Hydrogenation of Pd-coated Zr-Cu-Ni-Al metallic glasses and quasicrystals

Zr-based metallic glasses and quasicrystals might be excellent materials for hydrogen storage because of their high number of tetrahedrally coordinated sites suitable for interstitial hydrogen and their favorable hydrogen chemistry. However, hydrogen desorption at low temperatures of the amorphous as well as quasicrystalline Zr-Cu-Ni-Al alloys is hindered by a thin ZrO₂ barrier and proceeds only at higher temperatures together or even after phase transformations of the metastable alloys. Pd coating was observed to improve the absorption and in particular the desorption kinetics significantly. Hydrogen charging was performed electrochemically in a 2:1 glycerin-phosphoric acid electrolyte. Hydrogen desorption was studied by means of DSC as well as TDA, the microstructure by X-ray diffraction and TEM. In Pd-coated alloys full desorption is observed even below 300°C, but only after hydrogenation up to about H/M=0.4; higher hydrogen contents led to irreversible microstructural changes, in amorphous as well as quasicrystalline materials. The characteristics of hydrogen desorption and the micromechanism of decomposition during annealing of the hydrogenated Pd-coated metastable alloys at higher temperatures are discussed in detail.