Nickel Phase Research Articles

Availability of steam impacts coke properties in steam reforming of acetic acid

Steam to carbon ratio (S/C) determines the availability of oxygen-containing species during steam reforming, which not only affect the amount of coke formed, but also might impact physicochemical properties of the coke generated. In this study, the effect of S/C on the coke formation in steam reforming of acetic acid was assessed. The results indicated that dissociative absorption of acetic acid generated the intermediates containing both CO and CC groups even at 100 °C. At low S/C, the insufficient ∗OH reacted with carbonaceous intermediates such as CHx to form more carbonyl species, leading to significant coking and lower gas yields. Sufficient ∗OH at high S/C facilitated transformation of the carbonyl-containing species into gases, minimizing coking. The varied amount of coke showed significant effect on the diffraction of metallic nickel phase, the particle size of Ni and the absorption for the Si–O–Si functional groups on spent catalysts. The coke formed at low S/C was more aromatic with high thermal stabilities, while the coke formed at high S/C was more aliphatic with low thermal stabilities. The involvement ∗OH species in coking process determined not only properties but also morphologies of the coke. The coke formed at low S/C showed bamboo-like, dendritic or twisted rope-like structure. While the higher S/C favored the generation of the carbon nanotubes with smooth outer surface.

Phase diagram of infinite layer praseodymium nickelate Pr1−xSrxNiO2 thin films

We report the phase diagram of infinite layer Pr$_{1-x}$Sr$_{x}$NiO$_2$ thin films synthesized via topotactic reduction from the perovskite precursor phase using CaH$_2$. Based on the electrical transport properties, we find a doping-dependent superconducting dome extending between $x$ = 0.12 and 0.28, with a maximum superconducting transition temperature $T_{\rm{c}}$ of 14 K at $x$ = 0.18, bounded by weakly insulating behavior on both sides. In contrast to the narrower dome observed in Nd$_{1-x}$Sr$_{x}$NiO$_2$, a local $T_{\rm{c}}$ suppression near $x$ = 0.2 was not observed for the Pr$_{1-x}$Sr$_{x}$NiO$_2$ system. Normal state Hall effect measurements indicate mixed carrier contributions of both electrons and holes, and show a sign change in the Hall coefficient as functions of temperature and $x$, quite similar to that in Nd$_{1-x}$Sr$_{x}$NiO$_2$. Also similar is the observation of a minimum in the normal state resistivity associated with the superconducting compositions. These findings indicate an infinite layer nickelate phase diagram that is relatively insensitive to the rare-earth element, but suggest that disorder arising from the variations of the ionic radii on the rare-earth site affects the superconducting dome.

Nanotubes with a structure of the «magnetic core-noble metal shell» type

Using a simple two-stage method including the electrochemical synthesis of Ni nanotubes in the pores of PET membranes and their coating with gold or platinum, nanotubes with a structure of the «magnetic core - noble metal shell» type have been synthesized. The morphology of the coating is a thin continuous film with growths of various shapes. X-ray diffraction analysis estimated separate phases of nickel (core) and noble metal (coating). The magnetic properties of coated nanotubes do not differ significantly from the properties of the initial nanotubes. The method allows one to synthesize structures such as one-dimensional nanostructures of the «magnetic core - noble metal shell» type for use in the detection of chemical and biological compounds, as magnetic carriers for the delivery of drugs and genes, which can also be used as multicyclic catalysts on a magnetic carrier.

(Invited) Compositionally Engineered Ceria-Nickelate Composite Electrodes as Oxygen Electrodes in SOFCs and SOECs

Composite electrodes comprising a rare-earth nickelate phase and a doped rare-earth ceria phase with a high level of rare-earth doping have been studied as oxygen electrodes. While rare-earth nickelates have shown great promise as oxygen electrodes in both solid oxide fuel cells (SOFC) and solid oxide electrolysis cells (SOECs), they become unstable in contact with rare-earth doped ceria. In this work we describe a strategy to eliminate this instability and enable the use of these electrodes as stable high performance oxygen electrodes in both SOFC and SOEC applications. The performance of such composite electrodes is explored using a symmetrical cell approach, and through the electrical conductivity relaxation (ECR) method and compare it to state-of-the-art oxygen electrodes comprising strontium doped lanthanum manganite (LSM) – yttria stabilized zirconia (YSZ) composite electrodes. The symmetrical cell tests which reveal the stabilized nickelate-ceria electrodes to be superior, are also well-correlated with the results of testing complete cells in both SOFC and SOEC modes. Based on these results we make the case for deploying these stabilized nickelate-ceria composite electrodes as oxygen electrodes in reversible SOFC-SOEC systems.

