Alloy Nanotubes Research Articles

Boosted Electron-Transfer Kinetics of Hydrogen Evolution Reaction at Bimetallic RhCo Alloy Nanotubes in Acidic Solution.

RhCo alloy nanotubes were synthesized via the reduction of single-phase Co2RhO4 nanotubes. The reduction was conducted by thermal annealing of the Co2RhO4 nanotubes under hydrogen gas flow. The crystallinity of the prepared RhCo alloy nanotubes depended on the reduction temperature: amorphous phase (200 °C reduction) and the crystalline phase (300 °C reduction). The hydrogen evolution reaction (HER) on RhCo alloys was investigated with voltammetry in 1.0 M HClO4 solution. Amorphous RhCo alloys provided lower overpotential than the crystalline counterpart despite their similar morphology and composition. Of great interest, amorphous RhCo alloy nanotubes exhibited an outstanding HER electroactivity verified with a low overpotential at -10 mA cm-2 (-22 mV) and a small Tafel slope (-24.1 mV dec-1), outperforming commercial Pt, pure Rh metal, and the other previously reported Rh-based catalysts. This excellent HER activity of amorphous RhCo nanotubes was attributed to the amorphous structure having a large electrochemical surface area and maximized Rh-Co interfaces in the alloy facilitating HER. Active but expensive Rh alloyed with less active but cheap Co was successfully demonstrated as a potential cost-effective HER catalyst.

Composition-dependent electrochemical activity of Ag-based alloy nanotubes for efficient nitrogen reduction under ambient conditions

The composition-activity relationship is highly desirable for electrocatalytic nitrogen reduction reaction (NRR) because it could guide the rational design of efficient NRR catalysts. In this work, the composition effect of Ag-based alloy nanotubes on electrocatalytic NRR activity is systematically investigated. It is found that, among AgAu nanotubes with atomic ratio from 8:1 to 1:2, Ag2Au1 alloy nanotubes achieve the largest enhancement for NRR catalytic activity. Specifically, the NH3 production rate and faradaic efficiency of Ag2Au1 nanotubes are 21.7 μg h−1 mgcat−1 and 3.8% at −0.30 V vs. RHE, respectively, which were 3.0 and 3.6 times higher than those of Ag nanowires. Compared with Ag2Pd1 and Ag2Pt1 nanotubes, Ag2Au1 hollow nanotubes also exhibit a better NRR catalytic activity. Theoretical calculation results indicate that the negative ion characteristic of Au atoms in the Ag2Au1 alloy is favorable for the adsorption and activation of N2. Moreover, Ag2Au1 nanotubes showed stable NH3 yield rate and faradaic efficiency up to 18 h, revealing its great potential for promising NRR electrocatalysis.

Correlation between structural and magnetic properties of FeNi nanotubes with different lengths

Fe20Ni80 alloy nanotubes with different lengths of 3 μm, 6 μm, 9 μm, 12 μm and with “caps” were formed using template synthesis in the pores of PET membranes. The “caps” begin to form over individual nanostructures due to uneven growth, when some tubes reach the template surface before the others at the end of active growth stage. The influence of growth mechanism at different formation stages on the nanotube structure and morphology as well as the correlation between their structural properties and magnetic behavior of arrays were comprehensively studied. The structural parameters (crystallinity degree, lattice parameter and microstresses) were demonstrated as a dependence on the nanotubes length. The structural and magnetic correlations with the processes taking place at various stages of nanotubes evolving from nucleation to active growth and to “caps” formation were analyzed. With increasing the nanotube length, the magnetization reversals in parallel and perpendicular magnetic field directions substantially differ which is explained by the formation of easy anisotropy direction of a helical type. The considerable contribution of “caps” to the magnetic properties of nanotubes was demonstrated for the first time.

NiFe Alloy Nanotube Arrays as Highly Efficient Bifunctional Electrocatalysts for Overall Water Splitting at High Current Densities.

