Alloy Nanosheets Research Articles

Atomically ultrathin RhCo alloy nanosheet aggregates for efficient water electrolysis in broad pH range

RhCo alloy nanosheets with 1.3 nm thickness grew on carbon foam. And their symmetric electrolyzer exhibits outstanding reversible switched ability for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER).

Facile synthesis of ultrathin Pt–Pd nanosheets for enhanced formic acid oxidation and oxygen reduction reaction

A facile solvothermal method was developed to synthesize ultrathin wrinkled Pt–Pd alloy nanosheets with enhanced catalytic properties towards the formic acid oxidation reaction and oxygen reduction reaction.

Visible-Light-Driven Efficient Hydrogen Production from CdS NanoRods Anchored with Co-catalysts Based on Transition Metal Alloy Nanosheets of NiPd, NiZn, and NiPdZn

Investigation of new catalysts to improve artificial photosynthesis efficiencies is an absolute need concerning energy demands and environmental issues. In the present study, nanosheets of NiPd, NiZn, and NiPdZn metal alloys, synthesized at the toluene–water interface, have been employed as co-catalysts for hydrogen evolution from water in the presence of CdS nanorods (NRs) as a photosensitizer. Anchoring of alloy nanosheets with CdS NRs resulted in exceptional enhancement in hydrogen evolution activity. Interestingly earth abundant cost-effective CdS/NiZn photocatalyst showed higher hydrogen evolution reaction (HER) activity than comparatively precious photocatalyst CdS/NiPd. Trimetallic alloy nanosheets of NiPdZn further exhibited superior HER activity concerning bimetallic alloys, NiZn and NiPd. An enhancement of 21 times in the hydrogen evolution activity of CdS has been achieved by optimum loading of NiPdZn. Hydrogen yields of 21347.3 μmol h–1 g–1 (AQY = 11.35%) and 53361.3 μmol h–1 g–1 (AQY = 28%) h...

Interconnected nanoparticle-stacked platinum-based nanosheets as active cathode electrocatalysts for passive direct methanol fuel cells

Interconnected nanoparticle-stacked two-dimensional Pt and porous PtNi alloy nanosheets are synthesized via galvanic replacement of Ni nanobelts. The Pt and porous PtNi nanosheets achieve a factor of approximately 1.3 and 2.3 enhancement in mass activity at 0.9 V versus RHE for oxygen reduction reaction relative to commercial Pt black, respectively. The practicability of Pt and porous PtNi nanosheets used as cathodic electrocatalysts for passive direct methanol fuel cells (DMFCs) is investigated. The passive DMFCs with Pt nanosheets (1.0 mg(Pt) cm−2) and porous PtNi nanosheets (0.8 mg(Pt) cm−2) exhibit excellent performance with satisfactory stability at 25 °C, which is slightly higher than that of the conventional cell with 2.0 mg(Pt) cm−2. The performance improvement of cells with Pt and porous PtNi nanosheets is attributed to the enhanced electrocatalytic activity and decreased charge transfer resistance of the cathodic catalyst layer. Benefiting from the porous structure of the PtNi nanosheets, the cell's performance is further boosted due to an increased Pt utilization. This work may provide an applicable approach to develop two-dimensional electrocatalysts for passive DMFCs, revealing a new strategy to decrease the usage of platinum.

Direct Electrochemical Deposition of Lithium from Lithium Oxide in a Highly Stable Aluminium‐Containing Solvate Ionic Liquid

AbstractLow‐temperature electrochemical extraction of active metals from their corresponding chlorides in ionic liquids has long been a scientific challenge, while extraction from oxides is even more difficult. Inspired by previous reports of the electrochemical deposition of various non‐active metals from their corresponding oxides in diverse ionic liquids, we demonstrate the successful electrodeposition of active Li on high‐purity Al‐plate substrates at relatively low temperature (353 K), as confirmed by X‐ray diffraction. Furthermore, Al−Li alloy nanosheets can also be obtained on the Al surface by solid‐state cathode alloying. The Li source was Li2O, which was dissolved in a highly stable Al‐containing solvate ionic liquid. The dissolution mechanism and electrodeposition behaviour of Li2O were investigated using multinuclear nuclear magnetic resonance spectroscopy, theoretical calculations, and electrochemical techniques. The findings are expected to provide a theoretical basis and method for low‐temperature electrochemical extraction of active metals from their oxides.

