Abstract:

The Nd in the La_0.5Nd_0.35Mg_0.15Ni_3.5 alloy has been substituted with Sm to improve the performance to price ratio. Herein, the phase structures, morphologies, and hydrogen storage properties of the La_0.5Nd_0.35-xSm_xMg_0.15Ni_3.5 alloys are studied using different methods. The Rietveld analysis pattern showed that the phase composition of the alloys containing multiphase structures, including the major phases (i.e., A₂B₇ and A₅B₁₉) and the residual phase (i.e., AB₅), remained unchanged after the partial substitution of Sm instead of Nd. Increasing the content of the substituted Sm (x=0-0.30) changes the phase abundance, causing the A₂B₇ and A₅B₁₉ phases to increase before decreasing, whereas the AB₅ phase showed the reverse trend. The a-axis parameter, c-axis, and unit cell volume of the major phases and the residual phase gradually decreased with the increasing Sm content. Further, the electrochemical properties of the alloy electrodes were improved by substituting Nd with Sm. The maximum discharge capacity of the alloy electrodes initially increased from 334.6 mA·h/g(x=0)to 346.5 mA·h/g (x=0.20). Then, it decreased to 331.1 mA·h/g(x=0.30). The high-rate dischargeability at a discharge current density of 2000 mA/g(HRD2000)initially increased from 41.4%(x=0) to 63.8% (x=0.20). Subsequently, it decreased to 52.1% (x = 0.30). The cycling capacity retention rate at the 100th cycle monotonically increased from 65.6% (x = 0) to 69.2% (x = 0.30), which should be attributed to the improvement in corrosion resistance of the alloy electrodes during the charge-discharge cycle.

Key words: La-Mg-Ni-based alloy, electrochemical characteristics, electrochemical kinetic property, superlattice structure