Patent Publication Number: US-9406951-B2

Title: Fuel cell and fuel cell system as described and claimed in

Description:
CROSS-REFERENCE to RELATED APPLICATIONS 
     This application is a U.S. national stage application of International Application No. PCT/JP2009/068033 filed Oct. 19, 2009, claiming a priority date of Oct. 28, 2008, and published in a non-English language. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to a fuel cell comprising an electrolyte membrane and an anode catalyst and a cathode catalyst provided on both sides of the electrolyte membrane, and to a fuel cell system including the fuel cell. 
     2. Background Art 
     A fuel cell has a membrane electrode assembly (hereinafter referred to as MEA) provided with an electrolyte membrane, and an anode catalyst and a cathode catalyst provided on both sides of the electrolyte membrane. The fuel cell includes an anode member (anode) provided with an anode fluid flow path for supplying an anode fluid to the anode catalyst of the MEA via a gas diffusion layer, and a cathode member (cathode) provided with a cathode fluid flow path for supplying a cathode fluid to the cathode catalyst of the MEA. 
     With such a fuel cell, air in the atmosphere (particularly, nitrogen which is an inert gas) mixes into the anode side as an impure gas via the electrolyte membrane when power generation is stopped. The problem arises here that even when an operation is started in this state and a hydrogen-rich anode fluid is introduced, hydrogen is not replaced immediately, and a sufficient electrical output (or amount of power generation) cannot be obtained. When the fuel cell is allowed to stand for a long term, in particular, the problem occurs that the partial pressure of the impure gas mixed into the anode rises, decreasing the amount of power generation. 
     To deal with these problems, a technology for purging the impure gas, which has been accumulated in the anode, with the hydrogen-rich anode fluid before start of operation has been proposed (see, for example, Patent Document 1). 
     Concretely, Patent Document 1 involves a purge valve for purging an impure gas accumulated in an anode with a hydrogen-rich anode fluid, and an exhaust gas treatment device for diluting an exhaust gas, which is discharged through the purge valve and contains hydrogen, and discharging the diluted gas to the outside. 
     According to this constitution of Patent Document 1, the impure gas on the anode side can be replaced by the hydrogen-rich anode fluid. Thus, a decrease in the amount of power generation can be prevented. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         
           
             [Patent Document 1] JP-A-2004-193107 
           
         
       
    
     The constitution of Patent Document 1, however, needs the purge valve and the exhaust gas treatment device, and is confronted with the problem that it results in the upsizing of equipment and a cost increase. 
     With the constitution of Patent Document 1, moreover, the impure gas can be excluded from the anode by purging at the starting of the equipment. However, the impure gas passes into the anode through the electrolyte membrane even during power generation. Thus, during long-term power generation, the opening and closing of the purge valve must be controlled, with the status of power generation being monitored, posing the problem of complicated control. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished in the light of the above-described circumstances. It is an object of the present invention to provide a downsized fuel cell and a downsized fuel cell system which can prevent a power generation failure due to the impure gas and can perform power generation continuously for a long term. 
     A first aspect of the present invention for solving the above problems is a fuel cell, comprising: a membrane electrode assembly equipped with an electrolyte membrane and an anode catalyst; and a supply member for supplying an anode fluid to the membrane electrode assembly, and wherein the supply member is provided with an anode fluid flow path for supplying the anode fluid toward the membrane electrode assembly, and an opening of the anode fluid flow path on a discharge side thereof for the anode fluid is provided in proximity to the membrane electrode assembly, with a predetermined space being disposed between the supply member and the membrane electrode assembly, the predetermined space being adapted to store a gas pushed away by supply of the anode fluid. 
     According to the first aspect mentioned above, the anode fluid is supplied toward the membrane electrode assembly by the anode fluid flow path. By so doing, the impure gas present on the surface of the anode catalyst can be pushed away by the anode fluid, and the anode fluid can be supplied uniformly throughout the surface of the anode catalyst. By this means, the amount of power generation, particularly, the initial voltage, can be rendered high, and power generation can be maintained for a long term. 
     A second aspect of the present invention is the fuel cell according to the first aspect, wherein the supply member is provided with a protruding portion which protrudes toward the membrane electrode assembly and within which the anode fluid flow path is provided. 
     According to the second aspect mentioned above, by providing the protruding portion, the space is defined between the membrane electrode assembly and the supply member in the region other than the protruding portion. Thus, the impure gas is easily pushed away into this space. Moreover, a large amount of the impure gas can be stored within the space, so that power generation can be continued for an even longer term. 
     A third aspect of the present invention is the fuel cell according to the second aspect, wherein the protruding portion has a tapered shape pointed toward the membrane electrode assembly. 
     According to the third aspect mentioned above, the protruding portion is pointed, whereby a large space can be defined in the region other than the protruding portion. Thus, an even larger amount of the impure gas can be stored within the space. 
     A fourth aspect of the present invention is the fuel cell according to any one of the first to third aspects, wherein the anode fluid flow path has a tapered shape pointed toward the membrane electrode assembly. 
     According to the fourth aspect mentioned above, the anode fluid flow path is pointed, whereby the flow velocity of the anode fluid jetted from the anode fluid flow path is increased, and the impure gas present on the surface of the anode catalyst can be pushed away by the anode fluid even more efficiently. 
     A fifth aspect of the present invention is the fuel cell according to any one of the first to fourth aspects, wherein a plurality of the anode fluid flow paths are provided in the single supply member. 
     According to the fifth aspect mentioned above, the anode fluid can be supplied uniformly to the surface of the anode catalyst having a relatively large area by the plurality of anode fluid flow paths. 
