Synthesis of Co2B nanostructures and their catalytic properties for hydrogen generation

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 500oC 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 500oC. 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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