Spray pyrolyzed NiO–C nanocomposite as an anode material for the lithium-ion battery with enhanced capacity retention

NiO–C nanocomposite was prepared by a spray pyrolysis method using a mixture of Ni(NO₃)₂ and citric acid solution at 600 °C. The microstructure and morphology of the NiO–C composite were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) mapping, and thermogravimetric analysis (TGA). The results showed that the NiO nanoparticles were surrounded by amorphous carbon. Electrochemical tests demonstrated that the NiO–C nanocomposites exhibited better capacity retention (382 mAh g^− 1 for 50 cycles) than that of pure NiO (141 mAh g^− 1 for 50 cycles), which was also prepared by spray pyrolysis using only Ni(NO₃)₂ as precursor. The enhanced capacity retention can be mainly attributed to the NiO–C composite structure, composed of NiO nanoparticles surrounded by carbon, which can accommodate the volume changes during charge–discharge and improve the electrical conductivity between the NiO nanoparticles.     

Magnetic properties of Ni/NiO nanocomposites synthesized by one step solution combustion method

Ni/NiO nanocomposites were synthesized using solution combustion method and characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX) and carbon, hydrogen, nitrogen (CHN) analyser. The Ni or NiO content in Ni/NiO nanocomposites vary with the quantity of HNO₃ used for the synthesis. Magnetic coercivity (H_c) of Ni/NiO nanocomposites is found to be 413 Oe which can be used in magnetic applications. A feeble exchange bias of 7 Oe is seen from the NiO rich Ni/NiO.     

Preparation of magnetic FeCo nanoparticles by coprecipitation route

Magnetic FeCo nanoparticles with high saturation magnetization (M_s = 148 emu/g) at 15 kOe were prepared by a coprecipitation route. The value of M_s for FeCo nanoparticles depends on the ratio of Fe to Co components. The size of the nanoparticles was confirmed by transmission electron microscopy (TEM) images, and morphology of the nanoparticles was obtained by field emission scanning electron microscopy (FE-SEM) images. The crystal structure of the nanoparticles dependent on annealing was characterized by X-ray diffraction data. The magnetic properties were characterized by saturation magnetization from a hysteresis loop by VSM.     

Large-scale synthesis and growth habit of 3-D flower-like crystal of PbTe

In this paper, 3-D flower-like crystal of PbTe was successfully synthesized using Pb(CH₃COO)₂·3H₂O and Na₂TeO₃ as precursors under hydrothermal conditions, and characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction pattern (XRD). The reaction parameters that influenced the evolution of PbTe synthesis and morphology were investigated. It was shown that the flower-like crystal of PbTe was composed of a nucleus with eight pods. A possible growth mechanism was proposed based on the calculation of the surface energies of PbTe and the SEM observation. Furthermore, the temperature-dependent transport properties of 3-D flower-like crystal of PbTe specimen have been evaluated with an average thermoelectric power of 120 S cm^?1 and electrical conductivity of 220 μV K^?1 at 740 K.     

Template-free sonochemical synthesis of hierarchically porous NiO microsphere

A novel template-free sonochemical synthesis technique was used to prepare NiO microspheres combined with calcination of NiO_2.45C_0.74N_0.25H_2.90 precursor at 500 °C. The NiO microspheres samples were systematically investigated by the thermograviometric/differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), fourier-transformed infrared spectroscopy (FT-IR), Brunnauer–Emmett–Teller (BET) nitrogen adsorption–desorption isotherms, laser particle size analyzer, and ultraviolet–visible spectroscopy (UV–Vis). The morphology of the precursor was retained even after the calcination process, and exhibited hierarchically porous sphericity. The morphology changed over the ultrasonic radiation time, and the shortest reaction time was 70 min, which was much less than 4 h for the mechanical stirring process. The mechanical stirring was difficult to form the complete hierarchically porous microsphere structure. The BET specific surface area and the median diameter of the hierarchically porous NiO microspheres were 103.20 m²/g and 3.436 μm, respectively. The synthesized NiO microspheres were mesoporous materials with a high fraction of macropores. The pores were resulted from the intergranular accumulation. The ultraviolet absorption spectrum showed a broad emission at the center of 475 nm, and the band gap energy was estimated to be 3.63 eV.     

