Ag-Ni Alloy Research Articles

Hierarchical AgNi Alloy@NiO/Ni(OH)2 nanosheets on Ni foam as 3D electrode towards methanol and formate oxidation

Direct liquid fuel cells (DLFCs) are regarded as promising technologies for clean energy conversion. However, the high cost of platinum-group-metal catalysts and the unsatisfactory performance of electrodes still limit their applications in DLFCs. Developing robust and low-cost electrode is highly desired for DLFC applications. In this paper, hierarchical NiO/Ni(OH)2 with the anchor of AgNi alloy is constructed on Ni foam through hydrothermal and annealing procedures. The constructed electrode is used for both formate oxidation reaction (FOR) and methanol oxidation reaction (MOR) in alkaline media. The electrochemical measurements suggest that the as-prepared electrodes exhibit high net oxidation current densities of 37.6 and 41.6 mA/cm2 at 1.5 V toward FOR and MOR, respectively, and show a satisfactory stability through chronoamperometric tests. These results demonstrate that the constructed electrodes through a facile pathway are promising to serve as high-efficient 3D binder-free electrodes for practical applications.

Ag-Ni alloy nanoparticles decorated reduced graphene oxide nanocomposite as highly efficient recyclable catalyst for the reduction of 4-nitrophenol and methylene blue

Ag-Ni alloy nanoparticles decorated reduced graphene oxide nanocomposite as highly efficient recyclable catalyst for the reduction of 4-nitrophenol and methylene blue

Synthesis and Catalytic Study of NiAg Bimetallic Core-Shell Nanoparticles.

This publication presents the synthesis of core-shell nanoparticles, where the core was Ni, and the shell was a Ag-Ni nano alloy. The synthesis was based on the reduction of Ni and Ag ions with sodium borohydride in the presence of trisodium citrate as a stabilizer. In order to determine the phase composition of the obtained nanoparticles, an XRD study was performed, and in order to identify the oxidation states of the nanoparticle components, an XPS spectroscopic study was performed. The composition and shape of the particles were determined using the HR-TEM EDS test. The obtained nanoparticles had a size of 11 nm. The research on catalytic properties was carried out in the model methylene blue reduction system. The investigation of the catalytic activity of colloids was carried out with the use of UV-Vis spectrophotometry. The Ag-Ni alloy was about ten times more active than were pure silver nanoparticles of a similar size.

Nitrogen doped carbon quantum dots conjugated with AgNi alloy nanoparticles as potential electrocatalyst for efficient water splitting

An ideal bifunctional electro-catalyst for water splitting is low cost, easily available and have lower over-potential. Here, a new nitrogen doped carbon dots (NDCDs)-AgNi alloy based electrocatalyst is used for electrochemical water splitting. NDCDs-AgNi alloy nanoparticles are synthesized by easy and scalable methods. NDCDs are prepared by pyrolizing ethanolamine and act as a good electrocatalyst for HER. Electrochemical activity of the catalyst is evaluated by cyclic voltammetry and linear swap voltammetry. The prepared electrocatalyst work well under acidic media. To enhance the catalytic performance of the material, the heat treatment at temperature from 300 °C to 500 °C is carried out. After series of optimizations, NDCDs-AgNi alloy demonstrated superior OER activity. The results show that the limiting current density has been increased and the heat treated samples shows HER phenomena.

The Chemical Alloying by a Solution Combustion Process and Its Application to the Synthesis of the Nanocrystalline Alloy Powders.

Various nanocrystalline metal alloy powders were synthesized by solution combustion synthesis in a reducing atmosphere in which a spray pyrolysis process was modified. Miscible Cu-Ni alloy powder and immiscible Ag-Ni alloy powder were synthesized, along with Cu-Y₂O₃ metal-ceramic composite powder. X-ray diffraction, SEM and TEM observations showed that the synthesized powders were nanocrystalline and well alloyed. Alloying occurred via the chemical routes of the decomposition of the metal salts, as well as the oxidation, reduction and sintering processes.

