Performance improvement of pasted nickel electrodes with multi-wall carbon nanotubes for rechargeable nickel batteries

Carbon nanotubes (CNTs) were employed as a functional additive to improve the electrochemical performance of pasted nickel-foam electrodes for rechargeable nickel-based batteries. The nickel electrodes were prepared with spherical β-Ni(OH)₂ powder as the active material and various amounts of CNTs as additives. Galvanostatic charge/discharge cycling tests showed that in comparison with the electrode without CNTs, the pasted nickel electrode with added CNTs exhibited better electrochemical properties in the chargeability, specific discharge capacity, active material utilization, discharge voltage, high-rate capability and cycling stability. Meanwhile, the CNT addition also lowered the packing density of Ni(OH)₂ particles in the three-dimensional porous nickel-foam substrate, which could lead to the decrease in the active material loading and discharge capacity of the electrode. Hence, the amount of CNTs added to Ni(OH)₂ should be optimized to obtain a high-performance nickel electrode, and an optimum amount of CNT addition was found to be 3 wt.%. The superior electrochemical performance of the nickel electrode with CNTs could be attributed to lower electrochemical impedance and less γ-NiOOH formed during charge/discharge cycling, as indicated by electrochemical impedance spectroscopy and X-ray diffraction analyses. Thus, it was an effective method to improve the electrochemical properties of pasted nickel electrodes by adding an appropriate amount of CNTs to spherical Ni(OH)₂ as the active material.     

SBA-15/Ni/TiO2/CNTs复合材料的制备及其光催化性能

通过溶胶凝胶法,经多次涂覆在SBA-15上负载掺杂镍的纳米TiO₂,得到SBA-15/NiO/TiO₂复合物;再以TiO₂中还原态金属镍为催化剂,通过化学气相沉积法（CVD）,在SBA-15/NiO/TiO₂表面原位生长碳纳米管,制得SBA-15/Ni/TiO₂/CNTs复合材料。通过XRD、SEM、TEM、UV-Vis和Raman等方法考察了SBA-15/Ni/TiO₂/CNTs复合材料的结构和性能,并通过降解亚甲基蓝溶液评价其光催化活性。结果表明,SBA-15/Ni/TiO₂/CNTs复合光催化剂的催化活性较SBA-15/NiO/TiO₂显著提高。 二次涂覆掺杂镍的二氧化钛制得的复合光催化剂的催化活性高于一次涂覆。     

Synthesis of nonstoichiometric NiO nanocatalysts and growth of bamboo-like carbon nanotubes

The growth behavior of carbon nanotubes from NiO nanoparticles was investigated in terms of vacancy concentration and nanostructure. The NiO nanoparticles were prepared using anhydrous ethanol as a solvent to lower hydroxyl groups, compared to distilled water. The Ni vacancies in NiO via less hydrolysis were confirmed by lattice expansion and the increased mean oxidation state of Ni³⁺ through X-ray absorption spectroscopy. The increased Ni³⁺ ratio determined from the photoelectron spectrum and ferromagnetism implied a high concentration of Ni vacancies on the surface. Nonstoichiometric NiO exhibited a small particle size of 10.13 nm and a narrow size distribution. For the growth of CNTs, the NiO nanocatalysts with vacancies resulted in thinner CNTs. The internal structures of the CNTs obtained from the defective particles were grown into bamboo-like CNTs, identifying the variation in the carbon diffusion path.     

Green nickel/nickel oxide nanoparticles for prospective antibacterial and environmental remediation applications

The extensive use of broad-spectrum antibiotics has resulted in antibiotic resistance for many human pathogenic bacteria making multi-drug resistance an increasing issue in the management of various infectious diseases. The current research focused on the green synthesis of nickel/nickel oxide nanoparticles (Ni^o/NiO nanoparticles) using seeds extract of Lactuca Serriola, bactericidal effect on human pathogenic bacteria and the photocatalytic activity. Highly crystalline nature of Ni^o/NiO nanoparticles was confirmed by X-ray diffraction (XRD). Infrared spectra of seeds extract of Lactuca Serriola (LS) evidenced the presence of many functional groups of phytochemicals acting as reducing or capping agents. From field emission scanning electron microscopic (FESEM) images of Ni^o/NiO nanoparticles, it was clearly observed that the particles were slightly spherical in shape with size <100 nm. The Ni^o/NiO nanoparticles were also tested against eight pathogenic bacteria (Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, Basilus subtilis, Basilus pumilus, Micrococcus luteus, E. coli and Bordetella bronchiseptica) which displayed significant antibacterial activity at low doses and almost complete inhibition at optimized concentration. From the bandgap study, the reduced bandgap energy value of 1.57 eV indicated its potential semiconductor photocatalytic behavior. Higher degradation efficiency against the model contaminant crystal violet dye, possibility of multiple degradation mechanisms and simple recovery suggested that the green synthesized Ni^o/NiO nanoparticles might be best suitable candidates for environmental remediation applications.     

