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, PL=0.2 MPa and PH=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 PL corresponds to the decomposition of Mg6Pd into Mg5Pd2 and MgH2, and the high-pressure plateau PH 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 PH and then the remaining MgH2 reformed Mg, and the Mg and Mg5Pd2 form Mg6Pd at the low-pressure plateau PL. According to this mechanism, the Mg6Pd can absorb and desorb hydrogen through reversibly disproportionation and recombination processes.