Ni-Mo Alloy Research Articles

Ni–Mo alloy nanostructures as cathodic materials for hydrogen evolution reaction during seawater electrolysis

In the case of hydrogen production involving seawater electrolysis, one of the main targets is to develop more active cathodic materials, to optimize the efficiency of hydrogen evolution reaction (HER) and, by doing so, enhance the overall energy efficiency of electrolysis. Thus, to develop suitable HER electrocatalysts either an increase of the electrode active surface area or a design of a material having high intrinsic catalytic activity should be taken into consideration, both of them decreasing the HER overpotential. In the present work, various Ni–Mo alloy nanostructures (10–40 wt% Mo) have been prepared involving electrochemical deposition from aqueous and deep eutectic solvent (DES)-based electrolytes as potential cathodic materials suitable for hydrogen evolution reaction during water electrolysis. The electrocatalytic activity of the obtained layers has been investigated using real seawater electrolyte. The determined Tafel slopes suggested that the electrodeposited Ni–Mo alloy coatings follow an HER mechanism controlled by the Volmer reaction step. The EIS results indicated that the use of choline chloride-based ionic liquids as electrolytes facilitated Ni–Mo alloy coatings showing a significant increase in surface roughness. Studies of the intrinsic activity showed that the main contribution towards the apparent activity comes from the increase of the real surface area, although a slight increase of the intrinsic electrocatalytic activity in the case of Ni–Mo alloy coatings electrodeposited on Ni foam was also noticed. These results showed that Ni–Mo alloy coatings electrodeposited from the novel electrolytes based on choline chloride–urea–citric acid ternary mixtures associated with a porous substrate may represent a promising technological approach to build cathodic materials suitable for seawater electrolysis.

Annealing‐Induced Hardening in Ultrafine‐Grained Ni–Mo Alloys

The influence of Mo alloying on annealing‐induced hardening in ultrafine‐grained (UFG) Ni is studied. The hardening observed after low temperature annealing is explained by the annihilation of mobile dislocations and a concomitant clustering of the remaining dislocations into low energy configurations. This study reveals that, with increasing Mo concentration, the hardening effect decreases as the Mo solute atoms hinder the annihilation and rearrangement of dislocations. This trend is the opposite to that observed in electrodeposited Ni–Mo alloys where the larger alloying element concentration yields a higher annealing‐induced strengthening effect. The difference is attributed to the different deformation mechanisms in UFG and nanocrystalline Ni–Mo alloys.

Colloidal Synthesis of Mo–Ni Alloy Nanoparticles as Bifunctional Electrocatalysts for Efficient Overall Water Splitting

AbstractThe practical use of overall water electrolysis is largely hindered by the need for precious noble metal‐based catalysts. Here, the colloidal synthesis of earth‐abundant electrocatalysts of Mo–Ni nanoparticles for efficient water splitting by thermal decomposition of Ni(acac)2 and Mo(CO)6 in the presence of 1‐octadecene and oleylamine at 320 °C is reported. It is shown that the optimized catalysts (Mo0.6Ni0.4) only require low overpotentials of 0.065 V for the hydrogen evolution reaction (HER) and of 290 mV for the oxygen evolution reaction (OER) to deliver a current density of 10 mA cm−2 in KOH (1.0 m). The as‐prepared Mo–Ni alloy nanoparticles also show extraordinary durability for both the HER and OER. A low potential of ≈1.62 V is required to yield a current density of 10 mA cm−2 when utilizing the alloy nanoparticles as bifunctional catalysts in a two‐electrode electrolyzer system. The ease of preparing either rigid or flexible high‐performance electrodes by making use of the alloy nanoparticle electrocatalysts without the need for binder further suggests the attractive application of colloidally stable nanoparticles in the field of electrochemical water splitting.

