Papers by Keyword: Nickel Hydroxide

Abstract: The incorporation of quasi-atomic Ni (OH)₂ clusters onto graphitic C₃N₄ (gCN) remarkably enhances the photocatalytic production of hydrogen peroxide (H₂O₂) and benzaldehyde (BAL) from benzyl alcohol (BA) in water under visible light at 440 nm. Upon loading Ni (OH)₂, H₂O₂ production reaches 306 µmol g⁻¹ h⁻¹ and BAL production reaches 270 µmol L⁻¹ h⁻¹. The high photocatalytic performance is attributed to the formation of ultrasmall clusters of Ni (OH)₂, which reduce recombination by trapping holes, thereby increasing the activity (BA conversion). Efficient hole transfer to BA is also facilitated, enhancing selectivity (BAL selectivity). Upon the addition of Ni (OH)₂, the steady-state electron population photoexcited by visible light increases 5.5-fold. The proposed modification of gCN with Ni achieves nearly 100% efficiency in both activity and selectivity to produce H₂O₂, while also generating BAL, a value-added product. This demonstrates its potential for sustainable chemical transformations using visible light and water as a green solvent.

Abstract: Transition metal oxides and hydroxides, specifically nickel (Ni), are currently being studied for their pseudocapacitive behaviors due to their high specific capacitance and efficient redox reactions. In this study, nickel oxide (NiO) and nickel hydroxide [Ni (OH)₂] hierarchical structures were grown on carbon fiber paper via hydrothermal treatment for a binder-free electrode for pseudocapacitor. Cyclic voltammetry was employed to determine the influence of annealing temperature on the specific capacitance of NiO-and/or Ni (OH)₂ – carbon fiber electrodes. The NiO – carbon fiber electrode annealed at 400°C exhibited the highest specific capacitance of about 1993.12 F/g at a scan rate of 2 mV/s. The carbon fibers were fully covered by NiO platelets which possibly provide efficient transport of electrolyte, enhancing the capacitance.

Abstract: A homogeneous Ni (OH)₂/ carbon nanotubes (CNTs) nanocomposite with excellent supercapacitive performance has been synthesized via a facile chemical precipitation. The microstructure and morphology of Ni (OH)₂/CNTs nanocomposite were investigated by XRD, SEM and TEM. It presented an ideal morphology with the nanosized Ni (OH)₂ particles homogeneously growing on the CNTs. The electrochemical performance of the Ni (OH)₂/CNTs nanocomposite was test by cyclic voltammetry, galvanostatic charge−discharge and electrochemical impedance spectroscopy techniques. The synthesized Ni (OH)₂/CNTs nanocomposite shows superior electrochemical performance, including high capacitance, excellent rate capability and good cycle life. The homogeneous Ni (OH)₂/ CNTs nanocomposite exhibited a high specific capacitance of 1741 F g^-1 at a current density of 1A g^-1 and maintained a good stability after 5000 cycles at 10A g^-1`, suggesting that it can be a promising candidate for supercapacitor.

Abstract: A homogeneous Ni (OH)₂/graphene nanosheet (GNS) nanocomposite with excellent supercapacitive performance has been synthesized by a facile chemical precipitation. The Ni (OH)₂/GNS nanocomposite presented an ideal morphology with the nanosized Ni (OH)₂ particles homogeneously growing on the GNS. Its microstructure, morphology were investigated by XRD, SEM and TEM. The electrochemical performance of the Ni (OH)₂/GNS nanocomposite was test by cyclic voltammetry, galvanostatic charge−discharge and electrochemical impedance spectroscopy techniques. The homogeneous Ni (OH)₂/GNS nanocomposite exhibited a high specific capacitance of 1667 F/g at a current density of 1A/g and maintained a good stability in 5000 cycles, suggesting that it can be a promising candidate for supercapacitor. The high specific capacitance and remarkable rate capability are promising for applications in supercapacitors with both high energy and power densities. The Ni (OH)₂/GNS nanocomposite exhibited large specific capacitance, high rate capability and good cycling stability.

