Alloy Nanocages Research Articles

Lattice-mismatch-induced formation of defect-rich Pd–Cu alloy nanocages for enhanced formic acid oxidation activity

Lattice-mismatch-induced formation of defect-rich Pd–Cu alloy nanocages for enhanced formic acid oxidation activity

High-entropy alloy nanocages with highly ordered {100} facets and ultrathin features for water splitting in an acidic medium

PtIrRuRhPd HEA cubic nanocages with ordered {100} facets and ultrathin shells exhibit high electro-catalytic activities for hydrogen and oxygen evolution reactions in an acidic medium.

Silver chloride as sacrificial template to form silver chloride and gold-silver alloy hybrid nanocages for the reduction of 4-nitrophenol

Hollow cubic silver chloride and gold-silver alloy hybrid nanocages (AgCl-AuAg HNCs) were synthesized using silver chloride as a sacrificial template. AgCl nanostructures were readily synthesized by a mixture of silver nitrate (AgNO3) and sodium chloride (NaCl) solution. Chloroauric acid (HAuCl4) and ascorbic acid (AA) served as the gold precursor and reducing agent. Due to the capping and directing effect of Ag+ and Cl− ions, gold-silver alloy nanocages were formed. The particle size and surface plasmon resonance (SPR) peak of AgCl-AuAg HNCs can be tunable from 97 to 116 nm, and 600 nm to 740 nm with different molar ratio of AgNO3 and HAuCl4. The average particle size and shell thickness were 113.5 ± 19.6 nm and 14.2 ± 5.2 nm at molar ratio of 1:1.225, respectively. The synthesized AgCl-AuAg HNCs exhibited excellent catalytic properties and the apparent rate constant (Kapp) increased from 0.2046 min−1 to 1.8894 min−1 with increasing catalyst valume from 10 to 70 μL. The maximum turnover frequency (TOF) of the AgCl-AuAg HNCs reached up to 6.51 min −1 (390.6 h − 1) with 50 μL of AgCl-AuAg HNCs solution. It is expected that these AgCl-AuAg HNCs can be applied in water pollution control and environmental detection applications.

Te-induced fabrication of Pt3PdTe0.2 alloy nanocages by the self-diffusion of Pd atoms with unique MOR electrocatalytic performance.

The key to the application of direct methanol fuel cells is to improve the activity and durability of Pt-based catalysts. Based on the upshift of the d-band centre and exposure to more Pt active sites, Pt3PdTe0.2 catalysts with significantly enhanced electrocatalytic performance for the methanol oxidation reaction (MOR) were designed in this study. A series of different Pt3PdTex (x = 0.2, 0.35, and 0.4) alloy nanocages with hollow and hierarchical structures were synthesized using cubic Pd nanoparticles as sacrificial templates and PtCl62- and TeO32- metal precursors as oxidative etching agents. The Pd nanocubes were oxidized into an ionic complex, which was further co-reduced with Pt and Te precursors by reducing agents to form the hollow Pt3PdTex alloy nanocages with a face-centred cubic lattice. The sizes of the nanocages were around 30-40 nm, which were larger than the Pd templates (18 nm) and the thicknesses of the walls were 7-9 nm. The Pt3PdTe0.2 alloy nanocages exhibited the highest catalytic activities and stabilities toward the MOR after electrochemical activation in sulfuric acid solution. CO-stripping tests suggested the enhanced CO-tolerant ability due to the doping of Te. The specific activity of Pt3PdTe0.2 for the MOR reached 2.71 mA cm-2 in acidic conditions, which was higher than those of Pd@Pt core-shell and PtPd1.5 alloy nanoparticles and commercial Pt/C. A DMFC with Pt3PdTe0.2 as the anodic catalyst output a higher power density by 2.6 times than that of commercial Pt/C, demonstrating its practicable application in clean energy conversions. Density functional theory (DFT) confirmed that the alloyed Te atoms altered the electron distributions of Pt3PdTe0.2, which could lower the Gibbs free energy of the rate-determining methanol dehydrogenation step and greatly improve the MOR catalytic activity and durability.

