Abstract:
An electrolyte membrane on the inside of annular frames with an anode-side electrode catalyst layer, a first gas diffusion layer and a first gas flow channel-forming body stacked on top of the membrane. An electrode catalyst layer, a second gas diffusion layer and a second gas flow channel-forming body are stacked on the underside. Frames have a supply channel supplying fuel gas to the gas flow channel in the first gas flow channel-forming body, a discharge channel discharges the fuel gas. An overhang part that extends outward is on the outer peripheral edge of the first channel-forming body to overlap a flange part of the frame beyond the outer peripheral edge of the anode-side electrode catalyst layer. Penetration of seeping water can be prevented by retaining the seeping water in the overhang part.

Description:
PRIORITY CLAIM 
     The present application is a National Phase entry of PCT Application No. PCT/JP2009/058914, filed May 13, 2009, which claims priority from Japanese Patent Application Number 2008-196835, filed Jul. 30, 2008, the disclosures of which are hereby incorporated by reference herein in their entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a power generating cell for a fuel battery that is mounted, for example, on an electric car. 
     BACKGROUND OF THE INVENTION 
     Typically, a fuel battery has a cell stack formed by a number of power generating cells stacked together. With reference to  FIGS. 9 to 12 , a prior art power generating cell will be described. As shown in  FIG. 9 , a pair of upper and lower frames  13 ,  14  are connected to each other, and an electrode structure  15  is installed at the joint portion of the frames  13 ,  14 . The electrode structure  15  is formed by a solid electrolyte membrane  16 , an electrode catalyst layer  17  on the anode side, and an electrode catalyst layer  18  on the cathode side. The outer periphery of the solid electrolyte membrane  16  is held between the frames  13 ,  14 . The anode-side electrode catalyst layer  17  is laid on the upper surface of the solid electrolyte membrane  16 , and the cathode-side electrode catalyst layer  18  is laid on the lower surface of the solid electrolyte membrane  16 . A first gas diffusion layer  19  is laid on the upper surface of the electrode catalyst layer  17 , and a second gas diffusion layer  20  is laid on the lower surface of the electrode catalyst layer  18 . Further, a first gas passage forming member  21  is laid on the upper surface of the first gas diffusion layer  19 , and a second gas passage forming member  22  is laid on the lower surface of the second gas diffusion layer  20 . A flat plate-like separator  23  is joined to the upper surface of the first gas passage forming member  21 , and a flat plate-like separator  24  is joined to the lower surface of the second gas passage forming member  22 . 
     The solid electrolyte membrane  16  is formed of a fluoropolymer film. As shown in  FIG. 10 , the electrode catalyst layer  17 ,  18  each have carbon particles  31  of diameters of several micrometers, and a great number of platinum (Pt) catalyst particles  32  adhere to the surface of each carbon particle  31 . The catalyst particles  32  have a diameter of 2 nm. When electricity is generated by the fuel battery, the catalyst particles  32  function as catalyst that increases the power generation efficiency. The gas diffusion layers  19 ,  20  are formed of carbon paper. 
       FIG. 11  is an enlarged perspective view showing a part of the first and second gas passage forming members  21 ,  22 . As shown in  FIG. 11 , the gas passage forming member  21  ( 22 ) is made of a metal lath plate, which has a great number of hexagonal ring portions  21   a  ( 22   a ) arranged alternately. Each ring portion  21   a  ( 22   a ) has a through hole  21   b  ( 22   b ). Fuel gas (oxidation gas) flows through gas passages formed by the ring portions  21   a  ( 22   a ) and the through holes  21   b  ( 22   b ). 
     As shown in  FIG. 9 , the frames  13 ,  14  form a supply passage M 1  and a discharge passage M 2  for fuel gas. The fuel gas supply passage M 1  is used for supplying hydrogen gas, which serves as fuel gas, to the gas passages of the first gas passage forming member  21 . The fuel gas discharge passage M 2  is used for discharging fuel gas that has passed through the gas passages of the first gas passage forming member  21 , or fuel off-gas, to the outside. Also, the frames  13 ,  14  form a supply passage and a discharge passage for oxidation gas. The oxidation gas supply passage is located at a position corresponding to the back side of the sheet of  FIG. 9 , and is used for supplying air serving as oxidation gas to the gas passages of the second gas passage forming member  22 . The oxidation gas discharge passage is located at a position corresponding to the front side of the sheet of  FIG. 9 , and is used for discharging oxidation gas that has passed through the gas passages of the second gas passage forming member  22 , or oxidation off-gas, to the outside. 
