Hydrogen storage in metastable MgyTi(1-y) thin films

The electrochemical properties of MgyTi(1 - y) thin films with gamma ranging from 0.50 to 0.95 during (de)hydrogenation are investigated. These metastable alloys were successfully prepared by means of electron-beam deposition at room temperature. X-ray diffraction confirmed that crystalline single-phase materials were obtained. Galvanostatic dehydrogenation measurements show that substituting Mg by Ti clearly affects the hydrogen storage properties. MgyTi(1 - y) alloys with less than 20 at.% Ti exhibit an extremely low rate-capability, whereas increasing the Ti-content leads to a enhanced rate-capability. A superior reversible hydrogen storage capacity, along with an excellent rate-capability, is found for the Mg0.80Ti0.20 alloy. To obtain a comprehensive view of the effect of Ti on the electrochemical hydrogen storage properties, pure Mg thin films are also included in the present study. The electrochemical deep-discharging behaviour of pure Mg shows a distinct evolution of the overpotential which might be due to a nucleation and growth process. Galvanostatic hydrogenation of the MgyTi(1 - y) alloys revealed the formation of products that do not correspond to the intrinsic thermodynamic properties of the individual Mg and Ti hydride, suggesting that no-segregation occurs. Moreover, the close analogy of the electrochemical behaviour of MgyTi(1 - y) and MgySc(1 - y) alloys points to a fcc-structured hydride. (c) 2005 Elsevier B.V. All rights reserved.