The enhanced dehydrogenation performances of 17MgH2-12Al composite with additive TiH2

- TiH2 and Al synergistically lower the dehydrogenation temperature of MgH2.
- The 17MgH2-12Al-TiH2 reduces the hydrogen release activation energy from 17MgH2-12Al.
- TiH2 destabilizes the 17MgH2-12Al system above 280 °C of dehydrogenation.

In this work, we introduced TiH2 into the 17MgH2-12Al composite by ball milling for improving the dehydrogenation performance of the reactive system. According to the measurements of non-isothermal dehydrogenation, the onset temperature of hydrogen release from 17MgH2-12Al-TiH2 was reduced by 50 °C from that of 17MgH2-12Al. The investigations by Kissinger's method showed that the activation energy of hydrogen desorption of 17MgH2-12Al-TiH2 (107 kJ mol−1) is much lower than 17MgH2-12Al (168 kJ mol−1), leading to enhanced dehydrogenation kinetics due to the TiH2 additive. X-ray diffraction (XRD) analysis suggests that TiH2 catalyzed the reaction between MgH2 with Al of the system during the dehydrogenation below 280 °C. At temperatures between 280 °C to 400 °C, however, TiH2 will thoroughly react with produced Mg17Al12 and liberate hydrogen. The overall reaction of the system may be represented by 17 MgH2 + 12 Al + TiH2 → 3/4 Mg17Al12 + Al3Ti + 17/4 Mg + 18 H2. Its theoretical dehydrogenation capacity (4.38 wt% H2) agrees well with that achieved by temperature programmed dehydrogenation (TPD) measurements, demonstrating the occurrence of such reaction(s). The dehydrogenation enthalpy of 17MgH2-12Al-TiH2 (71.7 kJ mol−1 H2) proceeding at lower hydrogen desorption plateau was significantly lowered from that of 17MgH2-12Al (81.9 kJ mol−1 H2) according to the measurements of pressure-composition isotherms (PCI) and van't Hoff plots. It means that TiH2 was involved in the end reaction proceeding in the 17MgH2-12Al system. We believe that TiH2 improves the dehydrogenation kinetics of 17MgH2-12Al initially and tailors its thermodynamics finally.

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