A melt of a mixture of alkaline carbonates is used as an electrolyte in these fuel cells and their operating temperature ranges between 600-700 °C. The mentioned carbonates form a melt of highly conductive salts.

Expensive catalysts are not required in these fuel cells as internal reforming increases their efficiency, so the fuel doesn't have to be extremely clean. Gas from the steam reforming of fossil fuels or biogas is used as fuel,. air is used as an oxidizing agent. These fuel cells are used in power plants and cogeneration units.