     A sixth aspect of the present invention is the fuel cell according to any one of the first to fourth aspects, wherein a plurality of the anode fluid flow paths are provided in the single supply member, there are provided a chamber communicating with the plurality of anode fluid flow paths on a side opposite to the membrane electrode assembly, and an anode fluid introduction port for supplying the anode fluid to the chamber, the supply member is provided with a protruding portion which protrudes toward the membrane electrode assembly and within which the anode fluid flow path is provided, the protruding portion having a first protruding portion and a second protruding portion, and the second protruding portion is at a longer distance from the anode fluid introduction port than a distance from the anode fluid introduction port to the first protruding portion, and an amount of protrusion of the first protruding portion is larger than an amount of protrusion of the second protruding portion. 
     According to the sixth aspect mentioned above, the pressures of the anode fluid jetted from the plurality of anode fluid flow paths are uniformized, so that the anode fluid can be supplied uniformly to the surface of the anode catalyst. 
     A seventh aspect of the present invention is the fuel cell according to any one of the first to sixth aspects, further comprising a chamber communicating with a plurality of the anode fluid flow paths on a side opposite to the membrane electrode assembly, and an anode fluid introduction port for supplying the anode fluid to the chamber, and wherein a pressure loss in the anode fluid flow path is greater than a pressure loss in an area from the anode fluid introduction port to each of the anode fluid flow paths. 
     According to the seventh aspect mentioned above, the anode fluid can be vigorously ejected from the anode fluid flow path to blow off the impure gas present on the surface of the anode catalyst. 
     An eighth aspect of the present invention is the fuel cell according to any one of the fifth to seventh aspects, further comprising a chamber communicating with the plurality of anode fluid flow paths on a side opposite to the membrane electrode assembly, and an anode fluid introduction port for supplying the anode fluid to the chamber, and wherein the plurality of anode fluid flow paths include a first of the anode fluid flow paths, and a second of the anode fluid flow paths whose distance from the anode fluid introduction port is longer than a distance from the anode fluid introduction port to the first anode fluid flow path, and a pressure loss in the first anode fluid flow path is greater than a pressure loss in the second anode fluid flow path. 
     According to the eighth aspect mentioned above, the pressures of the anode fluid jetted from the plurality of anode fluid flow paths are uniformized, so that the anode fluid can be supplied uniformly to the surface of the anode catalyst. 
     A ninth aspect of the present invention is the fuel cell according to any one of the fifth to eighth aspects, further comprising a chamber communicating with the plurality of anode fluid flow paths on a side opposite to the membrane electrode assembly, and an anode fluid introduction port for supplying the anode fluid to the chamber, and wherein the plurality of anode fluid flow paths include a first of the anode fluid flow paths, and a second of the anode fluid flow paths whose distance from the anode fluid introduction port is longer than a distance from the anode fluid introduction port to the first anode fluid flow path, and a pressure loss in a first guide path within the chamber in an area from the anode fluid introduction port to the first anode fluid flow path is greater than a pressure loss in a second guide path within the chamber in an area from the anode fluid introduction port to the second anode fluid flow path. 
     According to the ninth aspect mentioned above, the pressures of the anode fluid jetted from the plurality of anode fluid flow paths are uniformized, so that the anode fluid can be supplied uniformly to the surface of the anode catalyst. 
     A tenth aspect of the present invention is the fuel cell according to the eighth aspect, wherein spacings between the adjacent anode fluid flow paths of the plurality of anode fluid flow paths of the supply member gradually decrease from the anode fluid flow paths at shorter distances from the anode fluid introduction port toward the anode fluid flow paths at longer distances from the anode fluid introduction port. 
     By varying the pressure losses in the anode fluid flow paths, variations occur in the flow velocity of the anode fluid, and the range of spread of the anode fluid differs according to the distribution of the flow velocity. According to the tenth aspect mentioned above, however, the spacings between the adjacent anode fluid flow paths are varied, whereby the unevenness in the in-plane distribution of the anode fluid can be reduced. 
     An eleventh aspect of the present invention is the fuel cell according to any one of the first to tenth aspects, further comprising removal means for removing the gas from the region storing the gas pushed away by the anode fluid. 
     According to the eleventh aspect mentioned above, the gas, such as an impure gas, pushed away within the space charged with the anode fluid can be removed from the space charged with the anode fluid. Thus, the amount of power generation can be increased further, and power generation can be maintained for a long term. 
     A twelfth aspect of the present invention is the fuel cell according to the eleventh aspect, wherein the removal means is a lead-out path which communicates with the region storing the gas pushed away by the supply of the anode fluid to discharge the gas as a buffer. 
     According to the twelfth aspect mentioned above, the gas such as an impure gas can be discharged via the lead-out path as a buffer. Thus, the amount of power generation can be increased further, and power generation can be maintained for a long term. 
     A thirteenth aspect of the present invention is the fuel cell according to the twelfth aspect, wherein the lead-out path is provided with a check valve which permits a flow of the gas from the region storing the gas to the buffer and restrains a flow of the gas in a reverse direction. 
     According to the thirteenth aspect mentioned above, the gas discharged to the buffer does not return because of the check valve. Thus, the amount of power generation can be increased further, and power generation can be maintained for a long term. 
     A fourteenth aspect of the present invention is the fuel cell according to the eleventh aspect, wherein the removal means is an adsorbent provided in the region storing the gas pushed away by the anode fluid. 
     According to the fourteenth aspect mentioned above, the gas, such as an impure gas, is selectively adsorbed to the adsorbent, and can be removed thereby. Thus, the amount of power generation can be increased further, and power generation can be maintained for a long term. 
