A kinetics model of hydrogen absorption and desorption in Ti-doped NaAlH4

The kinetics of the hydrogen sorption of Ti-doped direct-synthesized NaAlH4 has been studied by measuring sorption rates at various temperatures and applied pressures. Formation and decomposition rate equations for NaAlH4 and Na3AlH6 are proposed, and pre-exponential factors and activation energies have been calculated for these reactions. These equations were used to calculate alanate decomposition curves. The results fit the experimental data very well. The predictive capabilities of this empirical approach provide a very useful modeling tool for optimizing the performance of the alanates over a range of hydrogen absorption temperatures and pressures. Under a typical hydrogen-loading condition (constant pressure), the optimum temperature for "fast fill" can be determined. (C) 2004 Elsevier B.V. All rights reserved.