Reduced graphene oxide supported PdNi alloy nanocrystals for the oxygen reduction and methanol oxidation reactions

The research on electrocatalysts with relatively lower price than Pt and excellent electrocatalytic performance for the cathode oxygen reduction reaction(ORR) and anode methanol oxidation reaction(MOR) is vital for the development of direct methanol fuel cells(DMFCs). In this work, we develop a cyanogel-reduction method to synthesize reduced graphene oxide(rGO) supported highly dispersed PdNi alloy nanocrystals(PdNi/rGO) with high alloying degree and tunable Pd/Ni ratio. The large specific surface area and the d-band center downshift of Pd result in excellent activity of Pd4 Ni1/rGO nanohybrids for the ORR. The modification of Pd electronic structure can facilitate the adsorption of CH3 OH on Pd surface and the highly oxophilic property of Ni can eliminate/mitigate the COadsintermediates poisoning, which make PdNi/r GO nanohybrids possess superior MOR activity. In addition, rGO improve the stability of PdNi alloy nanocrystals for the ORR and MOR. Due to high activity and stability for the ORR and MOR, PdNi/rGO nanohybrids are promising to be an available bifunctional electrocatalyst in DMFCs.

Strain rate sensitivity and activation volume of electrodeposited nanocrystalline Ni and Ni-Co alloys

Tensile deformation behaviors of the electrodeposited 40 nm grain sized Ni,25 nm Ni-1.7 wt.%Co,and 13 nm Ni-8.6 wt.%Co alloys at various strain rates and room temperature were reviewed with emphasis on strain rate sensitivity and activation volume,respectively.It is found that the strain rate sensitivity and activation volume were strongly grain size dependent.An analytic model based on the bow out of a single dislocation well predicted the relationship between the strain rate sensitivity and the activation volumes for these nanocrystaline metals.

Shape-controlled synthesis of novel precursor for fibrous Ni-Co alloy powders

A novel precursor of nickel-cobalt alloy powders with an appropriate Ni to Co molar ratio was prepared under selectively synthetic conditions. The composition and morphology of the precursor were characterized by X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, Fourier transform infrared spectrometry （FT-IR） and energy dispersive spectrometry （EDS）. The effects of pH value, reaction temperature, metal ion concentrations and surfactant on the morphology and the dispersion of precursor were investigated. The results show that the morphology of precursor depends on ammonia content in the precursor. A fibriform precursor is a complicated ammonia-containing nickel-cobalt oxalate. The uniform shape-controlled fibrous precursor is obtained under the following optimum conditions： ammonia as complex agent as well as pH adjustor, oxalate as coprecipitator, 50-65 °C of reaction temperature, 0.5-0.8 mol/L of total concentration of Ni2＋ and Co2＋, PVP as dispersant, and pH 8.0-8.4.

Encapsulated Ni-Co alloy nanoparticles as efficient catalyst for hydrodeoxygenation of biomass derivatives in water

Catalytic hydrodeoxygenation(HDO)is one of the most promising strategies to transform oxygen-rich biomass derivatives into high value-added chemicals and fuels,but highly challenging due to the lack of highly efficient nonprecious metal catalysts.Herein,we report for the first time of a facile synthetic approach to controllably fabricate well-defined Ni-Co alloy NPs confined on the tip of N-CNTs as HDO catalyst.The resultant Ni-Co alloy catalyst possesses outstanding HDO performance towards biomass-derived vanillin into 2-methoxy-4-methylphenol in water with 100%conversion efficiency and selectivity under mild reaction conditions,surpassing the reported high performance nonprecious HDO catalysts.Impressively,our experimental results also unveil that the Ni-Co alloy catalyst can be generically applied to catalyze HDO of vanillin derivatives and other aromatic aldehydes in water with 100%conversion efficiency and over 90%selectivity.Importantly,our DFT calculations and experimental results confirm that the achieved outstanding HDO catalytic performance is due to the greatly promoted selective adsorption and activation of C=O,and desorption of the activated hydrogen species by the synergism of the alloyed Ni-Co NPs.The findings of this work affords a new strategy to design and develop efficient transition metal-based catalysts for HDO reactions in water.

