NiO Grains Research Articles

Mixed Ni–Cu-oxide nanowire array on conductive substrate and its application as enzyme-free glucose sensor

We report the synthesis of mixed Ni–Cu-oxide nanowire array on flexible metal substrate by a hydrothermal process and subsequent decomposition-related annealing treatment. Every single nanowire is a particles matrix with embedded NiO and CuO grains. To the best of our knowledge, this is the first report that mixed oxides exist in this aligned architecture. As an example of the functional properties of the compound materials, the mixed Ni–Cu-oxide nanowire array is investigated as the additive-free electrode for enzyme-free glucose sensor. Compared with previously reported Ni or Cu-contained biosensors, this Ni–Cu–oxide array electrode possesses higher performance. The detection limit can be as low as 0.1 μM, linear range as wide as 0.1–1200 μM and sensitivity as high as ∼1600 μA mM−1 cm−2. Besides the above, other excellent properties such as anti-interferences and long-term stability, are demonstrated as well. All these improvements can be attributed to the synergetic effect between the mixed oxide grains and the unique 1D array feature.

Characterization of composite cermet with 68 wt.% NiO and BaCe 0.2Zr 0.6Y 0.2O 3−δ

Protonic ceramic fuel cells, steam electrolyzers, membrane reactors, and related intermediate temperature electrochemical devices require thin, dense membranes of protonic ceramic electrolytes that are supported by a porous substrate. A cofired cermet consisting of reduced 68 wt.% NiO and the proton conductor, BaCe 0.2Zr 0.6Y 0.2O 3−δ (68NiBCZY26) is described. It is shown that a composite of two distinct interpenetrating and percolating phases – Ni and BCZY26 – with about 25% open porosity, is produced from a fully dense sintered ceramic body. This is possible because the protonic ceramic phase can transport hydrogen to the NiO grains and remove the water vapor reaction product of reduction by solid-state diffusion, which makes it possible to begin reducing NiO grains even before gas percolation channels are fully formed. By eliminating the need for pore-formers in the cermet fabrication step, thin electrolyte membranes may be fabricated without the need to bridge open pores at the surface or develop pin-holes due to burn-out of pore-forming organic binders. Furthermore, the processing window for sintering is expanded, permitting the microstructure of the dense membrane to fully develop, since there is no requirement to limit the time at peak sintering temperature, that would otherwise cause the pores to collapse. The cermet described in this monograph was prepared by the process of solid-state reactive sintering, whereby the BCZY26 phase was formed during sintering from precursor oxides and carbonates. Since no preliminary calcination step is required, ceramic fabrication is very cost-effective. The subsequent in situ reduction of NiO by a combination of gas phase and solid-state diffusion results in an unusual nickel microstructure, and makes it possible to tailor electrical properties and pore size distribution for a wide range of specialized applications by adjusting the amount and grain size of NiO in the sintered body. The reduced cermet exhibits a bimodal pore diameter distribution, with one group centered at 0.5 μm and a second group centered at 7 nm.

Hydrogen Production via Catalytic Steam Reforming of Fast Pyrolysis Bio-oil in a Fluidized-Bed Reactor

Bio-oil reforming to produce hydrogen could be an attractive option for sustainable hydrogen. Hydrogen production via catalytic steam reforming of bio-oil in a fluidized-bed reactor was studied in this paper. The optimum conditions on hydrogen production were obtained at 700 °C, steam/carbon mole ratio (S/C) of 17, and weight hourly space velocity (WHSV) of 0.4 h−1. In addition, the reason for catalyst deactivation in a fluidized-bed reactor was investigated. The fresh and deactivation catalysts were analyzed by X-ray diffraction (XRD), Brunauer−Emmett−Teller (BET), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), which showed that the carbon deposition is not the main reason for catalyst deactivation. The main reason for fresh catalyst deactivation was the NiO grain sintered on the supporter surface.

