Patent Publication Number: US-2007099048-A1

Title: Fuel cell

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention generally relates to fuel batteries, and more specifically, to a vaporized fuel supply type fuel cell having a small size and a proton conductive solid electrolyte layer.  
      2. Description of the Related Art  
      Recently, a portable electronic device, such as a portable phone, portable information terminal device, notebook type personal computer, or the like has been having multiple functions and high properties. It is required that a cell as a driving electric power source of such a portable electronic device have an improved property.  
      At present, a lithium ion secondary cell is mainly used for the portable electronic device. However, since dramatic improvement of energy density of the lithium ion secondary cell may not be expected, it is difficult for the lithium ion secondary cell to have a required energy density. In addition, the secondary cell is required to be charged and therefore is limited in usefulness.  
      A fuel cell is now being paid attention to as a driving electric power source because the fuel cell has high energy density and solves the limiting charging problem.  
      More specifically, attention is being paid to a direct methanol type fuel cell (hereinafter “DMFC”) as the driving electric power source of portable electronic devices. In theory, the DMFC has several times the capacity of a lithium ion cell having the same volume.  
      In the DMFC, polymer solid electrolyte is used as electrolyte, and an organic fuel such as methanol is directly supplied on an electrode so that electric power is generated. Since the DMFC does not use a modifier for modifying the organic fuel to hydrogen, it is easy to make the DMFC be small and light-weight. Hence, the DMFC is proper for the electric power source of the portable electric device.  
      In the DMFC, methanol is supplied from a liquid fuel storage part to a catalyst layer of a fuel electrode so that proton (H + ), electron (e − ) and carbon dioxide are generated (reaction formula:
 
CH 3 OH+H 2 O→CO 2 +6H + +6e − ).
 
      Protons permeate a polymer solid electrolyte film and combine with the catalyst layer of an air electrode so that water is generated. In this case, the fuel electrode and the air electrode are connected with an outside circuit so that electric power can be taken out by generated electrons.  
      The DMFC is classified into an active type and a passive type. In the active type DMFC, an auxiliary device such as a pump is used to supply methanol as a fuel. In the passive type DMFC, methanol is supplied by a capillary force or natural diffusion.  
      Since the active type DMFC uses the auxiliary device for supplying the fuel, the active type DMFC is disadvantageous compared to the passive type DMFC from the view point of making the cell small. In addition, since an electric power is required for driving the auxiliary device, the active type DMFC is disadvantageous compared to the passive type DMFC from the view point of energy efficiency. Thus, for the use of the portable electronic device, the passive type DMFC which does not use the auxiliary device for supplying the fuel is more advantageous than the active type DMFC  
      A fuel supplying method for the passive fuel cell is classified into a liquid supply type and a vaporization supply type.  
      In the liquid supply type, a liquid state fuel is directly supplied on a surface of the fuel electrode. In the vaporization supply type, the liquid fuel is vaporized and then supplied to the electrode part. In the liquid supply type, if a methanol high density solution is used as fuel, the methanol high density solution permeates an electrolyte film so that methanol cross over happens, that is, methanol not contributing to electric power generation increases and a property of the air electrode is degraded.  
      On the other hand, in the vaporization supply type, since methanol gas is supplied to the fuel electrode, the methanol cross over can be avoided. As a result of this, in the vaporization supply type, it is possible to make the fuel supplied from inside the tank have a high density. In a case of the same volume, as compared with the case with a low density methanol aqueous solution, energy density is improved. In other words, in the case where the liquid fuel having the same volume is used, the vaporization supply type DMFC is better from the perspective of obtaining a fuel cell having a high energy density.  
      Meanwhile, a method whereby the methanol aqueous solution is vaporized by using a carbon porous plate is suggested as the vaporization supply type DMFC. See Japan Laid-Open Patent Application Publication No. 2000-106201. The methanol aqueous solution is transferred in pores of the carbon porous plate by capillary force and vaporized on a surface at a side of the fuel electrode of the carbon porous plate.  
      However, in the related art of the above-mentioned Japan Laid-Open Patent Application Publication No. 2000-106201, since the capillary force is used, transferring speed in the carbon porous plate is slow. Hence, in a case where a high power discharge capability for the portable type electronic device of the methanol aqueous solution is implemented, reaction unevenness is generated at the fuel electrode due to lack of the supply of methanol so that the amount of the electric power generated and efficiency of the electric power generation may be reduced. In addition, in order to control the transferring speed of the methanol aqueous solution in the carbon porous plate, a carbon porous plate having a structure where the diameter of the pores is controlled is required and the manufacturing of such a carbon porous plate is not easy.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is a general object of the present invention to provide a novel and useful fuel cell.  
      Another and more specific object of the present invention is to provide a vaporized fuel supply type fuel cell wherein fuel supply speed can be controlled under a simple structure.  
