Patent Publication Number: US-2006003196-A1

Title: Fuel cell and electronic device equipped with the same

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a fuel cell, in particular a fuel cell having one or more membrane electrode assembly modules, and electronic device equipped with the fuel cell.  
      Recently, direct methanol fuel cells (DMFCs), which directly use methanol as a liquid fuel to generate power, have been attracting attention as portable power sources capable of driving codeless devices, e.g., laptops, continuously for extended periods. Therefore, they are strongly demanded to be compacter for satisfying these purposes. As part of the efforts to satisfy these demands, various attempts have been made to develop fuel cells of reduced size or increased power output, e.g., arranging membrane electrode assemblies (MEAs) as power-generating elements two-dimensionally or electrically connecting them to each other in series.  
       FIG. 8  is a sectional view of conventional fuel cell.  
      The conventional fuel cell  1  comprises a plurality of membrane electrode assemblies  2  (five membrane electrode assemblies in the figure) arranged two-dimensionally with their anodes facing the fuel chamber  3 , where the adjacent assemblies are electrically connected to each other in series, with the anode of one assembly connected to the cathode of the other assembly by the collecting plate  7 .  
      The fuel chamber  3 , which holds an aqueous methanol solution  4  as a liquid fuel, is provided with a number of holes  9  in the principal plane coming into contact with the membrane electrode assemblies  2 . The aqueous methanol solution  4  moves upwards through the lifting member  5  to reach the holes  9  and come into contact with the anode of each membrane electrode assembly. This triggers the electrode reaction to generate a potential difference across the anode and cathode, producing power to be outputted to an external load. The aqueous methanol solution  4  is depleted as power is continuously outputted to an external load. However, the fuel cell is serviceable continuously for extended periods, because the aqueous methanol solution  4  is made up, as required, from the fuel supply device  6  (refer to, e.g., Patent Document 1). Patent Document 1 JP-A-2004-79506  
     BRIEF SUMMARY OF THE INVENTION  
      The conventional fuel cell  1  involves the following problems. For example, a direct methanol fuel cell (DMFC) stoichiometrically needs a 50/50 by mol methanol/water mixture for the anode reaction. However, the aqueous solution of such a high methanol concentration, when used as a liquid fuel, will cause the crossover phenomenon, in which the membrane electrode assembly  2  passes more methanol molecules than water molecules to deteriorate activity on the air side, decreasing power output. Therefore, the fuel cell uses a much diluted solution containing methanol of about 10% to avoid the undesirable phenomenon.  
      The aqueous methanol solution  4  to be supplied to each of the membrane electrode assemblies  2  (five membrane electrode assemblies in the figure) is transferred via the supply pipe  8 , shown in the left side in the figure, from the left side to the right side end. The aqueous methanol solution  4 , initially containing methanol at a lower concentration than the stoichiometric level, further loses methanol concentration as it is consumed by the membrane electrode assemblies one by one, where methanol and water are consumed evenly. In other words, there is a methanol concentration distribution in the fuel chamber  3 , the concentration at the starting point to which the supply pipe  8  is connected decreasing sequentially as the aqueous methanol solution  4  goes to the end.  
      Basically, the liquid fuel  4  has an optimum methanol concentration for maximizing power generating efficiency of a fuel cell. However, in a fuel cell with membrane electrode assemblies arranged two-dimensionally, uneven methanol concentration on a planar area will cause problems resulting from a lower than expected output even when fuel cell capacity is increased to produce high output.  
      The present invention is developed to solve these problems. It is an object of the present invention to provide a fuel cell which can supply a fuel of uniform concentration to its membrane electrode assemblies to generate power at a high efficiency.  
      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. 1A  shows a vertical sectional view illustrating basic structure of a fuel cell of the first embodiment.  
       FIG. 1B  shows a vertical sectional view illustrating another fuel cell of the first embodiment.  
       FIG. 1C  shows a vertical sectional view illustrating still another fuel cell of the first embodiment.  
       FIG. 1D  shows a vertical sectional view illustrating still another fuel cell of the first embodiment.  
       FIG. 2  shows an oblique view of a membrane electrode assembly module for a fuel cell.  
       FIG. 3  shows horizontal sectional views of several fuel supply gear shapes.  
