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solid oxide fuel cell
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| A solid oxide fuel cell consists of a non-porous
metal oxide electrolyte (typically zirconium oxide) sandwiched between
an anode (negatively charged electrode) and a cathode (positively
charged electrode). The processes that take place in the fuel cell
are as follows: 1. Hydrogen fuel is channeled through field flow plates
to the anode on one side of the fuel cell, while oxygen from the air
is channeled to the cathode on the other side of the cell. 2. At the
cathode, a catalyst causes electrons from the electrical circuit to
combine with oxygen to create negatively charged oxygen ions. 3. The
negatively charged oxygen ions flow through the electrolyte to the
anode. 4. At the anode, the catalyst causes the hydrogen to react
with the oxygen ions forming water and free electrons. 5. The negatively
charged electrons cannot flow through the electrolyte to reach the
positively charged cathode, so they must flow through an external
circuit, forming an electrical current. 6. At the cathode, the electrons
combine with oxygen to create negatively charged oxygen ions, and
the process repeats. |
Solid oxide fuel cells operate at very high temperatures – around 1,000°C (1,830°F). High-temperature operation removes the need for precious-metal catalyst, thereby reducing cost. It also allows SOFCs to reform fuels internally, which enables the use of a variety of fuels and reduces the cost associated with adding a reformer to the system.
SOFCs are also the most sulfur-resistant fuel cell type; they can tolerate several orders of magnitude more of sulfur than other cell types. In addition, they are not poisoned by carbon monoxide (CO), which can even be used as fuel. This property allows SOFCs to use gases made from coal.
High-temperature operation has disadvantages. It results in a slow startup and requires significant thermal shielding to retain heat and protect personnel, which may be acceptable for utility applications but not for transportation and small portable applications. The high operating temperatures also place stringent durability requirements on materials. The development of low-cost materials with high durability at cell operating temperatures is the key technical challenge facing this technology.
Scientists are currently exploring the potential for developing lower-temperature SOFCs operating at or below 800°C that have fewer durability problems and cost less. Lower-temperature SOFCs produce less electrical power, however, and stack materials that will function in this lower temperature range have not been identified.
Related category
• FUEL CELLSSource: U.S. Department of Energy
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