Electrodeposition of compact Ag–Ni films from concentrated chloride baths and their test in the reduction of nitrate in alkali

Compact Ag and Ag–Ni alloy layers have been electrodeposited from a concentrated chloride bath. The composition of the alloy can be controlled by regulation of the deposition current density jdep under conditions of accurate transport control like those ensured by the rotating disk electrode. XRD analyses suggest formation of Ag-rich crystalline phases in all samples and of Ni-rich crystalline phases only in samples with Ni fraction ≥50 at%. Test experiments of nitrate reduction in alkali show: almost exclusive reduction to nitrite on Ag; prevalent reduction to ammonia on Ni, with an important side evolution of hydrogen; predominant and more efficient reduction to ammonia on Ag–Ni, with lower hydrogen evolution and better current stability.

Facile fabrication of hierarchically porous Ni foam@Ag-Ni catalyst for efficient hydrazine oxidation in alkaline medium

Abstract With the procedure of H2 gas templated electrodeposition and subsequent galvanic replacement reaction, we successfully fabricate the Ni foam@Ag-Ni (Ni foam coated with Ag-Ni bimetals) electrode. Results show the electrodeposition time of 1.5 min produces Ni foam@Ni (Ni foam coated with Ni) with the largest mass specific surface area, and the galvanic replacement time of 8 min yields Ni foam@Ag-Ni with the most favorable catalytic activity toward hydrazine oxidation reaction (HzOR). Materials characterizations reveal the formation of Ag-Ni alloy, the presence of hierarchical pore-structure, the large superficial metallic Ni content and the low amount of Ag mass loading (0.0765 mg cm−2) in Ni foam@Ag-Ni. Electrochemical evaluations show the optimized Ni foam@Ag-Ni electrode delivers the significantly lowest onset potential toward HzOR, with a negative shift of ∼260 mV than Ni foam, ∼220 mV than Ni foam@Ni and ∼60 mV than Ni foam@Ag. Furthermore, it exerts the highest current density in 1.0 mol L–1 KOH and 25 mmol L–1 N2H4, more than 2 fold that of the Ni foam, Ni foam@Ni and Ni foam@Ag at –0.05 V versus Ag/AgCl. The superiority in micro-scale construction and surface composition also endows Ni foam@Ag-Ni electrode with the remarkable durability and considerable whole-cell performance.

Synthesis and Study of Catalytic, Anti–Bacterial, Anti–Oxidant, and DNA Cleavage Properties of Ag–Co and Ag–Ni Magnetic Nanoparticles

Magnetic Ag-Co and Ag-Ni alloy nanoparticles were prepared through a chemical reduction method using their corresponding [Co(NH3)6]Cl3 and [Ni(C2O4)2]K2 complexes, and AgNO3. In this reaction, hydrazine monohydrate was used as reducing agent. The obtained nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). Ag-Co and Ag-Ni nanoalloys exhibited excellent catalytic performance in the preparation of 1,8-dioxooctahydroxanthenes from the reaction of 5,5-dimethyl-1,3-cycloheanedione (dimedone) with aromatic aldehydes. Catalysts were separated by an external permanent magnet and reused. Both, Ag-Co and Ag-Ni nanoalloys posess antibacterial and antioxidant properties and have no significant effect on DNA cleavage.

Surface, Interface, and Temperature Effects on the Phase Separation and Nanoparticle Self Assembly of Bi-Metallic Ni0.5Ag0.5: A Molecular Dynamics Study.

Classical molecular dynamics (MD) simulations were used to investigate how free surfaces, as well as supporting substrates, affect phase separation in a NiAg alloy. Bulk samples, droplets, and droplets deposited on a graphene substrate were investigated at temperatures that spanned regions of interest in the bulk NiAg phase diagram, i.e., miscible and immiscible liquid, liquid-crystal, and crystal-crystal regions. Using MD simulations to cool down a bulk sample from 3000 K to 800 K, it was found that phase separation below 2400 K takes place in agreement with the phase diagram. When free surface effects were introduced, phase separation was accompanied by a core-shell transformation: spherical droplets created from the bulk samples became core-shell nanoparticles with a shell made mostly of Ag atoms and a core made of Ni atoms. When such droplets were deposited on a graphene substrate, the phase separation was accompanied by Ni layering at the graphene interface and Ag at the vacuum interface. Thus, it should be possible to create NiAg core-shell and layer-like nanostructures by quenching liquid NiAg samples on tailored substrates. Furthermore, interesting bimetallic nanoparticle morphologies might be tuned via control of the surface and interface energies and chemical instabilities of the system.

