A study on the effects of K2ZrF6 as an additive on the microstructure and hydrogen storage properties of MgH2

Abstract

In this work, the hydrogenation properties of MgH₂-doped K₂ZrF₆ with X wt% (X = 5, 10, 15 and 20) have been investigated for the first time. Analysis indicated that MgH₂ doped with 10 wt% K₂ZrF₆ is the best composite for the improvement of the hydrogen storage properties of MgH₂. The results showed that the onset desorption temperature after the addition of 10 wt% K₂ZrF₆ was 250 °C, which experienced the reduction of 100 °C and 200 °C from 350 °C and 450 °C for as-milled and as-received MgH₂, respectively. The re/dehydrogenation kinetics also significantly improved compared to the un-doped MgH₂. The results of the Arrhenius plot exhibited that the activation energy for the hydrogen desorption of MgH₂ was reduced from 164 kJ mol⁻¹ to 80 kJ mol⁻¹ after the addition of 10 wt% K₂ZrF₆. Moreover, the X-ray diffraction spectra displayed the formation of new phases of KH and ZrH₂ by the doping of K₂ZrF₆ with MgH₂ after the dehydrogenation and rehydrogenation processes. These two compounds are believed to act as the active species and play a catalytic role in improving the hydrogen storage properties. It is, therefore, concluded that this newly developed catalytic doping system works well in improving the hydrogen sorption properties of MgH₂.