Reactivation behaviour of TiFe hydride

Abstract

The reactivation of TiFe by means of heating—absorption—desorption cycling in pure hydrogen was investigated. An interesting irreversible hydrogen absorption—desorption was observed, i.e. the deactivated sample is found to absorb pure hydrogen to its full capacity at room temperature after an incubation period when heated to 300 °C in pure hydrogen, but the desorption is much less. With increasing cycle number the incubation period becomes shorter and shorter, the amount of hydrogen desorbed increases, the evolution temperature of retained hydrogen decreases and finally the irreversibility disappears. During heating, the change in the surface chemical state was examined by X-ray photoelectron spectroscopy. It is believed that the metallic Fe and suboxidized Ti formed during the heat treatment catalyse the hydrogen dissociation-association and that the hydrogen permeability in the surface layer improves with increasing reductility of Ti. The irreversible hydrogen absorption—desorption was ascribed to the various surface strain states which give rise to different permeabilities in the hydriding and dehydriding processes.