The activation of FeTi for hydrogen absorption

FeTi is an interesting hydrogen storage material which has to be activated at ≈670 K for the absorption of hydrogen. We review critically the great number of previously published results and models on this activation process and emphasize the controversial points. To eliminate the controversy we analysed the variation of the surface composition of FeTi upon activation in the high-pressure cell of a photoelectron spectrometer. The initially passivating surface oxide is shown to be converted into a mixture of TiO₂ and Fe by surface segregation and chemical reduction. No evidence for the formation of Fe₂Ti₄O _x , FeTiO _x , and TiH _x is found. H₂/D₂ exchange reactions show that H₂ dissociates rapidly on Fe and FeTi, but not on TiO₂. The surface of FeTi is activated easily at 670 K. Difficulties encountered with the initial hydrogen absorption by virgin high purity FeTi are probably related to bulk (H diffusion, fracture toughness) rather than surface properties.