Photonic spin Hall effect: a new window in D-shaped fiber by weak measurements.

The enhanced photonic spin Hall effect (SHE) based on the D-shaped fiber with Ag-Ni alloy/silicon layers is proposed and theoretically investigated under excitation of surface plasmon resonance (SPR). In order to achieve the maximum transverse spin-dependent displacements for practical photonic devices, parameters such as the thickness of the Ag-Ni alloy and silicon layers in the D-shaped fiber are optimized. Theoretical modeling and numerical simulation demonstrate that the multilayer structure can effectively enhance the photonic SHE. The maximum transverse shift of 420 μm obtained with optimized parameters is larger than those in the literature. In addition, a maximum angular sensitivity of 114.6°/RIU is achieved by the wavelength interrogation method. Our concept and theoretical assessment suggest a novel and effective means to enhance the photonic SHE, bring us one step closer to the possibility to characterize parameters of dielectric layers by weak measurements, and accelerate the development of optical fibers based on the photonic SHE.

Electrochemical Performance and Carbon Resistance Comparison between Tin, Copper and Silver-Doped Nickel/Yttria-Stabilized Zirconia Anodes SOFCs Operated with Biogas

Traditional Ni/YSZ anode SOFCs were modified by Sn, Cu and Ag by an infiltration method to obtain Sn-Ni, Cu-Ni and Ag-Ni alloy anode catalysts on the anode. The obtained maximum power density of Ni/YSZ, Sn-doped Ni/YSZ, Cu-doped Ni/YSZ, and Ag-Ni/YSZ cells fuelled by simulated biogas (14 mL min−1 CH4, 7mL min−1 CO2 and 7mL min−1 N2) at 750°C were 0.101, 0.272, 0.085 and 0.102 W cm−2 respectively. Stability tests of SOFCs in biogas revealed that the stability of Sn-Ni/YSZ and Ag-Ni/YSZ cells in operation was greatly improved compared to the undoped Ni/YSZ cell. Both Sn-Ni/YSZ and Ag-Ni/YSZ cells stably operated for 48 h, but Ni/YSZ cell ceased operation after 19 h due to carbon deposition. The addition of small amount of Cu did not enhance the anti-coking ability. Other than with the severe carbon deposition on the Ni/YSZ anode surface, no observable fibrous carbon could be identified on the Sn-Ni/YSZ and Ag-Ni/YSZ anode surfaces.

Role of surfactants: One step facile synthesis of hetero structured Ag-Ni alloy by seed less approach

Surfactant assisted seedless synthesis of Ag-Ni alloy nanoparticles were carried out in an one step process by co- reduction of mixed metal salts (AgNO3 + Ni(NO3)2) solutions using ascorbic acid as reducing agent. To explore the role of surfactant, two types of surfactants were studied; cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecylbenzenesulphonate (SDBS). The surface plasmon resonance peak (SPR) of CTAB capped Ag-Ni and SDBS capped Ag-Ni located at 450 nm and 410 nm wavelengths, respectively. For SDBS, visual observations and time resolved spectra indicates that the reaction mixture containing different mixing orders of reactants (SDBS + Ag+ + Ni2+ + ascorbic acid and SDBS + Ni2+ + Ag+ + ascorbic acid) have different colours as well as different SPR band positions with time. Presence of SDBS delayed the nucleation processes. The Ag-Ni alloy with both surfactants shows that the a red shift to ca. 410 nm and 450 nm with respect to the SPR of AgNPs. The absence of SPR bands at ca. 375 nm and 500–700 nm ruled out the possibility to the formation and /or deposition NiO + Ni(OH)2 on the surface of Ag-Ni alloy. The average number of Ag-Ni atoms per nanoparticle, molar concentration of Ag-Ni and free energies (surface, volume and excess energy due to mixing) were calculated and discussed. The Ag-Ni alloy used as a catalyst to the photo-assisted degradation methyl orange and showed a higher photo catalytic activity. The synthetic method reported here suggests a very promising use of the suitable stabilizer for the preparation of an alloy nanoparticles having different optical properties, which is a subject of immense interest.

