Hydriding properties of MmNi 5 system with aluminium, manganese and tin substitutions

Abstract

The hydrogen storage properties of annealed MmNi 5 - xM x (M  Al, Mn and Sn) systems containing Indian mischmetal (Mm) (composition (wt.%): Ce, 43; La, 23; Nd, 18; Pr, 5; Sm, 3; Fe, 8) were studied using desorption pressure-composition isotherms. The compositions studied were MmNi 4.6Al 0.4, MmNi 4.2Al 0.8, MmNi 4.6Mn 0.4, MmNi 4.2Mn 0.8 and MmNi 4.6Sn 0.4. The partial substitution of Ni in MmNi 5 by Al, Mn and Sn led to a decrease in the hydride formation plateau pressure. The decrease in the plateau pressure was enhanced with increasing Al and Mn substitution. The enthalpy ΔH and entropy ΔS of hydride formation of these compounds were obtained. The enthalpy of hydriding decreased with increasing substitution. The variation in the enthalpy of hydriding and plateau pressure with Al, Mn and Sn substitution was explained by considering the increase in the unit cell volume of MmNi 5 caused by substitution. The hydrogen storage capacity of MmNi 5 was unaffected by Al and Mn substitution whereas Sn substitution led to a decrease in capacity.