     Hydrogen gas from a hydrogen gas supply source (not shown) is supplied to the first gas passage forming member  21  through the supply passage M 1  as shown by arrow P of  FIG. 9 , and air is supplied to the second gas passage forming member  22  from an air supply source (not shown). Accordingly, electricity is generated through an electrochemical reaction in the power generating cell. Specifically, hydrogen gas (H 2 ) supplied to the first gas passage forming member  21  flows into the electrode catalyst layer  17  through the first gas diffusion layer  19 . In the electrode catalyst layer  17 , hydrogen (H 2 ) is broken down to hydrogen ions (H + ) and electrons (e − ) as shown by chemical formula (1), and the potential of the electrode catalyst layer  17  becomes zero volts, or standard electrode potential, as known in the art.
 
H 2 →2H + +2 e   −   (1)
 
     Hydrogen ions (H + ) obtained through the above reaction reaches the cathode-side electrode catalyst layer  18  from the anode-side electrode catalyst layer  17  through the solid electrolyte membrane  16 . Oxygen (O 2 ) in the air supplied to the electrode catalyst layer  18  from the second gas passage forming member  22  chemically reacts with the hydrogen ions (H + ) and the electrons (e − ), which generates water as shown by the formula (2). Through the chemical reaction, the potential of the electrode catalyst layer  18  becomes approximately 1.0 volt, or standard electrode potential, as known in the art.
 
½.O 2 +2H + +2 e   − →H 2 O  (2)
 
     In a normal power generation condition of the fuel battery, the potential of the anode-side electrode catalyst layer  17  (the first gas diffusion layer  19 ) is lower than the potential of the cathode-side electrode catalyst layer  18  (the second gas diffusion layer  20 ). Thus, compared to the second gas passage forming member  22 , the first gas passage forming member  21  is less susceptible to metallic oxidation due to a high potential. Therefore, as shown in  FIG. 12 , an inexpensive stainless steel such as ferrite-based SUS having a low corrosion resistance. On the other hand, the second gas passage forming member  22 , the potential of which can become high, is formed by a metal having a high corrosion resistance such as gold as shown in  FIG. 12 . Patent Document 1 discloses a power generating cell for a fuel battery having a similar structure to the structure shown in  FIG. 9 .
     Patent Document 1: Japanese Laid-Open Patent Publication No. 2007-87768   

     DISCLOSURE OF THE INVENTION 
     Problems that the Invention is to Solve 
     In the above described fuel battery, some of the hydrogen gas is not used in power generation and is discharged as fuel off-gas to the outside through the gas passage of the first gas passage forming member  21  and the discharge passage M 2 . Some of the oxygen gas that has not been reduced during the power generation is discharged as oxidation off-gas to the outside through the discharge passage (not shown) formed in the frames  13 ,  14 , together with water generated through the reaction of the formula (2) and nitrogen gas in air. Some of the water generated through the reaction of the formula (2) flows into the gas passage of the first gas passage forming member  21 , while seeping as seepage water through the cathode-side electrode catalyst layer  18 , the solid electrolyte membrane  16 , the anode-side electrode catalyst layer  17 , and the first gas diffusion layer  19 . The seepage water is discharged to the outside through the gas passage of the first gas passage forming member  21  and the discharge passage M 2 , together with the fuel off-gas. 
     As described above with reference to  FIG. 11 , the first gas passage forming member  21  is made of a metal lath plate, which has a great number of hexagonal ring portions  21   a  arranged alternately. Fuel gas flows through gas passage formed by the ring portions  21   a  and the through holes  21   b . In this configuration, the seepage water is likely to adhere to the wall surfaces of the gas passage, which meanders in an complex manner, due to surface tension. Therefore, some of the seepage water from the gas passage of the first gas passage forming member  21  is not discharged to the outside but remains in the gas passage as droplets. The seepage water remaining in the gas passage causes the following problems. 
     That is, the flow rate of fuel gas flowing through the gas passage in the first gas passage forming member  21  becomes higher toward the center as shown by flow rate distribution curve L of  FIG. 11 , and becomes lower toward the left and right edges. Thus, seepage water tends to remain at the left and right edges of the first gas passage forming member  21 . Also, since the downstream edge of the first gas passage forming member  21  is open to the discharge passage M 2 , the flow resistance at the downstream edge is lower than the flow resistance of the gas passage inside the first gas passage forming member  21 . In this configuration, when fuel gas starts flowing to the discharge passage M 2  through a part of the downstream edge of the first gas passage forming member  21 , the flow resistance at the part is smaller than that of the remaining parts. Thus, the fuel gas flows to the discharge passage M 2  through the part of the downstream edge, and the flow in the remaining parts becomes stagnant. Accordingly, in addition to the left and right edges of the first gas passage forming member  21 , the flow rate of fuel gas is low at the downstream edge, and seepage water is likely to remain. Since the flow rate of fuel gas in the gas passage of the first gas passage forming member  21  increases toward the center, fuel gas flows to the discharge passage M 2  mainly through the center portion at the downstream edge of the first gas flow passage forming member  21 , and seepage water tends to remain at the left and right edges. 
