Patent Publication Number: US-2006003219-A1

Title: Fuel cell having mechanism for pressurizing membrane electrode assembly and electronic device equipped with the same

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a fuel cell, more particularly a pressurizing mechanism which can adjust pressure applied to a membrane electrode assembly (MEA) as a power-generating element.  
      Recently, direct methanol fuel cells (DMFCs), which directly use methanol as a liquid fuel to generate power, have been attracting attention as power sources for portable electronic devices, because they are compact, can produce high outputs and are serviceable continuously for extended periods.  
       FIG. 13  is a sectional view of conventional fuel cell, where (a) is a vertical sectional view of the whole fuel cell, and (b) is a partly enlarged sectional view of the membrane electrode assembly.  
      The conventional fuel cell  6  comprises the membrane electrode assembly  4  (composed of each layer of the cathode  1 , electrolytic membrane  2  and anode  3 ) with the collecting plates  11  on both sides, where the assembly  6  is placed on the fuel chamber  5  filled with a liquid fuel (aqueous methanol solution). The fuel chamber  5  is provided with a plurality of through-holes  13  in one side in contact with the membrane electrode assembly through which the aqueous methanol solution flows to come into contact with the anode  3 . This generates a potential difference across the anode  3  and cathode  1  by the electrode reaction, to output power to an external load via the collecting plate  11  (refer to, e.g., Patent Document 1).  
      The membrane electrode assembly  4  and fuel chamber  5  are held between the pressurizing member  7  and counter member  8  via the clamping member  9 . In other words, the pressurizing member  7  and counter member  8  apply a pressure to the membrane electrode assembly  4  in the thickness direction to fix it on one side of the fuel chamber  5  under pressure.  
      Patent Document 1  
      JP-A-2004-79506 (Paragraphs 0022 to 0049, and FIG. 1)  
     BRIEF SUMMARY OF THE INVENTION  
      The conventional fuel cell  6  involves the following problems. There is a relationship between pressure applied to one side of the membrane electrode assembly  4  and power output. Increasing the pressure improves contact in the interface between the layers constituting the membrane electrode assembly  4  to decrease the contact resistance there and improve power generating efficiency. On the other hand, increasing the pressure collapse more voids in the catalytic layer (cathode  1  and anode  3 ) for the membrane electrode assembly  4  to prevent smooth movement of the electrode reaction products (carbon dioxide and water) and the like. This retards the electrode reaction to decrease power generating efficiency.  
      It is, therefore, preferable to apply an adequate pressure to the membrane electrode assembly  4  in order to realize high-efficiency power generation by balancing the above conflicting effects.  
      However, it is structurally very difficult for the conventional fuel cell  6  to control pressure to the membrane electrode assembly at a given level.  
      It is also essential to uniformly apply an adequate pressure to each portion of the membrane electrode assembly  4  in order to realize high-efficiency power generation. However, the structure shown in  FIG. 13  may not always apply a uniform pressure, when the portion in contact with the membrane electrode assembly  4  (e.g., pressurizing member  7  or one side of the fuel chamber  3 ) bends.  
      The present invention is developed to solve these problems. It is an object of the present invention to provide a fuel cell having a pressurizing mechanism which can apply an adequate pressure to a membrane electrode assembly working as a power-generating element, and apply a pressure to the assembly uniformly over the entire surface. It is another object to provide an electric device driven by the fuel cells.  
      Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       FIG. 1  shows a basic structure of a fuel cell of the first embodiment of the present invention, (a): vertical sectional view, and (b) plan view.  
       FIG. 2  shows an oblique view of a disassembled membrane electrode assembly module as a constitutional element of the present invention, and also an oblique view of the assembled membrane electrode assembly.  
       FIG. 3  shows an oblique view of a plate spring (elastic member) as a constitutional element of the present invention.  
       FIG. 4  shows (a) a plan view of a membrane electrode assembly module as a constitutional element of the present invention, and (b) a plan and vertical sectional views of a pressurizing member also as a constitutional element of the present invention.  
       FIG. 5  shows a plan and vertical sectional views of a pressurizing member as a constitutional element of the present invention.  
       FIG. 6  shows an oblique view of a disassembled fuel cell of the second embodiment of the present invention.  
       FIG. 7  shows plan views of (a) a membrane electrode assembly module of the fuel cell of the second embodiment of the present invention, and (b) that of a conventional fuel cell.  