     A fifteenth aspect of the present invention is a fuel cell system, comprising: the fuel cell according to any one of the first to fourteenth aspects; and fuel supply means for supplying the anode fluid to the fuel cell. 
     According to the fifteenth aspect mentioned above, a fuel cell system can be realized which prevents a power generation failure due to an impure gas, which can perform power generation continuously for a long term, and which has been downsized. 
     With the present invention, the anode fluid is flowed toward the membrane electrode assembly by the anode fluid flow path. By so doing, the impure gas on the surface of the anode catalyst is pushed away, and the anode fluid can be supplied throughout the surface of the anode catalyst. Thus, there is no need to provide a complicated mechanism such as a purge valve or a gas treatment device. Also, a power generation failure, or a decrease in the amount of power generation, due to the impure gas is prevented, the amount of power generation is increased, and long-term power generation can be maintained. Moreover, it suffices to provide the anode fluid flow path for flowing the anode fluid toward the membrane electrode assembly. Thus, the provision of a purge valve, or a procedure such as complicated opening and closing of the purge valve becomes unnecessary, downsizing can be achieved, and the cost can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing the schematic configuration of a fuel cell system according to Embodiment 1 of the present invention. 
         FIG. 2  is an exploded perspective view showing the fuel cell according to Embodiment 1 of the present invention. 
         FIG. 3  is a sectional view showing the fuel cell according to Embodiment 1 of the present invention. 
         FIG. 4  is a sectional view of essential parts showing the supply state of an anode fluid in the fuel cell according to Embodiment 1 of the present invention. 
         FIG. 5  is a sectional view of essential parts of a fuel cell according to Embodiment 2 of the present invention. 
         FIG. 6  is a sectional view of essential parts of another example of the fuel cell according to Embodiment 2 of the present invention. 
         FIG. 7  is a plan view of essential parts of a fuel cell according to another embodiment of the present invention. 
         FIG. 8  is a plan view of essential parts of a fuel cell according to still another embodiment of the present invention. 
         FIG. 9  is a sectional view of essential parts of the fuel cell according to the still another embodiment of the present invention. 
         FIG. 10  is a plan view of essential parts of a fuel cell according to a further embodiment of the present invention. 
         FIG. 11  is a sectional view of essential parts of a fuel cell according to a still further embodiment of the present invention. 
         FIG. 12  is a sectional view of essential parts of a fuel cell according to an additional embodiment of the present invention. 
         FIG. 13  is a sectional view of essential parts of a fuel cell according to a further additional embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION of the INVENTION 
     Hereinbelow, the present invention will be described in detail based on its embodiments. 
     (Embodiment 1) 
       FIG. 1  is a view showing the schematic configuration of a fuel cell system according to the present invention. 
     As shown in  FIG. 1 , a fuel cell system  1  of the present embodiment comprises a fuel supply means  100 , a fuel cell  200 , and a control circuit  300 . 
     The fuel supply means  100  supplies a fuel as an anode fluid to the fuel cell  200 . Hydrogen is optimal as the fuel, and a hydrogen absorbing or storage alloy, a cylinder enclosing hydrogen, etc. are named as the fuel supply means  100 . The fuel supply means  100  may be one for gene rating hydrogen, and an example thereof is of a configuration in which a hydrogen generating substance and a hydrogen generation accelerator are mixed to produce hydrogen. For example, sodium borohydride can be used as the hydrogen generating substance, and an aqueous solution of malic acid can be used as the hydrogen generation accelerator. Moreover, a solution of methanol may be supplied as the fuel. 
     The control circuit  300  is connected to the fuel cell  200 , and driven by a voltage supplied by the fuel cell  200 . 
     The fuel cell  200  will be described in detail by reference to  FIGS. 2 to 4 .  FIG. 2  is an exploded perspective view showing the schematic configuration of the fuel cell.  FIG. 3  is a sectional view of the fuel cell.  FIG. 4  is a sectional view of essential parts showing the supply state of the anode fluid in the fuel cell. 
     As shown in  FIGS. 2 and 3 , the fuel cell  200  has a membrane electrode assembly  204  (hereinafter referred to as MEA) composed of a solid polymer electrolyte membrane  201  as an electrolyte membrane, and an anode catalyst  202  and a cathode catalyst  203  provided on both sides of the solid polymer electrolyte membrane  201 . 
     An anode member  210  and a cathode member  220  are provided on the respective surfaces of the MEA  204 . That is, the MEA  204  is sandwiched between the anode member  210  and the cathode member  220 . 
     The cathode member  220  is composed of a plate-shaped member provided on a side of the MEA  204  where the cathode catalyst  203  is located. The cathode member  220  is provided with a cathode fluid flow path  221  for supplying an oxidizing agent (air containing oxygen), as a cathode fluid, to the cathode catalyst  203 . That is, the cathode member  220  functions as a supply member for supplying the cathode fluid to the cathode catalyst  203 . The cathode fluid flow path  221 , in the present embodiment, has a concave shape opening at a side of the cathode member  220  facing the cathode catalyst  203 . In the bottom surface of the cathode fluid flow path  221 , a cathode fluid introduction port  222  is provided for supplying air into the cathode fluid flow path  221 . 
     The anode member  210  is composed of a plate-shaped member provided on a side of the MEA  204  where the anode catalyst  202  is located. The anode member  210  has a chamber  211  of a concave shape opening toward the anode catalyst  202 , and an anode fluid introduction port  212  provided as a through-hole in the thickness direction of the bottom surface of the chamber  211 . 