核壳结构镍基纳米催化剂的制备及其在肉桂醛加氢反应中的性能

分别以硝酸镍和氯化镍为镍源,利用热分解法和水合肼还原法制得镍纳米粒子,再经模板剂造孔法在镍核外部包裹一层介孔壳,通过焙烧和氢气还原制备了核壳结构催化剂Ni@mSiO₂和Ni-N₂H₄@mSiO₂,并以肉桂醛加氢为探针反应考察了核壳结构镍基催化剂与负载型镍基催化剂的加氢性能。结果表明,核壳结构镍基催化剂在肉桂醛加氢反应中比共沉淀法制备的负载型镍基催化剂具有更高的活性,氢化肉桂醛的收率可达90%以上。同时,Ni-N₂H₄@mSiO₂催化剂具有较高的磁饱和度,可实现该催化剂在反应后高效回收并循环套用。采用X射线衍射、比表面及孔分析、透射电子显微镜、H₂-程序升温还原和H₂-化学吸附等表征手段,研究了所制催化剂的结构特征,初步探讨了催化剂结构与性能的构效关系。     

Synthesis of hermetically-sealed graphite-encapsulated metallic cobalt (alloy) core/shell nanostructures

Hermetically-sealed graphite encapsulated cobalt core/shell nanostructures have been prepared by the CO Boudouard reaction using in situ generated cobalt as the catalyst. Only core/shell nanostructures were obtained, rather than a mixture of cobalt nanoparticles with carbon nanotubes or nanofibers. The magnetic cobalt nanoparticles are highly crystallized with a hexagonal-close packed crystal phase (average diameter of ca. 25 nm) and coated with an 8–9 nm thick graphitic shell. The nanostructures have a high saturation magnetization of 85 emu/g and can be easily separated by an external magnet. The creation of the hermetically-sealed graphitic shell not only keeps the magnetic cobalt nanoparticles from reacting with strong mineral acids, but also has biocompatibility and makes further functionalization easy. A pseudo-planar aromatic molecule, xylenol orange, was used as the model molecule because it can be absorbed on the graphitic shell mainly by π–π stacking interaction. This was confirmed by Raman and ultraviolet–visible spectroscopy. Graphite encapsulated Fe₂Co and Fe_0.64Ni_0.36 alloy core/shell nanostructures were also fabricated by this method.     

Hollow nickel microspheres covered with oriented carbon nanotubes and its magnetic property

A composite structure consisting of hollow nickel microspheres coated with oriented carbon nanotubes (CNTs) was synthesized via chemical vapor deposition at 800 °C. The hollow microspheres were composed of discrete Ni nanoparticles which acted as the catalyst. FESEM images showed that the CNTs grew on the surface of the Ni spheres. HRTEM, Raman and XRD analyses showed that the CNTs were highly graphitized. Magnetic measurements demonstrated that these composite structures exhibited enhanced ferromagnetic behaviour compared with hollow Ni spheres and bulk Ni.     

Single-step functionalization of vertically aligned MWCNTs with Cu and Ni by chemical reduction of copper and nickel acetyl acetonate in benzyl alcohol

We report a one-step functionalization reaction of forests of vertically aligned multi-walled carbon nanotubes (MWCNTs) with Cu or Ni nanoparticles. The benzyl alcohol assisted deposition reaction reduces copper or nickel acetyl acetonate to metallic homogeneously distributed nanoparticles and a 1 μm thick metallic capping layer normal to the MWCNT forests. Scanning electron microscopy and transmission electron microscopy images reveal a trimodal diameter regime for the Cu nanoparticles and a bimodal distribution for the Ni nanoparticles. Electron energy loss spectroscopy (EELS) and X-ray diffraction measurements confirm the metallic form of the particles and layers; however EELS reveals surface oxidation of the Cu particles. The metallic layer on top of the functionalized MWCNT forests can serve as a back contact and is deposited simultaneously with the nanoparticles. Field emission measurements reveal a lower contact resistance than for samples prepared by metal sputtering. Comparison with a sputtering process shows the uniqueness of this new Cu functionalization method for CNTs.     