Dual Active Sites of CO Adsorption and Activation over PtCu Alloy Nanocages for Preferential Oxidation of Carbon Monoxide

Dual Active Sites of CO Adsorption and Activation over PtCu Alloy Nanocages for Preferential Oxidation of Carbon Monoxide

NIR-driven PtCu-alloy nanocages via photothermal enhanced fenton catalytic degradation of pollutant dyes under neutral pH

In this work, near-infrared (NIR) light driven concave octopod PtCu alloy nanocages (OPtCu-NCs) were fabricated and first developed as photothermal synergetic Fenton catalyst for degradation of pollutant dyes. Moreover, by irradiating with NIR laser (808 nm), the obtained OPtCu-NCs exhibit excellent NIR absorption capacity and thus produce hyperpyrexia over 50 °C. Concomitantly, by the photothermal effect, the OPtCu-NCs nanocatalysts was used for elimination of organic dyes such as Methylene blue (MB) and Rhodamine B (RhB). The NIR-driven photothermal degradation mechanism under NIR irradiation can be attributed to the Fenton-like catalytic performance of Cu ions, then -NC- and/or C-C bonds in the molecular skeleton were fractured and electrons were donated intensively. As confirmed by a typical radical trapping experiment, electrons trigger the formation of miscellaneous reactive species (O2-, HO2, especially •OH) subsequently. Moreover, the photothermal Fenton-catalytic activity of the as-prepared OPtCu-NCs had maintained at 93.15% (for MB) and 91.87% (for RhB) after ten circulating degradation processes. All acquired results reveal that the OPtCu-NCs have the potential applied value in dyestuff-wastewater treatment under neutral pH.

Improve the Hole Size–Dependent Refractive Index Sensitivity of Au–Ag Nanocages by Tuning the Alloy Composition

In this study, Au–Ag nanoboxes are converted into Au–Ag alloy nanocages by increasing the hole size. The extinction spectrum and the refractive index sensing characteristics of Au–Ag alloy nanocages with different geometric parameters are studied by using discrete dipole approximation method (DDA). With the increase of Au composition, the peak of local surface plasmon resonance (LSPR) shows approximately linear redshift and the sensitivity factor shows approximately linear decrease. The refractive index sensitivity can be effectively controlled by the Au–Ag ratio at large hole size because the hole and cavity surfaces distribute more environmental dielectric components. Therefore, increasing the hole size and decreasing the Au–Ag ratio can improve the refractive index sensitivity. These calculation results have also been verified experimentally. In order to illustrate the influence of alloy composition on the LSPR characteristics and the refractive index sensitivity, the local electric field distributions under different geometric parameters are plotted. We find that the electric field direction on the hole and cavity surfaces is controlled by the Au–Ag ratio and environmental dielectric constant. Moreover, the field vectors on the hole and cavity surfaces are formed by the superposition of the incident field, the electric field generated by the oscillating electrons on the outer surface, and the polarized field in the environmental dielectric constant.

Dopant-Assisted Control of the Crystallite Domain Size in Hollow Ternary Iridium Alloy Octahedral Nanocages toward the Oxygen Evolution Reaction

The dissolution of Ir-oxide-based catalysts remains a roadblock in the development of durable electrocatalytic oxygen evolution reaction (OER) catalysts. Both the activity and stability of Ir-based catalysts are critically dependent on the ratio of stable rutile IrO2 and unstable amorphous Ir oxide (a-IrOx), as well as the spatial relationship between them. Here, we report that the domain size in hollow ternary Ir alloy nanocages can be fine-tuned by the introduction of dopant elements during the growth of parent core-shell nanoparticles, [email protected] After electrochemical oxidation under OER conditions, Ir alloy nanocages possessing multiple crystallites in their structure are transformed into hollow aggregates of loosely knit crystalline IrO2@a-IrOx domains, whereas single-crystalline Ir alloy nanocages are transformed to hollow Ir oxides with a random mixture of a-IrOx and IrO2. The loosely knit IrO2@a-IrOx structure achieves high OER activity and long-term stability, which is not feasible with the random mixture of a-IrOx and IrO2.