     The chamber  211  has an opening area comparable to the surface area of the anode catalyst  202 . The interior of the chamber  211  is supplied with the anode fluid via the anode fluid introduction port  212  provided in the bottom surface thereof. 
     Between the anode member  210  and the MEA  204 , there are provided a gas diffusion layer  230 , and a supply member  240  for supplying the anode fluid within the chamber  211  to the gas diffusion layer  230 . 
     The gas diffusion layer (GDL)  230  is provided between the anode member  210  and the MEA  204  to face the MEA  204 , that is, to be located on the anode catalyst  202  of the MEA  204 , and comprises a member having permeability which allows the anode fluid to pass therethrough. As the gas diffusion layer  230 , a well-known material can be used, for example, a metal mesh or a material having a porous structure such as a carbon cloth, a carbon paper, or a carbon felt. 
     The supply member  240  comprises a plate-shaped member provided on a side opposite to the MEA  204  across the gas diffusion layer  230 . The supply member  240  is disposed in such a state as to be separated from the gas diffusion layer  230  by a predetermined spacing, and a predetermined space  250  is defined between the supply member  240  and the gas diffusion layer  230 . A surface of the supply member  240  on a side opposite to the gas diffusion layer  230  seals one surface of the chamber  211 . 
     The supply member  240  is provided with an anode fluid flow path  241  to penetrate the supply member  240  in its thickness direction, thereby bringing the chamber  211  and the space  250  into communication. That is, the anode fluid flow path  241  has one end opening into the chamber  211  and the other end opening into the space  250 , thereby establishing communication between them. As described above, the one surface of the supply member  240  is not brought into contact with the gas diffusion layer  230 , but is separated therefrom by a predetermined spacing. Because of this configuration, the one surface of the supply member  240  is provided in proximity to the anode catalyst  202 , with the space  250  being disposed between the opening of the anode fluid flow path  241  on its discharge side for the anode fluid (the opening facing the gas diffusion layer  230 ) and the gas diffusion layer  230 . 
     In the present embodiment, there are provided two rows of the anode fluid flow paths  241 , each row including a plurality of (six) the anode fluid flow paths  241  arranged with predetermined spacing, so that 12 of the anode fluid flow paths  241  are provided. The anode fluid flow path  241  is provided such that a pressure loss in the anode fluid flow path  241  is greater than a pressure loss occurring in a region ranging from the anode fluid introduction port  212  to each anode fluid flow path  241 . Concretely, in the present embodiment, the chamber  211  is provided to be of such a size as to be in common communication with the plurality of anode fluid flow paths  241  (namely, the opening area of the chamber  211  is comparable to the surface area of the anode catalyst  202 ), and the opening areas (cross-sectional areas) of the anode fluid flow paths  241  are much smaller than the opening area of the chamber  211 . Consequently, the pressure loss in the anode fluid flow path  241  is rendered greater than the pressure loss occurring in the region ranging from the anode fluid introduction port  212  of the chamber  211  to each anode fluid flow path  241 . By so increasing the pressure loss in the anode fluid flow path  241 , the anode fluid supplied into the chamber  211  can be supplied as jets at a desired pressure toward the surface of the anode catalyst  202  by the anode fluid flow path  241 , although the details of this action will be described later. The anode fluid flow path  241  may be of a shape pointed toward the anode catalyst  202 . Of course, the anode fluid flow path  241  is not limited in size (opening area), number or position, and the size, number and position may be determined, as appropriate, based on the pressure of the anode fluid within the chamber  211 , the partial pressure of an impure gas on the surface side of the anode catalyst  202 , the flow velocity of the anode fluid supplied to the anode catalyst  202  to push away the impure gas, and so on. If the anode fluid flow path  241  is shaped to be pointed or tapered toward the anode catalyst  202 , as mentioned above, the flow velocity of the anode fluid jetted from the anode fluid flow path  241  can be increased. By so doing, the anode fluid can be easily supplied to the surface of the anode catalyst  202 ; that is, the impure gas existent on the surface of the anode catalyst  202  can be easily pushed away, although the details will be offered later. 
     The anode fluid flow path  241  of the supply member  240  penetrates the supply member  240  in its thickness direction, and is thereby provided along a direction intersecting the surface of the anode catalyst  202 . By this measure, the anode fluid supplied into the chamber  211  can be passed through the gas diffusion layer  230  by way of the anode fluid flow path  241 , and supplied as jets toward the surface of the anode catalyst  202 . That is, it suffices for the anode fluid flow path  241  of the supply member  240  to be provided along the direction intersecting the surface of the anode catalyst  202 . The anode fluid flow path  241  may be orthogonal to the surface of the anode catalyst  202 , or may be inclined at a predetermined angle with respect to this surface. 
     With the above-described fuel cell  200 , the cathode fluid flow path  221  is open to the atmosphere. If the fuel cell is allowed to stand for a long term, therefore, air in the atmosphere (particularly, nitrogen as an inert gas) slips, as an impure gas, into a space where the anode catalyst  202  is provided, i.e., within the gas diffusion layer  230  or the space  250 , through the solid polymer electrolyte membrane  201 . Arise in the partial pressure of the impure gas (nitrogen) causes a drop in the partial pressure of the anode fluid in the anode catalyst  202 . Thus, a sufficient amount of the anode fluid for power generation cannot be supplied, so that the amount of power generation decreases. 
