2nd May 2012 - 10:18 AM
The fuel cells with ceramic electrolyte named SOFC (solid oxide fuel cell) are a credible alternative to the hydrogen fuel cells.
The operations of these fuel cells are:
- the oxygen in air is reduced at the cathode by electrons that arrive from the external circuit,
- the oxygen ions negatively charged cross the electrolyte made of a solid oxide,
- at the anode, the fuel reformed in the form of hydrogen and carbon monoxide is oxidized by oxygen ions, the released electrons go in the external circuit.
The essential element of the SOFC is the electrolyte made of a conducting ceramic. Conduction is provided by the displacement of oxygen ions.
The advantages of SOFC compared to the hydrogen fuel cells are:
- an operation at high temperature that avoids the use of a catalyst,
- the tolerance to carbon monoxide: contrary to hydrogen fuel cell where the carbon monoxide quickly poisons the catalyst of the anode, the SOFC is insensitive to carbon monoxide.
The SOFC has a drawback: sensitivity to sulfur. Sulfur in fuel poisons the metal of the anode. A fuel treatment is necessary to eliminate sulfur.
It is perhaps possible to make the SOFC insensitive to sulfur.
To neutralize the harmful effect of sulfur, I propose the following changes:
- the cyclic inversion cathode/anode,
- the use of an oxidizing flame at cathode.
If sulfur is not removed from fuel, it reacts with the metal of the anode and forms a metal sulfide. The oxidizing flame at the cathode can be generated by the combustion of a small amount of fuel. The great part of oxygen present at the cathode is simply heated by this flame. During the cyclic inversion anode/cathode, the metal sulfide is exposed to the oxidizing flame that should transform it into metal oxide; the formed SO2 is removed with the flue gas. With the following inversion cathode/anode, metal oxide is exposed to hydrogen and carbon monoxide that should reduce it at the metal state.
The oxidizing flame of the cathode requires an increase of fuel consumption in regard of the classical SOFC but the cyclic inversion anode/cathode would avoid the preliminary treatment of the fuel to remove sulfur.