Nickel–cobalt oxide/activated carbon composite electrodes for electrochemical capacitors

Nanostructured synthesis of nickel–cobalt oxide/activated carbon composite by adapting a co-precipitation protocol was revealed by transmission electron microscopy. X-ray diffraction analysis confirmed that nickel–cobalt oxide spinel phase was maintained in the pure and composite phases. Cyclic voltammetry, galvanostatic charge–discharge tests and ac impedance spectroscopy were employed to elucidate the electrochemical properties of the composite electrodes in 1.0 M KCl. The specific capacitance which was the sum of double-layer capacitance of the activated carbon and pseudocapacitance of the metal oxide increased with the composition of nickel–cobalt oxide before showing a decrement for heavily-loaded electrodes. Utilisation of nickel–cobalt oxide component in the composite with 50 wt. % loading displayed a capacitance value of ～59 F g^?1. The prepared composite electrodes exhibited good electrochemical stability.     

Structural analysis of nickel doped cobalt ferrite nanoparticles prepared by coprecipitation route

Magnetic nanoparticles of nickel substituted cobalt ferrite (Ni_xCo_1−xFe₂O₄:0≤x≤1) have been synthesized by co-precipitation route. Particles size as estimated by the full width half maximum (FWHM) of the strongest X-ray diffraction (XRD) peak and transmission electron microscopy (TEM) techniques was found in the range 18–28±4 nm. Energy dispersive X-ray (EDX) analysis confirms the presence of Co, Ni, Fe and oxygen as well as the desired phases in the prepared nanoparticles. The selective area electron diffraction (SAED) analysis confirms the crystalline nature of the prepared nanoparticles. Data collected from the magnetization hysteresis loops of the samples show that the prepared nanoparticles are highly magnetic at room temperature. Both coercivity and saturation magnetization of the samples were found to decrease linearly with increasing Ni-concentration in cobalt ferrite. Superparamagnetic blocking temperature as determined from the zero field cooled (ZFC) magnetization curve shows a decreasing trend with increasing Ni-concentration in cobalt ferrite nanoparticles.     

Synthesis and characterization of Ni magnetic nanoparticles in AlMCM41 host

Superparamagnetic nickel nanoparticles were prepared by incorporating nickel ion into AlMCM41 as a nanoreactor and then reduced with sodium borohydride or H₂ gas. Products were characterized by elemental analysis, transmission electron microscopy, X-ray powder diffraction, and magnetic susceptibility. The nickel particle size and blocking temperature depend on the reduction method.     

Properties of ferromagnetic micropowders

Very small particles of iron, cobalt, and iron-cobalt alloys have been prepared by an evaporation-condensation technique. The crystal structure and shape of these particles have been investigated by X-ray diffraction and electron microscopy.The iron and alloy particles were all found to be bcc and the cobalt particles fcc. No hcp cobalt was observed. The shape of all particles was predominantly spherical. The electron microscope showed that the particles possessed a distribution of sizes and were linked together to form chains.Magnetic measurements have been carried out at 290 K on assemblies of these particles. Coercivity, saturation and remanence curves obtained using a Faraday balance magnetometer and pulsed field magnetometer are presented. These show the particles to have fairly high coercivities (typically 1 kOe) but fairly low remanence to saturation ratios (typically 0.25).     

Structural and magnetic properties of high magnetic moment electroplated CoNiFe thin films

CoNiFe alloy thin films deposited at various cobalt concentrations were galvanostatically electrodeposited on the pre-cleaned copper substrates. The effects of cobalt concentration on the structural, compositional, morphological, and magnetic properties of the films were investigated. X-ray diffraction patterns revealed that the deposited films possess polycrystalline in nature with mixed (fcc–bcc) cubic structure at optimized cobalt concentration. Microstructural properties of the films were calculated from predominant diffraction lines. The surface morphology and surface roughness were characterized using scanning electron microscopy and atomic force microscopy, respectively. EDAX results were revealed that the cobalt content increases as nickel content decreases whereas ferrous content initially increases and then eventually decreases in the CoNiFe alloy. VSM results show a higher value of saturation magnetization (4πM _s) above 2 T with coercivity 154 A/m for films deposited in the optimized deposition condition.     