Study of the Redox Behavior of SOFC’s Anode Functional Layers

The cermet Ni-YSZ is the most common fuel electrode used for solid oxide fuel cells[i]. Under polarization, the Nickel phase remains metallic because of the reducing atmosphere. However, troubleshooting like system emergency shutdown may cause the Ni phase to be completely/partially oxidized, resulting in a large bulk volume change (volume expansion >65%)[ii]. Microstructure failures can then occur in the Ni-YSZ matrix. Redox cycles of the Nickel could also degrade the microstructure of the Ni-YSZ anode (for instance, coarsening of the Ni phase yielding loss of Ni percolation), and thus the performance of the cell[iii]. All these phenomena lead to an increase of the polarization resistance of the anode.The target of the OxiGEN project is to develop the next-generation all ceramic Solid Oxide Fuel Cell stack and hot box solution for small stationary applications[iv]. One of the objectives of the project is the improvement of the redox tolerance of the anode functional layer, in order to prevent nickel coarsening. A large experimental matrix with various combinations of parameters (NiO / YSZ ratio, porosity and electrolyte particle size) was established to investigate innovative anode functional layers with better redox resistance and improved electrochemical performance compared to a reference anode prepared with the same NiO powder and a proprietary YSZ based composition. Thin ceramic-polymer tapes (<100µm) have been manufactured by a tape-casting process developed by EIfER following the industrial requirements provided by Saint-Gobain. The microstructural characterization performed after sintering show homogeneous anode functional layers with a thickness below 30 µm and a good repartition between the ceramic phases and the porosity for all samples prepared in this study (see Figure 1). The influence of the modification of the microstructure resulting from the variation of the electrolyte particle size properties was investigated by SINTEF on the electrical properties of the reduced anodes using Van der Paw method. An increase of the total electrical conductivity from 100 to 900 S.cm-1 was observed between the reference and innovative layers, respectively.Specific redox cycle protocols were defined to observe the modification of the microstructure of single layers and complete cells after redox cycles simulating specific emergency shutdown (see figure 2). They are composed of two main steps. The first one corresponds to an oxidation phase where the temperature is decreased while the supply of hydrogen is stopped (controlled emergency shutdown). An air leakage was also simulated by introducing a small quantity of air into the fuel chamber. The second phase represents the restart of the system with an increase of the temperature and the reintroduction of hydrogen to the fuel side. The intermediate stage was also optimized in order to emphasize the effect of the oxidation phase on the fuel electrode. The influence of the integration of advanced layers on the microstructure and redox behavior of layers and complete cells will be discussed. “This project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 779537 . This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme and Hydrogen Europe and Hydrogen Europe Research”. [i] S.P.S. Shaikh, A. Muchtar, M.R. Somalu, Ren. Sus. Energy Reviews 51 (2015) 1-8. [ii] S. Toros, Ceram. Int. 42 (2016) 8915-8924. [iii] T. Shimura, Z. Jiao, S. Hara, N. Shikazono, J. Power Sources 267 (2014) 58-68. [iv] http://oxigen-fch-project.eu/ Figure 1

Fast relaxation of stresses in solid oxide cells through reduction. Part I: Macro-stresses in the cell layers

To assess the risk of failure of various components in solid oxide cell (SOC) stacks, the temporal evolution of stresses from sintering and thermal gradients in the operating stacks must be known. In this work it is shown experimentally that the residual stresses in a solid oxide cell are relaxed and, in most cases, go to zero at the point of chemical reduction of the structurally dominant fuel electrode from NiO-YSZ to Ni-YSZ. This is essential for understanding and modeling the stresses during the SOC stack assembly and after. In part I, the in-plane macro-strain and stresses in each layer is determined by in-situ X-ray diffraction at different temperatures and during the chemical reduction. The stresses are also analyzed by a multilayer model of the cell. The relaxation of stresses is explained and attributed to so-called accelerated creep occurring in the nickel phase of fuel electrode.

