Tuning the hydrogen desorption of Mg(BH${}_4$)${}_2$ through Zn alloying

Abstract

We study the effect of Zn alloying on the hydrogen desorption properties of Mg(BH${}_4$)${}_2$ using $abinitio$ simulations. In particular, we investigate formation/reaction enthalpies/entropies for a number of compounds and reactions at a wide range of temperatures and Zn concentrations in Mg${}_{1-x}$Zn${}_x$(BH${}_4$)${}_2$. Our results show that the thermodynamic stability of the resulting material can be significantly lowered through Zn alloying. We find that e.g. the solid solution Mg${}_{2/3}$Zn${}_{1/3}$(BH${}_4$)${}_2$ has a reaction enthalpy for the complete hydrogen desorption of only 25.3 kJ/mol H${}_2$$-$a lowering of 15 kJ/mol H${}_2$ compared to the pure phase and a corresponding lowering in critical temperature of 123 K. In addition, we find that the enthalpy of mixing is rather small and show that the decrease in reaction enthalpy with Zn concentration is approximately linear.

arXiv comment12 pages including appendix and references, 2 figures

References in corpus (5)

• Van der Waals Density Functional for General Geometries
• Van der Waals density functional: Self-consistent potential and the nature of the van der Waals bond
• Ab initio study on the effects of transition metal doping of Mg2NiH4
• Van der Waals interactions in the ground state of Mg(BH4)2 from density functional theory
• Thermodynamic stability of alkali metal/zinc double-cation borohydrides at low temperatures

Cited by in corpus (2)

• Decomposition mechanisms in metal borohydrides and their ammoniates
• Suppressing diborane production during the hydrogen release of metal borohydrides: The example of alloyed Al(BH${}_4$)${}_3$