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Highlights: [•] Samples of commercial Mg were processed by ECAP and Cold-Rolling. [•] ECAPed cross-section samples were oriented in the (101) direction. [•] Rolled samples were oriented in the (002) direction favorable to the hydrogenation. [•] The best H-sorption results were obtained for rolled with less texture toward (101). [ABSTRACT FROM AUTHOR]

Abstract: Mg is a promising candidate material for hydrogen storage but its application is restricted by high sorption temperatures and slow sorption kinetics. Major efforts have focused on overcoming these two obstacles. Alloying, nanostructuring and/or catalysts, particularly at low temperatures, have considerably improved the hydrogenation kinetics of Mg powders. Further investigation is still desirable to reach the same properties for bulk materials because hydrogen desorption in bulk Mg-based systems still remains at a critical high temperature, and this, represents a major obstacle to their practical application. The aim of this work was to evaluate the reduction in desorption temperature and the increase in hydrogenation kinetics of bulk Mg-based composites in response to the following variables: particle/grain size, density of defects, the use of iron as catalyst, volume modifications, and the presence of carbon as a pore-confining element. We compared the behavior of 2Mg–Fe powder mixtures produced by high-energy ball milling processed as follows to produce bulk samples: (i) hot extrusion of 2Mg–Fe with extrusion ratio of 5/1 (S-1), (ii) hot compaction of 2Mg–Fe (S-2), and (iii) hot compaction of ball-milled 2Mg–Fe+5%C, all processed at 300°C (S-3). The samples were activated and subsequently hydrogenated at 15bar, sample S-1 for 24h and sample S-2 and S-3 for 5h. After the hydrogenation treatments, the complex hydride Mg2FeH6 was formed in all the conditions. Desorption temperatures varied according to the processing conditions and the results indicated that porosity was an important factor, as it was the addition of carbon, which accelerated the desorption kinetics. [Copyright &y& Elsevier]

Abstract: Mg-based nanocrystalline alloys or nanocomposites are promising materials for hydrogen storage in the solid state, which is a more effective and safer storage medium than pressurized or liquefied hydrogen. Among the many Mg-based hydrides of interest for hydrogen storage, Mg2FeH6 is in a special position due to its relatively high gravimetric capacity of 5.5% and excellent volumetric density of 150kgH2/m3. This work involved a study of the synthesis and processing of Mg-based alloys of this type, produced by high-energy ball milling and hot extrusion. A mixture of 2Mg–Fe was prepared by high-energy ball milling under argon gas. The resulting powder was cold-pressed to produce cylindrical pre-forms, which were then extruded and the sorption properties were analyzed in a microbalance and in a Sieverts apparatus. Phase formation, microstructural evolution, desorption temperatures, and hydrogen storage capacity were analyzed by X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry, and thermogravimetric techniques. The results showed that Mg2FeH6 was formed and the hydrogen reaction was reversible. SEM observations indicate a microstructure composed of nanosized grains in the range of 30–80nm inside particles of about 50μm, and Mg2FeH6 formed mainly at the particle interfaces. The desorption temperature started at about 225°C, reaching a maximum at 440°C with low capacity of absorption, indicating low absorption/desorption kinetics, probably due to bulk diffusion limitations. [ABSTRACT FROM AUTHOR]