DNA-Mediated Three-Dimensional Assembly of Hollow Au–Ag Alloy Nanocages as Plasmonic Crystals

Oligonucleotide–nanoparticle conjugates are promising building blocks for stimuli responsive, reconfigurable functional materials in wet environments. Here, we demonstrate the self-assembly of DNA-...

Pd‐Ru Alloy Nanocages with a Face‐Centered Cubic Structure and Their Enhanced Activity toward the Oxidation of Ethylene Glycol and Glycerol

AbstractThis article reports a facile method for the synthesis of Pd‐Ru nanocages by activating the galvanic replacement reaction between Pd nanocrystals and a Ru(III) precursor with I‐ ions. The as‐synthesized nanocages feature a hollow interior, ultrathin wall of ≈2.5 nm in thickness, and a cubic shape. Our quantitative study suggests that the reduction rate of the Ru(III) precursor can be substantially accelerated upon the introduction of I‐ ions and then retarded as the ratio of I‐/Ru3+ is increased. The Pd‐Ru nanocages take an alloy structure, with the Ru atoms in the nanocages crystallized in a face‐centered cubic structure instead of the hexagonal close‐packed phase taken by bulk Ru. Using Pd nanocubes with different edge lengths, the dimensions of the nanocages in the range of 6−18 nm can readily be tuned. When tested as catalysts toward the electro‐oxidation of ethylene glycol and glycerol, respectively, the Pd‐Ru cubic nanocages prepared from 18 nm Pd cubes exhibit 5.1‐ and 6.2‐fold enhancements in terms of mass activity relative to the commercial Pd/C. After 1000 cycles of accelerated durability test, the mass activities of the nanocages are still 3.3 and 3.7 times as high as that of the pristine commercial Pd/C catalyst, respectively.

Practical fuel cells enabled by unprecedented oxygen reduction reaction on 3D nanostructured electrocatalysts

Bunched platinum–nickel (Pt–Ni) alloy nanocages exhibit excellent oxygen reduction reaction activity and stability, which can be effectively applied in the practical H 2 O 2 fuel cells.

Engineering bunched Pt-Ni alloy nanocages for efficient oxygen reduction in practical fuel cells.

Development of efficient and robust electrocatalysts is critical for practical fuel cells. We report one-dimensional bunched platinum-nickel (Pt-Ni) alloy nanocages with a Pt-skin structure for the oxygen reduction reaction that display high mass activity (3.52 amperes per milligram platinum) and specific activity (5.16 milliamperes per square centimeter platinum), or nearly 17 and 14 times higher as compared with a commercial platinum on carbon (Pt/C) catalyst. The catalyst exhibits high stability with negligible activity decay after 50,000 cycles. Both the experimental results and theoretical calculations reveal the existence of fewer strongly bonded platinum-oxygen (Pt-O) sites induced by the strain and ligand effects. Moreover, the fuel cell assembled by this catalyst delivers a current density of 1.5 amperes per square centimeter at 0.6 volts and can operate steadily for at least 180 hours.

Fabrication of bilayer Pd-Pt nanocages with sub-nanometer thin shells for enhanced hydrogen evolution reaction

The hydrogen evolution reaction (HER), which generates molecular hydrogen through the electrochemical reduction of water, is an important clean-energy technology. Platinum (Pt) is an ideal material for HER electrocatalysts in terms of low overpotential and fast kinetics. An effective method to improve the atom utilization efficiency of Pt is to fabricate Pt-based core-shell or nanocage structures with ultra-thin walls. This paper describes the construction of bilayer palladium (Pd)-Pt alloy nanocages catalyst with enhanced HER catalytic activity. The nanocages were fabricated by etching away the Pd templates of multishelled nanocubes composed of alternate shells of Pd and Pt with well-defined (100) facets. The bilayer Pd-Pt nanocages with sub-nanometer shells have a high dispersion of the active atoms on the outside and inside surfaces of outer layer and inner layer, respectively. Moreover, the Pd-Pt alloy lowers the overpotential for HER and speeds up the reaction rate of HER due to the synergies between Pd and Pt. The rational design of bilayer nanocages provided a novel route for boosting the atom utilization efficiency of Pt catalysts.