       FIG. 4  shows sectional views of several supply hole types, illustrating a by-product gas leaving as bubbles.  
       FIG. 5  is an oblique view of a disassembled fuel cell of the second embodiment.  
       FIG. 6  is an oblique view illustrating connection of membrane electrode assembly modules for a fuel cell of the second embodiment.  
       FIG. 7  is an oblique view of an electronic device of the present invention.  
       FIG. 8  shows a vertical sectional view of a conventional fuel cell. 
    
    
     DESCRIPTION OF REFERENCE NUMERALS  
       10 A,  10 B,  10 C,  10 D and  10 E: Fuel cell  
       20 : Membrane electrode assembly module  
       21 : Membrane electrode assembly  
       22 : Electrolyte membrane  
       23   a : Anode  
       23   c : Cathode  
       24   a : Collecting plate for anode  
       24   c : Collecting plate for cathode  
       25   a : Negative terminal  
       25   c : Positive terminal  
       26   a : Fuel hole  
       26   c : Oxygen hole  
       30  ( 30 A,  30 B,  30 C,  30 D and  30 E): Fuel chamber  
       31 ,  31   e : Principal plane plate  
       32  ( 32 E): Lid  
       33 : Fuel injection hole  
       34 : Discharge hole  
       35 : Aperture  
       36  ( 36 E): Gas-permeable membrane  
       37 : Fuel separating membrane  
       38  ( 38   a ,  38   b  and  38   c ): Supply hole  
       39 ,  43 : Fine pore  
       40  ( 40   a  and  40   b ): Liquid fuel  
       41 : Fuel supply device  
       42 ,  42 E: Fuel supply gear  
       50 ,  50 E: Cell body  
       51 : Cell partition  
       52 : Inner space  
       53 : Holding plate  
       54 : Bolt  
       55 : Supply hole  
       56 : Communicating hole  
      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 the fuel cell having a structure described in each claim first fills up the fuel supply gear totally with a fuel (e.g., aqueous methanol solution), supplied from the outside into the inner space of the fuel chamber, and then sends it via the fine pores to the membrane electrode assemblies from nearby supply holes for generating power. The fuel is not consumed by the membrane electrode assemblies (MEAs) while it is held in the fuel supply gear and has a uniform composition when it is released from the gear at any point.  
      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 from  FIG. 1 (A-D) to  FIG. 4 .  
      Referring to  FIG. 1A , the fuel cell  10 A is mainly composed of the membrane electrode assembly module  20  which consumes the liquid fuel  40  to generate power, fuel chamber  30 A from which the liquid fuel  40  is supplied to the membrane electrode assembly module  20 , fuel supply device  41  which holds the liquid fuel  40  outside of the fuel chamber  30 A, fuel supply gear  42  which supplies the liquid fuel  40  from the fuel supply device  41  to the vicinity of each membrane electrode assembly module  20 , and holding plate  53  which presses the membrane electrode assembly module  20  to, and fixes it on, the fuel chamber  30 A. The fuel supply device  41  and fuel supply gear  42  are in communication with each other via the fuel injection hole  33 , to send the liquid fuel  40  from the fuel supply device  41  to the fuel supply gear  42  under pressure.  
      As illustrated in  FIG. 2 , the membrane electrode assembly module  20  is composed of the membrane electrode assembly  21  held between two 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 , 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 , by which the anode  23   a  is exposed to the outside.  
      On the other hand, the collecting plate for cathode  24   c , 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 , by 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 for anode  24   a , 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 (trade mark)-or Aciplex (trade mark).  
