Improvement in hydrogen storage capacity in [formula omitted] through substitution of Ni by Fe

Abstract

This paper deals with improvement in the hydrogenation behavior of LaNi 5 type alloys brought in through material tailoring by substitution of elements having higher electron attractive power and bigger sizes than that of Ni. Although substitutions by both Co and Fe were investigated, optimum results were obtained only through Fe. The higher electron attractive power of Fe, Co ( 3 d 6 , 3 d 7 as against 3 d 8 of Ni) is expected to lead to possibility of higher number of hydrogen atoms in the unit cell, thus resulting in higher storage capacity. Fe substitution has been found to be more affective in the enhancement of storage capacity. The size of the Fe atom ( 1.72 A ˚ ) is higher than that of Ni ( 1.67 A ˚ ) by about 6.13%. This may lead to larger size of interstitial voids. Thus, there may be higher number of interstitial voids occupied by hydrogen for the Fe substituted version as compared to Ni alone. Keeping these aspects in view, we have investigated Fe substituted version of LaNi 5 , i.e. the material La ( Ni 1 - x Fe x ) 5 . It has been found that all the phases of La ( Ni 1 - x Fe x ) 5 exhibit better hydrogenation characteristics than the parent material LaNi 5 . Thus, the storage capacity of La ( Ni 1 - x Fe x ) 5 for x = 0 , 0.05 , 0.10 , 0.20 , 0.25 , 0.30 are ∼ 1.5 , 1.93 , 1.96 , 2.20 , 1.78 and 1.60 wt%, respectively. The material La ( Ni 0.80 Fe 0.20 ) 5 has been found to exhibit the highest storage capacity ∼ 2.20 wt % . The possible reasons for the enhancement of storage capacity of Fe substituted LaNi 5 have been described and discussed.