Surface modification of Ni and Co metal nanowires through MeV high energy ion irradiation

Nickel (Ni) and cobalt (Co) metal nanowires were fabricated by using an electrochemical deposition method based on an anodic alumina oxide (Al₂O₃) nanoporous template. The electrolyte consisted of NiSO₄ · 6H₂O and H₃BO₃ in distilled water for the fabrication of Ni nanowires, and of CoSO₄ · 7H₂O with H₃BO₃ in distilled water for the fabrication of the Co ones. From SEM and TEM images, the diameter and length of both the Ni and Co nanowires were measured to be ∼ 200 nm and 5–10 μm, respectively. We observed the oxidation layers in nanometer scale on the surface of the Ni and Co nanowires through HR–TEM images. The 3 MeV Cl²⁺ ions were irradiated onto the Ni and Co nanowires with a dose of 1 × 10¹⁵ ions/cm². The surface morphologies of the pristine and the 3 MeV Cl²⁺ ion-irradiated Ni and Co nanowires were compared by means of SEM, AFM, and HR–TEM experiments. The atomic concentrations of the pristine and the 3 MeV Cl²⁺ ion-irradiated Ni and Co nanowires were investigated through XPS experiments. From the results of the HR–TEM and XPS experiments, we observed that the oxidation layers on the surface of the Ni and Co nanowires were reduced through 3 MeV Cl²⁺ ion irradiation.     

Characterization of NiO–yttria stabilised zirconia (YSZ) hollow fibres for use as SOFC anodes

NiO–yttria stabilised zirconia (YSZ) hollow fibres with varying NiO content and a desired microstructure were prepared using a phase inversion technique and sintering. By controlling the fabrication parameters, microstructures with predominately finger-like pores near the inner and outer surfaces and a denser central layer with sponge-like pores were produced, for use as substrates for anode-supported hollow fibre solid oxide fuel cells (HF-SOFC). The NiO–YSZ fibres were reduced to Ni–YSZ at 250–700 °C in hydrogen flowing at 20 cm³ min^? 1 to produce Ni–YSZ hollow fibres, the mechanical and electrical properties of which were determined subsequently, reduction to Ni being verified by X-ray diffraction. The effects of NiO concentration and sintering temperature of the fibre precursors on the conductivity, strength and porosity of the reduced hollow fibres were investigated to assess their suitability for use as anode substrates. As expected, increasing Ni concentration increased electrical conductivities and decreased mechanical strength. Sintering temperature had a critical effect in producing axially conductive hollow fibres of sufficient mechanical strength for use as SOFC anodes. The hollow fibres retained their initial microstructure through the reduction process, though ca. 41% volume contraction is predicted on reduction of NiO to Ni, producing increased porosity in the reduced fibres. The mean porosity of the Ni–YSZ hollow fibres was ca. 60% and ca. 40% after sintered at 1250 °C and 1400 °C, respectively. The mean pore sizes for all the fibres after reduction varied between ca. 0.3 and 1 µm. The hollow fibres produced with 60% NiO, of length ca. 300 mm, electrical conductivities of ca. (1–2.25) × 10⁵ S m^? 1 and a porosity of ca. 43% are being used currently to construct and test the electrical behaviour of an anode-supported HF-SOFC.     

Large-scale synthesis and magnetic properties of cubic CoO nanoparticles

We present the synthesis, microstructural and magnetic characterization of cubic CoO nanoparticles with well-controlled size and shape. The as-synthesized CoO nanoparticles are stable because of the organic coating that occurred in situ. The Néel temperature is 225 and 280 K for the 42 and 74 nm CoO particles, respectively. The CoO nanoparticles exhibit anomalous magnetic properties, such as large moments, coercivities and loop shifts. These results provide evidence for the formation of spin compensated random system in CoO. The structurally distorted and magnetically disordered surface layer ferromagnetic phase played an important role in the magnetic behavior of CoO nanoparticles. The smaller is the particle size, the stronger is the contribution of the ferromagnetic phase and the more is the surface layer helpful to enhance the observed coercivity and the exchange bias.     

Performance and durability of Ni-coated YSZ anodes for intermediate temperature solid oxide fuel cells

NiO-coated YSZ composite powders were synthesized through the Pechini process in order to improve the performance and durability of SOFC anodes. Their microstructures and electrical properties have been investigated with thermal and redox cycling tests. The coverage of NiO crystals on the YSZ surface could be modulated by controlling the composition of the reaction mixture and the ratio of NiO and YSZ. Ni–YSZ electrodes were manufactured by sintering the die-pressed NiO–YSZ pellet at 1400 °C for 3 h, followed by reducing it to 800 °C under hydrogen atmosphere. The anode made from NiO/YSZ composite powder, which has a high homogeneity and plenty of contact sites between Ni and YSZ, has an excellent tolerance against thermal and redox cycling. The maximum power density of a single cell made from NiO/YSZ composite powder was 0.56 W cm^− 2 at 800 °C in reactive gases of humidified hydrogen and air. It can be concluded that the functional NiO/YSZ composite powder will suppress the degradation of anodes and enhance the long-term and redox stability of the unit cell at elevated temperatures.     

