Patent Publication Number: US-2012028161-A1

Title: Fuel cell

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation Application of PCT Application No. PCT/JP2010/055256, filed Mar. 25, 2010 and based upon and claiming the benefit of priority from prior Japanese Patent Application No. 2009-096108, filed Apr. 10, 2009, the entire contents of all of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to fuel cells and, more particularly, to a fuel cell in which a liquid fuel is used. 
     BACKGROUND 
     Recently, attempts have been made to use fuel cells as a power sources for portable various types of electronic device, such as notebook computers and cellular phones, in order to allow long hours of use without charging. A fuel cell has the advantages of generating electricity merely by being supplied with fuel and air, and continuing generating electricity for long hours merely by replenishing the fuel. Therefore, a fuel cell having a smaller size would be exceptionally advantageous as a power source for portable electronic devices. 
     A direct methanol fuel cell (DMFC) is a promising candidate as a power source for portable electronic devices, since a DMFC can be formed in a small size and the fuel is easy to handle. 
     Known methods for supplying a DMFC with a liquid fuel include active types such as a gas supply type and liquid supply type, and passive types such as an internal vaporization type, in which a liquid fuel in a fuel container is vaporized inside the cell and supplied to the fuel electrode. 
     Various schemes can be adopted in order to supply the anode (fuel electrode) with fuel. For example, there is a scheme to directly distribute a liquid fuel such as a methanol solution to below an anode conductive layer. In an external vaporization type, methanol, for example, is vaporized outside the fuel cell so as to produce a gaseous fuel, and the gaseous fuel is distributed to below an anode conductive layer. In an internal vaporization type, a liquid fuel such as pure methanol and a methanol solution is contained in a fuel container, and the liquid fuel is vaporized inside the cell and supplied to the anode. 
     Means for supplying the cathode (air electrode) with air as an oxidant include active types in which air is forcibly supplied by a fan or a blower, and spontaneous breathing (passive) types in which air is supplied only by natural distribution of the atmosphere. 
     Of these types, the passive types such as the internal vaporization type have a special advantage in reducing the size of a DMFC. A passive DMFC has been proposed in which a membrane electrode assembly (fuel cell) including a fuel electrode, an electrolyte membrane, and an air electrode, for example, is arranged on a box-shaped fuel container made of resin. The membrane electrode assembly is interposed between an anode conductive layer provided on the fuel electrode side, and a cathode conductive layer provided on the air electrode side. 
     A liquid fuel supplied to a fuel supply through a duct from the fuel container is supplied to an anode gas diffusion layer of the fuel cell via a fuel distribution layer and the anode conductive layer in the original form of the liquid fuel, or in a state in which the liquid fuel and an evaporated fuel into which the liquid fuel has evaporated are mixed. The fuel supplied to the anode gas diffusion layer is diffused in the anode gas diffusion layer and supplied to the anode catalyst layer. When methanol fuel is used as the liquid fuel, an internal reforming reaction of methanol occurs in the anode catalyst layer, as represented by formula (1), as follows: 
       CH 3 OH+H 2 O→CO 2 +6H + +6e −   Formula (1)
 
     When pure methanol is used as the methanol fuel, the methanol is reformed by the internal reforming reaction represented by (1) with water produced in the cathode catalyst layer or water in the electrolyte membrane, or is reformed by another reaction mechanism that does not require water. 
     The electrons (e − ) produced in this reaction are drawn to the outside via the conductive layer, operate a portable electronic device, for example, as electricity, and are then drawn to the cathode. Integrally forming the conductive layer on a fix layer formed of an insulating film, for example, has also been considered. 
