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

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 CeH 2.73 -MgH 2 -Ni nanocomposites, from the hydrogenation of as-melt Mg 80 Ce 18 Ni 2 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 H 2 for the composites, which is significantly lower than those of Mg 3 Ce alloy and pure Mg (104 ± 7 and 158 ± 2 kJ/mol H 2 , 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 CeH 2 /CeH 2.73 and Ni to Mg/MgH 2 . In addition, this nanocomposite structure can effectively suppress Mg/MgH 2 grain growth and enable the material to maintain its high performance for more than 500 hydrogenation dehydrogenation cycles.

Hydrogen induced amorphization of LaMgNi4 phase in metal hydride alloys

“…Four possible mechanisms were considered to explain the apparent disappearance of LaMgNi 4 phase on X-ray scans: amorphization, decomposition, severe pulverization, and selective oxidation. Decomposition was reported in some hydrides [36] but was ruled out due to lack of new phase in the XRD pattern. In order to investigate this phenomenon, seven consecutive PCT measurements were performed at 30 C on a newly activated E26 alloy.…”

An investigation on hydrogen storage thermodynamics and kinetics of Nd–Mg–Ni-based alloys synthesized by mechanical milling

“…As for the x ¼ 200 alloy, it decreases from 71 to 58 kJ/mol. Ouyang et al [37] also reported that E a values can be determined as 63 ± 3 kJ/mol H 2 for CeH 2.73 -MgH 2 -Ni composites and 104 ± 7 kJ/mol H 2 for CeH 2.73 -MgH 2 , respectively. This is mainly because of catalyst effects of CeH 2.73 and Mg 2 NiH 4 .…”

Severely deformed ZK60 + 2.5% Mm alloy for hydrogen storage produced by two different processing routes

“…Moreover, plastic deformation and the addition of catalysts are often applied together [14]. Catalysts such as Li [15], nanotubes [16], Ni [17] and rare earth elements [18,19] are especially effective at improving kinetics of hydrogen absorption/desorption. Nanocrystalline magnesium alloys can be prepared by rapid solidification methods such as melt spinning (MS) [9].…”

“…Ouyang et al also investigated the effect of Pr in Mg 3 Pr and Mg 3 PrNi 0.1 [26] reaching fast kinetics, similarly to Mg 3 La. Recently, Ouyang et al [18] investigated the alloy Mg 80 Ce 18 Ni 2 prepared by induction melting that was further comminuted. The authors reported fast kinetics and outstanding stability even after 500 hydrogenation/dehydrogenation cycles.…”