Investigation on the in Situ Generated Tih2 and Mg2ni for the Hydrogen Absorption and Desorption Performance of Mg90ni10-Ti

Abstract

ABTRACTMagnesium-based alloys are considered as a prospective material for solid-state hydrogen storage, but its absorption and desorption kinetics at moderate temperatures are very slow, which has a great challenge in its application. In this study, Mg90Ti10 and Mg90Ni10-Ti nanocomposites have prepared by hydriding combustion synthesis and ball milling techniques. According to the X-ray diffraction and transmission electron microscopy, the composite is composed with Mg (MgH2) phase, Mg2Ni (Mg2NiH4) phase and TiH1.5 (TiH2) phase. The results of isothermal hydrogenation and dehydrogenation kinetics test showed that the addition of nano Ti effectively promoted the activation process of Mg90Ti10. It has significantly improved the isothermal hydrogen absorption and desorption kinetics. The Johnson-Mehl-Avrami-Kolmogorov fitting results show that the dehydrogenation activation energy decreased from 64.2 kJ/mol for Mg90Ni10 to 57.9 kJ/mol for Mg90Ni10-5Ti. Mg90Ni10-5Ti can desorbs 3.24 wt% H2 in 30min at 523 K. Pressure-composition-temperature test results show that the addition of nano Ti has not reduce the thermodynamic stability of the composites. The optimization of adsorption and desorption kinetics is attributed to the enhancement of electron transfer by in-situ formation of titanium hydride as an intermediate for electron transfer between Mg2+ and H-, which promote it easier for H2 to disassociate and recombine on the surface of Ti during the hydrogen ab/desorption process. Additionally, it can greatly improve the kinetic performances with sufficient channel for the transport of H atoms owing to the catalytic effect of Mg2Ni/Mg2NiH4 and the formation of a large number of phase boundaries with Mg/MgH2, which can provide guidance for the design and development of reversible metal hydrides.

Keywords: Hydrogen storage, Hybrid synthesis, Desorption kinetics, Activation energies, Thermodynamic