Water Electrolysis Different Methods
It can be defined as supplying electricity between two electrodes to break down water into hydrogen and oxygen. Water electrolysis can be divided into three different types; Alkaline Water Electrolysis (AWE), Proton Exchange Membrane (PEM), and Solid Oxide Electrolyzers SOE). Alkaline electrolysis systems are most common as compared to other systems. SOE is the electrically most efficient but is still under development. PEM electrolysis systems are more efficient than AWE systems but the cost of PEM is too high compared with alkaline electrolyzer systems. The alkaline system has the lowest capital cost as compared to other systems.?
[A] Alkaline Water Electrolyzer (AWE)
Alkaline systems are commonly used in large-scale hydrogen production. The electrolytes are divided into two types; the first electrolyte type is KOH with a weight percent of 20 to 40%. NaOH and NaCl are used as the second type of electrolyte. Hydrogen and hydroxide are generated in the cathode, then hydroxide is moved to the anode part generating oxygen. The efficiencies of this type of electrolyzer are reported as 50 to 60%. Corrosion is the main challenge of this system.?
[B] Proton Exchange Membrane (PEM)
To minimize the corrosion problem of the alkaline systems, the solid polymer membrane has been investigated to use in the PEM fuel cell technology. However, highly pure deionized water is needed for this process. The oxidation of water happens in the anode part by releasing oxygen. The electrons and protons are moved to the cathode part through the membrane, then hydrogen gas is generated at the cathode part. High manufacturing cost is a major challenge of this method.
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[C] Solid Oxide Electrolyzers (SOE)
SOE can be operated at a very high temperature above 1000 C. This system uses both thermal as well as electrical energy for water splitting. The electrolyzer efficiency is increased by increasing the electrolyzer operating temperature. Therefore, SOE has higher operating efficiency as compared to AWE and PEM systems. In SOE, hydrogen is generated at the cathode part and oxide anions are passed to the anode where oxygen will form through the solid electrolyte.?
Specifications of AWE, PEM, and SOE: