Effect of Na3FeF6 catalyst on the hydrogen storage properties of MgH2

Abstract

The effects of Na₃FeF₆ catalyst on the hydrogen storage properties of MgH₂ have been studied for the first time. The results showed that for the MgH₂ sample doped with 10 wt% Na₃FeF₆, the onset dehydrogenation temperature decreased to 255 °C, which was 100 °C and 162 °C lower than those of the as-milled and as-received MgH₂ sample, respectively. The re/dehydrogenation kinetics were also significantly enhanced compared to the un-doped MgH₂. The absorption kinetics showed that the as-milled MgH₂ only absorbed 3.0 wt% of hydrogen at 320 °C in 2 min of rehydrogenation, but about 3.6 wt% of hydrogen was absorbed within the same period of time after 10 wt% Na₃FeF₆ was added to MgH₂. The desorption kinetics showed that the MgH₂ + 10 wt% Na₃FeF₆ sample could desorb about 3.8 wt% of hydrogen in 10 min at 320 °C. In contrast, the un-doped MgH₂ sample desorbed only 0.2 wt% of hydrogen in the same period of time. The activation energy for the decomposition of the as-milled MgH₂ was 167.0 kJ mol⁻¹, and this value decreased to 75.0 kJ mol⁻¹ after the addition of 10 wt% Na₃FeF₆ (a reduction by about 92.0 kJ mol⁻¹). It is believed that the in situ formation of the active species of NaMgF₃, NaF and Fe during the heating process could enhance the hydrogen storage properties of MgH₂, due to the catalytic effects of these new species.