     With the fuel cell  200  of the present embodiment, however, the anode fluid is supplied by the anode fluid flow paths  241  to be blown toward the surface of the anode catalyst  202 , as shown in  FIG. 4 . Thus, the impure gas existent on the surface of the anode catalyst  202  is pushed away, and the anode fluid can be supplied to the surface of the anode catalyst  202 . That is, the anode fluid supplied by the anode fluid flow paths  241  toward the surface of the anode catalyst  202  (from the direction intersecting the surface) spreads along the surface of the anode catalyst  202  while pushing away the impure gas within the gas diffusion layer  230  filled as an atmosphere for the anode catalyst  202 . On this occasion, the impure gas pushed away from the surface side of the anode catalyst  202  remains in regions on a side of the gas diffusion layer  230  opposite to the anode catalyst  202 , and within the space  250 , namely, in regions A shown in  FIG. 4 . Since the space  250  is present, the impure gas is easily pushed away from the surface of the anode catalyst  202 . 
     As described above, the anode fluid is supplied toward the surface of the anode catalyst  202  by the anode fluid flow paths  241  to push away the impure gas (nitrogen) from the surface of the anode catalyst  202 , whereby the efficiency of power generation or the power efficiency of the anode catalyst  202  can be increased. For example, if the anode fluid flow path  241  is not provided, namely, if the chamber  211  is provided to face the gas diffusion layer  230  directly, the anode fluid supplied from the anode fluid introduction port  212  is supplied along the surface of the anode catalyst  202 . If the anode fluid is supplied in the planar direction of the surface of the anode catalyst  202  in this manner, power generation takes place only on the side where the anode fluid is supplied. In a region extending long from the side where the anode fluid is supplied, on the other hand, the partial pressure of the impure gas becomes so high that power generation substantially does not occur. That is, when the anode fluid is supplied along the surface of the anode catalyst  202 , the entire surface of the anode catalyst  202  cannot be used efficiently, so that the amount of power generation decreases. By contrast, the anode fluid flow path  241  supplying the anode fluid in such a manner as to blow it against the surface of the anode catalyst  202  is provided as in the present embodiment, whereby the anode fluid can be supplied uniformly over the entire surface of the anode catalyst  202 . Thus, power generation can be performed with the use of the entire surface of the anode catalyst  202 , and the amount of power generation, particularly, the initial voltage, can be rendered high. 
     With the fuel cell  200 , moreover, the mixing of the impure gas, such as nitrogen in the air, into the anode catalyst  202  (gas diffusion layer  230 ) occurs during power generation as well. Thus, long-term power generation cannot be maintained, if the anode fluid flow path  241  is not provided. In the present embodiment, on the other hand, the anode fluid is supplied toward the surface of the anode catalyst  202  by the anode fluid flow paths  241 . By so doing, the anode fluid can continue to be supplied to the surface of the anode catalyst  202 , with the impure gas present on the surface of the anode catalyst  202  being constantly pushed away, so that long-term power generation can be maintained. 
     In the present embodiment, moreover, the anode fluid is blown against the surface of the anode catalyst  202  by the anode fluid flow path  241 . Thus, the thickness of the gas diffusion layer  230  can be rendered relatively small. Even if the gas diffusion layer  230  is not provided, the anode fluid can be supplied uniformly throughout the surface of the anode catalyst  202 . 
     (Embodiment 2) 
       FIG. 5  is a sectional view of essential parts of a fuel cell according to Embodiment 2 of the present invention. The same members as those in the aforementioned Embodiment 1 will be assigned the same numerals as in the Embodiment 1, and duplicate explanations will be omitted. 
     As shown in  FIG. 5 , a fuel cell  200 A of Embodiment 2 has an MEA  204 , an anode member  210 , a cathode member  220  (not shown), a gas diffusion layer  230 , and a supply member  240 A. 
     A surface of the supply member  240 A facing the gas diffusion layer  230  is provided with protruding portions  242  which protrude toward the gas diffusion layer  230  and inside each of which an anode fluid flow path  241  is provided. That is, the protruding portion  242  is provided in a cylindrical nozzle-like form within which the anode fluid flow path  241  is provided. The shape of the protruding portion  242  is not limited to the cylindrical form, but may be a prismatic shape, or a tapered shape which is pointed toward the MEA  204 . For example, the protruding portion  242  is formed in a tapered shape pointed toward the MEA  204 , whereby the volume of the space between the adjacent protruding portions  242  can be rendered larger than that of the space between the adjacent cylindrical protruding portions  242 , and further the amount of the impure gas storable in this space is increased, thereby making it possible to maintain long-term power generation. Details in this connection will be described later. 
     The protruding leading end surface of the protruding portion  242  is provided in such a state as to be separated from the gas diffusion layer  230  by a predetermined spacing, that is, with a space  250  being disposed between the protruding portion  242  and the gas diffusion layer  230 . In a region of the supply member  240 A other than the protruding portion  242 , a space  251  broader than the space  250  is provided between the supply member  240 A and the gas diffusion layer  230 . 
     With the fuel cell  200 A described above, the anode fluid is supplied toward the surface of the anode catalyst  202  by the anode fluid flow paths  241 , as in the aforementioned Embodiment 1. Thus, the impure gas such as nitrogen is pushed away, so that the amount of initial power generation can be increased, and power generation can be maintained for a long term. In the present embodiment, moreover, the wider space  251  is defined between the gas diffusion layer  230  and the supply member  240 A in the region of the supply member  240 A other than the protruding portion  242 . By this configuration, the impure gas such as nitrogen which has been expelled from the surface of the anode catalyst  202  can be stored in a region A′ including this space  251 . Thus, the impure gas on the surface side of the anode catalyst  202  is easily pushed away toward the region A′. Furthermore, the impure gas pushed away can be stored in the relatively wide region A′, so that power generation of an even longer duration can be maintained. 
