Phosphate‐Mediated Immobilization of High‐Performance AuPd Nanoparticles for Dehydrogenation of Formic Acid at Room Temperature

Dehydrogenation of formic acid (FA) is a promising alternative to fossil fuels, to provide clean energy for the future energy economy. The synthesis of highly active catalysts for FA dehydrogenation at room temperature has attracted a lot of attention. Herein, for the first time, highly active aurum–palladium nanoparticles (AuPd NPs) immobilized on nitrogen (N)‐doped porous carbon are fabricated through a phosphate‐mediation approach. The N‐doped carbon anchored with phosphate, which can be removed in alkaline solution during the reduction process of metal ions, shows an enhanced performance of absorbing and dispersion of both Au and Pd ions, which is a key to the synthesis of highly dispersed ultrafine AuPd NPs. The as‐prepared catalyst (designated as Au₂Pd₃@(P)N‐C) exhibits an extraordinarily high turnover frequency of 5400 h^?1 and a 100% H₂ selectivity for FA dehydrogenation at 30 °C. This phosphate‐mediation approach provides a new way to fabricate highly active metal NPs for catalytic application, pushing heterogeneous catalysts forward for practical usage in energy storage and conversion.     

Single‐Step Deposition of Au‐ and Pt‐Nanoparticle‐Functionalized Tungsten Oxide Nanoneedles Synthesized Via Aerosol‐Assisted CVD,and Used for Fabrication of Selective Gas Microsensor Arrays

Tungsten oxide nanostructures functionalized with gold or platinum NPs are synthesized and integrated, using a single‐step method via aerosol‐assisted chemical vapour deposition, onto micro‐electromechanical system (MEMS)‐based gas‐sensor platforms. This co‐deposition method is demonstrated to be an effective route to incorporate metal nanoparticles (NP) or combinations of metal NPs into nanostructured materials, resulting in an attractive way of tuning functionality in metal oxides (MOX). The results show variations in electronic and sensing properties of tungsten oxide according to the metal NPs introduced, which are used to discriminate effectively analytes (C₂H₅OH, H₂, and CO) that are present in proton‐exchange fuel cells. Improved sensing characteristics, in particular to H₂, are observed at 250 °C with Pt‐functionalized tungsten oxide films, whereas non‐functionalized tungsten oxide films show responses to low concentrations of CO at low temperatures. Differences in the sensing characteristics of these films are attributed to the different reactivities of metal NPs (Au and Pt), and to the degree of electronic interaction at the MOX/metal NP interface. The method presented in this work has advantages over other methods of integrating nanomaterials and devices, of having fewer processing steps, relatively low processing temperature, and no requirement for substrate pre‐treatment.     

Mesostructured Intermetallic Compounds of Platinum and Non‐Transition Metals for Enhanced Electrocatalysis of Oxygen Reduction Reaction

Alloying techniques show genuine potential to develop more effective catalysts than Pt for oxygen reduction reaction (ORR), which is the key challenge in many important electrochemical energy conversion and storage devices, such as fuel cells and metal‐air batteries. Tremendous efforts have been made to improve ORR activity by designing bimetallic nanocatalysts, which have been limited to only alloys of platinum and transition metals (TMs). The Pt‐TM alloys suffer from critical durability in acid‐media fuel cells. Here a new class of mesostructured Pt–Al catalysts is reported, consisting of atomic‐layer‐thick Pt skin and Pt₃Al or Pt₅Al intermetallic compound skeletons for the enhanced ORR performance. As a result of strong Pt–Al bonds that inhibit the evolution of Pt skin and produce ligand and compressive strain effects, the Pt₃Al and Pt₅Al mesoporous catalysts are exceptionally durable and ≈6.3‐ and ≈5.0‐fold more active than the state‐of‐the‐art Pt/C catalyst at 0.90 V, respectively. The high performance makes them promising candidates as cathode nanocatalysts in next‐generation fuel cells.     