Synthesis and characterization of stable Co and Cd doped nickel hydroxide nanoparticles for electrochemical applications

The present paper describes the physical-chemical characterization and electrochemical behavior of a new nanomaterial formed by the addition of cadmium and cobalt atoms into the structure of nickel hydroxide nanoparticles, these ones synthesized by an easy sonochemical method. Particles of about 5nm diameter were obtained and characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction and Raman spectroscopy. Different nickel hydroxide nanoparticles were immobilized onto transparent conducting substrates by using electrostatic layer-by-layer providing thin films at the nanoscale and the electrochemical behavior was investigated. The formation of a mixed hydroxide was corroborated by observation of very interesting properties as redox potential shifting to less positive potentials and high stability when submitted to long electrochemical cycling or high times of ultrasonic synthesis, suggesting practical applications.     

Characterization and magnetic properties of Fe–Co ultrafine particles

Characterization and magnetic properties of Fe–Co ultrafine particles were investigated systematically by means of X-ray diffraction, Mössbauer spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, energy disperse spectroscopy analysis, chemical analysis, oxygen determination and magnetization measurement. In comparison with bulk iron–cobalt alloys, the corresponding Fe–Co ultrafine particles have significant difference in the phase structure and magnetic properties, depending on the condition of evaporating and subsequent quenching. The mechanism for the formation of the ultrafine particles as well as the origin of ferromagnetism and paramagnetism (or superparamagnetism) were discussed.     

不同催化剂热解法制备硼碳氮纳米管过程中的影响

对以钴、镍、钴/镍、钴/二茂铁、镍/二茂铁和二茂铁为催化剂高温热解法制备的硼碳氮（BCN）纳米管的结构、产率等的影响进行了分析.实验中发现催化剂在BCN纳米管的生长过程中有重要作用.高分辨率透射电子显微镜图像显示在860℃时，以镍/二茂铁、钴/二茂铁为催化剂生成的BCN纳米管具有“竹节状”结构，且管壁较薄，镍、钴或镍/钴作催化剂生成的BCN纳米管不具有明显的“竹节状”结构，管壁较厚，且粗细不均匀，而以二茂铁作催化剂没有BCN纳米管生成.在所有生成的BCN纳米管中含有催化剂颗粒.通过对生成的BCN纳米管的结 关键词： BCN纳米管 热解 催化剂 拉曼光谱     

醇热反应低温合成锰钴镍热敏薄膜

锰钴镍复合氧化物是一种具有半导体性质的热敏材料. 本文采用金属有机沉积技术于室温条件下、在Si衬底上沉积一定 厚度的Mn_1.74Co_0.72Ni_0.54O₄金属 有机化合物薄膜, 并通过醇热反应进行低温结晶化合成, 可得到Mn_1.74Co_0.72Ni_0.54O₄结晶薄膜. 通过X 射线衍射、场发射扫描电子显微镜 (FESEM) 以及阻温特性等测试方法表征, 讨论了醇热反应对锰钴镍热敏薄膜的物相结构、微观形貌以及电学性能的影响. X射线衍射图显示薄膜已出现尖晶石结构的特征峰. 电镜照片说明结晶薄膜的表面较为平整、孔隙率低. 阻温特性关系表明薄膜具有明显的负温度系数效应, 室温(≈27°) 电阻率约为303.13 Ω·cm. 关键词： 醇热反应 锰钴镍薄膜 热敏电阻 低温合成     

Magnetic composites based on hybrid spheres of aluminum oxide and superparamagnetic nanoparticles of iron oxides

Materials containing hybrid spheres of aluminum oxide and superparamagnetic nanoparticles of iron oxides were obtained from a chemical precursor prepared by admixing chitosan and iron and aluminum hydroxides. The oxides were first characterized with scanning electron microscopy, X-ray diffraction, and Mössbauer spectroscopy. Scanning electron microscopy micrographs showed the size distribution of the resulting spheres to be highly homogeneous. The occurrence of nano-composites containing aluminum oxides and iron oxides was confirmed from powder X-ray diffraction patterns; except for the sample with no aluminum, the superparamagnetic relaxation due to iron oxide particles were observed from Mössbauer spectra obtained at 298 and 110 K; the onset six line-spectrum collected at 20 K indicates a magnetic ordering related to the blocking relaxation effect for significant portion of small spheres in the sample with a molar ratio Al:Fe of 2:1.     