Influence of Ni^(2+)/Co^(2+)ratio in electrolyte on morphology,structure and magnetic properties of electrolytically produced Ni-Co alloy powders

Nickel-cobalt(Ni-Co) alloy powders were produced galvanostatically by using sulphate electrolytes with various ratios of Ni2+/Co2+(mole ratios). The morphology, phase structure, chemical composition and magnetic properties were examined by scanning electron microscope(SEM), X-ray diffractometer(XRD), atomic emission spectrometer(AES), and SQUID-based magnetometer, respectively. Morphology of the particles changed from cauliflower-like and dendritic to coral-like and spongy-like ones with increasing Ni2+/Co2+ ratio from 0.25 to 4.0. XRD analysis of the Ni-Co powders revealed that the decrease of Ni2+/Co2+ ratios(the increase of Co content) caused a change of structure from face centered cubic(FCC) obtained for the ratios of 4.0, 1.5 and 0.67 to a mixture of FCC and hexagonal closed-packed(HCP) phases for the ratio of 0.25. The increasing content of nickel led to change of mechanism of electrolysis from irregular(up to 40 wt.% Ni in the electrolytes) to close to equilibrium(between 40 and 60 wt.% Ni in the electrolytes) and anomalous co-deposition(over 60 wt.% Ni in the electrolytes) type. All of the obtained Ni-Co alloy samples behaved as soft magnetic materials while their magnetic parameters showed immediate composition dependence since both coercivity and saturation magnetization almost linearly increased with increase of the Co content.

Surface Tension of Molten Ni and Ni-Co Alloys

Surface tension of molten Ni and Ni-Co (5 and 10 mass fraction) alloys was measured at the temperature range of 1773-1873 K using an improved sessile drop method with an alumina substrate in an Ar+3%H2 atmosphere. The error of the data obtained was analyzed. The surface tension of molten Ni and Ni-Co (5 and 10 mass fraction) alloys decreases with increasing temperature. The influence of Co on the surface tension of Ni-Co alloys is little in the studied Co concentration range.

Effect of Rare Earth on Microstructure and Corrosion Resistance of Pulse Reversal Current Electrodeposition Ni-Co Alloy Coatings

The effect of adding RE to plating bath on microstructure and corrosion resistance of Ni-Co alloy coatings prepared by pulse reversal current electrodeposition was studied by means of SEM/EDS, electrochemical analysis and corrosion mass loss etc. The results show that adding proper RE to plating solution can promote the microstructure of coatings compacter, the surface smoother and the crystal finer, and improve the corrosion resistance. The coatings exhibite the highest corrosion resistance when the concentration of RE reaches 0.25 g·L -1. The reason of increasing corrosion resistance by adding RE was also investigated.

Nanocrystalline 2J4 alloy processed by equal channel angular pressing

Nanocrystalline 2J4 alloy was fabricated by equal-channel angular pressing (ECAP). Microstructural evolution at different passes of ECAP and the effect of angle (φ) on the ECAP were researched. The results reveal that α phase slowly turns to γ phase and follows the formation of dislocation cells in the 2J4 alloy with increasing severe plastic deformation. At last, it becomes reasonably finer bands of subgrains. The results with intersect at angle (φ) of 90° are better than that at angle (φ) of 120°. After three passes of ECAP, at angle φ of 90°, nanocrystalline microstructure can be obtained. The grain size is reduced from 30μm in the initial state to 400nm.

Measurement and analyses of molten Ni-Co alloy density

With the advent of powerful mathematical modeling techniques for material phenomena,there is renewed interest in reliable data for the density of the Ni-based superalloys.Up to now,there has been few report on the density of molten Ni-Co alloy.In order to obtain more accurate density data for molten Ni-Co alloy,the density of molten Ni-Co alloy was measured with a modified sessile drop method,and the accommodation of different atoms in molten Ni-Co alloy was analyzed.The density of alloy is found to decrease with increasing temperature and Co concentration in the alloy.The molar volume of molten Ni-Co alloy increases with increasing Co concentration.The molar volume of Ni-Co alloy determined shows a positive deviation from the linear molar volume,and the deviation of molar volume from ideal mixing increases with increasing Co concentration over the experimental concentration range.