Electrocatalytic Properties of Nickel Foam-Based Ni-Mo, Ni +Mo and Ni+Mo/Ni-Mo Electrodes for Hydrogen Evolution Reaction

Nickel foam-based Ni-Mo alloy electrodes, Ni+Mo composite electrodes and Ni+Mo/Ni-Mo composite alloy electrodes were prepared by eletrodeposition, and the electrocatalytic characteristics for hydrogen evolution reaction (HER) in 30wt% KOH solution were investigated by cathode polarization curve and electrochemical impedance spectroscopy (EIS). The experimental results show that in comparison with nickel foam electrodes, these electrodes exhibit a lower overpotential, a higher exchange current density and a larger real surface area for HER. At 30°C and current density of 200 mA/cm2, the overpotentials of foam Ni electrodes, nickel foam-based Ni-Mo alloy electrodes, Ni+Mo composite electrodes, Ni+Mo/Ni-Mo electrodes are respectively 506, 252, 336, 202 mV. The nickel foam-based Ni+Mo/Ni-Mo composite alloy electrode had the highest HER electrocatalytic activity.

Cooperation between holey graphene and NiMo alloy for hydrogen evolution in an acidic electrolyte

The development of noble-metal-free hydrogen evolution reaction (HER) materials for electrochemical water splitting is the key to achieving low-cost and efficient electrocatalysis that drives electrochemical hydrogen evolution. However, the electrocatalytic activities of most non-noble metals decrease in acidic electrolytes. Here, we have fabricated non-noble-metal electrodes using a bicontinuous and open porous NiMo alloy covered by nitrogen-doped (N-doped) graphene with nanometer-sized holes. This noble-metal-free HER catalyst exhibits performance almost identical with that of a Pt/C electrode, while its original catalytic activity is preserved even in acidic electrolytes. Density functional theory calculations indicate that the interfacial fringes between the nanoholes and NiMo surface induce charge transfer and promote hydrogen adsorption and desorption. The nanometer-sized holes simultaneously provide minimal surface area for chemical reactions, while delaying NiMo dissolution in excessive amounts of...

Pd surface functionalization of 3D electroformed Ni and Ni-Mo alloy metallic nanofoams for hydrogen production

The paper presents some experimental results regarding the functionalization of 3D electroformed Ni and Ni-Mo alloy nanofoams with Pd nanoclusters, as potential cathodic materials suitable for HER during seawater electrolysis. The electrodeposition from aqueous electrolytes containing NiCl2 and NH4Cl has been applied to prepare the 3D Ni nanofoams. Ni-Mo alloys have been electrodeposited involving aqueous ammonium citrate type electrolytes. Pd surface functionalization has been performed using both electroless and electrochemical procedures. Pd content varied in the range of 0.5 – 8 wt.%, depending on the applied procedure and the operation conditions. The use of a porous structure associated with alloying element (i.e. Mo) and Pd surface functionalization facilitated enhanced performances from HER view point in seawater electrolyte (lower Tafel slopes). The determined Tafel slope values ranged from 123 to 105 mV.dec-1, suggesting the Volmer step as rate determining step. The improvement of the HER catalytic activity may be ascribed to a synergistic effect between the high real active area of the 3D electroformed metallic substrate, Ni alloying with a left transition metal and surface modification using Pd noble metal.

Correlation between disorder-order transformations in a Ni-based alloy and its mechanical properties

It is demonstrated that the disorder-order transformations in a commercial Ni-Mo alloy with minor concentrations of Fe and Cr and the corresponding effect on mechanical strength are sensitive functions of the exact chemical composition. A slight change in composition within the specified limits of the alloy is found to change the nature of the ordered phases as well as the kinetics of the transformation and the mechanical strength. The results show that while the increase in tensile yield strength due to atomic order is accompanied by moderate decrease in tensile ductility, additional loss of ductility can occur at constant yield strength due to changes in morphology of the ordered microstructure during isothermal aging. It is also shown that the state of short-range order present in an otherwise disordered solid-solution acts as a pre-existing nucleus for the transformation, which accelerates the respective kinetics. However, elimination of the short-range order by cold work is found to decelerate the kinetics of the transformation. It is concluded that although the disorder-order transformations in the alloy investigated have detrimental effects on mechanical strength, some beneficial effects of technological importance can be realized.

