Hydrogen release from solid state NaBH₄

The aim of this work is the study of the H₂ release from the thermal decomposition reaction of sodium tetrahydroboride (NaBH₄) in the solid state. Computational and experimental methods have been used. NaBH₄ thermodynamic properties at room temperature and its energy of formation from NaH and BH₃ have been theoretically studied using a first-principles approach. Results obtained from ab initio calculations compared well with thermodynamic properties assessed by the CALPHAD method. The effect of annealing on phase transformations in NaBH₄ has been followed with various experimental analytical techniques and the structure of the samples, after suitable thermal treatments, has been analysed by X-ray diffraction. A multi-step reaction has been observed after annealing, in both isothermal and scanning conditions. The conditions for H₂ release from NaBH₄ in the solid state have been clarified combining experimental and computational results.