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 Mg-Al 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