     In the present embodiment, a plurality of the protruding portions  242  having the same amount of protrusion are provided. However, this is not limitative, and the amount of protrusion of the protruding portion  242  may be varied based on the distance within the chamber  211  from the anode fluid introduction port  212  to each anode fluid flow path  241 . Such an example is shown in  FIG. 6 .  FIG. 6  is a sectional view of essential parts showing a modification of the fuel cell according to Embodiment 2 of the present invention. 
     In the fuel cell  200 A, as shown in  FIG. 6 , the amount of protrusion of the protruding portion  242  is larger for the anode fluid flow path  241  at a shorter distance from the anode fluid introduction port  212  in the chamber  211 , while the amount of protrusion of the protruding portion  242  is smaller for the anode fluid flow path  241  at a longer distance from the anode fluid introduction port  212 . In this case, the opening of the anode fluid flow path  241  provided in each protruding portion  242  is provided not to contact the gas diffusion layer  230 A. 
     By so changing the amount of protrusion of the protruding portion  242 , the pressure loss in the anode fluid flow path  241  close to the anode fluid introduction port  212  is increased, while the pressure loss in the anode fluid flow path  241  distant from the anode fluid introduction port  212  is decreased. As a result, the pressure of the anode fluid supplied from each anode fluid flow path  241  can be uniformized, regardless of the distance from the anode fluid introduction portion  212 . Consequently, the amount of power generation in the plane of the anode catalyst  202  can be uniformized to increase the power efficiency. 
     In the present embodiment, the gas diffusion layer  230 A can be rendered relatively thin, and it is permissible not to provide the gas diffusion layer  230 A. Even in this case, the anode fluid can be supplied uniformly throughout the surface of the anode catalyst  202 . 
     (Other Embodiments) 
     The respective embodiments of the present invention have been described above. However, the basic features of the present invention are not limited to those mentioned above. 
     For example, in the aforementioned Embodiments 1 and 2, the plurality of anode fluid flow paths  241  having the same opening area are provided in the supply member  240 ,  240 A. However, this is not limitative and, for example, the pressure loss in the anode fluid flow path  241  may be varied according to the distance from the anode fluid introduction port  212 . A concrete example is shown in  FIG. 7 .  FIG. 7  illustrates a modification of the aforementioned Embodiment 1, but the configuration of  FIG. 7  can be applied to the aforementioned Embodiment 2 as well. As shown in  FIG. 7 , of the plurality of anode fluid flow paths  241 , the anode fluid flow path  241  at a shorter distance (distance L 1 ) from the anode fluid introduction port  212  (projected part  212 A obtained by projection of the anode fluid introduction port  212 ) is given a smaller cross-sectional area to impart a larger pressure loss, while the anode fluid flow path  241  at a longer distance (distance L 6 ) from the anode fluid introduction port  212  is given a larger cross-sectional area to impart a smaller pressure loss. That is, let the anode fluid flow path  241  at the short distance from the anode fluid introduction port  212  be the first anode fluid flow path, and let the anode fluid flow path  241  at the long distance from the anode fluid introduction port  212  be the second anode fluid flow path. In this case, the pressure loss in the first anode fluid flow path may be greater than the pressure loss in the second anode fluid flow path. 
     In the present embodiment, the anode fluid introduction port  212  is provided in the bottom surface of the chamber  211  and outside the rows of the juxtaposed anode fluid flow paths  241 . However, the anode fluid introduction port  212  may be provided halfway through the rows of the juxtaposed anode fluid flow paths  241 . The distance from the anode fluid introduction port  212  to the anode fluid flow path  241  may be actually taken on the premise that the position of the anode fluid introduction port  212  is the position of the projected part  212 A obtained by projecting the anode fluid introduction port  212  onto the supply member  240 . 
     As noted above, the opening area (cross-sectional area) of the anode fluid flow path  241  is varied based on the distance from the anode fluid introduction port  212 , whereby the pressure loss in the anode fluid flow path  241  can be varied based on the distance from the anode fluid introduction port  212 . That is, the fact that the opening area of the anode fluid flow path  241  is small means that the pressure loss in the anode fluid flow path  241  is great, whereas the fact that the opening area of the anode fluid flow path  241  is large means that the pressure loss in the anode fluid flow path  241  is small. The path within the chamber  211  from the anode fluid introduction port  212  to the anode fluid flow path  241  at a short distance therefrom is short. Thus, the pressure loss of the anode fluid passing along this path in the chamber  211  is small. The longer the distance over which the anode fluid passes through the chamber  211  from the anode fluid introduction port  212  until its supply to the anode fluid flow path  241 , the larger its pressure loss becomes. Hence, variations in the pressure loss of the anode fluid passing within the chamber  211  can be counterbalanced by varying the pressure loss in the anode fluid flow path  241 , whereby the pressure of the anode fluid supplied from each anode fluid flow path  241  can be rendered uniform. By this measure, the anode fluid can be supplied uniformly to the surface of the anode catalyst  202  to provide a uniform amount of power generation in the plane of the anode catalyst  202  and increase the efficiency of power generation (i.e., power efficiency). 
