Influence of multiple oxide (Cr₂O₃/Nb₂O₅) addition on the sorption kinetics of MgH₂

The influence of multiple additions of two oxides, Cr₂O₃ and Nb₂O₅, as additives on the hydrogen sorption kinetics of MgH₂ after milling was investigated. We found that the desorption kinetics of MgH₂ were improved more by multiple oxide addition than by single addition. Even for the milled MgH₂ micrometric size powders, the high hydrogen capacity with fast kinetics were achieved for the powders after addition of 0.2 mol% Cr₂O₃ + 1 mol% Nb₂O₅. For this composition, the hydride desorbed about 5 wt.% hydrogen within 20 min and absorbed about 6 wt.% in 5 min at 300 °C. Furthermore, the desorption temperature was decreased by 100 °C, compared to MgH₂ without any oxide addition, and the activation energy for the hydrogen desorption was estimated to be about 185 kJ mol^-1, while that for MgH₂ without oxide was about 206 kJ mol^-1.