This invention relates to fuel cells and, in particular, to improvements in the catalyst used in internal reforming fuel cells.
The fuel cell is emerging as a viable device for efficiently converting chemical energy of a fuel directly to electrical energy. In a fuel cell, energy conversion is accomplished via electrochemical reactions involving a fuel and an oxidant taking place within the fuel cell. Although the fuel cell is an efficient converter of chemical energy to direct electrical power, the part of the fuel energy which is not converted to electricity in the fuel cell is available as heat. This by-product heat is removed to achieve isothermal operation. Water is another by-product of the fuel cell reactions.
The fuel used in practical and commercially viable fuel cells is hydrogen. Hydrogen is produced by steam reforming of a hydrocarbon fuel in an endothermic reforming reaction. Therefore, it requires a supply of both water and heat from an external source. In a conventional fuel cell power plant, an external reformer is used (see, e.g., U.S. Pat. No. 3,909,299) to produce hydrogen for the fuel cell. To improve overall efficiency of energy conversion, the fuel cell by-product heat is utilized in the reformer. This requires heat exchange equipment and hot piping.
Because the fuel cell reaction produces water and heat and the reforming reaction consumes water and heat, a technique for combining both of these reactions within the fuel cell, called internal reforming, has been proposed (see, e.g., U.S. Pat. Nos. 4,182,795 and 4,877,693). In the internal reforming fuel cell, the reforming reaction is carried out in situ in the fuel cell anode compartment so that the fuel cell produced water and heat is directly available at the reforming reaction site. This requires that the fuel cell anode compartment be loaded with an appropriate reforming catalyst.
The fuel cell anode compartment is usually a planar structure. This structure typically comprises a separator plate for isolating fuel from the neighboring cell oxidant stream, an anode for providing fuel cell reaction sites, and a current collector for conducting of electrons from the anode to the cathode of a next neighboring cell and for providing a flow path for the gaseous fuel stream.
As indicated above, the anode compartment of the internally reforming fuel cell is loaded with the reforming catalyst. Various methods for loading reforming catalyst in the fuel cell anode compartment have been used (see, e.g., U.S. Pat. No. 4,788,110). The reforming catalysts are usually available in different shapes such as tablet, pellet, rod, ring and spherical. In the conventional methods, the reforming catalyst of the pellet and/or the tablet shape are loaded into the pockets of the corrugated current collector.
The aforesaid catalyst loading methods suffer from several drawbacks. Uniform loading of the catalysts in the direction normal to the gas flow as well as in the direction of the gas flow is difficult to achieve resulting in fuel flow maldistribution, in the fuel cell. Handling of small catalyst particles during assembly is cumbersome and is difficult to automate and, therefore, is not cost effective. Also, cell-to-cell loading uniformity is difficult to achieve and catalyst shifting and spilling during assembly, handling, transportation, and during operation may be difficult to avoid.
Furthermore, it is important that any contact between the catalyst and the anode be avoided during operation to prevent catalyst deactivation by electrolyte adsorption. In the most advanced designs to date, this has been achieved only if the fuel cells are situated vertically. Angular or the horizontal positions are not permitted because the catalyst particles in an inclined cell will shift and/or may come in contact with the anode and adsorb electrolyte resulting in deactivation and loss of reforming activity.
It is, therefore, an object of the present invention to provide a catalyst assembly for an internal reforming fuel cell which avoids these disadvantages.
It is a further object of the present invention to provide a catalyst assembly for an internal reforming fuel cell in which the catalyst assembly is easily assembled in the fuel cell.
It is yet a further object of the present invention to provide a catalyst assembly for an internal reforming fuel cell in which the catalyst assembly has minimum displacement and permits vertical and horizontal orientations of the fuel cell.