Fuel cells, which generate electricity by converting chemical energy to electrical energy via an electrochemical reaction that uses, as raw materials, an oxidizing gas such as oxygen or air, and a reducing gas (a fuel gas) such as hydrogen or methane or a liquid fuel such as methanol are attracting considerable attention as one possible countermeasure to environmental problems and resource problems. In a fuel cell structure, a fuel electrode (an anode catalyst layer) on one surface of an electrolyte film and an air electrode (a cathode catalyst layer) on the other surface are provided facing one another across the electrolyte film, a diffusion layer is provided on the outside of each of these catalyst layers that sandwich the electrolyte film, and these diffusion layers are then sandwiched between separators that include raw material supply passages, and electricity is then generated by supplying the raw materials such as hydrogen and oxygen to each of these catalyst layers.
Tubular fuel cells are one known example of this type of fuel cell. As shown in the cross-sectional view along the lengthwise direction of the tube shown in FIG. 7, a typical structure for a tubular fuel cell includes an inner electrode 10, a first catalyst layer 12, an electrolyte layer 14, a second catalyst layer 16, an external coil 18, and a resin seal 20. FIG. 8 shows a cross-sectional view along the line A-A shown in FIG. 7. As shown in FIG. 8, the inner electrode 10, the first catalyst layer 12, the electrolyte layer 14, and the second catalyst layer 16 are laminated in sequence from the inside out, and are formed as substantially concentric circular cylinders.
In FIG. 7, the end portion of the inner electrode 10 is designed to be exposed externally. This is advantageous when a plurality of cells are used to form a module by connecting together the inner electrodes and external coils respectively of a plurality of tubular fuel cells in a parallel arrangement, and is particularly useful in those cases when the inner electrodes are connected in parallel.
Methods of fabricating the type of tubular fuel cell shown in FIGS. 7 and 8 in which, for example, the first catalyst layer 12, the electrolyte layer 14, and the second catalyst layer 16 are formed using an extrusion molding method or the like are already known.
For example, Japanese Patent Laid-Open Publication No. 2002-124273 discloses an apparatus and a method wherein a catalyst for the fuel electrode, a solid electrolyte polymer for the electrolyte film, and a catalyst for the air electrode are each converted to a flowable fluid using an appropriate solvent, and integrated extrusion molding is then conducted to form a bonded material comprising, from the inside out, a layer of each of the fuel electrode catalyst, the solid electrolyte polymer, and the air electrode catalyst.
However, in conventional techniques, in order to produce a tubular fuel cell similar to that shown in FIG. 7, an additional step is required for exposing the end portion of the inner electrode, namely, a step for removing the first catalyst layer, the electrolyte layer, and the second catalyst layer formed on the outer peripheral surface of the inner electrode end portion. Accordingly, there is a possibility of an associated increase in the production costs.