Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7716782 | International Journal of Hydrogen Energy | 2014 | 10 Pages |
Abstract
Reactive ball milling (RBM) technique was employed to synthesize ultrafine powders of MgH2, using high energy ball mill operated at room temperature under 50 bar of a hydrogen gas atmosphere. The MgH2 powders obtained after 200 h of continuous RBM time composed of β and γ phases. The powders possessed nanocrystalline characteristics with an average grain of about 10 nm in diameter. The time required for complete hydrogen absorption and desorption measured at 250 °C was 500 s and 2500 s, respectively. In order to improve the hydrogenation/dehydrogenation kinetics of as synthesized MgH2 powders, three different types of nanocatalysts (metallic Ni, Nb2O5 and (Ni)x/(Nb2O5)y) were utilized with different weight percentages and independently ball milled with the MgH2 powders for 50 h under 50 bar of a hydrogen gas atmosphere. The results showed that the prepared nanocomposite MgH2/5Ni/5Nb2O5 powders possessed superior hydrogenation/dehydrogenation characteristics, indexed by low values of activation energy for β-phase (68 kJ/mol) and γ-phase (74 kJ/mol). This nanocomposite system showed excellent hydrogenation/dehydrogenization behavior, indexed by the short time required to uptake (41 s) and release (121 s) of 5 wt% H2 at 250 °C. At this temperature the synthesized nanocomposite powders possessed excellent absorption/desorption cyclability of 180 complete cycles. No serious degradation on the hydrogen storage capacity could be detected and the system exhibited nearly constant absorption and desorption values of +5.46 and â5.46 wt% H2, respectively.
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Physical Sciences and Engineering
Chemistry
Electrochemistry
Authors
M. Sherif El-Eskandarany, Ehab Shaban, Ahmed Al-Shemmiri,