Evaluation of hydrogen absorption and desorption properties of Mg/Al based laminated thin films

Abstract

This study investigated the effect of the Mg/Al laminated films, Mg/Al/Pd, Al/Mg/Pd, and Al/Mg/Al/Pd prepared by the pulsed laser deposition (PLD) method, on hydrogen storage/release characteristics. X-ray diffraction (XRD) analysis is performed before and after hydrogenation at 200℃ and 0.99MPa, and then all samples were confirmed to absorb hydrogen. According to differential scanning calorimetry (DSC), Mg/Al/Pd and Al/Mg/Pd released hydrogen at 239 to 452℃ and 173 to 236℃ respectively and Al/Mg/Al/Pd did not release hydrogen. According to pressure-composition-temperature (PCT) line measurement performed at 200℃, Mg/Al/Pd absorbed 1.4 to 3.0 wt.% hydrogen at 0.99 MPa and Al/Mg/Pd film absorbed 1.0 to 1.6 wt.%, that is less than Mg/Al/Pd, and Al/Mg/Al/Pd had an absorption of 2.1 wt.% under the same condition. By electron microscopic observation for the cross section of the films and element mapping by EDS, Mg/Al/Pd was in a state where Mg, Al, and Pd layers were laminated in the order of vapor deposition. In Al/Mg/Pd expect for the Al60/Mg/Pd, Mg diffused into Al to form a Mg-Al solid solution, and Pd was deposited on it. Although Al60/Mg/Pd was in a lamination state like Mg/Al/Pd, the boundary between Al and Mg was ambiguous. Al/Mg/Al/Pd appeared the lamination state in some area and the solid solution state in the other area that means a mixed state. Since the hydrogen storage amount and the release temperature of MgAl solid solution is less and lower than those of Mg alone respectively, the hydrogen storage amount and release temperature of Mg/Al/Pd, i.e., lamination state, is more and higher than that of Al/Mg/Pd, i.e., solid solution state respectively. The hydrogen storage capacity of Al/Mg/Al/Pd was situated between Mg/Al/Pd and the Al/Mg/Pd since Al/Mg/Al/Pd has both states.