The impact of La/Y and Ni/Co substitutions on the gas-phase and electrochemical hydrogenation properties of the La3-xMgxNi9 alloys

This paper presents the results of investigations of the impact of elemental substitution on the hydrogenation properties of La3-xMgxNi9-based alloys, focusing on both gas-phase and electrochemical hydrogenation processes. Alloys derived from La3-xMgxNi9 with La → Y and Ni → Co substitutions were synthesized using powder metallurgy methods. All of them were crystallized with PuNi3 structure type. Gas-phase hydrogenation studies revealed that Y-free samples exhibited faster gas-phase hydrogenation rates compared to Y-substituted ones, whereas electrochemical performance measurements showed the opposite behaviour. Notably, the La1.5Y0.5MgNi6Co3 alloy demonstrated a discharge capacity of approximately 400 mAh/g, while the La1.5Y0.5MgNi7Co2 alloy exhibited good cyclic stability with a discharge capacity of 389.5 mAh/g and preserved approximately 84% of its capacity after 50 charge/discharge cycles at a current density of 50 mA/g. Y-containing samples demonstrated improved electrochemical characteristics, especially in terms of the HRD (high-rate dischargeability) parameter. The La1.5Y0.5MgNi9 alloy has shown ∼86% of its maximum discharge capacity at 1 A/g current density. This electrode with the highest HRD rate demonstrated highest diffusion coefficient (DH = 2.67·10−11 cm2/s), which also correlates with the highest value of exchange current density (I0 = 222 mA/g) and higher limit of the anodic current (IL=878 mA/g). This highlights the prospects of application of Y-containing alloys for areas where high-rate discharge capabilities are required for Ni-MH batteries.