Synchrotron Diffraction Studies of Hydrogen Absorption/Desorption on CaH2+ MgB2Reactive Hydride Composite Mixed With Fluorinated Compounds

The reactive hydride composites 9CaH2+ CaF2+ 10MgB2, 10Ca(BH4)2+ 9MgH2+ MgF2, and 9Ca(BH4)2+ Ca(BF4)2+ 10MgH2were 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)2on 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+ 10MgB2reactive hydride composites. These studies indicate the formation of a complex mixture of phases.