Phase Structures and Hydrogen Storage Properties of Mg2Ni1-xCox Alloys Prepared by Solid Solution Sintering

Mg2Ni1-xCox (x=0.10, 0.15, 0.20) alloys were prepared by a novel method combining solid solution with sintering process. The effect of Co content on the phase structures and hydrogen storage properties were investigated by XRD and pressure-composition-temperature analyser. It was found that the alloys consisted of a Mg2Ni-type major phase Mg-2(Ni, Co), minor Mg and a new phase MgNi3Co. The Mg-2(Ni, Co) compounds displayed a reversible hydrogen storage process. After hydrogenation, the quaternary Mg2Ni0.9Co0.1H4-type hydride was formed with an enthalpy change of the hydrogen desorption(Delta H-d=63.9 kJ/mol H-2) approximate to the parent hydride HT-Mg2NiH4. The Mg2Ni1-xCox(x=0.10, 0.15, 0.20) alloys showed a superior desorption kinetics and the desorption process was mainly controlled by two-dimensional phase-boundary migration. For the Mg2Ni1-xCox (x=0.10, 0.15, 0.20) alloys, the activation energy of hydrogen desorption (E-a) decreased with the increase of Co content. As a result, the E-a value of the Mg2Ni0.8Co0.2 alloy was significantly lowered to 54.0 kJ/mol.