Synthesis of Co2B nanostructures and their catalytic properties for hydrogen generation

Authors : Tuncay ŞİMŞEK, Mustafa BARIŞ

Pages : 28-36

View : 47 | Download : 27

Publication Date : 2017-03-16

Article Type : Research Paper

Abstract :Pure cobalt (II) boride nanoparticles/nanocylinders were synthesized in aqueous media under Argon blanket using cobalt chloride (CoCl 2 ) and sodium borohydride (NaBH 4 ) as reactants. CoCl 2 (0.325 g) was dissolved in cold distilled water (DDI) and the solution was introduced into a sealed glass reactor. Then, NaBH 4 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 NaBH 4 (10 mL, 0.225 g) solution, amorphous b lack cobalt boride particles were synthesized immediately.   The presence of crystalline Co 2 B phase with high purity in the nanocylinders which is obtained by calcination at 500 o C was shown by X-ray diffraction spectroscopy. An amorphous Co 2 B structure was observed with the sample dried under vacuum. In the synthesis runs, Co 2 B nanoparticles with different morphological characteristics were achieved by changing the initial CoCl 2 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. CoCl 2 initial concentration was also found another factor increasing the nanocylinder diameter. The nanocylinders with diameters between 80-500 nm were obtained by increasing CoCl 2 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-Co 2 B mixture) and amorphous Co 2 B sample obtained by vacuum-drying, respectively. Amorphous and crystalline Co 2 B samples were used as catalyst for Hydrogen generation by the hydrolysis of NaBH 4 in aqueous media. Amorphous Co 2 B gave significantly higher H 2 generation rate with respect to the catalysts prepared by calcination of amorphous Co 2 B under air or Argon at 500 o C.  The maximum H 2 generation rate was obtained as 1.1 L/g catalyst.min by using amorphous Co 2 B with 1 % w/w of initial NaBH 4 concentration. 
Keywords : Cobalt boride, H2 generation, sodium borohydride, hydrolysis, cobalt oxide

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