A thermodynamic assessment of the decomposition and rehydrogenation of o1-Ba(BH4)2 based on DFT calculations and correlation functions

Abstract

In this study, an estimate is given for the enthalpy of formation at 298.15 K for the room temperature phase of barium boranate, o1-Ba(BH₄)₂, based on correlations between well known enthalpies of formation of boranates and the corresponding values of the respective metal perchlorates and bromides as well as the Pauling electronegativity. A new procedure for estimating the absolute entropy at 298.15 K using metal bromides is presented as well. To evaluate this method, the absolute entropy value at 298.15 K was calculated from the Gibbs free energy function of o1-Ba(BH₄)₂. The Gibbs free energy function and corresponding heat capacity values between 5 K and 700 K were calculated applying density functional theory (DFT) and statistical thermodynamics using the quasi-harmonic approach. Furthermore, several thermodynamic calculations regarding possible synthesis reactions and decomposition routes of o1-Ba(BH₄)₂ are discussed.