Hydrogen storage via the hydrolysis of NaBH4 basic solution:: Optimization of NaBH4 concentration

Generation of hydrogen via the hydrolysis of sodium borohydride (NaBH4) 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, NaBO2 is produced after the hydrolysis of NaBH4. When the NaBH4 concentration is high enough, NaBO2 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 NaBH4-NaOH-H2O and NaBO2-NaOH-H2O systems. The optimal concentration of NaBH4 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.