Efficient Catalytic Hydrogenation of Butyl Levulinate to γ-Valerolactone over a Stable and Magnetic CuNiCoB Amorphous Alloy Catalyst

A series of low-cost, magnetic, and high-efficiency CuNiCoB amorphous alloy catalysts were developed by the chemical reduction method for selective hydrogenation of butyl levulinate (BL) to γ-valerolactone (GVL). The catalysts were characterized by inductively coupled plasma optical emission spectrometry, Brunauer–Emmett–Teller, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and hydrogen temperature-programmed desorption techniques. The results indicated that the CuNiCoB amorphous alloy nanosheets with well-dispersed Cu nanoparticles played an important role in enhancing the hydrogenation activity. The reaction temperature, pressure, time, and substrate concentration were optimized. The maximum GVL yield of 89.5% with BL conversion of 99.7% was achieved over the best Cu0.5Ni1Co3B catalyst using 3 wt % dosage relative to BL at 473 K under 3.0 MPa H2 after 3 h. The considerable stability of Cu0.5Ni1Co3B during catalytic rec...

Enhanced exciton emission behavior and tunable band gap of ternary W(SxSe1-x)2 monolayer: temperature dependent optical evidence and first-principles calculations.

Up to date, the electronic and optical properties of WS2 and WSe2 have been widely explored. However, the synthesis and characterization of their ternary alloy nanosheets have been rarely reported. Here, we fabricated single layer W(SxSe1-x)2 nanosheets by a one-step chemical vapor deposition (CVD) method. It is demonstrated that exciton emission behavior of single layer W(SxSe1-x)2 nanosheets (0 ≤ x ≤ 1) can be remarkably tuned by changing the sulfur content. The theoretical calculations proved that single layer W(SxSe1-x)2 alloy has a direct gap, and the band gap can be tuned by the sulfur content, which is in accordance with the spectral experiments. Moreover, we present temperature-dependent photoluminescence (PL) measurements in monolayers of W(SxSe1-x)2 alloys from 80 K to 320 K. The neutral exciton (X) and charged exciton (trion, T) can be observed at all measured temperatures. In sulfur-rich ternary W(SxSe1-x)2 alloys, the trion dominates the PL spectra at low temperatures while the exciton dominates the PL spectra at higher temperatures. In selenium-rich ternary alloys, however, the exciton is dominant in PL spectra at all measured temperatures. As the sulfur content gradually increases, the intensity ratio of the trion to exciton becomes dramatically larger. There is an obvious upward trend of the trion intensity in W(SxSe1-x)2 monolayers, which results from the significant growth of the two-dimensional electron gas (2DEG) concentration. On the other hand, the strong exciton-trion coupling mediated by an optical phonon also contributes to this improvement. These results indicate that exciton emission behavior of W(SxSe1-x)2 monolayers is controllable with the sulfur content. It highlights the importance of further detailed characterization on exciton features in ternary alloy nanosheets, and can enable spectral tunability for potential optoelectronic applications.

Synthesis and electrocatalytic properties for oxygen reduction of Pd4Fe nanoflowers.

Pd4Fe alloy nanoflowers with hierarchical nanosheet petals that mainly exposed the (111) crystal plane were prepared. The Pd4Fe nanoflowers possessed the advantage of hierarchical architectures and 2D alloy nanosheets simultaneously, with excellent catalytic performances for the oxygen reduction reaction.

Superaerophobic Ultrathin Ni-Mo Alloy Nanosheet Array from In Situ Topotactic Reduction for Hydrogen Evolution Reaction.