In situ graphitized hard carbon xerogel: A promising high-performance anode material for Li-ion batteries

Abstract

Deposition of High-Density Carbon Nanotube-Containing Nickel-Based Composite Films by Low-Pressure Cold Spray

Carbon nanotubes (CNTs) have a large specific surface area and, thus, are expected to have applications as electrodes, e.g., in fuel cells. A CNT-containing composite metal film with high electrode performance could be realized by implementing a large number of CNTs on the film. However, a composite film with a high density of CNTs has not yet been obtained. In the thermal spray field, including cold spray, metal–CNT composite films with more than 20 wt% of carbon nanotubes has not yet been deposited. In this study, high-density CNT-containing metal-based composite films were deposited onto an aluminum substrate by low-pressure cold spray from electroless nickel-plated CNT particles. The electroless nickel plating process caused slight structural damage to the CNTs, whereas the cold spray process did not cause any significant structural damage to the CNTs. Two phases were observed in the films: a CNT-rich layer and a nickel-rich layer. However, the CNTs maintained sufficient adhesive strength to remain attached to the bottom nickel phase. Composite films with at least 65 wt% CNT were produced with our method.

Heterogeneous Metal Oxide Coatings with Magnetoactive Nickel, Cobalt, and Iron Phases Formed by the Method of Pulsed Microplasma Oxidation for Radiation Absorption in the Middle and Near-IR Regions

Heterogeneous coatings with high ability to absorb electromagnetic radiation in the middle (4000–400 cm–1) and near-IR regions (11000–2000 cm–1) are formed by the method of pulsed microplasma oxidation on aluminum and titanium alloys in inorganic electrolytes containing nickel, cobalt, and iron compounds. The electromagnetic radiation absorption is provided not only by the oxide coating itself, but also mainly by the heterogeneous metal particles of nickel, cobalt, and iron forming a dispersed metal phase and having magnetic properties that are incorporated into the coating pores by the method of microplasma oxidation under the action of a constant magnetic field. The influence of the electrolyte compositions and of the parameters of pulsed microplasma oxidation on the structure, composition, and radiation absorption properties of coatings is studied. It has been revealed that coatings formed in a phosphate-borate electrolyte with addition of nickel at a voltage of 300 V, a pulse duration of 100 μs, and a process duration of 5 min have the best absorption ability.

In Situ Formation of Extremely High Corrosion Resistant Ni–Ni3Si Nanocomposite Coating Using Spark Plasma Sintering and Subsequent Heat Treatment

In this study, the coating of Ni–Ni3Si nanocomposite was produced in-situ on plain carbon steel using spark plasma sintering process of Ni and Si powders followed by heat treatment. Increasing Si content in the powders from 6 to 13 wt% increased the amount of Si in the coatings (from 5.1 to 11.8 wt%). The corrosion behavior of the coated samples in 1 M sulfuric acid solution was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. In the 13 wt% Si coating, the eutectic structure consisting of the Ni and Ni3Si phases was observed to be uniformly distributed. Ni3Si nanoparticles with an approximate size of 90 nm were obtained in the coating by heat treatment. The results showed that passive behavior is obtained by heat treatment due to the uniform distribution of Ni3Si nanoparticles and also the uniform diffusion of silicon into the nickel phase. The excellent passivation results in the highest corrosion resistance in 13 wt%Si coating after the heat treatment.

