Boosting the de-/rehydrogenation properties of MgH2 with the addition of BaCoF4

Abstract

In this study, the effect of barium cobalt fluoride (BaCoF4) on the de-/rehydrogenation properties of magnesium hydride (MgH2) was investigated for the first time. It was found that the 10 wt% BaCoF4-added MgH2 sample began to release hydrogen at 265 °C, which was about 75 °C lesser than the post-milled MgH2. Regarding dehydrogenation kinetic, the BaCoF4-added MgH2 composite rapidly released hydrogen 50 times faster than post-milled MgH2. The BaCoF4-added MgH2 sample released approximately 5.0 wt% within 30 min of dehydrogenation at 300 °C, whereas the post-milled MgH2 only released approximately 0.1 wt% hydrogen. Furthermore, the BaCoF4-added MgH2 sample obtained a hydrogen absorption capacity of 6.4 wt% in 5 min at 300 °C. In comparison, post-milled MgH2 absorbed only 5.5 wt% hydrogen in 5 min at 300 °C. Moreover, the addition of 10 wt% of BaCoF4 reduced the activation energy for the hydrogen desorption of MgH2 to 100.0 kJ/mol compared with 130.0 kJ/mol for the post-milled MgH2. The addition of BaCoF4 is believed to improve the hydrogen storage properties of MgH2 through the formation of the CoF3 and Ba or Ba-containing species during the dehydrogenation process, which plays a substantial role in lowering the desorption temperature and improves the sorption kinetics of MgH2.