Universal Surfactant‐Free Strategy for Self‐Standing 3D Tremella‐Like Pd–M (M = Ag,Pb, and Au) Nanosheets for Superior Alcohols Electrocatalysis

Pd‐based nanosheet materials have emerged as efficient catalysts for monobasic and polyhydric alcohol oxidation reactions. However, most reported synthetic methods of Pd‐based nanosheets (NSs) are nonuniversal and surfactant‐involved, leading to residue‐covered surfaces with drastically damaged electrocatalytic properties. Herein, a universal, surfactant‐free, simple one‐pot route is developed for the precise synthesis of a kind of novel self‐standing Pd–M (M = Ag, Pb, Au, Ga, Cu, Pt, etc.) NSs with tremella‐like superstructures are assembled using ultrathin two‐dimensional (2D) NSs. Benefiting from the universal surfactant‐free methods, the obtained Pd–M NSs exhibit clean surfaces and stable three‐dimensional (3D) self‐standing structures that overcome the difficulty of normal close packing and overlapping 2D NSs. The Pd–M (M = Ag, Pb, and Au) NSs with tremella‐like structures all show excellent ethanol oxidation reaction (EOR) and ethylene glycol oxidation reaction (EGOR) properties. In particular, with the optimal superstructure, better electronic effect, and promoted toxicity tolerance, the EOR/EGOR mass activities of Pd₇Ag NSs, Pd₇Pb NSs, and Pd₇Au NSs are 8.2/7.3, 7.2/5.7, and 5.3/4.4 times higher than that of commercial Pd/C catalysts. This advanced 3D construction also endows Pd–M NSs with more favorable stability than Pd/C. This study may be extended to Pd–M (M = other metals) NSs and open up more opportunities for broad catalytic applications.     

Structure Design Reveals the Role of Au for ORR Catalytic Performance Optimization in PtCo‐Based Catalysts

Au‐incorporation is a promising strategy to retard composition‐loss in Pt‐based catalyst. However, the unclear mechanism limits guided catalyst design and the performance optimization. Here, direct evidence is provided to validate the outward diffusion of Au atoms in Au‐core/Pt‐based‐shell structures. A Co interlayer is built between the Au‐core and PtCo‐based shell to exclude the possibility of atomic diffusion caused by interfacial alloying. In conjunction with the improved catalytic durability of the Au‐core@Pt‐based‐shell structure, it is reasonable to conclude that it is the subsurface segregated Au atoms rather than interfacial interaction that boosts the catalytic durability of Au‐core/Pt‐based‐shell structured catalysts towards oxygen reduction reaction. More importantly, by constructing Au‐core@Co‐interlayer@PtCoAu‐shell multilayer structure, the specific (1.730 mA cm^?2) and mass (0.692 A mg^?1_Pt) activities are enhanced 7‐ and 4‐ fold relative to the commercial Pt/C. After 10 000 cycles of accelerated durability test, the mass activity loss for the multilayered catalyst is as low as 6.14% while the loss exceeds 35% for the commercial Pt/C catalyst. The improved catalytic performance of the Au@Co@PtCoAu multilayer structure can be ascribed to the finely modulated electronic structure and the compensated composition loss owing to the delicate structure and composition profile design.     

Mesostructured Arrays of Nanometer‐spaced Gold Nanoparticles for Ultrahigh Number Density of SERS Hot Spots

A novel one‐trough synthesis via an air‐water interface is demonstrated to provide hexagonally packed arrays of densely spaced metallic nanoparticles (NPs). In the synthesis, a mesostructured polyoxometalate (POM)‐silicatropic template (PSS) is first self‐assembled at the air‐water interface; upon UV irradiation, anion exchange cycles enable the free‐floating PSS film to continuously uptake gold precursors from the solution subphase for diffusion‐controlled and POM‐site‐directed photoreduction inside the silica channels. NPs ≈ 2 nm can hence be homogeneously formed inside the silica‐surfactant channels until saturation. As revealed via X‐ray diffraction, small‐angle X‐ray scattering (SAXS), grazing incidence SAXS, and transmission electron microscopy, the Au NPs directed by the PSS template are arrayed into a 2D hexagonal lattice with inter‐channel spacing of 3.2 nm and a mean along‐channel NP spacing of 2.8 nm. This corresponds to an ultra‐high number density (≈10¹⁹ NPs cm^?3) of narrowly spaced Au NPs in the Au‐NP@PSS composite, leading to 3D densely deployed hot‐spots along and across the mesostructured POM‐silica channels for surface‐enhanced Raman scattering (SERS). Consequently, the Au‐NP@PSS composite exhibits prominent SERS with 4‐mercaptobenzoic acid (4‐MBA) adsorbed onto Au NPs. The best 4‐MBA detection limit is 5 nm , with corresponding SERS enhancement factors above 10⁸.     

