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

This study investigates the microstructure and hydrogen absorption properties of a rare-earth high-entropy alloy, YGdTbDyHo. Results indicate that the YGdTbDyHo alloy has a microstructure of equiaxed grains, with the alloy elements distributed homogeneously. Upon hydrogen absorption, the phase structure of the high-entropy alloy changes from the solid solution with HCP structure to the high-entropy hydride with FCC structure, without any secondary phase precipitated. The alloy demonstrates a maximum hydrogen storage capacity of 2.33 H/M at 723 K, with enthalpy change (ΔH) of -141.09 kJ·mol-1 and entropy change (ΔS) of -119.14 J·mol-1·K-1. The kinetic mechanism of hydrogen absorption is hydride nucleation and growth, with an apparent activation energy (Ea) of 20.90 kJ·mol-1. Without any activation, YGdTbDyHo alloy can absorb hydrogen quickly (180 s at 923 K) with nearly no incubation period observed. The reason for 2.33 H/M is suggested that the hydrogen atoms occupy both the tetrahedral and octahedral interstice. These results demonstrate the potential application of High-Entropy Alloys (HEAs) as a high-capacity hydrogen storage material with a large H/M ratio, which can be used in the deuterium storage field.