Molybdenum and Nickel Nanoparticles Synthesis by Laser Ablation towards the Preparation of a Hydrodesulfurization Catalyst

A clean straightforward laser ablation method in deionized (DI) water is reported for the synthesis of Molybdenum (Mo) and Nickel (Ni) nanoparticles (NPs). The structural, morphological, and optical properties of the as-synthesized nanoparticles were investigated. Particle size was estimated to be less than 10 nm, the UV–vis spectra of the samples show the formation of H2MoO4 and NiO. The XRD results for the Ni sample show the presence of two phases, cubic nickel oxide, and an fcc metallic nickel phase, indicating the possible formation of Ni/NiO compound. The nanoparticles synthesized were used as precursors in the production of a NiMo/γ-Al2O3 catalyst. The textural and structural properties, chemical composition, and catalytic performance in a hydrodesulfurization (HDS) reaction are reported. The textural and structural properties results show the lack of pore-blocking due to the small sizes and the distribution of the metallic nanoparticles on the support. Chemical composition measured by XPS shows a ratio Ni/Mo of 1.34. Therefore, possibly Ni was deposited on Mo covering part of its active area, occupying active sites of Mo, removing its effective surface and resulting in a relatively low conversion of DBT (17%). A lower Ni/Mo ratio is required to improve the model system, which could be achieved by changing parameters at the production of the nanoparticles. The model system can also be further tuned by changing the size of the nanoparticles.

Tunable resistivity exponents in the metallic phase of epitaxial nickelates

We report a detailed analysis of the electrical resistivity exponent of thin films of NdNiO3 as a function of epitaxial strain. Thin films under low strain conditions show a linear dependence of the resistivity versus temperature, consistent with a classical Fermi gas ruled by electron-phonon interactions. In addition, the apparent temperature exponent, n, can be tuned with the epitaxial strain between n = 1 and n = 3. We discuss the critical role played by quenched random disorder in the value of n. Our work shows that the assignment of Fermi/Non-Fermi liquid behaviour based on experimentally obtained resistivity exponents requires an in-depth analysis of the degree of disorder in the material.

Study of nanostructural changes in a Ni-containing cermet material during reduction and oxidation at 600 °C

In this work, the nanostructural changes in a Ni/NiO cermet material, during its reduction and oxidation at 600 °C have been studied. A series of the NiO ceramic specimens (mode 1) were undergone to the next three treatment modes at 600 °C, namely: (2) one-time reduction in hydrogen of 99.99 vol% H2 purity; (3) one-time reduction in Ar–5 vol% H2 mixture; (4) redox cycling (5 cycles), each redox cycle comprises the stages of isothermal holding in Ar–5 vol% H2 mixture and in air, with intermediate stages of degassing. Increased porosity, along with an increased amount of reduced Ni, has been revealed in specimens after mode 2 test. In contrast to treatment in pure hydrogen, no substantial volume changes in the material after mode 3 test were found, and single micropores were detected only at the sites of contact of nickel phase particles. In contrast to modes 2 and 3, the following structural peculiarities in the course of redox cycling of as-sintered NiO ceramics (mode 4) were detected: (1) formation of a network of nanopores in the outer layer of a Ni-phase particle; (2) reduction of Ni-phase particle size by separating thin pieces of reduced Ni subgrains; (3) coagulation of fine Ni pieces that allows the porosity to be partially decreased and “bridges” to be formed; (4) clustering of the initial Ni-phase particles with the formation of nanopores at the sites of former boundaries; (5) formation of a network of reduced Ni that consists of Ni fringes and “bridges” and improves electrical conductivity and structural strength of the cermet.

Preparation of highly active unsupported Ni–Si–Mo catalyst for the deep hydrogenation of aromatics

Abstract A mesoporous nickel-silicon-molybdenum composite oxide with the phase of ammonium nickel (or silicon) molybdate was synthesized by chemical precipitation and unsupported nickel-silicon-molybdenum sulfide catalysts with various Ni/Si ratios were obtained by sulfidation of the oxide precursors. The oxide precursors and unsupported sulfide catalysts were characterized by XRD, N2 adsorption-desorption, SEM, TPR, and HRTEM. The unsupported nickel-silicon-molybdenum sulfide catalysts were tested in the hydrogenation of naphthalene. It was found that the introduction of Si could increase the specific surface area and improve the pore structure of precursors, and reduce the reduction temperature of Mo species. The results of naphthalene hydrogenation showed that the introduction of Si could significantly improve the hydrogenation activity of the catalysts, especially the Ni9.5Si0.5Mo10 catalyst exhibited the highest aromatic hydrogenation activity at low temperature. Interestingly, it is found that the tetralin selectivity is 100% in the low temperature range (220–260 °C) over Si10Mo10 catalyst, which might be attractive in the production of tetralin and other industrial application.