Synthesis of Polystyrene Microsphere-Supported Ag–Ni-Alloyed Catalysts with Core–Shell Structures for Electrocatalytic Performance

ABSTRACTRationally designed synthesis strategy for well-defined morphology which can endow the catalysts with unexpectedly enhanced catalytic properties remains a significant challenge in heterogeneous catalytic reactions. Hence, here we report a facile and controllable synthesis of polystyrene microsphere-supported Ag–Ni-alloyed catalysts (PS@Ag–Ni) with uniform core–shell structures through sulfonated treatment coupled with the subsequent liquid-phase reduction strategy. In this typical synthesis, sulfuric acid acts as the bifunctional roles in directing the core–shell morphology and the linker between the polystyrene microspheres and Ag–Ni alloy. The as-obtained PS@Ag–Ni optimized by tuning in a mass ratio of 1:1 shows superior oxygen reduction reaction activity and electrocatalytic performance toward the degradation of p-nitrophenol in comparison with other range of polystyrene microspheres and Ag–Ni alloy feeding ratios. The superior electrocatalytic and oxygen reduction reaction activity are attributed to its highly uniform core–shell morphology and exposure of much more active sites. Moreover, our as-prepared core–shell electrocatalysts will enable further investigation in other catalytic reactions.

First principles study of bimetallic Ni13-nAgn nano-clusters (n = 0-13): Structural, mixing, electronic, and magnetic properties.

Using spin polarized density functional theory based calculations, combined with ab initio molecular dynamics simulation, we carry out a systematic investigation of the bimetallic Ni13-nAgn nano-clusters, for all compositions. This includes prediction of the geometry, mixing behavior, and electronic properties. Our study reveals a tendency towards the formation of a core-shell like structure, following the rule of putting Ni in a high coordination site and Ag in a low coordination site. Our calculations predict negative mixing energies for the entire composition range, indicating mixing to be favored for the bimetallic small sized Ni-Ag clusters, irrespective of the compositions. The magic composition with the highest stability is found for the NiAg12 alloy cluster. We investigate the microscopic origin of a core-shell like structure with negative mixing energy, in which the Ni-Ag inter-facial interaction is found to play a role. We also study the magnetic properties of the Ni-Ag alloy clusters. The Ni dominated magnetism consists of parallel alignment of Ni moments while the tiny moments on Ag align in anti-parallel to Ni moments. The hybridization with the Ag environment causes reduction of Ni moment.

In Situ Solid-State Synthesis of a AgNi/g-C3 N4 Nanocomposite for Enhanced Photoelectrochemical and Photocatalytic Activity.

A graphitic carbon nitride (g-C3 N4 ) polymer matrix was embedded with AgNi alloy nanoparticles using a simple and direct in situ solid-state heat treatment method to develop a novel AgNi/g-C3 N4 photocatalyst. The characterization confirms that the AgNi alloy particles are homogeneously distributed throughout the g-C3 N4 matrix. The catalyst shows excellent photoelectrochemical activity for water splitting with a maximum photocurrent density of 1.2 mA cm-2 , which is the highest reported for doped g-C3 N4 . Furthermore, a detailed experimental study of the photocatalytic degradation of Rhodamine B (RhB) dye using doped g-C3 N4 showed the highest reported degradation efficiency of approximately 95 % after 90 min. The electronic conductivity increased upon incorporation of AgNi alloy nanoparticles on g-C3 N4 and the material showed efficient charge carrier separation and transfer characteristics, which are responsible for the enhanced photoelectrochemical and photocatalytic performance under visible light.

Synthesis and formation mechanism of Ag–Ni alloy nanoparticles at room temperature

Ag–Ni nanoparticles were prepared with a chemical reduction method in the presence of polyvinylpyrrolidone (PVP) used as a stabilizing agent. During the synthesis of Ag–Ni nanoparticles, silver nitrate was used as the Ag+ source while nickel sulfate hexahydrate was used as Ni2+ source. Mixed solutions of Ag+ source and Ni2+ source were used as the precursors and sodium borohydride was used as the reducing agent. Five ratios of Ag+/Ni2+ (9:1, 3:1, 1:1, 1:3, and 1:9) suspensions were prepared in the corresponding precursors. Ag–Ni alloy nanoparticles were obtained with this method at room temperature. Scanning electronic microscope (SEM), energy dispersive spectrum (EDS), high resolution transmission electron microscope (HRTEM) were used to characterize the morphology, composition and crystal structure of the nanoparticles. The crystal structure was also investigated with X-ray diffraction (XRD). In all five Ag/Ni ratios, two kinds of particle structures were observed that are single crystal structure and five-fold twinned structure respectively. Free energy of nanoparticles with different crystal structures were calculated at each Ag/Ni ratio. Calculated results revealed that, with identical volume, free energy of single crystal particle is lower than multi-twinned particle and the difference becomes smaller with the increase of particle size; increase of Ni content will lead the increase of free energy for both structures. Formation of different crystal structures are decided by the structure of the original nuclei at the very early stage of the reduction process.