      The above object of the present invention is achieved by a fuel cell, including:  
      an electric power generation part;  
      the electric power generation part including  
      an air electrode to which oxygen gas is supplied,  
      a fuel electrode to which fuel gas is supplied, and  
      a solid electrolyte layer having a proton conductivity and put between the air electrode and fuel electrode;  
      a fuel storage part storing a liquid fuel;  
      a liquid fuel vaporization film made of non-porous material and configured to vaporize the liquid fuel so as to supply fuel gas to the fuel electrode; and  
      a gas fuel supply speed control plate provided between the liquid fuel vaporization film and the fuel electrode and configured to control a supply speed of the fuel gas to the fuel electrode;  
      wherein the gas fuel supply speed control plate includes a plurality of openings piercing between the liquid fuel vaporization film and the fuel electrode.  
      According to the above-mentioned fuel cell, the control plate, having plural openings piercing between the fuel electrode and the liquid fuel vaporization film made of non-porous material and configured to vaporize the liquid fuel and supply the fuel gas to the fuel electrode, is provided between the liquid fuel vaporization film and the fuel electrode. By forming the plural openings in the control plate, it is possible to control the supply speed of the fuel gas. Therefore, it is possible to provide a fuel cell with a simple structure whereby the fuel supply speed can be controlled.  
      In the fuel cell, the supply speed of the fuel gas to the fuel electrode may be controlled based on a numerical aperture of the control plate.  
      According to the above-mentioned fuel cell, it is possible to control the amount of the fuel gas passing through the opening by changing the numerical aperture (%) of the control plate, that is the whole area of the opening part/an area of the control plate×100 (%). As a result of this, it is possible to control the supply speed of the fuel gas to the fuel electrode.  
      The fuel cell may further include:  
      another control plate provided at a side of the fuel storage part of the liquid fuel vaporization film, the other control plate making contact with the liquid fuel vaporization film, the other control plate having a plurality of other openings piercing between the fuel storage part and the liquid fuel vaporization film.  
      According to the above-mentioned fuel cell, it is possible to control the supply speed of the fuel gas to the liquid fuel vaporization film by providing the above-mentioned control plate. As a result of this, it is possible to control the supply speed of the fuel gas to the fuel electrode in a wider range.  
      In the fuel cell, the supply speed of the liquid fuel to the liquid fuel vaporization film may be controlled based on a numerical aperture of the other control plate.  
      According to the above-mentioned fuel cell, it is possible to control the permeation speed of the fuel gas permeating the liquid fuel vaporization film. As a result of this, it is possible to control the supply speed of the fuel gas to the fuel electrode in a wider range.  
      Other objects, features, and advantages of the present invention will be come more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional view of a fuel cell of a first embodiment of the present invention;  
       FIG. 2  is a cross-sectional view of the fuel cell for explaining control of methanol gas supply speed;  
       FIG. 3  is a schematic diagram of the fuel cell for explaining the control of the methanol gas supply speed;  
       FIG. 4  is a cross-sectional view of a fuel cell of a second embodiment of the present invention; and  
       FIG. 5  is a table showing methanol gas supply speed of a third embodiment and a comparison example. 
    
    
     DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS  
      A description is given below, with reference to the  FIG. 1  through  FIG. 5  of embodiments of the present invention.  
      [First Embodiment] 
       FIG. 1  is a cross-sectional view of a fuel cell of a first embodiment of the present invention.  
      Referring to  FIG. 1 , a fuel cell  10  includes an electric generation part  20 , an air supply part  30 , a fuel supply part  40  and others. The air supply part  30  supplies oxygen gas included in air to the electric generation part  20 . The fuel supply part  40  vaporizes liquid fuel so as to supply fuel gas such as methanol gas or the like to the electric generation part  20 .  
      The electric generation part  20  has a structure where an air electrode  21 , a solid electrolyte layer  22 , and a fuel electrode  23  are stacked in this order. Since the air electrode  21  is a thin film, the illustration of the air electrode  21  is omitted. The air electrode  21  includes, for example, a porous carbon paper and a catalyst layer.  
      The catalyst layer includes, for example, Pt (platinum) fine particle or a carbon powder wherein Pt is carried on a surface of the carbon powder. Such a catalyst layer is provided so as to come in contact with the solid electrolyte layer  22 .  
      The solid electrolyte layer  22  is formed by a proton conductive polymer solid electrolyte. Resin having a strong acid group such as a phosphoric acid, sulfone group, or the like or a weak acid group such as carboxyl group or the like is an example of a polymer solid electrolyte. It is possible to use, for example, NAFION (trademark) NF117 (product name of Dupont) or ACIPLEX (product name of Asahi-Kasei) as the solid electrolyte layer  22 .  
      Since the fuel electrode  23  is a thin film, the illustration of the fuel electrode  23  is omitted. The fuel electrode  23  includes, for example, a porous carbon paper and a catalyst layer. The catalyst layer is formed by, for example, fine particles of Pt—Ru (ruthenium) alloy or a carbon powder wherein the Pt—Ru alloy is carried on the surface of the powder. Such a catalyst layer is provided so as to come in contact with the solid electrolyte layer  22 .  