Hydrogen evolution reaction (HER) has prospect to becoming clean and renewable technology for hydrogen production and Ni-Mo alloy is among the best HER catalysts in alkaline electrolytes. Here, an in situ topotactic reduction method to synthesize ultrathin 2D Ni-Mo alloy nanosheets for electrocatalytic hydrogen evolution is reported. Due to its ultrathin structure and tailored composition, the as-synthesized Ni-Mo alloy shows an overpotential of 35 mV to reach a current density of 10 mA cm-2 , along with a Tafel slope of 45 mV decade-1 , demonstrating a comparable intrinsic activity to state-of-art commercial Pt/C catalyst. Besides, the vertically aligned assemble structure of the 2D NiMo nanosheets on conductive substrate makes the electrode "superaerophobic," thus leading to much faster bubble releasing during HER process and therefore shows faster mass transfer behavior at high current density as compared with drop drying Pt/C catalyst on the same substrate. Such in situ topotactic conversion finds a way to design and fabricate low-cost, earth-abundant non-noble metal based ultrathin 2D nanostructures for electrocatalytic issues.

Growth and optoelectronic property of two-dimensional semiconductors

Two-dimensional (2D) nanosheets of layered transition metal dichalcogenides (TMDs) have received significant attention because some of them are semiconductors with sizable band gaps and are naturally abundant. Here, we report the photolithographic-pattern transfer (PPT) technology used to fabricate FETs of two-dimensional materials. To explore the electrical properties and realize functional optoelectronics and electronics from semiconductors, the fabrication of devices (such as field-effect transistors (FET), diodes and Hall bars) and integrated circuits is necessary and important. An essential step in fabricating micro-/nanoelectronics is making the metal electrode arrays. Such a PPT method can be used to efficiently design and prepare complicated electrode arrays for electronics and optoelectronics, and is especially suitable for 2D materials. Few-layer MoS2 made by electron beam lithography (EBL), gold-wire mask moving (GWM), and this method are used as templates for comparison. The mobility of our thin MoS2 flake is comparable to the results of devices from EBL and better than the results of the GWM method. Further complicated device applications such as a top-gate FET, a Hall bar, and heterostructure transistors could also be easily realized based on such a method. We also report the growth and electric transport of Co doped MoS2 bilayer. As the initial loading of the sulfur increases, the morphology of the Co x Mo1– x S2 (0 x x Mo1− x S2 nanosheet gradually and forms hexagonal film induced by the nanosheet. Electrical transport measurements reveal that the Co x Mo1− x S2 nanosheets and CoS2 films exhibit n-type semiconducting transport behavior and half-metallic behavior, respectively. Theoretical calculations of their band structures agree well with the experimental results. These alloy nanosheets of Co x Mo1− x S2 should have large potential applications in the tunable optoelectronics. Then, we report the vapor phase growth and optoelectronic property of vertical bilayer SnS2/MoS2 heterostructure. 2D van der Waals heterostructures with different types of band alignment have recently attracted great attention due to their unique optical and electrical properties. Most 2D heterostructures are formed by transfer-stacking two monolayers together, but the interfacial quality and controllable orientation of such artificial structures are inferior to those epitaxial grown heterostructures. An extremely Type II band alignment exists in this 2D heterostructure, with band offset larger than any other reported. Consistent with the large band offset, distinctive optical properties including strong photoluminescence quenching in the heterostructure area are observed in the heterostructure. The SnS2/MoS2 heterostructures also exhibit well-aligned lattice orientation between the two layers, forming a periodic Moire superlattice pattern with high lattice mismatch. Electrical transport and photoresponsive studies demonstrate that the SnS2/MoS2 heterostructures exhibit an obvious photovoltaic effect and possess high on/off ratio (>106), high mobility (27.6 cm2 V−1 s−1) and high photoresponsivity (1.36 A W−1). Efficient synthesis of such vertical heterostructure may open up new realms in 2D functional electronics and optoelectronics. Finally we give some perspectives on studies of two-dimensional materials in future.

Synthesis of Ultrathin PdCu Alloy Nanosheets Used as a Highly Efficient Electrocatalyst for Formic Acid Oxidation.

