Dynamic surface barrier effects on hydrogen storage capacity in Mg-Ni films

Hydrogen distribution profiles in Mg-Ni films deposited on quartz substrate by the magnetron-sputter co-deposition of Mg and Ni atoms have been investigated after hydrogenation at 8 x 105 Pa hydrogen pressure at temperatures 210, 230 and 250 deg. C during 1, 3, 6 and 72 h using elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA) methods. Oxygen distribution profiles in the near-surface region have been measured by ERDA. It is shown that hydrogen storage capacity decreases as hydrogenation temperature increases from 210 to 250 deg. C for fixed hydrogenation duration and changes not monotonously as function of hydrogenation time for a fixed temperature. To explain variations of storage capacity as function of hydrogenation temperature and time, the structural film changes have been studied by X-ray diffraction technique, and surface topography was analysed using scanning electron microscopy. We suggest that registered results may be explained on the basis of assumption about the dynamic properties of surfaces which modify the hydrogen uptake mechanism.