Binary Solid Solutions Research Articles

Understanding the bond-energy, hardness, and adhesive force from the phase diagram via the electron work function

Properties of metallic materials are intrinsically determined by their electron behavior. However, relevant theoretical treatment involving quantum mechanics is complicated and difficult to be applied in materials design. Electron work function (EWF) has been demonstrated to be a simple but fundamental parameter which well correlates properties of materials with their electron behavior and could thus be used to predict material properties from the aspect of electron activities in a relatively easy manner. In this article, we propose a method to extract the electron work functions of binary solid solutions or alloys from their phase diagrams and use this simple approach to predict their mechanical strength and surface properties, such as adhesion. Two alloys, Fe-Ni and Cu-Zn, are used as samples for the study. EWFs extracted from phase diagrams show same trends as experimentally observed ones, based on which hardness and surface adhesive force of the alloys are predicted. This new methodology provides an alternative approach to predict material properties based on the work function, which is extractable from the phase diagram. This work may also help maximize the power of phase diagram for materials design and development.

YCeZrO Ternary Oxide Solid Solution Supported Nonplatinic Lean-Burn NOx Trap Catalysts Using LaCoO3 Perovskite as Active Phase

A series of nonplatinic ceria-based oxides supported catalysts LaCoO3/K2CO3/S (S=CeO2, Ce0.75Zr0.25O2 or 5%Y/Ce0.75Zr0.25O2) were prepared by successive impregnation and employed for lean-burn NOx trapping. It is found that the doping of Zr or YZr into CeO2 facilitates the formation of CeZrO binary or YCeZrO ternary solid solutions, increasing the specific surface area and improving the redox property of ceria. The results of EXAFS and H2-TPR reveal that the LaCoO3 in the solid solution supported catalysts possesses higher dispersion and better reducibility than that in CeO2 supported one. The result of O2-TPD shows that the surface active oxygen species are remarkably increased after loading LaCoO3 on the supports. The YCeZrO ternary solid solution supported catalyst containing 5 wt % K2CO3 exhibits the best performance for NO oxidation and reduction at 350 °C, showing a high NO-to-NO2 conversion (66.5%) at lean condition, and a very high NOx reduction percentage (98.2%) and an extremely high NOx-to-N2 s...

First-principles calculations of finite-temperature thermodynamic properties of binary solid solutions in the Al–Cu–Mg system

Based on first-principles calculations in terms of the 16-atom special quasirandom structures (SQSs), enthalpy of mixing at 0K as well as thermodynamic properties, including Gibbs energy of mixing, enthalpy of mixing, and entropy of mixing (ΔG, ΔH, ΔS), have been investigated for the binary solid solutions in the Al–Cu–Mg system. The targeted binary solid solutions include fcc, bcc, hcp phases in the Al–Cu, Al–Mg, and Cu–Mg systems. For the Al–Cu system, the present first-principles predictions are in good agreement with the experimental data and the CALculation of PHAse Diagram (CALPHAD) modeling results. For the Al–Mg and Cu–Mg systems, where the reliable experimental information is not available, it is expected that the presently predicted thermodynamic properties could yield a helpful insight into the phase stabilities in these two systems, in particular for the metastable phases.

Ferroelectric and piezoelectric properties of high temperature perovskite-type 0.69BiFeO3–0.02Bi(Mg1/2Ti1/2)O3–0.29BaTiO3 ceramics

Lead-free high-temperature piezoceramics of MnO2-doped 0.69BiFeO3–0.02Bi(Mg1/2Ti1/2)O3–0.29BaTiO3 (BF69–BMT2–BT29) were prepared with solid state reaction method. Those ceramics were crystallized in a pure pseudocubic perovskite-structured phase. In contrast to high dielectric loss BF–BT binary solid solution ceramics, low dielectric loss ceramics were obtained here with combined strategies of refined electroceramic processing, Mn-doping and adding BMT third member. Ferroelectric and piezoelectric properties were systematically measured. Here, the 0.30 wt% MnO2-doped BF69–BMT2–BT29 ceramics sintered at 900 °C for 10 h showed a better combination of ferroelectric and piezoelectric properties than those BiFeO3–BaTiO3 piezoceramics.

