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The hydrogen storage properties of thin films of FeTi evaporated on Si substrates and covered with 20 nm Pd were studied. The films serve as a model system for powdered FeTi, with grains that are (partly) covered with Pd. This material could serve as a practical hydrogen storage material. The 20 nm Pd layer prevents the oxidation of the FeTi layer during air exposure up to temperatures of 200 °C and during H charging and discharging in impure hydrogen. The FeTi is a mixture of amorphous and nano-crystalline material. Two FeTi compositions (43 at.% Fe, i.e. Ti-rich, and 56 at.% Fe, i.e. Fe-rich) were studied. The H charging and discharging characteristics as a function of temperature and pressure are determined from a differential pressure measurement for Fe and Ti-rich material before and after annealing. After discharging in vacuum at a temperature of 150 °C a H residue of H/M ∼ 0.12 is observed. The recoverable charging capacity of FeTi (also after many cycles) is 0.9 ΔH/M (H atoms per metal atom) for RT charging at 2700 mbar and vacuum discharging at 150 °C. |
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