Au-Ni Alloys Research Articles

Tuning the electronic structure of AuNi homogeneous solid-solution alloy with positively charged Ni center for highly selective electrochemical CO2 reduction

Designing bimetallic electrocatalysts with homogenous element distribution and tunable electronic structure is attractive strategy to enhance the CO selectivity in electrochemical carbon dioxide reduction reaction (CO2RR). Herein, we report a concept of atom-polymer hybridization to synthesize AuNi homogeneous solid-solution alloy nanoparticles (NPs) with positively charged Ni center supported on electrospun carbon nanofibers (CNFs). The nanofibers host can strong restrict the separated growth of Au and Ni nanoclusters during the directly graphitization process, leading to the formation of homogeneous AuNi alloy. In-situ characterizations reveal the formation process and phase evolution of the AuNi alloy during the carbonization. The positively charged Ni when alloying with Au lead to the enhanced local electronic structure on AuNi homogeneous solid-solution alloy due to the electron-withdrawal effect of nearby Au atoms. The AuNi homogeneous solid-solution alloy exhibits a high CO selectivity with an optimal CO Faradaic efficiency (FECO) of 92% at −0.98 V (vs. RHE). Theoretical calculations indicate that the incorporation of Ni into Au can make the d-band center more positive and reduce the free energy barrier for the CO2 activation into *COOH and *CO desorption. Operando Raman spectroscopy provides the evidences that AuNi homogeneous solid-solution alloy can facilitate the activation of CO2 into *COOH and enhance the interaction between *COOH and AuNi (111) due to the change of electronic structure.

Fabrication of Non-enzymatic Ni–Au Alloy Nanowire Glucose Sensor

Fabrication of Non-enzymatic Ni–Au Alloy Nanowire Glucose Sensor

Electrodeposition of bimetallic NiAu alloy dendrites on carbon papers as highly sensitive disposable non-enzymatic glucose sensors

The bimetallic NiAu alloy dendrites were directly grown on the carbon papers using template free electrodeposition approaches, which demonstrated superior non-enzymatic glucose sensing performance. The enhanced electrochemical performance may be due to the dendrite structure and the low charge transfer resistance originating from the synergistic effect of Ni and Au.

Thermodynamic Prediction of the Free Energy of Mixing and Activities of some Goldbased Binary Liquid Alloys

The free energy of mixing and activities of gold in selected six Au-based binary liquid Au-Cu, Au-Zn, Au-Pb, Au-Ni, Au-Sn and Al-Au alloys at different working temperatures have been studied using the quasi-chemical approximation model (QCAM). The predicted free enegry of mixing and activities results were compared with available experimental values. The predicted results are in reasonable agreement with reported experimental data and confirms that the model is reliable and, thus should serve as an alternative for the prediction of thermodynamic properties of binary liquid alloys.
 Keywords: free energy of mixing, activities, Au, Binary liquid alloys, concentration

Reversible loss of core–shell structure for Ni–Au bimetallic nanoparticles during CO2 hydrogenation

The high catalytic performance of core–shell nanoparticles is usually attributed to their distinct geometric and electronic structures. Here we reveal a dynamic mechanism that overturns this conventional understanding by a direct environmental transmission electron microscopy visualization coupled with multiple state-of-the-art in situ techniques, which include synchrotron X-ray absorption spectroscopy, infrared spectroscopy and theoretical simulations. A Ni–Au catalytic system, which exhibits a highly selective CO production in CO2 hydrogenation, features an intact ultrathin Au shell over the Ni core before and after the reaction. However, the catalytic performance could not be attributed to the Au shell surface, but rather to the formation of a transient reconstructed alloy surface, promoted by CO adsorption during the reaction. The discovery of such a reversible transformation urges us to reconsider the reaction mechanism beyond the stationary model, and may have important implications not only for core–shell nanoparticles, but also for other well-defined nanocatalysts. The structure of core–shell catalysts is often assumed to be conserved over a reaction. Now, an in situ study reveals that the shell of Ni@Au nanoparticles is reversibly converted into a Ni–Au alloy during CO2 hydrogenation, with important mechanistic implications.

