Sodium borohydride regeneration via direct hydrogen transformation of sodium metaborate tetrahydrate

Irreversibility negatively impacts the application of NaBH4 hydrolysis for hydrogen generation. Byproduct regeneration is key to solving this issue. In this work, the direct byproduct of aqueous NaBH4 hydrolysis, NaBO2·4H2O, is reacted with Mg2Si to regenerate NaBH4 via ball milling at room temperature under an argon atmosphere. In this process, the H− in NaBH4 is exclusively from the H+ in NaBO2·4H2O. The regenerated NaBH4, with a maximum yield of 74%, has the same physicochemical properties as a commercial sample. We also demonstrate that Mg2Si reacts with NaBO2·4H2O to generate NaBO2·2H2O, followed by a direct reaction between the residual Mg2Si and NaBO2·2H2O to produce NaBH4. The energy efficiency of this method is approximately 40%.