| Autor: |
Gao, Jinbao, Adelhelm, Philipp, Verkuijlen, Margriet H. W., Rongeat, Carine, Herrich, Monika, van Bentum, P. Jan M., Gutfleisch, Oliver, Kentgens, Arno P. M., de Jong, Krijn P., de Jongh, Petra E. |
| Zdroj: |
The Journal of Physical Chemistry - Part C; 20240101, Issue: Preprints |
| Abstrakt: |
Metal hydrides are likely candidates for the solid state storage of hydrogen. NaAlH4is the only complex metal hydride identified so far that combines favorable thermodynamics with a reasonable hydrogen storage capacity (5.5 wt %) when decomposing in two steps to NaH, Al, and H2. The slow kinetics and poor reversibility of the hydrogen desorption can be combatted by the addition of a Ti-based catalyst. In an alternative approach we studied the influence of a reduced NaAlH4particle size and the presence of a carbon support. We focused on NaAlH4/porous carbon nanocomposites prepared by melt infiltration. The NaAlH4was confined in the mainly 2−3 nm pores of the carbon, resulting in a lack of long-range order in the NaAlH4structure. The hydrogen release profile was modified by contact with the carbon; even for ∼10 nm NaAlH4on a nonporous carbon material the decomposition of NaAlH4to NaH, Al, and H2now led to hydrogen release in a single step. This was a kinetic effect, with the temperature at which the hydrogen was released depending on the NaAlH4feature size. However, confinement in a nanoporous carbon material was essential to not only achieve low H2release temperatures, but also rehydrogenation at mild conditions (e.g., 24 bar H2at 150 °C). Not only had the kinetics of hydrogen sorption improved, but the thermodynamics had also changed. When hydrogenating at conditions at which Na3AlH6would be expected to be the stable phase (e.g., 40 bar H2at 160 °C), instead nanoconfined NaAlH4was formed, indicating a shift of the NaAlH4↔Na3AlH6thermodynamic equilibrium in these nanocomposites compared to bulk materials. |
| Databáze: |
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