Screening of electrocatalysts for hydrogen evolution reaction using bipolar electrodes fabricated by composition gradient magnetron sputtering

This paper reports the facile fabrication of bipolar electrodes using composition gradient magnetron sputtering and subsequent activity screening of the prepared electrodes for hydrogen evolution reaction using bipolar electrochemistry. The electrocatalysts layers based on Ni–Mo, Au–Mo and Au–Ni alloys were deposited in form of compositional gradients on the bipolar electrodes. Concentration of the elements in the gradients varies from 40 to 60 at. % across the bipolar electrodes depending on the deposition conditions. The results of the screening experiments for the hydrogen evolution activity were also confirmed by conventional voltammetry measurements. We find that optimal compositions of the electrocatalyst for hydrogen evolution reaction are Au2Ni, AuMo2, Ni2Mo and Ni2Mo alloy has the highest catalytic activity. Mechanisms of HER on selected alloy compositions was also studied in more detail using voltammetry experiments.

Chromium(VI) sensor based on catalytic reduction using the nanoporous layer of poly(aminopyrimidyl- terthiophene) and AuNi composite

Nanoporous layer of Ni-dealloyed AuNi composited with a functionalized conductive polymer (poly[3′-(2-aminopyrimidyl)-2,2′:5′,2′′-terthiophene] (pPAT)) was electrochemically synthesized, characterized, and applied for a Cr(VI) sensor. At first, we examined the voltammetric response of different kinds of Au alloys (AuCu, AuCo, and AuNi) for the Cr(VI) reduction reaction, where porous AuNi alloy reveals the best performance to the catalytic reduction. Hence, the final sensor was prepared through composition of AuNi and pPAT followed by Ni dealloying, which enhances the catalytic performance through increasing the electrochemical active area by about 12.6 times. The sensor revealed a well-behavioural catalytic Cr(VI) reduction at around +0.5 V. The surface analysis and electrochemical characterization were performed for each sensor layer to elucidate morphology and surface composition. Experimental parameters affecting the Cr(VI) analysis were optimized and the interference effects were also investigated. The dynamic range of square wave voltammetry was between 1.0 ppb and 10.0 ppm Cr(VI) with the detection limit of 0.25 ± 0.05 ppb (n = 3). The reliability of proposed sensor was evaluated by analysing real water samples and standard reference material.

Ni-Au alloy nanoparticles as a high performance heterogeneous catalyst for hydrogenation of aromatic nitro compounds

Selective hydrogenation of nitro compounds requires highly active and less expensive materials as a heterogeneous catalyst. As a good candidate, the Ni-Au alloy nanoparticles (NPs) have been synthesized by simple in-situ reduction method, which was loaded to the active carbon with 10 wt % loading amount. The Ni-Au/C catalyst shows superior catalytic performance for hydrogenation of nitro compounds with 100% conversion and selectivity without any by-products, which also indicates good recycle performance for several times use. The prepared catalyst not only reduces the usage amount of noble metal, but also keeps the high catalytic activity, which is a promising catalyst for industry applications.

Bimetallic Au–Ni alloy nanoparticles in a metal–organic framework (MIL-101) as efficient heterogeneous catalysts for selective oxidation of benzyl alcohol into benzaldehyde