     If seepage water remains in the gas passage in the outer peripheral portion of the first gas passage forming member  21  and forms a droplet W as shown in  FIG. 10 , fuel gas is blocked by the droplet W. That is, the fuel gas is not provided to portions of the first gas diffusion layer  19  and the electrode catalyst layer  17  that correspond to the droplet W. This can cause a local hydrogen deficiency. Further, seepage water can enter the narrow clearance at the outer periphery of the first gas diffusion layer  19  and the narrow clearance at the outer peripheral portion of the electrode catalyst layer  17 . This further worsens the hydrogen deficiency. 
     As is commonly known, some of the hydrogen in the first gas diffusion layer  19  enters the second gas diffusion layer  20  after seeping through the electrode catalyst layer  17 , the solid electrolyte membrane  16 , and the electrode catalyst layer  18 . Some of the oxygen in the second gas diffusion layer  20  enters the first gas diffusion layer  19  after seeping through the electrode catalyst layer  18 , the solid electrolyte membrane  16 , and the electrode catalyst layer  17 . That is, although the amount is small, cross leakage of hydrogen and oxygen occurs between the first gas diffusion layer  19  and the second gas diffusion layer  20 . In a part of the electrode catalyst layer  17  that is deficient in hydrogen, hydrogen for reducing oxygen (O 2 ) does not exist. Thus, if such cross leakage of hydrogen and oxygen occurs, the following phenomenon will be observed. 
     That is, oxygen (O 2 ) that has entered the anode-side electrode catalyst layer  17  is reduced by hydrated protons (hydrogen ions with water molecules H + .xH 2 O) that exist in the fluoropolymer film forming the solid electrolyte membrane  16 . That is, the hydrated protons react with oxygen and electrons to generate water as shown by the formula (3) below. The hydrated protons are charge carriers of the polymer film forming the solid electrolyte membrane  16 , and move among sulfonate groups (—SO 3   − —). The hydrated protons then move from the solid electrolyte membrane  16  to the electrode catalyst layer  17 .
 
½×O 2 +2H + +2 e   − →H 2 O  (3)
 
     As a result, although the potential of the anode-side electrode catalyst layer  17  and the first gas diffusion layer  19  is 0 volts as described above, the standard electrode potential of the layers  17 ,  19 , which are deficient in hydrogen due to the reaction of the formula (3), increases to approximately 1.0 volt. The increase of the standard electrode potential of the layers  17 ,  19  corrodes and oxidizes the first gas passage forming member  21 , which is formed of ferrite-based SUS having a low corrosion resistance, thus reducing the durability. When the first gas passage forming member  21  is corroded and oxidized, its electric resistance is increased. This in turn lowers the power generation output. 
     On the other hand, in the cathode-side electrode catalyst layer  18 , the hydrated protons (hydrogen ions H + .xH 2 O) that form the solid electrolyte membrane  16  decrease. To compensate for the reduction in the hydrated protons, carbon (C) forming the electrode catalyst layer  18  and water are reacted as shown by the formula (4), so that carbon dioxide and hydrogen ions (H + ) are generated.
 
C+2H 2 O→CO 2 +4H + +4 e   −   (4)
 
     Through this reaction, carbon particles in the cathode-side electrode catalyst layer  18  are reduced, and the electrode catalyst layer  18  becomes prematurely thin, which reduces the durability of the battery. Further, when the carbon particles of the electrode catalyst layer  18  are eroded, the power generation output is lowered. That is, catalyst particles  32  are adhered onto the surface of each carbon particle  31  in order to improve the power generation efficiency at the power generation based on the above described formulae (1) and (2). When the carbon particles  31  are eroded, the catalyst particles  32  are drained to the gas passage of the second gas passage forming member  22  from the electrode catalyst layer  18  through the second gas diffusion layer  20 . When the amount of catalyst (platinum) of the electrode catalyst layer  18  is reduced, the catalyst performance of the electrode catalyst layer  18  is lowered. This lowers the power generation efficiency, resulting in the power generation output. 