      In the electric generation part  20 , fuel gas is supplied to the fuel electrode  23 . As liquid fuel being the base of the fuel gas, for example, dimethyl ether, ethanol, methanol having substantially 100% density or aqueous solutions of them can be used. In the first and second embodiments, a methanol aqueous solution is used as an example.  
      In the catalyst layer of the fuel electrode  23 , a reaction of the following reaction formula  1  proceeds. As a result of this, water vapor and methanol gas being fuel gas are consumed and carbon dioxide gas, protons (H + ), electron (e − ), and methyl formate and dimethoxymethane as sub-products are generated. In the catalyst layer, oxidation reaction of methyl formate and dimethoxymethane which reaction is different from the reaction of the following reaction formula 1 proceeds so that proton and electron are generated.
 
CH 3 OH+H 2 O→CO 2 +6H + +6e −   [Reaction formula 1]
 
      The protons pass through the solid electrolyte layer  22  and reach to the air electrode  21 . The electrons work for a load connected to the fuel cell  10  as an outside circuit (not shown in  FIG. 1 ) via a fuel gas diffusion layer  54  and a fuel electrode current collector  53 .  
      In addition, the electron reach to the air electrode  21  via an air electrode current collector  33  and an air electrode gas diffusion layer  34 .  
      In the catalyst layer of the air electrode  21 , a reaction of the following reaction formula 2 proceeds. As a result of this, protons, electron and oxygen gas are consumed and water vapor is generated.
 
3/2O 2 +6H + +6e − →3H 2 O  [Reaction formula 2]
 
      The generated water vapor is discharged to the outside via the air electrode gas diffusion layers  32  and  34  and an oxygen supply opening  31   a . Furthermore, carbon dioxide gas generated at the fuel electrode  23  is discharged to the outside via a generation gas discharge part not shown in  FIG. 1 .  
      Thus, the fuel cell  10  generates electricity by using the methanol aqueous solution as liquid fuel.  
      The air supply part  30  includes an air electrode housing  31 , the air electrode gas diffusion layers  32  and  34 , and the air electrode current collector  33 . By the air electrode gas diffusion layers  32  and  34 , oxygen gas led from the oxygen supply opening  31   a  of the air electrode side housing  31  is diffused and is led to the air electrode  21 .  
      The air electrode side housing  31  is formed by a metal material or a resin material. Although there is no limitation as the resin material, it is preferable to use resin of the polyolefin group such as polypropylene or polyethylene, fluorine resin such as PTFE (polytetrafluoroethylene) or PFA, polyvinyl chloride, poly butylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethersulfone (PES), polysulfone, poly phenylene oxide (PPO), polyetheretherketone, acrylic, or the like, as the above-mentioned resin material from the perspective of durability with alcohol such as methanol.  
      A large number of the oxygen supply openings  31   a  piercing the air electrode side housing  31  are provided in the air electrode side housing  31 . It is preferable that the oxygen supply openings  31   a  be provided so that the oxygen gas is evenly led to the entirely of the air electrode gas diffusion layer  32 .  
      The air electrode gas diffusion layer  32  is formed by a porous material. Although there is no limitation as the porous material, it is preferable to use, for example, a ceramic porous body, a carbon paper, a carbon bonded-fiber fabric, a fluoride resin porous body, a polypropylene porous body, or the like.  
      The air electrode current collector  33  has conductivity. The air electrode current collector  33  also has a mesh or porous structure. The air electrode current collector  33  makes oxygen gas permeate from a side of the air electrode gas diffusion layer  32  to a side of the air electrode gas diffusion layer  34 .  
      It is preferable that the air electrode current collector  33  be made of a metal material having a high resistance to corrosion such as Ni, SUS304, SUS316, or the like. The air electrode current collector  33  may have a structure of, for example, a metal mesh, expanded metal, a metal bonded-fiber fabric, or a foam metal having a three dimensional network structure.  
      In addition, it is preferable that a metal film having a high conductivity and high resistance to corrosion, such as Au film or Au alloy film, be formed on a surface of the air electrode current collector  33 . By providing such a metal film, it is possible to improve the resistance to corrosion of the air electrode current collector  33  and reduce contact resistance with the air electrode gas diffusion layer  34 .  
      The air electrode gas diffusion layer  34  is formed by a conductive porous material. As the conductive porous material, a carbon paper, a carbon bonded-fiber fabric, or the like can be used.  
      In the air supply part  30 , oxygen gas in the air is led from the oxygen supply opening  31   a  of the air electrode side housing  31 . The oxygen gas is diffused via opening parts of the air electrode gas diffusion layers  32  and  34  or a pore so as to be evenly led on the surface of the air electrode  21 .  
      If oxygen gas can be supplied sufficiently diffused on the surface of the air electrode  21  without the air electrode gas diffusion layer  32  and/or the air electrode gas diffusion layer  34 , the air electrode gas diffusion layers  32  and  34  are not required to be provided.  