Catalytic dechlorination of 2,4-dichlorophenol by Ni/Fe nanoparticles prepared in the presence of ultrasonic irradiation

In this study, nickle/iron (Ni/Fe) nanoparticles were synthesized by liquid phase reductive method in the presence of 20 kHz ultrasonic irradiation to improve nanoparticles’ disparity and avoid agglomeration. The characterized results showed that this method has obviously modified most of the particles in term of sizes and specific surface areas. Meanwhile, the improved nanoscale Ni/Fe particles were employed for the reductive dechlorination of 2,4-dichlorophenol (2,4-DCP) as a function of some influential factors (Ni content, Ni/Fe nanoparticles dosage, reaction temperature and initial pH values) and degradation path. Experimental results showed that 2,4-DCP was first adsorbed by Ni/Fe nanoparticles, then quickly reduced to o-chlorophenol (o-CP), p-chlorophenol (p-CP), and finally to phenol (P). The application of ultrasonic irradiation for Ni/Fe nanoparticles synthesis was found to significantly enhance the removal efficiency of 2,4-DCP. Consequently, the phenol production rates increased from 68% (in the absence of ultrasonic irradiation) to 87% (in the presence of ultrasonic irradiation) within 180 min. Nearly 96% of 2,4-DCP was removed after 300 min reaction with these optimized conditions: Ni content over Fe⁰ 3 wt%, initial 2,4-DCP concentration 20 mg L⁻¹, Ni/Fe dosage 3 g L⁻¹, initial pH value 3.0, and reaction temperature 25 °C. The degradation of 2,4-DCP followed pseudo-first-order kinetics reaction and the apparent pseudo-first-order kinetics constant was 0.0737 min⁻¹. This study suggested that the presence of ultrasonic irradiation in the synthesis of nanoscale Ni/Fe particles could be a promising technique to enhance nanoparticle’s disparity and avoid agglomeration.     

Controllable synthesis of layered Co–Ni hydroxide hierarchical structures for high-performance hybrid supercapacitors

A facile solvothermal method is developed for synthesizing layered Co–Ni hydroxide hierarchical structures by using hexamethylenetetramine (HMT) as alkaline reagent. The electrochemical measurements reveal that the specific capacitances of layered bimetallic (Co–Ni) hydroxides are generally superior to those of layered monometallic (Co, Ni) hydroxides. The as-prepared Co_0.5Ni_0.5 hydroxide hierarchical structures possesses the highest specific capacitance of 1767 F g⁻¹ at a galvanic current density of 1 A g⁻¹ and an outstanding specific capacitance retention of 87% after 1000 cycles. In comparison with the dispersed nanosheets of Co–Ni hydroxide, layered hydroxide hierarchical structures show much superior electrochemical performance. This study provides a promising method to construct hierarchical structures with controllable transition-metal compositions for enhancing the electrochemical performance in hybrid supercapacitors.     

Sono-synthesis and characterization of bimetallic Ni–Co/Al2O3–MgO nanocatalyst: Effects of metal content on catalytic properties and activity for hydrogen production via CO2 reforming of CH4

Sono-dispersion of Ni, Co and Ni–Co over Al₂O₃–MgO with Al/Mg ratio of 1.5 was prepared and tested for dry reforming of methane. The samples were characterized by XRD, FESEM, PSD, EDX, TEM, BET and FTIR analyses. In order to assess the effect of ultrasound irradiation, Ni–Co/Al₂O₃–MgO with Co content of 8% prepared via sonochemistry and impregnation methods. The sono-synthesized sample showed better textural properties and higher activity than that of impregnated one. Comparison of XRD patterns indicated that the NiO peaks became broader by increasing Co content over the support. The FESEM images displayed the particles are small and well-dispersed as a result of sonochemistry method. Also, EDX analysis demonstrated better dispersion of Ni and Co as a result of sonochemistry method in confirmation of XRD analysis. The sono-synthesized Ni–Co/Al₂O₃–MgO as a superior nanocatalyst with Co content of 3% illustrates much higher conversions (97.5% and 99% for CH₄ and CO₂ at 850 °C), yields (94% and 96% for H₂ and CO at 850 °C) and 0.97 of H₂/CO molar ratio in all samples using an equimolar feed ratio at 850 °C. During the 1200 min stability test, H₂/CO molar ratio remained constant for the superior nanocatalyst.     

