Yanjuan Zhu

Hydrogen storage for carbon nanotubes synthesized by the pyrolysis method using lanthanum nickel alloy as catalyst

We have investigated the adsorption of hydrogen of multiwall carbon nanotubes synthesized by the pyrolysis method using a lanthanum nickel hydrogen storage alloy as a catalyst. The mechanism of carbon nanotubes synthesized using a La–Ni alloy catalyst is discussed. In the hydrogen atmosphere and high-temperature process of carbon nanotube preparation, the LaNi5 alloy particle may be changed into an intermetallic compound of Ni and La by the analysis of the x-ray diffraction patterns and energy-dispersive x-ray spectroscopy of the nanotubes samples using a La–Ni alloy as a catalyst. The H2 uptake capacity of the carbon nanotubes using a La–Ni alloy catalyst is about 5 wt % through to the pressure of 10 MPa. Using a La–Ni alloy as a catalyst increases the effect of chemistry adsorption in the H2 adsorption of the La–Ni alloy catalyzed carbon nanotubes. The P–C–T curve has an approximate plateau. The La–Ni alloy catalyzed carbon nanotubes have better activation for H2 uptake and larger hydrogen uptake in com...

Structural, morphological and optical properties of C60 cluster thin films produced by thermal evaporation under argon gas

C60 cluster thin films were obtained by thermal evaporation under argon atmosphere. The surface morphology, optical absorption characteristics and structure of these films have been investigated. The ultraviolet-visible optical absorption spectrum of this C60 film is obviously different from that of the film obtained under vacuum conditions. The position and intensity of absorption peaks of the films grown in argon are modified compared with the film grown in vacuum. The bandgap energy changes from 2.02?eV to 2.24?eV. IR analyses show no evidence of chemical change. The x-ray diffraction pattern reveals the existence of a mixture of face-centred cubic and hexagonal close-packed phases. The collisions of C60 molecules and buffer gas molecules are discussed. We also found the surface particles of these C60 cluster films are larger and sharper than those of C60 films prepared in vacuum by the observation of atomic force microscopy (AFM). This may be advantageous for using C60 for electron field emission.

Structural and electrochemical performance of additives-doped α-Ni(OH)2

The additives-doped α-nickel hydroxides were prepared by supersonic co-precipitation method. The crystal structure and grain size of the prepared samples were characterized by X-ray diffraction (XRD) and Particle size distribution (PSD), respectively. Cyclic voltammetry (CV) tests show that Al-Co-Y doped Ni(OH)2 has better reaction reversibility, higher proton diffusion coefficient than those of Al-Co doped Ni(OH)2. Al-Co-Y doped Ni(OH)2 also has lower charge-transfer resistance as shown by electrochemical impedance spectroscopy (EIS). Charge/discharge tests show that the discharge capacity of Al-Co-Y doped Ni(OH)2 reaches 328 mAh/g at 0.2 C and 306 mAh/g at 0.5 C, while Al-Co doped Ni(OH)2 can only discharge a capacity of 308 mAh/g at 0.2 C and 267 mAh/g at 0.5 C.

Morphology and characteristics of C60 thin films grown in argon atmosphere by thermal evaporation

The surface morphology, structure, and optical absorption characteristics of C60 thin films grown in argon atmosphere by thermal evaporation have been studied. X-ray diffraction studies reveal a mixture phase of face-centered-cubic and hexagonal-close-packed phases for this film. Infrared analyses show no evidence of chemical change. The observations of atomic force microscopy of C60 thin films grown in argon atmosphere found that surface particles are larger and sharper than that grown in vacuum, thus C60 thin films grown in argon atmosphere may be advantageous to using C60 for electron field emission. Ultraviolet-visible optical absorption spectrum of this film in the range of wavelength from 200 to 600 nm is very different than that of the film obtained under vacuum conditions. The position and intensity of absorption peaks are obviously changed compared to vacuum C60 thin film. The band gap energy of this film also changes from 2.02 to 2.24 eV compared to the film prepared under vacuum.The surface morphology, structure, and optical absorption characteristics of C60 thin films grown in argon atmosphere by thermal evaporation have been studied. X-ray diffraction studies reveal a mixture phase of face-centered-cubic and hexagonal-close-packed phases for this film. Infrared analyses show no evidence of chemical change. The observations of atomic force microscopy of C60 thin films grown in argon atmosphere found that surface particles are larger and sharper than that grown in vacuum, thus C60 thin films grown in argon atmosphere may be advantageous to using C60 for electron field emission. Ultraviolet-visible optical absorption spectrum of this film in the range of wavelength from 200 to 600 nm is very different than that of the film obtained under vacuum conditions. The position and intensity of absorption peaks are obviously changed compared to vacuum C60 thin film. The band gap energy of this film also changes from 2.02 to 2.24 eV compared to the film prepared under vacuum.

The impact of nickel source/doping elements/buffer on the structure of Ni(OH)2

The nano-nickel hydroxide samples were prepared by means of ultrasonic-assisted precipitation and the impact of source/doping element/buffer on the structure of Ni(OH)2 was studied. The results of XRD, IR and TEM testing clearly revealed that larger anionic radius of the nickel sources or the buffer solution was conducive to the formation of α-Ni(OH)2. The proportion of α-Ni(OH)2 samples doped with two elements was larger than that doped with single element. Additionally, speciation, valence as well as the radius of doping ions can directly affect the phase of Ni(OH)2.

Influence of Sodium Carbonate Amount on Crystalline Phase and Structure Stability for Doping Nickel Hydroxide

Alpha nickel hydroxide has better performances than commercial beta nickel hydroxide. However, the main defect is that α-phase is difficult to synthesize and easily transformed to β-phase Ni(OH)2 upon aging in a strong alkaline solution. In this study, the Al-Co, Al-Yb, Yb-Co and Al-Yb-Co multiple doping was used respectively. By controlling the amount of sodium carbonate, the α-Ni(OH)2 was prepared by ultrasonic-assisted precipitation. And the influence of sodium carbonate on the crystalline phase and structure stability for alpha nickel hydroxide was studied. The results demonstrate that, with increasing amount, the biphase nickel hydroxide transforms to pure alpha nickel hydroxide gradually, and the structure stability is also improved. When the amount of sodium carbonate is 2 g, the sample still keeps α-Ni(OH)2 after being aged for 30 days, for Al-Yb-Co-Ni(OH)2. And when the amount is less than 2 g, the phase transformations exist in the samples with different extents. These results demonstrated that the amount of sodium carbonate is a critical factor to maintain the structural stability of α-Ni(OH)2.