Thermodynamics and performance of the Mg-H-F system for thermochemical energy storage applications
© 2018 the Owner Societies. Magnesium hydride (MgH 2 ) is a hydrogen storage material that operates at temperatures above 300 °C. Unfortunately, magnesium sintering occurs above 420 °C, inhibiting its application as a thermal energy storage material. In this study, the substitution of fluorine f...
| Main Authors: | , , , , , , , |
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| Format: | Journal Article |
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R S C Publications
2018
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| Online Access: | http://purl.org/au-research/grants/arc/LP120101848 http://hdl.handle.net/20.500.11937/65723 |
| _version_ | 1848761190296059904 |
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| author | Tortoza, Mariana Humphries, Terry Sheppard, Drew Paskevicius, Mark Rowles, Matthew Sofianos, M. Veronica Aguey-Zinsou, K Buckley, Craig |
| author_facet | Tortoza, Mariana Humphries, Terry Sheppard, Drew Paskevicius, Mark Rowles, Matthew Sofianos, M. Veronica Aguey-Zinsou, K Buckley, Craig |
| author_sort | Tortoza, Mariana |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | © 2018 the Owner Societies.
Magnesium hydride (MgH 2 ) is a hydrogen storage material that operates at temperatures above 300 °C. Unfortunately, magnesium sintering occurs above 420 °C, inhibiting its application as a thermal energy storage material. In this study, the substitution of fluorine for hydrogen in MgH 2 to form a range of Mg(H x F 1-x ) 2 (x = 1, 0.95, 0.85, 0.70, 0.50, 0) composites has been utilised to thermodynamically stabilise the material, so it can be used as a thermochemical energy storage material that can replace molten salts in concentrating solar thermal plants. These materials have been studied by in situ synchrotron X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, temperature-programmed-desorption mass spectrometry and Pressure-Composition-Isothermal (PCI) analysis. Thermal analysis has determined that the thermal stability of Mg-H-F solid solutions increases proportionally with fluorine content, with Mg(H 0.85 F 0.15 ) 2 having a maximum rate of H 2 desorption at 434 °C, with a practical hydrogen capacity of 4.6 ± 0.2 wt% H 2 (theoretical 5.4 wt% H 2 ). An extremely stable Mg(H 0.43 F 0.57 ) 2 phase is formed upon the decomposition of each Mg-H-F composition of which the remaining H 2 is not released until above 505 °C. PCI measurements of Mg(H 0.85 F 0.15 ) 2 have determined the enthalpy (?H des ) to be 73.6 ± 0.2 kJ mol -1 H 2 and entropy (?S des ) to be 131.2 ± 0.2 J K -1 mol -1 H 2 , which is slightly lower than MgH 2 with ?H des of 74.06 kJ mol -1 H 2 and ?S des = 133.4 J K -1 mol -1 H 2 . Cycling studies of Mg(H 0.85 F 0.15 ) 2 over six absorption/desorption cycles between 425 and 480 °C show an increased usable cycling temperature of ~80 °C compared to bulk MgH 2 , increasing the thermal operating temperatures for technological applications. |
| first_indexed | 2025-11-14T10:27:44Z |
| format | Journal Article |
| id | curtin-20.500.11937-65723 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T10:27:44Z |
| publishDate | 2018 |
| publisher | R S C Publications |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-657232021-01-19T02:47:02Z Thermodynamics and performance of the Mg-H-F system for thermochemical energy storage applications Tortoza, Mariana Humphries, Terry Sheppard, Drew Paskevicius, Mark Rowles, Matthew Sofianos, M. Veronica Aguey-Zinsou, K Buckley, Craig © 2018 the Owner Societies. Magnesium hydride (MgH 2 ) is a hydrogen storage material that operates at temperatures above 300 °C. Unfortunately, magnesium sintering occurs above 420 °C, inhibiting its application as a thermal energy storage material. In this study, the substitution of fluorine for hydrogen in MgH 2 to form a range of Mg(H x F 1-x ) 2 (x = 1, 0.95, 0.85, 0.70, 0.50, 0) composites has been utilised to thermodynamically stabilise the material, so it can be used as a thermochemical energy storage material that can replace molten salts in concentrating solar thermal plants. These materials have been studied by in situ synchrotron X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, temperature-programmed-desorption mass spectrometry and Pressure-Composition-Isothermal (PCI) analysis. Thermal analysis has determined that the thermal stability of Mg-H-F solid solutions increases proportionally with fluorine content, with Mg(H 0.85 F 0.15 ) 2 having a maximum rate of H 2 desorption at 434 °C, with a practical hydrogen capacity of 4.6 ± 0.2 wt% H 2 (theoretical 5.4 wt% H 2 ). An extremely stable Mg(H 0.43 F 0.57 ) 2 phase is formed upon the decomposition of each Mg-H-F composition of which the remaining H 2 is not released until above 505 °C. PCI measurements of Mg(H 0.85 F 0.15 ) 2 have determined the enthalpy (?H des ) to be 73.6 ± 0.2 kJ mol -1 H 2 and entropy (?S des ) to be 131.2 ± 0.2 J K -1 mol -1 H 2 , which is slightly lower than MgH 2 with ?H des of 74.06 kJ mol -1 H 2 and ?S des = 133.4 J K -1 mol -1 H 2 . Cycling studies of Mg(H 0.85 F 0.15 ) 2 over six absorption/desorption cycles between 425 and 480 °C show an increased usable cycling temperature of ~80 °C compared to bulk MgH 2 , increasing the thermal operating temperatures for technological applications. 2018 Journal Article http://hdl.handle.net/20.500.11937/65723 10.1039/c7cp07433f http://purl.org/au-research/grants/arc/LP120101848 http://purl.org/au-research/grants/arc/LP150100730 http://purl.org/au-research/grants/arc/LE0775551 http://purl.org/au-research/grants/arc/FT160100303 R S C Publications fulltext |
| spellingShingle | Tortoza, Mariana Humphries, Terry Sheppard, Drew Paskevicius, Mark Rowles, Matthew Sofianos, M. Veronica Aguey-Zinsou, K Buckley, Craig Thermodynamics and performance of the Mg-H-F system for thermochemical energy storage applications |
| title | Thermodynamics and performance of the Mg-H-F system for thermochemical energy storage applications |
| title_full | Thermodynamics and performance of the Mg-H-F system for thermochemical energy storage applications |
| title_fullStr | Thermodynamics and performance of the Mg-H-F system for thermochemical energy storage applications |
| title_full_unstemmed | Thermodynamics and performance of the Mg-H-F system for thermochemical energy storage applications |
| title_short | Thermodynamics and performance of the Mg-H-F system for thermochemical energy storage applications |
| title_sort | thermodynamics and performance of the mg-h-f system for thermochemical energy storage applications |
| url | http://purl.org/au-research/grants/arc/LP120101848 http://purl.org/au-research/grants/arc/LP120101848 http://purl.org/au-research/grants/arc/LP120101848 http://purl.org/au-research/grants/arc/LP120101848 http://hdl.handle.net/20.500.11937/65723 |