Dependence of Memory Characteristics on Crystallinity in NiO-ReRAM

Resistance Random Access Memory (ReRAM) is often made in the sandwiched structure where a transition metal oxide (TMO) film with polycrystalline structure is placed between the upper and the lower electrodes. Although whether resistance switching effect occurs in grains or in the grain boundary is key issue which decides the downsizing limit of memory cells, it has not been clarified yet. We prepared NiO/Pt structure using the DC sputtering method, and investigated the property of resistance change effect in the local area using conducting atomic force microscope. As a result, it was clarified that the resistance change occurred not in the NiO grain but in the NiO grain boundary. Therefore, it was suggested that the limitation of downsizing is decided according to the grain diameter.

Well-crystallized mesoporous samaria-doped ceria from EDTA-citrate complexing process with in situ created NiO as recyclable template

Abstract A facile EDTA-citrate complexing process with in situ created recyclable NiO as inorganic template was developed for the synthesis of mesoporous samaria-doped ceria (SDC) at high temperatures. By applying metal nitrates as the raw materials for the cation sources and EDTA and citric acid as the chelants, the molecular-level homogeneous mixing of the metal ions was successfully preserved to the solid precursor. Low-temperature calcination resulted in the formation of mixture oxides of nano-size SDC and NiO oxides, as demonstrated by XRD, FT-IR and BET analysis. A possible mechanism for the formation of mesoporous SDC was proposed, in which the SDC particles surrounded the nano-size NiO grains and sintered during the high-temperature calcination. Dissolving the coated NiO in SDC and self-aggregated NiO particulates from the mixture with diluted HNO3 resulted in a porous pure-phase SDC oxide. At optimal SDC to NiO ratios, mesoporous, thermally stable and well-crystallized SDC powder with narrow pore size distribution and high surface area was synthesized.

Exchange bias and training effect in Ni/Ag-doped NiO bilayers

A series of polycrystalline Ag-doped Ni 1− x Ag x O/Ni bilayers with x up to 0.2 were prepared by magnetron sputtering. X-ray diffraction, atomic force microscopy and transmission electron microscopy analyses reveal that Ag doping significantly reduces the mean NiO grain size and leads to the appearance of Ag nanoparticles on the surface of the Ag-doped NiO films. As x increases, the exchange bias field and coercivity at room temperature decrease as a consequence of the reduced thermal stability of smaller NiO grains and the screening effect resulting from the interfacial Ag nanoparticles. At lower temperatures, a slight enhancement of the exchange bias field is observed in the Ag-doped sample, indicating that the Ag doping increases the uncompensated NiO spin density. In addition, our studies find that the training effect of the Ag-doped sample can be well described by a spin configurational relaxation model, regardless of the presence of Ag nanopartiles at the interface.

In situ Reduction and Oxidation of Nickel from Solid Oxide Fuel Cells in a Transmission Electron Microscope

Environmental transmission electron microscopy was used to characterize in situ the reduction and oxidation of nickel from a Ni/YSZ solid oxide fuel cell anode support between 300-500{degree sign}C. The reduction is done under low hydrogen pressure. The reduction initiates at the NiO/YSZ interface, then moves to the center of the NiO grain. At higher temperature the reduction occurs also at the free NiO surface and the NiO/NiO grain boundaries. The growth of Ni is epitaxial on its oxide. Due to high volume decrease, nanopores are formed during reduction. During oxidation, oxide nanocrystallites are formed on the nickel surface. The crystallites fill up the nickel porosity and create an inhomogeneous structure with remaining voids. This change in structure causes the nickel oxide to expand during a RedOx cycle.

A comparison of mechanochemical methods for the synthesis of nanoparticulate nickel oxide

In this study, mechanochemical processing has been investigated as a means of manufacturing nanoparticulate powders of NiO. Two different reactant mixtures were examined and compared. The first system was based on mechanical milling of Ni(OH) 2 with NaCl diluent. Milling of this reactant mixture resulted in disintegration of the Ni(OH) 2 precursor and its progressive dispersal into the NaCl matrix. Subsequent heat treatment and washing yielded a nanocrystalline powder of NiO, which contained a significant proportion of particles with an unusual platelike morphology. The second system that was examined was based on mechanically activated reaction of NiCl 2 + Na 2CO 3 + 4NaCl. Milling resulted in mixing and microstructural refinement of the reactant mixture. Chemical reaction during post-milling heat treatment resulted in the formation of a powder consisting of nanocrystalline NiO grains embedded in NaCl. Removal of the NaCl by washing with water yielded NiO nanoparticles with an equiaxed particle shape.