     Further, the protons (H + ) produced in the internal reforming reaction represented by formula (1) are drawn to the cathode through the electrolyte membrane. Air is supplied to the cathode as an oxidant gas via a moisturizing layer. The electrons (e − ) and protons (H + ) that have reached the cathode react with atmospheric oxygen in the cathode catalyst layer, which electricity generating reaction yields water, as represented in formula (2), as follows: 
       (3/2)O 2 +6e − +6H + →3H 2 O   Formula (2)
 
     In order to cause the internal reforming reaction to occur smoothly and obtain a high, stable output in the fuel cell, at least a portion of the water (H 2 O) produced in the cathode catalyst layer as represented in formula (2) needs to smoothly undergo the cycle of penetrating the electrolyte membrane, diffusing across the anode catalyst layer, and being consumed in the reaction represented in formula (1). 
     In order to achieve this, a moisturizing layer, which impregnates the water produced in the cathode catalyst layer so as to prevent vaporization, is provided in the vicinity of the cathode, such that the amount of water retained in the cathode catalyst layer becomes greater than the amount of water retained in the anode catalyst layer, and the water produced in the cathode catalyst layer is supplied to the anode catalyst layer via the electrolyte membrane using the osmotic pressure effect. 
     In the above-described fuel cell in which supply of water from the cathode to the anode is facilitated using a moisturizing layer, a large amount of water is constantly retained in the cathode catalyst layer while the fuel cell generates electricity. Continuation of electricity generation in this state over a long time may cause flooding, in which pores of the cathode catalyst layer are blocked by water, and the diffusibility of air in the cathode catalyst layer decreases, thereby decreasing electricity generating properties. 
     The frequent occurrence of flooding is closely associated with the temperature of the cathode of the fuel cell that is generating electricity. When the temperature of the cathode is high, since the steam pressure of water in the cathode catalyst layer is high, the steam easily permeates the moisturizing layer and evaporates into the open air. When the temperature of the cathode is low, on the other hand, since the steam pressure of water is low in the cathode catalyst layer and in the periphery thereof, the steam does not greatly evaporate into the open air, causing flooding to occur easily. 
     In a conventional fuel cell, however, the temperature of the cathode is not necessarily uniform at all areas, and temperature distribution usually occurs in a plane direction (X-Y direction shown in  FIG. 1 ) of the membrane electrode assembly. In particular, in the portion at the border between the cathode catalyst layer and the neighboring space thereof, the steam easily condenses due to a sudden change in temperature. Therefore, flooding easily occurs in the peripheral portion of the cathode catalyst layer, in particular. 
     When air is not supplied smoothly to the cathode, the above-described reaction at the cathode does not occur smoothly, thereby decreasing electricity generating properties. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating a configuration example of a fuel cell according to First example; 
         FIG. 2  illustrates a configuration example of a current collector of the fuel cell according to First example; 
         FIG. 3  illustrates a configuration example of a current collector of a fuel cell according to Second example; 
         FIG. 4  illustrates an example of the result of measuring output voltages of the fuel cells, according to First example, Second example, and First comparative example; 
         FIG. 5  is a cross-sectional view illustrating a configuration example of a fuel cell according to Third example; 
         FIG. 6  illustrates a configuration example of a current collector of the fuel cell according to Third example; 
         FIG. 7  illustrates a configuration example of a current collector of a fuel cell according to Fourth example; 
         FIG. 8  illustrates a configuration example of a current collector of a fuel cell according to Sixth example; and 
         FIG. 9  illustrates an example of the result of measuring output voltages of the fuel cells according to Third to Sixth examples and Second comparative example. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, a fuel cell comprises a membrane electrode assembly including a plurality of anodes, a plurality of cathodes each forming a pair with a corresponding one of said plurality of anodes, an electrolyte membrane interposed between the anodes and the cathodes; a current collector configured to interpose the membrane electrode assembly in between; a fuel supply mechanism arranged on the side of the anodes of the membrane electrode assembly and configured to supply the anodes with a fuel; and a moisturizing layer arranged on the side of the cathodes of the membrane electrode assembly. The current collector includes a slit arranged so as to face a region between the cathodes. 
