Breaking the Passivation: Sodium Borohydride Synthesis by Reacting Hydrated Borax with Aluminum

Abstract

A significant obstacle in the large-scale applications of sodium borohydride (NaBH 4 ) for hydrogen storage is its high cost. Herein, we report a new method to synthesize NaBH 4 by ball milling hydrated sodium tetraborate (Na 2 B 4 O 7 • 10H 2 O) with low-cost Al or Al 88 Si 12 , instead of Na, Mg or Ca. An effective strategy is developed to facilitate mass transfer during the reaction by introducing NaH to enable the formation of NaAlO 2 instead of dense Al 2 O 3 on Al surface, and by using Si as a milling additive to prevent agglomeration and also break up passivation layers. Another advantage of this process is that hydrogen in Na 2 B 4 O 7 • 10H 2 O serves as a hydrogen source for NaBH 4 generation. Considering the low cost of the starting materials and simplicity in operation, our studies demonstrate the potential of producing NaBH 4 in a more economical way than the commercial process.

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

“…The latter with high peak intensities is a contaminant due to the high atomic weight of Fe, which originated from the jar and ball due to the high hardness of the raw materials. As known from previous studies, 23,24 the regenerated NaBH 4 is decomposed after long-time ball-milling. This is most likely due to the reaction of NaBH 4 and Fe contamination, as evidenced by the generation of Fe 2 B.…”

Effect of Metaborate Additive Modification on Hydrolysis Performance of MgH2

“…No obvious XRD diffraction peaks of NaBH 4 were detected, which can be ascribed to the lower quantities of the formed NaBH 4 and also the poor crystallinity of NaBH 4 . This is similar to previous studies. , The diffraction peaks of other Na-containing species are invisible in Figure a also likely due to the poor crystallinity. It is worthwhile mentioning that the diffraction peaks of γ-MgH 2 are highly visible, and the full width at half maximum of β-MgH 2 increases because the crystal size decreases after ball milling.…”

“…This is similar to previous studies. 24,25 The diffraction peaks of other Na-containing species are invisible in Figure 3a 3d). NaBO 2 and in situ-formed MgO serve as a cutter during the milling process to reduce the size of particles, which could improve the hydrolysis performance.…”

“…After hydrolysis, the hydrolysis byproduct was dried by freeze-drying. To calculate the activation energy, the hydrolysis of the MgH 2 −4 mol % NaBO 2 composite milled for 6 h was conducted using a constant temperature water bath at various temperatures (25,35,45, and 55 °C). More details of FTIR measurements can be found in our previous studies.…”

Exploring the technological maturity of hydrogen production by hydrolysis of sodium borohydride

“…For instance, a SB yield of 93.1% was achieved when the system MgH2-NaH-Na2B4O7•5H2O was ball-milled 3.5 h. A SB yield of 85.2% was obtained with the system Mg17Al12-NaH-Na2B4O7•10H2O after a milling of 20 h [136]. The use of aluminum (without or with silicon) to hydrogenate Na2B4O7•10H2O was also explored, and the SB yields were lower than 62% [137]. In the main, Ouyang and co-workers have been much active and are currently the leading researchers on this matter [138].…”