Local polar structure and multiferroic properties of (1−x)Bi0.9Dy0.1FeO3−xPbTiO3 solid solution

The multiferroic (1–x)[0.9BiFeO3–0.1DyFeO3]–xPbTiO3 (BDF–xPT) solid solution with compositions around the morphotropic phase boundary (x = 0.25, 0.28, 0.31, 0.34, and 0.37) has been synthesized in the form of ceramics. The phase symmetry, microstructure, ferroelectricity, piezoresponse, and ferromagnetic properties have been characterized by various techniques. It is found that, with increasing content of lead titanate from x = 0.25 to x = 0.37, the grain size increases and the ferroelectric property is improved. The ferroelectric performance is further enhanced by the introduction of an excess amount (2%) of TiO2 or by sintering in oxygen atmosphere, which reduces the leakage. The local polar structure is imaged by piezoresponse force microscopy. Both the out-of-plane and in-plane images reveal distinct ferroelectric domain structures, with the amplitude and the average domain size decreasing with the increase of lead titanate amount. Compared with the (1–x)BiFeO3–xPbTiO3 binary solid solution of about the same concentration of PT, the magnetic properties are enhanced in BDF–xPT due to the presence of dysprosium, as demonstrated by the ferromagnetic hysteresis loops displayed at room temperature and at 10 K, but the remnant magnetization decreases with increasing PT content. The simultaneous presence of ferroelectricity and ferromagnetism entitles the BDF–xPT solid solution a room-temperature multiferroic material.

Interdiffusion and impurity diffusion in polycrystalline Mg solid solution with Al or Zn

Interdiffusion and impurity diffusion in Mg binary solid solutions, Mg(Al) and Mg(Zn) were investigated at temperatures ranging from 623 to 723K. Interdiffusion coefficients were determined via the Boltzmann–Matano Method using solid-to-solid diffusion couples assembled with polycrystalline Mg and Mg(Al) or Mg(Zn) solid solutions. In addition, the Hall method was employed to extrapolate the impurity diffusion coefficients of Al and Zn in pure polycrystalline Mg. For all diffusion couples, electron microprobe analysis was utilized for the measurement of concentration profiles. The interdiffusion coefficient in Mg(Zn) was higher than that of Mg(Al) by an order of magnitude. Additionally, the interdiffusion coefficient increased significantly as a function of Al content in Mg(Al) solid solution, but very little with Zn content in Mg(Zn) solid solution. The activation energy and pre-exponential factor for the average effective interdiffusion coefficient in Mg(Al) solid solution were determined to be 186.8 (±0.9)kJ/mol and 7.69×10−1 (±1.80×10−1)m2/s, respectively, while those determined for Mg(Zn) solid solution were 139.5 (±4.0)kJ/mol and 1.48×10−3 (±1.13×10−3)m2/s. In Mg, the Zn impurity diffusion coefficient was an order of magnitude higher than the Al impurity diffusion coefficient. The activation energy and pre-exponential factor for diffusion of Al impurity in Mg were determined to be 139.3 (±14.8)kJ/mol and 6.25×10−5 (±5.37×10−4)m2/s, respectively, while those for diffusion of Zn impurity in Mg were determined to be 118.6 (±6.3)kJ/mol and 2.90×10−5 (±4.41×10−5)m2/s.

Cl-RICH FLUORAPATITE, DEVOID OF OH, FROM THE THREE PEAKS AREA, UTAH: THE FIRST REPORTED STRUCTURE OF NATURAL Cl-RICH FLUORAPATITE

Abstract Apatite is the most abundant phosphate mineral on Earth and forms the foundation of the global phosphorus cycle. Interest in apatite crosses many disciplines, including geology, agriculture, material science, dentistry, and medicine, and the phase is also used extensively in many manufacturing processes. Apatite is the main source of phosphate for fertilizer, and adequate sources of apatite are essential for production of fertilizers that are necessary for feeding the world’s population. Despite the importance of the phase, the atomic arrangement of apatite is not well understood. The natural apatite anion solid solution among F, OH, and Cl (fluorapatite, hydroxylapatite, and chlorapatite, respectively) is one of those rare solid solutions wherein the atomic arrangements of the binary and ternary solid solutions are not predictable from the atomic arrangements of the endmembers of the ternary system; the steric interactions in the (F, OH, Cl) apatite anion column are complex as the three anions mix. Although the first detailed account of the atomic arrangement of binary apatites along the F-Cl join was recently reported using painstakingly synthesized samples, natural Cl-rich fluorapatite, although long-sought, had not been identified; an Earth environment that has high fugacity of F and Cl, but is devoid of OH, is rare. Here we report the atomic arrangement of a natural Cl-rich fluorapatite from the Three Peaks area of Utah (USA) that is essentially devoid of OH. The structure ( R 1 = 0.0145) of the P 6 3 / m apatite is similar to that obtained from synthetic samples, and demonstrates that solid solution along the F–Cl join in natural apatites is achieved by creation of a second F site (F b ) in the Cl-rich fluorapatite [0, 0, z ] anion column, an off-mirror site at z = 0.178, coupled with the presence of a site for Cl (Cl b ), that differs from the Cl site in endmember chlorapatite. The combination of a Cl site that relaxes toward its associated mirror plane and a neighboring F site that relaxes away from its associated mirror plane allows sufficient separation of F and Cl in the anion column for the two anions to coexist. The structure described herein is the first reported structure of a natural Cl-rich fluorapatite.