Calcium-dependent cyto- and genotoxicity of nickel metal and nickel oxide nanoparticles in human lung cells

Background

Genotoxicity is an important toxicological endpoint due to the link to diseases such as cancer. Therefore, an increased understanding regarding genotoxicity and underlying mechanisms is needed for assessing the risk with exposure to nanoparticles (NPs). The aim of this study was to perform an in-depth investigation regarding the genotoxicity of well-characterized Ni and NiO NPs in human bronchial epithelial BEAS-2B cells and to discern possible mechanisms. Comparisons were made with NiCl₂ in order to elucidate effects of ionic Ni.

Methods

BEAS-2B cells were exposed to Ni and NiO NPs, as well as NiCl₂, and uptake and cellular dose were investigated by transmission electron microscopy (TEM) and inductively coupled plasma mass spectrometry (ICP-MS). The NPs were characterized in terms of surface composition (X-ray photoelectron spectroscopy), agglomeration (photon cross correlation spectroscopy) and nickel release in cell medium (ICP-MS). Cell death (necrosis/apoptosis) was investigated by Annexin V-FITC/PI staining and genotoxicity by cytokinesis-block micronucleus (cytome) assay (OECD 487), chromosomal aberration (OECD 473) and comet assay. The involvement of intracellular reactive oxygen species (ROS) and calcium was explored using the fluorescent probes, DCFH-DA and Fluo-4.

Results

NPs were efficiently taken up by the BEAS-2B cells. In contrast, no or minor uptake was observed for ionic Ni from NiCl₂. Despite differences in uptake, all exposures (NiO, Ni NPs and NiCl₂) caused chromosomal damage. Furthermore, NiO NPs were most potent in causing DNA strand breaks and generating intracellular ROS. An increase in intracellular calcium was observed and modulation of intracellular calcium by using inhibitors and chelators clearly prevented the chromosomal damage. Chelation of iron also protected against induced damage, particularly for NiO and NiCl₂.

Conclusions

This study has revealed chromosomal damage by Ni and NiO NPs as well as Ni ionic species and provides novel evidence for a calcium-dependent mechanism of cyto- and genotoxicity.

     

Synthesis of spherical NiO nanoparticles using a solvothermal treatment with acetone solvent

Nanometer-sized nickel oxide (NiO) particles were synthesized by thermal reactions with nickel (II) carbonate as a metal-containing precursor and four solvents: water, ethanol, butanol, and acetone. The optimal reaction conditions to obtain spherical NiO were determined to be the acetone solvent, nickel carbonate precursor, and a reaction temperature and time of 200 °C and 48 h, respectively. TEM images revealed perfectly spherical NiO nanoparticles of size ranging from 2.0 to 10.0 nm in the acetone solvent. The reaction mechanism for the formation of the NiO nanoparticles is proposed based on a pathway of chelated Ni complex during crystal growth. Although metallic Ni was also formed from reactions using the two alcoholic solvents, the Ni(OH)₂ structure remained in the water solvent after thermal treatment.     

Steam carbon gasification of a nickel based oxygen carrier

Ni-based oxygen carriers are promising candidates for Chemical Looping applications due to a combination of excellent methane conversion performance, mechanical stability, oxygen transfer capacity. However, experiments conducted on NiO/NiAl₂O₄ in a micro-fluidized bed reactor show that methane forms coke on active nickel sites. In subsequent tests, water vapour was fed to the coked Ni oxygen carrier producing a highly concentrated stream of CO/H₂ (1/1). In the absence of water vapour, production of hydrogen dropped with time while a methane/argon mixture was fed to the reactor. Co-feeding water together with methane improves stability - both H₂ production and carbon deposition were constant for over 1 h. Despite the tremendous lay down of carbon, catalytic activity remained stable at levels as low as 3 vol.% water vapour (and 10% methane). Water vapour is an effective oxidant for Ni(0) but is insufficient to entirely re-oxidize the oxygen carrier from Ni to NiO.     

X-ray absorption spectroscopy studies of nickel oxide thin film electrodes for supercapacitors

Nickel oxide films were synthesized by electrochemical precipitation of Ni(OH)₂ followed by heat-treatment in air at various temperatures (200-600 °C). Their structure and electrochemical properties were studied by cyclic voltammetry, X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). XRD results showed that the nickel oxide obtained at 250 °C or above has a crystalline NiO structure. The specific capacitance of the oxide depends on the heat-treatment temperature, showing a maximum value at 300 °C. XAS results revealed that the non-stoichiometric nickel oxide (Ni_1−xO) approached the stoichiometric NiO structure with increasing heat-treatment temperature due to the defect healing effect. The defective nature of the nickel oxide could be utilized to improve its specific capacitance for supercapacitor application.     