     The total of the decrease in the power generation output due to reduction in the catalyst (platinum) of the cathode-side electrode catalyst layer  18  and the decrease in the above described power generation output due to corrosion of the first gas passage forming member  21  was measured in a output test, under a condition that was equivalent to ten years of use. The test revealed that ten years of use reduced the power generation output to 40% compared to 100% of the output at the time when the operation was started. 
     If a material such as titanium, which has a superior corrosion resistance, or a material obtained by applying gold plating on a ferrite-based SUS, the first gas passage forming member  21  can be prevented from being corroded and its durability is improved. However, this inevitably increases the costs. 
     Accordingly, it is an objective of the present invention to provide a power generating cell for a fuel battery that, if seepage water remains in the gas passage at the outer peripheral portion of an anode-side gas passage forming member, prevents a cathode-side electrode catalyst layer from being eroded, improves the durability of the anode-side gas passage forming member, and prevents the power generation output from being reduced. 
     Means for Solving the Problems 
     To achieve the forgoing objective and in accordance with one aspect of the present invention, a power generating cell for a fuel battery is provided that includes a looped frame, an electrolyte membrane attached inside the frame, an anode-side electrode catalyst layer laid on a first surface of the electrolyte membrane, a cathode-side electrode catalyst layer laid on a second surface of the electrolyte membrane, a first gas passage forming member that is laid on the surface of the anode-side electrode catalyst layer and has a first gas passage for supplying fuel gas, and a second gas passage forming member that is laid on the surface of the cathode-side electrode catalyst layer and has a second gas passage for supplying oxidation gas. A supply passage for supplying fuel gas to the first gas passage and a discharge passage for discharging fuel off-gas from the first gas passage are formed in the frame. Water ingression preventing means that prevents water remaining in a part of the first gas passage at an outer peripheral portion of the first gas passage forming member from entering the anode-side electrode catalyst layer. 
     Also, according to the present invention, it is preferable that the frame surround the outer periphery of the anode side electrode catalyst layer, that the water ingression preventing means include a projecting portion that is formed on the outer peripheral portion of the first gas passage forming member and extends outward beyond the outer periphery of the anode-side electrode catalyst layer so as to overlap with the frame, and that the water ingression preventing means prevent water from entering the anode-side electrode catalyst layer by causing the water to remain on the projecting portion. 
     Also, it is preferable that a distance by which the projecting portion extends beyond the outer periphery of the anode-side electrode catalyst layer be set to 5 to 10 mm. 
     According to the present invention, it is also preferable that the frame be rectangular, and that the projecting portion be one of a plurality of projecting portions that are formed at left, right and downstream edges in the outer peripheral portion of the first gas passage forming member with respect to a flowing direction of the first gas passage. 
     Further, it is preferable that the water ingression preventing means include a band plate-like shield plate that is located at an inner periphery of the frame and between the electrolyte membrane and the outer peripheral portion of the first gas passage forming member. 
     It is also preferable that the first gas passage forming member be made of a metal lath. 
     It is also preferable that the a gas diffusion layer be provided between the anode-side electrode catalyst layer and the first gas passage forming member and between the cathode side electrode catalyst layer and the second gas passage forming member. 
     (Operation) 
     According to the present invention, the water ingress preventing means prevents water remaining in the gas passage at the outer peripheral portion of the first gas passage forming member on the anode side from entering the outer peripheral portion of the anode-side electrode catalyst layer, so that hydrogen deficiency is inhibited in the outer peripheral portion of the electrode catalyst layer. Therefore, this prevents the potential of the anode-side electrode catalyst layer from being increased by the hydrogen deficiency, and also inhibits corrosion of the gas passage forming member, thereby inhibiting erosion of the cathode-side electrode catalyst layer. 
     Effects of the Invention 
     According to the present invention, in a state where seepage water remains in the gas passage at the outer peripheral portion of the anode-side gas passage forming member, it is possible to improve the durability of the anode-side gas passage forming member, prevent the cathode-side electrode catalyst layer from being eroded, and prevent the power generation output from being reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal cross-sectional view illustrating a fuel battery according to a first embodiment of the present invention; 
         FIG. 2  is a cross-sectional view taken along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view illustrated first and second frames, an electrode structure, first and second flow passage forming members, and a separator; 
         FIG. 4  is an enlarged longitudinal cross-sectional view illustrating a part of the fuel battery; 
         FIG. 5  is a perspective view illustrating a gas passage forming member; 
         FIG. 6  is a longitudinal cross-sectional view illustrating a fuel battery according to a second embodiment of the present invention; 
         FIG. 7  is a perspective view illustrating a shield plate used in the fuel battery shown in  FIG. 6 ; 
         FIG. 8  is a perspective view illustrating a first frame according to another embodiment of the present invention; 
         FIG. 9  is a cross-sectional view illustrating a prior art fuel battery; 
         FIG. 10  is an enlarged partial cross-sectional view illustrating the fuel battery shown in  FIG. 9 ; 
         FIG. 11  is a perspective view illustrating a gas passage forming member used in the fuel battery shown in  FIG. 9 ; and 
         FIG. 12  is a graph showing the relationship between a corrosion current and the potential at the anode side and the cathode side of a fuel battery. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     A power generating cell for a fuel battery according to a first embodiment of the present invention will now be described with reference to  FIGS. 1 to 5 . 