       FIG. 8  shows an oblique view illustrating an assembled electronic device of the present invention.  
       FIG. 9 ( a ) to ( e ) show vertical sectional views illustrating several types of fuel cell of the third embodiment of the present invention.  
       FIG. 10  shows a fuel cell of the second embodiment of the present invention, (a) plan view, (b) vertical sectional view of the cell cut along the line X-X.  
       FIG. 11  shows a fuel cell of the second embodiment of the present invention, (a) plan view, (b) vertical sectional view of the cell cut along the line X-X.  
       FIG. 12  shows a fuel cell of the second embodiment of the present invention, (a) plan view, (b) vertical sectional view of the cell cut along the line X-X.  
       FIG. 13  shows a conventional fuel cell, (a) vertical sectional view of the assembled cell, and (b) partly enlarged view. 
    
    
     DESCRIPTION OF REFERENCE NUMERALS  
     
         
           10 A,  10 B,  10 C,  10 D,  10 E,  10 F and  10 G: Fuel cell  
           20 ,  20 B: Membrane electrode assembly module  
           21 : Membrane electrode assembly  
           22 : Electrolyte membrane  
           23 ,  23   a : Anode  
           23 ,  23   c : Cathode  
           24   a : Collecting plate for anode  
           24   c : Collecting plate for cathode  
           26   a : Fuel hole  
           26   c : Oxygen hole  
           28 : Notch  
           30 ,  30 B,  30 C and  30 E: Fuel chamber  
           31 : Aperture  
           32 : Basal lid  
           33 : Fuel injection port  
           34 : Cell body  
           35 : Cell partition  
           36 : Communicating hole  
           37 : Cell space  
           40 : Liquid fuel  
           41 : Supporting column  
           52 : Counter member  
           53 : Clamping member  
           53   a : Bolt  
           53   b : Nut  
           54   a ,  54   c : Coil spring (elastic member)  
           54   b ,  54   h : Plate spring (elastic member)  
           54   e : Cushion member (elastic member)  
           54   f : Plate spring (elastic member)  
           54   g : Beam member (elastic member)  
           57   a ,  57   b ,  57   c : Gap-regulating member  
           60 ,  60 A,  60 B,  60 C: Pressurizing member  
           61  ( 61   a ,  61   b ): Supply and discharge hole  
           62 A,  62 B,  62 C: Pressurizing plate  
           63 : Aperture  
           64 : Groove  
          P: Portable terminal (electronic device)  
       
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention is developed to solve the problems involved in conventional fuel cells, where an elastic member placed in a fuel chamber is an essential means for the fuel cell of the present invention, described in each claim. It can control pressure applied to a membrane electrode assembly for the fuel cell at an optimum level for high-efficiency power generation, when its spring constant or displacement amount is replaced for adequate ones, as required. Moreover, pressure can be applied to the membrane electrode assembly uniformly over the entire surface when a plurality of elastic members are used.  
      The embodiments of the present invention are described by referring to the attached drawings.  
     First Embodiment  
      The first embodiment of the present invention is described by referring to  FIG. 1 , wherein (a) is vertical sectional view and (b) is a plan view of the fuel cell.  
      As illustrated in  FIG. 1 , the fuel cell  10 A is composed of the essential components of membrane electrode assembly module  20  which consumes the liquid fuel  40  to generate power, fuel chamber  30  from which the liquid fuel  40  is supplied to the membrane electrode assembly module  20 , and member (composed of the counter member  52 , clamping member  53 , pressurizing member  60  and coil spring an elastic member  54   a ).  
      As illustrated in  FIG. 2 , the membrane electrode assembly module  20  is composed of the membrane electrode assembly (MEA)  21  held between 2 collecting plates (collecting plate for anode  24   a  and collecting plate for cathode  24   c ).  
      The membrane electrode assembly module  21  is composed of the electrolytic membrane  22  held between the anode  23   a  and cathode  23   c.    
      The collecting plate for anode  24   a , which is placed on the anode  23   a  on the side opposite to the electrolytic membrane  22 , is provided with a plurality of fuel holes  26   a  on the surface from which the anode  23   a  is exposed to the outside.  
