Designed Synthesis of Well‐Defined Pd@Pt Core–Shell Nanoparticles with Controlled Shell Thickness as Efficient Oxygen Reduction Electrocatalysts

Improving the electrocatalytic activity and durability of Pt‐based catalysts with low Pt content toward the oxygen reduction reaction (ORR) is one of the main challenges in advancing the performance of polymer electrolyte membrane fuel cells (PEMFCs). Herein, a designed synthesis of well‐defined Pd@Pt core–shell nanoparticles (NPs) with a controlled Pt shell thickness of 0.4–1.2 nm by a facile wet chemical method and their electrocatalytic performances for ORR as a function of shell thickness are reported. Pd@Pt NPs with predetermined structural parameters were prepared by in situ heteroepitaxial growth of Pt on as‐synthesized 6 nm Pd NPs without any sacrificial layers and intermediate workup processes, and thus the synthetic procedure for the production of Pd@Pt NPs with well‐defined sizes and shell thicknesses is greatly simplified. The Pt shell thickness could be precisely controlled by adjusting the molar ratio of Pt to Pd. The ORR performance of the Pd@Pt NPs strongly depended on the thickness of their Pt shells. The Pd@Pt NPs with 0.94 nm Pt shells exhibited enhanced specific activity and higher durability compared to other Pd@Pt NPs and commercial Pt/C catalysts. Testing Pd@Pt NPs with 0.94 nm Pt shells in a membrane electrode assembly revealed a single‐cell performance comparable with that of the Pt/C catalyst despite their lower Pt content, that is the present NP catalysts can facilitate low‐cost and high‐efficient applications of PEMFCs.     

One‐Pot Synthesis and Electrocatalytic Properties of Pd@Pt Core‐Shell Nanocrystals with Tailored Morphologies

Pd@Pt core‐shell nanocrystals consisting of well‐defined Pd nanocube cores and dendritic Pt shells were prepared by a new facile aqueous one‐pot synthetic method. The prepared Pd@Pt nanocrystals exhibited efficient catalytic activity and stability toward methanol electrooxidation, and their catalytic function was highly dependent on their Pt shell thickness due to the different synergism between Pt and Pd.     

Pd@Pt Core–Shell Nanoparticles with Branched Dandelion‐like Morphology as Highly Efficient Catalysts for Olefin Reduction

A facile synthesis based on the addition of ascorbic acid to a mixture of Na₂PdCl₄, K₂PtCl₆, and Pluronic P123 results in highly branched core–shell nanoparticles (NPs) with a micro–mesoporous dandelion‐like morphology comprising Pd core and Pt shell. The slow reduction kinetics associated with the use of ascorbic acid as a weak reductant and suitable Pd/Pt atomic ratio (1:1) play a principal role in the formation mechanism of such branched Pd@Pt core–shell NPs, which differs from the traditional seed‐mediated growth. The catalyst efficiently achieves the reduction of a variety of olefins in good to excellent yields. Importantly, higher catalytic efficiency of dandelion‐like Pd@Pt core–shell NPs was observed for the olefin reduction than commercially available Pt black, Pd NPs, and physically admixed Pt black and Pd NPs. This superior catalytic behavior is not only due to larger surface area and synergistic effects but also to the unique micro–mesoporous structure with significant contribution of mesopores with sizes of several tens of nanometers.     

Synthesis of a Hierarchical Three‐Component Nanocomposite Structure System with Enhanced Electrocatalytic and Photoelectrical Properties

Effective control over the morphology and size of Pd/Pt nanoparticles is currently of immense interest because their electronic, optical, and catalytic properties are superior to pure platinum nanoparticles. However, control over the nanoparticle shape is still challenging. Therefore, a novel design and synthetic route needs to be developed to obtain a high‐performance catalyst. Herein, a hierarchical three‐component nanocomposite structure system (HTNSS) composed of graphene, TiO₂, and Pd@Pt core–shell nanoparticles was designed and synthesized by a sequential strategy that focuses on constructing the monolithic structure rather than limited single‐component counterparts. The resulting composites were characterized by various techniques, which showed that the Pd@Pt core–shell nanoparticles were preferentially deposited on the peripheral interface of the graphene and TiO₂ nanoparticles. The photoelectrical and catalytic performances were obviously improved relative to the commercially available E‐TEK Pt/C owing to their synergistic effect.     

