The impact of La/Y and Ni/Co substitutions on the gas-phase and electrochemical hydrogenation properties of the La3-Mg Ni9 alloys

This paper presents the results of investigations of the impact of elemental substitution on the hydrogenation properties of La _3-xMg _xNi ₉ -based alloys, focusing on both gas-phase and electrochemical hydrogenation processes. Alloys derived from La _3-xMg _xNi ₉ with La → Y and Ni → Co substitutions were synthesized using powder metallurgy methods. All of them were crystallized with PuNi ₃ 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 La _1.5Y _0.5MgNi ₆Co ₃ alloy demonstrated a discharge capacity of approximately 400 mAh/g, while the La _1.5Y _0.5MgNi ₇Co ₂ 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 La _1.5Y _0.5MgNi ₉ 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 ( D _H = 2.67·10 ⁻¹¹ cm ² /s), which also correlates with the highest value of exchange current density ( I ₀ = 222 mA/g) and higher limit of the anodic current (I _L =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.