Reversible hydrogen storage properties of NaAlH4 catalyzed with scandium

A systematic study was carried out to compare the reversible hydrogen storage properties of Sc-doped NaAlH4 with Ti-doped NaAlH4. Uncycled and cycled (five times) samples of 1, 2 and 4 mol% Sc-doped NaAlH4 and 4 mol% Ti-doped NaAlH4 were examined. Temperature programmed desorption, constant temperature desorption, and constant temperature cycling results revealed the following: Sc-doped NaAlH4 realized very fast hydrogenation kinetics, reasonably fast dehydrogenation kinetics and minimal hydrogen capacity losses during cycling over a broad range of temperatures without any additives or co-dopants. Sc-doped NaAlH4 also exhibited comparable kinetics and a higher hydrogen storage capacity compared to Ti-doped NaAlH4, depending on the temperature, metal dopant level, and cycling. Sc exhibited this superior performance over Ti perhaps because Sc is an earlier transition metal than Ti. (c) 2006 Elsevier B.V. All rights reserved.