Synthesis of Co2B nanostructures and their catalytic properties for hydrogen generation

Öz

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. 

Anahtar Kelimeler

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

Kaynakça

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