Development of black Ni-Co alloy films from modified Watts electrolyte and its morphology and structural characteristics

The electrodeposition of black Ni-Co alloy film from Watts nickel solution and the effects of benzotriaozole and imidazole as the additives were studied. The electrolyte consists of NiSO4, NiC12, H3BO3, COSO4 and KNO3. The cathode current efficiency and the throwing power of the solution and the film adhesion to the mild steel metallic foil were determined by standard methods. The crystal structure, lattice parameter, crystal orientation and crystal size were analyzed by X-ray diffraction （XRD）. Moreover, the surface morphology and elemental composition of the black Ni-Co alloy films were analyzed by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDX） techniques. The darkness of the black films increases with increasing the incorporation of Co ion into the films. The XRD studies reveal that the black Ni-Co alloy films exhibit Ni （11 l） as the preferred orientation.

Discrete composition control of two-dimensional morphologic all-inorganic metal halide perovskite nanocrystals

Metal halide perovskite nanocrystals(NCs)exhibit impressive optical and electronic properties,making them an important class of functional materials with promising applications in solar cells,light emitting diodes(LEDs),photodetectors,and photocatalysts.In addition to the widely studied 0-dimensional(0 D)metal halide perovskite NCs,such as nanocubes,low dimensional perovskites,such as 2 D all-inorganic perovskite(AIP)NCs,subsist with directionally relevant quantum confinement.These anisotropic NCs have the propensity to exhibit interesting optoelectronic properties that are exceedingly difficult to introduce into 0 D systems,yet as of late are largely unexplored.In this review,we discuss the recent synthetic progress of 2 D all-inorganic metal halide perovskite NCs with ABX3 structure.Specifically,we highlight the discrete composition control of the cations(A and B sites)and anions(X site)by dopant incorporation and alloying in 2 D metal halide perovskite NCs.We will also discuss more complex perovskite crystal structures,such as Ruddlesden-Popper double perovskites,and compare these materials to 0 D perovskite systems.Ultimately,our work culminates in the future interests and perspectives of this field with a focus on the wide applicability of 2 D systems and the large variance in structure capable with discrete compositional tuning.

Possibility of Using Ni-Co Alloy As Catalyst for Oxygen Electrode of Fuel Cell

In recent years, the scale of use of fuel cells （FCs） has been increasing continuously. One of the essential elements that affect their work is a catalyst. Precious metals （mainly platinum） are known for their high efficiency as FC catalysts. However, their high cost holds back the FCs from application on a large scale. Therefore, catalysts that do not contain precious metals are sought. Studies are focused mainly on the search for fuel electrode catalysts, but for the efficiency of FCs also the oxygen electrode catalyst is of great significance. The paper presents an analysis of the possibilitiesof using Ni-Co alloy as a catalyst for the oxygen electrode of the FC.

Effect of heat treatment on tensile deformation behavior of Ni-Co film/Fe substrate systems

The effects of heat treatment on microstructure and tension property of Ni-Co film/Fe substrate systems were investigated. The deformation and fracture morphologies of Ni-Co films/Fe substrate systems were studied by in-situ scanning electron microscopy（in-situ SEM）before and after heat treatment.The results show that a Ni-Co/Fe diffusion layer appears between the film and substrate after heat treatment;the elongation of film/substrate system increases with increasing the heat treatment temperature. Both the strength and ductility of the film/substrate system are preferable when heat treatment temperature is 650 o C,meanwhile the maximum elongation is up to 46%.During tensile deformation,the deformation behaviors of Ni-Co film/Fe substrate are quite different before and after heat treatment.The samples after heat treatment went through the progress of holes’emergence,growth and extension,whereas the samples without heat treatment accompanied with no holes,just cracked instead,showing that appropriate heat treatment is helpful to improve the toughness of material,and mechanical properties.

Electrochemical characterization of Ni-Co and Ni-Co-Fe for oxidation of methyl alcohol fuel with high energetic catalytic surface

