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Naji, M. |
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Motta, Antonella |
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Aletan, Dirar |
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Mohamed, Tarek |
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Ertürk, Emre |
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Taccardi, Nicola |
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Kononenko, Denys |
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Petrov, R. H. | Madrid |
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Alshaaer, Mazen | Brussels |
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Bih, L. |
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Casati, R. |
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Muller, Hermance |
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Kočí, Jan | Prague |
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Kalteremidou, Kalliopi-Artemi | Brussels |
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Azam, Siraj |
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Ospanova, Alyiya |
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Blanpain, Bart |
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Ali, M. A. |
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Popa, V. |
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Rančić, M. |
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Ollier, Nadège |
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Azevedo, Nuno Monteiro |
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Landes, Michael |
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Rignanese, Gian-Marco |
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Pottmaier, Daphiny
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article
Structure and thermodynamic properties of the NaMgH3 perovskite
Abstract
<p>One of the bottlenecks in the implementation of a hydrogen economy is the development of storage materials that can uptake high content of H<sub>2</sub> and release it within a suitable temperature and pressure range. Among the proposed hydride systems, the perovskite NaMgH<sub>3</sub> is receiving increasing attention, not only as the Mg ternary based hydride with the highest hydrogen gravimetric (6 wt %) and volumetric density (88 g L<sup>-1</sup>) but also as a stable hydride likely to be formed in the transformation reactions of mixed hydrides. However, there is a large scatter in the literature for both the structure of the NaMgH<sub>3</sub> compound and the thermodynamics of the hydrogenation/dehydrogenation processes. In this paper a critical review of the literature data, supported by a new set of experimental (in situ synchrotron X-ray diffraction, infrared spectroscopy, high-pressure differential scanning calorimetry, pressure composition isotherms) and theoretical data is presented. The influence of ball milling on the microstructure is studied in the NaMgH <sub>3</sub> in comparison to NaH and MgH<sub>2</sub>. The infrared spectrum of NaMgH<sub>3</sub> compound, assigned by calculated and experimental results, is characterized by vibrational regions around 1100 and 600 cm<sup>-1</sup>. In situ synchrotron X-ray diffraction measurements show the desorption reaction of NaMgH<sub>3</sub> into NaH and Mg at about 673 K under 0.2 MPa H<sub>2</sub>, and the successive reabsorption of NaH and Mg back to NaMgH<sub>3</sub> at 623 K under 0.5 MPa H<sub>2</sub>. From high-pressure differential calorimetry, it was measured a formation enthalpy of 141 kJ/mol f.u for NaMgH<sub>3</sub> compound. It was confirmed the possible reaction of NaH with Mg with observation of NaMgH<sub>3</sub> formation in 1.0 MPa H<sub>2</sub>. Finally, this work provides a thermodynamic description of the NaMgH<sub>3</sub> phase by a critical assessment of the available information using the CALPHAD approach and the equilibrium pressure-temperature phase diagram is presented.</p>