The Influence of Pr and Nd Substitution on Hydrogen Storage Properties of Mechanically Alloyed (La,Mg) 2 Ni 7 -Type Allo
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JMEPEG https://doi.org/10.1007/s11665-018-3644-8
The Influence of Pr and Nd Substitution on Hydrogen Storage Properties of Mechanically Alloyed (La,Mg)2Ni7-Type Alloys M. Balcerzak
, M. Nowak, and M. Jurczyk
(Submitted January 5, 2018; in revised form April 23, 2018) The (La,Mg)2Ni7-type alloys are candidates for hydrogen storage materials. In this study, mechanical alloying with subsequent annealing under the argon atmosphere at 1123 K for 0.5 h is applied to produce La1.52xPrxMg0.5Ni7 and La1.52xNdxMg0.5Ni7 alloys (x = 0, 0.25, 0.5, 1). A shaker-type ball mill is used in the study. The objective of the present study is to investigate the influence of the amount of Pr or Nd in the LaMg-Ni alloy on the electrochemical, hydrogenation and dehydrogenation properties of (La,Mg)2Ni7-type materials. The x-ray diffraction analysis reveals the formation of multi-phase structure materials. The obtained alloys were studied by a conventional SievertÕs type apparatus at 303 K. It has been observed that a chemical modification by Pr and Nd can affect the kinetics of the hydrogen absorption process and the maximum hydrogen storage capacity. Moreover, the stability of the electrochemical discharge capacity during cyclic work of the (La,Mg)2Ni7-type alloys is improved by a substitution with the La by Pr or Nd atoms. Keywords
energy, intermetallic, microscope electron, powder metallurgy, rare earths, x-ray
1. Introduction The La2Ni7 intermetallic alloy of a superstacking structure (1:1 LaNi5 to LaNi2 slabs ratio) is characterized by greater Huptake than the LaNi5 phase. Therefore, it is attractive for hydrogen storage systems and for secondary Ni-MHx batteries as negative electrode materials (Ref 1, 2). However, the practical use of this phase is limited due to several factors such as poor cycle stability of the electrochemical discharge capacity during the charging/discharging process. There are several methods to improve the performance of hydrogen storage alloys, one of which is chemical modification. This approach is based on the fact that the final hydrogen storage properties of materials are directly related to the crystallographic structure and phase composition. It was revealed in the past that apartial substitution of the A and/or B atoms in A2B7-type materials by rare earth and/or transition metals can affect their structure and phase composition and therefore improve the cycling stability, the diffusion rate, the maximum hydrogen storage capacity, etc. (Ref 1, 3-5). For example, the effect of the Mg content on the properties of the La2 xMgxNi7 system was investigated (Ref 6-8). The concentration of Mg in the basic system is very impactful on the final phase composition. It was shown that when x = 0.48-0.5,
M. Balcerzak, M. Nowak, and M. Jurczyk, Institute of Materials Science and Engineering, Poznan´ University of Technology, Jana Pawla II no 24, 61-138 Poznan, Poland. Contact e-mail: [email protected].
Journal of Materials Engineering and Performance
x = 0.6 and x > 0.48, the following main phases (La,M
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