Solid-State Synthesis of Hydrogen Storage Mg2Co Alloys via Bulk Mechanical Alloying

Mg–Co system is employed to investigate the solid-state reactivity of Mg2Co from the elemental powder mixture of magnesium and cobalt and to describe the hydrogenation and de-hydrogenation processes of Mg2Co. Mg2Co is successfully solid-state synthesized as a non-equilibrium phase compound by the bulk mechanical alloying. This solid-state reactivity is controlled by the repeated plastic flow of ductile elements in the powder mixture. This non-equilibrium phase, Mg2Co is stable up to 833 K. Its hydrogenation and de-hydrogenation processes are described by DSC, PCT and XRD. These processes take place in multi-step with strong dependency on the holding temperature. Hydrogenation process from Mg2Co is composed of two steps to Mg2CoH5 and dehydrogenation from Mg2CoH5, one step to Mg2Co, at 633 K. Maximum hydrogen absorption capacity at 633 K is still limited to 2.03 mass% since hydrogenation and de-hydrogenation steps, working at higher temperature, are never activated without chemical modification to original Mg2Co.