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

Sodium borohydride (NaBH4) 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 NaBH4 with high yield and low costs. The hydrolytic product NaBO2 in aqueous solution reacts with CO2, forming Na2B4O7.10 H2O and Na2CO3, 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 Na2B4O7.10 H2O, 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 NaBH4 regeneration and hydrolysis, enabling a wide deployment of NaBH4 for hydrogen storage.