Investigations on synthesis, characterization and hydrogenation behavior of hydrogen storage alloys,

The present study deals with investigations on the synthesis and characterization of Ca substituted versions of MmNi 5 -type hydrogen storage materials typified by the compositions Mm 1 - x Ca x Ni 5 - y - z Al y Fe z ( x = 0 , 0.05 , 0.1 , 0.2 , 0.3 ; y = 0 , 0.1 ; z = 0 , 0.1 ) . A comparative study of Ca concentration present in the materials, with emphasis on their hydrogen storage capacity, was carried out and then the role of Al and Fe was studied. The structural characterization revealed formation of CaCu 5 -type structure and small amount of free Ni in the as-synthesized alloys. Some extra XRD-peaks, corresponding to CaH 2 were detected in dehydrogenated versions which disappeared in Fe containing samples. The hydrogenation behavior of these materials was monitored through pc-isotherms and kinetic curves. A composition, Mm 0.9 Ca 0.1 Ni 4.8 Al 0.1 Fe 0.1 having maximum storage capacity of 1.6 wt% was resynthesized using composite pellet route which improved hydrogen storage capacity drastically, i.e. 1.9 wt%.