AbstractThe reactive hydride composites 9CaH2 + CaF2 + 10MgB2, 10Ca(BH4)2 + 9MgH2 + MgF2, and 9Ca(BH4)2 + Ca(BF4)2 + 10MgH2 were prepared by ball milling. Their properties toward hydrogen absorption/desorption were tested by means of manometric measurements. The highest hydrogen storage capacity was obtained for 9CaH2 + CaF2 + 10MgB2 (7.6 wt %) at the first cycle. The effects of CaF2, MgF2, or Ca(BF4)2 on the dehydrogenation reaction were studied by means of in situ synchrotron radiation powder X-ray diffraction (in situ SR-PXD) and differential scanning calorimetry (DSC). The high resolution SR-PXD technique was used to confirm the formation of hydrogenated products and side products in the 9CaH2 + CaF2 + 10MgB2 reactive hydride composites. These studies indicate the formation of a complex mixture of phases.