Hydrogen Storage Properties and Corresponding Phase Transformations of Mg/Pd Laminate Composites Prepared by a Repetitive-Rolling Method

Abstract

Mg/Pd laminate composites (Mg/Pd = 6) prepared by a repetitive-rolling method can reversibly absorb and desorb a large amount of hydrogen, up to 1.47 H/M (4 mass%) at 573 K. Pressure-composition isotherms of the Mg/Pd laminate composites show two plateaux, P_L=0.2 MPa and P_H=2 MPa, during hydrogen absorption and desorption. To clarify the correlation between hydrogen storage properties and phase transformations, we investigated structural changes of the Mg₆Pd intermetallic compound with in-situ XRD. The low-pressure plateau P_L corresponds to the decomposition of Mg₆Pd into Mg₅Pd₂ and MgH₂, and the high-pressure plateau P_H to the decomposition of Mg₅Pd₂ into MgPd and MgH₂. In subsequent dehydrogenation processes, part of the MgH₂ reformed Mg, and the Mg and MgPd form Mg₅Pd₂ at the high-pressure plateau P_H and then the remaining MgH₂ reformed Mg, and the Mg and Mg₅Pd₂ form Mg₆Pd at the low-pressure plateau P_L. According to this mechanism, the Mg₆Pd can absorb and desorb hydrogen through reversibly disproportionation and recombination processes.