     Hereinafter, a fuel cell according to an embodiment will be described with reference to the accompanying drawings. A fuel cell according to an embodiment comprises a membrane electrode assembly  10 , including a plurality of anodes (fuel electrodes), a plurality of cathodes (air electrodes), and an electrolyte membrane  15  interposed between the anodes and the cathodes, as shown in  FIG. 1 , for example. 
     Each of the anodes includes an anode gas diffusion layer  12 , and an anode catalyst layer  11  arranged on the anode gas diffusion layer  12 . Each of the cathodes includes a cathode gas diffusion layer  14  and a cathode catalyst layer  13  arranged on the cathode gas diffusion layer  14 . 
     The membrane electrode assembly  10  is interposed by the current collector A. The current collector A includes a cathode conductive layer  17  contacting the cathode gas diffusion layer  14 , an anode conductive layer  16  contacting the anode gas diffusion layer  12 , and a fixing layer  18  configured to fix the cathode conductive layer  17  and the anode conductive layer  16 . 
     A fuel supply mechanism  40  designed to supply the anodes with a fuel is arranged on the anode side of the membrane electrode assembly  10 . A moisturizing layer  21  configured to retain water produced at the cathodes so as to suppress vaporization is arranged on the cathode side of the membrane electrode assembly  10 . 
     According to the fuel cell of the present embodiment, a slit  18 A is provided in the fixing layer  18  so as to face a region between the cathode gas diffusion layer  14  and the cathode catalyst layer  13  (which will be collectively referred to as “cathode”), which are arranged side by side. Hereinafter, examples of the fuel cell according to the present embodiment will be described. 
     FIRST EXAMPLE 
     Hereinafter, a fuel cell according to First example will be described. A perfluorocarbon sulfonic acid solution as a proton-conductive resin, and water and methoxypropanol as a disperse medium are added to carbon black that supports anode catalyst particles (Pt:Ru=1:1), and the carbon black that supports the anode catalyst particles is dispersed so as to prepare paste. 
     The paste thus obtained is applied to a porous carbon paper as the anode gas diffusion layer  12 , thereby obtaining the anode catalyst layer  11  having an approximately rectangular shape. 
     A perfluorocarbon sulfonic acid solution as a proton-conductive resin, and water and methoxypropanol as a disperse medium are added to carbon black that supports cathode catalyst particles (Pt), and the carbon black that supports the cathode catalyst particles is dispersed so as to prepare paste. The obtained paste is applied to a porous carbon paper as the cathode gas diffusion layer  14 , thereby obtaining the cathode catalyst layer  13  having an approximately rectangular shape. In a direction approximately parallel to the X-Y plane, the anode gas diffusion layer  12  and the cathode gas diffusion layer  14  have the same size and shape, and the anode catalyst layer  11  and the cathode catalyst layer  13  applied on the gas diffusion layers  12 ,  14  have the same size and shape as well. 
     A perfluorocarbon sulfonic acid membrane (trade name Nafion® by DuPont) as the electrolyte membrane  15  is arranged between the anode catalyst layer  11  and the cathode catalyst layer  13  prepared as described above, and the anode catalyst layer  11  and the cathode catalyst layer  13  are aligned so as to face each other and hot-pressed, and thereby the membrane electrode assembly  10  is obtained. 
     According to the fuel cell of the present example, as shown in  FIGS. 1 and 2 , the membrane electrode assembly  10  is formed by forming each of the anode gas diffusion layer  12  and the cathode gas diffusion layer  14  in an approximately rectangular outer shape, and hot-pressing the two pairs of anode gas diffusion layers  12  and the two cathode gas diffusion layers  14  so as to be arranged side by side at intervals of 1.5 mm, approximately parallel to one another in the longitudinal direction (Y-direction). 
     After that, the membrane electrode assembly  10  is interposed by the current collector A. The current collector A is formed by integrating the anode conductive layer  16  and the cathode conductive layer  17  including a plurality of openings with the fixing layer  18  including openings with the same shape. Each of the anode conductive layer  16  and the cathode conductive layer  17  can be formed of, for example, a porous layer (such as a mesh) formed of metal materials such as gold and nickel, or a composite obtained by coating a conductive metal material such as a foil, a thin film, or stainless steel (SUS) with a high-conductive metal such as gold. The fixing layer  18  can be formed of an insulating film formed of polyethylene terephthalate (PET) in the same outer shape as that of the electrode. 