      A sealing material  55  is made of resin having good sealability such as, for example, epoxy resin or olefin group resin. The sealing material  55  prevents carbon monoxide gas or methanol gas in the fuel cell  10  or liquid such as the methanol aqueous solution from leaking to the outside of the fuel cell  10 . In addition, the sealing material  55  is used for a fuel supply part  40  discussed below in the same way as the above-mentioned way.  
      The fuel supply part  40  includes a fuel electrode side housing  41 , a fuel storage part  42 , a liquid fuel vaporization film  49 , fuel gas diffusion layers  52  and  54 , the fuel electrode current collector  53 , and others. The methanol aqueous solution is received in the fuel storage part  42 . Methanol in the methanol aqueous solution is vaporized so as to change to methanol gas by the liquid fuel vaporization film  49 . The methanol gas is diffused and led in the fuel electrode  23  by the fuel gas diffusion layers  52  and  54 .  
      In addition, the fuel supply part  40  includes a first control plate  48  provided at a side of the fuel storage part  42  of the liquid fuel vaporization film  49  and a second control plate  50  at a side of the fuel gas diffusion layer  52  of the liquid fuel vaporization film  49 , so that the supply speed of the methanol gas can be controlled.  
      The fuel electrode side housing  41  is formed by a metal material or a resin material. Although there is no limitation as the resin material, it is preferable to select it from the resin material similar or the same as the material used for the above-mentioned air electrode side housing  31 , from the perspective of durability with alcohol such as methanol.  
      The fuel storage part  42  is a space forming part put between the fuel electrode side housing  41  and the first control plate  48 . The methanol aqueous solution is supplied from a fuel cartridge  43  to the fuel storage part  42  via the fuel supply opening  44 . The methanol aqueous solution in the fuel storage part  42  comes in contact with the surface of the liquid fuel vaporization film  49  via the surface of the first control plate  48  and an opening part  48   a.    
      The fuel cartridge  43  stores the methanol aqueous solution and supplies methanol aqueous solution to the fuel storage part  42 . Although there is no limitation as a supply driving source of the methanol aqueous solution, for example, a pump (not shown in  FIG. 1 ), a pressure applying part  45  discussed below, or the combination of the pump and the pressure applying part  45  can be used. A valve may be provided at the fuel supply opening  44  so as to control an inflow or back-flow of the methanol aqueous solution.  
      The pressure applying part  45  is provided at the fuel cartridge part  43 . The pressure applying part  45  applies a back pressure to the methanol aqueous solution, so that the vaporization speed of the methanol in the liquid fuel vaporization film  49  can be improved and the supply speed of the methanol gas can be increased.  
      The pressure applying part  45  applies, directly or via gas such as nitrogen gas, the back pressure to the methanol aqueous solution filling the fuel cartridge  43 . The amount of the back pressure is properly selected based on the material of the liquid fuel vaporization film  49 . It is preferable that the amount of back pressure be in the range 10 kPa-100 kPa.  
      The pressure applying part  45  may be directly connected to the fuel storage part  42  so as to directly apply the back pressure to the methanol aqueous solution filling the fuel storage part  42 . In this case, a valve or the like is provided so as to prevent the back-flow of the methanol to the fuel cartridge  43 .  
      Furthermore, in a case where the methanol aqueous solution is sufficiently supplied to the liquid fuel vaporization film  49 , the pressure applying part  45  may not be required.  
      Details of the first control plate  48 , the liquid fuel vaporization film  49  and the second control plate  50  are discussed below. In a simple structure, methanol aqueous solution can be changed to methanol gas and the methanol supply speed to the fuel electrode  23  can be controlled.  
      The fuel gas diffusion layer  52  is formed by a porous material having durability with alcohol such as methanol. Ceramic, a carbon paper, a carbon bonded-fiber fabric, a fluoride resin, polypropylene, or the like may be used as a porous material proper for the fuel gas diffusion layer  52 .  
      The range between 30% and 95% is desirable as the porosity of the fuel gas diffusion layer  52 . The range 40% through 90% is more desirable as the porosity of the fuel gas diffusion layer  52 . If the porosity exceeds 95%, the mechanical strength of the fuel gas diffusion layer  52  is degraded.  
      Although there is no limitation regarding the thickness of the fuel gas diffusion layer  52 , it is preferable that the fuel gas diffusion layer  52  have a thickness equal to or less than 1 mm. If the thickness of the fuel gas diffusion layer  52  exceeds 1 mm, the fuel cell will be too thick.  
      Although it is preferable to provide the fuel gas diffusion layer  52 , the fuel gas diffusion layer is not required if the diffusion of the fuel gas is sufficient.  
      It is preferable that the fuel electrode current collector  53  be made of the same material as the material of the air electrode current collector  33  and a metal film having a high conductivity and high resistance to corrosion, such as Au film, is formed on a surface of the fuel electrode current collector  53 .  
      The fuel gas diffusion layer  54  is formed by a conductive porous material having durability with alcohol such as methanol. As the conductive porous material, a carbon paper, a carbon bonded-fiber fabric, or the like can be used.  