Formation of Metal Nano‐ and Micropatterns on Self‐Assembled Monolayers by Pulsed Laser Deposition Through Nanostencils and Electroless Deposition

Patterns of noble‐metal structures on top of self‐assembled monolayers (SAMs) on Au and SiO₂ substrates have been prepared following two approaches. The first approach consists of pulsed laser deposition (PLD) of Pt, Pd, Au, or Cu through nano‐ and microstencils. In the second approach, noble‐metal cluster patterns deposited through nano‐ and microstencils are used as catalysts for selective electroless deposition (ELD) of Cu. Cu structures are grown on SAMs on both Au and SiO₂ substrates and are subsequently analyzed using X‐ray photoelectron spectroscopy element mapping, atomic force microscopy, and optical microscopy. The combination of PLD through stencils on SAMs followed by ELD is a new method for the creation of (sub)‐micrometer‐sized metal structures on top of SAMs. This method minimizes the gas‐phase deposition step, which is often responsible for damage to, or electrical shorts through, the SAM.     

Cover Picture: Formation of Metal Nano‐ and Micropatterns on Self‐Assembled Monolayers by Pulsed Laser Deposition Through Nanostencils and Electroless Deposition (Adv. Funct. Mater. 10/2006)

The cover illustrates two‐step fabrication of metal micro‐ and nanostructures on self‐assembled monolayers (SAMs) by pulsed laser deposition and electroless deposition. Metal–SAM–metal junctions are a key component of molecular electronic devices. Pt was deposited in a micropattern by pulsed laser deposition through a stencil. XPS maps show how the Pt pattern is developed into a Cu pattern using electroless deposition as reported by Ravoo, Brugger, Reinhoudt, Blank, and co‐workers on p. 1337. The Cu pattern can also be observed by optical microscopy (background). Patterns of noble‐metal structures on top of self‐assembled monolayers (SAMs) on Au and SiO₂ substrates have been prepared following two approaches. The first approach consists of pulsed laser deposition (PLD) of Pt, Pd, Au, or Cu through nano‐ and microstencils. In the second approach, noble‐metal cluster patterns deposited through nano‐ and microstencils are used as catalysts for selective electroless deposition (ELD) of Cu. Cu structures are grown on SAMs on both Au and SiO₂ substrates and are subsequently analyzed using X‐ray photoelectron spectroscopy element mapping, atomic force microscopy, and optical microscopy. The combination of PLD through stencils on SAMs followed by ELD is a new method for the creation of (sub)‐micrometer‐sized metal structures on top of SAMs. This method minimizes the gas‐phase deposition step, which is often responsible for damage to, or electrical shorts through, the SAM.     

Facile Synthesis of Manganese‐Oxide‐Containing Mesoporous Nitrogen‐Doped Carbon for Efficient Oxygen Reduction

Developing low‐cost non‐precious metal catalysts for high‐performance oxygen reduction reaction (ORR) is highly desirable. Here a facile, in situ template synthesis of a MnO‐containing mesoporous nitrogen‐doped carbon (m‐N‐C) nanocomposite and its high electrocatalytic activity for a four‐electron ORR in alkaline solution are reported. The synthesis of the MnO‐m‐N‐C nanocomposite involves one‐pot hydrothermal synthesis of Mn₃O₄@polyaniline core/shell nanoparticles from a mixture containing aniline, Mn(NO₃)₂, and KMnO₄, followed by heat treatment to produce N‐doped ultrathin graphitic carbon coated MnO hybrids and partial acid leaching of MnO. The as‐prepared MnO‐m‐N‐C composite catalyst exhibits high electrocatalytic activity and dominant four‐electron oxygen reduction pathway in 0.1 M KOH aqueous solution due to the synergetic effect between MnO and m‐N‐C. The pristine MnO shows little electrocatalytic activity and m‐N‐C alone exhibits a dominant two‐electron process for ORR. The MnO‐m‐N‐C composite catalyst also exhibits superior stability and methanol tolerance to a commercial Pt/C catalyst, making the composite a promising cathode catalyst for alkaline methanol fuel cell applications. The synergetic effect between MnO and N‐doped carbon described provides a new route to design advanced catalysts for energy conversion.     