Optical and Nonlinear Optical Limiting Properties of AgNi Alloy Nanostructures

Silver-nickel alloy nanoparticles with varying size were synthesized by reducing the metal precursors chemically using a single-step solution-based synthesis route. The structural, optical, and nonlinear optical properties of the prepared samples were investigated. The synthesized samples having highly agglomerated, interconnected nature and found to exhibit dipole and multipole surface plasmon resonance related optical absorption bands. Nonlinear optical and optical limiting properties were investigated using a single beam open aperture z-scan technique with the use of 532 nm, 5-ns laser pulses. The nonlinearity observed was found to have contributions from saturable absorption (SA) and excited state absorption (ESA) related to free carriers. The effective nonlinear optical absorption was enhanced in AgNi alloy compared to pure Ag nanostructures.

Ag-Ni alloy nanoparticles for electrocatalytic reduction of benzyl chloride

Ag-based nanocatalysts exhibit good catalytic activity for the electrochemical reduction of organic halides. Ag-Ni alloy nanoparticles (NPs) were facilely prepared by chemical reduction, and the as-prepared nanocatalysts were characterized by X-ray diffraction, ultraviolet-visible spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The electrocatalytic activity of Ag-Ni NPs for benzyl chloride reduction was studied in organic medium using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The results show that the addition of Ni element can obviously decrease the size of Ag-Ni NPs, shift the reduction peak potential (fp) of benzyl chloride positively, and increase the catalytic activity of Ag-Ni NPs. However, when the Ni content reaches a certain value, the catalytic activity of Ag-Ni NPs decreases. Meanwhile, the synergistic catalytic effect of Ag-Ni NPs was also discussed.

The effect of Ni pre-implantation on surface morphology and optical absorption properties of Ag nanoparticles embedded in SiO2

The effect of Ni ion fluence on Ag nucleation and particle growth was investigated by sequentially implantation of 60keV Ni ions at fluences of 1×1016, 5×1016, 1×1017 ions/cm2 and 70keV Ag ions at a fluence of 5×1016 ions/cm2. Due to the modification of the deposition and accumulation process of Ag implants caused by Ni pre-implantation, the surface morphology, structures, and optical absorption properties of the Ag nanoparticles (NPs) depends strongly on the Ni fluences. UV–vis absorption spectroscopy study showed that the introducing of Ni atoms lead to intensity decrease in the Ag SPR band. Remarkable local concentration increase of Ag profiles appeared for the sample pre-implanted by Ni ions of 5.0×1016 ions/cm2. In particular, the AgNi alloy NPs with dual absorption peaks centered at 406nm and 563nm have been formed after 600°C annealing in Ar atmosphere. However, at a low fluence of 1.0×1016 ions/cm2, only small increase of the local Ag concentration than the Ag ions singly implanted sample can be observed. At a high fluence of 1.0×1017 ions/cm2, lots Ag atoms are trapped close to the surface, which result in heavy sputtering loss of Ag atoms and the sublimation of Ag atoms after 600°C annealing.

AgNi alloy nanoparticles embedded SiO2 films: Synthesis and structure

AgNi alloy nanoparticles (NPs) embedded in SiO2 were prepared by sequentially implantation of 60keV Ni ions and 70keV Ag ions at the same fluence of 5.0×1016cm−2 and post-thermal annealing at 600°C in Ar atmosphere. UV–vis absorption spectroscopy study showed that the introducing of Ni atoms lead to dual absorption peaks centered at 406nm and 563nm. The incorporation of Ni elements in Ag NPs damped SPR absorption intensity. X-ray photoelectron spectroscopy and Grazing X-ray diffraction results were consistent with the presence of metallic Ag surrounded by Ni or NiO. Cross-sectional transmission electron microscopy observations further confirmed the fabrication of AgNi alloy NPs with high volume fraction.