Hydrothermal synthesis and magnetic properties of gadolinium-doped CoFe2O4 nanoparticles

CoFe_2−xGd_xO₄ (x=0-0.25) nanoparticles were synthesized via a simple hydrothermal process at 200 °C for 16 h without the assistance of surfactant. The as-synthesized powders were characterized by X-ray diffraction, transmission electron microscopy, and a vibrating sample magnetometer. The X-ray diffraction results showed that the as-synthesized powders were in the pure phase with a doping amount of ≤0.25, and the peaks could be readily indexed to the cubic spinel cobalt ferrite. Transmission electron microscopy and high resolution transmission electron microscopy observations revealed that the gadolinium-doped cobalt ferrite nanoparticles were single crystal, roughly spherical, uniformly distributed, and not highly agglomerated. The room temperature magnetic field versus magnetization measurements confirmed a strong influence of gadolinium doping on the saturation magnetization and coercivity due to large lattice distortion and grain growth of small particles.     

The partial structure factors of amorphous nickel-phosphorus alloys

A detailed analysis of X-ray scattering intensity of electrodeposited amorphous nickel-phosphorus alloys has been carried out by X-ray diffraction with anomalous scattering technique. The scattering powers of these alloys were changed by the anomalous scattering of nickel atom for molybdenum, copper and cobalt radiations and the three partial structure factors required to characterize a binary disordered alloy were estimated. It is found that the partial structure factors are approximately independent of the concentration of alloys and the partial structure factors of Ni-Ni and Ni-P pairs contribute mainly to the splitting of the second peak in the total structure factor directly obtained from experiments.     

Spray pyrolytic synthesis of large area NiOx thin films from aqueous nickel acetate solutions

Non-stoichiometric nickel oxide thin films were prepared by pyrolytic decomposition of aerosol droplets of aqueous nickel acetate solution. Conventional un-nebulized spray pyrolysis system was used for the synthesis of thin films. The fine droplets were atomized by employing compressed air as carrier gas and allowed to decompose onto pre-heated Sn doped In₂O₃ (ITO) coated glass. The preparative parameters such as substrate temperature, solution concentration, distance from spray-nozzle to substrate, pressure of carrier air, etc., were optimized to obtain large area, uniform, thin films. The appropriate substrate temperature was selected after thermo-gravimetric analysis of nickel acetate. The temperature range of 330-420 °C was investigated for pyrolysis. Structural studies using X-ray diffraction (XRD) show the formation of cubic NiO. Morphological aspects of the films as-prepared and air annealed films have been studied by employing scanning electron microscopy. The optical absorption studies give direct band gap equal to 3.61 eV. The compositional analysis was carried out from the elemental depth profiles employing Auger electron spectroscopy. These indicate the formation of non-stoichiometric nickel oxide thin films. By studying I-V characteristics in alkaline electrolyte, electrocatalytic activity is tested.     

Facile synthesis of flower-like nickel nanocrystals and properties

A solvo-hydrothermal synthesis approach for the preparation of a new type of flowerlike nickel nanostructure is reported. The as-synthesized flower-like nickel nanocrystallites were characterized by X-ray diffraction and scanning electron microscopy. The nickel flowers modified glassy carbon electrode can be prepared and used to detect methanol and ethanol in the solution. The results show that the nickel flowers give a very high activity for detecting the methanol and ethanol, which provide a new application of nickel flowers. Compared with that of bulk nickel, thus-prepared nickel flowers showed a much enhanced coercivity.     