Efficient Polysulfide Redox Enabled by Lattice-Distorted Ni3Fe Intermetallic Electrocatalyst-Modified Separator for Lithium-Sulfur Batteries.

Exploring efficient electrocatalysts for lithium-sulfur (Li-S) batteries is of great significance for the sulfur/polysulfide/sulfide multiphase conversion. Herein, we report nickel-iron intermetallic (Ni3Fe) as a novel electrocatalyst to trigger the highly efficient polysulfide-involving surface reactions. The incorporation of iron into the cubic nickel phase can induce strong electronic interaction and lattice distortion, thereby activating the inferior Ni phase to catalytically active Ni3Fe phase. Kinetics investigations reveal that the Ni3Fe phase promotes the redox kinetics of the multiphase conversion of Li-S electrochemistry. As a result, the Li-S cells assembled with a 70 wt % sulfur cathode and a Ni3Fe-modified separator deliver initial capacities of 1310.3 mA h g-1 at 0.1 C and 598 mA h g-1 at 4 C with excellent rate capability and a long cycle life of 1000 cycles at 1 C with a low capacity fading rate of ∼0.034 per cycle. More impressively, the Ni3Fe-catalyzed cells exhibit outstanding performance even at harsh working conditions, such as high sulfur loading (7.7 mg cm-2) or lean electrolyte/sulfur ratio (∼6 μL mg-1). This work provides a new concept on exploring advanced intermetallic catalysts for high-rate and long-life Li-S batteries.

Synergistic Effect of Nickel Nanoparticles and Carbon Nanotubes Buckypaper for Enhancement of Microwave Shielding Properties

Carbon nanotubes (CNTs) are considered as the most promising materials to solve the electromagnetic interference (EMI) issue. Various forms of CNTs including CNTs/polymer composites, metal nanoparticles-decorated CNTs and freestanding CNT buckypapers (CNT BPs) have been proposed to enhance shielding effectiveness. In this study, the synergistic effect of nickel nanoparticles (NPs) and relatively short CNTs for the enhancement of microwave shielding properties was investigated. CNT BPs were prepared by vacuum filtration of well-dispersed multi-walled CNTs and subsequently nickel was decorated on the CNT BPs (Ni/CNT) by pulsed DC sputtering technique with different deposition times of 0, 5, 10 and 15 min (hereinafter referred to as CNi0, CNi05, CNi10 and CNi15, respectively). The diameter of Ni/CNT increased from 8.74±0.53 to 72.5±3.2 nm and the conductivity improved from 9.57±0.87 to 12.57±0.59 S/cm when the nickel deposition time was 15 min. Nickel NPs were the mixed phases of nickel and nickel oxide with a dominant nickel phase. The shielding effectiveness at the frequency of 9.5 GHz achieved to -34.1 dB for CNi15. The enhancement of shielding effectiveness of CNi15 is attributed to the synergistic effect of CNTs and nickel NPs on wave dissipation

Nickel oxide reduction in CO/CO2 gas mixtures in reverberatory furnaces

This study present laboratory experiments carried out for nickel oxide reduction in a reverberatory furnace at medium pressure and a temperature range of 400˚C-1050˚C. Analyses were carried out on nickel nanostructures and their partially reduced metallic nickel products using Zeiss Leo Supra 35 SEM. It became evident from the experimental processes that the reduction process of nickel oxide under those given pressure and temperature conditions can result in fractionation of a dense layer of nickel from the melt surface which is in association with continuous growth of gaseous pores in nickel oxide. Therefore thermodynamic processes and temperature conditions are regarded as the most important factors which play a fundamental role in the reduction process of nickel oxide (gas-metal, or/and oxide-metal). The results indicate a positive correlation between formation mechanism and the rate of reduction of metallic nickel phases upon inter. Our research took a step-by-step assessment of technological processes and a scientific observation on nickel reduction at chemical equilibrium state of an ideal gas was made, and an account was taken with regards to limitations of variables and melting parameters.

