Solid oxide electrolyser cell electrolysers

SOEC electrolysers operate at very high temperatures (700-850°C) at atmospheric pressure. Using heat energy as well as electricity, they split water into hydrogen and oxygen. The high temperatures increase the overall electrical efficiency of SOEC electrolysers and enable the use of non-precious metals as catalysts. SOEC electrolysers can also electrolyse carbon dioxide (CO2) to carbon monoxide (CO) and oxygen. The CO can then be used to produce syngas, a basic building block for the chemical industry. SOEC electrolysers can also be operated in reverse, producing electricity like fuel cells. This functionality increases their hours of operation and keeps them at operating temperature for longer periods. Most current SOEC electrolysers are small, kilowatt-scale demonstration plants, although some projects have already exceeded 1 MW capacity (Neste, 2021). SOEC electrolysers have high capital costs (at more than USD 2 000/kW for 1 MW stacks), although the target for 2050 is to reduce this to less than USD 200/kW.

Considering that SOEC electrolysers are much less flexible than other electrolyser technologies, they are less suited to direct coupling with variable renewable energy production. However, they do have important advantages. Their use of heat in addition to electricity raises their electrical efficiency. Thus, SOEC electrolysers would bring about a significant reduction in overall electricity demand compared with any other electrolyser technology (IRENA, 2020c). In addition, the heat that they require could be supplied by sources such as industrial waste heat streams or concentrated solar power (CSP) plants. This would facilitate the coupling of SOEC electrolysers to heat production technologies. SOEC electrolysers also enable the production of syngas as well as hydrogen, and the potential for reversable operation increases their lifetimes.