Thermodynamical properties of La–Ni–T (T = Mg, Bi and Sb) hydrogen storage systems

The hydrogen absorption properties of LaNi4.8T0.2 (T = Mg, Bi and Sb) alloys are reported. The effects of the substitution of Ni in the LaNi5 compound with Mg, Bi and Sb are investigated. The ability of alloys to absorb hydrogen is characterized by the pressure–composition (p–c) isotherms. The p–c isotherms allow the determining thermodynamic parameters enthalpy (ΔHdes) and entropy (ΔSdes) of the dehydrogenation processes. The calculated ΔHdes and ΔSdes data helps to explain the decrease of hydrogen equilibrium pressure in alloys doped with Al, Mg and Bi and its increase in the Sb-doped LaNi5 compound. Generally, partial substitution of Ni in LaNi5 compound with Mg, Bi and Sb cause insignificant changes of hydrogen storage capacity compared to the hydrogen content in the initial LaNi5H6 hydride phase. However, it is worth to stress that, in the case of LaNi4.8Bi0.2, a small increase of H/f.u. up to 6.8 is observed. The obtained results in these investigations indicate that the LaNi4.8T0.2 (T = Al, Mg and Bi) alloys can be very attractive materials dedicated for negative electrodes in Ni/MH batteries.