Tunable hydrogen storage in magnesium-transition metal compounds: first-principles calculations

S. Er, Dhirendra Tiwari, D. Tiwari, Gilles A. de Wijs, G. Brocks

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Abstract

Magnesium dihydride (MgH2) stores 7.7 wt % hydrogen but it suffers from a high thermodynamic stability and slow (de)hydrogenation kinetics. Alloying Mg with lightweight transition metals (TM) (=Sc,Ti,V,Cr) aims at improving the thermodynamic and kinetic properties. We study the structure and stability of MgxTM1−xH2 compounds, x=[0–1], by first-principles calculations at the level of density functional theory. We find that the experimentally observed sharp decrease in hydrogenation rates for x0.8 correlates with a phase transition of MgxTM1−xH2 from a fluorite to a rutile phase. The stability of these compounds decreases along the series Sc, Ti, V, and Cr. Varying the TM and the composition x, the formation enthalpy of MgxTM1−xH2 can be tuned over the substantial range of 0–2 eV/f.u. Assuming however that the alloy MgxTM1−x does not decompose upon dehydrogenation, the enthalpy associated with reversible hydrogenation of compounds with a high magnesium content (x=0.75) is close to that of pure Mg.
Original languageUndefined
Pages (from-to)024105/1-024105/8
Number of pages8
JournalPhysical review B: Condensed matter and materials physics
Volume79
Issue number2
DOIs
Publication statusPublished - 2009

Keywords

  • enthalpy
  • vanadium compounds
  • titanium compounds
  • density functional theory
  • magnesium compounds
  • heat of formation
  • IR-68604
  • hydrogen storage
  • scandium compounds
  • Chromium compounds
  • Ab initio calculations
  • METIS-257190
  • solid-state phase transformations

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