      As discussed above, the fuel supply part  40  vaporizes the methanol aqueous solution supplied to the fuel storage part  42  by the liquid fuel vaporization film  49  and supplies the methanol gas to the fuel electrode  23 . Based on the reaction of the above-mentioned reaction formula 1, the electrons and protons are generated.  
      Next, details of the first control plate  48 , the liquid fuel vaporization film  49  and the second control plate  50  are discussed.  
      The liquid fuel vaporization film  49  is formed by a non-porous material of a polymer having durability with alcohol such as methanol. By using such a non-porous material of the polymer, the methanol in the liquid is sufficiently vaporized and the methanol gas permeates at a sufficient permeating speed in the liquid fuel vaporization film  49 . Hence, it is possible to sufficiently secure the supply speed of the methanol gas to the fuel electrode  23 .  
      Perfluoro sulfonic acid group resin is used as a proper non-porous material for the liquid fuel vaporization film  49 . The perfluoro sulfonic acid group resin has, for example, a fluoride resin main chain and a side chain having a sulfonic acid group. For example, NAFION (trademark) manufactured by Dupont or ACIPLEX (product name of Asahi-Kasei) can be used as a resin film of such a material.  
      A resin whose main material is a perfluoro carbon group including carboxyl is also used as the proper non-porous material for the liquid fuel vaporization film  49 . The resin of the perfluoro carbon group including carboxyl has, for example, a fluoride resin main chain and a side chain having a carboxyl group. For example, FLEMION manufactured by Asahi-Kasei can be used as the resin of such a material.  
      In addition, a resin whose main material is selected from polysulfone, polyimide, polyetheretherketone and polyamide is also used as the proper non-porous material for the liquid fuel vaporization film  49 .  
      Furthermore, a polymer material including silicon such as silicon rubber is also used as the proper non-porous material for the liquid fuel vaporization film  49 .  
      Here, resin in which the above-mentioned designated resins are equal to or greater than 50 weight % of the entire resin is included.  
      In the above-discussed non-porous material, the resin whose main material is perfluoro sulfonic acid group resin and the perfluoro carbon group resin including carboxyl provide permeation speed of the methanol gas (fuel gas) greater than other materials. More specifically, it is possible to obtain effective permeation speed of the methanol gas (fuel gas) by the first control plate  48  and the second control plate  50 .  
      Plural opening parts  48   a  configured to pierce the first control plate  48  in a plate thickness direction are formed in the first control plate  48 . The opening parts  48   a  are formed, for example, along a Y axis direction and a Z axis direction with a designated distance.  
      The supply speed of the methanol aqueous solution to the liquid fuel vaporization film  49  depends on an area where the liquid fuel vaporization film  49  comes in contact with the methanol aqueous solution. Therefore, the supply speed of the methanol aqueous solution to the liquid fuel vaporization film  49  can be controlled by changing the entire area of the openings  48   a  of the first control plate  48 , namely by changing a numerical aperture of the first control plate which equals to “(entire area of the openings  48   a )/(the area of the first control plate  48 )×100”.  
      In addition, plural opening parts  50   a  configured to pierce the second control plate  50  in a plate thickness direction are formed in the second control plate  50 . The opening parts  50   a  are formed, for example, along a Y axis direction and a Z axis direction with a designated distance.  
      The supply speed of the methanol gas to the fuel electrode  23  depends on the entire area of the openings  50   a  of the second control plate  50 , namely a numerical aperture of the second control plate  50 . Therefore, the supply speed of the methanol gas to the fuel electrode  23  can be controlled by changing the numerical aperture of the second control plate  50 .  
      The numerical apertures of the first control plate  48  and the second control plate  50  are properly set based on a permeating speed of the methanol gas of the liquid fuel vaporization film  49  or a distance between the opening part  48   a  of the first control plate  48  and the opening part  50   a  of the second control plate  50 .  
      However, it is preferable to set the numerical apertures in a range equal to or less than 50% from the perspective of sufficient mechanical strengths of the first control plate  48  and the second control plate  50 . There is no lower limitation of the numerical apertures of the first control plate  48  and the second control plate  50 . However, the numerical aperture at which at least the methanol or the methanol gas permeates, a numerical aperture greater than 0% for example, is set.  
      There is no limitation of configurations of the opening parts  48   a  and  50   a . For example, the configurations may be circular including elliptic, triangular, rectangular, or slit-shape extending in a single direction. In a case where the opening parts  48   a  and  50   a  have circular-shaped configurations, the diameters of the opening parts  48   a  and  50   a  may be, for example, 10 μm through 10 mm.  
      There is no limitation of material forming the first control plate  48  and the second control plate  50  as long as the material has a plane plate shaped configuration and durability with alcohol such as methanol. However, a metal plate, a ceramic plate or a plastic plate can be used for the first control plate  48  and the second control plate  50 . It is preferable to use a metal plate for the first control plate  48  and the second control plate  50  because the metal plate has sufficient mechanical strength and it is easy to form holes, namely openings  48   a  and  50   a.    
