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Figure 38: Schematic Diagram of a PEM electrolysis system
Figure 38 shows the schematic diagram of a PEMEL system.
Figure 38: Schematic Diagram of a PEM electrolysis system
PEMEL can operate at much higher current densities of up to 2 A cm-2, which reduces the operational and overall cost of electrolysis. The thin solid PEM allows the cell to be thinner than the AEL cell. The low gas crossover rate of the PEM yields hydrogen with high purity. Proton transport across the membrane responds quickly to the power input, not delayed by the inertia of a liquid electrolyte. Unlike AEL, PEMEL covers practically the full nominal power density range (10-100%).
c. Anionic Exchange Membrane (AEM) Electrolysis (AEMEL)
The AEMEL cell has the same structure as PEMEL cell but the anionic exchange membrane transports anionslike the hydroxyl ions (OH−) instead of cations like protons (H+) as in the PEMEL. The AEMEL is classified as alkaline electrolysis because the reactions that occur in the electrodes are the same as in the traditional alkaline cells. The AEMEL has no carbonates deposits due to lack of metallic cations, lower ohmic losses because of thinner AEM, cheaper because AEM is less expensive than PEM and no concentrated KOH solution, making it easier to install and operate.
In addition, due to its basic/alkaline condition, AEMEL does not require platinum-group-metal (PGM) catalysts such as in PEMEL. Instead, transition-metal catalysts had been used successfully, which makes it cheaper. Moreover, it is possible to improve the purity of the gases by operating at high pressure, which is a clear advantage over the traditional alkaline electrolysis. However, one major drawback of the alkaline membrane is its low chemical stability.
