Effect of transition metals on ball-milled MmNi^sub 5^ hydrogen storage alloy

Abstract

MmNi^sub 5^ hydrogen storage alloy has been ball-milled with transition metal Co/Ni/Mn/Fe, one at a time in small amount of 0.5, 1.0, 2.0 and 5.0 wt%. Optimum hydrogenation behaviour has been observed for the sample containing 2.0 wt% of transition metal. Maximum hydrogen storage capacities of the MmNi^sub 5^ alloy have been obtained as 1.68, 1.64, 1.56 and 1.52 wt%. Time taken for the maximum hydrogen absorption was recorded as 3.0, 4.0, 4.0 and 4.5 min and desorption took 1.9, 3.0, 3.5 and 4.0 min. Short-term cyclic performance has been improved as 98, 98, 97 and 96 % storage capacity retention after 20 cycles upon ball-milling with Co, Ni, Mn and Fe, respectively. The improvement in hydrogenation behaviour due to addition of transition metal has been obtained as Co > Ni > Mn > Fe. Structural and microstructural characterizations have been carried out by XRD and SEM techniques. Several factors have been discussed which affect catalytic action of transition metals in ball-milled MmNi^sub 5^ alloy.