Thermodynamic Stability of Hydrogen Storage Material Zn(BH4)2: First-Principles Study

摘要

Ab initio calculations using density functional theory were performed to establish the most stable crystal structure of Zn(BH4)2. It was found to be of orthorhombic structure in the space group of Pmc2_1 with lattice parameters of a = 4.118 A, b = 4.864 A, c = 7.916 A. It is an insulating material having a band gap of around 3.529 eV. Our calculations showed nearly tetrahedral shape of the BH4 complex with B-H bond lengths d_(B-H)=1.20-1.25 A and H-B-H bond angles θ_(H-B-H)= 104.16-120°. The reaction enthalpy was also found for the reaction Zn(BH4)2 = Zn + 2B + 4H2(g) to be 59.31 kJ/mol of H2 including zero point energy at OK.