Nickel Hydride Formation Research Articles

Thermodynamic calculations using reverse Monte Carlo: A computational workflow for accelerated construction of phase diagrams for metal hydrides

Metal hydrides are promising candidates for hydrogen storage applications. From a materials discovery perspective, an accurate, efficient computational workflow is urgently required that can rapidly analyze/predict thermodynamic properties of these materials. In this paper, we develop a thermodynamic property estimation/phase diagram construction framework based on the lattice reverse Monte Carlo (RMC) method. We apply the technique to the nickel hydride (NiHx) system by calculating the pressure-composition-temperature (PCT) isotherm and constructing its phase diagram. Formation of nickel hydride entails significant volume expansion, strong interaction between hydrogen and the host atoms, lattice strain, and a phase transition. An attractive feature of our approach is that the entire phase diagram can be accurately constructed in few minutes by considering <10 configurations. In contrast, a popular technique based on grand canonical Monte Carlo would require sampling of several million configurations. The promising results obtained with our computational workflow suggest that the approach can be used in future for wider materials search and discovery.

Development of (Fe-Co-Ni)-Si-B metallic glass catalyst for promoting degradation of acid orange II azo-dye

Fe-based metallic glass (MG) catalyst, also called amorphous zero-valent iron (AZVI), is a functional material that has recently been in the spotlight due to its high reactivity compared to conventional catalysts for wastewater purification. In this study, novel Fe-based MG with excellent degradation rate and reusability was developed through systematic investigation by tailoring the contents of Co and Ni and structural design to form (Fe, Co, Ni)-rich clusters. We found that the process of dye degradation by a Fenton-like oxidative reaction with H2O2 can have low activation energy, assisted by a reductive reaction with nickel hydride formation. Consequently, the reductive and oxidative complex dye degradation mechanism can be effectively implemented to improve degradation rate and reusability, significantly superior to that of the commercial zero-valent iron(Fe0, ZVI) powder. Our findings revealed the compositional and structural key principles of Fe-based MG design, and are expected to provide new opportunities for industrial applications of advanced Fe-based MG.

Nitrile modulated-Ni(0) phosphines in trans-selective phenylpropenoids isomerization: An allylic route by a regular η1-N(end-on) or an alkyl route via a flipped-nitrile?

Acetonitrile has been widely viewed as a weakly coordinating solvent in metal-catalyzed reactions. Evidence is presented herein that it worked as an actor ligand in nickel-catalyzed stereoselective isomerizations of eugenol, methyl eugenol, estragole, and allylphenol, with trans-isomerized products of ≥95%. Nickel(0)(nitrile)phosphines were generated in situ from Ni(II) salt in the presence of phosphines, Zn, and nitrile with Ni/phosphines/Zn/nitrile mole ratio as low as 1:2:1:1. The isomerization of eugenol gave trans-isoeugenol of >97% in 30 min at r.t. with Ni turnover frequency (TOF) up to 1,116 h−1 and the activation energy of 61 kJ·mol−1. High selectivity of trans-isoeugenol was retained in continuous and multi-gram trials. Density functional theory (DFT)/PBE0-D3 calculations rationalized the possible formation of nickel hydride (i.e., Ni(H)(η1-CH2CN)(phosphine) complex) from η1-N(end-on)-Ni complex. This nitrile modulated-Ni(0) complex indicated the complex followed an alkyl-type isomerization, instead of a conventional allylic-type one.

Tritopic NHC Precursors: Unusual Nickel Reactivity and Ethylene Insertion into a C(sp3)–H Bond

AbstractThe imidazolium chloride [C3H3N(C3H6NMe2)N{C(Me)(=NDipp)}]Cl (1; Dipp=2,6‐diisopropyl phenyl), a potential precursor to a tritopic NimineCNHCNamine pincer‐type ligand, reacted with [Ni(cod)2] to give the NiI‐NiI complex 2, which contains a rare cod‐derived η3‐allyl‐type bridging ligand. The implied intermediate formation of a nickel hydride through oxidative addition of the imidazolium C−H bond did not occur with the symmetrical imidazolium chloride [C3H3N2{C(Me)(=NDipp)}2]Cl (3). Instead, a Ni−C(sp3) bond was formed, leading to the neutral NimineCHNimine pincer‐type complex Ni[C3H3N2{C(Me)(=NDipp)}2]Cl (4). Theoretical studies showed that this highly unusual feature in nickel NHC chemistry is due to steric constraints induced by the N substituents, which prevent Ni−H bond formation. Remarkably, ethylene inserted into the C(sp3)−H bond of 4 without nickel hydride formation, thus suggesting new pathways for the alkylation of non‐activated C−H bonds.