Surface-spin magnetism of antiferromagnetic NiO in nanoparticle and bulk morphology

The surface-spin magnetism of the antiferromagnetic (AFM) material NiO in nanoparticleand bulk morphology was investigated by magnetic measurements (temperature-dependentzero-field-cooled (zfc) and field-cooled (fc) dc susceptibility, ac susceptibility and zfc and fchysteresis loops). We addressed the question of whether the multisublattice ordering of theuncompensated surface spins and the exchange bias (EB) effect are only present in thenanoparticles, originating from their high surface-to-volume ratio or if these surfacephenomena are generally present in the AFM materials regardless of their bulky ornanoparticle morphology, but the effect is just too small to be detected experimentally inthe bulk due to a very small surface magnetization. Performing experiments on theNiO nanoparticles of different sizes and bulk NiO grains, we show that coercivityenhancement and hysteresis loop shift in the fc experiments, considered to be the keyexperimental manifestations of multisublattice ordering and the EB effect, are truenanoscale phenomena only present in the nanoparticles and absent in the bulk.

Basic Nickel Carbonate: Part I. Microstructure and Phase Changes during Oxidation and Reduction Processes

A significant industrial problem associated with the production of nickel from basic nickel carbonate has been identified. Fundamental studies of the change of phase, product surface, and internal microstructures taking place during oxidation and reduction processes at temperatures between 110 °C and 900 °C have been carried out. The various elemental reactions and fundamental phenomena that contribute to the change of the physical and chemical characteristics of the samples during the processes taking place in Ni metal production through gas/solid-reduction processes have been identified and thoroughly investigated. The following phenomena affecting the final-product microstructure were identified as follows: (1) chemical changes, i.e., decomposition, reduction reactions, and oxidation reactions; (2) NiO and Ni recrystallization and grain growth; (3) NiO and Ni sintering and densification; and (4) agglomeration of the NiO and Ni particles.

Anode-supported ScSZ-electrolyte SOFC with whole cell materials from combined EDTA–citrate complexing synthesis process

The potential application of combined EDTA–citrate complexing process (ECCP) in intermediate-temperature solid-oxide fuel cells (IT-SOFCs) processing was investigated. ECCP-derived scandia-stabilized-zirconia (ScSZ) powder displayed low packing density, high surface area and nano-crystalline, which was ideal material for thin-film electrolyte fabrication based on dual dry pressing. A co-synthesis of NiO + ScSZ anode based on ECCP was developed, which showed reduced NiO(Ni) and ScSZ grain sizes and improved homogeneity of the particle size distribution, as compared with the mechanically mixed NiO + ScSZ anode. Anode-supported ScSZ electrolyte fuel cell with the whole cell materials synthesized from ECCP was successfully prepared. The porous anode and cathode exhibited excellent adhesion to the electrolyte layer. Fuel cell with 30 μm thick ScSZ electrolyte and La 0.8Sr 0.2MnO 3 cathode showed a promising maximum peak power density of 350 mW cm −2 at 800 °C.

Electrochemical Performance of Ni-CGO Nano-Grained Thin Film Anodes for Micro SOFCs

NiO-Ce0.8Gd0.2O1.9-x (CGO) thin film anodes with thicknesses around 400 nm were prepared by air blast spray pyrolysis. The film composition was 60/40 vol.% Ni/CGO in the reduced state. The films were deposited on tape-cast YSZ electrolytes. The material was amorphous after deposition and was crystallized by sintering in air between 650 and 1200{degree sign}C. The temperature treatment resulted in films with average grain sizes of the NiO and CGO grains between 5 and 250 nm. The area specific resistance of the thin film anodes was measured in a humidified 1:4 H2:N2 atmosphere as a function of grain size within the temperature interval of 400{degree sign}C- 600{degree sign}C. The area specific resistance (ASR) was predominantly depending on the grain size of the films. At 550{degree sign}C, an ASR of 0.5 Ωcm2 was found for the 5 nm grain size anode. The value increased to 30 Ωcm2 for the 250 nm grain size anode.