Preparation and Characterization of Pt/Co‐Core Au‐Shell Magnetic Nanoparticles

Pt/Co‐core Au‐shell nanoparticles were synthesized via a two‐step route using NaBH₄ as a reducing agent. The nanoparticles are characterized by UV‐vis spectroscopy, transmission electron microscopy (TEM) and powder X‐ray diffraction (XRD). The results indicate that the as‐synthesized Pt/Co‐core Au‐shell nanoparticles have a disordered face centered cubic (fcc) structure, whereas the annealed Pt/Co‐core Au‐shell nanoparticles exhibit an ordered face centered tetragonal (fct) structure. Superconducting quantum interference device (SQUID) studies reveal that the coercivity of the annealed Pt/Co‐core Au‐shell nanoparticles increases to 510 Oe after heat treatment at 500 °C for 2 h.     

Facile Self‐Assembly Synthesis of PdPt Bimetallic Nanotubes with Good Performance for Ethanol Oxidation in an Alkaline Medium

PdPt bimetallic nanotubes were prepared by the self‐assembly of Pt and Pd on Te nanowires at room temperature. The morphologies of the as‐prepared PdPt nanotubes were investigated by scanning electron microscopy and transmission electron microscopy, and the results display a large amount of PdPt bimetallic nanotubes with a diameter of 10–20 nm and a length of several micrometers. The composition and structure of the nanotubes were characterized by X‐ray diffraction, high‐resolution transmission electron microscopy, scanning transmission electron microscopy, and energy spectrum analysis, and the results display uniform compositional distributions of both elements (Pd and Pt). The mechanism of the formation of the nanotube structure was supposed. The electrocatalytic performance of PdPt nanotubes were studied by cyclic voltammetry and chronoamperometry. Electrochemical results show that the as‐prepared PdPt nanotube catalysts have not only high activity but also good stability for ethanol oxidation in alkaline medium.     

Biosensor Based on Self‐Assembling Glucose Oxidase and Dendrimer‐Encapsulated Pt Nanoparticles on Carbon Nanotubes for Glucose Detection

A novel amperometric glucose biosensor based on layer‐by‐layer (LbL) electrostatic adsorption of glucose oxidase (GOx) and dendrimer‐encapsulated Pt nanoparticles (Pt‐DENs) on multiwalled carbon nanotubes (CNTs) was described. Anionic GOx was immobilized on the negatively charged CNTs surface by alternatively assembling a cationic Pt‐DENs layer and an anionic GOx layer. Transmission electron microscopy images and ζ‐potentials proved the formation of layer‐by‐layer nanostructures on carboxyl‐functionalized CNTs. LbL technique provided a favorable microenvironment to keep the bioactivity of GOx and prevent enzyme molecule leakage. The excellent electrocatalytic activity of CNTs and Pt‐DENs toward H₂O₂ and special three‐dimensional structure of the enzyme electrode resulted in good characteristics such as a low detection limit of 2.5 μM, a wide linear range of 5 μM–0.65 mM, a short response time (within 5 s), and high sensitivity (30.64 μA mM^?1 cm^?2) and stability (80% remains after 30 days).     

Facile Synthesis of Carbon‐Supported Ultrasmall Ag@Pd Core‐Shell Nanocrystals with Superior Electrocatalytic Activity for Direct Formic Acid Fuel Cell Application

To design electrocatalysts with excellent performance, morphology, composition and structure is a decisive influential factor. In this work, ultrasmall Ag@Pd core‐shell nanocrystals supported on Vulcan XC72R carbon with different Ag/Pd atomic ratios are synthesized via a facile successive reduction approach with formaldehyde and ethylene glycol as reducing agents, respectively. The Ag‐core/Pd‐shell nanostructures are revealed by high‐resolution transmission electron microscopy (HRTEM). Ag@Pd core‐shell nanocrystals possess a narrow size distribution with an average size of ca. 4.3 nm. In comparison to monometallic Pd/C and commercial Pd black catalysts, such Ag@Pd core‐shell nanocrystals display excellent electrocatalytic activities for formic acid oxidation, which may be due to high Pd utilization derived from the formation of Ag@Pd core‐shell nanostructure and the strong interaction between Ag and Pd.     

