Study on the hydrogen absorption properties of a YGdTbDyHo rare-earth high-entropy alloy

This study investigated the microstructure and hydrogen absorption properties of a rare-earth high-entropy alloy (HEA), YGdTbDyHo. Results indicated that the YGdTbDyHo alloy had a microstructure of equiaxed grains, with the alloy elements distributed homogeneously. Upon hydrogen absorption, the phase structure of the HEA changed from a solid solution with an hexagonal-close-packed (HCP) structure to a high-entropy hydride with an faced-centered-cubic (FCC) structure without any secondary phase precipitated. The alloy demonstrated a maximum hydrogen storage capacity of 2.33 H/M (hydrogen atom/metal atom) at 723 K, with an enthalpy change (ΔH) of −141.09 kJ·mol⁻¹ and an entropy change (ΔS) of −119.14 J·mol⁻¹·K⁻¹. The kinetic mechanism of hydrogen absorption was hydride nucleation and growth, with an apparent activation energy (E_a) of 20.90 kJ·mol⁻¹. Without any activation, the YGdTbDyHo alloy could absorb hydrogen quickly (180 s at 923 K) with nearly no incubation period observed. The reason for the obtained value of 2.33 H/M was that the hydrogen atoms occupied both tetrahedral and octahedral interstices. These results demonstrate the potential application of HEAs as a high-capacity hydrogen storage material with a large H/M ratio, which can be used in the deuterium storage field.