Cycling properties of Sc- and Ce-doped NaAlH4 hydrogen storage materials prepared by the one-step direct synthesis method
Introduction
At present the metal-doped NaAlH4 is the only reversible complex metal hydride with high hydrogen content (5.6 wt.%), a decomposition temperature near the working temperature of a PEM fuel cell and potential low prices for the compounds NaH and Al metal, which are the basic materials for the preparation of NaAlH4 [1]. These features are the reasons, that these hydrogen storage materials nowadays are intensively investigated, especially as a potential material for hydrogen supply of PEM fuel cells. To enhance the kinetics of hydrogen desorption and (re)hydrogenation, the reactions must be catalyzed by incorporation of metal containing dopants in the storage material, selected from the transition metals with titanium being the most frequently employed one.
Metal-doped sodium alanate hydrogen storage materials were up to now prepared mainly by the following methods:
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by ball-milling (b.m.) or wet chemical reaction of pre-synthesized NaAlH4 with doping agents [2], [3], [4], [5], [6], [7];
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by “direct synthesis” [8], [9], [10], [11], that is doping by ball-milling or wet chemical reaction of NaH/Al powder mixtures with doping agents and subsequent hydrogenation of doped mixtures under pressure;
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by the “one-step direct synthesis” [12], i.e. simultaneous ball-milling under hydrogen (preferentially under elevated pressure) of NaH/Al powder/doping agent mixtures. Using a commercial ball mill with a telemetric equipment [12], [13] temperature and pressure during the ball-milling reaction can be monitored, thus enabling a direct control of the progress of the ball-milling reaction.
Section snippets
Experimental
Materials doped with Sc and Ce in one step were prepared analogously to the corresponding Ti material according to Eq. (1). Hydrogenation of NaH/Al/Sc(Ce)Cl3 mixtures in the molar ratio of 1:1:0.4 were carried out in a commercial planetary ball mill (Fritsch Pulverisette P7) equipped with a telemetric system for the recording of the temperature and pressure during the milling process [12], [13] at 30–65 °C/85–55 bar of H2 pressure. Hydrogen absorption was completed in 5–6 h (Fig. 1). 1–1.5 g
Results and discussion
During the investigations of cycling properties of the present storage materials it was noted that hydrogenation rates are higher than those of materials prepared by doping of pre-synthesized NaAlH4 with the same dopants ScCl3 or CeCl3. So, for example, the above-mentioned Sc-doped material, Eq. (1), in the cycles 2, 3, 5 and 9 of the present cycle test (Table 1) was hydrogenated at 122–123 °C/105–100 bar. The hydrogenations (Fig. 2) were practically completed in 10–12 min. For comparison, a
Conclusions
According to the relatively simple preparation way, superior cycling properties and outstanding kinetics, the presented Ce-doped NaAlH4 storage material appears to be a good candidate to be used for supplying hydrogen in combination with advanced fuel cells [20]. The storage capacities fall short of the long-term targets for use in mobile applications and cannot be increased above 5.5 wt.% due to the nature of the system, but presently this and related systems seem to come closest to the
Acknowledgements
Support of our research in this field by General Motors Fuel Cell Activities, in addition to the basic funding provided by the Max-Planck Gesellschaft, is gratefully acknowledged.
References (20)
- et al.
J. Alloys Compd.
(2000) - et al.
J. Alloys Compd.
(1999) - et al.
Int. J. Hydrogen Energy
(1999) - et al.
J. Alloys Compd.
(2002) - et al.
J. Alloys Compd.
(1997) - et al.
J. Power Sources
(2007) - et al.
J. Alloys Compd.
(2005) - et al.
J. Alloys Compd.
(2007) - et al.
Phys. Chem. Chem. Phys.
(2007) - et al.
Adv. Mater.
(2003)
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