On the poisoning effect of O ₂ and N ₂ for the Zr _0.9Ti _0.1V ₂ hydrogen storage alloy

Homogeneously annealed Zr _0.9Ti _0.1V ₂ samples are firstly exposed to contamination gases of O ₂ and N ₂ for 30, 60 and 180 s at the ambient temperature, respectively. Hydrogen absorption properties are examined after poisoning and regeneration. The compositions and valence in the surface and sub-surface are investigated by X-ray photoelectron spectroscopy (XPS). The hydrogen absorption capacity of the alloy has been almost entirely degraded by the oxygen poisoning. After the regeneration, the oxygen-poisoned sample can hardly absorb hydrogen while the nitrogen-poisoned sample re-obtains the hydrogen absorption capacity with the value as 2.85 H A ^-1 (molar ratio of hydrogen to alloy). The activation temperature of the oxygen-poisoned sample is ∼100 K higher than the value of the un-poisoned one. With the help of ion etching, it is found the thickness of the passivated surface layer of the oxygen-poisoned sample was ∼58 nm. However, the thickness of the passivated surface layer of the un-poisoned sample is only ∼36 nm. That is the reason why the oxygen-poisoned sample cannot renew the hydrogen absorption capacity under the same regeneration conditions as in the un-poisoned one.