Mechanochemical Synthesis of Sodium Borohydride by Recycling Sodium Metaborate

摘要

Hydrogen can be easily produced from the catalytic hydrolysis of sodium borohydride (NaBH_4), with sodium metaborate (NaBO_2) being the co-product. If NaBO_2 can be economically recycled in the process, NaBH_4 could be considered as a promising hydrogen carrier in fuel cells because of its high hydrogen content. In this paper, we report our investigation into the synthesis of NaBH_4 from NaBO_2 via ball milling. The starting materials for the synthesis were NaBO_2 and magnesium hydride (MgH_2). After ball milling at ambient temperature in inert gas, NaBH_4 and magnesium oxide (MgO) were produced. The synthesized NaBH_4 was extracted from the admixture by isopropylamine. Our results indicated that the yield of NaBH_4 from this process was 71 wt % when the MgH_2/NaBO_2 mole ratio, ball/powder ratio (BPR), inert gas (argon) pressure, and milling time were 2.07:1, 50:1, 200 kPa, and 2 h, respectively. The mole ratio of the reactants (MgH_2 and NaBO_2), ball-milling time, BPR, and milling atmosphere were found to have significant influence over NaBH_4 synthesis. We present the results and discuss the effects of these key parameters in this paper.