Mobile System In the mobile fuel cell both reactant gas lines are dead-ended. The product water and the excess heat are removed via the electrolyte loop and a reconcentrator, as shown in Fig- 6. The water storage tank operates at fuel cell pressure level (4 bar) and is used as an accumulator for the water loop of the reconcentrator. This water loop needs a separate heat exchanger connected to the TCS. In the mobile KOH electrolyzer, the electrolyte is pumped through the anode and cathode compartments of the stack, feeding the process water and removing the product gases and the excess heat on both sides. Hydrogen as well as oxygen has to be removed from the electrolyte by gas/liquid separators (possibly centrifuges). The electrolyte lines are combined behind the separators. Due to incomplete separation, reactant recombiners will be necessary to prevent accumulation of an explosive mixture in the storage tanks. The electrolyte loop requires an accumulator, which equalizes expansion caused by temperature changes and is simultaneously used for concentration sensing for the KOH electrolyte (to control the water feed pump). Performance Comparison The fuel cell performance curves and system efficiencies are summarized in Figs 7 and 8. The immobile KOH fuel cell shows the highest performance whereas the mobile FC has the poorest performance. This is probably due to the relative large, but necessary, electrolyte gap between the electrodes (I-R drop) [1,2]. The reason for the lower PEM fuel cell performance may be the lower real electrode surface (two
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