The influence of deposition parameters on the morphology of sputtered Mg84Al8Ti8 thin films and their potential for hydrogen storage

Magnesium alloys are increasingly researched as potential hydrogen storage materials due to their high hydrogen capacity, lightweight nature, and abundance. These alloys can absorb significant amounts of hydrogen, forming magnesium hydride (MgH2), which offers a high hydrogen storage density. However, challenges such as slow absorption and desorption kinetics and high operating temperatures need to be addressed. Typical alloying elements are Al, Ti and Fe and in this contribution the ternary alloy Mg84Al8Ti8 (MAT) was chosen as promising candidate.
This alloy was deposited as thin film via DC-magnetron sputtering from a target with similar composition. Energy dispersive X-ray analysis (EDX) was used to verify the transfer of the target stoichiometry to the thin film over an extended period of time. Special focus was put on adjusting the deposition parameters in order to yield high deposition rates and obtain a rough morphology for enhancing the hydrogen absorption kinetics. Additionally, the influence of different substrates (glass&titanium foil) on the morphology were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM).
The potential for hydrogen storage in this alloy was investigated by two hydrogenation methods. Firstly, the thin films were exposed to hydrogen gas in a Sievert apparatus at 300°C. This led to a successful hydrogenation of the material, which could be observed with X-ray diffraction (XRD). However, the formation of a TiAl-intermetallic phase could be observed as well. The second method was electrochemical hydrogen loading, for which the thin films were covered with a catalyst (PdAu) and negatively polarized in a 4.2 M KOH electrolyte. Here, a colour change could be seen, which went hand in hand with a change in morphology, as could observed in the materials by XRD by diminished MAT signals. However, only minor signals from a MgH2 phase could be seen with this hydrogenation technique.