Creating the hydrogen absorption capability of CeNi₅ through the addition of Al

The hydrogenation capacities of CeNi_5−xAl_x (x = 0, 0.75, 1.0, 1.25, 1.5 and 1.75) alloys were assessed. In contrast to LaNi₅-based alloys, the addition of Al to CeNi₅ enables hydrogen absorption by creating larger interstitial sites as the result of an expanded lattice. Structure analyses indicate that each of these alloys maintained a CeNi₅ (CaCu₅-type) structure in which Al atoms exclusively occupied Ni 3g sites. Among these specimens, CeNi₄Al absorbed the greatest proportion of hydrogen atoms, decreasing its c/a ratio from 0.826 to 0.802 upon the formation of CeNi₄AlH_4.3. This drastic decrease in the c/a ratio is attributed to an anisotropic lattice expansion along the a-axis, as verified by in situ X-ray diffraction under H₂. The enhanced hydrogen absorption of these alloys is thought to be associated with the preferential situation of hydrogen atoms at interstitial sites located at the centers of octagons as well as a charge transition of Ce ions upon hydrogenation. It is verified that CeNi₄Al after hydrogenation shows high catalytic activity toward propyne hydrogenation: 100% conversion of propyne even at room temperature.