     As shown in  FIG. 1 , a fuel battery  11  of the present embodiment is a solid polymer type, and is formed by a number of staked power generating cells  12 . 
     As shown in  FIGS. 1 and 3 , each power generating cell  12  is shaped like a rectangular frame and includes first and second frames  13 ,  14  made of synthetic rubber (or synthetic resin) and a membrane electrode assembly (MEA)  15 , which serves as an electrode structure. The first frame  13  defines in it a passage space S 1  for fuel gas, and the second frame  14  defines in it a passage space S 2  for oxidation gas. The MEA  15  is arranged between the frames  13 ,  14 . 
     The power generating cell  12  has a first gas passage forming member  21 , which is formed by ferrite-based SUS (stainless steel) accommodated in the fuel gas passage space S 1 , and a second gas passage forming member  22 , which is accommodated in the oxidation gas passage space S 2  and is made of titanium or gold. Further, the power generating cell  12  has a first separator  23  and a second separator  24 , which are made of titanium. The first separator  23  is shaped like a flat plate, and is bonded to the upper surfaces of the first frame  13  and the first gas passage forming member  21  as viewed in the drawing. The first separator  24  is shaped like a flat plate, and is bonded to the upper surfaces of the first frame  14  and the first gas passage forming member  22  as viewed in the drawing. In  FIG. 3 , the gas passage forming members  21 ,  22  are illustrated as flat plates in a simplified manner. 
     As shown in  FIGS. 1 and 2 , the MEA  15  is formed by a solid electrolyte membrane  16 , electrode catalyst layers  17  and  18 , and conductive first and second gas diffusion layers  19 ,  20 . The electrode catalyst layer  17  is formed of a catalyst that is laid on the anode-side surface of the solid electrolyte membrane  16 , that is, on the upper surface as viewed in the drawing. The electrode catalyst layer  18  is formed of a catalyst that is laid on the cathode-side surface of the solid electrolyte membrane  16 , that is, on the lower surface as viewed in the drawing. The gas diffusion layers  19 ,  20  are bonded to the surfaces of the electrode catalyst layers  17 ,  18 , respectively. 
     The solid electrolyte membrane  16  is formed of a fluoropolymer film. As shown in  FIG. 4 , the electrode catalyst layer  17 ,  18  each have carbon particles  31  of diameters of several micrometers, and a great number of platinum (Pt) catalyst particles  32  adhere to the surface of each carbon particle  31 . The catalyst particles  32  have a diameter of 2 nm. When electricity is generated by the fuel battery, the catalyst particles  32  function as catalyst that increases the power generation efficiency. The gas diffusion layers  19 ,  20  are formed of carbon paper. As shown in  FIG. 5 , the gas passage forming member  21  ( 22 ) is formed of a metal lath plate, which has a great number of hexagonal ring portions  21   a  ( 22   a ) arranged alternately. Each ring portion  21   a  ( 22   a ) has a through hole  21   b  ( 22   b ). Fuel gas (oxidation gas) flows through gas passages formed by the ring portions  21   a  ( 22   a ) and the through holes  21   b  ( 22   b ).  FIG. 5  is an enlarged and simplified view showing a part of the gas passage forming member  21 ,  22 . 
     As shown in  FIG. 3 , the fuel gas passage space S 1  of the first frame  13  is shaped rectangular as viewed from above. A flange portion S 1   b  is formed integrally with the first frame  13  and is located in a lower portion of an inner peripheral surface S 1   a  of the passage space S 1 . The flange portion S 1   b  horizontally extends inward from the inner peripheral surface S 1   a  and is formed like a rectangular loop. Elongated fuel gas inlet port  13   a  and fuel gas outlet port  13   b  are formed in two parallel and facing sides  131 ,  132  of the flange portion S 1   b , respectively. Elongated oxidation gas inlet port  13   c  and oxidation gas outlet port  13   d  are formed in two sides  133 ,  134  of the flange portion S 1   b , which are perpendicular to the sides  131 ,  132 , respectively. 