The Dy–Ni–Si system as a representative of the rare earth–Ni–Si family: Its isothermal section and new rare-earth nickel silicides

The Dy–Ni–Si system has been investigated at 1070K by X-ray and microprobe analysis. The system contains the 12 known compounds DyNi10Si2, DyNi5Si3, DyNi6Si6, DyNi4Si, DyNi2Si2, Dy2Ni3Si5, DyNiSi3, Dy3Ni6Si2, DyNiSi2, DyNiSi, Dy3NiSi3, Dy3NiSi2, and the new compounds Dy34Ni16−27Si50−39 (AlB2-type), Dy2Ni15.2−14.1Si1.8−2.9 (Th2Zn17-type), ~Dy11Ni65Si24, ~Dy16Ni62Si22 (unknown structures), DyNi7Si6 (GdNi7Si6-type), Dy3Ni8Si (Ce3Co8Si-type), DyNi2Si (YPd2Si-type), ~Dy40Ni47Si13 and ~Dy5Ni2Si3 (unknown structures). Quasi–binary solid solutions were detected at 1070 (870K) for Dy2Ni17, DyNi5, DyNi7, DyNi3, DyNi2, DyNi, DySi2 and DySi1.67. No detectable solubility is observed for the other binary compounds of the Dy–Ni–Si system.The crystal structures of new phases RNi7Si6 (GdNi7Si6-type), R3Ni8Si (Ce3Co8Si-type), RNi2Si (YPd2Si-type) and R3Ni12Si4 (Gd3Ru4Al12-type), with R=Y, Gd–Tm, has been studied. Magnetic properties of few representative compounds are also reported.

On the structural relaxation around Cr3+ along binary solid solutions

The structural relaxation occurring along binary solid solutions ( i.e . intended as the measure of the mismatch between average and local bond distances at a crystallographic site) was reappraised with the aim of revealing possible correlations of bulk properties with the departure of short-range from the long-range crystal structure. For this purpose, fourteen end-terms belonging to solid solutions, all characterized by Al 3+ ↔Cr 3+ replacement at octahedral site, were selected from literature among those of mineralogical interest ( i.e . clinopyroxene, garnet, spinel, corundum, and perovskite, using alumoniobite as a check). Along with X-ray diffraction and electronic absorption spectroscopy data used to define the structural relaxation coefficient, bulk properties were available (density and bulk modulus) or were calculated (deviation from the closest sphere packing) for each end-term. The structural relaxation coefficients exhibit a linear inverse correlation with the difference between crystal field strengths of end-members (Δ10 Dq ): the larger the deviation of local arrangement from average structure, the larger Δ10 Dq . Evidence that the structural framework, encompassing polyhedral arrangement and anion packing, affects the structural relaxation is presented and discussed. Solid solutions based on dense structures tend to relax less than those with a less compact atomic arrangement. The greater the difference in compressibility between end-members, the more the structure will behave as predicted by Vegard’s law.

Mechanical properties of Mg–RE (RE = Sc, Y, Gd–Tm) solid solutions: first-principles determination

To understand the effect of rare earth (RE) solute atoms on the mechanical properties of the Mg matrix, the elastic parameters and ideal shear strengths of Mg52RE2 (RE = Sc, Y, Gd–Tm, ∼3.7 at% RE) binary solid solutions were systematically investigated by first-principles calculations based on density function theory. The independent elastic constants (Cij) were obtained by quadratic fitting the deformation energy–strain relation, then the bulk modulus (B), shear modulus (G), Young's modulus (Y), Poisson's ratio (v) and anisotropy factor (A) at zero temperature were predicted in the framework of the Voigt–Reuss–Hill approximation. Furthermore, elastic moduli at room temperature were estimated using a semi-empirical formula. It was found that the bulk modulus and hardness of Mg52RE2 strongly depend on the degree of localization of the valence electron orbitals of the solute atoms. Based on the study of ideal shear stress–strain relations, we propose that the addition of RE elements into an Mg lattice increases the shear strength and anisotropy of the mechanical properties, but reduces the deformation-to-failure strain. The results show that Sc is the most effective element for strength while Gd is most effective for ductility in the studied Mg–RE solid solutions.