      On the other hand, the collecting plate  24   c  for cathode, which is placed on the cathode  23   c  on the side opposite to the electrolytic membrane  22 , is provided with a plurality of oxygen holes  26   c  on the surface from which the cathode  23   c  is exposed to the outside. It is preferable that these fuel holes  26   a  and oxygen holes  26   c  stand face to face with the electrolytic membrane  22  in-between, as illustrated in  FIG. 2 .  
      When the fuel cell  10 A is of a type of direct methanol fuel cell (DMFC), each constitutional element for the membrane electrode assembly module  20  responsible for power generation exhibits the following function(s).  
      First, the anode  23   a  oxidizes methanol (liquid fuel  40 ) which comes into contact with the anode  23   a  to generate the hydrogen ions and electrons. It is composed of a mixture of catalyst of fine ruthenium/platinum alloy particles which are supported by fine carbon particles. The electrons generated move towards the collecting plate  24   a  for anode, from which they are transmitted to the outside via an interconnection (not shown).  
      The electrolytic membrane  22  transmits the hydrogen ions generated at the anode  23   a  towards the cathode  23   c  as the counter electrode, while blocking the electrons. It is composed, e.g., of a polyperfluorosulfonic acid resin, more specifically Nafion (Trademark) or Aciplex (Trademark).  
      The cathode  23   c  works to reduce oxygen with the hydrogen ions moving through the electrolyte membrane  22 . It is composed of a mixture of catalyst of fine platinum particles which are supported by fine carbon particles. The electrons required for the reduction are supplied from the collecting plate for cathode  24   c  via an interconnection (not shown).  
      The reactions occurring on the electrodes for the membrane electrode assembly  21 , producing carbon dioxide as a by-product gas on the anode  23   a  and water as a by-product on the cathode  23   c , are summarized below:  
      On the anode  23   a  
 
CH 3 OH+H 2 O→CO 2 +6H + +6 e   −   (1) 
 
 On the cathode  23   c  
 
O 2 +4H + +4 e   − →2H 2 O  (2) 
 
 Total reaction 
 
CH 3 OH+3/2O 2 →CO 2 +2H 2 O  (3) 
 
      The coil spring  54   a  is an elastic member, with the basal end coming into contact with the inner basal surface of the fuel chamber  30  and the front end pressing the membrane electrode assembly  20  in the thickness direction via the collecting plate for anode  24   a  (refer to  FIG. 1 ). The pressure acting on the membrane electrode assembly  20  collapses irregularities in the interface between the anode  23   a  and collecting plate for anode  24   a  and that between the cathode  23   c  and collecting plate for cathode  24   c  to increase contact area and decrease electrical contact resistance. The pressure, when exceeding an adequate level, collapses voids formed by the carbon particles which support the catalyst in the anode  23   a  or cathode  23   c , to prevent smooth movement of the by-product gas (carbon dioxide) on the anode  23   a  or by-product (water) on the cathode  23   c , each being discharged through the voids, leading to deteriorated power generating efficiency.  
      Therefore, the coil spring (elastic member)  54  is set at an adequate spring constant and displacement in such a way to apply an optimum pressure at which the membrane electrode assembly module  20  generates power at the highest efficiency.  FIG. 1 ( a ) shows only one coil spring  54   a . However, a plurality of the coil springs  54   a  may be used to apply a pressure to the membrane electrode assembly module  20  uniformly over the entire surface.  
      In the structure shown in  FIG. 1 , the membrane electrode assembly module  20  is clamped by the clamping member  54  at the four corners, with the result that it is subjected to a higher pressure at the four corners than in the center. Therefore, the coil spring  54   a  placed in the center presses the center of the membrane electrode assembly module  20  to secure a uniform pressure over the entire surface.  
      The plate spring  54   b  as an elastic member may be placed in the fuel chamber  30 , instead of the coil spring  54   a , as illustrated in  FIG. 3 . In this case, the angular spring is adjusted to have a spring force in such a way that it can press the membrane electrode assembly module  20  more strongly in the portion insufficiently clamped by the clamping member  53 .  
      The fuel chamber  30  is filled with the liquid fuel  40  in its internal space, to work to supply the fuel  40  to the membrane electrode assembly module  20 . The fuel chamber  30  is provided with one or more fuel injection ports ( 33  shown in  FIG. 6 ), although not shown in  FIG. 1 , to supply the liquid fuel  40  from the outside into the inside. The liquid fuel  40  may be supplied by another method to make up the fuel consumed for power generation, e.g., continuous supply from a back-up tank (not shown) under a given pressure, or forced recycling.  