Study of the radiation resistance of Ni nanotubes to irradiation with Xe22+ ions with an energy equal to fission fragments

The paper presents data on the radiation resistance of Ni nanotubes when irradiated with heavy Xe22+ ions with an energy of 230 MeV and fluences of 5 × 1010–5 × 1012 ion/cm2. The choice of fluences of 5 × 1010–5 × 1012 ion/cm2 is due to the possibility of simulating the effects of single ion collisions at low irradiation fluences, for which the probability of two ions entering one point is quite low, and by modeling the effects of overlapping defects from two or more ions at high radiation densities. The initial nanostructures are polycrystalline nanotubes with a face-centered nickel phase. According to the results of X-ray phase analysis, no oxide impurities or oxide phases are observed in the structure of nanotubes, which indicates the absence of oxidative processes in the synthesized nanostructures. Also, for the irradiated samples, there are no new diffraction peaks, which indicates the absence of phase transition processes as a result of irradiation. It was found that, at low irradiation fluences, a change in the orientation of crystallites occurs, which indicates a rearrangement of the crystal structure and partial ordering. However, an increase in the irradiation fluence above 1 × 1011 ion/cm2 leads to a sharp decrease in long-range intensities, as well as a shift of diffraction maxima to the region of small angles, which indicates a distortion of the crystal structure and its partial disordering as a result of irradiation. In the case of large irradiation fluences, which are characterized by the occurrence of areas of overlapping ion trajectories, the material exhibits disorientation of crystallites in the structure, as well as the absence of pronounced texture orientations.

Nickel concentration dependent evolution of magnetic domain structures in electrodeposited carbon composite thin films

Modification of magnetic domain structure of Ni-C composite thin films has been investigated with the variation in nickel content in the films. Ni-C thin films were synthesized by electrodeposition method with different nickel molar concentration in the electrolyte. Compositional analysis of the films performed by EPMA mapping assured nearly homogeneous distribution of nickel and carbon in the films at a scale much larger than the crystallographic features within the films. GIXRD and TEM studies reveal the presence of crystalline phase of nickel along with diamond and graphite phases within amorphous carbon. Morphological properties studied by AFM showed granular features with variation in roughness. Within amorphous carbon matrix of the films, presence of sp3 and sp2 phases (Ni-DLC) were confirmed by Raman spectroscopy in low nickel content thin films. Stripe magnetic domain structures of varying width and density were observed in the films with change in nickel content without application of external magnetic field at room temperature by magnetic force microscopy. Ni-DLC thin films exhibit the highest domain density of all Ni-C composite thin films.

Biogas dry reforming over Ni-Al catalyst: Suppression of carbon deposition by catalyst preparation and activation

Biogas dry reforming is as an alternative renewable route for the hydrogen production. However, the major drawback of this process is the catalyst deactivation by carbon deposition and sintering. In this work, Ni-Al catalysts were studied aiming to suppress the carbon deposition in the dry reforming of biogas. The catalysts were prepared by coprecipitation and evaluated the washing step. The reactions were carried out with unreduced and reduced catalysts in a fixed bed tubular reactor using a synthetic biogas (60% CH4 and 40% CO2). The washing and activation steps influenced the characteristics of the catalysts and the catalytic properties in the biogas reforming. The unwashed sample resulted in an oxide containing potassium nickelate with high basicity and low surface area. Both washed samples, reduced and unreduced, showed a high amount of carbon formation, whereas no carbon formation was observed in the unwashed samples for the reactions in the temperature range of 500–750 °C. The unwashed and unreduced sample was the only one that maintained the activity during all the reaction time at 700 °C (40% CH4 conversion and 75% CO2 conversion), low coke amount and no evidence of sintering, which was confirmed by XRD, TPO, and SEM analyses. The carbon suppression was related to the nickelate phase and to the Ni carbide formation in the unwashed and unreduced catalyst. In summary, the carbon deposition in biogas dry reforming was completely controlled between 600 and 750 °C using the unwashed and unreduced Ni-Al catalyst.