Journal of Alloys and Compounds 417 (2006) 39–44 27 Al and 1 H MAS NMR and 27 Al multiple quantum studies of Ti-doped NaAlH 4 Julie L. Herberg a, ∗ , Robert S. Maxwell a , Eric H. Majzoub b a Lawrence Livermore National Laboratories, Livermore, CA 94551, USA b Sandia National Laboratories, Livermore, CA 94551, USA Received 16 August 2005; received in revised form 11 September 2005; accepted 26 September 2005 Available online 4 November 2005 Abstract Previous X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) studies on Ti-doped NaAlH 4 revealed the reaction products of two heavily doped (33.3at.%) samples. This investigation revealed that nano-crystalline or amorphous Al 2 O 3 forms from the possible coordination of aluminum with the oxygen atom of the furan ring system from added tetrahydrofuran (THF) in solvent-mixed samples, and that TiAl 3 forms in mechanically-milled samples [E.H. Majzoub, J.L. Herberg, R. Stumpf, R.S. Maxwell, J. Alloys Compd. 394 (2005) 265], indicating the importance of understanding the processing conditions of these potentially important hydrogen storage materials. The present paper provides a more sophisticated NMR investigation of these materials and resolves some unanswered questions. On heavily doped (33.3 at.%) solvent-mixed samples, 27 Al Magic Angle Spinning (MAS) NMR 27 Al multiple quantum MAS (MQMAS) indicates the presence of an oxide layer of Al 2 O 3 on the surfaces of potentially bulk nanocrystalline Ti, nanocrystalline TiAl 3 , and/or metallic aluminum. The 1 H MAS NMR data also indicate the possible coordination of aluminum with oxygen atoms in the THF molecules. In addition, the 1 H MAS NMR and 1 H spin-lattice relaxation (T 1 ) measurements are consistent with the presence of TiH 2 . These results are in agreement with recent XAFS measurements indicating both Al and H within the first few coordination shells of Ti in the doped alanate. © 2005 Elsevier B.V. All rights reserved. Keywords: Hydrogen storage; Ti-doped NaAlH 4 ; 27 Al MAS NMR; 27 Al MQMAS NMR 1. Introduction The development of Ti-doped sodium aluminum hydrides has gained attention because of its large weight percentage of hydro- gen (5.5% ideal) compared to interstitial hydrides. The kinetics of the absorption and desorption of H 2 improves dramatically by the addition of transition metal dopants, in the form of Ti-halides such as TiCl 3 [1,2]. However, the mechanism of enhanced ki- netics due to the Ti-dopant in sodium aluminum hydride is still unknown. Recently, we reported on Ti-doped sodium aluminum hy- drides that were completely-reacted (33.3 at.%-doped) with TiCl 3 . These samples were processed in two different ways: one was solvent-mixed and the other was mechanically-milled [1]. The present paper explores the 27 Al and 1 H solid state NMR ∗ Corresponding author. Tel.: +1 925 422 5900 E-mail address: herberg1@llnl.gov (J.L. Herberg). results of these fully-reacted samples in more complete detail. We do not address Ti-catalytic activity, but rather the importance of Ti-containing phases during material preparation. These re- actions and the resultant products are crucial for understanding the conditions under which these materials can be most effec- tively doped for large scale applications. The ease of solution doping over mechanical milling is clear, however, the products of the doping process in THF, as presented in this paper, sug- gest that other solvents may be more suitable for large scale production. In this paper, we performed 27 Al MAS NMR, 27 Al MQ MAS NMR, 1 H MAS NMR, and 1 H spin-lattice relaxation measure- ments (T 1 ) on fully-reacted samples that were either dissolved in THF or mechanically-milled. THF is known to coordinate strongly with transition metals in solution, and we show that this results in the formation of Al 2 O 3 in heavily doped samples. Our results indicate that Al and H coordinate with the Ti in so- lution mixed samples, in agreement with recent XAFS studies on lightly doped (a few at.%) NaAlH 4 [3]. 0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.09.047