Effect of SrFe12O19 nanopowder on the hydrogen sorption properties of MgH2

Abstract

In this study, the effects of different amounts (5, 10, 15, 20 and 50 wt%) of an SrFe₁₂O₁₉ nanopowder, doped into MgH₂ and prepared by the ball milling method, were investigated with the aim of improving hydrogen storage properties. The results indicated that 10 wt% SrFe₁₂O₁₉ showed the best performance, compared with un-doped MgH₂, in terms of the onset dehydrogenation temperature. The desorption temperature of MgH₂ + 10 wt% SrFe₁₂O₁₉ decreased to about 270 °C compared to the 350 °C and 420 °C for as-milled and as-received MgH₂, respectively. The de/rehydrogenation kinetics of MgH₂ also improved after doping with SrFe₁₂O₁₉. Increasing the doping amount of SrFe₁₂O₁₉ to 15, 20 and 50 wt% brought about negative effects, such as lower capacity and slower sorption rates. From Kissinger plot differential scanning calorimetry, the apparent activation energy was 133.31 kJ mol⁻¹ for as-milled MgH₂ and 114.22 kJ mol⁻¹ for MgH₂ + 10 wt% SrFe₁₂O₁₉, indicating that SrFe₁₂O₁₉ addition decreased the activation energy for hydrogen desorption of MgH₂. From the X-ray diffraction results, it is believed that the formation of new phases of Fe, MgFe₂O₄ and SrO during the dehydrogenation process might be responsible for the catalytic effects which further enhanced the hydrogen storage properties of MgH₂.