Hydrogen content of CeCl 3 -doped sodium alanate powder samples measured in-situ by ATR-FTIR-spectroscopy and gravimetry during desorption

Transcription

1 Hydrogen content of CeCl 3 -doped sodium alanate powder samples measured in-situ by ATR-FTIR-spectroscopy and gravimetry during desorption Ingo Franke, Hans-Dieter Bauer, Birgit Scheppat International Conference on Optical Characterization of Materials , Karlsruhe

2 Overview AiF-Project HYDEMON Hydrogen Storage Alanates for Hydrogen Storage Vibrational Spectroscopy on Alanates FTIR-ATR-Spectroscopy + Gravimetry on Alanates Conclusions Perspective and Visions 2

3 AiF-Project HYDEMON Financial support: AiF Program: FHprofUnt Partners: Nano Energy GmbH, Institut für Fahrzeugkonzepte, Hessisches Zentrum für Qualitätssicherung und Qualitätsmanagement Project duration: 3 years Objective: Construction of a hydrogen storage container with an integrated level sensor

4 Hydrogen Storage Gravimetric energy density Volumetric energy density Hydrogen Gasoline 33,33 kwh/kg 12,7 kwh/kg 0,77 kwh/l (350 bar, 300 K) 8,67 kwh/l Fig. 1: Volumetric and gravimetric storage capacities of different hydrogen storage methods.

5 Alanates for Hydrogen Storage Fig. 2: Volumetric and gravimetric storage capacities of some selected hydrides. A. Züttel, Mater. Today 6 (2003) 24

6 Alanates for Hydrogen Storage Alanates belong to the group of complex hydrides. In contrast to interstitial metal hydrides, hydrogen desorption of complex hydrides involves three different phases (accordingly, to three different configurations). 3,7 wt.% 1,9 wt.% NaAlH 4 <--> 1/3 Na 3 AlH 6 + 2/3 Al + H 2 <--> NaH + Al + 3/2 H 2

7 Alanates for Hydrogen Storage Synthesis by high energy ball milling NaAlH 4 + xcecl 3 Ce-doped NaAlH 4 International Conference on Characterisation of Optical Materials, Karlsruhe Fig. 3: Difference between pure and doped sodium alanate. A. Léon, Hydrogen Technology-Mobile and Portable Applications (2008) 112

8 Vibrational Spectroscopy on Alanates NaAlH 4, tetragonal body centered crystal system. Ionic bond between Na + und [AlH 4 ] -. [AlH 4 ] - tetrahedron with IR-active modes. Asymmetric Al-H stretch vibration [4,5]: 1680, /cm. H-Al-H bending vibration [4,5]: 900, 800, 735, 690 1/cm. Fig. 4: Crystallographic structure of NaAlH 4. 8

9 Vibrational Spectroscopy on Alanates Na 3 AlH 6, monoclinic crystal system. Ionic bond between Na 3+ und [AlH 6 ] 3-. IR-active [AlH 6 ] 3- octahedron. Asymmetric Al-H stretch vibration [4-6]: 1440, /cm. H-Al-H bending vibration [4-6]: 930, 842, 690 1/cm. Fig. 5: : Crystallographic structure of Na 3 AlH 6. 9

10 Vibrational Spectroscopy on Alanates Fully loaded NaAlH 4 phase and the first desorption NaAlH 3 phase show different IR active modes. Thus, each phase is characteristic for a charging level of the alanate. Next step, quantification of the ATR signal. Combination of FTIR-ATR-spectroscopy and gravimetry enable the quantification of the spectroscopic signal. NaAlH 4 <--> 1/3 Na 3 AlH 6 + 2/3 Al + H 2 <--> NaH + Al + 3/2 H 2 10

11 FTIR-ATR-Spectroscopy + Gravimetry on Alanates Fig. 6: Schematic diagram of the measurement scheme. Usual spectroscopic technique for strong absorbing media. No need for a KBr mixture for producing a pellet. Therefore contaminations by moisture could be excluded. Combination with an analytical balance is possible. Housing of the sample in a gas-tight chamber, with inlet/outlet prevent contamination by moisture or air. Inductive heating system for heating the cuvette. Maximum applicable pressure is 11 MPa. 11

12 FTIR-ATR-Spectroscopy + Gravimetry on Alanates Fig. 7: Desorption of hydrogen from CeCl 3 -doped NaAlH 4 at 80 C and a backpressure of 7 kpa. Every measurement point represents a spectrum in Fig.8. Fig. 8: Time sequence of ATR spectra of CeCl 3 -doped NaAlH 4, measured in-situ, showing the transformation to the Na 3 AlH 6 phase at 80 C and at a backpressure of 7 kpa. Time interval between two subsequent spectra is 45 min. 12

13 FTIR-ATR-Spectroscopy + Gravimetry on Alanates Fig. 9: Hydrogen desorption of CeCl 3 -doped Na 3 AlH 6, at 140 C and a backpressure of 7 kpa. Time interval between two subsequent spectra is 45 min. 13

14 FTIR-ATR-Spectroscopy + Gravimetry on Alanates Fig. 10: Gravimetrical data during the hydrogen desorption measurement of CeCl 3 -doped NaAlH 4 at 80 C and a backpressure of 7 kpa. Every measurement point represents a spectrum in Fig.11. Fig. 11: Gravimetrical data during the hydrogen desorption measurement of CeCl 3 -doped NaAlH 4 at 80 C and a backpressure of 7 kpa. Every measurement point represents a spectrum in Fig

15 CONCLUSION FTIR-ATR-spectroscopy and gravimetry reflect the 2- phase hydrogenation mechanism. The spectra of the non-activated and activated sample correspond to each other reproducibility is given. The quantified optical signal could be used as charging level for alanate powder samples. 15

16 OUTLOOK IR-spectroscopic measurements on other hydrogen storage materials. Further ab- and desorption cycles of a powder sample, in order to show the influence of degradation or particle size effects on the optical signal. Kinetic measurements for studying the solid state reaction of NaAlH 4 or other hydrogen storage materials. Furthermore, information about reaction mechanism, rate constants or activation energies could be deduced with this method. 16

17 Thank you for your attention. Literature: [1] L. Schlapbach, A. Züttel, Nature 414, pp , 2001 [2] A. Züttel, Mater. Today 6, pp , 2003 [3] A. Leon, Hydrogen Technology Mobile and Portable Applications, Berlin: Springer Verlag, 2008 [4] S. Gomes, G. Renaudin, H. Hagemann, K. Yvon, M.P. Sulic, CM. Jensen, J. of Alloys and Compounds 390, pp , 2005 [5] S.F. Parker, Coordination Chemistry Reviews 254, pp , 2010 [6] J.C. Bureau, Z. Amri, P. Claudy, J.M. Létoffé, Mat. Res. Bull. 24, pp