Regulation of high-efficient regeneration of sodium borohydride by magnesium-aluminum alloy

Sodium borohydride (NaBH 4 ) is considered to be an excellent hydrogen-generation material via hydrolysis. However, it remains challenge to regenerate it after hydrolysis in practical applications. Therefore, a low-cost regeneration method from hydrolysis by-products for recycling is the key issue. In this study, NaBH 4 was successfully regenerated by direct high-energy ball milling of magnesium alloy (Mg 17 Al 12 ) and hydrolysis by-product NaBO 2 ·2H 2 O with addition of a small amount of NaH. Notably, unlike traditional method, here there is no need of adding extra hydrogen and the H − in the regenerated NaBH 4 is mainly from the H + in the coordinated water. It was found that through adding a small amount of NaH, the highest yield may reach 57% after optimizing the regeneration process. In addition, it is the first time we found that not only Mg can participate in the reaction, but also Al; and the addition of NaH can promote the reaction. Furthermore, the regeneration mechanism of NaBH 4 was analyzed and the transition pattern [B(OH) 4 ] − /[BH 3 (OH)] − /[BH 4 ] − was successfully observed during the regeneration process. It is worth emphasizing that NaBH 4 can be regenerated through ball milling method, which is energy-saving and suitable for up-scaling in the future.