Analysis of Intermediates and Products from the Dehydrogenation of Mg(BH).

The thermodynamic properties of key compounds Mg(BH), MgBH, MgBH, Mg(BH), Mg(BH), and MgBH, proposed to be formed in the release of hydrogen from magnesium borohydride Mg(BH) and the uptake of hydrogen by MgB, have been investigated using solid-state density functional theory (DFT) calculations. More accurate tretment of the cell-size effects with respect to the entropies was also investigated in order to improve the accuracy of the thermodynamic properties of complex borohydrides. We find that the zero-point energy corrections can lower the electronic energies of reaction by 20-30 kJ/(mol H) for these intermediates, while adding the thermal and entropy contibutions results in a total decrease of up to ∼50 kJ/(mol H).