An investigation of the hydrogen desorption from Nd_2Fe _(17)H_x and Dy_2Fe_(17)H_x compounds by differential scanning calorimetry

摘要

Hydrogen desorption from R_2Fe_(17)H_x (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 R _2Fe_(17)H_x 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.