Supported bimetallic nanoparticles (NPs) are extensively used as efficient oxidation catalysts. A series of Au–Ni bimetallic alloy NP catalysts with Au:Ni mole ratios varying from 1:0.35 to 1:4.76 was successfully synthesized via impregnation and H2 reduction. The catalysts are supported by a metal–organic framework MIL-101. For comparison, monometallic Au/MIL-101 with an Au loading amount of 2.97 wt% and Ni/MIL-101 with a Ni loading amount of 2.11 wt% were also prepared. The catalysts were thoroughly characterized through X-ray diffraction, N2 adsorption–desorption isotherms, transmission electron microscopy (TEM), scanning TEM with line mapping energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma atomic emission. Characterization results suggested that the AuNi bimetallic NP catalysts were homogeneously deposited on the MIL-101 surface, and an AuNi alloy structure was formed. The bimetallic Au–Ni and monometallic catalysts were evaluated for the oxidation of benzyl alcohol under O2 atmosphere. The bimetallic AuNi/MIL-101-1 catalyst displayed a higher catalytic activity under identical conditions compared with the monometallic catalysts due to the synergistic effects between Au and Ni metals. The Au–Ni/MIL-101-1 catalyst with an Au–Ni mole ratio of 1:0.35 exhibited the highest turnover frequency value of 15.4 h−1 for the oxidation of benzyl alcohol. In addition, the bimetallic AuNi/MIL-101-1 catalysts could be recovered easily by centrifugation and used repetitively for at least four times. These features make the catalysts particularly attractive in benzaldehyde synthesis.

Comparison of enzymatic and non-enzymatic glucose sensors based on hierarchical Au-Ni alloy with conductive polymer

Enzymatic and non-enzymatic amperometric glucose sensors based on nanostructured Au-Ni alloy were prepared and compared in their performance. The hierarchically structured Au-Ni surface was merely used for the non-enzymatic glucose sensor, while glucose oxidase attached poly-3′(benzoic acid) −2,2′:5′,2′- terthiophene (pTBA) formed on the alloy surface was used as the enzymatic sensor. The fabricated sensor was characterized using surface analysis and electrochemical experiments. In case of the enzymatic sensor, the anodic current of H2O2 generated from the enzyme reaction was used as the analytical signal, while the direct oxidation of glucose was observed on a mere Au-Ni alloy electrode without enzyme immobilization, which shows an excellent catalytic oxidation of glucose even in physiological pH. The potential pulse pretreatment of the sensor surfaces improved the performance, which allowed both the sensors reproducible and reusable (enzymatic sensor: coefficient of variation = 1.82%, n = 5, non-enzymatic: coefficient of variation = 2.93%). The enzymatic biosensor reveals the advantages of increased sensitivity, selectivity, and stability, compared with the non-enzymatic sensor. The linear range of enzymatic sensor was attained from 1.0 µM to 30.0 mM with a detection limit of 0.29 μM. The reliabilities of the sensors were also demonstrated through the glucose analysis in human blood samples, and the result was compared with the commercially available glucometer.

NiAu Single Atom Alloys for the Non-oxidative Dehydrogenation of Ethanol to Acetaldehyde and Hydrogen

Gold is examined here as an alternative to copper for the selective dehydrogenation of ethanol to acetaldehyde and hydrogen. Despite its high selectivity, gold is only active at temperatures higher than 250 °C for this reaction. We demonstrate that addition of a small amount of Ni on either supported or unsupported Au surfaces induces resistance to sintering, along with a beneficial effect on the catalytic activity. NiAu alloys prepared here with Ni as the minority component to the limit of atomic dispersion in the gold surfaces, catalyze the reaction beginning below 150 °C. A significant decrease of the apparent activation energy from 96 ± 3 kJ/mol for the monometallic Au to 59 ± 5 kJ/mol for the alloy was found. The Ni dispersion and concentration as a function of gas environment was followed by in situ DRIFTS and by XPS. The stability of the catalyst morphology was investigated through post-reaction microscopy imaging and long-term stability tests under reaction conditions. As shown via dynamic reaction experiments, acetaldehyde and H2 were selectively produced up to 280 °C. A small drop of selectivity at higher temperatures is attributed to the formation of Ni clusters, as proven by CO-DRIFTS on the used sample. Comparison with samples of higher Ni loading, where Ni clusters are formed, clearly shows that they catalyze the undesired full decomposition of ethanol to CO, CH4, and H2.

Sulphur tolerance of Au-modified Ni/GDC during catalytic methane steam reforming

Au doping and high calcination temperatures improve the sulphur tolerance of Ni/GDC, a potential SOFC anode.

