Formation reaction of Mg2FeH6: effect of hydrogen absorption/desorption kinetics

Asselli, Alexandre Augusto Cesário; Filho, Walter José Botta; Huot, Jacques

doi:10.1590/s1516-14392013005000122

Cited by 10 publications

(4 citation statements)

References 14 publications

(23 reference statements)

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“…The heat of reaction for hydrogenation and dehydrogenation of Mg 2 FeH 6 was found to be D R H = 77 kJ mol -1 H 2 [12]. Since both Mg 2 FeH 6 and MgH 2 phases are present during the reaction [13,14], the D R H = 74 kJ mol -1 H 2 for MgH 2 [11] should also be taken into account for calculation. Since the exact phase composition was not known, the results are given in the range between a lower value using the heat of reaction for pure MgH 2 and the upper value using the heat of reaction for pure Mg 2 FeH 6 .…”

Section: Heat Storage and Heat Release Experimentsmentioning

confidence: 99%

Demonstration of Mg2FeH6 as heat storage material at temperatures up to 550 °C

et al. 2016

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The storage of heat at high temperatures, which can be used to generate electricity after sunset in concentrating solar power plants, is one of the most challenging technologies. The use of metal hydride could be one possibility to solve the problem. During the endothermic heat storage process, the metal hydride is decomposed releasing hydrogen, which then can be stored. During the exothermic reaction of the metal with the hydrogen gas, the stored heat is then released. Previous research had shown that Mg and Fe powders can be used at temperatures up to 550°C for heat storage and shows excellent cycle stability over hundreds of cycles without any degradation. Here, we describe the results of testing of a tube storage tank that contained 211 g of Mg and Fe powders in 2:1 ratio. Twenty-three dehydrogenations (storage) and 23 hydrogenations (heat release) in the temperature range between of 395 and 515°C and pressure range between 1.5 and 8.6 MPa were done. During the dehydrogenation, 0.41-0.42 kWh th kg-1 of heat based on material 2 Mg/Fe can be stored in the tank. After testing, mainly Mg 2 FeH 6 was observed and small amounts of MgH 2 and Fe metal can be detected in the hydride samples. This means that the heat storage capacity of the system could be further increased if only Mg 2 FeH 6 is produced during subsequent cycles.

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Section: Heat Storage and Heat Release Experimentsmentioning

confidence: 99%

Demonstration of Mg2FeH6 as heat storage material at temperatures up to 550 °C

et al. 2016

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“…Therefore, the formation of both β-MgH 2 and Mg 2 FeH 6 phases are thermodynamically favorable at 400 °C under 2.5 MPa of H 2 . We recently showed that under conditions where the formation of both hydrides are thermodynamically possible, Mg 2 FeH 6 is preferentially formed from a two-step reaction where β-MgH 2 plays the role of Mg 2 FeH 6 precursor [27,28]. Despite being thermodynamically less stable than Mg 2 FeH 6 , β-MgH 2 is firstly formed due to its faster kinetics of formation [27].…”

Section: Kinetics Of Hydrogen Absorption and Desorptionmentioning

confidence: 99%

“…We recently showed that under conditions where the formation of both hydrides are thermodynamically possible, Mg 2 FeH 6 is preferentially formed from a two-step reaction where β-MgH 2 plays the role of Mg 2 FeH 6 precursor [27,28]. Despite being thermodynamically less stable than Mg 2 FeH 6 , β-MgH 2 is firstly formed due to its faster kinetics of formation [27]. Afterward, Mg 2 FeH 6 nucleates between β-MgH 2 and α-Fe phases, and grows with a columnar morphology in a slow diffusional process [28].…”

Section: Kinetics Of Hydrogen Absorption and Desorptionmentioning

confidence: 99%

“…Some authors reported that Mg 2 FeH 6 is formed from the metallic elements [2,4,19,24], while others claimed that MgH 2 is the Mg 2 FeH 6 precursor [9,20,21,25,26]. Recently, we studied the transformation of phases during hydrogen absorption of a ball milled 2Mg + Fe mixture [27]. We showed that MgH 2 is formed with very fast kinetics, and then, in a much slower reaction, MgH 2 reacts with Fe to form Mg 2 FeH 6 .…”