      The cathode  23   c  works to reduce oxygen, moving through the oxygen holes to come into contact with the cathode  23   c , with the electrons supplied from the collecting plate for cathode  24   c , and to react the oxygen with the hydrogen ions moving from the electrolytic 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  
 
3/2O 2 +6H + +6 e   − →3H 2 O  (2) 
 
 Total reaction 
 
CH 3 OH+3/2O 2 →CO 2 +2H 2 O  (3) 
 
      The liquid fuel  40  (refer to  FIG. 1A ) is an aqueous methanol solution, as described earlier. The fuel present in the inner space extending from the fuel supply device  41  to the fuel supply gear  42  is marked with  40   a , and that present in the fuel chamber  30  but outside of the fuel supply gear  42  is marked with  40   b  for convenience to distinguish them from each other. The liquid fuel  40   b  held in the fuel chamber  30  is diluted to have a significantly lower methanol concentration (about 10%) than the stoichiometric ratio (50/50 by mol) to avoid the above-described crossover phenomenon, which can decrease power output. However, methanol and water are actually consumed on the anode  23   a  in a ratio close to the stoichiometric level, with the result that the liquid fuel  40   b  in the fuel chamber  30  gradually loses its methanol concentration. Therefore, it is necessary for the make-up liquid fuel  40   a  to have a higher methanol concentration than the liquid fuel  40   b , preferably a stoichiometric concentration at which the liquid fuel is actually consumed on the anode  23   a.    
      The above structure allows the liquid fuel  40   b  in the fuel chamber  30  to be kept at a methanol concentration needed to continuously secure power generation at a maximum output, even when it is diluted, because the liquid fuel  40   a  of higher concentration is sequentially supplied from the fuel supply device  41 . The methanol concentration which can continuously secure power generation at a maximum output, set at around 10% for the above structure, widely varies depending on the constitutional elements for the membrane electrode assembly module  20 . At the same time, the liquid fuel  40   a  in the fuel supply device  41  can have a methanol concentration much lower than the stoichiometric level, in consideration that a fairly large quantity of water passes through the membrane electrode assembly  21 . Therefore, there may be cases where need for distinguishing the liquid fuels  40   b  from each other is essentially saved.  
      The fuel chamber  30  is composed of the cell body  50 , principal plane plate  31  and lid  32  as shown in  FIG. 1A , and is filled with the liquid fuel  40   b  in its internal space to work to supply the fuel  40   b  to the membrane electrode assembly module  20 .  
      The cell body is cylindrical in shape with the principal plane plate  31  and lid  32  at the ends, to form the inner space to be filled with the liquid fuel  40 . It is provided with the O-rings  37  at each end, with which the principal plane plate  31  or lid  32  is in contact, to seal the inner space and prevent leakage of the liquid fuel  40   b.    
      The cell body  50  is provided, on one lateral side, with the fuel injection hole  33  through which the liquid fuel  40   a  is passed into the inner space of the fuel chamber  30  from the fuel supply device  41  outside.  
      Moreover, the fuel supply gear  42 , which is in communication with the fuel injection hole  33 , is provided in the inner space of the fuel chamber  30  in such a way to come close to the membrane electrode assembly modules  20 . The fuel supply gear  42  is provided, on the surface, with a number of fine pores  43  through which the liquid fuel  40   a  can pass.  
      The fuel supply gear  42  preferably has a shape to cover a wide area over the principal plane plate  31  so that the liquid fuel  40  leaving the fine pores  43  can be uniformly supplied to the membrane electrode assembly module  20  surfaces.  FIG. 3  shows several shapes which the fuel supply gear  42  can take; (a) I-shape, (b) U-shape, (c) fishbone, (d) wide rectangle, (e) volute and (f) shape having a ball in the center.  
      The fuel supply gear  42  may be a varying material, e.g., porous ceramic, hard resin, metal or soft resin film formed into a bag shape. The fine pores  43  provided on the fuel supply gear  42  surface preferably have a controlled size and are adequately arranged to uniformly release the liquid fuel  40   a  sent from the fuel injection hole  33  under a given pressure. More specifically, the fine pores  43  have a diameter of 0.1 to 100 μm, preferably around 1 μm in actuality, and are arranged to secure a porosity of 20 to 85%.  
      The fine pores  43  shown in  FIG. 1  are arranged at the same density over the entire fuel supply gear  42  surface. However, other arrangements can be adopted. For example, they may be arranged more densely on the membrane electrode assembly module  20  side. The fuel supply gear  42  having the above shape and arrangement can minimize concentration distribution of the liquid fuel  40  in the fuel chamber  30 .  
