First-principles study of the formation and migration of native defects in NaAlH4

We present a first-principles study of native defects in NaAlH4. Our analysis indicates that the structure and energetics of these defects can be interpreted in terms of elementary building blocks, which include VAlH4 + , VNa − , VH + , Hi , and H2 i. We also calculate migration barriers for several key defects, in order to compare enthalpies of diffusion to experimentally measured activation energies of desorption. From this, we estimate activation energies for the diffusion of defects and defect pairs. We suggest that VAlH4 + and Hi , or VNa − and VH + , may be responsible for diffusion necessary for desorption. We discuss the possible role of VH + -Hi − complex formation. The values we find are in the range of activation energies reported for catalyzed desorption.