Bottom-up Synthesis of Porous NiMo Alloy for Hydrogen Evolution Reaction

Bottom-up synthesis of porous NiMo alloy reduced by NiMoO4 nanofibers was systematically investigated to fabricate non-noble metal porous electrodes for hydrogen production. The different annealing temperatures of NiMoO4 nanofibers under hydrogen atmosphere reveal that the 950 °C annealing temperature is key for producing bicontinuous porous NiMo alloy without oxide phases. The porous NiMo alloy acts as a cathode in electrical water splitting, which demonstrates not only almost identical catalytic activity with commercial Pt/C in 1.0 M KOH solution, but also superb stability for 12 days at an electrode potential of −200 mV vs. reversible hydrogen electrode (RHE).

Electrodeposition of Ni–Mo–rGO composite electrodes for efficient hydrogen production in an alkaline medium

Enhanced performance of Ni–Mo alloy coatings due to the incorporation of rGO into the alloy matrixviaan electrodeposition method.

Corrosion inhibiting action of Ni–Mo alloy coatings in the presence of mixed metal oxide nanocomposites

Enhanced anti-corrosion properties of Ni–Mo alloy coatings by addition of mixed metal oxide nanoparticles via an electrodeposition method.

A triple synergistic effect from pitaya-like MoNix–MoCx hybrids encapsulated in N-doped C nanospheres for efficient hydrogen evolution

A facile strategy of using organic–inorganic precursor and followed carbonization is adopted to prepare ternary core–shell nanostructures composed of ultrafine hybrids of MoNi alloys and MoCx nanoparticles encapsulated in N-doped carbon nanospheres (MoNix–MoCx@NC).

Simple routes for the improvement of hydrogen evolution activity of Ni-Mo catalysts: From sol-gel derived powder catalysts to graphene supported co-electrodeposits

Development of noble metal-free catalysts for hydrogen production is one of the cores of the sustainable energy economy. Here we present results of systematic analysis of catalytic activity of Ni-Mo alloy powders in alkaline media towards hydrogen evolution reaction (HER). Catalysts were prepared in a wide concentration range (from Ni0.2Mo0.8 to Ni0.9Mo0.1), and resulted with a volcano shaped activity-composition relationship, with maximum catalytic activity achieved for the powder with nominal composition Ni0.6Mo0.4. Improved HER activity is ascribed to reduced deactivation by hydride formation and adequate hydrogen-surface energetics on Ni-Mo catalysts. In the second part, we demonstrate a novel method for electrochemical formation of NiMo@rGO composites. Prepared composite electrodes show improved electrocatalytic activity compared to both pure Ni and Ni@rGO electrodes. Activity was observed to depend on the deposition time and is contributed by two factors: (i) formation of Ni-Mo system and (ii) formation of an interfacial region with rGO. We expect that the provided activity-composition relationship in combination with novel electrochemical NiMo-rGO composite formation procedure will provide a route for the development of new highly efficient noble metal-free HER electrocatalysts.

Preparation and characterization of porous Ni-Mo alloy and its electrocatalytic performance for hydrogen evolution in filter-press type electrolyzer

In the study, the device parameters for filter-press type electrolyzer including internal structure of unit cell, diaphragm, electrolyte temperature, pore number of nickel foam, and cathode were investigated. And the porous Ni-Mo alloy had been successfully prepared by a new method. The results of SEM, XRD, and UV spectrophotometry presented that the porous Ni-Mo alloys exhibited a three-dimensional network structure and were full of reticulate pore, having a considerably higher specific surface area, with NiMo and Ni4Mo mixed state when the Mo content of the porous Ni-Mo alloy coatings was 17.56 wt.%. The electrocatalytic performance for hydrogen evolution reaction of porous Ni-Mo alloy was also studied in 30 wt.% KOH using steady-state polarization and cell test. The results clearly demonstrated that the porous Ni-Mo alloy with 17.56 wt.% Mo content showed better and relative stable electrocatalytic performance for hydrogen evolution in a certain electrolysis time, which can be attributed to its chemical composition, porous structure, and specific surface area.

