Dynamic in situ X-ray diffraction of catalyzed alanates

The discovery that hydrogen can be reversibly absorbed and desorbed from NaAlH4 by the addition of catalysts has created an entirely new prospect for lightweight hydrogen storage. NaAlH4 releases hydrogen through the following set of decomposition reactions: NaAlH4 --> (1)/(3)(alpha-Na3AlH6) + (2)/Al-3 + H-2 --> NaH + Al + (3)/H-2(2) These decomposition reactions as well as the reverse recombination reactions were directly observed using time-resolved in situ X-ray powder diffraction. These measurements were performed under conditions similar to those found in PEM fuel cell operations (hydrogen absorption, 50-70degreesC, 10-15 bar H-2; hydrogen desorption, 80-110degreesC, 5-100 mbar H-2). Catalyst doping was found to dramatically improve kinetics under these conditions. In this study, the alanate was doped with a catalyst by dry ball-milling NaAlH4 with 2 mol.% solid TiCl3 X-ray diffraction clearly showed that TiCl3 reacts with NaAlH4 to form NaCl during the doping process. Partial desorption of NaAlH4 was even observed to occur during the catalyst doping process. Published by Elsevier Science B.V.