Study of intermetallics and phase equilibria of Mg–Zn–La system in Mg-rich corner at 345 °C

Phase compositions, lattice structures and phase equilibria of Mg–Zn–La system in Mg-rich corner at 345°C have been investigated by equilibrated alloy method and diffusion couple technique. The results show that a binary solid solution of Mg12La is confirmed as (Mg,Zn)12La with 0–4.96at.% Zn. It has a body-centred tetragonal lattice structure with giant unit cell of a=b≈1.032nm and c≈7.748nm. Another linear ternary intermetallic (Mg,Zn)11La (Zn≈8.66–43.39at.%) has been identified too. (Mg,Zn)11La has a C-centred orthorhombic structure, and the unit cell of which becomes smaller with the increase of Zn content. The smallest lattice parameters of it are a≈1.1191nm, b≈0.9701nm and c≈0.9498nm. Both (Mg,Zn)12La and (Mg,Zn)11La are in equilibrium with Mg solid solution in their composition range. A three-phase equilibrium of Mg+(Mg,Zn)12La+(Mg,Zn)11La is also ascertained. In addition, MgZn phase containing about 1.53at.% La is confirmed, which is in equilibrium with Mg solid solution and (Mg,Zn)11La at 345°C. This result indicates that it is impossible for Mg17Zn21La2 reported in literature to be in equilibrium with Mg solid solution as a stable phase at this temperature.

Fully Reversible De/hydriding of Mg Base Solid Solutions with Reduced Reaction Enthalpy and Enhanced Kinetics

This paper presents a new approach to tune the de/hydriding thermodynamic properties of Mg via forming reversible Mg base solid solutions in the Mg–In and Mg–In–Al systems by mechanical milling. The effect of solubility of In and Al on the reversible formation of solid solution structure and hydrogen storage properties were investigated. It is found that although the solute atoms unavoidably are rejected upon hydriding, the hydrogenated products of MgH2 and intermediate MgIn compound could fully transform back to solid solution after dehydrogenation. In the hydriding of Mg(In, Al) ternary solid solution, Al would get dissolved into MgIn compound rather than forming free Al like the Mg(Al) binary solid solution. Therefore, the presence of In improves the dehydriding reversibility of Mg(Al) solid solution, and the reversible Al concentration could be increased up to the 8 at. %, which is just the solubility limit of Al in Mg by mechanical milling. The reversible phase transformation is responsible for the reduction in the desorption enthalpy of MgH2, being 12 kJ/(mol·H2) reduction for the alloy Mg0.9In0.1 relative to the desorption enthalpy of pure MgH2. Further, the hydrogen sorption kinetics of Mg(In) solid solutions are enhanced. Comparatively, both the thermodynamic destabilizing effect and the kinetic enhancing effect due to the Al dissolving are inferior to those due to the In dissolving. This work demonstrates a feasible way to improve the thermodynamics and kinetics of Mg base hydrogen storage alloys through traditional metallurgical method.

Compositional dependence of serrated flow in nickel binary solid solutions during high-temperature microindentation

At 450 °C, pure nickel and nickel binary solid solutions, containing Ru, Rh, W, Re, Ir and Pt, have a smooth load–depth curves. In contrast, the alloying addition of Nb, Mo, Pd and Ta results in the occurrence of serrations in their load–depth profiles. Analyses show the load increment of the quasi-elastic segments scales linearly with the load at their starting point. The slope of such linear relationships was normalized by the solute concentration and then plotted against the diffusion rate of transition metal solutes within the nickel lattice and along dislocation cores. Linear relationships were observed in both cases. Results suggest that the solute diffusion along dislocation cores coupled with the atomic size misfit are mainly responsible for such serrations.

On the Issue of Radiation-Induced Instability in Binary Solid Solutions

The stability of a binary solid solution under irradiation has been studied. This has been done by performing linear stability analysis of a set of nonlinear reaction-diffusion equations under uniform irradiation. Owing to the complexity of the resulting system of eigenvalue equations, a numerical solution has been attempted to calculate the dispersion relations. The set of reaction-diffusion equations represent the coupled dynamics of vacancies, dumbbell-type interstitials, and lattice atoms. For a miscible system (Cu-Au) under uniform irradiation, the initiation and growth of the instability have been studied as a function of various control parameters.

