Efficient Synthesis of Sodium Borohydride: Balancing Reducing Agents with Intrinsic Hydrogen Source in Hydrated Borax

Abstract

Sodium borohydride (NaBH4) has been identified as one of the most promising hydrogen storage materials; however, it is still challenging to produce NaBH4 with low cost and high efficiency, which are largely determined by the sources of boron and hydrogen and reducing agents used. Herein, we report an economical method to produce NaBH4 by ball milling hydrated borax (Na2B4O7·10H2O and/or Na2B4O7·5H2O) with different reducing agents such as MgH2, Mg, and NaH under ambient conditions. The direct use of natural hydrated borax avoids the dehydration process (at 600 °C) and consequently reduces cost and improves overall energy efficiency. A high yield of 93.1% can be achieved for a short ball mill duration (3.5 h) for Na2B4O7·5H2O-NaH-MgH2 system. In this system, H2 is generated in situ which subsequently reacts with Mg forming MgH2. Low cost Mg is therefore employed to replace the majority of MgH2, leading to an attractive yield of 78.6%. To further reduce the cost of raw materials and improve the utilization of hydrogen source in the hydrated borax, Na2B4O7·10H2O is used to partially substitute for Na2B4O7·5H2O, leading to a complete replacement of MgH2. Compared with literature results, the optimized recipe features low cost and high efficiency since it utilizes hydrogen from the hydrated water in natural borax and avoids high temperatures. Our finding is expected to facilitate applications of NaBH4 for hydrogen storage.

Facile regeneration of lithium borohydride from anhydrous lithium metaborate using magnesium hydride

“…More details of the solid-state 11 B MAS NMR and FTIR measurements can be found in previous studies. 22…”

A multifunctional sustainable ionohydrogel with excellent low-hysteresis-driven mechanical performance, environmental tolerance, multimodal stimuli-responsiveness, and power generation ability for wearable electronics

“…The peaks at 14.0 and À1.0 ppm are assigned to free boron and didiol-complex boron, respectively. 42,47 Moreover, the fractions of boron in the free state and didiol-complex state are approximately 54.5% and 45.5% of the total boron amount, respectively. The free states of B(OH) 4À and Na + play a key role in the SPBG ionohydrogel due to ionic conductance.…”

Hydrogen Production via Hydrolysis and Alcoholysis of Light Metal-Based Materials: A Review

“…15 (3, 4)) was also substituted by H − from MgH 2 , forming BH 4 − . Furthermore, they achieved a higher yield of 93.1% for a short duration (3.5 h) by ball milling hydrated borax (Na 2 B 4 O 7 ·10H 2 O and/or Na 2 B 4 O 7 ·5H 2 O) with different reducing agents such as MgH 2 , Mg, and NaH under ambient conditions [ 197 ]. By replacing the majority of MgH 2 with low-cost Mg, an attractive yield of 78.6% was obtained.…”