     The cathode conductive layer  17 , the anode conductive layer  16 , and the fixing layer  18  are formed in the shapes shown in  FIG. 2  by folding the current collector A in two interposing the membrane electrode assembly  10  in between, such that the above-described two pairs of anode catalyst layers  11  and the cathode catalyst layers  13  are electrically connected in series. As shown in  FIG. 1 , the cathode conductive layer  17  is integrated with the fixing layer  18  in a position in which the cathode conductive layer  17  contacts the cathode. The anode conductive layer  16  is integrated with the fixing layer  18  in a position in which the anode conductive layer  16  contacts the anode. 
     As shown in  FIG. 1  and  FIG. 2 , one slit  18 A is formed in the fixing layer  18 . The slit  18 A is arranged in a portion of the fixing layer  18  facing a region between the two cathodes, so as to extend approximately parallel to the longitudinal direction 
     (Y-direction) of the cathodes. The width of the slit  18 A in a direction (X-direction) approximately orthogonal to the longitudinal direction of the slit  18 A is approximately 0.3 mm. The slit is provided so as to have a length half the length of the electrode in the longitudinal direction, and is arranged such that the central portion of the electrode in the longitudinal direction is aligned with the central portion of the slit in the longitudinal direction. 
     A rubber O-ring  19  is interposed between the electrolyte membrane  15  and the fixing layer  18  and is sealed, so as to have a width of 2 mm in the cross section shown in  FIG. 1  and an approximately rectangular outer shape, which is the same as that of the fixing layer  18 . Further, a gas discharge vent  20  is provided in a portion of the electrolyte membrane  15  facing a region between the anode gas diffusion layers  12  arranged approximately parallel to each other. 
     On the cathode conductive layer  17 , there are provided a moisturizing layer  21 , and a surface cover  22  including a plurality of air inlets  23  laminated on the moisturizing layer  21 . 
     The moisturizing layer  21  is positioned on the other side of the electrolyte membrane  15  with respect to the cathode gas diffusion layer  14 . The moisturizing layer  21  has the functions of suppressing vaporization of water by impregnating a portion of water produced in the cathode catalyst layer  13 , and facilitating uniform diffusion of the oxidant (air) into the cathode catalyst layer  13  by uniformly introducing the oxidant into the cathode gas diffusion layer  14 . The moisturizing layer  21  is formed of a porous member, for example, and specific constituent materials include porous bodies of polyethylene and polypropylene. In the present example, the moisturizing plate  9  is a foamed polyethylene sheet. 
     The surface cover  22  is positioned on the other side of the cathode conductive layer  17  with respect to the moisturizing layer  21 . The surface cover  22  has an approximately box-shaped outer appearance, and is formed of stainless steel (SUS), for example. Further, the surface cover  22  includes a plurality of air inlets  23  designed to take in air as an oxidant. The air inlets  23  are formed in a matrix pattern, for example. 
     In each of the moisturizing layer  21  and the surface cover  22 , a hole is provided in a position corresponding to the gas discharge vent  20 , so as not to obstruct the gas discharged from the gas discharge vent  20 . 
     The fuel supply mechanism  40 , which supplies liquid fuel F to the fuel distribution layer  30 , mainly comprises a fuel container  41 , a fuel supply  42 , and a duct  43 , as shown in  FIG. 1 . The fuel container  41  contains the liquid fuel F compliant with the fuel cell. Examples of the liquid fuel F include methanol fuels, such as methanol solutions of various concentrations, and pure methanol. The liquid fuel F is not necessarily limited to methanol fuels. 