High‐Throughput Fabrication of Au–Cu Nanoparticle Libraries by Combinatorial Sputtering in Ionic Liquids

Materials libraries of binary alloy nanoparticles (NPs) are synthesized by combinatorial co‐sputter deposition of Cu and Au into the ionic liquid (IL) 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₁C₄im][Tf₂N]), which is contained in a micromachined cavity array substrate. The resulting NPs and NP‐suspensions are investigated by transmission electron microscopy (TEM), X‐ray diffraction (XRD), UV‐Vis measurements (UV‐Vis), and attenuated total reflection Fourier transformed infrared (ATR‐FTIR) spectroscopy. Whereas the NPs can be directly observed in the IL using TEM, for XRD measurements the NP concentration is too low to lead to satisfactory results. Thus, a new NP isolation process involving capping agents is developed which enables separation of NPs from the IL without changing their size, morphology, composition, and state of aggregation. The results of the NP characterization show that next to the unary Cu and Au NPs, both stoichiometric and non‐stoichiometric Cu–Au NPs smaller than 7 nm can be readily obtained. Whereas the size and shape of the alloy NPs change with alloy composition, for a fixed composition the NPs have a small size distribution. The measured lattice constants of all capped NPs show unexpected increased values, which could be related to the NP/surfactant interactions.     

Synthesis of Ternary and Quaternary Au and Pt Decorated CdSe/CdS Heteronanoplatelets with Controllable Morphology

A variety of new ternary and quaternary metal–semiconductor inorganic nanostructures with unprecedented structural morphologies is achieved by the decoration of five monolayer‐thick CdSe/CdS core/crown nanoplatelets with Au and Pt domains. Significant differences in metal growth behavior are observed by varying the CdSe core and the CdS crown dimensions. Depending on the core size, Au growth can be directed only to the CdS edges, or both at the edges and at the center of the nanoplatelets. In contrast, the nucleation of Pt domains always happens at the CdS edges independently of the core and crown dimensions. Furthermore, quaternary structures are obtained by additional Au growth on Pt‐decorated CdSe/CdS nanoplatelets, where the effect of steric hindrance of the existing Pt domains results in the Au nucleation to occur only at the CdSe core. Instead, a change in the order of growth of the two noble metals results in Pt‐Au alloys present only at the surrounding edges of the nanoplatelets. Additionally, the metal‐decorated nanoplatelets are found to be efficient catalysts for H₂ fuel generation under white light irradiation. The highest apparent quantum efficiency measured is 19.3% ± 1.4% with a turnover frequency of ≈10⁵ molecules of H₂ per hour per nanoplatelet.     

Rational Assembly of Optoplasmonic Hetero‐nanoparticle Arrays with Tunable Photonic–Plasmonic Resonances

Metallic and dielectric nanoparticles (NPs) have synergistic electromagnetic properties but their positioning into morphologically defined hybrid arrays with novel optical properties still poses significant challenges. A template‐guided self‐assembly strategy is introduced for the positioning of metallic and dielectric NPs at pre‐defined lattice sites. The chemical assembly approach facilitates the fabrication of clusters of metallic NPs with interparticle separations of only a few nanometers in a landscape of dielectric NPs positioned hundreds of nanometers apart. This approach is used to generate two‐dimensional interdigitated arrays of 250 nm diameter TiO₂ NPs and clusters of electromagnetically strongly coupled 60 nm Au NPs. The morphology‐dependent near‐ and far‐field responses of the resulting multiscale optoplasmonic arrays are analyzed in detail. Elastic and inelastic scattering spectroscopy in combination with electromagnetic simulations reveal that optoplasmonic arrays sustain delocalized photonic–plasmonic modes that achieve a cascaded E‐field enhancement in the gap junctions of the Au NP clusters and simultaneously increase the E‐field intensity throughout the entire array.     

