Energy distribution of hydrogen sites for MgNi_0.86M1_0.03 (M1 = Cr, Fe, Co; Mn) alloys desorbing hydrogen at low temperature

The energy distribution of hydrogen sites for MgNi_0.86M1_0.03 (M1 = Cr, Fe, Co, Mn) alloys prepared by the ball milling technique was investigated. From the results of DSC, TG analysis and the calculation of the enthalpy of hydrogenation, we derived that the Cr and Fe-substituted alloys have a broad energy distribution and the averaged enthalpy of hydrogenation is about -82 kJ mol^-1 H₂^-1. Because of the broad distribution, the hydride of larger enthalpy decomposes at low temperature. However, the Co and Mn-substituted alloys have sharp energy distributions though the averaged value of hydrogenation is about -67 kJ mol^-1 H₂^-1. Therefore, these alloys do not desorb hydrogen at low temperature. In order to develop Mg-based alloys that desorb hydrogen at low temperature, the dependence of substitution element on the energy distribution should be considered and substitution elements that make the energy distribution broad must be selected.