     The liquid fuel F may be, for example, an ethanol fuel such as an ethanol solution and pure ethanol, a propanol fuel such as a propanol solution and pure propanol, a glycol fuel such as a glycol solution and pure glycol, dimethyl ether, formic acid, or other liquid fuels. In either case, a liquid fuel compliant with the fuel cell is contained in the fuel container  41 . 
     The fuel supply  42  is connected to the fuel container  41  through the duct  43  of the liquid fuel F formed of plumbing, for example. The liquid fuel F is introduced into the fuel supply  42  through the duct  43  from the fuel container  41 , and the introduced liquid fuel F and/or vaporized components of the liquid fuel F are supplied to the membrane electrode assembly  10  through the fuel distribution layer  30  and the anode conductive layer  16 . 
     The duct  43  is not limited to plumbing independent of the fuel supply  42  and the fuel container  41 . When the fuel supply  42  and the fuel container  41  are laminated and integrated, for example, the duct  43  may be formed as a duct of the liquid fuel F connecting the fuel supply  42  and the fuel container  41 . That is, the fuel supply  42  only needs to communicate with the fuel container  41  via a duct or the like. 
     The liquid fuel F contained in the fuel container  41  can be dropped and transported to the fuel supply  42  via the duct  43  by means of gravity. Further, the duct  43  may be filled with a porous body, for example, such that the liquid fuel F contained in the fuel container  41  is transported to the fuel supply  42  by a capillary phenomenon. Moreover, as shown in  FIG. 1 , a pump  44  may be intervened in a portion of the duct  43 , such that the liquid fuel F contained in the fuel container  41  is forcibly transported to the fuel supply  42 . 
     The fuel distribution layer  30  is formed of a flat plate in which a plurality of openings  31  are formed, for example, and is interposed between the anode gas diffusion layer  12  and the fuel supply  42 . The fuel distribution layer  30  is formed of a material that does allow the liquid fuel F and the vaporized components of the liquid fuel F to permeate. More specifically, the fuel distribution layer  30  is formed of a polyethylene terephthalate (PET) resin, a polyethylene naphthalate (PEN) resin, a polyimide-based resin, or the like. 
     Further, the fuel distribution layer  30  may be formed of a vapor-liquid separation film configured to separate vaporized components of the liquid fuel F from the liquid fuel F and let the vaporized components to permeate the side of the membrane electrode assembly  10 , for example. The vapor-liquid separation film can be formed of silicone rubber, a low-density polyethylene (LDPE) film, a polyvinyl chloride (PVC) film, a polyethylene terephthalate (PET) film, or a fluorine resin (such as polytetrafluoroethylene (PTFE) and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA)) microporous film, for example. 
     In an environment where the temperature was 25° C. and the relative humidity is 50%, pure methanol having a purity of 99.9% by weight was supplied to the fuel cell prepared as described above. Under the above-described conditions, the output voltage of the fuel cell after generating electricity for 100 hours (or at the time of start of electricity generation) was measured. 
     SECOND EXAMPLE 
     Hereinafter, a fuel cell according to Second example will be described. In the description that follows, the same structural elements as those of the fuel cell of First example will be denoted by the same reference numbers and detailed descriptions of such elements will be omitted. 
     In the fuel cell of the present example, four slits  18 A are provided in portions facing regions between cathodes of a current collector A, as shown in  FIG. 3 . The four slits  18 A are arranged side by side in the Y-direction such that the longitudinal direction thereof is approximately parallel to the longitudinal direction (Y-direction) of the cathodes. The width of the slits  18 A in a direction (X-direction) approximately orthogonal to the longitudinal direction of the slits  18 A is approximately 0.3 mm. The slits are provided so as to have a length of ⅕ of the length of the electrode in the longitudinal direction, and are arranged at equal intervals at diametrically opposed positions with respect to the central portion of the electrode in the longitudinal direction. 
     Other than the configuration of the slits  18 A, the fuel cell of the present example has the same configuration as that of the above-described fuel cell of First example. In the same manner as in First example, the output voltage of the fuel cell of the present example was measured. 