Magnetoresistance behaviour of La 0.7Sr 0.3MnO 3 /NiO composites

(La 0.7Sr 0.3MnO 3) 1− x / (NiO) x ( x ∼ 0 , 0.05, 0.10, 0.15 and 0.20) composites were prepared via a solid state reaction process. Detailed studies of magnetic and magnetotransport properties of the composite samples have been performed. X-ray diffraction and scanning electron microscopy observations reveal that there is no evidence of reaction between the La 0.7Sr 0.3MnO 3 (LSMO) and NiO grains. It has been observed that the incorporation of NiO phase into the La 0.7Sr 0.3MnO 3 matrix lowers the metal–insulator transition temperature ( T p ) . Magnetic measurement reveals that the ferromagnetic order of LSMO is weakened by addition of NiO. An enhancement in magnetoresistance (MR) is observed at low temperature, below 120 K, for the composites with x = 0.05 , x = 0.10 and x = 0.15 and at high temperature (near room temperature) for all the composites at applied magnetic field H ∼ 3 kOe. In the present work, it is suggested that the large MR at low temperature (below 120 K) is low field magnetoresistance (LFMR) caused by spin polarized tunneling, whereas at around room temperature it is high field magnetoresistance (HFMR) caused by magnetic disordering.

Electrochromic Properties of Sputtered Ni Oxide Thin Films in Acidic KCl+H[sub 2]SO[sub 4] Aqueous Solutions

Electrochromic (EC) properties of sputtered Ni oxide films have been examined in KCl + H 2 SO 4 acidic aqueous solutions. KCl concentration was kept constant at 1 M while H 2 SO 4 concentrations were varied from 0 to 50 mM. EC coloration efficiency was found to be ∼30 cm 2 /C in all the solutions, and maximum charge capacity and maximum change in optical density were obtained in a I M KCl solution with 0.5 mM H 2 SO 4 . Intercalation of hydrogen ions into NiO grains is believed to be the reason for the improvement of charge capacity and optical density change. These results offer support for the practical construction of efficient complementary EC devices using dilute acidic aqueous electrolytes.

High-temperature operating characteristics of mixed-potential-type NO 2 sensor based on stabilized-zirconia tube and NiO sensing electrode

This paper focuses on the gas sensing properties of the mixed-potential-type yttria stabilized zirconia (YSZ)-based NO 2 sensor aiming at monitoring high-temperature car emission. The sensor device was fabricated by using an YSZ tube and a NiO sensing electrode (SE), and then its NO 2 sensing properties were investigated in the operating temperature range of 800–900 °C. The X-ray diffraction (XRD) patterns confirmed that the SE film containing the face-centered cubic NiO phase was thermally stable after the 1400 °C sintering. The scanning electron microscope (SEM) observations showed that the SE film sintered at 1400 °C was smooth and uniform with 3–5 μm sized NiO grains. The thickness of the SE film was about 33 μm. The emf output of the sensor increased linearly with an increase in NO 2 concentration on a logarithmic scale at each temperature examined. Among the various single-oxide SEs tested here and reported to date, NiO provided the highest sensitivity to NO 2 even at 850 °C. The present NO 2 sensor using NiO-SE showed faster recovery rate in the wet sample gas containing 5 vol.% water vapor than that in a dry sample gas. The Δemf value to 400 ppm NO 2 under the wet condition was as high as 75 mV at 850 °C, while the value under dry condition was 60 mV. The improvement effect of water vapor on the sensing performances was examined by means of impedance and polarization techniques.