Recent Progress in MOF‐Derived,Heteroatom‐Doped Porous Carbons as Highly Efficient Electrocatalysts for Oxygen Reduction Reaction in Fuel Cells

Currently, developing nonprecious‐metal catalysts to replace Pt‐based electrocatalysts in fuel cells has become a hot topic because the oxygen reduction reaction (ORR) in fuel cells often requires platinum, a precious metal, as a catalyst, which is one of the major hurdles for commercialization of the fuel cells. Recently, the newly emerging metal‐organic frameworks (MOFs) have been widely used as self‐sacrificed precursors/templates to fabricate heteroatom‐doped porous carbons. Here, the recent progress of MOF‐derived, heteroatom‐doped porous carbon catalysts for ORR in fuel cells is systematically reviewed, and the synthesis strategies for using different MOF precursors to prepare heteroatom‐doped porous carbon catalysts, including the direct carbonization of MOFs, MOF and heteroatom source mixture carbonization, and MOF‐based composite carbonization are summarized. The emphasis is placed on the precursor design of MOF‐derived metal‐free catalysts and transition‐metal‐doped carbon catalysts because the MOF precursors often determine the microstructures of the derived porous carbon catalysts. The discussion provides a useful strategy for in situ synthesis of heteroatom‐doped carbon ORR electrocatalysts by rationally designing MOF precursors. Due to the versatility of MOF structures, MOF‐derived porous carbons not only provide chances to develop highly efficient ORR electrocatalysts, but also broaden the family of nanoporous carbons for applications in supercapacitors and batteries.     

The ohmic contact formation mechanism of Au/Pt/Pd ohmic contact to p-ZnTe

The ohmic contact formation mechanism and the role of Pt layer of Au(500Å) Pt(500Å)/Pd(100Å) ohmic contact to p-ZnTe were investigated. The specific contact resistance of Au/Pt/Pd contact depended strongly on the annealing temperature. As the annealing temperature increased, the specific contact resistance decreased and reached a minimum value of 6×10^?6 Θcm² at 200°C. From the Hall measurement, the hole concentration increased with the annealing temperature and reached a maximum value of 2.3×10¹⁹ cm^?3 at 300°C. The Schottky barrier height decreased with the increase of annealing temperature and reached a minimum value of 0.34 eV at 200°C and it was due to the interfacial reaction of Pd and ZnTe. Therefore, the decrease of contact resistance was due to the increase of doping concentration as well as the decrease of Schottky barrier height by the interfacial reaction of Pd ZnTe. The specific contact resistances of Au Pd, Au/Pt/Pd and Au/Mo/Pd as a function of annealing time was investigated to clarify the role of Pt layer.     

用于多种组装技术的厚膜导体复合结构

厚膜导体Ｐｄ－Ａｇ／Ａｕ、Ｐｔ－Ｐｄ－Ａｕ／Ａｕ平面复合结构，Ｐｄ－Ａｇ／Ａｕ立体复合结构可使多种组装技术相互兼容。立体复合结构还可有效地降低导体线电阻，减少线损耗。而且，其超声键合性尤佳     

PdAg Nanorings Supported on Graphene Nanosheets: Highly Methanol‐Tolerant Cathode Electrocatalyst for Alkaline Fuel Cells

Due to the high costs, slow reaction kinetics, and methanol poisoning of platinum‐based cathode catalysts, designing and exploring non‐Pt or low‐Pt cathode electrocatalysts with a low cost, high catalytic performance, and high methanol‐tolerance are crucial for the commercialization of fuel cells. Here, a facile method to fabricate a system of PdAg nanorings supported by graphene nanosheets is demonstrated; the fabrication is based on the galvanic displacement reaction between pre‐synthesized Ag nanoparticles and palladium ions. X‐ray diffraction and high‐resolution transmission electron microscopy show that the synthesized PdAg nanocrystals exhibit a ring‐shaped hollow structure with an average size of 27.49 nm and a wall thickness of 5.5 nm. Compared to the commercial Pd–C catalyst, the PdAg nanorings exhibit superior properties as a cathode electrocatalyst for oxygen reduction. Based on structural and electrochemical studies, these advantageous properties include efficient usage of noble metals and a high surface area because of the effective utilization of both the exterior and interior surfaces, high electrocatalytic performance for oxygen reduction from the synergistic effect of the alloyed PdAg crystalline phase, and most importantly, excellent tolerance of methanol crossover at high concentrations. It is anticipated that this synthesis of graphene‐based PdAg nanorings will open up a new avenue for designing advanced electrocatalysts that are low in cost and that exhibit high catalytic performance for alkaline fuel cells.     

