Y-Co binary alloys with superlattice structures: Relationship between hydrogenation cyclic stability and crystal structures of hydride phases

This study investigates the cyclic stability and structural changes of hydride phases in YCo 3 , Y 2 Co 7 and Y 5 Co 19 superlattice compounds. After 110 absorption–desorption cycles, hydrogen capacity retention rates are 78 %, 85 %, and 99 % retention rates from the first cycle, respectively. X-ray diffraction (XRD) analysis reveals that the full-hydride phases retain the original alloy structures. Peak broadening in XRD patterns is observed in Y 5 Co 19 hydrides at both the first (phase III) and 111th cycle (phase VI). The CaCu 5 -type-cell in YCo 3 and Y 2 Co 7 hydrides expands by less than half of the MgZn 2 -type cell. In Y 5 Co 19 H 14.9 at the 111th cycle, the CaCu 5 -type I cell exhibits greater expansion, while the CaCu 5 -type II cell contracts slightly compared to the MgZn 2 -type cell. Similarly, in YCo 3 H 3.0 and Y 2 Co 7 H 6.4 at the 111th cycle, the CaCu 5 -type cell expands by less than half of the MgZn 2 -type cell. • Hydrogen absorption-desorption in YCo 3 , Y 2 Co 7 , Y 5 Co 19 with superlattices examined. • Y 5 Co 19 retained 99 % capacity after 110 cycles, YCo 3 78 % and Y 2 Co 7 85 %. • Y 5 Co 19 hydride phase showed greater CaCu 5 -type cell expansion than MgZn 2 -type cell. • Cyclic hydrogen behavior influenced by MgZn 2 -type to CaCu 5 -type cell ratio in lattice. • High cyclic stability of Y 5 Co 19 makes it a strong candidate for durable H 2 storage.