     The second frame  14  has a fuel gas inlet port  14   a , a fuel gas outlet port  14   b , an oxidation gas inlet port  14   c , and an oxidation gas outlet port  14   d , which correspond to the fuel gas inlet port  13   a , the fuel gas outlet port  13   b , the oxidation gas inlet port  13   c , and the oxidation gas outlet port  13   d  of the first frame  13 , respectively. 
     A fuel gas inlet port  23   a , a fuel gas outlet port  23   b , an oxidation gas inlet port  23   c , and an oxidation gas outlet port  23   d  are formed in the four sides of the first separator  23  to correspond to the fuel gas inlet port  13   a , the fuel gas outlet port  13   b , the oxidation gas inlet port  13   c , and the oxidation gas outlet port  13   d  formed in the first frame  13 , respectively. Likewise, a fuel gas inlet port  24   a , a fuel gas outlet port  24   b , an oxidation gas inlet port  24   c , and an oxidation gas outlet port  24   d  are formed in the four sides of the second separator  24  to correspond to the fuel gas inlet port  14   a , the fuel gas outlet port  14   b , the oxidation gas inlet port  14   c , and the oxidation gas outlet port  14   d  formed in the second frame  14 , respectively. 
     In the fuel gas passage space S 1  and the oxidation gas passage space S 2  of the first and second frames  13 ,  14 , the first and second gas passage forming members  21 ,  22  contacts the surfaces of the gas diffusion layers  19 ,  20  and the inner surfaces of the first and second separators  23 ,  24 , respectively. 
     As shown in  FIGS. 1 and 3 , the fuel gas inlet port  23   a  of the first separator  23 , the fuel gas inlet port  13   a  of the frame  13 , the fuel gas inlet port  14   a  of the second frame  14 , and the fuel gas inlet port  24   a  of the second separator  24  form a supply passage M 1  for supplying fuel gas to each power generating cell  12 . The fuel gas outlet port  23   b  of the first separator  23 , the fuel gas outlet port  13   b  of the first frame  13 , the fuel gas outlet port  14   b  of the second frame  14 , the fuel gas outlet port  23   b  of the separator  23 , and the fuel gas outlet port  24   b  of the second separator  24  form a fuel gas discharge passage M 2  through the power generating cells  12 . Fuel gas that is supplied to the supply passage M 1  from the outside of the fuel battery passes through the gas passage of the first gas passage forming member  21  and is used for generating electricity. Thereafter, the fuel gas is drawn to the discharge passage M 2  as fuel off-gas. 
     The oxidation gas inlet port  23   c  of the first separator  23 , the oxidation gas inlet port  13   c  of the frame  13 , the oxidation gas inlet port  14   c  of the second frame  14 , and the oxidation gas inlet port  24   c  of the second separator  24  form a supply passage R 1  for supplying oxidation gas to each power generating cell  12 . The oxidation gas outlet port  23   d  of the first separator  23 , the oxidation gas outlet port  13   d  of the frame  13 , the oxidation gas outlet port  14   d  of the second frame  14 , and the oxidation gas outlet port  24   d  of the second separator  24  form a discharge passage R 2  for discharging oxidation off-gas to each power generating cell  12 . Oxidation gas that is supplied to the supply passage R 1  from the outside of the fuel battery passes through the gas passage of the second gas passage forming member  22  and is used for generating electricity. Thereafter, the oxidation gas is drawn to the discharge passage R 2  as oxidation off-gas. 
     The configuration of important part of the preferred embodiment will now be described. 
     As shown in  FIGS. 1 ,  3  and  5 , in the outer peripheral portion of the first gas passage forming member  21 , projecting portions  25  are formed in edges on the left, right and downstream edges with respect to the flowing direction of the gas passage. The projecting portions  25  extend outward beyond the outer periphery of the anode-side electrode catalyst layer  17  and are overlapped onto flange portion S 1   b  of the frame  13 . The projecting portions  25  contact the upper surface of the flange portion S 1   b . This structure, which includes the projecting portions  25 , serves as water ingress preventing means, which prevents seepage water in the gas passage of the projecting portions  25  from entering narrow clearance at the outer peripheral portion of the first gas diffusion layer  19 . That is, even if seepage water exists on the projecting portions  25  when the fuel battery generates electricity, the seepage water is received by the upper surface of the flange portion S 1   b . This prevents the seepage water from entering the narrow clearances at the outer peripheral portion of the first gas diffusion layer  19  and the electrode catalyst layer  17 . 