Tritopic NHC Precursors: Unusual Nickel Reactivity and Ethylene Insertion into a C(sp3 )-H Bond.

The imidazolium chloride [C3 H3 N(C3 H6 NMe2 )N{C(Me)(=NDipp)}]Cl (1; Dipp=2,6-diisopropyl phenyl), a potential precursor to a tritopic Nimine CNHC Namine pincer-type ligand, reacted with [Ni(cod)2 ] to give the NiI -NiI complex 2, which contains a rare cod-derived η3 -allyl-type bridging ligand. The implied intermediate formation of a nickel hydride through oxidative addition of the imidazolium C-H bond did not occur with the symmetrical imidazolium chloride [C3 H3 N2 {C(Me)(=NDipp)}2 ]Cl (3). Instead, a Ni-C(sp3 ) bond was formed, leading to the neutral Nimine CHNimine pincer-type complex Ni[C3 H3 N2 {C(Me)(=NDipp)}2 ]Cl (4). Theoretical studies showed that this highly unusual feature in nickel NHC chemistry is due to steric constraints induced by the N substituents, which prevent Ni-H bond formation. Remarkably, ethylene inserted into the C(sp3 )-H bond of 4 without nickel hydride formation, thus suggesting new pathways for the alkylation of non-activated C-H bonds.

Formation of nickel hydrides in reactive plasmas

The behaviour of hydrogen in metals has attracted scientific attention for many decades and is interesting from both basic research and technological points of view. Metal hydrides find a wide range of applications of which the most prominent is the reversible hydrogen storage. This is of great importance in view of possible future hydrogen economy. Moreover the high diffusivity of hydrogen also makes nanoscaled Me-H systems interesting possibilities for sensor applications, and surface reactions with hydrogen on Pt, Pd, Ni, and other metals are applied in catalysis, particularly in fuel cells.

Electrochemical hydrogen storage and usage aspects: Nickel electrode in acidic electrolyte

The conditions of electrochemical formation of nickel hydride are investigated. The electrochemical properties of different nickel-based materials (bulk, porous, foamed tapes) are examined to state the hydrogen adsorption/absorption phenomena and possibility to use them as a negative electrode in hydrogen devices (electrolyzers, rechargeable batteries, fuel cells). Surface activation of nickel materials are made by electroplating and etching methods. Thin palladium coating is used to prove the formation of nickel hydride during cathodic charging. Volt-amperometric and kinetic measurements show that not only palladium, but also activated nickel plays important role in the surface activation of electrode materials and promotion of hydrogen absorption in nickel substrate materials.

Facile Preparation and Activation of High‐Productivity Single‐Site Nickel Catalysts for Highly Linear Polyethylene

AbstractA easy‐to‐prepare series of nickel complexes are reported, which, upon activation with near‐stoichiometric alkylating agents, polymerize ethylene with turnover number (TON) of over 105, which brings the catalyst into the range of commercial single‐site catalysts based on early transition metals. However, in contrast to the usual metallocenes, the catalyst shows the same activity in coordinating solvents such as THF and dioxane as it shows in toluene. Moreover, the polymer produced is highly linear, which, together with the long catalyst lifetime, suggests that the combination of the nickel catalyst and a Lewis acid suppresses formation of nickel hydrides.

XRD studies of nickel hydride formation in alkaline solutions containing a promotor

An effect of cathodic charging conditions on the amount of the β-NiH x phase formed in nickel electrode in alkaline solutions was studied by means of X-ray diffraction technique. Electrolytic nickel coatings on copper substrate were hydrogenated in KOH, NaOH, LiOH and NH 4OH solutions containing promoters such as As 2O 3, Sb and GeO 2. Dependences of the β-NiH x phase volume fraction on the promotor concentration, charging current density and charging duration were studied. Optimal values of these charging conditions parameters were determined. The volume fraction of the β-NiH x phase amounted up to ∼56% of 10 μm thick nickel coating. The quantity of nickel hydride did not depend on the alkali and its concentration. Promoters were arranged in the following order of effectiveness in causing nickel hydride formation: S>As>Sb>Ge. It was suggested that NiAs type compounds could take part in the nickel hydride formation.