A bubble-releasing assisted pulse electrodeposition method was developed to create metallic alloy, NiFe, nanotube arrays in one step. The NiFe alloy nanotube array exhibited excellent bifunctional electrolytic activities, achieving low overpotentials of 100 mV for the hydrogen evolution reaction and 236 mV for the oxygen evolution reaction at 10 mA cm-2, both in 1 M KOH at room temperature. For overall water splitting, the NiFe alloy nanotube array delivered 10 mA cm-2 at an ultralow cell voltage of 1.58 V, among the top tier of the state-of-the-art bifunctional electrocatalysts. The NiFe alloy nanotube array also exhibited ultrastability at high current densities, experiencing only a minor chronoamperometric decay of 6.5% after a 24 h operation at 400 mA cm-2. The success of the present binder-free nanotube array-based electrode can be attributed to the much enlarged reaction surface area, one-dimensionally guided charge transport and mass transfer offered by the nanotube structure, and improved product crystallinity provided by the pulse current electrodeposition. The nanotube array structure proves to be a promising new architecture design for electrocatalysts.

Synergy between Plasmonic and Electrocatalytic Activation of Methanol Oxidation on Palladium–Silver Alloy Nanotubes

AbstractLocalized surface plasmon resonance (LSPR) excitation of noble metal nanoparticles has been shown to accelerate and drive photochemical reactions. Here, LSPR excitation is shown to enhance the electrocatalysis of a fuel‐cell‐relevant reaction. The electrocatalyst consists of PdxAg alloy nanotubes (NTs), which combine the catalytic activity of Pd toward the methanol oxidation reaction (MOR) and the visible‐light plasmonic response of Ag. The alloy electrocatalyst exhibits enhanced MOR activity under LSPR excitation with significantly higher current densities and a shift to more positive potentials. The modulation of MOR activity is ascribed primarily to hot holes generated by LSPR excitation of the PdxAg NTs.

Synergy between Plasmonic and Electrocatalytic Activation of Methanol Oxidation on Palladium-Silver Alloy Nanotubes.

Localized surface plasmon resonance (LSPR) excitation of noble metal nanoparticles has been shown to accelerate and drive photochemical reactions. Here, LSPR excitation is shown to enhance the electrocatalysis of a fuel-cell-relevant reaction. The electrocatalyst consists of Pdx Ag alloy nanotubes (NTs), which combine the catalytic activity of Pd toward the methanol oxidation reaction (MOR) and the visible-light plasmonic response of Ag. The alloy electrocatalyst exhibits enhanced MOR activity under LSPR excitation with significantly higher current densities and a shift to more positive potentials. The modulation of MOR activity is ascribed primarily to hot holes generated by LSPR excitation of the Pdx Ag NTs.

Composition- and shape-controlled synthesis of the PtNi alloy nanotubes with enhanced activity and durability toward oxygen reduction reaction

The development of the fuel cell catalysts with high durability and high activity for oxygen reaction reduction remains a great challenge. Various material designs such as alloys, core@shell structure and shape control provide the promising ways to improve the electrocatalytic performance. Herein, on the basis of both the alloy effect and the nanotube structure effect, we demonstrate a high-performance PtNi alloy catalyst with one-dimensional nanotube structure via a galvanic replacement reaction combined with Kirkendall effect. Meanwhile, the PtNi alloy phase and the tube structure are selectively controlled by tuning the PtNi atomic ratio and the wall thickness of the nanotube, respectively. Subsequently, the understanding of the composition effect and the shape effect on the activity and the durability is systematically investigated. The optimized PtNi nanotube catalyst shows significant improvements on the activity (6.2-fold increase in specific activity compared to the commercial Pt/C) and the durability (only 8.6% loss in mass activity after 10000 cycles), attributing to the alloy effect by introducing Ni to the Pt lattice, the Pt-rich surface and the shape effect of the unique one-dimensional hollow tube structure.

Energy-saving hydrogen production coupling urea oxidation over a bifunctional nickel-molybdenum nanotube array

Hydrogen production via water electrolysis is promising but impeded by sluggish cathodic and anodic reactions. Consequently, highly-efficient and earth-abundant electrocatalysts are attracting considerable attention. Herein we report a bifunctional NiMo alloy nanotube for efficient hydrogen production coupled with anodic urea oxidation in a hybrid water electrolysis system. Specifically, ultralow potentials of −44 mV and 1.36 V (vs. RHE) are required to deliver 10 mA cm−2 current density for cathodic and anodic reactions, respectively. Density functional theory (DFT) calculation results show the Mo center is the main reaction site for the chemisorption and OH bond cleavage of H2O while Ni center is identified as the hydrogen-evolving site. Based on this bifunctional NiMo electrocatalyst, a hybrid water electrolysis cell is proposed and the overall cell voltage of ∼1.43 V is achieved for outputting 10 mA cm−2 current density during the 10 h operation. The understandings in alternative electrode reactions coupled with highly-efficient and earth-abundant electrocatalysts for hybrid water electrolysis in this work holds encouraging potential in future energy conversion technologies and urea-related water treatments.