     In the present embodiment, the thickness of the first gas passage forming member  21  is 0.5 to 1 mm, and the distance D, by which each projecting portion  25  extends outward beyond the outer periphery of the anode-side electrode catalyst layer  17 , is 5 to 10 mm. If the distance D is set to an excessively small value (for example, a value less than 5 mm), seepage water on the projecting portions  25  is likely to be moved toward the first gas diffusion layer  19 . On the other hand, if the distance D is set to an excessively great value (for example, a value greater than 10 mm), the size of the first gas passage forming member  21  is likely to be excessively large. 
     The operation of the fuel battery configured as described above will now be described. 
     As shown in  FIGS. 1 and 2 , fuel gas and oxidation gas that are supplied to the supply passage M 1  and the supply passage R 1  are diffused in the fuel gas passage space S 1  and the oxidation gas passage space S 2  by means of the first and second gas passage forming members  21 ,  22 , respectively. That is, the fuel gas in the fuel gas passage space S 1  passes through the gas passage formed in the first gas passage forming member  21  so as to become turbulence, thereby being diffused in the fuel gas passage space S 1 . The fuel gas is further properly diffused by passing through the first gas diffusion layer  19 , so as to be evenly supplied to the electrode catalyst layer  17 . On the other hand, the oxidation gas in the oxidation gas passage space S 2  passes through the gas passage formed in the second gas passage forming member  22  so as to become turbulence, thereby being diffused in the oxidation gas passage space S 2 . The oxidation gas is further properly diffused by passing through the second gas diffusion layer  20 , so as to be evenly supplied to the electrode catalyst layer  18 . The supply of the fuel gas and the oxidation gas initiates an electrode reaction, so that electricity is generated. The fuel battery  11 , which is formed by the power generating cells  12 , thus outputs a desired electricity. 
     The above described power generation is similar to that discussed in the BACKGROUND ART. That is, in the anode-side electrode catalyst layer  17 , hydrogen (H 2 ) is broken down to hydrogen ions (H + ) and electrons (e − ) as shown by the chemical formula (1) below, and the potential of the electrode catalyst layer  17  becomes zero volts, or standard electrode potential.
 
H 2 →2H + +2 e   −   (1)
 
     Hydrogen ions (H + ) obtained through the above reaction reaches the cathode-side electrode catalyst layer  18  from the anode-side electrode catalyst layer  17  through the solid electrolyte membrane  16 . Oxygen (O 2 ) in the air supplied to the electrode catalyst layer  18  from the second gas passage forming member  22  chemically reacts with the hydrogen ions (H + ) and the electrons (e), which generates water as shown by the formula (2). Through the chemical reaction, the potential of the electrode catalyst layer  18  becomes approximately 1.0 bolt, or standard electrode potential.
 
½.O 2 +2H + +2 e   − →H 2 O  (2)
 
     In the fuel battery, some of the hydrogen gas is not used in power generation and is discharged as fuel off-gas to the outside through the gas passage of the first gas passage forming member  21  and the discharge passage M 2 . Some of the oxygen gas that has not been reduced during the power generation is discharged as oxidation off-gas to the outside through the discharge passage R 2  formed in the frames  13 ,  14 , together with water generated through the reaction of the formula (2) and nitrogen gas in air. Some of the generated water flows into the gas passage of the first gas passage forming member  21 , while seeping as seepage water through the cathode-side electrode catalyst layer  18 , the solid electrolyte membrane  16 , the anode-side electrode catalyst layer  17 , and the first gas diffusion layer  19 . The seepage water is discharged to the outside through the discharge passage M 2 , together with the fuel off-gas. 
     The flow rate of fuel gas flowing through the gas passage in the first gas passage forming member  21  becomes higher toward the center as shown by flow rate distribution curve L of  FIG. 5 , and becomes lower toward the left and right edges. Thus, as shown in  FIGS. 1 ,  2  and  4 , at the three projecting portions  25  located on the left, right, and downstream edges of the first gas passage forming member  21  with respect to the direction of the gas passage, the flow rate of gas is slow and seepage water is likely to remain. Since the seepage water W remaining on the projecting portions  25  is received by the upper surface of the flange portion S 1   b , which forms the fuel gas passage space S 1  in the frame  13 , the seepage water is prevented from entering the narrow clearances at the outer peripheral portions of the first gas diffusion layer  19  and the electrode catalyst layer  17 . Therefore, the fuel gas (hydrogen gas) is properly supplied to the narrow clearances at the outer peripheral portions of the layers  19 ,  17 , so that deficiency in hydrogen is inhibited. As discussed in the BACKGROUND ART, this prevents the potential of the anode-side electrode catalyst layer  17  from being increased by deficiency in hydrogen, and also inhibits corrosion of the first gas passage forming member  21 , thereby inhibiting erosion of the carbon of the cathode-side electrode catalyst layer  18 . As a result, the durability of the electrode catalyst layer  18  is improved, and the power generation output is prevented from being reduced. 