     First Comparative Example 
     Hereinafter, a fuel cell according to First comparative example will be described. The fuel cell of the present comparative example is the same the fuel cell of First example, except that a slit is not formed in a portion of a current collector A facing a region between cathodes. In the same manner as in First example, the output voltage of the fuel cell of First comparative example was measured. 
     As shown in  FIG. 4 , assuming the measured output voltage of the fuel cell according to First comparative example to be  100 , the output voltage of the fuel cell according to First example was  105 , and the measured output voltage of the fuel cell according to Second example was  115 . 
     That is, the fuel cells of First example and Second example exhibited output voltages higher than that of the fuel cell of First comparative example, since the slits  18 A provided in a portion of the current collector A facing the region between the cathodes allowed the steam produced at the cathode to escape and air to be taken in from the outside, causing the reaction at the cathode to occur smoothly. 
     That is, according to the above-described fuel cells of First example and Second example, it is possible to provide a fuel cell capable of maintaining a stable output over a long time. 
     THIRD EXAMPLE 
     A fuel cell according to Third example will be described below. In the fuel cell of the present example, as shown in  FIGS. 5 and 6 , a membrane electrode assembly  10  is formed by forming an anode gas diffusion layer  12  and a cathode gas diffusion layer  14  in an approximately rectangular outer shape, and hot-pressing four pairs of anode gas diffusion layers  12  and four cathode gas diffusion layers  14  such that the anode gas diffusion layers  12  and the cathode gas diffusion layers  14  are arranged side by side at intervals of 1.5 mm approximately parallel to one another in the longitudinal direction (Y-direction). 
     An O-ring  19  is formed in an approximately rectangular outer shape, which is the same as that of the electrode, so as to have a width of 2 mm in the cross section shown in  FIG. 5 . A gas discharge vent  20  is provided in four portions of an electrolyte membrane  15  between anode gas diffusion layers arranged approximately parallel to one another. 
     A cathode conductive layer  17 , an anode conductive layer  16  and a fixing layer  18  are formed in the shapes shown in  FIG. 6 , such that the four pairs of anode catalyst layers  11  and the cathode catalyst layers  13  are electrically connected in series. Further, in the fuel cell of the present example, two slits  18 A are provided in a fixing layer  18 . The slits are provided so as to have a length of ⅓ of the length of the electrode in the longitudinal direction, and are arranged at equal intervals at diametrically opposed positions with respect to the central portion of the electrode in the longitudinal direction. 
     The two slits  18 A are arranged side by side in the 
     Y-direction in portions of the current collector A facing regions between the cathodes, such that the longitudinal direction of the slits  18 A is approximately parallel to the longitudinal direction (Y-direction) of the cathodes. In the present example, two slits  18 A are provided in the central part of portions of the current collector A facing regions between the three cathodes arranged side by side in the X-direction. The width of the slits  18 A in a direction (X-direction) approximately orthogonal to the longitudinal direction of the slits  18 A is approximately 0.3 mm. 
     Other than the above-described configuration, the fuel cell of the present example has the same configuration as that of the fuel cell of First example. In the same manner as in First example, the output voltage of the fuel cell according to Third example was measured. 
     FOURTH EXAMPLE 
     Hereinafter, a fuel cell according to fourth example will be described. In the description that follows, the same configuration as that of the fuel cell of Third example will be denoted by the same reference numbers and detailed descriptions of such elements will be omitted. 
     In the fuel cell of the present example, nine slits  18 A are provided in portions of the current collector A facing regions between the cathodes. As shown in  FIG. 7 , three slits  18 A are provided in portions facing regions between three cathodes arranged side by side in the X-direction. The three slits  18 A are arranged side by side in the Y-direction such that the longitudinal direction of the slits  18 A is approximately parallel to the longitudinal direction (Y-direction) of the cathodes. The width of the slits  18 A in a direction (X-direction) approximately orthogonal to the longitudinal direction of the slits  18 A is 0.3 mm. 