Structural Stability and Electronic and Optical Properties of Coinage-Metal (4, 2) Alloy Nanotubes: A First-Principles Study

Using first-principles calculations, we have systematically investigated the structural stability and the electronic and optical properties of bimetallic Ag−Au, Cu−Au, and Cu−Ag (4, 2) alloy nanotubes (NTs). We found that the tip-suspended Ag−Au and Cu−Au alloy NTs were stable structures due to the existence of local minima in both the binding energies and the string tensions variation with their unit-cell lengths and that the stability was enhanced when the content of Au was increased. However, a tip-suspended Cu−Ag alloy NT would be difficult to form in future experiments. We also found that both the relativistic effect of elemental gold and the string tension applied by the tip contacts play important roles in suppressing effectively the self-purification effect, leading to the formation of these coinage alloy NTs. The quantum conductance of the stable alloy NTs is increased by 1G0 as compared with that of the corresponding pure coinage-metal NTs.

High-Performance Non-enzymatic Glucose Sensors Based on CoNiCu Alloy Nanotubes Arrays Prepared by Electrodeposition

Transition metal alloys are good candidate electrodes for non-enzymatic glucose sensors due to their low cost and high performance. In this work, we reported the controllable electrodeposition of CoNiCu alloy nanotubes electrodes using anodic aluminum oxide (AAO) as template. Uniform CoNiCu alloy arrays of nanotubes about 2 μm in length and 280 nm in diameter were obtained by optimizing the electrodeposition parameters. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) measurements indicated that the as-prepared alloy nanotubes arrays are composed of 64.7 wt% Co-19.4 wt% Ni-15.9 wt% Cu. Non-enzymatic glucose sensing measurements indicated that the CoNiCu nanotubes arrays possessed a low detection limit of 0.5 μM, a high sensitivity of 791 μA mM −1 cm −2 from 50 to 1,551 μM and 322 μA mM −1 cm −2 from 1,551 to 4,050 μM. Besides, they showed high reliability with the capacity of anti-jamming. Tafel plots showed that alloying brought higher exchange current density and faster reaction speed. The high performance should be due to the synergistic effect of Co, Ni, and Cu metal elements and high surface area of nanotubes arrays.

Recent Advances on Controlled Synthesis and Engineering of Hollow Alloyed Nanotubes for Electrocatalysis.

The past decade has witnessed great progress in the synthesis and electrocatalytic applications of 1D hollow alloy nanotubes with controllable compositions and fine structures. Hollow nanotubes have been explored as promising electrocatalysts in the fuel cell reactions due to their well-controlled surface structure, size, porosity, and compositions. In addition, owing to the self-supporting ability of 1D structure, hollow nanotubes are capable of avoiding catalyst aggregation and carbon corrosion during the catalytic process, which are two other issues for the widely investigated carbon-supported nanoparticle catalysts. It is currently a great challenge to achieve high activity and stability at a relatively low cost to realize commercialization of these catalysts. An overview of the structural and compositional properties of 1D hollow alloy nanotubes, which provide a large number of accessible active sites, void spaces for electrolytes/reactants impregnation, and structural stability for suppressing aggregation, is presented. The latest advances on several strategies such as hard template and self-templating methods for controllable synthesis of hollow alloyed nanotubes with controllable structures and compositions are then summarized. Benefiting from the advantages of the unique properties and facile synthesis approaches, the capability of 1D hollow nanotubes is then highlighted by discussing examples of their applications in fuel-cell-related electrocatalysis. Finally, the remaining challenges and potential solutions in the field are summarized to provide some useful clues for the future development of 1D hollow alloy nanotube materials.

Efficiency of nanoparticle reinforcement using finite element analysis of titanium alloy mandible plate.