      The fuel supply device  41  sends the liquid fuel  40   a  which it holds, injecting it under a pressure of 1 atm. or more into the inner space of the fuel chamber  30  from the fuel injection hole  33  (refer to  FIG. 1A ). The liquid fuel  40   a  to be injected may be pressurized by various means. For example, it may be forced out of the fuel supply device  41  by a freely movable piston driven by an elastic spring, both provided in the device  41  inside, or by a pressure gas evolving in the device  41  inside. These means are not described in detail in this specification.  
      The principal plane plate  31  serves as a main side of the fuel chamber  30 , and is provided with a plurality of supply holes  38  which correspond to a plurality of the fuel pores  26   a  provided on the membrane electrode assembly module  20  coming into contact with the plate  31 . The liquid fuel  40   b  held in the inner space of the fuel chamber  30  is sent to the anode  23   a , exposed through the fuel holes  26   a , via the supply holes  38 .  
      When the principal plane plate  31  is made of an electroconductive material, e.g., metal, it is necessary to provide an insulation membrane (not shown) in the interface between the plate  31  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 .  
       FIG. 4  (a) to (c) are sectional views illustrating several types of the supply hole  38  ( 38   a ,  38   b  and  38   c ), each of which is an enlarged section indicated by the arrow Y in  FIG. 1A . It shows how the by-product gas bubbles evolved by the power-generating reaction on the anode  23   a  grow in each type of the supply hole  38  step by step in Steps 1 to 4.  
       FIG. 4  (a) illustrates growth of the bubbles in the supply hole  38   a  having a rectangular section. The fine bubbles evolving on the anode  23   a  grow in the lateral direction while repeatedly coalescing with each other and expanding (Step 1). The grown bubble comes to totally cover the anode  23   a  portion exposed through the supply hole  38  (Step 2). Then, it grows vertically (Step 3), and comes off from the supply hole  38  by buoyancy (Step 4). The supply hole  38  may no longer contribute to power generation, when covered with the bubble(s) semi-permanently.  
      The supply holes  38   b  and  38   c  in  FIG. 4  (b) and (c) have a tapered section flaring towards the inner space of the fuel chamber  30 , in a straight line ( 38   b ) or curved line ( 38   c ). In the tapered supply hole,  38   b  or  38   c , the bubbles grow similarly in Steps 1 and 2, but move away from the hole more quickly in Steps 3 and 4 while they are growing vertically, leaving behind no residual component. Therefore, shut-down of power generation at the hole for extended periods can be avoided.  
      The anode  23   a , exposed through the fuel holes  26   a , is surface-treated by a known method to be hydrophilic from its surface to the inner surface of each of the supply holes  38 . This prevents the formed bubbles from remaining on the surface for extended periods, allowing them to move away in a shorter time.  
      Returning back to  FIG. 1A , the description is continued.  
      The holding plate  53  is placed on the side of the collecting plate for cathode  24   c  in the membrane electrode assembly module  20 , and is provided with a plurality of the supply and discharge holes  55  which are in communication with a plurality of the oxygen holes  26   c  to take air (oxygen) into the module  20 . It is clamped to the fuel chamber  30  by a plurality of bolts  54  (2 in the figure) running through the cell body  50  to hold the membrane electrode assembly module  20  in-between. This presses the membrane electrode assembly module  20  to the principal plane plate  31  under a uniformly distributed surface pressure provided by the holding plate. As a result, the principal plane plate  33  and collecting plate  24   a  for anode come into contact closely with each other to have a tight interface, preventing leakage of the liquid fuel  40   b  from the supply holes  38  to the outside.  
      When the holding plate  53  is made of an electroconductive material, e.g., metal, it is necessary to provide an insulation membrane (not shown) in the interface between the holding plate  53  and collecting plate  24   c  for cathode. This is to prevent the hydrogen ions from being neutralized by the electrons flowing into from the outside.  
      The discharge holes  34  are provided each at a position in the inner space of the fuel chamber  30 , where the by-product gas (carbon dioxide) discharged from the fuel holes  26  in the membrane electrode assembly module  20  is collected. They are opened in the direction of buoyancy. Therefore, they are provided in the central part of the lid  32  in the structure shown in  FIG. 1A . However, their position is not limited to the above. For example, one or more holes may be provided at any position(s) in the fuel chamber  30 , depending on various conditions, e.g., direction in which the fuel cell  10 A is installed. Moreover, the discharge hole  34  is provided with the gas-permeable membrane  36  which can allow carbon dioxide to pass while blocking the liquid fuel  40   b.    
