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Fundamental Studies of Diffusion and Reactions in Hydrogen Storage Materials

  • Author(s): Van de Walle, Chris G
  • Peles, Amra
  • Janotti, Anderson
  • Wilson-Short, Gareth
  • et al.
Abstract

Hydrogen can serve as an energy carrier in a carbon-neutral system of energy production and use [1,2], but adequate hydrogen storage materials are still lacking in spite of many decades of investigations. In addition to being reversible and meeting stringent weight % and volume criteria, candidate materials must exhibit favorable kinetics for hydrogen uptake and release. The fundamental mechanisms of the (de)hydrogenation process have remained elusive to date. We have initiated a study of the relevant reactions, resulting in an identification of the dominant defect species involved in hydrogen transport in non-metallic hosts. While the concepts discussed here are general, we illustrate them with detailed first-principles results for sodium alanate. We identify hydrogen-related point defects as the essential mediators of hydrogen transport. A novel finding of this work is that the defects are positively or negatively charged, and hence their formation energies are Fermi-level dependent−an important feature that has not been recognized in past studies. This dependence enables us to explain why small amounts of transition-metal additives drastically alter the kinetics of dehydrogenation.

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