      Adhesive layers  51  are formed between the first control plate  48  and the liquid fuel vaporization film  49  and between the second control plate  50  and the liquid fuel vaporization film  49 . The adhesive layers  51  fix the surface of the liquid fuel vaporization film  49  to the first control plate  48  and the second control plate  50  so that the liquid fuel vaporization film  49 , the first control plate  48 , and the second control plate  50  are in a body. As a result of this, volume change of the liquid fuel vaporization film  49  can be prevented so that breaking off due to volume change of the liquid fuel vaporization film  49  can be controlled.  
      More specifically, if the liquid fuel vaporization film  40  is wetted by the methanol aqueous solution, the liquid fuel vaporization film  40  swells. If supply of the methanol aqueous solution is stopped, the liquid fuel vaporization film  40  dries and contracts. If such a volume change is repeated, the liquid fuel vaporization film  49  is broken off so that the methanol aqueous solution leaks to the fuel electrode side and the amount of electric generation is reduced.  
      On the other hand, by providing the liquid fuel vaporization film  49  by using the adhesive layer  51 , it is possible to prevent the liquid fuel vaporization film  49  from being broken off so that it is possible to make the service life of the fuel cell  10  long. Providing the adhesive layer  51  is effective especially when the liquid fuel vaporization film  49  is made of resin whose main material is resin of the perfluoro sulfonic acid group or perfluoro carbon group including carboxyl.  
      The adhesive layers  51  are provided at parts where the liquid fuel vaporization films  49  come in contact with the first control plate  48  and the second control plate  50 . No adhesive layer  51  is provided at a part exposed by the opening  48   a  and the opening  50   a  of the liquid fuel vaporization film  49 .  
      There is no limitation of the material of the adhesive layer  51  as long as the liquid fuel vaporization film  49  can be adhered to the first control plate  48  and the second control plate  50  by the adhesion layer  51 . As the adhesive, for example, a silicon group adhesive, an epoxy group adhesive, a cyanoacrylate group adhesive, and a urethane group adhesive can be used.  
      In a case where the liquid fuel vaporization film  49  is made of the resin of the perfluoro sulfonic acid group, for example, it is preferable to use the silicon group adhesive as the adhesive. Furthermore, it is preferable to apply a silane coupling agent on a surface of the silicon group adhesive and make the resin of the perfluoro sulfonic acid group come in contact with the silane coupling agent so that a strong fixing can be obtained.  
      Instead of providing the adhesive layer  51 , an engaging member such as a screw (not shown) may be used so that the first control plate  48  and the second control plate  50  between which the liquid fuel vaporization film is put are engaged. As a result of this, the volume change of the liquid fuel vaporization film  49  can be prevented.  
      In addition, as discussed below, it is possible to control the supply speed of the methanol gas to the fuel electrode  23  by making positions of the opening parts  48   a  of the first control plate  48  and the opening parts  50   a  of the second control plate  50  different.  
       FIG. 2  is a cross-sectional view of the fuel cell for explaining a control of a methanol gas supply speed.  FIG. 3  is a schematic diagram of the fuel cell for explaining the control of the methanol gas supply speed.  
      In  FIG. 2 , while the illustration of the adhesive layer  51  is omitted, the fuel storage part  42 , the first control plate  48 , the fuel vaporization film  49 , and the second control plate  50  are shown. In  FIG. 3 , the opening parts  50   a  of the second control plate  50  are shown by solid line and the opening part  48   a  of the first control plate  48  are shown by dotted lines. In the examples shown in  FIG. 2  and  FIG. 3 , the opening parts  48   a  and  50   a  have circular-shaped configurations as examples.  
      Referring to  FIG. 2  and  FIG. 3 , the opening parts  48   a  of the first control plate  48  are separated from the corresponding closest opening parts  50   a  of the second control plate  50  via the liquid fuel vaporization film  49  by a designated length L 0 . In this case, the methanol aqueous solution permeating from the opening parts  48   a  of the first control plate  48  to the liquid fuel vaporization film  49  permeates and is vaporized in the liquid fuel vaporization film  49  so that the methanol gas is mainly discharged from the opening parts  50   a  of the second control plate  50  being separated from the opening parts  48   a  of the first control plate  48  with the shortest distance L 0 .  
      Here, the distance L 0  is between the center of the opening part  48   a  in the surface at a side of the first control plate  48  of the liquid fuel vaporization film  49  and the center of the corresponding closest opening part  50   a  in the surface at a side of the second control plate  50  of the liquid fuel vaporization film  49 . The distance L 0  is determined by a gap L 1  in a Y-axis direction between the opening part  48   a  and the opening part  50   a , a gap L 2  in a Z-axis direction between the opening part  48   a  and the opening part  50   a , and a thickness L 3  of the liquid fuel vaporization film  49  in an X-axis direction.  
      The time period from when the methanol aqueous solution permeates the liquid fuel vaporization film  49  to the time when the methanol aqueous solution is discharged as methanol gas depends on the length L 0 .  
