An investigation of the hydrogen desorption from Nd2Fe17Hx and Dy2Fe17Hx compounds by differential scanning calorimetry

• We investigate the hydrogen desorption from R2Fe17Hx (R = Nd and Dy) compounds.
• The heat of hydrogen desorption is 29.2 ± 0.8 kJ mol H−1 for both R2Fe17Hx family compounds.
• Hydrogen desorption activation energies have been determined from DSC.
• Thermodynamical data are analysed for both heavy (Dy) and light (Nd) rare earth elements in the light of the precise knowledge of the crystal structure.

Hydrogen desorption from R2Fe17Hx (R = Nd and Dy) compounds with x ≤ 5 has been studied using differential scanning calorimetry (DSC). Overall hydrogen binding energies are very similar in both systems regardless their different crystal structures. The heat of hydrogen desorption is 29.2 ± 0.8 kJ mol H−1 for both R2Fe17Hx family compounds. Desorption activation energies are also very close: 78 ± 8 kJ and 79 ± 4 kJ mol H−1 for Nd and Dy-containing compounds, respectively. The rare earth nature modifies however the local interaction between hydrogen and the intermetallic compound. For Nd, H-atoms occupy two non-equivalent and well-defined energy sites whereas a unique energy site with a broad energy distribution is detected for Dy. This peculiar behavior is discussed in terms of the different structural properties of the light (Nd) and heavy (Dy) rare-earth R2Fe17 compounds.