Synthesis of Co2B nanostructures and their catalytic properties for hydrogen generation

Year 2017, Volume: 2 Issue: 1, 28 - 36, 16.03.2017

Tuncay Şimşek Mustafa Barış

Abstract

Pure cobalt
(II) boride nanoparticles/nanocylinders were synthesized in aqueous media under
Argon blanket using cobalt chloride (CoCl₂) and sodium borohydride (NaBH₄)
as reactants. CoCl₂ (0.325 g) was
dissolved in cold distilled water (DDI) and the solution was introduced into a
sealed glass reactor. Then, NaBH₄ was then dissolved in DDI (90 mL)
and the solution was added drop-wise into the reactor and stirred magnetically
at 300 rpm. By the addition of NaBH₄ (10 mL, 0.225 g) solution,
amorphous black cobalt boride particles were synthesized
immediately.  The presence of crystalline Co₂B phase with high purity in
the nanocylinders which is obtained by calcination at 500^oC was shown by X-ray
diffraction spectroscopy. An amorphous Co₂B structure was observed with the sample dried under
vacuum. In the synthesis runs, Co₂B nanoparticles with different morphological
characteristics were achieved by changing the initial CoCl₂
concentration and the reaction period. A microscopic structure in the form of nanocylinders
was observed for the calcined products. The nanocylinder diameter increased
from ca. 30 nm to 100 nm by increasing the reaction time from 3 to 120 min.
CoCl₂ initial concentration was also found another factor increasing
the nanocylinder diameter. The nanocylinders with diameters between 80-500 nm were
obtained by increasing CoCl₂ concentration from 12.6 to 100.1
mM. The lowest and highest saturation
magnetization values were obtained 19 and 69 emu/g for crystalline sample
calcined under air (Co-Co₂B mixture) and amorphous Co₂B sample
obtained by vacuum-drying, respectively. Amorphous and crystalline Co₂B
samples were used as catalyst for Hydrogen generation by the hydrolysis of NaBH₄
in aqueous media. Amorphous Co₂B gave significantly higher H₂
generation rate with respect to the catalysts prepared by calcination of
amorphous Co₂B under air or Argon at 500^oC.  The maximum H₂ generation rate was
obtained as 1.1 L/g catalyst.min by using amorphous Co₂B with
1 % w/w of initial NaBH₄ concentration. 

Keywords

Cobalt boride, H2 generation, sodium borohydride, hydrolysis, cobalt oxide

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