Large-scale screening of metal hydrides for hydrogen storage from first-principles calculations based on equilibrium reaction thermodynamics

Abstract

Systematic thermodynamics calculations based on density functional theory-calculated energies for crystalline solids have been a useful complement to experimental studies of hydrogen storage in metal hydrides. We report the most comprehensive set of thermodynamics calculations for mixtures of light metal hydrides to date by performing grand canonical linear programming screening on a database of 359 compounds, including 147 compounds not previously examined by us. This database is used to categorize the reaction thermodynamics of all mixtures containing any four non-H elements among Al, B, C, Ca, K, Li, Mg, N, Na, Sc, Si, Ti, and V. Reactions are categorized according to the amount of H₂ that is released and the reaction's enthalpy. This approach identifies 74 distinct single step reactions having that a storage capacity >6 wt.% and zero temperature heats of reaction 15 ≤ ΔU₀ ≤ 75 kJ mol⁻¹ H₂. Many of these reactions, however, are likely to be problematic experimentally because of the role of refractory compounds, B₁₂H₁₂-containing compounds, or carbon. The single most promising reaction identified in this way involves LiNH₂/LiH/KBH₄, storing 7.48 wt.% H₂ and having ΔU₀ = 43.6 kJ mol⁻¹ H₂. We also examined the complete range of reaction mixtures to identify multi-step reactions with useful properties; this yielded 23 multi-step reactions of potential interest.