Effect of Manganese substitution on hydrogen storage properties of LaNi4.25-xAl0.75Mnx alloy

The effect of Mn substitution on phase structure, hydrogen hydriding/dehydriding properties (plateau pressure and slope) and reaction heat enthalpy of LaNi4.25-xAl0.75Mnx alloys (x = 0, 0.25, 0.35, 0.45, 0.55 and 0.65) were studied. The experimental results show that all LaNi4.25-xAl0.75Mnx alloys have single phase and have the same hexagonal structure as that of LaNi5 alloy (CaCu5 type, P6/mmm). With increasing Mn substitution content, the cell parameters of LaNi4.25-xAl0.75Mnx alloy greatly increase, but the maximum hydrogen storage capacity and the equilibrium absorption pressure of LaNi4.25-xAl0.75Mnx alloy decrease from 1.38 wt. % to 1.18 wt. % and from 1.61 to 0.0712 MPa, respectively. Moreover, the hydrogen pressure plateau slope factor σ increases from 0.014 to 0.18, but the hysteresis factor is nearly constant. The heat enthalpy absolute value |ΔHplat| increases from 46.7 kJ · mol−1 H2 to 56.1 kJ · mol−1 H2 as the Mn content x increases from 0 to 0.65.