Influence of different amounts of FeCl3 on decomposition and hydrogen sorption kinetics of MgH2

In the present work, the hydrogen storage properties of MgH2-X wt.% FeCl3 (X = 5, 10, 15 and 20) are investigated experimentally. It is found that the MgH2 + 10 wt.% FeCl3 sample exhibits the best comprehensive hydrogen storage properties, in terms of the onset dehydrogenation temperature, the hydrogen amounts de/reabsorbed as well as the relative de/rehydrogenation rates. The onset dehydrogenation temperature of the 10 wt.% FeCl3-doped MgH2 sample is reduced by about 90 °C compared to the as-milled MgH2, and the sorption kinetics measurements indicate that the FeCl3-doped sample displays an average dehydrogenation rate 5–6 times faster than that of the undoped MgH2 sample. Higher levels of doping introduce negative effects, such as lower capacity and slower absorption/desorption rates compared to samples with lower FeCl3 doping levels. The apparent activation energy for hydrogen desorption is decreased from 166 kJ•mol−1 for as-milled MgH2 to 130 kJ•mol−1 by the addition of 10 wt.% FeCl3. It is believed that the improvement of the MgH2 sorption properties in the MgH2/FeCl3 composite is due to the catalytic effects of the in-situ generated Fe species and MgCl2 that are formed during the heating process.