     In the example shown in  FIG. 7 , the flow rate of the anode fluid supplied from each anode fluid flow path  241  can be uniformized. However, as the distance from the anode fluid introduction port  212  (projected part  212 A obtained by projection of the anode fluid introduction port  212 ) to the anode fluid flow path  241  increases, the bore of the anode fluid flow path  241  differs, so that the flow velocity of the anode fluid flowed out of the anode fluid flow path  241  changes. If the flow velocity of the anode fluid flowed out of the anode fluid flow path  241  changes in this manner, the range of spread of the anode fluid differs according to the distribution of the flow velocity. As a result, unevenness occurs in the in-plane distribution of the anode fluid, causing a possibility for a decrease in the power efficiency. Thus, in the plurality of anode fluid flow paths  241 , the spacing between the adjacent anode fluid flow paths  241  is gradually decreased as the distance from the anode fluid introduction port  212  increases. By so doing, the unevenness in the in-plane distribution of the anode fluid can be curtailed. An example of such a configuration is shown in  FIGS. 8 and 9 .  FIG. 8  is a plan view of essential parts of a fuel cell according to other embodiment of the present invention.  FIG. 9  is a sectional view of essential parts of  FIG. 8 . 
     As shown in  FIGS. 8 and 9 , in the plurality of anode fluid flow paths  241  having the opening areas differentiated in the same manner as in  FIG. 7 , the spacing (e.g., spacing d 5 ) between the adjacent anode fluid flow paths  241  at a longer distance from the anode fluid introduction port  212  (projected part  212 A) is rendered smaller than the spacing (e.g., spacing d 1 ) between the adjacent anode fluid flow paths  241  at a shorter distance from the anode fluid introduction port  212  (projected part  212 A). Because of this configuration, the flow velocity slows from a side where the spacing between the adjacent anode fluid flow paths  241  is wide (i.e., spacing d 1  side) toward a side where the spacing between the adjacent anode fluid flow paths  241  is narrow (i.e., spacing d 5  side). Even if the range of spread of the anode fluid flowed out gradually narrows, therefore, the unevenness in the in-plane distribution of the anode fluid can be reduced. Hence, the impure gas (nitrogen) present on the surface of the anode catalyst  202  can be uniformly pushed away from the surface of the anode catalyst  202 , and power generation can be carried out with high efficiency. In this connection, assume that the spacings between the adjacent anode fluid flow paths are all set to be identical. When, in this case, the anode fluid flow path  241  at a short distance from the anode fluid introduction port  212  is taken as the first anode fluid flow path, and the anode fluid flow path  241  at a long distance from the anode fluid introduction port  212  is taken as the second anode fluid flow path, the flow velocity of the anode fluid flowing out from the second anode fluid flow path is lower than the flow velocity of the anode fluid flowing out from the first anode fluid flow path. In this state, the range in which the anode fluid of a lower flow velocity flowing out of the second anode fluid flow path pushes away the gas and spreads on the surface of the anode catalyst  202  is narrower than the range in which the anode fluid of a higher flow velocity flowing out of the first anode fluid flow path spreads on the surface of the anode catalyst  202 . Consequently, unevenness occurs in the distribution of the concentration at which the anode fluid is supplied in the plane of the surface of the anode catalyst  202 , posing a possibility for the occurrence of a deficiency, such as the failure to push away the impure gas, or a decrease in the power efficiency. 
     The example shown in  FIGS. 8 and 9  can reduce the unevenness in the in-plane distribution of the anode fluid flowed out of the plurality of anode fluid flow paths  241 . Thus, the distribution of the concentration at which the anode fluid is supplied in the plane of the surface of the anode catalyst  202  is uniformized, so that the power efficiency of the anode catalyst  202  can be increased, and the amount of power generation can be maintained for a long term. In the example shown in  FIGS. 8 and 9 , the spacings between the centers of the adjacent anode fluid flow paths  241  are taken as the spacings d 1  to d 5  between the anode fluid flow paths. However, this is not limitative, and the spacing between the edges of the openings of the anode fluid flow paths may be taken as the spacing between the anode fluid flow paths. 
     Furthermore, it is permissible to form a guide path within the chamber  211 , the guide path serving for communication from the anode fluid introduction port  212  to the anode fluid flow path  241 , and change the pressure loss in this guide path, without changing the pressure loss in the anode fluid flow path  241 . Such an example is shown in  FIG. 10 . 
     As shown in  FIG. 10 , a guide path  213  serving for communication from the anode fluid introduction port  212  to each anode fluid flow path  241  is provided within the chamber  211 . The guide path  213  is configured such that the guide path  213  for communication from the anode fluid introduction port  212  to the anode fluid flow path  241  at a shorter distance therefrom has a smaller width (cross-sectional area) to undergo a larger pressure loss, and the guide path  213  for communication from the anode fluid introduction port  212  to the anode fluid flow path  241  at a longer distance therefrom has a larger width (cross-sectional area) to undergo a smaller pressure loss. That is, when the anode fluid flow path  241  at a short distance from the anode fluid introduction port  212  is taken as the first anode fluid flow path, and the anode fluid flow path  241  at a long distance from the anode fluid introduction port  212  is taken as the second anode fluid flowpath, it is advisable that a pressure loss in the first guide path from the anode fluid introduction port  212  to the first anode fluid flow path be rendered greater than a pressure loss in the second guide path from the anode fluid introduction port  212  to the second anode fluid flow path. Because of this configuration, the pressure of the anode fluid supplied from each anode fluid flow path  241  can be uniformized. By this measure, the anode fluid can be supplied uniformly to the surface of the anode catalyst  202  to provide a uniform amount of power generation in the plane of the anode catalyst  202  and increase the power efficiency. 
     Furthermore, in a region where the gas pushed away by the anode fluid flowed out of the anode fluid flow path  241  is stored, a removal means for discharging the gas in this region to the outside may be provided. Such an example is shown in  FIG. 11 .  FIG. 11  is a sectional view of essential parts of a fuel cell showing a modification of the aforementioned Embodiment 2. 
