Hydrogen storage in Mg₂Ni(Fe)H₄ nano particles synthesized from coarse-grained Mg and nano sized Ni(Fe) precursor

In this work, Mg₂Ni(Fe)H₄ was synthesized using precursors of nano Ni(Fe) composite powder prepared through arc plasma method and coarse-grained Mg powder. The microstructure, composition, phase components and the hydrogen storage properties of the Mg-Ni(Fe) composite were carefully investigated. It is observed that the Mg₂Ni(Fe)H₄ particles formed from the Mg-Ni(Fe) composite have a diameter of 100-240 nm and a portion of Fe in the Ni(Fe) nano particles transformed into α-Fe nano particles with the diameter of 40-120 nm. DSC measurements showed that the peak desorption temperature of the Mg₂Ni(Fe)H₄ was reduced to 501 K and the apparent activation energy for hydrogen desorption of the Mg₂Ni(Fe)H₄ was 97.2 kJ mol^-1 H₂. The formation enthalpy of Mg₂Ni(Fe)H₄ was measured to be -53.1 kJ mol^-1 H₂. The improvements in hydrogen sorption kinetics and thermodynamics can be attributed to the catalytic effect from α-Fe nano particles and the destabilization of Mg₂NiH₄ caused by the partial substitution of Ni by Fe, respectively.