Abstract
MgH2 + mischmetal nanostructured composite was synthesized from MgH2 plus 6 and 10 wt% of mischmetal by ball-milling at various times. XRD studies revealed that cerium hydride was produced during the milling in all samples. Sievert test results indicated that the samples containing 6 wt% of mischmetal showed a higher desorption compared with the ones containing 10 wt% of mischmetal. The high amount of cerium hydride in the samples may be the reason, while hydrogen desorption properties decreased by adding more catalyst. Furthermore, BET results showed that the addition of the catalyst to the samples resulted in agglomerate formation in shorter milling times. The agglomerate formation increased with adding more amounts of mischmetal, thus decreasing the hydrogen desorption properties of the composite. The best results were obtained from the 30 h-milled sample containing 6 wt% of catalyst. The on-set desorption temperature of this sample was 100 °C lower than that of as-received MgH2.
Highlights
Supplying energy through fossil fuels creates challenges such as global warming and climate change due to the emission of greenhouse gases, pollution of urban areas, and reduction of oil resources [1]
Considering the lower Gibbs free energy of formation for cerium hydride (− 204.8 kJ/mol H2) in comparison with MgH2 (− 75 kJ/mol H2), it seems that cerium reacted with MgH2 during high-energy ball-milling according to Eq 3 and formed cerium hydride [23]
According to the SEM images of MgH2-10 wt% of mischmetal milled for 20 and 30 h in Fig. 12, the mean particle size of the 20 h-milled sample increased in comparison with the M gH2-6 wt% of mischmetal milled for the same time
Summary
Supplying energy through fossil fuels creates challenges such as global warming and climate change due to the emission of greenhouse gases, pollution of urban areas, and reduction of oil resources [1]. The storage of hydrogen in the form of reversible metal hydrides is the main alternative for low-capacity methods such as storage under pressure or in liquid form at low temperatures. Extensive research on magnesium and its alloys for use as hydrogen storage has been carried out due to its high storage capacity and low price [3]. The main disadvantages of MgH2, as a hydrogen storage medium, are its high hydrogen desorption temperature, slow kinetics of hydrogen absorption, and high tendency to react with oxygen [6]. These problems can be solved by methods such as mechanical milling and catalyst addition
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