Abstract: Nickel hydroxide nanoporous electrochromic thin films were obtained by chemical bath deposition method using nickel nitrate in two different formulations. In one case, ammonium hydroxide controlled the precipitation of the β-Ni (OH)₂ phase through the formation of coordination compounds. In the second case, the decomposition of urea yielded the α-Ni (OH)₂ phase. After thermal annealing in air in between 250 and 300 °C, the electrochromic behavior of the films was examined by cyclic voltammetry and single wavelength transmittance. The optical contrast and structural transformations between colored and bleached states of the samples were studied by ex-situ optical transmittance, X-ray diffraction, as well as Raman and infrared reflectance spectroscopies. The α-Ni (OH)₂ films showed higher optical contrast and reversibility, properties associated with their porous morphology which is revealed by scanning electron microscopy studies.

Abstract: Nickel hydroxide electrodes with flower-like structure were prepared by pulse electrodeposition method. The samples were characterized by XRD, SEM and electrochemical measurements. XRD results show a typical characteristics of α-Ni(OH)₂. SEM results show the morphology can be controlled by the ratio between on-time (T_on) and off-time (T_off). If T_on is constant to 10s, a flower-like structure will be obtained when T_off is bigger than 20s. Electrochemical tests revealed that the Nickel hydroxide electrodes prepared atT_on=10 s and T_off = 30s not only has higher discharge capacity but also exhibits superior stability of capacity during charge-discharge cycling. The maximum specific capacitance in the first cycle is 737.74 F/g and their specific capacitance become stable after cycling 20 times.

Abstract: We present an experimental study of the Ni+2/Ni(OH)2/NH3 reaction-diffusion system in a gel (agar). The system, which consists of a gel containing an inner electrolyte Ni+2 and a diffusing outer electrolyte (NH3/OH-), exhibits pulse propagation due to the concomitant precipitation reaction between Ni+2 and hydroxide ions and re-dissolution due to ammonia. During the propagation of the pulse, a transition to Liesegang banding is shown to take place. The bands are characterized by IR and XRD and are shown to consist of the polymorph -Ni(OH)2 whereas the pulse contains the other polymorph -Ni(OH)2. SEM measurements also reveal a morphological change accompanying the polymorphic transition between the pulse and the bands and uncovering an Ostwald ripening mechanism.

Abstract: Amorphous nickel hydroxide powders doped with rare earth La3+ and Al3+ were synthesized by the combined chemical precipitation and rapid freezing method. The microstructure of the samples was characterized by XRD and Raman spectra. The electrochemical performance of the prepared samples was analyzed by electrochemical impedance spectroscopy and charge-discharge tests. The results showed that this amorphous nickel hydroxide codoped with La3+ and Al3+ had more structural defects than those of the undoped amorphous nickel hydroxide and La3+ singly doped amorphous nickel hydroxide. These abundant structural defects with La3+ and Al3+ codoped amorphous nickel hydroxide decreased the electrochemical impedance spectroscopy and improved the electrochemical reversibility of the amorphous nickel hydroxide electrode.

Abstract: A new and facile route has been developed to synthesize β-Ni(OH)2 nanostructures using ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) as reaction media under solvothermal conditions. The β-Ni(OH)2 with different morphologies, such as nanoflakes, nanoplatelet and nanorods, can be obtained by controlling the volume ratio of the ionic liquid to water and reaction temperature. The as-prepared products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).

Abstract: Hollow microspheres of nickel hydroxide and nickel oxide were prepared with as-synthesized PS/Ni(OH)2 composite particles by sacrificing core method, respectively. The composite particles were synthesized by deposition of the Ni(OH)2 nanoflakelets formed by the hydrolysis of nickel nitrate onto the surfaces of polystyrene (PS) particles. The effects of different concentrations of nickel salt and urea on the deposition of the nanoflakelets of nickel hydroxide were studied. It was found that the uniform nanoflakelets were deposited on the polystyrene particles under the conditions of the 4╳10-3 M nickel salt and 0.667M urea. Compared with the directly calcinating of composite particles, Integral hollow microspheres of nickel hydroxide were attained by removal of cores of polystyrene in composite particles with toluene and NiO hollow microspheres by calcinating of these Ni(OH)2 hollow spheres in oven at 600°C for 2h.