      In order words, as the length L 0  is shorter, the time period during which the methanol gas having a unit volume permeates is short and the supply speed of the methanol gas increases. As the length L 0  is longer, the time period during which the methanol gas having a unit volume permeates is long and the supply speed of the methanol gas decreases. Therefore, it is possible to control the supply speed of the methanol gas by changing the length L 0 .  
      In addition, in a case where the supply speed of the methanol gas needs to be decreased, it is preferable to increase the gaps L 1  and L 2  between the opening part  48   a  and the opening part  50   a , rather than to increase the thickness L 3 . Because of this, it is possible to decrease the supply speed of the methanol gas without increasing the volume of the fuel cell  10  and to change the supply speed of the methanol gas in a wider range. Furthermore, it is possible to set a desirable supply speed of the methanol gas and make the fuel cell  10  thin in an X axis direction.  
      In a case where the supply speed of the methanol gas needs to be increased, the gaps L 1  and L 2  between the opening part  48   a  and the opening part  50   a  may be made small or zero. In addition, in this case, the methanol aqueous solution may be pressured by the pressure applying part  45 .  
      Furthermore, the numerical aperture of the first control plate  48  and the numerical aperture of the second control plate  50  may be different so that the supply speed of the methanol gas can be controlled. By combining the numerical apertures of the first control plate  48  and the second control plate  50 , the gaps L 1  and L 2 , and the thickness L 3 , the supply speed of the methanol gas can be controlled.  
      According to the first embodiment of the present invention, the liquid fuel vaporization film  49  is provided between the fuel storage part  42  of the fuel supply part  40  and the fuel gas diffusion layer  52 . At corresponding sides of the liquid fuel vaporization film  49 , the first control plate  48  having plural opening parts  48   a  and the second control plate  50  having plural opening parts  50   a  are arranged. The supply speed of the methanol gas to the fuel electrode  23  can be controlled by setting the numerical apertures of the control plates  48  and  50  and relative position of the opening parts  48   a  and  50   a.    
     FIRST EXAMPLE AND SECOND EXAMPLE  
      In the first and second example, the fuel cell has the substantially same structure as the fuel cell shown in  FIG. 1  through  FIG. 3 . In the following explanation,  FIG. 1  through  FIG. 3  are referred to.  
      First, a structure common to both the first and second examples is discussed. Materials discussed below are used for the fuel cells in the first example and the second example.  
      [Electric Generation Part] 
      An area of the electric generation part is 20 cm 2 . Pt—Ru alloy carrying catalyst TEC61E54 made by Tanaka Kikinzoku Company is used for a catalyst layer of the fuel electrode  23 . Pt carrying catalyst TEC10E50E is used for a catalyst layer of the air electrode  21 . NAFION (trademark) NH117 (product name of Dupont) is used for the solid electrolyte layer  22 .  
      The carbon paper having a thickness of 280 μm and manufactured by Toray Company is used for the air electrode gas diffusion layers  32  and  34 . SUS  304  having a mesh structure is used for the air electrode current collector  33 .  
      [Fuel Supply Part] 
      NAFION (trademark) NH117 (product name of Dupont) is used for the liquid fuel vaporization film  49 . The carbon paper having a thickness of 280 μm and manufactured by Toray Company is used for the fuel gas diffusion layers  52  and  54 . SUS304 having a mesh structure is used for the fuel electrode current collector  53 .  
      SUS  316  is used for the first control plate  48  and the second control plate  50 . The opening parts  48   a  and  50   a  have diameters in a range 1.2 mm through 1.5 mm. A silicon adhesive and a silane coupling adhesive are used as the adhesive layer  51 .  
      Next, differences of structures between the first and second examples are discussed.  
      In the first example, the gaps between the opening part  48   a  of the first control plate  48  and the corresponding opening part  50   a  of the second control plate  50 , namely L 1  and L 2  shown in  FIG. 3 , are 0.25 mm and the intervals in Y-axis and Z-axis directions between the opening part  48   a  of the first control plate  48  and the opening part  50   a  of the second control plate  50  are 3 mm.  
      In the second example, the gaps between the opening parts  48   a  of the first control plate  48  and the corresponding opening parts  50   a  of the second control plate  50 , namely L 1  and L 2  shown in  FIG. 3 , are set 0.20 mm and the intervals in Y-axis and Z-axis directions between the opening parts  48   a  of the first control plate  48  and the opening parts  50   a  of the second control plate  50  are set 3 mm.  
      The numerical apertures of the first control plate  48  and the second control plate  50  in the first example are the same as the numerical apertures of the first control plate  48  and the second control plate  50  in the second example. Here, the numerical aperture of the control plate is expressed as “a whole area of the opening part/an area of the control plate×100”(%)  
      Next, a constant voltage discharge property test (voltage of 0.3 V) for the first and second examples are implemented. Methanol having a 100% density is used as the liquid fuel. The constant voltage discharge property of the first example shows an electrical current value of 0.39 and the constant voltage discharge property of the second example shows an electrical current value of 0.68.  
