A hydrogen electrolyzer uses electricity to split water molecules into hydrogen and oxygen. As zero-carbon hydrogen can be produced if the electrolyzer is powered by wind, solar or nuclear sources, this technology is expected to play a significant role in decarbonizing energy, refining, transportation and other sectors.
Low-temperature electrolyzers use a polymer electrolyte membrane (PEM) or a more porous membrane filled with alkali solution. Both PEM and alkaline electrolyzers operate at a little higher than room temperature and have electrical efficiencies of 65% to 75%.
Solid oxide electrolyzers (SOECs), however, have a ceramic electrolyte and run at higher temperatures, which allows them to operate at 90% efficiency. This higher efficiency requires less electricity consumption, significantly reducing the cost of producing hydrogen.
A SOEC consists of the cathode (the negative electrode), the anode (the positive electrode) and the electrolyte. When a voltage is applied between the cathode and anode, an electrical current is produced, which flows through the cell. As can be seen in the above diagram, water in the form of steam enters the cathode side of the cell. The electrical current drives an electrochemical reaction that splits the water into hydrogen and oxygen.
Source: FuelCell Energy, Inc.
The electrolyte of this cell has a unique property that can transport oxygen ions but is impermeable to hydrogen. As a result, hydrogen is concentrated on the cathode side and exits the cell as pure hydrogen plus some residual steam. The cells are configured into stacks, and multiple stacks are used in the electrolysis system. One key aspect of SOECs is that they do not require noble metal catalysts such as platinum or iridium, avoiding higher costs and critical material supply issues.
