Mg-Fe Thin Films: A Phase-separated Structure with Fast Kinetics of Hydrogenation
Shiyou Zheng, Ke Wang, Vladimir Oleshko, Leonid A. Bendersky
In this paper we suggest a new approach to improve the kinetics of hydrogenation based on a material with high density of interfaces between hydride-forming solid (HFS) and hydrogen-diffusing solid media (HDM). Such materials can be realized for phase-separated systems when synthesised in the conditions limiting kinetics of phase separation, e.g., in thin film deposition. Mg-Fe was selected as a model system: 1) It has phase separation; 2) MgH_(2) is a high-capacity hydride; 3) Fe has high diffusivity of hydrogen. Mg_(1-x)Fe_(x) thin films (x=0-0.30) capped with Pd were prepared by electron beam co-deposition and their hydrogenation/dehydrogenation kinetics and cycling properties were studied at 413 K. The structures of the thin films before and after hydrogenation during different cycles were investigated by X-ray diffraction and transmission electron microscopy. It has been found that there is a remarkable improvement in reversible hydrogen storage capacity and kinetics for the Mg_(1-x)Fe_(x) films in comparison to pure Mg film. These improvements are attributed to the presence of Fe layers percolating throughout the Mg matrix. For the Mg_(1-x)Fe_(x) films with x≤0.15 more than 4.0 % mass fraction hydrogen can be absorbed under hydrogen pressures of 0.1 MPa in less than 5 min, and about 3.5 % mass fraction hydrogen can be desorbed in 10 min. For x>0.15 films the reversible hydrogen storage properties significantly degrade; structural study of the higher concentration films shows the presence of a stable ternary hydride Mg2FeH6, formation of which is responsible for interruption of fast hydrogen delivery.
, Wang, K.
, Oleshko, V.
and Bendersky, L.
Mg-Fe Thin Films: A Phase-separated Structure with Fast Kinetics of Hydrogenation, The Journal of Physical Chemistry C, [online], https://doi.org/10.1021/jp307982p
(Accessed October 4, 2023)