      The fuel chamber  30  is also provided with one or more discharge holes (not shown) at optional position(s), through which the by-product gas (carbon dioxide) generated on the anode  23   a  and accumulating inside, is discharged. The discharge hole is provided with a porous membrane (not shown) which can allow carbon dioxide to pass while blocking the liquid fuel  40  to selectively discharge carbon dioxide while allowing the fuel chamber  30  to securely seal the liquid fuel  40 .  
      One side on the fuel chamber  30  is also provided with the aperture  31  having an area corresponding to the total area of the fuel holes  26   a , and the membrane electrode assembly module  20  is designed to have these fuel holes  26   a  exposed through the aperture  31 .  
      When the fuel chamber  30  is made of an electroconductive material, e.g., metal, it is necessary to provide an insulation membrane (not shown) in the interface between the fuel chamber  30  and collecting plate for anode  24   a . This is to prevent the electrons generated on the anode  23   a  from running out through the fuel chamber  30 .  
      The pressurizing member  60 , located on the side of the collecting plate for cathode  24   c  in the membrane electrode assembly module  20 , is provided with a plurality of the supply and discharge holes  61  which are in communication with a plurality of the oxygen holes  26   c  to take oxygen from air into the membrane electrode assembly module  20 . The pressurizing member  60  and counter member  52  hold the membrane electrode assembly module  20  and fuel chamber  30  in-between by a clamping force provided by a plurality of bolts  53   a  and nuts (2 sets in the figure) running through these members where the module  20  is pressed to and fixed on the fuel chamber  30  at the aperture  31 .  
      When the pressurizing member  60  is made of an electroconductive material, e.g., metal, it is necessary to provide an insulation membrane (not shown) in the interface between the pressurizing member  60  and collecting plate for cathode  24   c . This is to prevent the hydrogen ions from being neutralized by the electrons flowing into from the outside.  
      The oxygen hole  26   c  and supply and discharge hole  61  may have an opening of circular shape as shown in  FIG. 1 . However, the oxygen hole  26   c  provided on the membrane electrode assembly module  20  may have an opening of almost rectangular shape with a long/short side ratio of 2 or more, as shown in  FIG. 4 ( a ) presenting a horizontally cut section. Similarly, each of the supply and discharge holes  61  provided in the pressurizing member  60  in such a way to be in communication with the oxygen hole  26   c , has an opening of almost rectangular shape in the horizontally cut section with a long/short side ratio of 2 or more, as shown in  FIG. 4 ( b ). Moreover, it is designed to have a vertical cut section with the outer side exposed to air having a larger opening area than the inner side on the oxygen hole  26   c . More specifically, it may have a step on the inner wall (supply and discharge hole  61   a , shown in  FIG. 4 ( b ) presenting a vertically cut section) or slanted inner wall (supply and discharge hole  61   b  shown in  FIG. 5  presenting a vertically cut section). The opening of the supply and discharge hole  61  and that of the oxygen hole  26   c  in communication with the hole  61  are not limited to a rectangular shape shown in the figure, so long as it has a ratio of a longitudinal direction in a vertical cut section to a perpendicular direction thereof. For example, it may be elliptical.  
      Moreover, the supply and discharge holes  61  are surface-treated to be water-repellant by a known method to easily remove water evolving by the power-generating reaction from the holes. Removal of water, which may hinder smooth flow of oxygen, keeps stable power generating efficiency even when the fuel cell is in service for extended periods.  
      The fuel cell of this embodiment can control pressure on the membrane electrode assembly  21  as a power-generating element by adequately selecting the elastic member (coil spring  54   a  or plate spring  54   b ). Even when the pressurizing member  60  is bent by a clamping force by the clamping member (in other words, when pressure on the module  20  decreases in the center), it can apply a pressure to the membrane electrode assembly  21  uniformly over the entire surface by the elastic member located in the center. Thus, this embodiment provides the fuel cell  10 A which can generate power at a high efficiency.  
      A gap-regulating member, described later, may be used also for the fuel cell of this first embodiment.  
     Second Embodiment  
      The second embodiment of the present invention is described by referring to  FIG. 6 .  
      As shown in  FIG. 6 , the fuel cell  10 B of this embodiment has a plurality of the membrane electrode assembly modules  20 B electrically connected to each other in series or parallel, and arranged two-dimensionally on one side of the fuel chamber  30 B.  
