Patent Publication Number: US-2023147601-A1

Title: Gas diffusion member, gas diffusion unit, and fuel cell

Description:
FIELD 
     The present invention relates to a gas diffusion member, a gas diffusion unit, and a fuel cell. 
     BACKGROUND 
     As disclosed in Patent Literatures 1 and 2, a fuel cell can generate electricity through electrochemical reaction by supplying hydrogen to an anode and air (oxygen) to a cathode. 
     PRIOR ART DOCUMENTS 
     Patent Literature 
     [Patent Literature 1] WO 2019/239605 
     [Patent Literature 2] WO 2019/239605 
     SUMMARY 
     Technical Problem 
     A fuel cell has internal resistance. Since power generation efficiency is lowered as the internal resistance becomes higher, it is desired to reduce the internal resistance. 
     The present invention has been made by taking these circumstances into consideration. The present invention provides a gas diffusion member capable of reducing internal resistance of a fuel cell. 
     Means to Solve the Problem 
     According to the present invention, a gas diffusion member arranged between a separator and a catalyst layer of a fuel cell, comprising:
     a porous material layer; and   a conductive material layer; wherein:   the porous material layer is formed of a conductive porous material;   the conductive material layer is formed of a conductive material; and   the conductive material layer is arranged on a surface of the porous material layer on a side of the separator and   is provided so that pores of the porous material are filled with the conductive material, is provided.   