Hydrogen distribution between the surface and the bulk of thin nickel film at low temperatures

Hydrogen interaction with a thin Ni film was studied by measuring simultaneously the surface potential and the H2 pressure. It has been found that the negatively and positively charged adspecies coexist on the surface at low temperature (78K). The negatively charged adspecies arise at the beginning of adsorption and are stable on the surface. The induced, positively charged adspecies incorporate below the surface, becoming a precursor state of the adsorbate for the nickel hydride formation. The electrostatic interaction within the positively charged, weakly bound adsorbate influences the kinetics of hydrogen adsorption and desorption.

Effect of the pH value of the hydrogenation solution upon the phase transformation of nickel into nickel hydride

The effect of pH value of the hydrogenation solution, containing H 2SeO 3 as a hydrogenation-enhancing additive upon the phase transformation of nickel into β-nickel hydride in electrodeposited bright nickel coatings during cathodic charging was studied using X-ray diffraction. The nickel hydride formation terminates at pH value over 2.1. At this pH value in the bulk of hydrogenation solution, the pH value within the layer in the vicinity of the nickel electrode shift during the cathodic process to the alkaline region as a result of hydrogen evolution. An indication of the alkalization is the shift of the nickel electrode potential towards more negative values (−1.3 V NHE) within the range of pH values where phase transformation terminates. The hydrogenation enhancing effect of H 2SeO 3 appears to occur when the deposition of selenium on nickel surface begins. Strong hydrogenation of samples with co-deposited selenium proceeds during cathodic polarization in an acidic medium without an enhancing additive.

Electrochemical formation of nickel hydride in alkaline solutions

The electrochemical formation of nickel hydride in alkaline solutions is discussed and compared with known results in acid solutions and investigations in high pressure electrolysis. It is supposed that probably surface or subsurface hydrides are formed in alkaline solutions, instead of the bulk, three-dimensional hydride. The importance of electrochemical investigations in this respect is stressed, but a warning is expressed for overinterpretations of the equivalence between the overvoltage and the effective thermodynamic activity on the electrode surfaces considered.

Formation of nickel hydrides by hydrogen evolution in alkaline media: effect of temperature

Abstract The effect of temperature on the hydrogenation of sintered Ni by the hydrogen evolution reaction (her) in 0.6 M K 2 CO 3 +H 2 O electrolyte was investigated in the range 25–95°C. At 25°C, hydrogenation leads to the formation of three different species, provisionally identified as β -Ni-, hexagonal-Ni- and α -Ni-hydride phases, based on their respective redox potentials and thermostability. Their penetration into the metal ranged from a few tens to a few hundred monolayers. Above room temperature, the overall efficiency and penetration of Ni hydrogenation increased significantly. Furthermore, there is definite evidence that, at T ≥65°C, the β -Ni-hydride phase evolves into new Ni–hydrogen species of higher thermal stability, regarding which there is no previous knowledge. The results of electrolytic Ni deuteration by electrolysis of K 2 CO 3 +D 2 O conformed to those obtained in light water.

In situ X-ray diffraction investigation of nickel hydride formation during cathodic charging of Ni

Abstract Investigations of nickel hydride formation were carried out using in situ X-ray diffraction (XRD) during cathodic charging of Ni in 2 M H2SO4 solution with and without thiourea. In the process of cathodic charging the XRD peak (200) of the phase β-NiH0.7 was determined to shift towards lower Bragg diffraction (2Θ) angles and go back within 3–5 min following interruption of charging. The shift corresponded to changes in the lattice parameter a of the β-NiHx phase. The a value depended on the cathode potential Ec or the charging current density iH and the quantity of thiourea in the solution, a always fell back to 0.3725–0.3728 nm after interruption of charging. Depending on Ec or iH, the change in x during cathodic charging was observed within the following ranges: 0.7≤x≤0.73 without thiourea, 0.7≤x≤0.76 with thiourea concentration being 0.2 g dm−3 and 0.7≤x≤0.81 with 5 g dm−3 thiourea in the solution. It is concluded that the x value of β-NiHx is related to the variations of the lattice parameter a.

Formation of nickel hydrides by hydrogen evolution in alkaline media

Abstract The feasibility of obtaining Ni hydride through electrolytic reduction of aqueous 0.6 M K 2 CO 3 at Ni electrodes of different types (solid Ni, Ni-fiber composite and sintered Ni) was investigated. It was found that potentiostatic electrolyses at the beginning of the hydrogen evolution reaction (her) lead to the formation of several hydrogenated species of Ni, which generally become degraded when more negative potentials are applied. The species oxidized reversibly with the her was identified as the β -Ni hydride phase, whereas the nature of the Ni hydrides oxidized at more positive potentials could not be definitely established. The interaction of Ni samples on open circuit with H 2 dissolved in the electrolyte was found to form the same Ni hydride species as that achieved after electrolysis.

