Solid Oxide Fuel Cell Technology

High temperature solid oxide fuel cell (SOFC) uses a hard ceramic electrolyte instead of a liquid and operates at temperatures up to 1,000 degrees C. A mixture of zirconium oxide and calcium oxide form a crystal lattice, though other oxide combinations have also been used as electrolytes. The solid electrolyte is coated on both sides with specialized porous electrode materials. At these high operating temperature, oxygen ions (with a negative charge) migrate through the crystal lattice. When a fuel gas containing hydrogen is passed over the anode, a flow of negatively charged oxygen ions moves across the electrolyte to oxidize the fuel. The oxygen is supplied, usually from air, at the cathode. Electrons generated at the anode travel through an external load to the cathode, completing the circuit and supplying electric power along the way. Generating efficiencies can range up to about 60 percent. In one configuration, the SOFC consists of an array of tubes. Another variation includes a more conventional stack of disks. Since SOFCs operate at such high temperatures, a reformer is not required to extract hydrogen from the fuel. Some demonstration units have capacities up to 100 kilowatts.