Catalytic effect comparison of TiO2 and La2O3 on hydrogen storage thermodynamics and kinetics of the as-milled La-Sm-Mg-Ni-based alloy

Abstract

In this investigation, mechanical grinding was applied to fabricating the Mg-based alloys La 7 Sm 3 Mg 80 Ni 10 + 5 wt.% M ( M = None, TiO 2 , La 2 O 3 ) (named La 7 Sm 3 Mg 80 Ni 10 –5 M ( M = None, TiO 2 , La 2 O 3 )). The result reveals that the structures of as-milled alloys consist of amorphous and nanocrystalline. The particle sizes of the added M ( M = TiO 2 , La 2 O 3 ) alloys obviously diminish in comparison with the M = None specimen, suggesting that the catalysts TiO 2 and La 2 O 3 can enhance the grinding efficiency. What's more, the additives TiO 2 and La 2 O 3 observably improve the activation performance and reaction kinetics of the composite. The time required by releasing 3 wt.% hydrogen at 553, 573 and 593 K is 988, 553 and 419 s for the M = None sample, and 578, 352 and 286 s for the M = TiO 2 composite, and 594, 366, 301 s for the La 2 O 3 containing alloy, respectively. The absolute value of hydrogenation enthalpy change |Δ H | of the M ( M = None, TiO 2 , La 2 O 3 ) alloys is 77.13, 74.28 and 75.28 kJ/mol. Furthermore, the addition of catalysts reduces the hydrogen desorption activation energy ( E a de ).