Enhanced Hydrogen Storage Kinetics and Stability by Synergistic Effects of <i>in Situ</i> Formed CeH_2.73 and Ni in CeH_2.73-MgH₂-Ni Nanocomposites

TLDR

Mg-based materials are promising for high‑capacity hydrogen storage, yet their poor hydrogenation/dehydrogenation kinetics and high desorption temperatures hinder practical use. The study develops an in situ method to form cycle‑stable CeH₂.₇₃–MgH₂–Ni nanocomposites from hydrogenating an Mg₈₀Ce₁₈Ni₂ alloy, aiming to achieve superior storage performance. X‑ray diffraction and TEM analyses reveal that the nanocomposites’ excellent cycle stability and rapid hydriding/dehydriding kinetics arise from the synergistic effect of finely dispersed CeH₂/CeH₂.₇₃ and Ni with Mg/MgH₂, which also suppress grain growth. The composites exhibit reversible hydrogen capacity exceeding 4.0 wt %, a full cycle temperature of 505 K (≈100 K lower than pure Mg), a desorption activation energy of 63 ± 3 kJ mol⁻¹ H₂, and maintain performance over more than 500 cycles.

Abstract

Mg-based materials are promising candidates for high capacity hydrogen storage. However, their poor hydrogenation/dehydrogenation kinetics and high desorption temperature are the main obstacles to their applications. This paper reports a method for in situ formation of cycle stable CeH2.73-MgH2-Ni nanocomposites, from the hydrogenation of as-melt Mg80Ce18Ni2 alloy, with excellent hydrogen storage performance. The nanocomposites demonstrate reversible hydrogen storage capacity of more than 4.0 wt %, at a low desorption temperature with fast kinetics and long cycle life. The temperature for the full hydrogenation/dehydrogenation cycle of the composites is significantly decreased to 505 K, which is about 100 K lower than that for pure Mg. The hydrogen desorption activation energy is 63 ± 3 kJ/mol H2 for the composites, which is significantly lower than those of Mg3Ce alloy and pure Mg (104 ± 7 and 158 ± 2 kJ/mol H2, respectively). X-ray diffraction and transmission electron microscopy have been used to reveal the mechanism that delivers this excellent cycle stability and fast hydriding/dehydriding kinetics. It is found that the hydriding/dehydriding process is catalyzed by the combination of in situ formed extremely fine CeH2/CeH2.73 and Ni to Mg/MgH2. In addition, this nanocomposite structure can effectively suppress Mg/MgH2 grain growth and enable the material to maintain its high performance for more than 500 hydrogenation dehydrogenation cycles.