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.