Evidence for the interfacial reaction between Ni adatoms and H-Si(001) surface

Hydrogen termination of Si surfaces (H-Si) does not stop the interfacial reaction between Ni adatoms and H-Si(001) surface at room temperature. At low Ni coverage of 0.1% (equivalent to 0.02 ML), X-ray photoelectron spectroscopy (XPS) reveals a binding energy shift of Ni 2p_3/2 to 854.0 eV, which corresponds to the formation a NiSi-like environment. As the coverage of Ni increases, the Ni 2p_3/2 eventually shifts to 852.8 eV, indicative of formation of metallic Ni. XPS intensity vs Ni coverage analysis reveals a growth process akin to pseudo-layer-by-layer growth mode, thereby suggesting the formation of bulk-Si(001)/NiSi-like/Ni-rich-silicide-like/metallic Ni structure as growth proceeds. For Ni coverage not more that 33% (equivalent to 12.68 ML), Ni remains protected by the silicide environment and no oxidation of Ni to form Ni-oxides was observed even after exposing the samples to air for 400 days. For samples with Ni coverage above 41%, oxidation of Ni is observed by presence of NiO and NiSiO₃ peaks at 854.5 and 857.0 eV, respectively. The current studies suggest that there is reaction between Ni adatoms and Si at the growth front on H-Si(001) surfaces upon Ni deposition at room temperature and hydrogen termination does not suppress the interface reaction between Ni and Si.     

Effects of Ni buffer layer on giant magnetoresistance in Co/Cu/Co sandwich

In order to increase the sensitivity of Co/Cu/Co sandwiches, different thickness Ni layers were used as buffer layer. It was found that in the Co 55 Å/Cu 35 Å/Co 55 Å sandwiches with different thickness Ni buffer layers, MR ratios between 3.5% and 5.6% could be obtained, and the coercive forces were about 12 Oe. Hence, the maximum field sensitivity could be enhanced to about 1%/Oe. Further investigation from the results of atomic force microscopy showed the improvement of the interfacial flatness in the sandwiches with Ni buffer layer. The microstructure observed by high-resolution electron microscope demonstrated the different structure of the two Co layers in the Ni buffered sandwich, which directly determined the small saturation field of the sandwich. This was confirmed by the magnetic behaviors of the two Co layers calculated from the experimental hysteresis loops. All these showed that the usage of a Ni buffer layer could result in interfacial improvement, different crystalline structure, and small saturation field in the Co/Cu/Co sandwich. These enhanced the electron spin scattering at the Co–Cu interfaces and finally enlarged the giant magnetoresistance and the sensitivity in the sandwich.     

Sonochemical synthesis of cobalt aluminate nanoparticles under various preparation parameters

Cobalt aluminate (CoAl₂O₄) nanoparticles were synthesized using a precursor method with the aid of ultrasound irradiation under various preparation parameters. The effects of the preparation parameters, such as the sonochemical reaction time and temperature, precipitation agents, calcination temperature and time on the formation of CoAl₂O₄ were investigated. The precursor on heating yields nanosized CoAl₂O₄ particles and both these nanoparticles and the precursor were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The use of ultrasound irradiation during the homogeneous precipitation of the precursor reduces the duration of the precipitation reaction. The mechanism of the formation of cobalt aluminate was investigated by means of Fourier transformation infrared spectroscopy (FT-IR) and EDX (energy dispersive X-ray). The thermal decomposition process and kinetics of the precursor of nanosized CoAl₂O₄ were investigated by means of differential scanning calorimetry (DSC) and thermogravimetry (TG). The apparent activation energy (E) and the pre-exponential constant (A) were 304.26 kJ/mol and 6.441 × 10¹⁴ s^?1, respectively. Specific surface area was investigated by means of Brunauer Emmett Teller (BET) surface area measurements.     

