Effect of synthesis temperature on the phase structure and electrochemical performance of nickel hydroxide

Nickel hydroxide powder is prepared by chemical precipitation method, and the effect of synthesis temperature on the phase structure and electrochemical performances of nickel hydroxide is investigated. The phase structure is characterized by X-ray diffraction (XRD), and the electrochemical performances are characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge tests. The XRD results show that low temperatures (0–20 °C) induce the precipitation of badly crystallized nickel hydroxide while at high temperatures (40–60 °C) crystallized β-nickel hydroxide is formed. Electrochemical performance tests show that the nickel hydroxide synthesized at low temperature has better electrochemical reversibility, lower electrochemical reaction impedance, and higher discharge capacity than that of the nickel hydroxide synthesized at high temperature.     

Electroless deposition of copper and fabrication of copper micropatterns on CVD diamond film surfaces

Electroless deposition of copper on as-grown and amino-modification diamond substrates was investigated. The compact and uniform copper films were successfully electrolessly deposited on as-grown and amino-modification diamond substrates after activation by Pd/Sn colloid nanoparticles. The adhesion interaction between copper films and diamond substrates was roughly estimated by the ultrasonic treatment. The results showed the higher adhesion interaction between copper films and amino-modification diamond substrates than that between the copper films and as-grown diamond substrates due to the greater attractive force between the Pd/Sn colloid nanoparticles and amino-modified diamond surface. The favorable copper micropatterns were successfully constructed on diamond film surfaces by means of the catalyst lift-off method and the copper lift-off method. Furthermore, the electrochemical behavior of copper-modified boron-doped diamond (BDD) was studied for glucose oxidation in 0.2 M sodium hydroxide solution by using cyclic voltammetry, and the result indicated that copper-modified BDD exhibited high catalytic activity to electrochemical oxidation of glucose in alkaline media.     

Structural and electrochemical characterization of nickel hydroxide obtained by the new synthesis route of electrodialysis. a comparison with spherical β-Ni(OH)2

Both structural and electrochemical properties of non-doped nickel hydroxide produced by a new synthesis route of electrodialysis are investigated. A comparison with two spherical β-type Ni(OH)₂ is made. Structural characterization is carried out by X-ray diffraction, vibrational spectroscopy and thermal analysis. Electrochemical properties are studied by cyclic voltammetric and chronoamperometric experiments. The material obtained by electrodialysis is found to have a highly defective structure, which corresponds to a complex electrochemical behavior. More particlarly, it is shown that this new nickel hydroxide is more stable regarding the β → γ transformation. Project financed by the E.U. under the Brite Euram program (#BRPR-CT97-0515) Paper presented at the 6th Euroconference on Solid State Ionics, Sept. 12–19, 1999, Cetraro, Calabria, Italy     

Structure and electrochemical performance of Y(III) and Al(III) codoped amorphous nickel hydroxide

Amorphous nickel hydroxide codoped with rare earths Y(III) and Al(III) has been synthesized by the chemical precipitation method combined with the rapid freezing technique. The microstructure and morphology of the prepared sample were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectra. The electrochemical performance of the sample was characterized by the charge/discharge test and cyclic voltammetry. The results show that this amorphous nickel hydroxide codoped with Y(III) and Al(III) has many structural defects and therefore results in a relatively high specific capacity (351.83 mA h g^?1 at a charge/discharge rate of 0.2 C) and good electrochemical reversibility.     

Synthesis and electrochemical performance of amorphous nickel hydroxide codoped with Fe<Superscript>3+</Superscript> and CO<Stack><Subscript>3</Subscript><Superscript>2−</Superscript></Stack>

Amorphous nickel hydroxide codoped with Fe³⁺ and CO₃²⁻ was synthesized by micro-emulsion precipitation method combined with rapid freezing technique. The microstructure and composition of the sample were characterized by X-ray diffraction and IR analysis. The electrochemical performance of the sample was analyzed by cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge tests. The results showed that the Fe³⁺ and CO₃²⁻ codoping enhances the amorphous feature of the prepared nickel hydroxide. Moreover, the Fe³⁺ and CO₃²⁻ codoping could increase the specific capacity and improve the electrochemical reversibility of the amorphous nickel hydroxide electrode.     

