The Study Of The Modification And Properties Of Mg-based Hydrogen Storage Materials

Magnesium is considered to be a promising candidate for hydrogen storage due to its high hydrogen storage capacities(7.6wt.%), abundance and low cost. However, practical application of magnesium is still limited, because of its poor sorption kinetics. In this paper, the Mg H2 powder had been directly synthesised at high temperature and high pressure. The influences of technological parameter on the content of Mg H2 had been discussed in this step. On this basis, the research scheme for magnesium hydride modified by milling with Cs F、Ti C and Ni F2 was chosen. The Mg H2+Li Al H4 has been also prepared by composite ball-milling. The influences of dopants and Li Al H4 on the hydrogen storage behaviors and microstructures of the composites had been investigated systemically.Mg H2 had been synthesised in the p-C-T measurement apparatus. The optimal technological parameter on the content of Mg H2 had been determined. The ball-milling parameters of Mg powder are as follows, argon atmosphere, speed 400 rpm, 40:1 ball-to-powder percentage, 6h grinding time. The hydriding parameter are as follows, 4MPa hydrogen pressure, 653 K, 48 h is the first hydriding time, 24 h is the second time. Analysis show that the content of the Mg H2 in the product that prepared by the above craft reach 98 wt.%.The investigation on hydrogen storage behaviors of the Mg H2+M(M:Cs F、Ti C、Ni F2)composites prepared by ball-milling shows that the hydriding/dehydriding kinetics of Mg H2 can be markedly improved by doping of Cs F、Ti C and Ni F2. The XRD patterns show that,Ti C keeping stable in the hydriding/dehydriding process, it’s act as the traditional catalyst to decorate the surface of Mg H2. However, Cs F and Ni F2 both benefit for the hydriding/ dehydriding kinetics of Mg H2 can ascribe to the corresponding reactions of Cs F+Mg H2→Cs H+Mg F2, Ni F2?4H2O+7Mg H2→Mg2Ni H4 +Mg F2+4Mg O+9H2, respectively. In regard to Cs F and Ti C, when the amount added to 5wt.%, the dopants possess the best catalytic effect. As to Ni F2, 2wt.% is the best additive amount. Synthetically, Mg H2+5wt.%Cs F possesses the best comprehensive performance. This system can release 7.06 wt.% hydrogen at 573 K, and its reversible capacity of absorption can reach 7.09 wt.%, in addition, the sample can absorbs 6.33 wt.% hydrogen at 473 K.The investigation on the desorption performance of Mg H2+Li Al H4 and Mg H2+ Li Al H4+5wt.%Ti C shows that the dehydriding kinetics of Mg H2+Li Al H4 is much better than Mg H2. At the relatively low temperature, Mg H2+Li Al H4 only exists the dehydriding behaviour of Li Al H4. The synergistic action between Mg H2 and Li Al H4 will be start when the temperature reach 523 K. At this point,the Al atoms come from the decomposion of Li Al H4 can destabilize Mg H2 and then generate Mg2Al3 and Mg17Al12. Consequently, the desorption performance of Mg H2 achieves enhancement. Moreover, the addition of Ti C in the Mg H2+Li Al H4 composite can further enhance the refinement by ball-milling. This effect can be in favour of the synergistic action between Mg H2 and Li Al H4, and then can further improve the decomposion property of the binary system.