     As shown in  FIG. 11 , one end of a lead-out path  260  communicating with the space  251  which is a region for storing the gas pushed away by the anode fluid is connected to the supply member  240 A, and the other end of the lead-out path  260  is connected to a storage means  261 . The storage means  261  has a space for storing the impure gas, such as nitrogen, from the space  251 , and serves as a buffer to discharge to the outside the gas stored in the space  251  connected via the lead-out path  260 . A hollow member having a sealed space is named, for example, as the storage means  261 . By providing the storage means  261  composed of the hollow member, the pressure inside the storage means  261  becomes comparable to the pressure inside the fuel cell (chamber  211 ), while the action of the fuel cell is kept at a standstill. When the anode fluid is flowed out of the anode fluid flow path  241 , the impure gas pushed away into the space  251  by the flowed-out anode fluid is discharged to the storage means  261 , as a buffer, via the lead-out path  260  under the introduction pressure of the anode fluid. Upon discharge of the impure gas in the space  251  to the storage means  261  as the buffer, the pressure inside the space  251  and the pressure inside the storage means  261  equal. When the action of the fuel cell is stopped, the pressure balance between the interior of the space  251  and the interior of the storage means  261  is disturbed, and the impure gas within the storage means  261  returns to the space  251 . In this manner, the impure gas in the space  251  is buffer-discharged to the outside of the fuel cell during the action of the fuel cell, whereby the amount of power generation (particularly, initial voltage) can be increased, and power generation can be maintained for a long term. 
     The hollow member has been named as an example of the storage means  261 , but it is not limitative. For example, an adsorbent for adsorbing the gas may be provided within the storage means  261 . For example, activated carbon, zeolite or the like can be used as the adsorbent, if it is desired to adsorb nitrogen as the gas. 
     A check valve may be provided in the lead-out path  260  shown in the aforementioned  FIG. 11 . Such an example is shown in  FIG. 12 . As shown in  FIG. 12 , a check valve  262  is provided halfway through the lead-out path  260 , namely, between the supply member  240  and the storage means  261 . The check valve  262  is mounted in a direction in which it permits the flow of the gas from the space  251 , where the gas is stored, to the storage means  261  (buffer), and restrains the flow of the gas in the reverse direction. By providing the lead-out path  260  with the check valve  262  in this manner, the gas stored in the storage means  261  does not flow backward to the space  251  and, even when the action of the fuel cell is stopped, the gas stored in the storage means  261  does not return to the space  251 .  FIG. 12  shows a modification of the aforementioned Embodiment 2, but this is not limitative. For example, even the configuration of the aforementioned Embodiment 1 without the space  251 , or even the configuration shown in any of  FIGS. 7 to 10  can exhibit the same effects as above, if provided with removal means for removing the gas in the region where the gas is stored. 
     Further, an adsorbent may be provided in the region where the gas pushed away by the supply of the anode fluid is stored. Such an example is shown in  FIG. 13 .  FIG. 13  is a sectional view of essential parts showing a modification of the aforementioned Embodiment 2. 
     As shown in  FIG. 13 , the supply member  240 A is provided with an adsorbent  270  in the space  251  which is the region where the gas pushed away by the anode fluid is stored. As the adsorbent  270 , activated carbon, zeolite or the like can be used, for example, if it is desired to adsorb nitrogen as the gas. Of course, the adsorbent is not limited thereto, but its material may be determined, as appropriate, depending on the gas whose adsorption is desired. 
     Even with such a configuration, the gas pushed away to the space  251  is adsorbed to the adsorbent  270 , and excess gas within the fuel cell can be removed, so that the amount of power generation (particularly, initial voltage) can be increased, and power generation can be maintained for a long term. Needless to say, the adsorbent  270  may be provided in the aforementioned Embodiment 1. 
     Any two or more of the configurations shown in the aforementioned configurations of  FIGS. 7 to 13  may be combined. 
     In the above embodiments, the supply member  240 ,  240 A has been provided as a member independent of the anode member  210 . However, these members may be configured as a member in which they are provided integrally. Moreover, the supply member  240 ,  204 A may be one in which only the region provided with the anode fluid flow path  241  is a supply member. That is, a member corresponding to any of the supply members  240 ,  240 A of the aforementioned Embodiments 1 and 2 may be composed of a base member comprising a plate-shaped member, and a plurality of supply members fixed to the base member and having anode fluid flow paths individually provided therein. 
     In the above embodiments, the gas diffusion layer  230  has been provided only on the side of the anode catalyst  202 . However, this is not limitative and, for example, a gas diffusion layer  230  comparable to that on the side of the anode catalyst  202  may be provided on the side of the cathode catalyst  203  as well. 
     The above-described fuel cell  200 ,  200 A can be utilized, for example, as a single cell constituting a cell stack. That is, a cell stack may be formed by stacking a plurality of the above fuel cells  200  or  200 A. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be utilized in the industrial field of fuel cells which uniformize the concentration distribution of the anode fluid in the plane of the surface of the anode catalyst to increase the amount of power generation and continue power generation for a long term. 
     DESCRIPTION OF THE NUMERALS 
     A, A′ Region 
       1  Fuel cell system 
       100  Fuel supply means 
       200  Fuel cell 
       201  Solid polymer electrolyte membrane (Electrolyte membrane) 
       202  Anode catalyst 
       203  Cathode catalyst 
       210  Anode member 
       212  Anode fluid introduction port 
       220  Cathode member 
       230 ,  230 A Gas diffusion layer 
       240 ,  240 A Supply member 
       241  Anode fluid flow path 
       242  Protruding portion 
       250  Space 
       251  Space 
       260  Lead-out path 
       261  Storage means 
       270  Adsorbent 
       300  Control circuit