Closing the Loop for Hydrogen Storage: Facile Regeneration of NaBH₄ from its Hydrolytic Product

Abstract

Sodium borohydride (NaBH₄ ) is among the most studied hydrogen storage materials because it is able to deliver high-purity H₂ at room temperature with controllable kinetics via hydrolysis; however, its regeneration from the hydrolytic product has been challenging. Now, a facile method is reported to regenerate NaBH₄ with high yield and low costs. The hydrolytic product NaBO₂ in aqueous solution reacts with CO₂ , forming Na₂ B₄ O₇ ⋅10 H₂ O and Na₂ CO₃ , both of which are ball-milled with Mg under ambient conditions to form NaBH₄ in high yield (close to 80 %). Compared with previous studies, this approach avoids expensive reducing agents such as MgH₂ , bypasses the energy-intensive dehydration procedure to remove water from Na₂ B₄ O₇ ⋅10 H₂ O, and does not require high-pressure H₂ gas, therefore leading to much reduced costs. This method is expected to effectively close the loop of NaBH₄ regeneration and hydrolysis, enabling a wide deployment of NaBH₄ for hydrogen storage.