Catalytic modification of MgH2 hydrogen storage properties by La-Ni catalysts

Abstract

In this paper, it is experimentally demonstrated that the La-Ni catalyst contributes to the hydrogen storage performance of MgH2. Firstly, La-Ni (La: Ni=1: 5.7) catalysts are prepared by CaH2 reduction method, and then MgH2+x wt.% La-Ni (x=0, 3, 5, 7) composite alloys were prepared by ball milling method. The present work focuses on the structural and hydrogen ab/desorption properties of the composite alloys, and analysis the modulatory effect and influence mechanism of different La-Ni catalyst additions on the hydrogen storage properties of MgH2. The findings show that the composite alloys have the same diffraction peaks and that the main phase of the composite alloys is the MgH2 phase, with the addition of the LaNi5 phase, the Mg2Ni phase and a small amount of Mg phase. The mutual reversible transformations of LaH3 and Mg2Ni and Mg2NiH4 play a catalytic role in the hydrogen ab/desorption process. Moreover, the addition of La-Ni catalyst plays a dramatic improvement effect on the kinetic performance of MgH2 ab/desorption. When the addition of La-Ni catalyst is 5 wt.%, the composite alloy exhibits the most excellent hydrogen uptake and release kinetics. The MgH2+5 wt.% La-Ni composite alloy absorbs 4.2 wt.% H2 within 2 min at 473 K and releases 3.43 wt.% H2 within 150 min at 503 K. Fitting the hydrogen release activation energy of the composite alloys shows that the hydrogen release activation energy of the composite alloys decreases first and then increases, and there is a minimum hydrogen release activation energy of 101.81 kJ/mol H2 when the addition amount x = 5 wt.%.