Section: Introductionmentioning

confidence: 97%

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Investigation of Effect of Milling Atmosphere and Starting Composition on Mg2FeH6 Formation

Asselli

Huot

2014

Metals

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Abstract:In this study we investigated the synthesis and the hydrogen storage properties of Mg 2 FeH 6 . The complex hydride was prepared by ball milling under argon and hydrogen atmosphere from 2Mg + Fe and 2MgH 2 + Fe compositions. The samples were characterized by X-ray powder diffraction and scanning electron microcopy. Kinetics of hydrogen absorption and desorption were measured in a Sievert's apparatus. We found that the milling atmosphere plays a more important role on Mg 2 FeH 6 synthesis than the starting compositions. Ball milling under hydrogen pressure resulted in smaller particles sizes and doubled the yield of Mg 2 FeH 6 formation. Despite the microstructural differences after ball milling, all samples had similar hydrogen absorption and desorption kinetics. Loss of capacity was observed after only five cycles of hydrogen absorption/desorption.

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Real‐Time Monitoring of the Dehydrogenation Behavior of a Mg₂FeH₆–MgH₂ Composite by In Situ Transmission Electron Microscopy

Kim

Fadonougbo

Bae

et al. 2022

Adv Funct Materials

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Herein, real-time observations of dehydrogenation of a Mg 2 FeH 6 -MgH 2 composite by means of in situ transmission electron microscopy (TEM) with advanced spatial (≈0.8 Å) and temporal (25 frames s −1 ) resolution are reported. Careful control and systematic variations of the reaction temperature and electron dose rate enable detailed and direct visualization of the characteristic decomposition of Mg 2 FeH 6 into Mg and Fe, which occurs on the nanometer scale under optimal experimental conditions defined to minimize the electron-beam-driven Mg oxidation and dehydrogenation that take place in TEM. First, the formation of nanostructured fine Fe clusters in Mg metal and their growth via coalescence during dehydrogenation are verified. Additionally, fine monitoring of the in situ diffraction patterns acquired during decomposition of the composite allows separate evaluations of the desorption kinetics of the two coexisting phases, which confirm the synergetic dehydrogenation of this dual-phase system. It is envisioned that these findings will provide useful guidelines for reducing the gaps between nanoscale and bulk-scale research and designing hydrogen sorption conditions to enable efficient operation of a solid-state hydrogen storage system.

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Formation reaction of Mg2FeH6: effect of hydrogen absorption/desorption kinetics

Cited by 10 publications

References 14 publications

Demonstration of Mg2FeH6 as heat storage material at temperatures up to 550 °C

Demonstration of Mg2FeH6 as heat storage material at temperatures up to 550 °C

Investigation of Effect of Milling Atmosphere and Starting Composition on Mg2FeH6 Formation

Real‐Time Monitoring of the Dehydrogenation Behavior of a Mg₂FeH₆–MgH₂ Composite by In Situ Transmission Electron Microscopy

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Formation reaction of Mg2FeH6: effect of hydrogen absorption/desorption kinetics

Cited by 10 publications

References 14 publications

Demonstration of Mg2FeH6 as heat storage material at temperatures up to 550 °C

Demonstration of Mg2FeH6 as heat storage material at temperatures up to 550 °C

Investigation of Effect of Milling Atmosphere and Starting Composition on Mg2FeH6 Formation

Real‐Time Monitoring of the Dehydrogenation Behavior of a Mg2FeH6–MgH2 Composite by In Situ Transmission Electron Microscopy

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Real‐Time Monitoring of the Dehydrogenation Behavior of a Mg₂FeH₆–MgH₂ Composite by In Situ Transmission Electron Microscopy