Autocatalytic Reduction Method Research Articles

Structural Analysis of Thin Ni-P Layers

The deposition mechanism by autocatalytic reduction method is a chemical one, which does not lead to structures as shown in the Ni-P balance diagram. In the experiments of the present work, Ni-P layers were made deposited on thin steel strip with low carbon content. By optical microscopy and scanning electron microscopy by (SEM) it was analyzed the appearance and surface morphology of the deposited layers depending on the content of phosphorus and working parameters (temperature, pH, stirring speed). The layer structure was analyzed in the cross section and on the break surface. The analysis results show that thin coatings of Ni-P have a surface topography that follows faithfully the steel support. Depending on the content of phosphorus, on the layer surface of low phosphorus content, spherical particles of different sizes can be seen while high and average phosphorus content coatings feature a smooth surface with nanometer-sized grains. Analysis of the cut-off /break section of the Ni-P layer structure, show a more or less porous structure depending on the stirring speed and pH level.

Effect of nickel phosphide nanoparticles crystallization on hydrogen evolution reaction catalytic performance

In order to investigate the effect of nickel phosphide nanoparticles' (Ni–P NPs) crystallization on hydrogen evolution reaction (HER) catalytic performance, amorphous Ni–P NPs and crystalline Ni12P5 were synthesized by a simple and low-cost autocatalytic reduction method and heat treatment process. The result of electrochemical tests shows that crystalline Ni12P5 has much higher HER catalytic activity than the amorphous one. X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy revealed that Ni–P bond formed during crystallization, making Ni positively charged and P negatively charged. This charged nature of Ni12P5 is similar to [NiFe] hydrogenase and its analogous, which make the removal of H2 less energy-cost.

Size Influence on Magnetic Properties of Nickel Hollow Spheres

Nickel hollow spheres (NHSs) with different diameter have been synthesized by the autocatalytic reduction method. The morphology, size distribution and magnetic properties of NHSs were characterized. The results indicate that when the nickel hollow spheres become smaller, mechanism of magnetization reversal varies from motion of domain wall to spin coherent rotation. After the heat treatment process, the grain size of samples becomes bigger and coercivity is enhanced because domain wall is pinned by local magnetic anisotropy induced spontaneously.

Autocatalytic-assembly based on self-decomposing templates: a facile approach toward hollow metal nanostructures

Hollow metal nanostructures have received increasing interest because they exhibit unique chemical and physical properties different from their solid counterparts. In this work, the autocatalytic-reduction approach based on the self-decomposing of metal hydroxides and oxides is reported, which is distinct from the traditional template methods. Under solution conditions of a reducing atmosphere, metal hydroxides can serve as both the autocatalytic reagent and the sacrificial templates in the reaction process. It is demonstrated that the autocatalytic-reduction method is a general approach to fabricate a series of metal hollow structures, including hollow Ni nanospheres (NSs), Ni nanotubes (NTs), bead-like Ni NSs, and hollow Cu microspheres. Moreover, the structural diversity of original M(OH)x or MOx/2 (M = metal) templates allows the preparation of size and shape-adjustable templates. A possible mechanism for hollow structure formation is also proposed.

Synthesis, characterization and microwave properties of Ni–Co–P hollow spheres

Abstract Ni–Co–P hollow spheres (HSs) with different component ratios were fabricated by autocatalytic reduction method. With an increase of cobalt content, coercivity of hollow spheres increased because of Co hcp structure with high magnetocrystal anisotropy. The microwave properties of Ni–Co–P HSs were investigated in the range of 2–18 GHz. Both permittivity and permeability of spheres–wax composites increased with the increase of cobalt content. For the Ni–Co–P hollow spheres, the minimum reflection loss (RL) (−41.7 dB) was found at 6.3 GHz with a thickness of 2.5 mm. Additionally, with the increase of cobalt content, the minimal reflection loss increases obviously, which means that introducing Co into Ni improves the microwave absorption capability.

Preparation and microwave absorption properties of Ni–Fe 3O 4 hollow spheres

Nickel–magnetite hollow spheres with the diameter about 150 nm were prepared by an autocatalytic reduction method. The effect of Fe 3O 4 content in hollow spheres on microwave absorption properties has been investigated. With an increase of magnetite content, permittivity of sphere–wax composite decreased, while permeability increased. For composite layers, a minimum reflection loss (RL, −38.4 dB) was predicted at 10.8 GHz with a thickness of 2.5 mm. In addition, the increasing content of magnetite resulted in the peak of RL moves to higher frequency and the minimal reflection loss increases obviously.

Size influence on microwave properties of Ni–Co–P hollow spheres

Ni–Co–P hollow spheres (HSs) of different sizes were fabricated by the autocatalytic reduction method. With the decrease in particle size, the value of complex permittivity increases and the permeability changes in the opposite direction. The resonance peaks appear in the curves of both permittivity and permeability. The former is due to atomic and electronic polarization, and the latter is caused by natural resonance. For sample 2, with a particle size of about 200 nm, the minimal reflection loss (RL) (−52.5 dB) was predicted at 11.2 GHz with a thickness of 1.6 mm. Additionally, for Ni–Co–P HSs, size dependence of minimal RL is not linear and the excellent microwave absorption property can be obtained in the size range around 200 nm.

Size influence on optical absorption property of ultra-fine nickel hollow spheres

Nickel hollow spheres (NHSs) with different diameter have been synthesized by the autocatalytic reduction method. The morphology, particle size distribution and optical absorption property of NHSs were investigated. The optical absorption intensity obviously increases in ultraviolet—near infrared region with the decrease of particle size. While in infrared region, nickel hollow spheres have almost no absorption. After the heat treatment process, the grain sizes of samples become bigger and the absorptances decrease in UV–Vis–NIR region. For smaller particles, the absorption peak in ultraviolet range moves from 375 to 440 nm because of the increase of grain size after heat treatment.

Microwave characterization of submicrometer-sized nickel hollow sphere composites

In this work, we report on the microwave properties of the nickel hollow spheres (NHSs) synthesized by a facile autocatalytic reduction method. The resonance characterization of the NHS-polyvinyl butyral composite, due to the skin effect, is observed in the microwave frequency. It is shown that the resonant and the matching frequencies of the composite largely depend on the particle size of the spheres.

Preparation and microwave characterization of submicrometer-sized hollow nickel spheres

The hollow structural submicrometer-sized nickel spheres were successfully fabricated by the autocatalytic reduction method. Because of the metallic and ferromagnetic behaviour of the nickel spheres, the low-density microspheres could obtain high dielectric constant and magnetic loss in microwave frequencies. The abrupt variation of the real part and the sharp peaks of the imaginary part of permittivity and permeability were observed for the micrometer-sized and nanometer-sized nickel hollow spheres. Reflection loss less than −25 dB were predicted over 11 GHz with a thickness of 1.5–2.0 mm.