      The second example obtains a larger discharge electrical current than the first example in which the gap between the opening parts  48   a  of the first control plate  48  and the opening parts  50   a  of the second control plate  50  is smaller than the first example. Such a difference of the electrical current value, namely the amount of the electrical generation, is caused by the difference of the supply amount of the methanol gas.  
      Thus, it can be found that the supply speed of the methanol gas can be controlled based on the gap between the opening parts  48   a  of the first control plate  48  and the opening parts  50   a  of the second control plate  50 . Here, the electric current value is indicated as a relative value.  
      [Second Embodiment] 
      A fuel cell of the second embodiment of the present invention is a modified example of the fuel cell of the first embodiment of the present invention. Here,  FIG. 4  is a cross-sectional view of a fuel cell of a second embodiment of the present invention. In  FIG. 4 , parts that are the same as the parts shown in  FIG. 1  through  FIG. 3  are given the same reference numerals, and explanation thereof is omitted.  
      Referring to  FIG. 4 , the fuel cell  60  of the second embodiment of the present invention has the same structure as the fuel cell  10  of the first embodiment of the present invention as shown in  FIG. 1 .  
      In the fuel cell  60  as well as the fuel cell  10  shown in  FIG. 1 , the second control plate  50  has a structure where plural openings  50   a  are formed at a side of the fuel electrode  23  of the liquid fuel vaporization film  49 .  
      As discussed in the first embodiment of the present invention, the supply speed of the methanol gas to the fuel electrode  23  can be controlled by controlling a ratio of the entire areas of the opening parts  50   a  to the area of the second control plate  50 , namely the numerical aperture. The range in which the supply speed of the methanol gas can be controlled in this case is narrower than the fuel cell of the first embodiment. However, since the fuel cell of this embodiment has a simpler structure than the fuel cell of the first embodiment, it is possible to achieve easy productivity, reduction of the manufacturing cost, and others.  
      According to this embodiment, in the second control plate  50 , plural openings  50   a  are formed at the side of the fuel electrode  23  of the liquid fuel vaporization film  49 . In addition, the supply speed of the methanol gas to the fuel electrode  23  can be controlled based on the numerical aperture of the second control plate  50 .  
      The second control plate  50  may be provided so as to come in contact with the liquid fuel vaporization film  49  or be separated from the liquid fuel vaporization film  49 . The second control plate  50  may be provided, for example, via a space or between the fuel gas diffusion layer  52  and the fuel electrode current collector  53 . In either case, the supply speed of the methanol gas to the fuel electrode  23  can be controlled by the second control plate  50 .  
      [Third Example] 
      In the third example, a structural body having the following modified structure of the fuel cell  60  shown in  FIG. 4  is manufactured. That is, parts from the fuel gas diffusion layer  52  to the air supply part  30  are not provided. The fuel electrode side housing  41 , the fuel storage part  42 , the fuel cartridge  43 , the fuel pressure part  45 , the liquid fuel vaporization film  49 , and the second control plate  50  are provided. A side of the fuel gas diffusion layer  52  of the second control plate  50  is exposed to outside air.  
      The fuel electrode side housing  41 , the fuel storage part  42 , the liquid fuel vaporization film  49 , and the second control plate  50  have the same structure as the structure of the first example. As the second control plate  50 , the structural body having the numerical aperture, that is “(entire area of the openings)/(the area of the control plate)×100” having a range of 50% through 90% is manufactured. In addition, for comparison, a structural body for the comparison example not using the second control plate  50  is manufactured.  
      Next, 10 cm 3  of methanol (liquid) having an approximately 100% density is supplied from the fuel cartridge to the fuel storage part  42  and a back pressure of 100 kPa is applied by the fuel pressure part  45  so that methanol is vaporized from the second control plate  50 . The change of the weight of methanol in the fuel storage part  42  is measured so as to be converted into the supply speed of methanol gas.  
       FIG. 5  is a table showing methanol gas supply speed of a third embodiment and a comparison example.  
      Referring to  FIG. 5 , in the third example, the supply speed of the methanol gas is in proportion to the numerical aperture of the second control plate  50 . As compared with a comparison example where the second control plate  50  is not used, it is possible to decrease the supply of the methanol gas by decreasing the numerical aperture of the second control plate  50  in the third example and the controllability of the supply of the methanol gas is good.  
      The present invention is not limited to these embodiments, but variations and modifications may be made without departing from the scope of the present invention.  
      For example, a case where both the first control plate  48  and the second control plate  50  are provided as shown in  FIG. 1  and a case where the second control plate  50  is provided as shown in  FIG. 4  are discussed in the above first embodiment and second embodiment. However, only the first control plate  48  shown in  FIG. 1  may be provided. In this case, since the supply speed of the methanol aqueous solution to the liquid fuel vaporization film  49  can be controlled, it is possible to control the supply speed of the methanol gas.  
      This patent application is based on Japanese Priority Patent Application No. 2005-313251 filed on Oct. 27, 2005, the entire contents of which are hereby incorporated by reference.