Nanoparticles in the form nanotubes and nanoplatelets have been compared for von Mises stresses by using them as low-composition reinforcements in titanium alloy-based mandible plate for different compositions and orientations. A finite element model has been designed to reconstruct a fractured human mandible with a titanium alloy mandible plate. A 500 N compressive force was applied on the mandible, and stress distribution across the plate sections was analysed for aligned two-dimensional random and three-dimensional random orientations for both tubes and platelets. Carbon material as graphene has been used for tube and platelet in the form of nanotubes and nanoplatelets, respectively. Using properties of graphene as the filler in titanium alloy plate, for both nanoplatelets and nanotubes, the stresses reduced between 5% and 25% for nanoplatelets and nanotubes graphene-titanium composite plates in comparison to non-reinforced plates, at critically stressed sections. Nanotubes exhibited stress reduction of nearly 23.4% for aligned configurations, while nanoplatelets exhibited stress reduction up to 21.2% for two-dimensional and three-dinemsional random configurations in comparison to non-reinforced titanium plates. Hence, it has been suggested that nanotubes exhibited superior mechanical reinforcement potential beyond that of aligned nanoplatelets, while nanoplatelets provided enhanced mechanical reinforcements for random configurations. Therefore, for biomedical implant applications nanocomposite materials can be designed with the same dimensional form but with lower compositions of filler materials by simply manipulating the appropriate orientations.

The promoted catalytic hydrogenation performance of bimetallic Ni-Co-B noncrystalline alloy nanotubes.

A noncrystalline Ni–B alloy in the shape of nanotubes has demonstrated its superior catalytic performance for some hydrogenation reactions. Remarkable synergistic effects have been observed in many reactions when bimetallic catalysts were used; however, bimetallic noncrystalline alloy nanotubes are far less investigated. Here, we report a simple acetone-assisted lamellar liquid crystal approach for synthesizing a series of bimetallic Ni–Co–B nanotubes and investigate their catalytic performances. The dilution effect of acetone on liquid crystals was characterized by small-angle X-ray diffraction (SAXRD) and scanning electron microscopy (SEM). The Ni/Co molar ratio of the catalyst was varied to study the composition, porous structure, electronic interaction, and catalytic efficiency. In the liquid-phase hydrogenation of p-chloronitrobenzene, the as-prepared noncrystalline alloy Ni–Co–B nanotubes exhibited higher catalytic activity and increased stability as compared to Ni–B and Co–B alloy nanotubes due to electronic interactions between the nickel and cobalt. The excellent hydrogenation performance of the Ni–Co–B nanotubes was attributed to their high specific surface area and the characteristic confinement effects, compared with Ni–Co–B nanoparticles.

Porous PtPd alloy nanotubes: towards high performance electrocatalysts with low Pt-loading

Porous PtPd alloy nanotubes with Pt contents down to 5 at% are powerful, Pt-lean electrocatalysts.

Ultrathin Pt–Ag Alloy Nanotubes with Regular Nanopores for Enhanced Electrocatalytic Activity

While creating open nanostructures represents a popular strategy for improving the utilization efficiency of Pt-based catalysts for electrochemical reactions, the exposed facets should be precisely controlled for further enhancement of the catalytic activity. Here, we report a novel strategy for creating regularly shaped nanopores in ultrathin nanotubes of bimetallic noble metals. By templating against Ag nanowires and then applying a thermal ripening process, we have successfully produced ultrathin (with a wall thickness of ∼1 nm) Pt–Ag alloy nanotubes containing high-density well-defined rectangular nanopores and a collapsed double-layer structure. The resulting porous nanotubes expose {100} facets at the basal sides and {110} facets with step sites at the edges of the rectangular nanopores. The particular surface structure and the bimetallic composition enable suppressed CO poisoning of the catalysts and consequently enhanced electrocatalytic activity in the methanol oxidation reaction. The typical spe...

PdAg@Pd core-shell nanotubes: Superior catalytic performance towards electrochemical oxidation of formic acid and methanol

The catalytic activity of alloy nanomaterials can be well modulated through the electrochemical dissolution of the more active component from alloy nanomaterials. In this paper, PdAg alloy nanotubes of diverse Pd to Ag ratio are prepared by galvanic displacement electrochemical reaction. The Ag-leached PdAg nanotubes are characterized by cyclic voltammetric scans, high-angle annular dark-field scanning transmission electron spectroscopy, energy dispersive X-ray elemental mapping and X-ray photoelectron spectroscopy measurements and demonstrate the formation of PdAg@Pd core-shell nanotubes structure with roughed surface and largely enhanced electrochemical surface area. The PdAg@Pd core-shell nanotubes show significantly enhanced catalytic activities and durability towards electro-oxidation of formic acid and methanol than the as-prepared PdAg nanotubes, with the mass activity and specific activity of 1.93 A mg−1 and 2.67 mA cm−2 towards formic acid respectively, which are 7.8 and 4.8 times that of Pd/C. The increased catalytic performance is ascribed to the unique surface and electronic structure of PdAg@Pd core-shell nanotubes.

