Study of Fe and Fe–based additives upon the sorption properties of the 2LiBH4 + MgH2 ↔2LiH + MgB2 + 4H2 reaction J.A. Puszkiel1,2, F. Karimi1, U. Vainio3, E. Welter3, F.C. Gennari2, P. Arneodo Larochette2, T. Klassen 1, J. Bellosta von Colbe1 and M. Dornheim1 1Institute of Materials Research, Helmholtz–Zentrum Geesthacht, Germany 2Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and Centro Atómico Bariloche, Argentina 3HASYLAB at Deutsches Elektronen-Synchrotron, Germany Motivation Results and Discussion Conclusions E-mails julian.puszkiel@hzg.de; jpuszkiel@cab.cnea.gov.ar References [1] A.S. Pedersen, J. Kjoller, B. Larsen, B. Vigeholm, Int. J. Hydrogen Energy, 8 (3), 205, 1983. [2] J.J. Vajo, S.L. Skeith, F. Mertens, J. Phys. Chem. B, 109, 3719, 2005. [3] N. Ohba; K. Miwa; M. Aoki; T. Noritake; S. Towata; Y. Nakamori; S. Orimo; A. Züttel, Phys. ReV. B, 74, 075110, 2006. [4] Ph. Mauron; F. Buchter; O. Friedrichs; A. Remhof; M. Bielmann; C.N. Zwicky; A. Züttel, J. Phys. Chem. B 2008, 112, 906, 2008. [5] P. Debye et al., J. Appl. Phys., 28, 679, 1957. Due to the beneficial catalytic effect of the Fe and Fe-based additives upon the kinetics of MgH2 and their low cost, they were added to the 2LiBH4 + MgH2 reactive hydride composite (RHC) in order to improve the operative condition at which the RHC uptakes/releases hydrogen. Suitable thermodynamic stability ΔH = 40.5 kJ/mol H2 Tdesorption = 225 ºC at 1 bar High capacity 11.45 wt.% H Sorption kinetic constraints - High Tdesorption > 390 ºC - Two steps desorption kinetic XAFS ASAXS VOLUMETRIC MEASUREMENTS + XRD results show that after milling irreversible phases such as LiCl and LiF are formed. + XANES measurements confirm that the oxidation state of Fe after milling is zero, suggesting that Fe, FeB or/and Fe2B can be present in the as-milled materials. + The of Fe is not persistent upon cycling due to the formation of FeB upon desorption and/or large Fe-based nanoparticles with typical lengths of 10 – 17 nm. The correlation lenghts (ξβ) of the Fe rich phase are between 10 – 17 nm. Random two phase model assumption: Debye–Bueche model [5]. The addition of Fe improves the absorption/desorption times during the first cycle. Irreversible phases such as LiF and LiCl are formed during milling. For all the as-milled material, the oxidation state of Fe is zero. After desorption at 400 ºC and 5.5 bar, FeB was clearly detected. XRD ξα ξβ Hydride phase Fe rich phase ) ( ) , ( ) , ( ) , ( q I E q I E q I E q I M M M Fe Fe Fe       C Bq a q a N r q I A e        2 2 2 2 2 3 2 2 ) 1( 8 ) (     / 1 / 1 / 1   a ) 1 /(      a Helmholtz-Zentrum Geesthacht • Max-Planck-Straße 1 • 21502 Geesthacht • Phone +49 (0)4152 87-0 • Fax +49 (0)4152 87-1403 • www.hzg.dehydrogen.hzg.de Acknowledgements 0 1 2 3 4 5 6 FeB Fe2B Fe 2LiH+MgB2+0.1Fe-Iso 2LiH+MgB2+0.1FeCl3 2LiH+MgB2+0.1FeF3 2LiH+MgB2+0.1Fe  (R).k2 R (Å) RHC after Desorption 0.1 Fe 0.1 Fe-Iso 0.1 FeCl3 0.1 FeF3 As-milled 9.0  0.1 nm 12.4  0.1 nm 14.6  0.3 nm 17.1  0.4 nm First absorption 15.1  0.2 nm 10.3  0.1 nm 11.9  0.1 nm 15.4  0.1 nm First desorption 11.9  0.1 nm 12.3  0.2 nm 14.4  0.2 nm 17.6  1.1 nm 0 2 4 6 8 10 Theoretical capacity 2LiH + MgB2  2LiBH4 + MgH2 wt. % H First absorption at 350 ºC and 50 bar 0 5 10 15 20 10 8 6 4 2 0 2LiBH4 + MgH2 2LiH + MgB2 wt. % H Time (h) First desorption at 400 ºC and 5.5 bar 7100 7120 7140 7160 7180 7200 E (eV) Normalized absorption (a.u.) FeB Fe 2LiH+MgB2+0.1Fe-Iso Fe-Iso 2LiH+MgB2+0.1FeCl3 FeCl3 2LiH+MgB2+0.1FeF3 FeF3 2LiH+MgB2+0.1Fe 7112 eV RHC after MM 0 2 4 6 8 10 Time (h) 2LiH+MgB2+0.05FeCl3 2LiH+MgB2+0.025Fe-Iso Theoretical capacity (wt%) wt. % H 2LiH+MgB2 2LiH+MgB2+0.05Fe wt. % H First absorption at 350 ºC and 50 bar 0 1 2 3 4 5 6 7 0 2 4 6 8 10 Second absorption at 350 ºC and 50 bar 10 8 6 4 2 0 Theoretical capacity (wt%) First desorption at 400 ºC and 5.5 bar 0 5 10 15 20 10 8 6 4 2 0 wt. % H wt. % H Time (h) Second desorption at 400 ºC an