Hydrogen absorption in Al doped MmNi5

There are many hydrogen storage alloys, but the MmNi5 family of alloys is of great importance as it has good properties for technological uses like hydrogen capacity, plateau pressure, repeatability and ease of activation. In the present paper we describe the hydrogen absorption mechanism of two samples of MmNi4.5Al0.5, having two different misch metal compositions. Sample-1 with misch metal composition (La 22%, Ce 52%, Nd 15% and Pr 11%) and sample-2 with misch metal composition (La 27.13%, Ce 51.57%, Nd 15.8%, Pr 5.50%). These two samples have a variation of the composition of misch metals in MmNi4.5Al0.5. The absorption–desorption cycles in these two samples have been studied in temperatures ranging from room temperature, 30°C to 85°C. H/M ratio of these samples was measured using a volume displacement method. It was found that the H/M ratio for the two samples have slight differences, varying from 0.06 to 0.8 in sample-1, and from 0.08 to 1.0 in sample-2, showing that sample-2 has the better composition of misch metal for hydrogen storage. The H/M for sample-1 becomes 0.8 at 80 psi of the hydrogen pressure while for sample-2 it attains a value of 1.0 at 30 psi. The time taken for activation of sample-2 was found to be small compared to sample-1, and the plateau pressure in sample-2 was found to be lower than sample-1. Therefore sample-2 has better hydrogen absorption–desorption properties and is therefore better for the technological uses of hydrogen energy.