Nickel-molybdenum alloy catalysts for the hydrogen evolution reaction: Activity and stability revised

Ni-Mo alloys and compounds are considered as highly active catalysts for the hydrogen evolution reaction (HER) in alkaline electrolytes. The origin of the reported high activity is, however, not yet fully understood. In this study, the fundamental activity for the HER and stability of metallurgically prepared Ni, Mo and different Ni-Mo alloy electrodes with comparable surface areas in alkaline electrolyte are studied in detail. Interestingly, the intrinsic activities of polished Ni-Mo electrodes were slightly lower than those of pure Ni electrodes. Moreover, using an electrochemical flow cell that is coupled to a mass spectrometer we show that Mo leaches out of the prepared samples and dissolves at HER relevant conditions. The Ni to Mo ratio of surface atoms was found to increase after electrochemical treatment, additionally confirming leaching of the less noble Mo. On the basis of our results we conclude that some of the previously reported high activities might be attributed to high surface areas that result from the manufacturing process and/or electrochemical de-alloying, rather than to intrinsic properties of the alloy.

Ni-Assisted Low Temperature Synthesis of MoCx with Enhanced HER Activity.

Here we report a novel one-pot approach to synthesize MoCx catalysts at much lowered temperature for hydrogen evolution reaction (HER) in acidic solution. A room-temperature co-precipitation reaction among Ni2+ , MoO42- and 2-methylimidazole in an aqueous solution produced a Mo-Ni-imidazole complex, which was used as the precursor to fabricate MoCx . The morphological and chemical properties of the obtained MoCx affected by calcination and other additive metal sources (like Fe, Co, Cu) were investigated in detail. We demonstrated that Ni-Mo alloying took place prior to MoCx formation during heating, which catalyzed the crystallization of MoCx at relatively low temperature. The MoCx /Ni-650 catalyst exhibited a quite low overpotential of 172 mV at 20 mA cm-2 . The high performance originates from the synergistic effect between MoCx and Ni-Mo alloy, high ratio of Mo3+ /Mo2+ , as well as high electrochemically active surface area and low charge-transfer resistance. This work would open a new way to the design and fabrication of other transition-metal carbide catalysts.

The influence of arabic gum on the catalytic properties of Ni-Mo alloy coatings to intensify hydrogen evolution reaction

PurposeBecause of its wide applications in the industry, the electrodeposition of Ni/Mo as corrosion barrier and decorative coating took the attention of numerous researchers. This paper aims to study the effect of electroplating current density on different characteristics of Ni/Mo alloy coatings, especially on the morphology and electrochemical comportment in 3.5 per cent NaCl corrosion medium.Design/methodology/approachIn this paper, the authors have used electrodeposition technique to codeposite molybdenum particles in nickel matrix as protective coating against corrosion attacks, in addition to test the intensification of hydrogen reaction of this alloy coatings using EIS technique.FindingsNi-Mo alloy coating is well adherent to the substrate. The deposited Ni-Mo was observed to be fissured and porous in morphology. The main phases identified in different exposed coatings are MoNi4, Ni3Mo and Mo1.24Ni0.76. The effect of applied current density on electrochemical properties was studied. Inhibitory efficiency of gum arabic was controlled by the electroplating current density.Originality/valueIn this paper, the authors report on the presence of Mo particles in Ni matrix also the effect of electroplating current density on different properties of alloy coatings Ni/Mo. This is significant because it reports on the effect of current density on Ni/Mo electrodeposited at economic conditions like low temperature and moderate pH. Moreover, this paper gives a solution to the corrosion of crude oil desalter by using Ni-Mo coatings and then injecting a small amount of gum arabic in the oil pipeline before dissalement which gives long life to the reactor.

Upgrade of the ultracold neutron source at the pulsed reactor TRIGA Mainz

The performance of the upgraded solid deuterium ultracold neutron source at the pulsed reactor TRIGA Mainz is described. The current configuration stage comprises the installation of a He liquefier to run UCN experiments over long-term periods, the use of stainless steel neutron guides with improved transmission as well as sputter-coated non-magnetic $^{58}$NiMo alloy at the inside walls of the thermal bridge and the converter cup. The UCN yield was measured in a `standard' UCN storage bottle (stainless steel) with a volume of 32 litres outside the biological shield at the experimental area yielding UCN densities of 8.5 /cm$^3$; an increase by a factor of 3.5 compared to the former setup. The measured UCN storage curve is in good agreement with the predictions from a Monte Carlo simulation developed to model the source. The growth and formation of the solid deuterium converter during freeze-out are affected by the ortho/para ratio of the H$_2$ premoderator.

