The discovery that hydrogen can be reversibly absorbed and desorbed from NaAlH 4 by the addition of catalysts has created an entirely new prospect for lightweight hydrogen storage. NaAlH 4 releases hydrogen through the following set of decomposition reactions:NaAlH4→ 1 3(α-Na3AlH6)+ 2 3Al+H2→NaH+Al+ 3 2H2These 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, 50–70°C, 10–15 bar H 2 ; hydrogen desorption, 80–110°C, 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 NaAlH 4 with 2 mol.% solid TiCl 3 . X-ray diffraction clearly showed that TiCl 3 reacts with NaAlH 4 to form NaCl during the doping process. Partial desorption of NaAlH 4 was even observed to occur during the catalyst doping process.