Structure Evolution of an NiO-YSZ Electrocatalytic Electrode

The microstructure and structural evolution in the composite NiO–YSZ electrocatalytic electrode during operation of electrochemical cells for NO decomposition has been observed and investigated. The structure of the electrocatalytic electrode was found to contain two types of pores. The first group includes pores with a size range of 10–100 nm forming chains or bands. They may form channels by overlapping. These pores are located in YSZ grains and they remain unchanged during cell operation. The second group includes smaller pores located in NiO grains at near-boundary regions with YSZ grains or directly in the NiO–YSZ interface. These regions are unstable during the cell operation and new Ni and NiO grains nucleate and grow in the interfacial areas. The formation of such new grains as a result of the electrochemical processes in the cell has been discussed. The correlation between structure and properties has been studied.

Phase changes of newly synthesized Co-coated Ni cathode in MCFC cathodic conditions

A molten carbonate fuel cell (MCFC) is expected to provide high efficiency generation of electricity and an environmentally clean means of power generation [1, 2]. However, the durability of the MCFC experiences difficulties at over 40 000 hr of operation. One of the lifetime limiting problems of a MCFC is the slow dissolution of the state of the art cathode material NiO into the electrolyte [3]. Two main methods have been adopted to solve this problem. One method is to use an alternative electrolyte. More basic molten carbonate melts adopting Li/Na eutectic carbonates instead of Li/K eutectic carbonates have been used to decrease the Ni dissolution rate in the electrolyte [4]. The other method is to develop alternative cathode materials. Among cathode materials, LiCoO2 seems to be one of the best candidates because of its higher stability in the molten carbonate, and the rate of dissolution is slower than that of the NiO cathode. However, application of LiCoO2 as a new cathode material has problems in scaling up the electrode area and a relatively higher manufacturing cost than that of the NiO cathode. Therefore, recently many investigators have attempted to resolve the problem by developing new cathode materials in which NiO grains have been coated with a small amount of LiCoO2 or CoO by various coating techniques to reduce their dissolution [5, 6]. In this study, we have tried to prepare a new candidate cathode material of Co3O4-coated Ni powders using the Pechini method [7] as a new coating technique. In addition, we report on the phase changes of the Co-coated Ni cathode in MCFC cathodic conditions. The Co3O4-coated Ni powders were prepared by the following method. A stoichiometric amount of cobalt acetate (Aldrich, USA, purity of 98+%) and citric acid (CA) (Aldrich., USA, purity of 99.5+%) were dissolved in distilled water and thoroughly mixed with an aqueous solution of ethylene glycol (EG) (CA:EG:cobalt ions = 2:1:1). After that, the solution was adjusted by adding NH4OH until pH 8 was achieved and Ni powder (filamentary nickel 255, Inco, USA) was immersed in the solution. The resultant solution was heated to 80 ◦C while being stirred until a gel precursor was produced. The gel precursor was calcined at 350 ◦C for 3 hr in air.

X-ray diffraction study of the hydrogen reduction of NiO/$alpha;-Al2O3 steam reforming catalysts

Hydrogen reduction of model steam reforming catalysts, comprising about 10 wt.% NiO on α-Al2O3 with and without the addition of 1–2 wt.% CaO or MgO, was studied with in situ hot-stage X-ray diffraction in the temperature range 175–900 °C. This technique has the ability to measure NiO disappearance and Ni appearance simultaneously, together with the crystallite size of each. Since the sample was a 50 μm slab of dispersed 20 μm diameter particles, textural and morphological features normally encountered during studies with fixed beds of NiO particles were absent and measurements reflected only the chemical mechanism and kinetics. The rates of disappearance of NiO and appearance of metallic Ni matched each other, with no time lag or induction period. The reaction followed pseudo-first-order kinetics with an apparent activation energy that increased from 95 kJ mol−1 for the catalyst with no additive to 122 and 322 kJ mol−1 with added CaO and MgO, respectively. When 2.2×10−2 atm of H2O was added to the reducing gas, activation energies increased by another 23 and 96 kJ mol−1 for the first two catalysts but showed little effect for the third. There was no indication of any phase other than NiO and α-Al2O3 and the lattice constants of NiO remain unchanged. Complimentary scanning electron microscopy (SEM) showed additive oxides as dispersed phases, concentrated in the vicinity of NiO grains. Upon reduction, the metallic Ni crystallites were smaller than the original NiO and were dispersed over a wider range of the surface, suggesting that Ni atoms released from the NiO migrated from the center of reduction. When the reduced catalyst containing MgO was re-oxidized, the ease of reduction approached that of the catalyst without additives, i.e. the reduction process was no longer inhibited by the presence MgO. These observations support a proposed mechanism in which water, adsorbed on the additive oxide in the form of hydrogen-bonded molecules or hydroxyl groups, inhibits the nucleation of Ni atoms, either at the site or in the vicinity, and the difficulty of reduction increases with the hydrophilic nature of the additive. This inhibition is removed following re-oxidation of the catalyst.

