Study of the correlation between the stability of mg-based hydride and the ti-containing agent

The thermal stability and hydrogen desorption kinetics for MgH2 and Mg2NiH4 before and after doping with TiF3 or Ti(OBU")(4) were studied by X-ray diffraction, differential thermal analysis, thermogravimetry, Fourier transform infrared spectroscopy, and X-ray absorption spectroscopy techniques. Unlike the previous work, the mixture of the hydrides and the dopants was gently ground for a short time to avoid the undesirable side effects accompanied by an intensive or prolonged grinding. It is shown that the onset temperature for hydrogen release is around 420 degrees C for the blank MgH2, but decreases to 360 and 410 degrees C for the TiF3- and the Ti(OBU")(4)-doped MgH2, respectively. For Mg2NiH4, it is reduced from 230 to 220 degrees C after doping with TiF3 but remains unchanged once doping with Ti(OBU")(4). These indicate that TiF3 is more efficient than Ti(OBU")(4) in reducing the stability of MgH2 and Mg2NiH4. The enhanced desorption kinetics is attained in the TiF3-doped MgH2, but not in the TiF3- or Ti(OBu")(4)-doped Mg2NiH4. It is believed that the interactions between the hydrides and the Ti-containing agents weaken the Mg(Ni)-H bonds and thus favors the recombination of hydrogen atoms toward the hydrogen molecules. These interactions are substantially influenced by both the hydrides and the Ti-containing agents.