A method is disclosed for directly preparing an alkaline earth metal borohydride, i.e. Mg(BH4)2, from the alkaline earth metal boride MgB2 by hydrogenating the MgB2 at an elevated temperature and pressure. The boride may also be doped with small amounts of a metal chloride catalyst such as TiCl3 and/or NiCl2. The process provides for charging MgB2 with high pressure hydrogen above at least 70 MPa while simultaneously heating the material to about 350° C. to about 400° C. The method is relatively simple and inexpensive and provides a reversible hydride compound having a hydrogen capacity of at least 11 wt %.