthesis of noble‐metal nanomaterials, their crystal‐phase‐controlled synthesis is still in its infancy. Here, for the first time, this study reports high‐yield synthesis of Au nanorods (NRs) with alternating 4H/face‐centered cubic (fcc) crystal‐phase heterostructures via a one‐pot wet‐chemical method. The coexistence of 4H and fcc phases is relatively stable, and the 4H/fcc Au NRs can serve as templates for crystal‐phase‐controlled epitaxial growth of other metals. As an example, bimetallic 4H/fcc Au@Pd core–shell NRs are synthesized via the epitaxial growth of Pd on 4H/fcc Au NRs. Significantly, the 4H/fcc Au@Pd NRs show superior mass activity toward the ethanol oxidation reaction, i.e., 6.2 and 4.9 times those of commercial Pd black and Pt/C catalysts, respectively. It is believed that this new synthetic strategy can be used to prepare other novel catalysts for various promising applications.     

Low‐cycle fatigue behavior of rolled WE43‐T5 magnesium alloy

This paper describes the main results from an investigation into the strength and low‐cycle fatigue (LCF) behavior of a rolled plate of WE43 Mg alloy in its T5 condition at room temperature. The alloy was found to exhibit small tension/compression yield asymmetry and small anisotropy being stronger in transverse direction (TD) than in rolling direction (RD) along with some anisotropy in strain hardening. The LCF tests were conducted under strain‐controlled conditions with the strain amplitudes ranging from 0.6% to 1.4% without the mean strain component. While the stress amplitudes during the LCF were higher for tests along TD than RD, the LCF life was similar for both directions. As revealed by electron microscopy, the fractured surfaces under tension consisted mainly of microvoid coalescence with some transgranular facets, while those fractured in LCF showed a combination of intergranular fracture and transgranular facets with minor content of microvoid coalescence.     

Fabrication of Supported AuPt Alloy Nanocrystals with Enhanced Electrocatalytic Activity for Formic Acid Oxidation through Conversion Chemistry of Layer‐Deposited Pt2+ on Au Nanocrystals

The exploitation of nanoconfined conversion of Au‐ and Pt‐containing binary nanocrystals for developing a controllable synthesis of surfactant‐free AuPt nanocrystals with enhanced formic acid oxidation (FAO) activity is reported, which can be stably and evenly immobilized on various support materials to diversify and optimize their electrocatalytic performance. In this study, an atomic layer of Pt²⁺ species is discovered to be spontaneously deposited in situ on the Au nanocrystal generated from a reverse‐microemulsion solution. The resulting Au/Pt²⁺ nanocrystal thermally transforms into a reduced AuPt alloy nanocrystal during the subsequent solid‐state conversion process within the SiO₂ nanosphere. The alloy nanocrystals can be isolated from SiO₂ in a surfactant‐free form and then dispersedly loaded on the carbon sphere surface, allowing for the production of a supported electrocatalyst that exhibits much higher FAO activity than commercial Pt/C catalysts. Furthermore, by involving Fe₃O₄ nanocrystals in the conversion process, the AuPt alloy nanocrystals can be grown on the oxide surface, improving the durability of supported metal catalysts, and then uniformly loaded on a reduced graphene oxide (RGO) layer with high electroconductivity. This produces electrocatalytic AuPt/Fe₃O₄/RGO nanocomposites whose catalyst‐oxide‐graphene triple‐junction structure provides improved electrocatalytic properties in terms of both activity and durability in catalyzing FAO.     

Gaseous Nanocarving‐Mediated Carbon Framework with Spontaneous Metal Assembly for Structure‐Tunable Metal/Carbon Nanofibers

Vapor phase carbon (C)‐reduction‐based syntheses of C nanotubes and graphene, which are highly functional solid C nanomaterials, have received extensive attention in the field of materials science. This study suggests a revolutionary method for precisely controlling the C structures by oxidizing solid C nanomaterials into gaseous products in the opposite manner of the conventional approach. This gaseous nanocarving enables the modulation of inherent metal assembly in metal/C hybrid nanomaterials because of the promoted C oxidation at the metal/C interface, which produces inner pores inside C nanomaterials. This phenomenon is revealed by investigating the aspects of structure formation with selective C oxidation in the metal/C nanofibers, and density functional theory calculation. Interestingly, the tendency of C oxidation and calculated oxygen binding energy at the metal surface plane is coincident with the order Co > Ni > Cu > Pt. The customizable control of the structural factors of metal/C nanomaterials through thermodynamic‐calculation‐derived processing parameters is reported for the first time in this work. This approach can open a new class of gas–solid reaction‐based synthetic routes that dramatically broaden the structure‐design range of metal/C hybrid nanomaterials. It represents an advancement toward overcoming the limitations of intrinsic activities in various applications.     

Self‐Assembled Au/CdSe Nanocrystal Clusters for Plasmon‐Mediated Photocatalytic Hydrogen Evolution

Plasmon‐mediated photocatalytic systems generally suffer from poor efficiency due to weak absorption overlap and thus limited energy transfer between the plasmonic metal and the semiconductor. Herein, a near‐ideal plasmon‐mediated photocatalyst system is developed. Au/CdSe nanocrystal clusters (NCs) are successfully fabricated through a facile emulsion‐based self‐assembly approach, containing Au nanoparticles (NPs) of size 2.8, 4.6, 7.2, or 9.0 nm and CdSe quantum dots (QDs) of size ≈3.3 nm. Under visible‐light irradiation, the Au/CdSe NCs with 7.2 nm Au NPs afford very stable operation and a remarkable H₂‐evolution rate of (10× higher than bare CdSe NCs). Plasmon resonance energy transfer from the Au NPs to the CdSe QDs, which enhances charge‐carrier generation in the semiconductor and suppresses bulk recombination, is responsible for the outstanding photocatalytic performance. The approach used here to fabricate the Au/CdSe NCs is suitable for the construction of other plasmon‐mediated photocatalysts.