Role of impurities, defects and their complexes on the trapping of hydrogen in bulk aluminum and on the Al(1Â 1Â 1) surface

First principles calculations are performed to explore and quantify the stability of hydrogen in several Al environments including bulk Al and Al(1 1 1) surface, with the possible presence of vacancies and Mg, Cu and Zn impurities as substitutional defects in bulk or in the surface or as adatoms on the surface. In contrast to common statement, we show that hydrogen has a natural propensity to self-organize in bulk Al and demonstrate that vacancies can serve as nucleation centers for this process leading to massive hydrogen accumulation into aluminum. We then discuss the surface adatom defect and observe that it activates molecular hydrogen dissociation enabling further hydride insertion into bulk Al. Finally, we find that Mg, Cu, or Zn isolated impurities do not significantly impact hydrogen trapping indicating that structural defects rather than the local chemistry of isolated impurities are governing hydrogen accumulation in aluminum.