The effects of the addition of B and Fe and a prior deformation on the hydrogen embrittlement of nickel

The resistance to hydrogen embrittlement of pure nickel was improved by the addition of B and Fe. This improvement is thought to be the effect of Fe on reducing the tendency for nickel hydride formation. Moreover, B segregated to the grain boundary improved the ductility of this alloy. The hydrogen embrittlement was reduced by the cold rolling. The cross rolling was better in reducing the embrittlement than the single rolling because the cross rolling developed well the stable dislocation cellular structures acting as a hydrogen trapping site.

The hydrogen evolution reaction on nickel surfaces stabilized by H-absorption

The hydrogen evolution reaction ( her) was studied on bright nickel electrodes in alkaline solutions at several temperatures. The formation of nickel hydrides in the potential region of the her was previously analyzed by cyclic voltammetry and the electrode surface was pre-conditioned to minimize the effect of the hydrides in the experimental response of the system. Data from polarization curves was conveniently analyzed by non-linear regression fitting resulting in a Volmer-Heyrovsky mechanism in which the second reaction must be the rds to explain the characteristics of the hydride formation. The calculated value of the rate constant for the electrochemical desorption step was 1.65 × 10 −11 mol cm 2 s −1 at 25°C. The apparent energy of activation was 58 kJ mol −1, a value somewhat higher than those in the literature and that was justified in terms of the specific pre-treatment of the surface. A voltammetric method for determining the real electrochemical active area of Ni electrodes is also described.

Electrodeposition of Corrosion‐Resistant Ni‐Zn Alloy: I . Cyclic Voltammetric Study

The interaction between different reacting species involved in the initial stage of electrodeposition of nickel‐zinc alloy was investigated. A cyclic voltammetric study indicates that codeposition of hydrogen and nickel occurs, with formation of two types of hydrogen‐nickel solid solution, i.e., β‐Ni and α‐Ni. This nickel hydride formation during Ni‐Zn alloy electrodeposition was verified by analyzing the voltammograms of nickel, zinc, and Ni‐Zn alloy during initial deposition on various substrates. The dissolution potential of zinc and nickel from electrodeposited nickel‐zinc alloy spans a wide range (ca. 400 mV). The influence of the interaction between nickel, hydrogen, and zinc on the nucleation of nickel‐zinc electrodeposition is reported in part II of this paper, p. 1304.

Routes to Diamond Heteroepiitaxy

AbstractThis paper reviews the status of diamond heteroepitaxy approached by chemical vapor deposition and by physical methods. Reported are experiments with cubic boron nitride and nickel conducted with the help of microwave plasma chemical vapor deposition. X-ray diffraction data confirm diamond heteroepitaxy on the (111) faces of cubic boron nitride crystals. Heteroepitaxy on nickel was not demonstrated yet nevertheless suppression of graphite nucleation was achieved by formation of nickel hydride.

Light-promoted catalytic hydrogenation of olefins with nickel complexes: the formation of nickel hydrides from the reaction of Ni(I) complexes with hydrogen

The conditions pertaining to triplet excited state ketone-sensitized photoreduction of Ni(acac)2 under hydrogen were shown to serve as a method for light-promoted hydrogenation of olefins with clean chemospecificity. For example, the double bond in the bicyclic system was preferentially hydrogenated over the other double bond in dicyclopentadiene and in 5-methylenebicyclo-[2.2.1]heptene. This photohydrogenation could be run under a wide range of conditions and was apparently a homogeneous catalytic process; in a late stage of photohydrogenation, concurrence of heterogeneous catalytic processes was not ruled out. The Ni(I) complexes of tetrahydrofuran and olefins generated from the photoreduction of Ni(acac)2 were shown to react with hydrogen to give nickel hydride complexes. By analogy with the generally accepted reaction pattern, coordinated olefins in these nickel hydride complexes probably spontaneously undergo intramolecular addition to give Ni–alkyl complexes. It is suggested that these Ni–alkyl complexes are photoexcited to generate a vacant coordination site so that the reaction with hydrogen can proceed to give products and regenerate a nickel hydride catalyst.