PdCu Alloy Flower-like Nanocages with High Electrocatalytic Performance for Methanol Oxidation

PdCu alloy flower-like nanocages are synthesized through corner-etched Cu2O octahedra as templates by galvanic reaction and disproportionation reaction. PdCu alloy nanocages are obtained with the molar ratio of H2PdCl4/Cu2O = 1:1, and the Pd nanoparticles are prepared with the molar ratio of H2PdCl4/Cu2O = 2:1. The PdCu alloy flower-like nanocages display the highest catalytic activity compared with Pd nanoparticles toward methanol oxidation reaction in alkaline medium, which is 2.7 times than that of commercial Pd/C. In addition, PdCu alloy nanocages also show high poison-tolerance and good stability. The superior electrocatalytic performance of PdCu flower-like nanocages may be attributed to the unique flower-like nanocage structure with high surface area and the synergic effect of Pd and Cu.

Catalyst and Electrode Advances for High Performing PEM and AEM Fuel Cells

Recent advances in polymer electrolyte membrane fuel cells have brought the technology extremely close to finally fulfilling its promise as a high efficiency, sustainable energy source for transportation applications1,2. An overwhelming amount of work in this area has focused on the proton exchange membrane fuel cell (PEMFC), where high performance has been achieved. However, proton-based systems still suffer from very high materials cost of both the membrane and catalysts, and the need to drive costs down by reducing material loading generally leads to accelerated degradation of otherwise stable systems as well as increased sensitivity to water due to the reduced water capacity with thinning catalyst layer thickness. To overcome these limitations, our group has developed an air-assisted cylindrical liquid jets spraying system that allows for the precise control of the catalyst layer microstructure, leading to high-performance catalyst-coated membranes. The system design and influence of operating parameters on PEMFC performance will be shown. On the materials side, our team has produced Ni-rich PtNi alloys and Pt3Ni alloy nanocages that have shown very highly activity for the oxygen reduction reaction (ORR) and excellent stability at PEMFC cathode conditions. This poster will show the structure and chemistry of the Pt-Ni catalysts as well as their in-situ and ex-situ performance. The Pt-Ni nanocage PEMFCs have shown behavior that well exceeds the DOE targets for activity and comes very close to the DOE targets for durability. From both an activity and durability perspective, these Pt-Ni nanocage catalysts considerably outperform state-of-the-art commercial Pt/C catalysts. Another low-temperature alternative to the PEMFC that has been widely discussed in recent years is the anion exchange membrane fuel cell (AEMFC). The AEMFC has an effective pKa much higher than the PEMFC, and this basic environment has several possible advantages over the acid system, including a less corrosive environment for the catalyst and catalyst support, which opens up the periodic table with regards to possible materials to be employed. Also, it is well known that the kinetics for the ORR are more facile in alkaline media than acid media3, though the converse is true for the hydrogen oxidation reaction, which necessitates the study for advanced Pt catalysts such as PtRu4. Our recent work has shown that the internal water dynamics in the AEMFC is likely more complex than the PEMFC. In this poster, the influence of the membrane, ionomer and gas diffusion layer as well as the flow rate and dew points of the anode and cathode gases on anion exchange membrane fuel cell performance will be shown. After cell optimization, a peak power density of 1.2 W/cm2 has been reproducibly achieved with radiation-grafted ETFE membranes and ionomers.