Effect of solute atoms on grain boundary sliding in magnesium alloys

The effect of solid-solution alloying on grain boundary sliding (GBS) was investigated using pure magnesium and six kinds of Mg–X (X = Ag, Al, Li, Pb, Y and Zn) dilute binary solid solutions with an average grain size of 10 µm. A sharp increase in damping capacity caused by GBS was observed above a certain temperature. The temperature at which a sharp increase in damping capacity occurred depended on the alloying element. The addition of Y and Ag markedly increased the onset temperature (more than 100 K) for a sharp increase in damping capacity, whereas the addition of Zn, Al and Li slightly increased the onset temperature (less than 50 K) as compared with that for pure magnesium. Tensile tests at a temperature of 423 K revealed that the higher the onset temperature, the lower the strain rate sensitivity of the flow stress. It is suggested that the former elements (Y and Ag) are more effective in suppressing GBS in magnesium alloys than the latter ones (Zn, Al and Li). The suppression of GBS was associated with low grain boundary energy, and the extent to which the energy is reduced depended on the alloying element. It was suggested that the change in the lattice parameter (the so-called c/a ratio) affects the grain boundary energy, and thus, the occurrence of GBS.

Interaction of salts in ionic melts of the ternary reciprocal systems Na,K‖BO2,MoO4 and Na,K‖BO2,WO4

The phase diagrams of the ternary reciprocal systems Na,K‖BO2,MoO4 and Na,K‖BO2,WO4 were studied for the first time by a calculation-experimental method and differential thermal analysis. The coordinates were determined for binary eutectics of the diagonal stable sections NaBO2-K2MoO4(K2WO4) and the ternary invariant points e(55 mol % NaBO2, 45 mol % K2MoO4, 740°C), e(55 mol % NaBO2, 45 mol % K2WO4, 730°C), E(4.5 mol % NaBO2, 78 mol % Na2MoO4, 17.5 mol % K2MoO4, 652°C), E(4.5 mol % NaBO2, 78 mol % Na2WO4, 17.5 mol % K2WO4, 643°C), P2(5 mol % NaBO2, 56 mol % Na2MoO4, 39 mol % K2MoO4, 673°C), P2(5 mol % NaBO2, 56 mol % Na2WO4, 39 mol % K2WO4, 671°C). Binary solid solutions based on sodium and potassium metaborates were shown to be stable. Analytical models of phase equilibrium states of the ternary reciprocal systems Na,K‖BO2,MoO4(WO4) were obtained, which enable one to calculate melting (crystallization) points and construct isotherms at any given composition. The specific heats of melting of samples of invariant compositions were found by quantitative differential thermal analysis.

Investigation of Transport Properties of Bzcy (BaZrxCe1-xY0.15O3- δ, x=0, 0.2, 0.4, 0.6)

