Mechanochemical Synthesis of Sodium Borohydride by Recycling Sodium Metaborate

Abstract

Hydrogen can be easily produced from the catalytic hydrolysis of sodium borohydride (NaBH4), with sodium metaborate (NaBO2) being the co-product. If NaBO2 can be economically recycled in the process, NaBH4 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 NaBH4 from NaBO2 via ball milling. The starting materials for the synthesis were NaBO2 and magnesium hydride (MgH2). After ball milling at ambient temperature in inert gas, NaBH4 and magnesium oxide (MgO) were produced. The synthesized NaBH4 was extracted from the admixture by isopropylamine. Our results indicated that the yield of NaBH4 from this process was 71 wt % when the MgH2/NaBO2 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 (MgH2 and NaBO2), ball-milling time, BPR, and milling atmosphere were found to have significant influence over NaBH4 synthesis. We present the results and discuss the effects of these key parameters in this paper.