Synthesis of Zn2TiO4 via solid-state method as a promising additive for dehydrogenation properties of NaAlH4

Abstract

Sodium alanate (NaAlH4) has a high capacity for hydrogen, making it one of the most promising materials for storing hydrogen, but its slow dehydrogenation kinetics make it less practical. In this study, to speed up NaAlH4's dehydrogenation rate and improve its dehydrogenation properties, Zn2TiO4 synthesised through the method of solid-state was milled with NaAlH4. Zn2TiO4 additive remarkably reduces the initial temperature for the NaAlH4 to release hydrogen and fastens the dehydrogenation rate of NaAlH4. After adding different weight percentages of Zn2TiO4, the initial temperature for the NaAlH4 to release hydrogen was reduced to approximately 150 °C-165 °C (first dehydrogenation stage) and 190 °C-224 °C (second dehydrogenation stage), which is lower by 40 °C-55 °C than as-milled NaAlH4. The NaAlH4–Zn2TiO4 system also fastened the dehydrogenation rate by 10–15 times more than as-milled NaAlH4. The dehydrogenation activation energies of the NaAlH4 were also downshifted to 86.2 kJ/mol (first dehydrogenation stage) and 92.4 kJ/mol (second dehydrogenation stage) with the addition of Zn2TiO4. The activation energies were reduced by 26% (first dehydrogenation stage) and 24% (second dehydrogenation stage) illustrating the superior effect of Zn2TiO4. X-ray diffraction analysis discovered that TiZn2 and AlTi3 formed during the heating process are responsible for the enhanced performance of NaAlH4.