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  Fuelcell: Solid Oxide Fuel Cells (SOFC)

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Solid Oxide l

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A SOFC uses yttria-stabilised zirconia as its electrolyte, sandwiched between the anode and the cathode. It runs at a temperature of around 1,000°C. The heat produced can be used in cogeneration applications or in a steam turbine to provide more electricity than that generated from the chemical reaction within the fuel cell (a bottoming cycle). A number of different fuels can be used, from pure hydrogen to methane to carbon monoxide, and the nature of the emissions from the fuel cell will vary correspondingly with the fuel mix.


There are three fundamental designs of SOFC:

  • tubular
  • planar
  • monolithic

The first of these was designed by the Westinghouse Electric Corporation and operates with the fuel on the outside surfaces of a bundle of tubes, and the oxidant on the inside, the tube itself being composed of the electrolyte and electrode 'sandwich'.

Planar SOFCs are developed by a number of companies, with Siemens and Fuji Electric two of the leaders. In this case the cells are flat plates bonded together and placed one on top of the other to form a stack. The advantages of this system over the tubular system are its relative ease of manufacture and a lower ohmic resistance of the electrolyte, resulting in reduced energy losses.

Monolithic SOFCs are in a very early stage of design, with the process one of sintering and corrugation of the electrodes and electrolyte to form a honeycomb structure. Basic laboratory tests have been conducted, with results indicating that this form of fuel cell may be one of the most efficient.

For further information contact David Hart (email: firstname.lastname@e4tech.com) from E4tech


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