     The above described embodiment has the following advantages. 
     (1) In the above described embodiment, the projecting portions  25  are formed in the left, right and downstream edges of the first gas passage forming member  21  with respect to the flowing direction of the gas passage. The projecting portions  25  extend outward beyond the outer periphery of the anode-side electrode catalyst layer  17 . Seepage water remains on the projecting portions  25 . This prevents the seepage water from entering the narrow clearances at the outer peripheral portions of the first gas diffusion layer  19  and the electrode catalyst layer  17 . Therefore, the fuel gas (hydrogen gas) is properly supplied to the narrow clearances at the outer peripheral portions of the layers  19 ,  17 , so that deficiency in hydrogen is inhibited. As a result, the potential of the anode-side electrode catalyst layer  17  is prevented from being increased by hydrogen deficiency, and corrosion of the first gas passage forming member  21  due to increase in the potential is prevented. Further, erosion of the carbon of the cathode-side electrode catalyst layer  18  is inhibited, so that the durability of the electrode catalyst layer  18  is improved. This prevents the power generation output from being reduced. 
     (2) In the above embodiment, since the projecting portions  25  are integrally formed with the first gas passage forming member  21 , the structure of the water ingression preventing means is simplified. This facilitates the manufacture and assembly of the structure, and thus reduces the costs. 
     Second Embodiment 
     A second embodiment of the present invention will now be described with reference to  FIGS. 6 and 7 . 
     Water ingression preventing means according to the present embodiment has a configuration in which a shield plate  26  made of an electrical conducting material is bonded to the inner surface of the flange portion S 1   b  with an adhesive. The examples of the material of the shield plate  26  include gold-plated copper. The shield plate  26  is located between the upper surface of the solid electrolyte membrane  16  and the lower surface of the first gas passage forming member  21 . As shown in  FIG. 7 , the shield plate  26  is U-shaped as viewed from above. In relation to the flowing direction of the gas passage, the shield plate  26  is arranged to correspond to the edges on the left, right and downstream edges of the first gas passage forming member  21 . The proximal portion of the shield plate  26  may be coupled to the flange portion S 1   b  by insert molding. 
     In the present embodiment, seepage water remaining at the left, right, and downstream edges of the first gas passage forming member  21  in relation to the flowing direction of the gas passage is received by the shield plate  26 , the seepage water is prevented from entering the narrow clearance at the outer peripheral portions of the anode-side electrode catalyst layer  17  and the first gas diffusion layer  19 . The present embodiment thus achieves the same advantage as the advantage ( 1 ) of the first embodiment. 
     The above described embodiments may be modified as follows. 
     As shown in  FIG. 8 , the inner periphery of the flange portion S 1   b  of the frame  13  may be extend by a certain length, so as to form a shield plate  26  as in the second embodiment is integrally formed with the frame  13 . This simplifies the structure of the water ingression preventing means, thereby facilitating the manufacture of the structure. 
     Other stainless plates, the first and second gas passage forming members  21 ,  22  may be formed by metal plates with conductive metal plates such as aluminum and copper. 
     The present invention may be applied to a fuel battery without the gas diffusion layers  19 ,  20 . 
     In the first embodiment, the projecting portions  25  are formed at the left, right, and downstream edges with respect to the gas flowing direction in the outer peripheral portion of the first gas flow passage forming member  21 . In addition to the three edges, another projecting portion  25  may be formed at the edge located on the upstream side with respect to the flowing direction of the gas passage. 
     In each of the above embodiments, the distance D by which the projecting portions  25  project beyond the outer periphery of the electrode catalyst layer  17  is set to 5 to 10 mm. However, the distance D may be changed as necessary based on the thickness of the first gas passage forming member  21 . 
     In the above illustrated embodiments, the configurations of the frames  13 ,  14  have been described. However, frames having different configuration may be employed as long as those frames are located outside of the solid electrolyte membrane  16  and form supply passages and discharge passages for fuel gas and oxidation gas. For example, in the illustrated embodiments, the frame  13  ( 14 ) is formed separately from the separator  23  ( 24 ). However, the frame  13  ( 14 ) and the separator  23  ( 24 ) may be formed integrally. Also, frames made of gaskets may be used. Further, frames can be formed by impregnating outer peripheral portions of the gas passage forming members  21 ,  22  with resin and hardening the resin.