      More specifically, the gas-permeable membrane  36  may be in the form of woven fabric, non-woven fabric, net, felt or the like, made of continuously porous polytetrafluoroethylene (expanded PTFE), e.g., GORE-TEX (trade mark).  
      Providing the discharge hole  34  with the gas-permeable membrane  36  allows the by-product gas to be selectively discharged while tightly sealing the liquid fuel  40   b  in the fuel chamber  30 . The gas-permeable membrane  36 , which allows the by-product gas to pass while blocking the liquid fuel, prevents leakage of the liquid fuel from the fuel chamber, even when the fuel cell is inclined while the surface of the liquid fuel is in contact with the discharge hole. The gas-permeable membrane  36  shown in  FIG. 1A  totally covers one side of the lid  32 . However, the structure is not limited to the above, so long as it covers the discharge hole  34  openings.  
      Next, the other fuel cell types of the first embodiment are described by referring to  FIG. 1B  to  1 D.  
      The fuel cell  10 B shown in  FIG. 1B  is provided with the supply and discharge hole  38   a , in place of the supply holes  38  for the cell shown in  FIG. 1A , through which a plurality of the fuel holes  26   a  are exposed, where the hole  38   a  has an opening area comparable to the total opening areas of the holes  38 .  
       FIG. 4  (d) shows the process of the by-product gas bubbles moving away from the collecting plate  23   a  for anode in the fuel cell  10 B. They move away quickly leaving behind no residual component to avoid shut-down of power generation at the hole for extended periods, as is the case shown in  FIG. 4  (b) or (c).  
      The fuel cell  10 C shown in  FIG. 1C  is provided with the membrane electrode assembly modules  20  on both sides of the fuel chamber  30 . It can double power output while keeping its volume unchanged. The discharge holes, although not shown in the figure, are provided at adequate positions.  
      The fuel cell  10 D shown in  FIG. 1D  is provided with the fuel separating membrane  37  in place of the fuel supply gear  42  for the cell shown in  FIG. 1A . The fuel separating membrane  37  divides the fuel chamber  30 D inside in the direction almost in parallel to the principal plane plate  31 , and is provided with the fine pores  39  through which the liquid fuel can pass. The fuel injection hole  33  is provided in the fuel chamber  30  in the divided space on the lid  32  side.  
      The fuel cell of the first embodiment, described above, totally fills the fuel supply gear  42 , provided in the fuel chamber  30 , with the liquid fuel (e.g., aqueous methanol solution) charged under pressure to the fuel chamber  30  via the fuel injection hole  33  from the fuel supply device  41  outside. The fuel is not consumed by the membrane electrode assemblies (MEAs) while it is spreading into every corner of the fuel supply gear  42 , and has a uniform composition at any point. The liquid fuel  40  filling the fuel supply gear  42  inside is supplied, via the fine pores  43  provided on the fuel supply gear  42  surface, to the exposed anode  26   a  from the near-by supply holes  38  for power generation. The liquid fuel  40  is not consumed while it is moving from the fuel injection hole  33  to the supply holes  38 , although they are removed from the hole  33 , keeping its composition unchanged. The tapered structure of the supply hole  38  allows the by-product gas formed by the power-generating reaction to move away from the anode  26   a  in a very short time. Therefore, the fuel cell can generate power constantly at a high efficiency, even when it is in service for extended periods.  
     Second Embodiment  
      Next, the other fuel cell types of the second embodiment are described by referring to  FIGS. 5 and 6 .  
      As shown in  FIG. 5 , the fuel cell  10 E of this embodiment has a plurality of the membrane electrode assembly modules  20  which are electrically connected to each other in series or parallel and arranged two-dimensionally on the principal plane plate  31 E for the fuel chamber  30 E.  
      A plurality of the membrane electrode assembly modules  20  shown in  FIG. 6  are connected to each other in series, where the negative terminal  25   a  of the membrane electrode assembly module  20  is connected to the positive terminal  25   c  of the adjacent module  20  to establish the series circuit as a whole. The line of the modules  27  is provided with interconnections at both ends to transmit power output to the outside.  