       FIG. 7 ( a ) is a plan view illustrating arrangement of the membrane electrode assembly modules  20 B in this embodiment. As shown, the notches  28  are provided each in the vicinity of the hole  53   a  through which a bolt (clamping member  53 ) is inserted in the interface between the adjacent membrane electrode assembly modules  20 B. As a result, these notches allow the membrane electrode assembly modules  20 B to be arranged at reduced gaps. It is apparent, when compared with arrangement in a conventional structure formed in the Comparative Example shown in  FIG. 7 ( b ), that this embodiment can improve a higher mounting density of the modules on one plane of the fuel cell.  
      These membrane electrode assembly modules  20 B shown in  FIGS. 6 and 7  are electrically connected to each other in series or parallel. When they are connected in series, the collecting plate  24   a  for anode and collecting plate  24   c  for cathode are connected to each other linearly (refer to  FIG. 2 ). The line of the modules  20 B is provided with interconnections (not shown) at both ends to transmit power output to the outside.  
      When the modules  20  are connected in parallel, the collecting plates for anode  24   a  of a plurality of the membrane electrode assembly modules  20 B are connected to each other, and so are the collecting plates for cathode  24   c.    
      Returning back to  FIG. 6 , the description is continued.  
      The fuel chamber  30 B in the second embodiment is composed of the cell body  34  and basal lid  32  working as the side wall and basal plane, respectively. A plurality of the membrane electrode assembly modules  20 B are provided on the cell body  34  in such a way that a plurality of the fuel holes  26   a  (refer to  FIG. 2 ) are exposed through the cell space  37  openings defined by the cell partitions  35 . The communicating holes  36  are provided to run through the cell partitions  35  to supply the liquid fuel (methanol) to all of the cell spaces  37 .  
      The fuel cell  10 B is composed of the pressurizing member  60 B, membrane electrode assembly modules  20 B, cell body  34 , basal lid  32  and counter member  52 B which are built-up in this order, and is clamped by a plurality of bolts (clamping members  53 ) running through these layers.  
      These bolts (clamping members  53 ) run through the cell partitions  35 , each located in the interface between a plurality of the membrane electrode assembly modules  20 B. It is important to symmetrically clamp the membrane electrode assembly module  20 B periphery by the clamping members  53  in order to apply a uniform pressure to the module surface. It is expected that such a uniform surface pressure reduces electrical contact resistance between the membrane electrode assembly module  20 B and collecting plate  24   a  or  24   c  (refer to  FIG. 2 ), and also improves contact between the upper side of the cell body  34  and module  20 B to prevent leakage of the liquid fuel.  
      The plate springs (elastic members)  54   b  are positioned in each of the cell spaces  37 , each with the basal end coming into contact with the inner basal surface of the basal lid  32  and the front end coming into contact with the membrane electrode assembly  20 B to provide a uniform pressure on the entire surface. In the structure shown in  FIG. 6 , the pressurizing  60 B will be bent when clamped by the clamping member  53  to cause a pressure distribution on the surface, as is the case with the first embodiment. However, the pressure can be uniformized and controlled by the actions of the plate springs  54   b.    
      When the fuel cell of this embodiment is of a type of direct methanol fuel cell (DMFC), a means for discharging the by-product gas (carbon dioxide) produced in the cell spaces  37  is an essential cell component. It can be discharged to the outside by, e.g., forced circulation of the liquid fuel, or through a window of special membrane which can selectively allow the by-product gas to pas while blocking the liquid fuel, provided on the fuel chamber.  
       FIG. 8  shows an oblique view illustrating the portable terminal P (electronic equipment) as an electronic device of the present invention to which the fuel cell  10 B having the pressurizing mechanism of the second embodiment can be attached. The membrane electrode assembly modules  20 B (refer to  FIG. 6 ) can provide a fuel cell of increased output and decreased thickness when arranged two-dimensionally without forming a gap between them. The fuel cell  10 B can be an optimum power source for the portable terminal P, which is required to be light, compact and serviceable for extended periods, even when it consumes much power. The electronic device of the present invention covers a wide concept, including a portable terminal shown in  FIG. 8  and other portable devices, e.g., cellular phones, PDAs and laptops, and indoor-outdoor devices, e.g., game devices.  
