Effects of cerium content on the structure and hydrogen-storage properties of the A2B7-type Lanthanum–Cerium–Yttrium–Nickel system

Abstract

A₂B₇-type intermetallic compounds based on La–Y–Ni are promising H₂-storage materials and have garnered widespread interest owing to their excellent properties. Herein, we report a systematic study of the structures and H₂-storage properties of La_2–xCe_xY₄Ni₂₁ (x = 0.5, 1, 1.5, and 2). All the fabricated alloys contain only Ce₂Ni₇ and Gd₂Co₇, and Ce atoms simultaneously and equally occupy the A₂B₄ and AB₅ subunits of these two phases. With an increase in the Ce content, the gaseous H₂-storage capacities of the alloys decrease, whereas the H₂ absorption/desorption plateau pressures increase. The volume of the A₂B₄ subunit associated with the low plateau decreases more than that of the AB₅ subunit related to the high plateau, leading to the elevation of the low plateau such that it matches the high plateau. Consequently, the double plateau transforms to a single plateau of the alloys. Although the maximum discharge capacities and cycling stabilities of the Ce-rich alloys are poor, their high-rate discharge (HRD) capabilities are high, specifically HRD₃₀₀₀ of La_0.5Ce_1.5Y₄Ni₂₁ can reach 66.97 %. Moreover, although Ce addition inhibits the amorphization of the alloys, it exacerbates their pulverization with severe oxidation/corrosion during cycling, resulting in rapid capacity decay. We believe that our findings will stimulate new ideas for improving the H₂-storage properties of La–Y–Ni-based alloys via Ce introduction.