Vapor Phase Metal‐Assisted Chemical Etching of Silicon

This work introduces and explores vapor phase metal‐assisted chemical etching (VP‐MaCE) of silicon as a method to bypass some of the challenges found in traditional liquid phase metal‐assisted chemical etching (LP‐MaCE). Average etch rates for Ag, Au, and Pd/Au catalysts are established at 31, 70, and 96 nm/min respectively, and the relationship between etch rate and substrate temperature is examined experimentally. Just as with LP‐MaCE, 3D catalyst motion is maintained and three‐dimensional structures are fabricated with nanoparticle‐ and lithography‐patterned catalysts. VP‐MaCE produces less microporous silicon compared with LP‐MaCE and the diffusion/reduction distance of Ag⁺ ions is significantly reduced. This process sacrifices etch rate for increased etch uniformity and lower stiction for applications in micro‐electromechanical systems (MEMS) processing.     

“Ship‐in‐a‐Bottle” Growth of Noble Metal Nanostructures

Noble metal nanostructures are grown inside hollow mesoporous silica microspheres using “ship‐in‐a‐bottle” growth. Small Au seeds are first introduced into the interior of the hollow microspheres. Au nanorods with synthetically tunable longitudinal plasmon wavelengths and Au nanospheres are obtained through seed‐mediated growth within the microspheres. The encapsulated Au nanocrystals are further coated with Pd or Pt shells. The microsphere‐encapsulated bimetallic core/shell nanostructures can function as catalysts. They exhibit high catalytic performance and their stability is superior to that of the corresponding unencapsulated core/shell nanostructures in the catalytic oxidation of o‐phenylenediamine with hydrogen peroxide. Therefore, these hollow microsphere‐encapsulated metal nanostructures are promising as recoverable and efficient catalysts for various liquid‐phase catalytic reactions.     

Weakening Intermediate Bindings on CuPd/Pd Core/shell Nanoparticles to Achieve Pt-Like Bifunctional Activity for Hydrogen Evolution and Oxygen Reduction Reactions

Although Pd is a potential substitution of Pt-based catalysts for the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), the binding of *H and oxygenated (*O, *OOH, *OH) intermediates on Pd are stronger than on Pt, leading to its inferior activity for HER and ORR. In this work, CuPd/Pd core/shell nanoparticles with an ultrathin Pd shell (0.5 nm) are developed, which demonstrate the Pt-like bifunctional activity for HER and ORR in acid electrolytes. The overpotential at 350 mA cm⁻² for HER and the half-wave potential for ORR on the optimal CuPd/Pd core/shell NPs are 76 mV and 0.854 V versus reversible hydrogen electrode (RHE), respectively, which are comparable to that of Pt and among the best of the reported Pd-based catalysts. Density functional theory calculations indicate that the significantly enhanced HER/ORR activity on CuPd/Pd core/shell NPs with 0.5 nm Pd shell stem from the compressive strain induced downshift of d-band center for Pd (by 2.0%), which weakens the binding strength of *H and oxygenated intermediates and promotes the reaction kinetics.     

Photochemical Formation of Au/Cu Bimetallic Nanoparticles with Different Shapes and Sizes in a Poly(vinyl alcohol) Film

Metal nanoparticle (NP)–polymer nanocomposite thin films are attractive for applications in various devices. Since bimetallic NPs provide additional opportunities for tuning the physical properties of the NP components, the development of bimetallic NP nanocomposite thin films should lead to further enhancements of various applications. Au/Cu bimetallic NPs are fabricated in a poly(vinyl alcohol) (PVA) film using a photochemical process. Interestingly, different sizes and shapes of Au/Cu bimetallic NPs are formed in the PVA film, resulting in a uniquely patterned nanocomposite structure. It is determined that the different formation and growth mechanisms of NPs inside and outside the UV‐light irradiation spot leads to the differences in size and shape.