Surface characterization of nickel alloy plasma-treated by O2/CF4 mixture

The micro- or nano-structured mold used for polymer embossing typically must be coated with an anti-adhesion material to reduce its interaction with the embossing. The mold is typically made by nickel sulphamate electroforming. For the anti-adhesion coating to adhere to the mold, the nickel mold surface must be clean and preferably unoxidized or possess reactive groups suitable for covalent bonding with the anti-adhesion coating. The effectiveness of plasma cleaning using mixtures of oxygen (O₂) and tetrafluoromethane (CF₄) with varying ratios versus liquid-only cleaning was investigated. To simulate the nickel mold, Ni200 alloy was used. Plasma treatment using mixtures of O₂ and CF₄ was found to be more effective in cleaning the Ni200 surface than liquid-only cleaning or pure O₂ or pure CF₄ plasma treatment. Using a 1 : 1 O₂ /CF₄ mixture plasma, the contact angles of water, glycerol and diiodomethane on Ni200 were the lowest and the calculated surface energy was the highest among the investigated treatments. From X-ray photoelectron spectroscopy (XPS), the amount of organic contamination on Ni200 was significantly reduced with plasma treatment. For liquid-only cleaned samples, metallic nickel, NiO and Ni(OH)₂ are present on the surface. With pure O₂ or pure CF₄ or 1 : 1 O₂ /CF₄ mixture plasma, both oxidation and fluorination occur and the surface contains combinations of NiF₂, Ni(OH)₂, Ni(OH)F, Ni₂O₃ and NiO₁₅F instead (without metallic nickel and NiO). The proportions of these different compounds vary according to the O₂/CF₄ ratio; O/Ni ratio is highest for pure O₂ plasma treatment, whilst F/Ni is highest for pure CF₄ plasma treatment.     

Ultrasonic-assisted synthesis of Pd–Ni alloy catalysts supported on multi-walled carbon nanotubes for formic acid electrooxidation

Pd–Ni alloys with different compositions (i.e. Pd₂Ni, PdNi, PdNi₂) dispersed on multi-walled carbon nanotubes (MWCNTs) are prepared by ultrasonic-assisted chemical reduction. The X-ray diffraction (XRD) patterns indicate that all Pd and Pd–Ni nanoparticles exist as Pd face-centered cubic structure, while Ni alloys with Pd. The transmission electron microscopy (TEM) images show the addition of nickel decreases the particle size and improves the dispersion. The X-ray photoelectron spectroscopy (XPS) spectra demonstrate the electronic modification of Pd by nickel doping. The electrochemical measurements reveal that the PdNi catalysts have better catalytic activity and stability for formic acid electrooxidation, among them PdNi/MWCNTs is the best. The performance enhancement is ascribed to the increase of electroactive surface area (EASA) and nickel doping effect which might modify the electronic structure.     

Nb effect in the nickel oxide-catalyzed low-temperature oxidative dehydrogenation of ethane

A method for the preparation of NiO and Nb–NiO nanocomposites is developed, based on the slow oxidation of a nickel-rich Nb–Ni gel obtained in citric acid. The resulting materials have higher surface areas than those obtained by the classical evaporation method from nickel nitrate and ammonium niobium oxalate. These consist in NiO nanocrystallites (7–13 nm) associated, at Nb contents >3 at.%., with an amorphous thin layer (1–2 nm) of a niobium-rich mixed oxide with a structure similar to that of NiNb₂O₆. Unlike bulk nickel oxides, the activity of these nanooxides for low-temperature ethane oxidative dehydrogenation (ODH) has been related to their redox properties. In addition to limiting the size of NiO crystallites, the presence of the Nb-rich phase also inhibits NiO reducibility. At Nb content >5 at.%, Nb–NiO composites are thus less active for ethane ODH but more selective, indicating that the Nb-rich phase probably covers part of the unselective, non-stoichiometric, active oxygen species of NiO. This geometric effect is supported by high-resolution transmission electron microscopy observations. The close interaction between NiO and the thin Nb-rich mixed oxide layer, combined with possible restructuration of the nanocomposite under ODH conditions, leads to significant catalyst deactivation at high Nb loadings. Hence, the most efficient ODH catalysts obtained by this method are those containing 3–4 at.% Nb, which combine high activity, selectivity, and stability. The impact of the preparation method on the structural and catalytic properties of Nb–NiO nanocomposites suggests that further improvement in NiO-catalyzed ethane ODH can be expected upon optimization of the catalyst.     