Au[sbnd]Ni alloy nanoparticles supported on reduced graphene oxide as highly efficient electrocatalysts for hydrogen evolution and oxygen reduction reactions

Bimetallic nanoparticles of Au and Ni in the form of alloy nanostructures with varying Ni content are synthesized on reduced graphene oxide (rGO) sheets via a simple solution chemistry route and tested as electrocatalysts towards the hydrogen evolution (HE) and oxygen reduction (OR) reactions using polarization and impedance studies. The AuNi alloy NPs/rGO nanocomposites display excellent electrocatalytic activity which is found to improve with increasing Ni content in the AuNi/rGO alloy nanocomposites. For HER, the best AuNi alloy NPs/rGO electrocatalyst, the one with the highest Ni content, exhibits high activity with an onset overpotential approaching zero versus the reversible hydrogen electrode and an overpotential of only 37 mV at 10 mA cm−2. Additionally, a low Tafel slope of 33 mV dec−1 and a high exchange current density of 0.6 mA cm−2 are measured which are very close to those of commercial Pt/C catalyst. Also, in the ORR tests, this electrocatalyst displays comparable activity to Pt/C. The Koutecky–Levich plots referred to a 4-electron mechanism for the reduction of dissolved O2 on the AuNi alloy NPs/rGO catalyst. The electrocatalyst thus demonstrates excellent activity towards HER and ORR. Additionally, it exhibits outstanding operational durability and activation after 10,000th cycles assuring its practical applicability.

Ni Alloy Monolayer Electrodeposition

The morphology and the microstructure of alloys grown by co-electrodeposition generally result from kinetics and depart from equilibrium. On the atomic scale key parameters include binding energies (e.g. adatom – surface, adatom – adatom etc.) and also on adatom mobility. In this presentation we will examine the impact of above parameters on Ni alloy monolayers electrodeposition. An unreconstructed AuPd(111) substrate is used to co-deposit Ni and Ag, Au [1] and Pd [2]. These elements were chosen because they present different bulk mixing enthalpies with Ni, from phase separation (Ag) to perfect mixing (Pd). These three elements present also quite different surface mobility. Complementary experiments in which the two metals are sequentially deposited [3] [4] as well as dealloying experiments (selective dissolution of Ni) [5] will be presented in support of discussion. References : [1] F. Lecadre et al. AuNi alloy monolayer films electrodeposited on Au(111): An in situ STM study, Surf. Sci. 607, 25 (2013). [2] A. Damian et al. Electrodeposition of NiPd monolayer on Au(111): An in situ scanning tunneling microscopy study, Electrochim. Acta 112, 824 (2013). [3] A. Damian et al. Selective Growth and Dissolution of Ni on a PdAu Bimetallic Surface by In Situ STM: Determining the Relative Adsorbate-Substrate Interaction Energy, Phys. Rev. Lett. 102, 196101 (2009). [4] F. Lecadre et al. Electrodeposition of Ag, Pd and Au on Ni monolayer islands on (1 × 1)-Au(111) by in-situ scanning tunneling microscopy, Electrochim. Acta 197, 241 (2016). [5] A. Damian et al. Electrochemical de-alloying in two dimensions: role of the local atomic environment, Nanoscale 8, 13985 (2016).

A flexible and highly effective paper based gold electrode for sodium borohydride electrocatalysis

