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.