Hydrogen generation from aqueous acid-catalyzed hydrolysis of sodium borohydride

In this study, the hydrogen feed from both Ru-catalyzed and organic acid-catalyzed hydrolysis of NaBH₄ was studied in terms of hydrogen generation rate and integrated PEMFC performance. Hydrogen feed generated from the conventional Ru-catalyzed hydrolysis of NaBH₄ caused a drastic loss of PEMFC performance. It was found that the presence of sodium ion in hydrogen feed was a main factor that increased the interfacial resistance of fuel cell and, consequently, reduced the performance. Acid-catalyzed hydrolysis with powder form of NaBH₄ was adopted in order to minimize the detrimental effect of sodium ion. The hydrogen feed from acid-catalyzed hydrolysis was quite dry so that even water vapor, the carrier of sodium ion, was not detected after condensation of hydrogen feed. It was confirmed by the several experiments that the hydrogen release rate can be controlled by varying the injection rate and concentration of aqueous acid. Various organic acids were employed in the production of hydrogen and found that acidity, acid type and chemical structure are also important factors on hydrolysis of NaBH₄. The performance from the integrated acid-catalyzed hydrogen generation system with PEMFC was quite stable and no significant loss was observed contrary to that from the integrated Ru-catalyzed hydrogen generation system-PEMFC test. This result also clarified that the detrimental effect of sodium ion could be removed by minimizing the water vapor in this manner. Based on the experiment of acid-catalyzed hydrolysis, a small-scale hydrogen-generating device was designed and fabricated, from which hydrogen release was controlled by the acid concentration and injection rate of aqueous acid solution.