Shiyou Zheng, Ke Wang, and Leonid A. Bendersky
Abstract: The influence of iron on the reversible hydrogen storage properties and crystal structure for Mg-Fe thin films were systematically studied in the present work. The Mg1-xFex thin films with a varying atomic amount of Fe (x=0-0.30) were prepared by electric beam technique. The cycling hydrogenation/dehydrogenation properties of the Mg1-xFex thin films were further compared. Moreover, the structures of the thin films before and after the hydrogenation/dehydrogenation processes during different cycles were analyzed by XRD. It has been found that the Mg thin film co-deposited with a few atomic percent of Fe shows fairly higher reversible hydrogen storage capacity and remarkably faster kinetics with respect to the pristine Mg thin film without Fe. As the value of x is 0.10, more than 4.0 wt.% hydrogen can be absorbed at temperatures of 413 K and hydrogen pressures of 0.1 MPa, and about 3.2~3.5 wt.% hydrogen can be desorbed in 60 min at the moderate temperate of 413 K. However, with x increasing to 0.30, the reversible hydrogen storage properties become dramatically degraded. These indicate that a few atomic percent of Fe can play a favorable role of the reversible hydrogen storage for the Mg thin film, but the higher concentration may lead to a negative effect. It is believed that the Fe phase is dispersed throughout the Mg and /or MgH2 grains and act as a catalyst to favor the dissociation and re-association of hydrogen, but to the higher concentrations, it may react with Mg in H2 presence to form the higher stable ternary hydride Mg2FeH6, and thus reduces the reversible hydrogen storage properties at moderate hydrogenation/dehydrogenation conditions.
Keywords: Thin film, Mg-Fe, Hydrogen storage