The synthesis and properties of nanocrystalline electrode materials by mechanical alloying

In this work, we have experimentally studied the structure and electrochemical properties of nanocrystalline TiFe- and LaNi₅-type alloys. These materials were prepared by mechanical alloying (MA) followed by annealing. The properties of hydrogen host materials can be modified substantially by alloying to obtain the desired storage characteristics. It was found that the respective replacement of Fe in TiFe by Ni and/or by Cr, Co, Mo, Zr improved not only the discharge capacity but also the cycle life of these electrodes. In the nanocrystalline TiFe_0.25Ni_0.75, powder discharge capacity up to 155 mA h g⁻¹ was measured (at 40 mA g⁻¹ discharge current). On the other hand, a partial substitution of Ni by Al or Mn in LaNi_5−xM_x alloy leads to an increase in discharge capacity. The alloying elements such as Al, Mn and Co greatly improved the cycle life of LaNi₅ material. For example, in the nanocrystalline LaNi_3.75Mn_0.75Al_0.25Co_0.25 powder, discharge capacity up to 258 mA h g⁻¹ was measured (at 40 mA g⁻¹ discharge current). The studies show, that electrochemical properties of Ni–MH batteries are the function of the microstructure and the chemical composition of used electrode materials.     

A comparative study of the magnetocaloric effect in Gd3Co and Gd3Ni

Magnetic and magnetocaloric properties of polycrystalline samples of Gd₃Co and Gd₃Ni have been studied. Both these compounds are antiferromagnets and undergo metamagnetic transitions in the antiferromagnetic phase. The Neel temperatures are found to be 128 and 99 K, respectively for Gd₃Co and Gd₃Ni. Though both these compounds have the same crystal structure, their magnetic structures seem to be different. It is found that Gd₃Ni possesses larger magnetic anisotropy compared to Gd₃Co. The maximum values of isothermal magnetic entropy change are 11 and 18.5 J Kg⁻¹ K⁻¹ for Gd₃Co and Gd₃Ni respectively, while their refrigerant capacities are 2.6 J cm⁻³ for both of them. Magnetic entropy change in the paramagnetic region shows a quadratic dependence on the magnetic field in the case of Gd₃Ni, indicating the presence of spin fluctuations above the Neel temperature.     

Electrochemical reactions of lithium with transition metal stannides

High-quality crystalline MSn₂ (M = Cr and Co) thin films have been successfully fabricated by reactive pulsed laser deposition. The physical and electrochemical properties of the as-deposited thin films have been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), galvanostatic cycling and cyclic voltammetry (CV). XRD measurement indicates that the as-deposited thin films prepared at 400 °C consisted mainly of MSn₂ (M = Cr and Co) with a small quantity of metal tin. The specific reversible capacities of CrSn₂ and CoSn₂ thin film electrodes are found to be 467 mA h/g and 465 mA h/g, respectively. A mechanism involving an irreversible decomposition of MSn₂ (M = Cr and Co) and a classical alloying process of Sn is proposed. MSn₂ (M = Cr and Co) as the starting anode materials for conversion to the Li–Sn alloy can improve its electrochemical performance with high reversible capacity and good stable cycle.     

Novel olivine and spinel LiMAsO4 (M = 3d-metal) as positive electrode materials in lithium cells

New olivines LiMAsO₄ (M = Mn, Fe, Co, and Ni) have been tested as positive electrode in lithium cells. Under the used experimental conditions we did not succeed to remove lithium ions from LiFeAsO₄, LiMnAsO₄ or LiNiAsO₄. More work is needed in order to verify whether the lack of electrochemical activity is intrinsic to these materials, or it is due to kinetical limitations such as particle size and poor conductivity. On the contrary lithium ions could be reversibly deinserted/inserted from/into LiCoAsO₄ at average voltages of 4.8 and 4.6 V respectively; the delithiated compound maintaining the olivine structural framework.The high pressure polymorph of LiMAsO₄ (M = Fe, Co, Ni) crystallizing with the spinel structure did not show any electrochemical activity potentially useful in rechargeable lithium batteries.     

Synthesis and luminescent properties of spindle-like YVO4:Ln3+ (Ln=Eu,Dy) self-assembled of nanoparticles

Large-scale spindle-like YVO₄ particles with an euatorial diameter of 100–150 nm and a length of 300–350 nm were synthesized by utilizing the Y(OH)CO₃ colloid spheres as the precursor and NH₄VO₃ as the vanadium source through a simple solution-based hydrothermal process, for the first time. In the first stage of the reaction, hierarchical flower-like YVO₄ spheres were formed. Then, petals of spindle-like YVO₄ particles were obtained via a following self-abscission process from these flower spheres. The possible formation mechanism has been discussed in detail. Moreover, the photoluminescent properties of spindle-like YVO₄:Ln³⁺ (Ln=Eu, Dy) nanoparticles were investigated. They might have potential application in advanced flat panel display, minioptoelectronic devices, and biological labeling.