Hydrogen generation system for fuel cells based on high pressure hydrolysis of solid-state sodium borohydride

Abstract

The aim of this study was to produce sufficient hydrogen for high-power fuel cell applications through acid-accelerated hydrolysis of sodium borohydride (SBH) with liquid water. Liquid hydrolysis of SBH was performed under high temperatures (160–200 ℃) and high pressure (40 bar) conditions. The characteristics of the liquid hydrolysis of SBH were analyzed according to the feed injection rate, reactant temperature, and excess stoichiometric number. In addition, 11B solid NMR spectroscopy was conducted to analyze the composition of the reaction product. In all experimental cases, the conversion of SBH was ≥95%, and a maximum of 6.71 wt% gravimetric hydrogen density was achieved. The experimental results indicated that it is possible to control the rate of hydrogen generation through the feed injection rate. This suggests that hydrogen can be supplied to varying-output fuel cell applications using this system. In addition, as a result of experiments according to the reactant temperature, it was demonstrated that the lower the reactant temperature, the less hydrogen produced, and the greater the unreacted residual SBH. Moreover, when the excess stoichiometric ratio increased, the gravimetric hydrogen density decreased. This reduced the viscosity of the reaction product and the amount of unreacted SBH observed when the reaction was conducted at low reactant temperatures. Therefore, it is possible to consider increasing the excess stoichiometric number for practical purposes.