Crystal structure and hydrogen storage properties of (La,Ce)Ni5−xMx (M = Al, Fe, or Co) alloys
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The effects of partial substitution of La by Ce and Ni by Al, Fe, or Co in LaNi5-based alloys on hydrogen storage performance were systematically studied. All samples were prepared using vacuum arc melting in an argon atmosphere. The results showed that for La-Ni5−xMx (M = Al, Fe, or Co) alloys, the lattice constants and unit cell volumes increased with an increasing amount of Al and Fe. On the other hand, these parameters decreased upon partial substitution of La by Ce. In addition, the lattice constant remained almost constant in the La0.6Ce0.4Ni5–xCox alloys regardless of the value of x (x = 0.3, 0.6, or 0.9), as Ce might enhance the homogeneity of the CaCu5-type phase in Co-containing alloys. The hydrogen storage properties of the alloys were investigated using pressure, composition, and temperature isotherms. The experimental results showed that the plateau pressure decreased with an increasing content of Al, Fe, or Co, but it increased with Ce addition. Furthermore, the plateau pressures of all Co-containing alloys were almost identical upon substitution with Ce. Finally, the enthalpy (ΔH) and entropy (ΔS) values for all alloys were calculated using van’t Hoff plots. The relationship between the lattice parameters and enthalpy changes for hydrogenation will be discussed.
Keywordsmetal hydride LaNi5 hydrogen storage alloys partial substitution P−C−T curves thermodynamics
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This work was partially supported by International Academic Exchange Program of Muroran Institute of Technology, Muroran (Japan) and University of Science and Technology Beijing, Beijing (China) and Environmentally Friendly Materials Education Program provided by Muroran MATERIA. This work was also supported by Beijing Key Laboratory of Energy Conservation and Emission Reduction for Metallurgical Industry, Beijing, China.
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