Hydrogen sorption in crystalline and amorphous Mg-Cu thin films

A study was carried out to examine the hydrogenation behavior of 300 nm, Pd-capped, Mg-Cu thin films with Cu contents of 5, 10 and 15 at.%. The films were produced via thermal evaporation of Mg and Cu co-deposited onto glass substrates at two different temperatures: 298 and 223 K. The samples produced at 298 K were all crystalline, the structure being refined with increase in the Cu content. The films deposited at 223 K developed structures that were either refined, i.e. Mg(95)Cu(5); or amorphous, i.e. Mg(90)Cu(10) and Mg(85)Cu(15). The hydrogen sorption of the films was followed by resistance measurements, with the samples heated isochronally, initially under hydrogen and then under vacuum. The resistance data have shown that an increase in Cu content, or a decrease in the substrate temperature, improves the sorption characteristics of the films by reducing both the absorption and desorption temperatures. The lowest desorption temperature achieved was 323 K. The study suggests that an amorphous alloy of Mg(90)Cu(10) could be used as hydrogen storage medium as it would store 5.9 wt.% hydrogen in near-ambient conditions and could desorp it at around 100 degrees C. 2009 Elsevier B.V. All rights reserved.