Losses and depolarization of ultracold neutrons on neutron guide and storage materials

At Institut Laue-Langevin (ILL) and Paul Scherrer Institute (PSI), we have measured the losses and depolarization probabilities of ultracold neutrons on various materials: (i) nickel-molybdenum alloys with weight percentages of 82/18, 85/15, 88/12, 91/9, and 94/6 and natural nickel Ni100, (ii) nickel-vanadium NiV93/7, (iii) copper, and (iv) deuterated polystyrene (dPS). For the different samples, storage-time constants up to $\ensuremath{\sim}460\phantom{\rule{0.16em}{0ex}}\mathrm{s}$ were obtained at room temperature. The corresponding loss parameters for ultracold neutrons, $\ensuremath{\eta}$, varied between $1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and $2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. All $\ensuremath{\eta}$ values are in agreement with theory except for dPS, where anomalous losses at room temperature were established with four standard deviations. The depolarization probabilities per wall collision $\ensuremath{\beta}$ measured with unprecedented sensitivity varied between $0.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ and $9.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. Our depolarization result for copper differs from other experiments by 4.4 and 15.8 standard deviations. The $\ensuremath{\beta}$ values of the paramagnetic NiMo alloys over molybdenum content show an increase of $\ensuremath{\beta}$ with increasing Mo content. This is in disagreement with expectations from literature. Finally, ferromagnetic behavior of NiMo alloys at room temperature was found for molybdenum contents of 6.5 at.% or less and paramagnetic behavior for more than 8.7 at.%. This may contribute to solving an ambiguity in literature.

Superaerophobic Ultrathin Ni-Mo Alloy Nanosheet Array from In Situ Topotactic Reduction for Hydrogen Evolution Reaction.

Hydrogen evolution reaction (HER) has prospect to becoming clean and renewable technology for hydrogen production and Ni-Mo alloy is among the best HER catalysts in alkaline electrolytes. Here, an in situ topotactic reduction method to synthesize ultrathin 2D Ni-Mo alloy nanosheets for electrocatalytic hydrogen evolution is reported. Due to its ultrathin structure and tailored composition, the as-synthesized Ni-Mo alloy shows an overpotential of 35 mV to reach a current density of 10 mA cm-2 , along with a Tafel slope of 45 mV decade-1 , demonstrating a comparable intrinsic activity to state-of-art commercial Pt/C catalyst. Besides, the vertically aligned assemble structure of the 2D NiMo nanosheets on conductive substrate makes the electrode "superaerophobic," thus leading to much faster bubble releasing during HER process and therefore shows faster mass transfer behavior at high current density as compared with drop drying Pt/C catalyst on the same substrate. Such in situ topotactic conversion finds a way to design and fabricate low-cost, earth-abundant non-noble metal based ultrathin 2D nanostructures for electrocatalytic issues.

Nickel molybdenum carbides: Synthesis, characterization, and catalytic activity in hydrodeoxygenation of anisole and ethyl caprate

Mo- and Ni-containing carbide catalysts were prepared by a Pechini-based method using citric acid as a complexing agent. All the catalysts were characterized by temperature-programmed reduction, X-ray diffraction (XRD), X-ray photoelectron spectroscopy, and N2 and CO sorption. The XRD experiments showed that the bimetallic systems contain phases: β-Mo2C and Mo3Ni2C and an alloy NixMo1−x with a high nickel content. The catalysts were tested in the hydrogenation of ethyl caprate and anisole. For the process with ethyl caprate, it was shown that the catalytic activity rises with an increase of the carbide phase content in the bimetallic catalysts. Further addition of nickel increases the amount of the Ni–Mo alloy, which leads to a drop in the catalytic activity and to an increase in the contribution of the decarboxylation pathway. The study of the carbide catalysts in anisole hydrogenation showed that a rise in the Ni/Mo ratio leads to an increase in activity.