Facile Synthesis of Pt–Pd Alloy Nanocages and Pt Nanorings by Templating with Pd Nanoplates

AbstractWe report a facile method for the synthesis of Pt–Pd nanocages and Pt nanorings by conformally coating Pd nanoplates with Pt‐based shells using polyol‐ and water‐based protocols, respectively, followed by selective removal of the Pd cores. For the polyol‐based system, Pd nanoplates were conformally coated with Pt–Pd alloy shells due to the use of a high reaction temperature of 200 °C and a slow injection rate for the Pt precursor. In comparison, Pt shells were formed on Pd nanoplates with a larger thickness on the side face than on the top/bottom face in the water‐based system due to the use of a low reaction temperature of 80 °C and the presence of twin boundaries on the side face. As such, the Pd@Pt nanoplates prepared using the polyol‐ and water‐based protocols evolved into Pt–Pd nanocages and Pt nanorings, respectively, when the Pd templates in the cores were selectively removed by wet etching. The wall thickness of the nanocages and the ridge thickness of the nanorings could be reduced down to 1.1 nm and 1.8 nm, respectively, without breaking the hollow structures.

Synthesis and Characterization of Pt-Ag Alloy Nanocages with Enhanced Activity and Durability toward Oxygen Reduction.

Engineering the elemental composition of metal nanocrystals offers an effective strategy for the development of catalysts or electrocatalysts with greatly enhanced activity. Herein, we report the synthesis of Pt-Ag alloy nanocages with an outer edge length of 18 nm and a wall thickness of about 3 nm. Such nanocages with a composition of Pt19Ag81 could be readily prepared in one step through the galvanic replacement reaction between Ag nanocubes and a Pt(II) precursor. After 10 000 cycles of potential cycling in the range of 0.60-1.0 V as in an accelerated durability test, the composition of the nanocages changed to Pt56Ag44, together with a specific activity of 1.23 mA cm-2 toward oxygen reduction, which was 3.3 times that of a state-of-the-art commercial Pt/C catalyst (0.37 mA cm-2) prior to durability testing. Density functional theory calculations attributed the increased activity to the stabilization of the transition state for breaking the O-O bond in molecular oxygen. Even after 30 000 cycles of potential cycling, the mass activity of the nanocages only dropped from 0.64 to 0.33 A mg-1Pt, which was still about two times that of the pristine Pt/C catalyst (0.19 A mg-1Pt).

Silver-Free Gold Nanocages with Near-Infrared Extinctions.

This article reports the preparation of silver-free Au nanocages from cubic palladium templates. Pd nanocubes were subjected to galvanic replacement with Au3+ to produce Pd@Au nanocages having tunable dimensions (i.e., edge length, gold layer thickness, and hollow pore size), which allowed selectable positioning of the optical extinction maxima from the visible to the near infrared. These new nanocages circumvent the problems associated with previous Ag-derived gold alloy nanocages, which suffer from the toxicity of residual silver and the possible fragmentation of such alloyed nanostructures, thereby limiting their potential applications. In contrast, the present materials represent stable, nontoxic, tunable, and hollow plasmonic nanostructures.

Enhanced Electrocatalytic Activity toward the Oxygen Reduction Reaction through Alloy Formation: Platinum–Silver Alloy Nanocages

Platinum–silver nanocage catalysts with a precisely defined shape and composition were synthesized using the galvanic replacement reaction (GRR) and utilized as electrocatalysts for the oxygen reduction reaction (ORR). The electrocatalytic activity of these platinum–silver nanocages was determined as a function of platinum content. The specific current density of all platinum–silver nanocages was found to be 2–3 times greater than the specific current densities previously reported for solid platinum catalysts under similar conditions. The highest specific current densities were observed for the platinum–silver nanocages with the lowest platinum content. After a thorough structural and electronic investigation by TEM, XRD, and XPS, it was determined that all platinum–silver nanocage catalysts exibit an expanded lattice compared to pure platinum materials. This resulted in a negative shift in the onset potential of the oxygen reduction reaction. However, despite this negative shift, the catalyst with a low ...

Partial-surface-passivation strategy for transition-metal-based copper-gold nanocage.

An effective strategy involving the corrosion of partial-surface-passivated Cu nanoparticles is proposed for synthesizing transition-metal-based Cu-Au alloy nanocages. Time-dependent X-ray absorption spectroscopy demonstrates that the hollow-cage Cu-Au alloy nanostructure is formed by sequential erosion of the partial surface and interior Cu and by the alloying of Au and Cu.