Hydriding/dehydriding properties of Mg-Ni-based ternary alloys synthesized by mechanical grinding

The Mg-Ni-based ternary alloys Mg2-xTixNi(x=0,0.2,0.4)and Mg2Ni1-xZrx(x=0,0.2,0.4)were successfully synthesized by mechanical grinding.The phases in the alloys and the hydriding/dehydriding properties of the alloys were investigated.Mg2Ni and Mg are the main hydrogen absorption phases in the alloys by XRD analysis.Hydriding kinetics curves of the alloys indicate that the hydrogen absorption rate increases after partial substitution of Ti for Mg and Zr for Ni.According to the measurement of pressure-concentration-isotherms and Van't Hoff equation,the relationship between ln p(H2)and 1 000/T was established.It is found that while increasing the content of correspondingly substituted elements at the same temperature,the equilibrium pressure of dehydriding increases,the enthalpy change and the stability of the alloy hydride decrease.

Effect of LaFeO_3 on hydrogenation/dehydrogenation properties of MgH_2

LaFeO3 was used to improve the hydrogen storage properties of Mg H2. The Mg H2＋20 wt.%La Fe O3 composite was prepared by ball milling method. The composite could absorb 3.417 wt.% of hydrogen within 21 min at 423 K while Mg H2 only uptaked 0.977 wt.% hydrogen under the same conditions. The composite also released 3.894 wt.% of hydrogen at 623 K, which was almost twice more than Mg H2. The TPD measurement showed that the onset dissociation temperature of the composite was 570 K, 80 K lower than the Mg H2. Based on the Kissinger plot analysis of the composite, the activation energy E des was estimated to be 86.69 k J/mol, which was 36 k J/mol lower than Mg H2. The XRD and SEM results demonstrated that highly dispersed La Fe O3 could be presented in Mg H2, benefiting the reduction of particle size and also acting as an inhibitor to keep the particles from clustering during the ball-milled process.