Sodium borohydride (NaBH 4 ) is attractive as a fuel for fuel-cell electric vehicles (FCEVs) and fuel-cell hybrid electric vehicles because of its high energy density. We proposed and constructed a high-density hydrogen generation system that generates a large amount of hydrogen by hydrolysis of powdery NaBH 4 . However, our ability to conduct long driving tests was restricted by the low hydrogen generation rate at the start of the proposed system, particularly under low temperature. To overcome this problem, we added a citric acid solution catalyst at the start, thereby increasing the rate of hydrogen generation by a factor of 25 compared with the case of using a conventional nickel catalyst. In addition, we confirmed that using such a rapid hydrogen generation system had little effect on the power generation characteristics of a 100-W fuel cell, and we succeeded in conducting our driving tests of a FCEV fueled by powdery NaBH 4 .
The authors have proposed and developed a hydrogen generation system for fuel cell vehicle, which can generate large amount of hydrogen by hydrolysis of powdery sodium tetrahydroborate (NaBH 4 ). This system is referred to as the "STEP system" (Sodium TEtrahydroborate Power system) in this paper. However, the required amount of the hydrogen to supply to the fuel cell widely varies according to the output power of the fuel cell. Moreover, it is difficult to control the amount of the hydrogen generated by the STEP system because hydrolysis is chemical reaction. Thus, it is necessary to simulate the chemical reaction in the STEP system under various conditions in order to investigate a pressure control method. Therefore, in this research, a simulation model of hydrogen generation has been developed. In addition, in order to evaluate the simulation model, analytical data obtained from the models are compared with the experimental results.
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