A binder-free and flexible Au electrode is prepared by spontaneous deposition of Au onto a A4 (A4-paper)-8B (8B pencil)-Ni Film substrate (ABNi) which is assembled by electrodeposition of nanoscale Ni particles on the surface of A4 paper coated by 8B pencil. The morphology and phase structure of the (A4-paper)-8B (8B pencil)-Ni Film-Au (ABNiAu) electrode are characterized by scanning electron microscopy equipped with energy dispersive X-ray spectrometer and X-ray diffractometer. The catalytic activity of the ABNiAu electrode for NaBH4 electrooxidation is investigated by means of cyclic voltammetry and chronoamperometry. The electrode exhibits a high electric conductivity and the activity substance attaches to the surface of paper substrate tightly and does not fall off at all and the nanoscale Ni and NiAu alloy enhance the broken of the BH bond in the BH4−, all of which lead to a high catalytic activity for NaBH4 electrooxidation. The oxidation current density reaches 300 mA cm−2 in 1 mol dm−3 NaOH and 0.1 mol dm−3 NaBH4 at −0.2 V. The exchanged electrons (n) is 6.0 (8.0 in theory), which indicates that the ABNiAu electrode has much higher utilization efficiency of the fuel than our reported LaNi5/Pd (n = 4) electrode.

Nanosized structural features of electrodeposited Au–Co and Au–Ni alloy coatings

The structure of Au–Co and Au–Ni alloy coatings deposited at low current density (2–20 mA cm−2) from weakly acidic additive-free electrolyte with higher (16–20 g L−1 Co or Ni) than usually employed (0.1–1.0 g L−1) concentration of the alloying element was investigated. Under these conditions, structural effects in the coatings were observed representing nanoscale, porous (in the case of Au–Co coatings) or hollow (in Au–Ni alloy coatings) formations, passing through the coating and ending at the surface as craters. They could be associated with the influence of the accompanying hydrogen evolution. On one hand, hydrogen bubbles are firmly adsorbed on the surface, and on the other hand, the electrolyte has very good penetrating and covering ability. As a result, depending on the dynamics of the deposition process, porous structures with different configurations are formed. The formation of the structures begins in the early stages of the electrocrystallisation and the substrate affects the number, size and distribution of the features.

SiO2-supported Au-Ni bimetallic catalyst for the selective hydrogenation of acetylene

Supported Au catalysts have been reported to exhibit high ethylene selectivity in the hydrogenation of acetylene, but the conversion is relatively low. Adding a second metal to Au has proven to be a promising approach to enhance its catalytic performance in acetylene hydrogenation. In this work, SiO2-supported Au-Ni bimetallic catalysts were synthesized and investigated in the selective hydrogenation of acetylene. The Au-Ni bimetallic catalysts exhibited much higher catalytic performance than that of the corresponding monometallic Au or Ni catalysts. By tuning the reduction temperature and/or Ni loading, we obtained an Au-Ni/SiO2 catalyst with optimal performance. The results of transmission electron microscopy imaging revealed that the Au-Ni bimetallic particles were highly dispersed on the SiO2 support. Meanwhile, analysis of the bimetallic catalyst by energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy demonstrated the formation of Au-Ni alloy, which contributed to the synergistic effect between Au and Ni in the hydrogenation of acetylene.

Non-bonding and bonding interactions of biogenic impurities with the metal catalyst and the design of bimetallic alloys

Interaction of biogenic impurities with the Ni (111) catalyst surface was studied to understand their important role in inhibiting catalysis. Non-bonding interactions of amino acids (Alanine (Ala), Cysteine (Cys), Methionine (Met), Tryptophan (Trp), Histidine (His), Lysine (Lys), Glutamic acid (Glu) and Threonine (Thr)) in aqueous environment were examined using classical molecular dynamics (MD) simulations. The potential of mean force (PMF) profiles of amino acids revealed qualitative differences, resulting into altered orientation and the choice of preferential interacting site with the metal surface. The side chains of all the amino acids were observed to align parallel to the metal surface. Amino acids containing sulfur (Met and Cys) and heterocyclic nitrogen (Trp, His) were observed to interact favorably with the Ni surface. Most of the preferential interacting sites were observed to be in direct contact with the surface except Lys which interacted with the backbone nitrogen oriented away from the surface. The strength of non-bonded interactions varied from −13 to −71kJ/mol with Ala as the weakest and Trp as the strongest interacting amino acids. The interaction energies scaled linearly with the solvent accessible surface area of the amino acids. Density functional theory (DFT) calculations were utilized to understand the bonding interactions of sulfur (S) containing amino acids (Met and Cys) and the irreversible catalyst deactivation caused by them. DFT calculations showed strong binding for both Cys (−123kJ/mol) and Met (−115kJ/mol), undergoing dissociation to form atomic S on the Ni (111) surface with an intrinsic activation barrier of 32kJ/mol and 133kJ/mol, respectively, for the CS bond cleavage. However, the mechanistic routes for dissociation followed by the two amino acids were a bit different. While in Cys, the C-H activation was followed by CS cleavage, in Met, CS bond was activated first to form S-CH3 species on the catalyst surface. In contrast to Met at higher coverage, Cys was observed to decompose to elemental S on the surface. The mechanistic insights thus obtained lead to an explorative theoretical framework for the design of a bimetallic catalyst, which may be used in an integrated bio and chemo-catalytic process with reduced chances of deactivation. The Ni-Au alloy surface showed lower binding energies for both Met (−88kJ/mol) and S (−132kJ/mol), as compared to pure Ni surface, indicating promising prospects for the activity of such an alloy catalyst.

