Phase Transformations in MgH<sub>2</sub>–TiH<sub>2</sub> Hydrogen Storage System by High‐Pressure Torsion Process

  • Kouki Kitabayashi
    WPI, International Institute for Carbon‐Neutral Energy Research (WPI‐I2CNER) Kyushu University Fukuoka 819‐0395 Japan
  • Kaveh Edalati
    WPI, International Institute for Carbon‐Neutral Energy Research (WPI‐I2CNER) Kyushu University Fukuoka 819‐0395 Japan
  • Hai‐Wen Li
    WPI, International Institute for Carbon‐Neutral Energy Research (WPI‐I2CNER) Kyushu University Fukuoka 819‐0395 Japan
  • Etsuo Akiba
    WPI, International Institute for Carbon‐Neutral Energy Research (WPI‐I2CNER) Kyushu University Fukuoka 819‐0395 Japan
  • Zenji Horita
    WPI, International Institute for Carbon‐Neutral Energy Research (WPI‐I2CNER) Kyushu University Fukuoka 819‐0395 Japan

Abstract

<jats:sec><jats:label /><jats:p>Magnesium hydride (MgH<jats:sub>2</jats:sub>) and titanium hydride (TiH<jats:sub>2</jats:sub>) are two potential candidates for solid‐state hydrogen storage, but strong hydride formation energy in these hydrides undesirably results in their high dehydrogenation temperature. First‐principles calculations show that the metastable hydrides in the MgH<jats:sub>2</jats:sub>–TiH<jats:sub>2</jats:sub> system have low hydrogen binding energy, which makes them more appropriate for low‐temperature hydrogen storage. In this study, severe plastic deformation (SPD) via the high‐pressure torsion (HPT) method is applied to the MgH<jats:sub>2</jats:sub>–TiH<jats:sub>2</jats:sub> system to synthesize metastable hydrides. While MgH<jats:sub>2</jats:sub> transforms to a high‐pressure orthorhombic <jats:italic>γ</jats:italic> phase, TiH<jats:sub>2</jats:sub> does not exhibit any cubic‐to‐tetragonal phase transformation even by HPT processing at cryogenic temperature. Application of large strains by 400 HPT turns to the immiscible MgH<jats:sub>2</jats:sub>/TiH<jats:sub>2</jats:sub> composite results in atomic‐scale mixing and formation of nanostructured ternary Mg–Ti–H hydride with the metastable FCC structure and lower dehydrogenation temperature than TiH<jats:sub>2</jats:sub>.</jats:p></jats:sec>

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