超细Pd纳米线表层富Pt作为耐久性氧还原催化剂研究

本文控制合成一维方向生长的直径为1.5 nm,长度为11.8 nm的超细Pd纳米线,结合欠电位沉积方法在其表面制备了不同Pt原子层的Pd@Pt核壳结构纳米电催化剂. 高分辨透射电镜和光电子能谱结果证实了这种核壳结构及Pt在Pd纳米线上的均匀分布. 相比于商业化Pt黑催化剂,该核壳结构电催化剂对酸性介质中的氧气还原反应呈现了较高的电催化活性和增强的耐久性. 显著增强的耐久性可归属于催化剂一维结构的稳定性.     

Boosting Photocatalytic Water Splitting: Interfacial Charge Polarization in Atomically Controlled Core–Shell Cocatalysts

Platinum is a commonly used cocatalyst for improved charge separation and surface reactions in photocatalytic water splitting. It is envisioned that its practical applications can be facilitated by further reducing the material cost and improving the efficacy of Pt cocatalysts. In this direction, the use of atomically controlled Pd@Pt quasi‐core–shell cocatalysts in combination with TiO₂ as a model semiconductor is described. As demonstrated experimentally, the electron trapping necessary for charge separation is substantially promoted by combining a Schottky junction with interfacial charge polarization, enabled by the three‐atom‐thick Pt shell. Meanwhile, the increase in electron density and lattice strain would significantly enhance the adsorption of H₂O onto Pt surface. Taken together, the improved charge separation and molecular activation dramatically boost the overall efficiency of photocatalytic water splitting.     

Control of Metal Arrays Based on Heterometallics Masquerading in Heterochiral Aggregations of Chiral Clothespin‐Shaped Complexes

Heterometal arrays in molecular aggregations were obtained by the spontaneous and ultrasound‐induced gelation of organic liquids containing the chiral, clothespin‐shaped trans‐bis(salicylaldiminato) d₈ transition‐metal complexes 1 . Heterometallic mixtures of complexes 1 a (Pd) and 1 b (Pt) underwent strict heterochiral aggregation entirely due to the organic shell structure of the clothespin shape, with no effect of the metal cores. This phenomenon provides an unprecedented means of generating highly controlled heterometallic arrangements such as alternating sequences [(+)‐Pd(?)‐Pt(+)‐Pd(?)‐Pt ??? ] as well as a variety of single metal‐enriched arrays (e.g., [(+)‐Pt(?)‐Pd(+)‐Pd(?)‐Pd(+)‐Pd(?)‐Pd ??? ] and [(+)‐Pd(?)‐Pt(+)‐Pt(?)‐Pt(+)‐Pt(?)‐Pt ??? ]) upon the introduction of an optically active masquerading unit with a different metal core in the heterochiral single‐metal sequence. The present method can be applied to form various new aggregates with optically active Pd and Pt units, to allow 1) tuning of the gelation ultrasound sensitivity based on the different hearing abilities of the metal units; 2) aggregation‐induced chirality transfer between heterometallic species; and 3) aggregation‐induced chirality enhancement. A mechanistic rationale is proposed for these molecular aggregations based on the molecular structures of the units and the morphologies of the aggregates.     

Strain‐Enhanced Metallic Intermixing in Shape‐Controlled Multilayered Core–Shell Nanostructures: Toward Shaped Intermetallics

Controlling the surface composition of shaped bimetallic nanoparticles could offer precise tunability of geometric and electronic surface structure for new nanocatalysts. To achieve this goal, a platform for studying the intermixing process in a shaped nanoparticle was designed, using multilayered Pd‐Ni‐Pt core–shell nanocubes as precursors. Under mild conditions, the intermixing between Ni and Pt could be tuned by changing layer thickness and number, triggering intermixing while preserving nanoparticle shape. Intermixing of the two metals is monitored using transmission electron microscopy. The surface structure evolution is characterized using electrochemical methanol oxidation. DFT calculations suggest that the low‐temperature mixing is enhanced by shorter diffusion lengths and strain introduced by the layered structure. The platform and insights presented are an advance toward the realization of shape‐controlled multimetallic nanoparticles tailored to each potential application.     