      When a plurality of the membrane electrode assembly modules  20  are connected in parallel, the collecting plates for anode  24   a  of the adjacent modules  20 B are connected to each other, and so are the collecting plates  24   c  for cathode, although the detailed description is omitted.  
      The cell body  50 E is provided with a plurality of the inner spaces  52 , each at a position to correspond to the pairing membrane electrode assembly module  20  and separated from the adjacent one by the cell partition  51 , as shown in  FIG. 5 . Moreover, each of the cell partitions  51  is provided with the communicating hole  56  which allows the fuel supply gear  42 E to run through all of the inner spaces  52 . Therefore, the liquid fuel  40   a  can be distributed from the fuel supply device  41  to each of the inner spaces  52  while keeping its methanol concentration unchanged.  
      Moreover, the principal plane plate  31 E and holding plate  53 E are provided with a plurality of the fuel holes  26   a  and oxygen holes  26   c , respectively, which are corresponding to the respective supply holes  38  and supply and discharge holes  55 . The lid  32 E, gas-permeable membrane  36 E, cell body  50 E, principal plane plate  31 E, membrane electrode assembly module  20  and holding plate  53 E, provided in this order, are clamped to each other by a plurality of the bolts  54  running through them.  
      Each of the cell partitions  51  is located between the adjacent membrane electrode assembly modules  20 , which allows the bolt(s)  54  to run therethrough, and hence allows the membrane electrode assembly module  20  peripheries to be clamped symmetrically. As a result, a surface pressure is uniformly applied to the membrane electrode assembly modules  20 . Application of a uniform surface pressure is expected to bring several favorable effects, e.g., decreased contact resistance between the membrane electrode assembly  21  (refer to  FIG. 2 ) and collecting plate  24   a  for anode or collecting plate for cathode  24   c , and improved contact between the principal plane plate  31  and membrane electrode assembly module  20  to prevent the liquid fuel  40  flowing from the supply holes  38  from leaking through the interface between them.  
      Presence of the cell partitions  51  can increase flexural rigidity of the fuel cell  10 E, which can contribute to solving the problems of reduced flexural rigidity, occurring when number of the membrane electrode assembly modules  20  is increased to increase cell power output, because this decreases relative cell thickness in the width direction (or height).  
      The inner spaces  52  are arranged two-dimensionally in the lateral direction in  FIG. 5 . However, they may be arranged in the vertical direction to form a stacked structure for the fuel cell.  
       FIG. 7  shows an oblique view illustrating the portable terminal P as an electronic device of the present invention, equipped with the fuel cell  10 E of the second embodiment. The portable terminal P is generally required to be light, compact and serviceable for extended periods, even when it consumes much power. The fuel cell  10 E, which can satisfy the above requirements, can be an optimum power source for the portable terminal P. The electronic device of the present invention covers a wide concept, including a portable terminal shown in  FIG. 7  and other portable devices, e.g., cellular phones, PDAs and laptops, and indoor-outdoor devices, e.g., game devices.  
      The fuel cell of the second embodiment described above, which is required to be compact and generate high output, can spread a liquid fuel of constant composition into every corner of the membrane electrode assembly module  20 , even when the area for the modules  20  is expanded to increase power output. Moreover, the by-product gas evolved by the power-generating reaction can move away from the anode in a very short time. Therefore, the fuel cell can generate power constantly at a high efficiency, even when it is in service for extended periods.  
      The present invention is described on the basis that the fuel cell is of a direct methanol fuel cell type. Therefore, it is provided with the discharge hole  34  (refer to  FIG. 1 ) as an essential component for discharging the by-product gas (carbon dioxide) evolving on the anode  23   a . It is to be understood, however, that a structure in which the discharge hole  34  is not an essential component is also within the technical scope of the present invention, in expectation that a combination of liquid fuel  40  and membrane electrode assembly  21  may be developed in the future to evolve no by-product gas on the anode  23   a.  It is also to be understood that the technical scope of the present invention is directly applicable to a fuel cell which uses a gas fuel, because it can contribute to solving the similar problems involved in gas fuels.  
      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 generate power at a high efficiency, because it can supply a fuel of uniform composition to the membrane electrode assembly module at any point.