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.