Complex metal hydrides of group 2 and 3 metals are potentially promising materials for on-board hydrogen storage in fuel cell vehicles. However, existing complex hydrides, such as NaAlH₄, are thermodynamically and/or kinetically unsuited for on-board storage. There are a tremendously large number of potential complex hydrides, including destabilized hydrides. Experimental synthesis and testing of new hydrides is extremely time consuming and expensive. Thermodynamic modeling is therefore a critical first-pass screening method needed to identify the most promising materials for further experimental investigation. We show how plane wave density functional theory (DFT) may be used to reliably predict the thermodynamics of new complex metal hydrides. We demonstrate how DFT calculations can be used to efficiently screen hundreds of compounds, eliminating to-date over 300 systems that do not have favorable thermodynamics or adequate hydrogen densities. Furthermore, we have identified about 15 potentially interesting destabilized metal hydride reactions having both favorable thermodynamics and high gravimetric and volumetric storage densities.

The kinetics of hydrogenation and dehydrogenation are issues that are just as important as the thermodynamics, but kinetics of condensed phase reactions, especially those involving solid-solid phase transitions, are extremely difficult to model from first principles. We have initiated a study of reaction kinetics in hydride-related systems by considering surface reactions. Our calculations help explain the experimentally observed difficulty of hydrogenating Mg₂Si, an otherwise promising destabilized metal hydride. We have found that Mg₂Si is very susceptible to oxidation, which completely passivates the surface toward hydrogen dissociation. We are also studying surface reactions on three different alkali metal hydrides. We present DFT calculations for the adsorption and dissociation energetics of H₂O and O₂ on the surfaces of LiH, NaH, and KH. We discuss how these reactions poison the surfaces.