Dehydrogenation associated with Ti catalyst in sodium alanate

Addition of small amount of Ti precursors to sodium alanate has recently been found to substantially improve the kinetics and thermodynamics of hydrogen sorption in sodium alanate. In spite of several attempts, a fundamental understanding of how the catalyst works has remained unattainable. Using first principles methods we have investigated the mechanisms for hydrogen desorption in this material. We conclude that Ti substituted at Al site is energetically most favorable. The small amount of Ti substitution does not introduce large lattice distortion. The Ti atom serves as a magnet that continues to attract nearby H atoms as the nearest ones are successively desorbed. The number of Al atoms near to the Ti site remains at four upon hydrogen desorption when Ti is substituted at the Al site. These results provide important new insight into the design of future catalysts for hydrogen storage materials.