Changes of crystal structure and hydrogen storage performances for multiphase La0.7Mg0.3Ni3 alloy upon gas–solid cycling

Abstract

In order to examine the effects of structure stability on the degradation behaviors of multiphase La 0.7 Mg 0.3 Ni 3 alloy, changes of the crystal structure and hydrogen storage properties after gas-solid cycling were investigated in detail. The structural analysis identifies that (La,Mg)Ni 3 (PuNi 3 -type) phase transforms to amorphous, i.e., hydrogen-induced amorphization(HIA) occurs whereas LaNi 5 (CaCu 5 -type), (La,Mg) 2 Ni 7 (Ce 2 Ni 7 -type), and (La,Mg) 5 Ni 19 (Pr 5 Co 19 -type) phases still keep crystalline upon hydriding/dehydriding cycling. Partial amorphization remarkably affects both the gas-solid and electrochemical storage performances. The plateau of PCT curves becomes narrow and steep with cycling. Moreover, the maximum electrochemical capacity decreases notably after gas-solid hydrogenation repeats. The electrochemical capacity reduction could be ascribed to both drop of the maximum storage capacity and the slope of plateau induced by partial amorphization. For direct electrochemical cycling, it is suggested that the capacity decay is mainly attributed to HIA in the initial stage.

Degradation Characters of La-Mg-Ni-Based Metal Hydride Alloys: Corrosion and Pulverization Behaviors

“…The particles with dimension of about 40-50 lm were used for the electrochemical test and details of preparation of the electrode pellets can be found in Ref. [18]. The electrode pellets were firstly immersed in 6 mol L -1 KOH aqueous solution for 1 d, charged at a current density of 105 mA g -1 for 4 h, followed by a rest for 10 min, then discharged at the same current density to the cutoff voltage of -0.6 V. and (La,Mg) 5 Ni 19 , respectively, and the structural parameters and phase contents are also listed in Table 2.…”

“…In addition, degradation of the hydrogen storage alloys is also demonstrated to be affected by the structural distortion upon the hydrogenation cyclings. Our previous works demonstrated that La-Mg-Ni alloys suffered hydrogen-induced amorphization (HIA) which remarkably worsened both the gas-solid and electrochemical storage capability [18,19].…”