The aim of this work has been to study the effect of B metal substitutions in CaNi5 (AB(5)) which is known to suffer from poor cycling stability as a hydride electrode material. Systematic monosubstitutions of nickel with the most common other B metals (i.e. Al, Cr, Mn, Fe, Co, Cu, Zn and Sn) and Mg were performed. The overall composition was in all cases CaNi5-xMx (x=0.5 or 1) where M is the substituting element. The alloys were prepared by mechanical alloying. The hydrogen storage capacity was measured electrochemically ranging from 39 to 390 mAh/g, but none of the substitutions increased the cycling stability to any significant extend compared to pure CaNi5. X-ray diffraction patterns of the alloys revealed that only in a few cases the hexagonal CaCu5 structure of a true AB(5) alloy was preserved. In most cases diffraction patterns matching Ca2Ni7, CaNi3 or CaNi2 were seen. It can be concluded that CaNi5 is much less tolerant towards B-metal substitution than LaNi5. This fact makes it less possible that the problem with cycling stability of Ca-based hydride electrodes can be solved by substitutions. (C) 1999 Elsevier Science S.A. All rights reserved.
Journal of Alloys and Compounds, 1999, Vol 293-295, p. 185-189