X-ray diffraction study of the hydrogen reduction of NiO/α-Al2O3 steam reforming catalysts

Hydrogen reduction of model steam reforming catalysts, comprising about 10wt.% NiO on α-Al2O3 with and without the addition of 1–2wt.% CaO or MgO, was studied with in situ hot-stage X-ray diffraction in the temperature range 175–900°C. This technique has the ability to measure NiO disappearance and Ni appearance simultaneously, together with the crystallite size of each. Since the sample was a 50μm slab of dispersed 20μm diameter particles, textural and morphological features normally encountered during studies with fixed beds of NiO particles were absent and measurements reflected only the chemical mechanism and kinetics.The rates of disappearance of NiO and appearance of metallic Ni matched each other, with no time lag or induction period. The reaction followed pseudo-first-order kinetics with an apparent activation energy that increased from 95kJmol−1 for the catalyst with no additive to 122 and 322kJmol−1 with added CaO and MgO, respectively. When 2.2×10−2atm of H2O was added to the reducing gas, activation energies increased by another 23 and 96kJmol−1 for the first two catalysts but showed little effect for the third.There was no indication of any phase other than NiO and α-Al2O3 and the lattice constants of NiO remain unchanged. Complimentary scanning electron microscopy (SEM) showed additive oxides as dispersed phases, concentrated in the vicinity of NiO grains. Upon reduction, the metallic Ni crystallites were smaller than the original NiO and were dispersed over a wider range of the surface, suggesting that Ni atoms released from the NiO migrated from the center of reduction. When the reduced catalyst containing MgO was re-oxidized, the ease of reduction approached that of the catalyst without additives, i.e. the reduction process was no longer inhibited by the presence MgO. These observations support a proposed mechanism in which water, adsorbed on the additive oxide in the form of hydrogen-bonded molecules or hydroxyl groups, inhibits the nucleation of Ni atoms, either at the site or in the vicinity, and the difficulty of reduction increases with the hydrophilic nature of the additive. This inhibition is removed following re-oxidation of the catalyst.

Formation of Al3Ni Nanofibers in an Al-Based Metal Matrix Composite Fabricated by Reaction Sintering

We developed an Al2O3 and Al3Ni intermetallic reinforced Al-based metal matrix composite by sintering an Al-20 wt% NiO powder compact at 1000 °C. Differential thermal analysis showed that a two-step reaction took place between Al and NiO in the temperature range 600–650 °C. The initial stage was a solid-state reaction, but it was soon paused by the newly formed Al2O3 and Al3Ni phases that separated the Al and NiO grains. A liquid–solid reaction was later resumed as the temperature was increased above the eutectic temperature of Al–Al3Ni at 640 °C when molten Al–Ni appeared. When the molten sample was quenched to room temperature, a two-phase Al–Al3Ni eutectic was found in the sample. In comparison with the air-quenched and the oil-quenched samples, the sizes of proeutectic Al3Ni grains and Al–Al3Ni eutectic phases in the salt-solution-quenched sample were much finer. The eutectic contained Al3Ni nanofibers with a diameter of approximately 50 nm. A reaction model of Al and NiO was proposed. A thermodynamic model was also proposed to describe the formation of the composite.