Hydrogen storage in metastable Mg yTi (1 − y) thin films

Abstract

The electrochemical properties of Mg y Ti (1 − y) thin films with y 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. Mg y Ti (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 Mg 0.80Ti 0.20 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 Mg y Ti (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 Mg y Ti (1 − y) and Mg y Sc (1 − y) alloys points to a fcc-structured hydride.