Some perovskite-type oxides have shown high proton conductivity in wet hydrogen atmosphere. In these perovskite oxides the partial substitution of an acceptor dopant for B-site results in formation of oxygen vacancies, which lead to the formation of protonic defects by the absorption of water in wet atmosphere. Among various proton conducting perovskite-type oxides, Y-doped Barium cerate and barium zirconate are nearly isomorphic. Therefore, the basic phases of a binary solid solution where B-sites are randomly occupied by either Zr4+ or Ce4+. This is because the chemical instability of Y-doped BaCeO3- δ in the presence of CO2-, H2O- or SO2-containing atmosphere below 973K was substantially improved by replacing Ce with Zr to form a solid solution, and the mechanical strength was also enhanced when the proton conductivity and thermal stability remained adequate over a wide range of operation conditions for the fuel cell.To elucidate the transport properties and defect structure of a Ce/Zr-coexisting preovskite structure, BZCY(BaZrxCe1-xY0.15O3- δ, x=0, 0.2, 0.4, 0.6) was chosen as the model system. First, we study the electrical properties of BZCY in various oxygen and water vapor atmospheres by four-probe DC measurements as a function of temperature. And then, these properties are analyzed analytically, based on the defect structure of the material. Furthermore, we use the conductivity relaxation measurement technique to monitor the monotonic/non-monotonic(two-fold) relaxation for the BZCY under various themodynamic conditions and extract the chemical diffusivities by solving Fick’s second law for each case on the basis of hydrogen- and oxygen- decoupled diffusion as proposed by Professor Yoo1-3.Fig. 1 shows the typical relaxation profiles of the mean total conductivity upon oxidation and reduction across an identical oxygen activity window. During the redox reaction driven by the oxygen chemical potential gradient at a fixed water vapor activity, oxygen may be incorporated into the BZCY by ambipolar diffusion of V•• o and 2h• in the p-type oxidizing regime. In Fig. 2, conductivity relaxation profiles upon hydration and dehydration at a fixed pO2(≈0.21 atm) are shown as a function of water vapor activities at 1023K. The figures clearly reveal the violation of monotonic relaxation governed by the chemical diffusion of water, according to the ambipolar diffusion of oxygen vacancies and proton. As shown in the fig. 2, non-monotonic twofold relaxation behavior was clearly observed for the BCZY system.1. H.I. Yoo et al., Phys Chem Chem Phys, 10, 974 (2008)2. H.I. Yoo et al., Solid State Ionics, 180, 1443 (2009)3. J.I. Yeon et al., Solid State Ionics, 181, 1323 (2010)4. S. Hamakawa et al., Solid State Ionics, 148, 71 (2002)5. S.-J. Song et al., Solid State Ionics, 167, 99 (2004)6. S.M. Haile et al., Nature, 125, 271 (1999)7. D. Pergolesi et al., Nature Materials, 9, 846 (2010)8. H. Iwahara et al., Solid State Ionics, 125, 271 (1999)9. Y.C. Yang et al., Sensors and Actuators B, 140, 273 (2009)10. C. Zuo et al., Advanced Materials, 18, 3318 (2006).

Thermodynamic assessment of orientationally disordered organic molecular crystals: Ternary system pentaerythritol–neopentylglycol–2-amino-2methyl-1,3, propanediol (PE–NPG–AMPL)

Organic crystals such as pentaerythritol [PE-C(CH2OH)4], neopentylglycol [NPG-(CH3)2C(CH2OH)2] and 2-amino-2methyl-1,3,propanediol [AMPL-(HOCH2)2C(NH2)CH3] store a large amount of thermal energy in their solid state high temperature phases with orientational disorder. There are very few pure compounds of these polyalcohol and amine family that are commercially available exhibiting these properties, leading to limited choices of energy storage materials. Binary and ternary solid solutions allow a wider selection of materials with different phase transition temperature, heat content, and compositions for practical applications. Thermodynamic calculations of the PE–NPG–AMPL system are presented that provide critical thermodynamic data for energy storage systems. Substitutional solution model is used for optimization of interaction parameters. Activities of binaries, ternary isotherms of PE–NPG–AMPL at various temperatures, and pseudo-binary isopleth are presented.

Chemical Synthesis of Binary Solid Solution Bismuth–Antimony Nanoparticles with Control of Composition and Morphology

Abstract Three chemical synthesis approaches were developed to obtain binary solid solution Bi–Sb nanoparticles (NP) with controllable compositions and sizes. In each synthesis approach, an array of Bi100−xSbx NPs with x ranging from 25 to 90 was synthesized via careful control of feeding ratios and synthetic conditions. The NP sizes can be varied from 30 to 60 nm for single-crystal NPs, and from 350 to 500 nm for polycrystal NPs. The synthesized Bi100−xSbx NPs can be used as thermoelectric materials or as seeds for growth of ternary solid solution Bi–Sb–Te NPs with different compositions.

Electrocatalytic performance of Pd–Ni nanowire arrays electrode for methanol electrooxidation in alkaline media

A successful approach to prepare the Pd–Ni nanowire arrays electrode without carbon supports was reported. The morphology and crystallinity of nanowire were characterized by transmission electron microscopy, selected-area electron diffraction (SAED), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses, respectively. The results show that the diameters of the nanowire are in the range of 65–75 nm, and the polycrystalline binary solid solution alloy is formed in the Pd–Ni nanowire. Cyclic voltammograms, chronoamperograms, and electrochemical impedance spectroscopy demonstrate that the Pd–Ni nanowire arrays electrodes show excellent electrocatalytic performance for methanol oxidation in alkaline media. The catalytic activity of Pd–Ni nanowire arrays electrode is ~1.39 times higher than that of the Pd nanowire arrays electrode and ~2.28 times higher than that of the commercial Pd/C catalyst. This is mostly owing to the transfer of electron density from Ni to Pd. These results indicate that Pd–Ni nanowire arrays electrode is very promising in an alkaline direct methanol fuel cell.