Phase structure and hydrogen storage properties of LaMg3.93Ni0.21 alloy

Abstract The phase structure and hydrogen storage property of LaMg 3.93 Ni 0.21 alloy were studied. XRD and SEM results exhibited that LaMg 3.93 Ni 0.21 alloy consisted mainly of LaMg 3 , La 2 Mg 17 and LaMg 2 Ni phases; after hydriding/dehydriding process, all the three phases transformed, La 3 H 7 phase existed and the actual hydrogen absorption phases were Mg and Mg 2 Ni phases. Pressure-composition-temperature (P-C-T) measurement showed that the reversible hydrogen storage capacity of LaMg 3.93 Ni 0.21 alloy was 2.63 wt.%, and the absorption time for reaching 90% of the storage capacity was 124 s at 523 K, and it was 1850 s for deabsorbing 90% of the maximum dehydrogen capacity. The hydriding process of LaMg 3.93 Ni 0.21 alloy followed the nucleation and growth mechanisms. The enthalpy and entropy for hydriding and dehydriding reactions of the Mg phase in LaMg 3.93 Ni 0.21 alloy were calculated to be −66.381.10 kJ/mol H 2 , −100.961.96 J/(K·mol) H 2 and 68.503.87 kJ/mol H 2 , 98.28 5.48 J/(K·mol) H 2 , respectively. A comparison of these data with those of MgH 2 (−74.50 kJ/mol H 2 , −132.30 J/Kmol H 2 ) suggested that the hydride of LaMg 3.93 Ni 0.21 alloy was less stable than MgH 2 . The existence of La hydride and synergetic effect of multiphase led to higher reversible hydrogen storage capacity and better kinetic property at lower temperature for LaMg 3.93 Ni 0.21 alloy.