Structures and hydrogen storage properties of RE–Mg–Ni–Mn-based AB₂-type alloys prepared by casting and melt spinning

Abstract

To ameliorate the electrochemical hydrogen storage properties of RE–Mg–Ni–Mn-based AB₂-type electrode alloys, La element was partially substituted by Ce, and La_1−xCe_xMgNi_3.5Mn_0.5 (x = 0, 0.1, 0.2, 0.3, 0.4) alloys were fabricated by casting and melt spinning. The effects of Ce content on structures and electrochemical hydrogen storage properties of prepared alloys were studied in detail. Results show that the experimental alloys consist of LaMgNi₄ and LaNi₅ phases. The variation of Ce content, instead of changing phase composition, results in an obvious phase abundance change in the alloys, namely the amount of LaMgNi₄ and LaNi₅ phases, respectively, increases and decreases with Ce content growing. Moreover, the partial substitution of Ce for La leads to that the lattice keeps constant, cell volumes clearly decreases and the alloy grains are markedly refined. The electrochemical measurements reveal that the as-cast and as-spun alloys obtain the maximum discharge capacities at the first cycling without any activation needed. With Ce content increasing, the discharge capacity of as-cast alloys visibly decreases. By contrast, the as-spun alloys have the maximum discharge capacity value. The substitution of Ce for La dramatically promotes the cycle stability. Moreover, the electrochemical kinetic performances of as-cast and as-spun alloys first increase and then decrease with Ce content increasing.