Thickness engineering of atomic layer deposited Al2O3 films to suppress interfacial reaction and diffusion of Ni/Au gate metal in AlGaN/GaN HEMTs up to 600 °C in air

In this paper, we describe the use of 50 nm atomic layer deposited (ALD) Al2O3 to suppress the interfacial reaction and inter-diffusion between the gate metal and semiconductor interface, to extend the operation limit up to 600 °C in air. Suppression of diffusion is verified through Auger electron spectroscopy (AES) depth profiling and X-ray diffraction (XRD) and is further supported with electrical characterization. An ALD Al2O3 thin film (10 nm and 50 nm), which functions as a dielectric layer, was inserted between the gate metal (Ni/Au) and heterostructure-based semiconductor material (AlGaN/GaN) to form a metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). This extended the 50 nm ALD Al2O3 MIS-HEMT (50-MIS) current-voltage (Ids-Vds) and gate leakage (Ig,leakage) characteristics up to 600 °C. Both, the 10 nm ALD Al2O3 MIS-HEMT (10-MIS) and HEMT, failed above 350 °C, as evidenced by a sudden increase of approximately 50 times and 5.3 × 106 times in Ig,leakage, respectively. AES on the HEMT revealed the formation of a Ni-Au alloy and Ni present in the active region. Additionally, XRD showed existence of metal gallides in the HEMT. The 50-MIS enables the operation of AlGaN/GaN based electronics in oxidizing high-temperature environments, by suppressing interfacial reaction and inter-diffusion of the gate metal with the semiconductor.

Effective site-energy model: A thermodynamic approach applied to size-mismatched alloys

We present a novel energetic model that takes into account atomistic relaxations to describe the thermodynamic properties of ${A}_{c}{B}_{1\ensuremath{-}c}$ binary alloys. It requires the calculation of the energies on each site of a random solid solution after relaxation as a function of both the local composition and the nominal concentration. These site energies are obtained by molecular static simulations using $N$-body interatomic potentials derived from the second-moment approximation (SMA) of the tight-binding scheme. This new model allows us to determine the effective pair interactions (EPIs) that drive the short-range order (SRO) and to analyze the relative role of the EPIs' contribution to the mixing enthalpy, with respect to the contribution due to the lattice mismatch between the constituents. We apply this formalism to Au-Ni and Ag-Cu alloys, both of them tending to phase separate in the bulk and exhibiting a large size mismatch. Rigid-lattice Monte Carlo (MC) simulations lead to phase diagrams that are in good agreement with both those obtained by off-lattice SMA-MC simulations and the experimental ones. While the phase diagrams of Au-Ni and Ag-Cu alloys are very similar, we show that phase separation is mainly driven by the elastic contribution for Au-Ni and by the EPIs' contribution for Ag-Cu. Furthermore, for Au-Ni, the analysis of the SRO shows an inversion between the tendency to order and the tendency to phase separate as a function of the concentration.