Non Pt based metals and alloys as electrode materials for methyl alcohol fuel cells have been investigated w ith an aim of finding high electrocatalytic surface property for the faster electrode reactions.Electrodes w ere fabricated by electrodeposition on pure Al foil,from an electrolyte of Ni,Co,Fe salts.The optimum condition of electrodeposition w ere found out by a series of experiments,varying the chemistry of the electrolyte,pH valve,temperature,current and cell potential.Polarization study of the coated Ni-Co or Ni-CoFe alloy on pure Al w as found to exhibit high exchange current density,indicating an improved electro catalytic surface w ith faster charge-discharge reactions at anode and cathode and low overvoltage.Electrochemical impedance studies on coated and uncoated surface clearly show ed that the polarization resistance and impedance w ere decreased by Ni-Co or Ni-Co-Fe coating.X-ray diffraction(XRD),energy dispersive X-ray spectroscopy(EDX)and atomic absorption spectroscopy(AAS)studies confirmed the presence of alloying elements and constituents of the alloy.The morphology of the deposits from scanning electron microscope(SEM)images indicated that the electrode surface w as a three dimensional space w hich increased the effective surface area for the electrode reactions to take place.

Preparation of nanocrystal modificator and its modification mechanism

In order to increase the modifying effect, the Cu-P master alloy was rapidly solidified with melt-spin method, and the nano-sized ribbon was gained at 105?106 ℃/s. Subsequently, ZL109 alloy was modified by nanocrystal and massive Cu-P master alloy, respectively, with molten metal casting method. The results show that the microscopic structure of ZL109 alloy modified by nanocrystal Cu-P master alloy is better than that modified by massive Cu-P master alloy, the original crystal silicon and eutectic silicon are refined more effectively and the mechanical properties are increased evidently: the tensile-strength is increased by 25%, the elongation is increased by 32.26% and the hardness is increased by 17.2%. Therefore, the melt-spin treatment is a feasible method to improve the modifying effect of Cu-P master alloy.

Interface-induced formation of onion-like alloy nanocrystals by defects engineering

The ability to controlled introduction of defects, particularly twin defects in Pt-based nanocrystals （NCs） provides a possibility to regulate the performance of Pt-based nanocatalyst. However, because of the high internal strain energy existed in twinned structures, the fabrication of defects in Pt-based NCs is sufficiently challenging. Here we demonstrate a ＂low-temperature interface-induced assembly＂ approach that provides precise control over Pt-Cu nanoparticles assembled at the hexadecylamine/water interface, yielding onion-like Pt-Cu NCs exposed a high density of twin defects. Moreover, a bending mechanism is proposed to elucidate the appearance of twin defects and lattice expanding （contraction） based on aberration corrected scanning transmission electron microscopy analysis. This work opens new routes to engineer defects in metal- based alloy NCs, enabling more opportunities in catalysis.

Surfactant dependent evolution of Au-Pd alloy nanocrystals from trisoctahedron to excavated rhombic dodecahedron and multipod： a matter of crystal growth kinetics

In wet chemical syntheses of noble metal nanocrystals,surfactants play crucial roles in regulating their morphology.To date,more attention has been paid to the effect of the surfactant on the surface energy of crystal facets,while less attention has been paid to its effect on the growth kinetics.In this paper,using the growth of Au-Pd alloy nanocrystals as an example,we demonstrate that different concentration of surfactant hexadecyltrimethyl ammonium chloride(CTAC)may cause the different packing density of CTA+bilayers on different sites(face,edge or vertex)of crystallite surface,which would change the crystal growth kinetics and result in preferential crystal growth along the edge or vertex of crystallites.The unique shape evolution from trisoctahedron to excavated rhombic dodecahedron and multipod structure for Au-Pd alloy nanocrystals was successfully achieved by simply adjusting the concentration of CTAC.These results help to understand the effect of surfactants on the shape evolution of nanocrystals and open up avenues to the rational synthesis of nanocrystals with the thermodynamically unfavorable morphologies.

Incorporation sodium ions into monodisperse lead-free double perovskite Cs_(2)AgBiCl_(6) nanocrystals to improve optical properties