      As discussed above, the fuel cell  10 B of the second embodiment comprises a plurality of the membrane electrode assembly modules  20  densely arranged without forming a gap between them, which can adequately control pressure on each of the membrane electrode assemblies  21 . These densely arranged modules  20 B can make the fuel cell compact as a whole with keeping a high output at a high efficiency. Therefore, the electronic device driven by the fuel cells of the present invention is serviceable for extended periods, even when it consumes much power.  
     Third Embodiment  
      The third embodiment of the present invention is described by referring to  FIG. 9 .  
      The fuel cell  10 C shown in  FIG. 9 ( a ) differs from the fuel cell  10 B of the second embodiment in several ways. First, the fuel chamber is provided with a plurality of the through-holes  38  in one side, each being in communication with each of the fuel holes  26   a . Second, the coil spring (elastic member)  54   c  has the basal end coming into contact with the pressurizing member  60  and the other end coming into contact with the collecting plate for cathode  24   c , to apply a pressure to the membrane electrode assembly module  20  in the thickness direction. It is optionally provided with the gap-regulating members  57   a . The component of the fuel cell  10 C of the third embodiment corresponding to that of the fuel cell  10 A of the first embodiment is marked with the same reference numeral, and its description is omitted to avoid unnecessary duplication.  
      The fuel cell  10 C of the third embodiment can change extent of clamping provided by the clamping member (bolt and nut) to arbitrarily control the gap between the pressurizing member  60  and fuel chamber  30 C. The coil spring (elastic member)  54   c  can be displaced in accordance with the changed gap to control (e.g., uniformize) pressure on the membrane electrode assembly module  20 .  
      The gap-regulating membrane  57   a  comes into contact with the pressurizing member at one end and with part of the fuel chamber  30 C (which includes the counter member  52  shown in the figure) at the other end to regulate the gap. The gap-regulating membrane  57   a  allows the fuel cell  10 C to be assembled to have a given gap between the pressurizing member  60  and fuel chamber  30 C without needing a special jig, thereby preventing pressure applied to the membrane electrode assembly module  20  from increasing to an excessive level.  
      In  FIG. 9 ( a ), the gap-regulating member  57   a  is structured to run through the bolt (clamping member  53 ), but it is not limited to this structure. For example, it may be fixed on the pressurizing member  60  or fuel chamber  30 C as shown in  FIG. 9 ( b ) (the pressurizing member  60  in the figure) at one end and come into contact with the other (fuel chamber  30 C in the figure) at the other end. Moreover, it may be divided into two segments, one being integrated into the pressurizing member  60  and the other into the fuel chamber  30 C as shown in  FIG. 9 ( c ). These segments come into contact with each other, when clamped by the nut (clamping member  53 ), to regulate the gap between the pressurizing member  60  and fuel chamber  30 C.  
       FIG. 9 ( b ) to ( e ) show other conceptual types of fuel cell of the third embodiment of the present invention. In the fuel cell  10 D shown in  FIG. 9 ( b ), the plate spring (elastic member)  54   d  arching upwards with both ends fixed is placed to come into contact with the pressurizing member  60  or collecting plate for cathode  24   c  (with the pressurizing member  60  in the figure) at the projection in the center. The arching direction of the plate spring  54   d  may be reversed, when the membrane electrode assembly module  20  is pressed insufficiently in the center.  
      The fuel cell  10 E shown in  FIG. 9 ( c ) provides an example with the porous cushion member  54   e  as an elastic member, where the porous cushion member  54   e  totally comes into contact with the upper and lower members on both sides, with the result that it applies a pressure to the membrane electrode assembly module  20  uniformly over the entire surface.  
      The fuel cell  10 F shown in  FIG. 9 ( d ) is further provided with the supporting column  41  in the fuel chamber  30 C. It runs through the fuel chamber  30 C to come into contact with the one side, working as a prop to receive a pressure from the elastic member  54   c  and thereby preventing a strain-caused deformation of a fuel cell  30 C portion pressed by the member  54   c . The supporting column  41  is effective particularly for a fuel cell with the fuel chamber  30 C which is made of a flexible material to cause an insufficient pressure applied to the membrane electrode assembly module  20  in the center.  