Joined ellipsometry and voltametry investigation on the second discharge plateau in Ni(OH)2

The electrochemical properties of nickel hydroxide, produced via an electrodialysis process are studied by means of cyclic voltametry and in-situ ellipsometry methods. The Ni(OH)₂ electrodes are thin layers of nickel hydroxide powder deposited on a polished platinum substrate. Electrochemical and optical properties are investigated in a voltage domain including the so-called “second discharge process”. The reduction of nickel hydroxide proceeds at two successive potentials with a recovering of the initial optical data only after the second discharge step. The first discharge step leads to a nickel hydroxide not fully discharged while the second discharge step is coupled both to a sudden change in the nickel hydroxide properties and an agglomeration of particles phenomenon. Project financed by the E.U., program Brite Euram BRPR-CT97-0515 (NEARBY) Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

电化学阴极沉积制备氧化钴/CNTs复合电极的准电容特性

采用电化学阴极沉积还原Co(NO3)2的方法制备了具有准电容特性的氧化钴电极材料,其比容量达到280 F／g,采用CNTs作为电极基体,在其表面均匀的沉积了纳米钴化镍颗粒并由此制备了氧化钴碳纳米管复合电极材料.采用循环伏安,恒流充放电,交流阻抗及扫描电镜等方法考察了复合电极材料的容量特性、阻抗特性、自放电特性以及电极表观特征．实验表明复合电极具有良好的电化学特性,CNTs基体在明显降低氧化镍材料的阻抗的同时还提高了电极材料的电化学容量并拓宽了电极材料的有效工作电位窗,复合电极在1 mol／L KOH电解液中比容量达到322 F／g且表现了良好的电化学可逆性．并分别采用氧化钴／CNTs复合电极作为正极,活性炭纤维作为负极制备了复合型电化学电容器,其工作电压达到1．4 V,电容器质量比容量达到47 F／g．在0．1 A／cm2放电时,复合型电容器的能量密度达到10 Wh／kg,兼具高能量特性和优良的大电流放电特性．     

Ageing of nickel used as sensitive material for early detection of sudomotor dysfunction

The surface ageing of nickel electrodes was studied in the frame of the development of non-invasive biomedical devices, dedicated to the detection of sudomotor dysfunction manifested by an alteration of the ionic balance in human sweat. In this kind of technology, low voltage potentials with variable amplitudes are applied to nickel electrodes, placed on skin regions with a high density of sweat glands, and the electrical responses are measured. The trick is that nickel electrodes play alternately the role of anode and cathode, thus the analysis of the temporal evolution of the physico-chemical properties of nickel is of prime importance to ensure the good performance of the device. Electrochemical measurements coupled to surface chemical characterizations (X-ray photoelectron spectroscopy (XPS), Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS)) were performed on pure Ni samples, immersed in buffered chloride solutions mimicking human sweat. The shapes of voltammograms, recorded in a restricted anodic potential range, show that the nickel surface was gradually passivated as a function of the number of scans. This was confirmed by XPS data, with the formation of a 1 nm thick duplex layer composed by nickel hydroxide (outermost layer) and nickel oxide (inner layer). In a negative extended potential range, though the electrochemical behavior of electrodes was not modified upon cycling the potential, XPS data show that the inner layer was thickening, indicating a surface degradation of the nickel electrode. Below pitting potentials, adsorbed chloride was only hardly detected by XPS, and the surface composition of the nickel samples was similar after treatments in chloride or chloride-free buffered solutions. In a larger potential range enabling to reach the breakdown potential, the highly chemically sensitive ToF-SIMS characterization pointed out that the surface concentration of adsorbed chloride was higher in pits than elsewhere on the surface sample.     

Structure and lithium storage performances of nickel hydroxides synthesized with different nickel salts

Nickel hydroxides with hierarchical micro-nano structures are prepared by a facile homogeneous precipitation method with different nickel salts (Ni(NO₃)₂·6H₂O, NiCl₂·6H₂O, and NiSO₄·6H₂O) as raw materials. The effect of nickel sources on the microstructure and lithium storage performance of the nickel hydroxides is studied. It is found that all the three prepared samples are α-nickel hydroxide. The nickel hydroxides synthesized with Ni(NO₃)₂·6H₂ or NiCl₂·6H₂O show a similar particle size of 20–30 μm and are composed of very thin nano-sheets, while the nickel hydroxide synthesized with Ni(SO₄)₂·6H₂O shows a larger particle size (30–50 μm) and consists of very thin nano-walls. When applied as anode materials for lithium-ion batteries (LIBs), the nickel hydroxide synthesized with NiSO₄·6H₂O exhibits the highest discharge capacity, but its cyclic stability is very poor. The nickel hydroxides synthesized with NiCl₂·6H₂O exhibit higher discharge capacity than the nickel hydroxides synthesized with Ni(NO₃)₂·6H₂O, and both of them show much improved cyclic stability and rate capability as compared to the nickel hydroxide synthesized with Ni(SO₄)₂·6H₂O. Moreover, pseudocapacitive behavior makes a great contribution to the electrochemical energy storage of the three samples. The discrepancies of lithium storage performance of the three samples are analyzed by ex-situ XRD, FT-IR, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) tests.     

