Stability and Decomposition of NaBH₄

We investigate the stability and hydrogen desorption of NaBH 4 . Dynamic pcT (pressure, concentration, and temperature) measurements under constant hydrogen flows are used to determine thermodynamic parameters of reaction. From the van’t Hoff equation the enthalpy and entropy of reaction, −108 ± 3 kJ mol −1 of H 2 and 133 ± 3 J K −1 mol −1 of H 2 released, are obtained, respectively. This corresponds to a decomposition temperature of T dec = 534 ± 10 °C at 1 bar of H 2 . The decomposition thereby occurs in one step; i.e., only one plateau is visible in the pressure composition isotherms. Elemental Na is identified as the major solid component in the residue by X-ray diffraction. The experimental results are discussed on the basis of theoretical calculations using the density functional theory approach. Starting from the optimized structure of the cubic α-phase of NaBH 4, we discuss possible decomposition routes involving elemental Na and B as well as Na−H and Na−B binary compounds as residual products.