      The fuel cell  10 G shown in  FIG. 9 ( e ) has the fuel chamber  30 E with the principal plane plate  33  and chamber body  34  to be filled with a liquid fuel, which are separated from each other. The principal plane plate  33  is served as side of the fuel chamber  30 E provided with through-holes is integrated into the leg  39  corresponding to the supporting column  41  and is made of a material having a higher elastic modulus than that for the chamber body  34 . This structure can reduce thickness of the fuel chamber  30 E side coming into contact with the membrane electrode assembly module  20 , and thereby reduce height of the whole fuel cell  10 G.  
      Thus, the fuel cell of the third embodiment can also apply an adequate pressure to the membrane electrode assembly  21  as a power-generating element by the actions of the elastic member (coil spring  54   c , plate spring  54   d  or cushion member  54   e ). Moreover, the pressure can be kept uniform even when one side of the fuel chamber  30 C coming into contact with the membrane electrode assembly module  20  is bent. Still more, the fuel cell of the third embodiment can prevent an excessive pressure and an ununiform pressure when the fuel chamber  30 C or  30 E side is bent.  
     Fourth Embodiment  
      The fourth embodiment of the present invention is described by referring to FIGS.  10  to  12 , where (a) is a plan view and (b) is a vertical sectional view of the cell cut along the line X-X in each figure.  
      Referring to  FIG. 10 , the fuel cell is structured to have the pressurizing plate  62 A coming into contact closely with the collecting plate for cathode  24   c , and a plurality of the supply and discharge holes  61  which are in communication with the corresponding oxygen holes  26   c , where the pressurizing member  60 A is provided with the aperture  63  through which the pressurizing plate  62 A runs. Moreover, the plate springs (elastic members)  54   f  are fixed around the aperture  63  (at the corners near the clamping member  53  in the figure) at the basal end, and fixed around the pressurizing plate  62 A (at the corners in the figure) at the front end. Thus, the pressurizing plate  62 A is supported in such a way that it can be elastically displaced in the direction of the membrane electrode assembly module  20  thickness towards the pressurizing member  60 A. The elastic force generated by the elastic displacement provides a pressure in the direction of the membrane electrode assembly module  20  thickness.  
      The pressure distribution is clearly found to be more uniform in the fuel cell of the fourth embodiment shown in  FIG. 10  than in the one shown in  FIG. 13  as confirmed by the analysis with a laser-aided strain distribution meter.  
       FIG. 11  shows another fuel cell type of the fourth embodiment. As shown, the pressurizing plate  62 B is separated by the pressurizing member  60 B by the groove  64  of a plate material hollowed out to leave the beams (elastic members)  54   g . These beams  54   g  work as the elastic members to support the pressurizing plate  62 B in such a way that it can be elastically displaced in the direction of the membrane electrode assembly module  20  thickness towards the pressurizing member  60 B. This structure is also found to generate more uniform pressure than the one shown in  FIG. 13 .  
       FIG. 12  shows still another fuel cell type of the fourth embodiment.  
      The fuel cell is structured to have the pressurizing plate  62 C closely coming into contact with the collecting plate  24   c  for cathode, and a plurality of the supply and discharge holes  61  which are in communication with the corresponding oxygen holes  26   c , where the elastic members  54   h  are located around the pressurizing plate  62 C (at the corners in the figure), integrated thereinto at the corner in this embodiment shown in the figure, with each terminal end fixed by the bolt and nut (clamping member  53 ). The terminal end corresponds to the pressurizing member  60 C, which, when clamped by the clamping member  53 , bends the elastic member  54   h  to generate a pressure. This structure is also found to generate a more uniform pressure than the one shown in  FIG. 13 .  
      The gap-regulating member, described earlier, may be used also for the fuel cell of the fourth embodiment.  
      As discussed above, the fuel cell of the fourth embodiment can also control a pressure on the power-generating element at an adequate level. The fuel cell of the fourth embodiment, in particular, can prevent generation of uneven pressure on the membrane electrode assembly module  20  because the members coming into contact with the module  20  will not be bent when clamped by the clamping member.  
      The present invention is described mainly by taking fuel cells of direct methanol fuel cell (DMFC) type as the examples. However, the concept of the present invention is also applicable to other types for power generation. In particular, it is applicable to a fuel cell, whether it uses a liquid or gas as a fuel, and whether it is large or small in size, within the technical concept of the present invention.  
      It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.  
     ADVANTAGES OF THE INVENTION  
      The present invention can apply an adequate pressure to the membrane electrode assembly as a power-generating element, uniformly over the entire surface.