高性能镍钴层状双金属氢氧化物的制备及其电化学性能研究

分别选用四种不同阴离子的镍、钴金属盐作为镍源和钴源,通过简单的水热法合成镍钴双金属氢氧化物,并对双金属氢氧化物的形貌结构及其电化学性能进行表征分析,以研究镍源和钴源阴离子的种类对所得材料形貌结构及其电化学性能的影响.结果表明:不同的镍、钴金属盐不仅影响着双金属氢氧化物的形貌结构,而且对其电化学性能也有很大的影响,其中,以硫酸镍和硫酸钴合成的镍钴双金属氢氧化物具有片层形貌结构和优异的电化学性能,在电位窗口为0.45 V、电流密度为1 A/g时,其比电容值可达1551 F/g.     

Solid solutions of nickel and cobalt disilicides

Lattice parameters, density, thermal expansion coefficients and electrical conductivity of alloys of higher silicide of nickel with cobalt disilicide were measured. The influence of the completeness of the crystal lattice of the continuous series of solid solutions formed by these compounds was analyzed. The anomalous variation in the lattice parameter observed when nickel is replaced by cobalt was attributed to a reduction in the electron concentration in antibonding states.     

Protection of iron against corrosion by coverage with Au nanoparticles and n-hexylthiol mixed films

Through a one-step thermal reaction, Au nanoparticles were synthesized and self-assembled mixed films of Au nanoparticles and n-hexylthiol were prepared on iron surface. The size distribution and shape of Au nanoparticles were examined using transmission electron microscopy (TEM). Results of two electrochemical methods - electrochemical impedance spectroscopy (EIS) and polarization curves indicate that self-assembled mixed films can form on the iron surface and prevent it from corrosion effectively. Energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) measurements were applied to identify the formation of the mixed films on iron surface.     

Ultrasonically assisted hydrothermal synthesis of nanocrystalline ZrO2, TiO2, NiFe2O4 and Ni0.5Zn0.5Fe2O4 powders

Ultrasonic-hydrothermal and hydrothermal treatment was used for synthesis of nanocrystalline zirconia, titania, nickel and nickel-zinc ferrites powders from precipitated amorphous zirconyl, titanyl, binary nickel-iron and ternary nickel-zinc-iron hydroxides, respectively. Resulted nanopowders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption (BET), and magnetic susceptibility measurements. It was established that ultrasonically assisted hydrothermal treatment of amorphous zirconyl and titanyl gels results in significant rise of the rate of ZrO2 and TiO2 crystallization and promotes formation of thermodynamically stable monoclinic zirconia, but does not affect the microstructure and mean particles size of resulting nanopowders. Ultrasonic-hydrothermal processing of co-precipitated amorphous nickel, zinc and iron hydroxides favours formation of nanocrystalline ferrite powders with narrower particle size distribution.     

Preparation and magnetic property of the composite of nitrogen-doped carbon nanotubes decorated with nickel nanoparticles

A magnetic composite of nitrogen-doped carbon nanotubes (CN_x) decorated with nickel nanoparticles was synthesized by a chemical precipitation and deoxidization method. The decorated CN_x were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The XRD pattern showed that CN_x, nickel nanoparticles and little nickel oxides coexisted in the composite, TEM observation indicated that nickel nanoparticles were highly dispersed on the outer walls of CN_x, Magnetic measurements by VSM demonstrated that the saturated magnetization and remanence of CN_x were improved, while the coercivity was lowered after decorating with nickel nanoparticles.     

Nanocomposite Ni–TiN coatings prepared by ultrasonic electrodeposition

Nanocomposite Ni–TiN coatings were prepared by ultrasonic electrodeposition and the effects of ultrasonication on the coatings were studied. X-ray diffraction analysis was utilized to detect the crystalline and amorphous characteristics of the composite coatings. The surface morphology and metallurgical structure were observed by scanning electron microscopy, high-resolution transmission electron microscopy and scanning probe microscopy. The results showed that ultrasonication had great effects on TiN nanoparticles in composite coatings. The moderate ultrasonication conduced to homogeneous dispersion of TiN particles in the coatings. Moreover, the TiN nanoparticles that entered and homogeneously dispersed in the composite coating led to an increase in the number of nuclei for nucleation of nickel grains and inhibition of grain growth. Therefore, the introduction of ultrasonication and TiN nanoparticles resulted in the formation of smaller nickel grains. The average grain diameter of TiN particles was ∼33 nm, while Ni grains measured approximately 53 nm.