Sodium borohydride regeneration via direct hydrogen transformation of sodium metaborate tetrahydrate

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