TePbPt alloy nanotube as electrocatalyst with enhanced performance towards methanol oxidation reaction

In this study, a ternary TePbPt alloy nanotube (NT) catalyst was designed based on the following rational considerations.

Galvanic exchange-formed ultra-low Pt loading on synthesized unique porous Ag-Pd nanotubes for increased active sites toward oxygen reduction reaction

Development of an inexpensive high performance catalyst with low Pt loading remains a great challenge. Herein galvanic exchange-formed ultra-low Pt loaded porous Ag-Pd binary alloy nanotubes (Pt/Ag-Pd) was prepared as a catalyst toward oxygen reduction reaction (ORR). With highly dispersed active but ultra-low Pt atoms (Pt: about 5.8 wt%) on the porous binary alloy surface, the Pt/Ag-Pd catalyst increases mass activity toward ORR by 1.82 times than commercial Pt/C while possessing excellent operation stability. The performance enhancement is mainly attributed to the unique porous Pt shell/Ag-Pd core tubular structure for increased active sites and facilitated interfacial electron transfer rate by a unique Ag-Pd jointly modified electronic structure. This catalyst holds great promise for practical applications in low temperature fuel cells.

Magnetic compensation and critical properties of a mixed spin-(2, 3/2) Heisenberg single-walled nanotube superlattice

In recent years, some theoretical interests have been focused on the binary alloy nanotubes and nanowires with mixed spins. Compared with ferrimagnetic nanowires, few studies have been done on ferrimagnetic nanotubes. In this paper, the magnetic properties of a mixed spin-(2, 3/2) Heisenberg single-walled nanotube superlattice are calculated by use of the double-time Green’s function method within the random phase approximation and the Anderson and Callen’s decoupling. Magnetic compensation and critical properties are obtained for a wide range of parameters in the Hamiltonian, and magnetic phase diagrams are plotted in the related planes. For Heisenberg single-walled nanotube superlattice model with Néel-type magnetic structure, anisotropy must be taken into account, and the easy-axis single-ion anisotropy is considered in this paper. The next nearest neighbor exchange interactions Jbb and/or single-ion anisotropy strength Db of the smaller spin sublattice were necessary in order to obtain a compensation point. The influence of the wall diameter number of the tubes, m, an important parameter of the system, on the compensation behavior is considered. Calculation shows that as Jbb and Db are fixed, only when m is beyond a certain minimum value, mmin, can compensation temperature Tcom appears, where the next nearest neighbor exchange interactions Jaa and single-ion anisotropy strength Da of the larger spin sublattice are absent. The compensation temperature and critical temperature increase with m rising, which indicates that the longitudinal correlation effect is enhanced and the fluctuation effect is weakened with the increase of m.

Polarization-dependent fluorescence of CdSe/ZnS quantum dots coupling to a single gold-silver alloy nanotube

The fluorescence intensities of CdSe/ZnS quantum dots on a silver nanowire and a gold-silver alloy nanotube with different molar ratios of gold and silver are investigated under excitation with different polarization angles. The ratio of the fluorescence intensity of perpendicular and parallel polarization excitations is measured to be 4.05 for a silver nanowire and decreases to 1.30, 1.10 and 1.07 for nanotube with Au:Ag molar ratios of 1:4.0, 1:2.5 and 1:1.5, respectively. The numerical simulation results show that the aforementioned experimental phenomena can be attributed to the variation in the distribution of the surface plasmon electromagnetic field under perpendicular polarized light excitation. The electromagnetic field is primarily distributed on the outer surface of the silver nanowire, while the field partially penetrates the interior of the silver nanotube and becomes completely concentrated at the interior of the gold nanotube. This research also found that the productivity and robustness of the chemical synthesis of the alloy nanotubes can be greatly improved by using a microwave reactor.