NiO/C nanocapsules with onion-like carbon shell as anode material for lithium ion batteries

The synthesis of NiO/C nanocapsules with NiO nanoparticles as the core and onion-like carbon layers as the shell is reported. The NiO/C nanocapsules deliver an initial discharge capacity of 1689.4 mAh g⁻¹ at 0.5 C and maintain a high reversible capacity of 1157.7 mAh g⁻¹ after 50 cycles compared to the NiO nanoparticles of 383.5 mAh g⁻¹. As an anode material for lithium ion batteries, the NiO/C nanocapsules exhibit a remarkable discharge capacity, a high rate charge–discharge capability and an excellent cycling stability. The improvements are ascribed to the fact that the onion-like carbon shells not only can provide enough voids to accommodate the volume change of NiO nanoparticles but also can prevent the formation of solid electrolyte interface (SEI) films on the surface of the NiO nanoparticles and hence the direct contact of Ni and SEI films upon lithium extraction.     

Synthesis and properties of highly stable nickel/carbon core/shell nanostructures

A simple and cost effective technique for obtaining highly stable carbon coated nickel nanostructures at relatively low reaction temperatures is reported. Thermogravimetric analysis was carried out to optimize the annealing temperatures. The powder X-ray diffraction pattern reveals peaks corresponding to face centered cubic nickel. High resolution transmission electron micrograph shows the formation of nickel nanostructures with ∼5 nm thick carbon coating. This is confirmed by Raman spectroscopy. The nickel/carbon core/shell nanostructures exhibited a shelf life of more than a year, with high thermal stability and excellent magnetic properties. This synthesis route provides scope for large scale production of nickel/carbon nanostructures.     

Calciothermic reduction of NiO by molten salt electrolysis of CaO in CaCl2 melt

Metallic nickel powders with low and uniform residual oxygen content were produced from NiO using the molten salt electrolysis of CaO in CaCl₂ melt. Suitable amount of CaO for the reduction was in the range of 0.5–3.0 mol% CaO.The electrical isolation of NiO from both electrodes could produce metallic Ni in CaCl₂ melt. Separating the metal oxides from the cathode confirmed the mechanism of calciothermic reduction that the electrolysis of dissolved CaO in CaCl₂ melt produces Ca, and that the dissolved Ca in molten CaCl₂ successfully reduces NiO to metallic Ni. An average of about 600 ppm oxygen in Ni sample was achieved directly from oxide, when NiO was detached from the cathode.     

Low temperature atomic layer deposition of nickel sulfide and nickel oxide thin films using Ni(dmamb)2 as Ni precursor

Nickel(II) 1-dimethylamino-2-methyl-2-butoxide (Ni(dmamb)₂) with water and hydrogen sulfide as oxygen and sulfur sources was employed in atomic layer deposition (ALD) of nickel oxide (NiO) and nickel sulfide (NiS) thin films. Both NiO and NiS thin films demonstrate temperature-independent growth rates per cycle of 0.128?nm/cycle and 0.0765?nm/cycle, at 130–150?°C and 80–160?°C, respectively. Comparison of two nickel-based thin film materials demonstrates dissimilar deposition features depending on the reactivity of the Ni precursor, i.e., Ni(dmamb)₂ with anion sources provided by the water and hydrogen sulfide reactants. Difference in reactivity observed for NiO and NiS ALD processes is further investigated by density functional theory (DFT) simulations of surface reactions, which indicated that H₂S demonstrate higher reactivity with surface-adsorbed Ni precursor than H₂O. The material properties of ALD NiO and NiS thin films including stoichiometry, crystallinity, band structure, and electronic properties were analyzed by multiple experimental techniques, showing potential of ALD NiS as electrode or catalyst for energy-oriented devices.     

Regeneration of used nickel catalyst

Regeneration of used nickel catalyst from a hydrogenation plant has been achieved by converting the nickel content of slurry into NiO and Ni(OH)₂, and the subsequent reduction of these compounds by hydrogen gas at temperatures of 450 C and 290 C respectively. A laboratory and plant apparatus for reduction are designed. Activity of regenerated catalyst was measured in comparison with reference catalyst (G15). Pretreatment of discarded catalyst prior to reduction is described.