Synthesis and magnetic characterization of nickel ferrite nanoparticles prepared by co-precipitation route

Magnetic nanoparticles of nickel ferrite (NiFe₂O₄) have been synthesized by co-precipitation route using stable ferric and nickel salts with sodium hydroxide as the precipitating agent and oleic acid as the surfactant. X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses confirmed the formation of single-phase nickel ferrite nanoparticles in the range 8-28 nm depending upon the annealing temperature of the samples during the synthesis. The size of the particles (d) was observed to be increasing linearly with annealing temperature of the sample while the coercivity with particle size goes through a maximum, peaking at ∼11 nm and then decreases for larger particles. Typical blocking effects were observed below ∼225 K for all the prepared samples. The superparamagnetic blocking temperature (T_B) was found to be increasing with increasing particle size that has been attributed to the increased effective anisotropy energy of the nanoparticles. The saturation moment of all the samples was found much below the bulk value of nickel ferrite that has been attributed to the disordered surface spins or dead/inert layer in these nanoparticles.     

Properties of pulsed laser deposited nanocomposite NiO:Au thin films for gas sensing applications

Nanocomposite thin films formed by gold nanoparticles embedded in a nickel oxide matrix have been synthesized by a new variation of the pulsed laser deposition technique. Two actively synchronized laser sources, a KrF excimer laser at 248 nm and an Nd:YAG laser at 355 nm, were used for the simultaneous ablation of nickel and gold targets in oxygen ambient. The structural, morphological, and electrical properties of the obtained nanocomposite films were investigated in relation to the fluence of the laser irradiating the gold target. The nanocomposite thin films were tested as electrochemical hydrogen sensors. It was found that the addition of the gold nanoparticles increased the sensor sensitivity significantly.     

Controlled synthesis of monodispersed superparamagnetic nickel ferrite nanoparticles

Nickel ferrite nanoparticles have been prepared through a gentle chemistry route, starting from iron nitrate, nickel nitrate and stearic acid. The nickel ferrite crystalline phase, the particle size and shape, and the homogeneity of the resulting nanoparticles were studied by X-ray diffraction and transmission electron microscopy. Fourier transform infrared techniques were used to study the composition characteristics of the as-prepared sample. Magnetization studies at room temperature showed superparamagnetic behavior for the nanoparticles. Magneto-optic rotation studies at different wavelengths of He-Ne lasers reveal non-linear behavior.     

Synthesis of nanofiber-composed dandelion-like CoNiAl triple hydroxide as an electrode material for high-performance supercapacitor

In this work, CoNiAl triple hydroxide with nanofiber-composed dandelion-like morphology was synthesized on nickel foam by a hydrothermal route. This delicate nanostructure was initiated from the rolling up of hydroxide nanosheets. The hierarchical nanostructure and optimized molar ratio of Co, Ni, and Al guarantees the high electrochemical performance of obtained samples. The maximum specific capacitance of 2,791 F g^?1 for the as-prepared CoNiAl hydroxides was achieved at scan rate of 5 mV s^?1 in 3 M KOH aqueous solution. The capacitance of material still remained 85 % after 2,000 charge–discharge cycles. These results demonstrated that the as-prepared CoNiAl triple hydroxide can be applied as a high-performance electrode material for supercapacitor.     

UV-Broadband Light Scattering Measurements During Metallic Particle Formation in a Combustion-Like Environment

The thermal evolution of aqueous solution droplets of lead and nickel nitrate was studied experimentally in a drop-tube furnace operated up to 1300 K. Dimensions and physico-chemical properties of the droplets/particles were obtained by coupling the analysis of the spectra of ultraviolet light scattered by the produced aerosol with scanning electron microscopy and numerical simulation of the scattering spectra by Mie theory. Lead nitrate forms solid hollow particles with sizes of the order of the original droplets during the drying process, whereas at higher temperature it decomposes, forming spherical micrometer-sized particles of lead oxide and even submicrometer-sized particles of pure lead. Nickel nitrate never forms solid particles owing to its high solubility in water, but precipitates as nickel hydroxide particles in the temperature range where this intermediate decomposition product is formed. At higher temperatures the decomposition of nickel hydroxide and the formation of oxide particles in the micrometer size range is observed. The mutual interaction of the salt properties were analyzed by studying the behavior of a lead–nickel nitrate mixture in the drop-tube reactor. The main peculiarity of the mixture evolution is the formation of composite particles of lead nitrate in a nickel hydroxide shell. The combined use of in situ ultraviolet spectral scattering and ex-situ scanning electron microscopy, along with the simulations of the scattering spectra by Mie theory, allows us to compile a database of scattering spectra attributed to specific droplets or particles of given chemical properties and size which may be useful for the continuous detection and speciation of metallic aerosols at the exit of real plants.     

