dimensional), problems with catalysts and the relatively high gas permeability of the membrane, leading to a depolarization of the electrodes [3]. The current efficiency is influenced by shunt currents—relatively high in the mobile KOH system—and by gas permeation through the electrolyte, which is much higher for the polymer membrane than for the alkaline electrolyte. The current efficiency of the PEM fuel cell has been taken from literature data [3]. The operational efficiency includes the power required for peripheral components like pumps, separators and the fan. The PEM fuel cell requires a fan for water removal via the oxygen loop, and therefore has the highest auxiliary power demand (leading to low operational efficiency).
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