Closing the Loop for Hydrogen Storage: Facile Regeneration of NaBH 4 from its Hydrolytic Product

Sodium borohydride (NaBH 4 ) is among the most studied hydrogen storage materials because it is able to deliver high‐purity H 2 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 NaBH 4 with high yield and low costs. The hydrolytic product NaBO 2 in aqueous solution reacts with CO 2 , forming Na 2 B 4 O 7 ⋅10 H 2 O and Na 2 CO 3 , both of which are ball‐milled with Mg under ambient conditions to form NaBH 4 in high yield (close to 80 %). Compared with previous studies, this approach avoids expensive reducing agents such as MgH 2 , bypasses the energy‐intensive dehydration procedure to remove water from Na 2 B 4 O 7 ⋅10 H 2 O, and does not require high‐pressure H 2 gas, therefore leading to much reduced costs. This method is expected to effectively close the loop of NaBH 4 regeneration and hydrolysis, enabling a wide deployment of NaBH 4 for hydrogen storage.