Synthesis,characterization and catalytic performance of core‐shell structure magnetic Fe3O4/P(GMA‐EGDMA)‐NH2/HPG‐COOH‐Pd catalyst

A strategy has been developed for the synthesis, characterization and catalysis of magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd core‐shell structure supported catalyst. The P(GMA‐EGDMA) polymer layer was coated on the surface of hollow magnetic Fe₃O₄ microspheres through the effect of KH570. The core‐shell magnetic Fe₃O₄/P(GMA‐EGDMA) modified by ‐NH₂ could be grafted with HPG. Then, the hyperbranched glycidyl (HPG) with terminal ‐OH were modified by ‐COOH and adsorbed Pd nanoparticles. The hyperbranched polymer layer not only protected the Fe₃O₄ magnetic core from acid–base substrate corrosion, but also provided a number of functional groups as binding sites for Pd nanoparticles. The prepared catalyst was characterized by UV–vis, TEM, SEM, FTIR, TGA, ICP‐OES, BET, XRD, DLS and VSM. The catalytic tests showed that the magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd catalyst had excellent catalytic performance and retained 86% catalytic efficiency after 8 consecutive cycles.     

Preparation,characterization and catalytic application of PdPt bimetallic nanoparticles stabilized by 15‐membered triolefinic macrocycle‐terminated poly(propylene imine) dendrimer

PdPt bimetallic nanoparticles stabilized by 15‐membered triolefinic macrocycle‐stabilized poly(propylene imine) dendrimer (G3‐M(Pd_x Pt_10−x ) DSNs) have been prepared via synthesis of a 15‐membered triolefinic macrocycle‐modified third‐generation poly(propylene imine) dendrimer (G3‐M) and then synchronous ligand exchange with Pd(PPh₃)₄/Pt(PPh₃)₄ complexes. The structure and catalytic activity of the DSNs were characterized using Fourier transform infrared, ¹H NMR, transmission electron microscopy, energy‐dispersive X‐ray and X‐ray photoelectron analyses. As a novel catalyst system, it can be concluded that the composition of the bimetallic nanoparticles has an influence on the catalytic activity of the hydrogenation reaction of acrylonitrile–butadiene rubber, which can be related to synergistic effect. Furthermore, the selectivity and recyclability of G3‐M(Pd_x Pt_10−x ) DSN catalyst are also discussed.     

Pd@tetrahedral hollow magnetic nanoparticles coated with N‐doped porous carbon as an efficient catalyst for hydrogenation of nitroarenes

Hollow magnetic nanoparticles (MNPs) with tetrahedral morphology were synthesized and then covered by a shell prepared by coating with melamine–formaldehyde followed by the introduction of glucose‐derived carbon. Subsequently, Pd nanoparticles were immobilized and the core–shell nanocomposite was carbonized. The obtained magnetic catalyst was successfully applied for the hydrogenation of nitroarenes in aqueous media. To investigate the effects of the morphology of MNPs, the nature of carbon shell, and the order of incorporation of Pd nanoparticles, several control catalysts, including the MNPs with different morphologies (disc‐like and cylinder); MNPs coated with different shells (sole glucose‐derived carbon or melamine–formaldehyde carbon shell); and a nanocomposite, in which Pd was immobilized after carbonization, were prepared and examined as catalyst for the model reaction. To justify the observed different catalytic activities of the catalysts, their Pd loadings, leaching, and specific surface areas were compared. The results confirmed that tetrahedral MNPs coated with porous N‐rich carbon shell exhibited the best catalytic activity. The high catalytic activity of this catalyst was attributed to its high surface area and the interaction of N‐rich shell with Pd nanoparticles that led to the higher Pd loading and suppressed Pd leaching.     