     Other than the configuration described above, the fuel cell of the present example has the same configuration as that of the fuel cell of Third example. In the same manner as in First example, the output voltage of the fuel cell of fourth example was measured. 
     FIFTH EXAMPLE 
     Hereinafter, a fuel cell according to Fifth example will be described. In the fuel cell of the present example, nine slits  18 A are provided in portions of a current collector A facing regions between the cathodes. In the same manner as in fourth example, three slits  18 A are provided in portions facing regions between three cathodes arranged side by side in the X-direction. The three slits  18 A are arranged side by side in the Y-direction such that the longitudinal direction of the slits  18 A is approximately parallel to the longitudinal direction (Y-direction) of the cathodes. In the present example, the width of the slits  18 A in a direction (X-direction) approximately orthogonal to the longitudinal direction of the slits  18 A is 0.05 mm. 
     Other than the configuration described above, the fuel cell of the present example has the same configuration as that of the fuel cell of Third example. In the same manner as in First example, the output voltage of the fuel cell of Fifth example was measured. 
     SIXTH EXAMPLE 
     Hereinafter, a fuel cell according to Sixth example will be described. In the fuel cell of the present example, twelve slits  18 A are provided in portions of a current collector A facing regions between the cathodes. As shown in  FIG. 8 , four slits  18 A are provided in portions facing regions between three cathodes arranged side by side in the X-direction. The four slits  18 A are arranged side by side in the Y-direction such that the longitudinal direction of the slits  18 A is approximately parallel to the longitudinal direction (Y-direction) of the cathodes. In the present example, the width of the slits  18 A in a direction (X-direction) approximately orthogonal to the longitudinal direction of the slits  18 A is 0.3 mm. 
     Other than the configuration described above, the fuel cell of the present example has the same configuration as that of the fuel cell of Third example. In the same manner as in First example, the output voltage of the fuel cell of Sixth example was measured. 
     Second Comparative Example 
     Hereinafter, a fuel cell according to Second comparative example will be described. In the fuel cell of the present comparative example, a slit is not formed in a portion of the current collector A facing regions between the cathodes. Other than that, the fuel cell of Second comparative example has the same configuration as that of Third example. In the same manner as in First example, the output voltage of the fuel cell of Second comparative example was measured. 
     As shown in  FIG. 9 , assuming the measured output voltage of the fuel cell according to Second comparative example to be  100 , the output voltage of the fuel cell according to Third example was  105 , the measured output voltage of the fuel cell according to fourth example was  110 , the measured output voltage of the fuel cell according to Fifth example was  103 , and the measured output voltage of the fuel cell according to Sixth example was  115 . 
     That is, the fuel cells according to Third to 
     Sixth examples exhibited output voltages higher than that of the fuel cell according to Second comparative example, since the slits  18 A provided in portions of the current collector A facing the regions between the cathodes allowed the steam produced at the cathode to escape and air to be taken in from the outside, causing the reaction at the cathode to occur smoothly. 
     That is, according to the above-described fuel cells of Third to Sixth examples, it is possible to provide a fuel cell capable of maintaining a stable output over a long time. 
     According to the present embodiment, it is possible to provide a fuel cell capable of maintaining a stable output for a long time. 
     The present invention is not limited to the above-described embodiment and may be embodied with modifications to the constituent elements within the scope of the invention. For example, in the fuel cell of the above-described embodiments, the current collector A includes a fixing layer configured to fix the cathode conductive layer and the anode conductive layer and a slit is provided in the fixing layer, but a slit may be provided in the conductive layer if the current collector A does not comprise a fixing layer. Even with that configuration, the same advantageous effect as that of the fuel cell of the above-described embodiment can be obtained. 
     Further, various inventions may be made by appropriately combining constituent elements disclosed in the above-described embodiment. For example, some of the constituent elements may be deleted from all the constituent elements disclosed in the embodiment. Moreover, constituent elements disclosed in different embodiments may be combined as appropriate. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.