Inspired by the unique properties of ultrathin 2D nanomaterials and excellent catalytic activities of noble metal nanostructures for renewable fuel cells, a facile method is reported for the high-yield synthesis of ultrathin 2D PdCu alloy nanosheets under mild conditions. Impressively, the obtained PdCu alloy nanosheet after being treated with ethylenediamine can be used as a highly efficient electrocatalyst for formic acid oxidation. The study implicates that the rational design and controlled synthesis of an ultrathin 2D noble metal alloy may open up new opportunities for enhancing catalytic activities of noble metal nanostructures.

Topotactic reduction of layered double hydroxides for atomically thick two-dimensional non-noble-metal alloy

Layered double hydroxides (LDHs) have been widely used as catalysts owing to their tunable structure and atomic dispersion of high-valence metal ions; however, limited tunability of electronic structure and valence states have hindered further improvement in their catalytic performance. Herein, we reduced ultrathin LDH precursors in situ and topotactically converted them to atomically thick (~2 nm) two-dimensional (2D) multi-metallic, single crystalline alloy nanosheets with highly tunable metallic compositions. The as-obtained alloy nanosheets not only maintained the vertically aligned ultrathin 2D structure, but also inherited the atomic dispersion of the minor metallic compositions of the LDH precursors, even though the atomic percentage was higher than 20%, which is far beyond the reported percentages for single-atom dispersions (usually less than 0.1%). Besides, surface engineering of the alloy nanosheets can finely tune the surface electronic structure for catalytic applications. Such in situ topotactic conversion strategy has introduced a novel approach for atomically dispersed alloy nanostructures and reinforced the synthetic methodology for ultrathin 2D metal-based catalysts.

Ni−Zn Alloy Nanosheets Arrayed on Nickel Foamas a Promising Catalyst for Electrooxidation of Hydrazine

AbstractThe development of cost‐effective electrocatalysts is a key issue to promote the practical application of hydrazine as a viable energy carrier. Herein, a nickel‐foam‐supported Ni−Zn alloy catalyst is synthesized by electrodeposition and anodic dissolution methods. The developed catalyst with an opennanowall network structure and robust adhesion exhibits high activity and good durability for electrooxidation of hydrazine in an alkaline medium. For example, a current density of 300 mA cm−2at 0.40 Vand an onset potential of −0.15 V vs. the reversible hydrogen electrode are achieved in a 0.10 M hydrazine and 1.0 M NaOH solution at 30 °C. Phase and structure analysis by XRD, SEM, and XPS is conducted to gain insight into the excellent catalytic performance of theNi−Zn alloy catalyst. Such an understanding is of particular importance in the design of efficient non‐precious catalysts.

Hydrogen sensor based on palladium-yttrium alloy nanosheet

This paper presents a hydrogen sensor based on palladium-yttrium (Pd-Y) alloy nanosheet. Zigzag-shaped Pd-Y nanosheet with a thickness of 19.3 nm was deposited on a quartz substrate by using an ultrahigh-vacuum magnetron sputtering system and shadow mask. The atomic ratio of palladium to yttrium in the nanosheet was 0.92/0.08. The fabrication process was simple and low-cost, and the sensor can be mass-produced. The experimental results show the sensor has a superior sensitivity, reversibility, and reproducibility. The resistive-based hydrogen detection mechanism in this research is much simpler and more compact compared to the optical-based detection method.

Self-Supported 3D PdCu Alloy Nanosheets as a Bifunctional Catalyst for Electrochemical Reforming of Ethanol.

3D PdCu alloy nanosheets exhibit enhanced electrocatalytic activity toward hydrogen evolution reaction and ethanol oxidation reaction in alkaline media. Simultaneous hydrogen and acetate production via a solar-powered cell for ethanol reforming has been fabricated using the nanosheets as bifunctional electrocatalysts. The device is promising for the production of both hydrogen and value-added chemicals using renewable energy.