A Mesoporous Nanorattle‐Structured Pd@PtRu Electrocatalyst

Pt‐based nanomaterials play important roles in the catalytic process toward oxygen reduction reaction (ORR). Rationally regulating the composition and morphology of the catalysts could enhance the catalytic performance effectively. In this work, an effective method is presented to synthesize Pd@ mesoporous PtRu nanorattles (Pd@mPtRu NRs) containing a Pd core and a mesoporous PtRu shell. Owing to the unique structure and PtRu alloy composition, the prepared Pd@mPtRu NRs exhibit an enhanced catalytic performance and durability toward ORR relative to mesoporous PtRu hollow nanoparticles (mPtRu HNs) and commercial Pt/C. The proposed approach may provide a general way to synthesize Pt‐based yolk‐shell structures with different compositions.     

Transition‐Metal Nitride Core@Noble‐Metal Shell Nanoparticles as Highly CO Tolerant Catalysts

Core–shell architectures offer an effective way to tune and enhance the properties of noble‐metal catalysts. Herein, we demonstrate the synthesis of Pt shell on titanium tungsten nitride core nanoparticles (Pt/TiWN) by high temperature ammonia nitridation of a parent core–shell carbide material (Pt/TiWC). X‐ray photoelectron spectroscopy revealed significant core‐level shifts for Pt shells supported on TiWN cores, corresponding to increased stabilization of the Pt valence d‐states. The modulation of the electronic structure of the Pt shell by the nitride core translated into enhanced CO tolerance during hydrogen electrooxidation in the presence of CO. The ability to control shell coverage and vary the heterometallic composition of the shell and nitride core opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.     

In situ structural characterization of platinum dendrimer-encapsulated oxygen reduction electrocatalysts

In situ electrochemical extended X-ray absorption fine structure (EXAFS) was used to evaluate the structure of Pt dendrimer-encapsulated nanoparticles (DENs) during the oxygen reduction reaction (ORR). The DENs contained an average of just 225 atoms each. The results indicate that the Pt coordination number (CN) decreases when the electrode potential is moved to positive values. The results are interpreted in terms of an ordered core, disordered shell model. The structure of the DENs is not significantly impacted by the presence of dioxygen, but other electrogenerated species may have a significant impact on nanoparticle structure.     

Synthesis and Cytotoxicity of 2‐(2′‐Pyridyl)benzimidazole Complexes of Palladium(II) and Platinum(II)

Compounds of type [MX₂(Hpben)] [M = Pd (X = Cl), Pt (X = Cl, I); Hpben = 2‐(2′‐pyridyl)benzimidazole] were prepared and characterized, and the structures of the Pt derivatives were determined by X‐ray crystallography. The crystals of [PtI₂(Hpben)] consist of discrete units in which the Pt atom is coordinated to two iodine atoms and to pyridine and imidazole N atoms in a distorted square planar arrangement. The structure of the chloro derivative is similar, except that the [PtCl₂(Hpben)] monomers are hydrogen‐bonded in zig‐zag chains. In assays of the interactions of the Pd and Pt chloro compounds with DNA, and of their in vitro cytotoxic activity against human cervical carcinoma cells (HeLa‐229), human ovarian carcinoma cells (A2780) and a cisplatin‐resistant mutant A2780 line (A2780cis), the only activity observed was modest cytotoxicity of the Pd derivative for A2780.     

Effects of the Pt Shell Thickness on the Oxygen Reduction Reaction on a Well-Defined Pd@Pt Core-Shell Model Surface

The effect of the Pt shell thickness on the oxygen reduction reaction (ORR) of a Pd@Pt core-shell catalyst was studied using surface science technics and computational approaches. We found Pt shells on Pd rods to be negatively charged because of charge transfer from the Pd substrate when the shell thicknesses were 0.5 or 1 monolayer (ML). The activities of the ORR of the model surface with a Pt shell of 0.5 or 1 ML were similar and more than twice the activities of a Pt/C or Pt rod. The relationship between the ORR activity and the thickness of the Pt shell was the exact opposite of the relationship between the Pt binding energy and the Pt shell thickness. The indication was that more negatively charged Pt had higher ORR activity. Density functional theory calculations confirmed that a single layer of Pt atoms located on Pd was negatively charged compared to pure Pt and resulted in a lower barrier to the rate-limiting step of the ORR.