Inhibition effect of self-assembled films formed by gold nanoparticles on iron surface

The self-assembled (SA) films formed by gold nanoparticles on iron surface had been proved to have inhibition effect for the substrate in 0.5 M H₂SO₄ solutions. The inhibition action was investigated using electrochemical impedance spectroscopy (EIS). The SA films formed by gold nanoparticles protected with sodium oleate had better corrosion protection to the iron substrate than only by sodium oleate. Scanning electron microscopy (SEM) was used to observe the imagines of the SA films. In addition, it was found that the gold nanoparticles could influence the nickel electroless plating films on the iron substrate. The structure and composition of the plating films were test by electron probe microanalyzer (EPMA). The mechanisms of the formation of the SA films and the nickel electroless plating reaction were also discussed.     

In situ μ-Raman spectroscopy study of an isolated micrometer-size pseudo-single crystal of β-H2NiO2 under electrochemical operation

The response of micrometric pseudo-single crystals of β-H₂NiO₂, deposited on an Au substrate and submitted to high rate charge/discharge cycling under controlled current conditions, is studied by in situ μ-Raman spectroscopy. The intensities of the Raman background and of the hydroxyl stretching band are used to probe in time the single-particle surface and bulk oxidation states respectively. Results, obtained in the absence of electrical binders and chemical dopants, substantiate previous electrochemical investigations suggesting that the occurrence of the nickel electrode activation process is related to the formation of a thin surface limiting layer hindering the active material capacity to store and deliver energy. The feasibility of in situ μ-Raman spectroscopy on nickel hydroxide single particles submitted to electrochemical operation is demonstrated for the first time.     

Chemical synthesis and magnetic properties of HCP and FCC nickel nanoparticles

In this study, we successfully synthesized single-phase hexagonal closed packed (HCP) and face-centered cubic (FCC) nickel nanoparticles via reduction of nickel nitrate hexahydrate and nickel acetate tetrahydrate, respectively, in polyethylene glycol-200. Structural information of the as-synthesized nickel nanoparticles are studied by X-ray diffraction (XRD) as a function of the molar concentration of the nickel precursor. XRD results reveal that low concentrations of nickel precursor (0.005?M and below) favor the HCP, while high concentrations favor the mixture of HCP and FCC crystal structures. Particle size of HCP structure is found in the range of ～15?nm via transmission electron microscope analysis. Vibratory sample magnetometer is employed to study its magnetic behavior and the results reveal that FCC crystalline phase shows ferromagnetic nature with high saturation magnetization (M _s?～?39.6?emu?gm^?1) as compared to metastable HCP crystalline structure (M _s?～?2?emu?gm^?1). The surfactants bonding on the surface of nickel nanoparticles are studied.     

Structural aspects of undoped and doped nickel hydroxides

Nickel hydroxide is widely used as an active material in Ni-Cd and Ni-MeH batteries. The electrochemical properties such as charge acceptance, electronic conductivity etc. can be dramatically influenced by doping β-Ni(OH)₂ with small amounts of Co, Cd or Zn. Stabilizing of α-Ni(OH)₂ offers the possibility to obtain nickel electrodes with enhanced capacity. The stabilizing of α-Ni(OH)₂ is achieved by replacing at least 20% of the nickel by a trivalent metal ion. The structural features of the undoped and doped nickel hydroxides and the resulting electrochemical properties are discussd and reviewed. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

Surface morphology and electrocatalytic properties of nickel nanoparticles formed in track pores

Structures, each of which is composed of a conducting substrate with a protective dielectric layer containing an array of equal-sized pores formed under the action of high-energy ions and chemical etching, are created. The created pores are electrochemically filled with nickel nanoparticles. With atomic-force microscopy (AFM), it is established that Ni nanoparticles are generated exclusively within ion tracks without film formation on the surface of a silicon-dioxide layer. Histograms illustrating the nanoparticle-diameter distribution are constructed, and areas of the nickel nanoparticles are calculated. The electrochemical and electrocatalytic properties of Ni nanoparticles inherent to ethanol-oxidation reactions are investigated. The catalytic activity per unit area of the nanocatalyst is estimated using voltammograms, AFM data, and histograms characterizing the particle size distribution.     

Magneto-orientational properties of ionically stabilized aqueous dispersions of Ni(OH)2 nanoplatelets

Magnetic and orientational behavior of nickel hydroxide nanoplatelets ionically stabilized in a liquid matrix is studied. Under an applied field the platelets orient their faces normal to its direction. For characterization of the individual behavior of dispersed and non-interacting particles three techniques are used: SAXS, SQUID and magneto-optics. Analysis reveals that nickel hydroxide in a platelet phase is paramagnetic with a pronounced anisotropy of the intrinsic susceptibility, the major component of which (in the direction normal to platelet face) exceeds the minor one by about 25%.