In situ confined synthesis of molybdenum oxide decorated nickel–iron alloy nanosheets from MoO42− intercalated layered double hydroxides for the oxygen evolution reaction

This work reports molybdenum oxide decorated NiFe alloy nanosheets with high OER activity by reducing MoO42− intercalated nickel–iron layered double hydroxides (LDHs).

Single Crystalline Ultrathin Nickel-Cobalt Alloy Nanosheets Array for Direct Hydrazine Fuel Cells.

Ultrathin 2D metal alloy nanomaterials have great potential applications but their controlled syntheses are limited to few noble metal based systems. Herein Ni x Co1-x alloy nanosheets with ultrathin (sub-3 nm) single-crystalline 2D structure are synthesized through a topochemical reduction method. Moreover, the optimized composition Ni0.6Co0.4 alloy nanosheets array exhibits excellent performances for hydrazine oxidation reaction and direct hydrazine fuel cells.

Synthesis and optoelectronic properties of quaternary GaInAsSb alloy nanosheets

Quasi-one-dimensional (1D) nanostructures have been extensively explored for electronic and optoelectronic devices on account of their unique morphologies and versatile physical properties. Here, we report the successful synthesis of GaInAsSb alloy nanosheets by a simple chemical vapor deposition method. The grown GaInAsSb alloy nanosheets are pure zinc-blende single crystals, which show nanosize-induced extraordinary optoelectronic properties as compared with bulk materials. μ-Raman spectra exhibit a multi-mode phonon vibration behavior with clear frequency shifts under varied laser power. Photoluminescence measurements reveal a strong light emission in the near-infrared region (1985 nm), and the obtained Varshni thermal coefficients α and β are smaller than those of the bulk counterparts due to the size confinement effect. In addition, photodetectors (PDs) based on these single-alloy nanosheets were constructed for the first time. The PDs show a strong response in the near-infrared region with the external quantum efficiency of 8.05 × 104%, and the responsivity of 0.675 × 103 A W−1. These novel nanostructures would make contributions to the study of fundamental physical phenomena in quasi-1D nanomaterial systems and can be potential building blocks for optoelectronic and quantum devices.

Electrochemical fabrication of porous Ni-Cu alloy nanosheets with high catalytic activity for hydrogen evolution

Porous Ni-Cu alloy films composed of nanosheets are directly fabricated on Cu substrate using a facile potentiostatic electrodeposition approach from a 1:2 choline chloride-ethylene glycol eutectic solvent (ethaline) containing nickel chloride and copper chloride. Electrochemical co-deposition of Ni-Cu alloy in ethaline is found to be thermodynamically favorable in comparison to conventional aqueous solutions. The deposition process occurs via an instantaneous nucleation and growth of nanoparticles at the initial stage and develops vertically to form nanoporous structures arrayed with nanosheets over deposition time. The as-prepared porous Ni-Cu alloy nanosheet arrays exhibit enhanced electrocatalytic activity for the hydrogen evolution reaction (HER) in alkaline media, which displays a small Tafel slope of 57.2mVdec−1 with a low onset potential of −48mV vs. RHE at an optimal condition. It requires small overpotentials of −128 and −150mV to drive catalytic current densities of 10 and 20mAcm−2, respectively. This facile electrodeposition method performed in ethaline provides an efficient way to fabricate porous Ni-based alloy nanosheets directly on a current collector, which is a promising technology for the synthesis of earth-abundant HER electrocatalysts.

Carbon‐Monoxide‐Assisted Synthesis of Ultrathin PtCu Alloy Nanosheets and Their Enhanced Catalysis

AbstractUltrathin PtCu alloy nanosheets are synthesized by a facile, one‐pot, templateless hydrothermal method with the use of carbon monoxide (CO) as the capping agent. Due to their unique structure and possible synergetic effect, the ultrathin nanosheets show higher catalytic activity in hydrogen evolution and hydrogenation reactions. The developed method is also expected to generate exciting opportunities in creating ultrathin nanostructures with a wide range of alloy compositions for various catalytic applications.