A study of the thermodynamic destabilization of sodium aluminum hydride (NaAlH₄) with titanium nitride (TiN) using X-ray diffraction and residual gas analysis

This project is designed to extend the limits of hydrogen storage technology for practical purposes. Currently, there is a need to develop systems which release hydrogen at lower temperatures. The addition of destabilizers are believed to lower the H₂ gas desorption temperatures by forming a stable product phase comprised of the hydrogen coordinated cation and the destabilizer phase cation. In this case, TiN is added to NaAlH₄ in order to destabilize the AlH₄^- complex by forming a stable Ti-Al alloy. Although the bond energy in the nitride phase is high, x-ray diffraction shows the product intermetallic phase TiAl to form. The sodium alanate powders were mixed using titanium nitride (TiN) and the mixture was high energy ball milled. The samples had varying concentrations of TiN (e.g. 25 mol%, 50 mol%, and 75 mol%). X-ray relative peak intensity analysis shows that the content of TiAl formed increases with increasing TiN added to the NaAlH ₄ system. Moreover, residual gas analysis of the 25 mol % TiN in NaAlH₄ sample shows that the onset of desorption occurs at 60-70°C, with the peak temperature of hydrogen evolution from this stoichiometry occurring at 110°C.