Hydrogen Storage via the Hydrolysis of NaBH₄ Basic Solution:  Optimization of NaBH₄ Concentration

Generation of hydrogen via the hydrolysis of sodium borohydride (NaBH 4 ) solution in the presence of metal catalysts is a promising method for hydrogen storage. The concentration of NabH 4 should be as high as possible in order to improve energy density. On the other hand, NaBO 2 is produced after the hydrolysis of NaBH 4 . When the NaBH 4 concentration is high enough, NaBO 2 will precipitate from the solution, which would block the active sites of the catalysts and bring about the complexity of solution transportation. This paper addressed the issue through thermodynamic modeling. A mathematical model was derived first using the equality of chemical potential of the solute in solution and in its solid state. The parameters in the model were determined using phase-diagram analysis and hydration analysis of the NaBH 4 −NaOH−H 2 O and NaBO 2 −NaOH−H 2 O systems. The optimal concentration of NaBH 4 in the hydrogen-generation system was then calculated and a comparison of the modeling results with experimental data, which were in good agreement, was given.