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

A significant obstacle in the large-scale applications of sodium borohydride (NaBH ) for hydrogen storage is its high cost. Herein, we report a new method to synthesize NaBH by ball milling hydrated sodium tetraborate (Na B O  ⋅ 10H O) with low-cost Al or Al Si , 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 instead of dense Al O 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 B O  ⋅ 10H O serves as a hydrogen source for NaBH generation. Considering the low cost of the starting materials and simplicity in operation, our studies demonstrate the potential of producing NaBH in a more economical way than the commercial process.