Effects of the Preparation Solvent on the Catalytic Properties of Cobalt–Boron Alloy for the Hydrolysis of Alkaline Sodium Borohydride

Abstract

Abstract:In this study, the effects of the solvent used to prepare Co-B alloy on its catalytic properties were investigated. The solvent effects on the morphology, composition, and specific surface area of the alloy particles were also examined. The morphology of the alloy particles was found to be dependent on the solvent. The particles were granular in water, methanol, and acetone, although the particle diameters differed, whereas they were nanoflake-like in acetonitrile. Acetonitrile produced the largest surface area of the alloy particles, but the lowest catalytic activity for the hydrolysis of NaBH 4 owing to the ready oxidation of the particles in air. The Co-B in acetone exhibited the highest catalytic activity, represented by a hydrogen generation rate of 5733 mL·min −1 ·g −1 during the hydrolysis of 1.5 wt % NaBH 4 at 298 K. This hydrogen generation rate is more than twice that produced by the Co-B in water.

Hydrogen Generation From Sodium Borohydride With Cobalt Boride Catalysts

“…Hydrogen is one of the cleanest energy source with its high efficiency, zero emission, and renewability in recent years [1][2][3][4][5]. The wide use of hydrogen is a potential route to reduce the negative impact of the enormous carbon emissions caused by fossil fuels burning [5].…”

“…Sodium borohydride (NaBH4) is the most promising hydrogen source because it has high hydrogen capacity (10.8 wt.%), excellent solubility, controllable hydrolysis reaction, moderate operation temperature, and is very stable in alkaline solutions, non-flammable, non-toxic in nature, environmentally friendly and renewable [1,2,6,7,[9][10][11]. Also byproduct (NaBO2) of the NaBH4 hydrolysis process is nontoxic and recyclable [1,2]. H2 generation rate of this reaction is low and decreases as the reaction proceeds owing to an increase of the solution pH, which is due to the formation of the borates.…”

“…Furthermore, hydrogen is generated by a water-based hydrolysis reaction of NaBH4 with the advantage of producing half of the hydrogen from the water solvent [6]. However, the hydrolysis reaction is kinetically slow in the absence of a suitable catalyst, this reaction can be accelerated by a suitable catalyst [2]. When contacting with a given catalyst, in alkaline solutions (the alkali usually acts as a stabilizer to restrain the self-hydrolysis of NaBH4 in aqueous solution) hydrogen can be released rapidly which is shown as follow reaction (1) [7]:…”

“…Pt, Ru, Pd, Rh, and other noble metal catalysts are very effective to accelerate the hydrolysis reaction of NaBH4. However, these precious metals have high costs and then non-noble catalysts research is very important [2]. The general constraint of the catalysts is their deterioration, which occurs owing to processes for instance agglomeration of catalyst particles, surface oxidation of catalysts, and dissolution of the catalyst component in the alkaline NaBH4 solution.…”

“…The perfect catalytic activity of metal borides can be based on their properties such as stability, amorphous structure, and many unsaturated sites. Cobalt boride is a leading candidate between the available metal borides owing to its outstanding catalytic properties, low cost, and easy preparation [2]. In addition to cobalt boride, cobalt borates have been also reported as the active catalysts.…”