Lead-free double perovskite nanocrystals(NCs)have emerged as a promising candidate in the optical field,owing to their non-toxic,good moist heat and chemical stability.However,their poor optical properties limited their application.To improve the optical properties of lead-free double perovskite NCs,metal ion doping or alloying had been suggested as a promising strategy.Here,we prepared monodisperse,uniformly sized,cubic morphology of Cs_(2)AgBiCl_(6)NCs with different Na^(+)incorporation amounts via a simple hot-injection method.The Na^(+)incorporation broke the parity-forbidden transition by reducing the inversion symmetry of the electron wave function at the Ag site,which changed the parity of the self-trapped exciton wave function and thus allowed radiative recombination.As a result,the photoluminescence quantum yield(PLQY)of Na^(+)-alloyed Cs_(2)AgBiCl_(6)NCs(12.1%)was higher than that of Cs_(2)AgBiCl_(6)NCs(2.4%),and the exciton lifetime of Na^(+)-alloyed Cs_(2)AgBiCl_(6)NCs increased to 36.98 ns from 17.58 ns for Cs_(2)AgBiCl_(6)NCs.By adjusting the amount of Na^(+)incorporation,the band gap of Cs_(2)AgBiCl_(6)NCs can be significantly tuned from~2.90 eV to~3.50 eV.Furthermore,the temperature-dependent photoluminescence spectra indicated that the Na^(+)-alloyed Cs_(2)AgBiCl_(6)NCs possessed higher longitudinal optical phonon energy and exciton binding energy compared to Cs_(2)AgBiCl_(6)NCs.This suggested that there were strong exciton-phonon interactions during exciton recombination,a reduced probability of non-radiative processes,and excellent thermal stability.It offers a promising strategy for improving the optical properties of lead-free double perovskite NCs,and have the potential to replace traditional lead halide perovskite NCs in future optoelectronic applications.

Nanocrystalline High Entropy Alloys with Ultrafast Kinetics and High Storage Capacity for Large-Scale Room-Temperature-Applicable Hydrogen Storage

High-entropy alloys(HEAs)are a promising solution for large-scale hydrogen storage(H-storage)and are therefore receiving increasing attention from the materials science community.In this study,we systematically investigated the microstructures and H-storage properties of V_(35)Ti_(35)Cr_(10) Fe_(10)M_(10)(M=Mn,Co,Sc,or Ni)HEAs prepared by arcmelting.The cast HEAs were found to be nanocrystalline.The crystal lattice parameters and hydrogen absorption energies of the alloys were calculated using density functional theory(DFT)calculations.The alloys can be fully activated in just one cycle of hydrogen absorption/desorption under mild conditions,after which they reach hydrogen absorption saturation in approximately 100 s at ambient temperature.The hydrogenation kinetics of the HEAs are approximately five times higher than that of conventional solid-solution alloys with a body-centered cubic(BCC)structure.By performing in-situ hydriding differential scanning calorimetry in combination with DFT calculations,we revealed that the alloys are more susceptible to hydrogenation than traditional BCC structural alloys.The H-storage capacity of V_(35)Ti_(35)Cr_(10) Fe_(10)M_(10) alloys at ambient temperature was higher than that of HEAs reported in the literature.Quasi-in-situ X-ray diffraction characterization of the HEAs’hydrogenation revealed a phase transition process from a BCC to facecentered cubic,passing through a pseudo-BCC structure.Our work introduces a new perspective for designing alloys with ultrafast hydrogen absorption kinetics and high capacity for large-scale,room-temperature-applicable H-storage.

Synthesis of composition-tunable octahedral Pt–Cu alloy nanocrystals by controlling reduction kinetics of metal precursors

In this paper, we reported a solvothermal method for the synthesis of octahedral Pt-Cu bimetallic alloy nanocrystals （NCs） with tunable composition. Inspired by the result from our previous exploration on octahedral Pt-Cu alloy NCs that Cu contents can be tuned from 10 % to 50 %, we further tuned the Cu portion from 50 % to 75 % by simply introducing n-butylamine in the reaction system. It is believed that n-butylamine plays a key role in breaking through a thermodynamic constraint in the formation of Pt-Cu alloy nanocrystals （NCs）. The synergistic effect of underpotential deposition-like Cu reduction and the different complexion abilities of amine group of n-butylamine with two metal species effectively tuned the reduction kinetics, by which each reduced Pt atom is able to catalyze reduction of more Cu atoms and be fully covered with 12 Cu atoms in the Pt-Cu alloy crystal, while Cu precursor is not able to be reduced solely and bind solely with Cu atoms, resulting in the successful tuning of Cu composition from 50 % to 75 %. In addition, we investigated the electro-catalytic activity of Pt-Cu bimetallic alloy NCs with different composition in electro-oxidation of methanol. The as-prepared PtCu3 NCs exhibit excellent electro-catalytic performance and stability in comparison with commercial Pt black and other compositional Pt-Cu alloy NCs.