Electrochemical hydrogen storage in MgSc alloys: A comparative study between thin films and bulk materials

The electrochemical hydrogen storage properties of MgxSc1-x alloys are investigated both in thin film and bulk form. A comparison is made between the electrochemical, thermodynamic and structural properties of both systems. It is shown that the electrochemical properties of the thin films and bulk materials strongly resemble one another. For compositions where x > 0.8, a sudden decrease in capacity is observed in both cases, which is argued to be due to a structural transformation of the resulting hydride from fluorite to rutile. The formation of a fluorite structure for the bulk hydride was confirmed by X-ray diffraction. Both galvanostatic and equilibrium voltage curves show a plateau in the electrode potential, indicative of a phase transition. Partial discharge of a MgSc bulk hydride showed retention of the face-centered cubic host structure. Overall, the thin film materials are able to give a good indication of the electrochemical processes that take place in a simplified two-dimensional model system. This knowledge can subsequently be used for understanding the bulk system, as both bulk and thin film materials complement each other very well. (c) 2005 Elsevier B.V. All rights reserved.