Hydrogen diffusion in MgH2 and NaMgH3 via concerted motions of charged defects

The transport properties of hydrogen in metal hydrides are crucial to the kinetics of H-2 storage in these materials. We use first principles calculations to identify the defects that are relevant for H transport in MgH2 and NaMgH3. In both materials, the physically relevant defects are charged and H diffusion is dominated by mobility of negatively charged interstitial H. Moreover, the diffusion of these species occurs via concerted "interstitialcy" mechanisms with low energy barriers. Our results indicate that any examination of H diffusion in light metal hydrides must consider the concerted diffusion of charged defects.