Application of nanostructured composites in a hydrogen storage device

Large batches (800 g) of nanostructured Mg – x wt % MmNi 5 ( x = 10 – 70 ) composites were prepared by ball milling elemental Mg with MmNi 5 in an attritor for 12 h under hydrogen atmosphere. There was no alloy formation between Mg and MmNi 5 within the milling times employed. The grain size of Mg in the composite varied from 28 to 45 nm, increasing with Mg content, whereas that of MmNi 5 was constant at 12 nm, irrespective of its concentration in the composite. BET surface area of the milled composites was in the range of 25 to 58 m 2 / g , increased with MmNi 5 content. sorption kinetics and capacities of these composites were measured at 100, 200 and 300 ∘ C under 30 bar hydrogen pressure on a small sample of about 8 g. The samples absorbed at all the temperatures, the absorption rate increases with increase in MmNi 5 content. But the rates decreased marginally with temperature and attained steady state in less than 400 s even at 100 ∘ C . However, the hydrogen absorption capacity of the composites followed the Mg content at all the temperatures, with Mg – 10 wt % MmNi 5 showing the highest capacity of 5.1 wt%. MmNi 5 has a significant effect on the absorption of hydrogen by Mg at temperatures as low as 100 ∘ C , even though hydride of MmNi 5 was not present in the hydrogenated composite. The nanostructure of Mg together with distribution of MmNi 5 on grain surface/grain boundary of Mg appears to have enhanced the absorption, with MmNi 5 probably acting as a conduit for hydrogen diffusing into Mg grain. rformance of hydrogen storage device with larger quantities of Mg – MmNi 5 composites (350–500 g) was evaluated in the temperature range of 100 – 150 ∘ C with supply pressure of 10–30 bar. The absorption rates and quantity of hydrogen absorbed increased with supply pressure and decreased with temperature. The fraction α was more than 70% in compositions with up to 10 – 30 wt % MmNi 5 , but was much lower at higher MmNi5 content. The absorption behaviour of these composites followed the same trend as in the case of testing on smaller sample size.