C. The produced gases are of much better purity and do not require any further separation. The main components of a PEM cell are: membrane, cathode and anode with electrocatalyst (can be platinum, iridium, ruthenium and rodium), bipolar plates that support the transport of liquids at the electrodes and gas diffuser that allows the current pass between the bipolar plates and the electrodes. PEM cells are characterized by low ionic resistance what results in high current densities (>1600 mAcm-2). The following advantages of this electrolysis technology can be distinguished: higher (in comparison to alkaline) efficiency ranging at 55-77 %, ability to work on a reduced load, good control over electical power variations, high purity of product gas, easy maintnance and use. The main disadvantages are: high costs mainly due to expensive membrane, utilization of noble metals as catalysts, lower than alkaline electrolizers life expectancy, low power range up to single megawats.
2.3 Solid oxide electrolysis (SOE)