     The present inventors have found that since the porous material layer of the gas diffusion member is porous, contact resistance between the porous material layer and the separator is high. Based on the finding, they have found that the contact resistance between the porous material layer and the separator can be reduced by providing the conductive material layer so that the pores of the porous material layer on the side of the separator are filled with the conductive material, and consequently the internal resistance can be reduced, thereby leading to completion of the invention. 
     The following are examples of various embodiments of the present invention. The embodiments shown below can be combined with each other. 
     Preferably, the gas diffusion member, wherein the porous material layer comprises a groove on the surface of the porous material layer on the side of the separator as a gas flow path. 
     Preferably, the gas diffusion member, wherein a microporous layer is provided on the surface of the porous material layer on the side of the catalyst layer. 
     Preferably, the gas diffusion member, wherein the conductive material is formed of a resin in which conductive particles are dispersed. 
     Preferably, the gas diffusion member, wherein a thickness of the conductive material layer is 1 to 100 μm. 
     Preferably, the gas diffusion unit comprising the gas diffusion member and the separator, wherein the gas diffusion member is adhered to the separator via the conductive material. 
     Preferably, the gas diffusion unit, wherein a gasket arranged to surround the gas diffusion member is fixed to the separator. 
     Preferably, a fuel cell comprising a cathode-side separator, a cathode gas diffusion member, a catalyst-coated membrane, an anode gas diffusion member and an anode-side separator in this order, wherein: the catalyst-coated membrane comprises a cathode catalyst layer, an electrolyte membrane and an anode catalyst layer in order from a side of the cathode gas diffusion member; and the cathode gas diffusion member and the anode gas diffusion member are each the gas diffusion member. 
     Preferably, the fuel cell, wherein: the cathode gas diffusion member is adhered to the cathode-side separator; and the anode gas diffusion member is adhered to the anode-side separator. 
     Preferably, the fuel cell, wherein: a cathode gasket arranged to surround the cathode gas diffusion member is fixed to the cathode-side separator; and 
     an anode gasket arranged to surround the anode gas diffusion member is fixed to the anode-side separator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an exploded perspective view of a fuel cell  1  of the first embodiment of the present invention as viewed from diagonally above. 
         FIG.  2    is an exploded perspective view of the fuel cell  1  of  FIG.  1    as viewed from diagonally below. 
         FIG.  3 A  is a plan view of a catalyst-coated membrane  2  and a support frame  3 . 
         FIG.  3 B  is a cross-sectional view along a B-B line in  FIG.  3 A . 
         FIG.  3 C  is an enlarged view of an area C in  FIG.  3 B . 
         FIG.  4 A  is a perspective view of the catalyst-coated membrane  2  and the support frame  3  as viewed from diagonally above. 
         FIG.  4 B  is a perspective view of a gasket  11  and a cathode gas diffusion member  31  as viewed from diagonally above. 
         FIG.  4 C  is a perspective view of a gasket  12  and an anode gas diffusion member  32  as viewed from diagonally above. 
         FIG.  5    is a perspective view of a gasket  13  and a cooling water diffusion member  33  as viewed from diagonally above. 
         FIG.  6 A  is a perspective view of a cooling water side of a cooling water/cathode separator  21  as viewed from diagonally above. 
         FIG.  6 B  is an enlarged view of an area B in  FIG.  6 A . 
         FIG.  7 A  is a perspective view of a cathode side of the cooling water/cathode separator  21  as viewed from diagonally below. 
         FIG.  7 B  is an enlarged view of an area B in  FIG.  7 A . 
         FIG.  8 A  is a perspective view of an anode side of an anode/cooling water separator  22  as viewed from diagonally above. 
         FIG.  8 B  is a perspective view of a cooling water side of the anode/cooling water separator  22  as viewed from diagonally below. 
         FIG.  9 A  is a schematic view showing the cross-sectional shape of a porous material layer  31   c.    
         FIG.  9 B  is a schematic view showing the cross-sectional shape of the gas diffusion member  31 . 
         FIG.  9 C  is a schematic view showing the cross-sectional shape of a gas diffusion unit  41 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present invention will be explained with reference to the drawings. Various distinctive features shown in the following embodiments can be combined with each other. In addition, an invention can be established independently for each of the distinctive features. 
     1. First Embodiment 
     As shown in  FIGS.  1  and  2   , the fuel cell  1  of the first embodiment of the present invention comprises a catalyst-coated membrane  2 , a support frame  3 , a cathode gasket  11 , an anode gasket  12 , a cooling water gasket  13 , a cooling water/cathode separator (an example of a “cathode-side separator”)  21 , and an anode/cooling water separator (an example of an “anode-side separator)  22 , a cathode gas diffusion member  31 , an anode gas diffusion member  32 , and a cooling water diffusion member  33 . Therefore, the fuel cell  1  comprises the cooling water/cathode separator  21 , the cathode gas diffusion member  31 , the catalyst-coated membrane  2 , the anode gas diffusion member  32 , and the anode/cooling water separator  22  in this order. 
     A single cell  4  is configured of the catalyst-coated membrane  2 , the support frame  3 , the gaskets  11  and  12 , and the gas diffusion members  31  and  32 . The gasket  13  and the diffusion member  33  constitute a cooling layer  5 . The cooling layer  5  is arranged above and below the single cell  4 , and the single cell  4  is separated from the upper and lower cooling layers  5  by the separators  21  and  22 . The single cell  4 , the separator  21 , the cooling layer  5 , and the separator  22  constitute a repeating unit. By stacking the required number of these repeating units, a stacked cell having the desired performance is obtained. A current collector, insulating sheet, and end plate (not shown) can be placed on the upper and lower surface of the stacked cell. By pressing each member from both sides using a pair of end plates, the members in the electrochemical stacked cell can be tightly bonded to each other. 
     As shown in  FIGS.  3  to  8   , the support frame  3 , the gaskets  11 ,  12 ,  13 , and the separators  21 ,  22  are provided with cathode gas inlets  3   a ,  11   a,    12   a,    13   a,    21   a,    22   a  (hereinafter referred to as “cathode gas inlets  3   a  etc.”) and cathode gas outlets  3   b,    11   b,    12   b,    13   b,    21   b,    22   b  (hereinafter referred to as “cathode gas outlets  3   b  etc.”) as a flow port (inlet or outlet) of the cathode gas such as air and oxygen; anode gas inlets  3   c,    11   c,    12   c,    13   c,    21   c,    22   c  (hereinafter referred to as “anode gas inlets  3   c  etc.”) and anode gas outlets  3   d,    11   d,    12   d,    13   d,    21   d,    22   d  (hereinafter referred to as “anode gas outlets  3   d  etc.”) as a flow port of the anode gas such as hydrogen; and cooling water inlets  3   e,    11   e ,  12   e,    13   e,    21   e,    22   e  (hereinafter referred to as “cooling water inlets  3   e  etc.”) and cooling water outlets  3   f,    11   f,    12   f,    13   f,    21   f,    22   f  (hereinafter referred to as “cooling water outlets  3   f  etc.”) as a flow port of the cooling water (an example of “fluid”), respectively. The cathode gas inlets  3   a  etc., the cathode gas outlets  3   b  etc., the anode gas inlets  3   c  etc., the anode gas outlets  3   d  etc., the cooling water inlets  3   e  etc., and the cooling water outlets  3   f  etc., are each communicated with each other. 
     Hereinafter, each configuration will be described in detail. 
     As shown in  FIG.  3   , the catalyst-coated membrane  2  is configured by applying a cathode catalyst layer  2   b  to one surface of an electrolyte membrane  2   a  and applying an anode catalyst layer  2   c  to the other surface of the electrolyte membrane  2   a.  Therefore, the catalyst-coated membrane  2  has, in order from the cathode gas diffusion member  31  side, the cathode catalyst layer  2   b,  the electrolyte membrane  2   a,  and the anode catalyst layer  2   c.  The periphery  2   d  of the catalyst-coated membrane  2  is supported by the support frame  3 . 
     As shown in  FIGS.  4  to  5   , the gaskets  11 ,  12 ,  13  are, for example, sheets formed of an elastic material such as rubber and are provided with accommodating part  11   g,    12   g,    13   g  to accommodate the diffusion members  31 ,  32 ,  33 , respectively. Therefore, the gaskets  11 ,  12 ,  13  are arranged to surround the diffusion members  31 ,  32 ,  33 , respectively. 
     As shown in  FIG.  4 B , the accommodating part  11   g  is communicated with the cathode gas inlet  11   a  and the cathode gas outlet  11   b.  The accommodating part  11   g  accommodates the gas diffusion member  31 , thereby easily positioning the gas diffusion member  31 . The gas diffusion member  31  diffuses the cathode gas supplied from the cathode gas inlet  11   a . The gas diffusion member  31  has an overlapping part  31   a  which overlaps the catalyst layers  2   b,    2   c  in a plan view, and a protruding part  31   b  which protrudes from the overlapping part  31   a  towards the cathode gas inlet  11   a  and cathode gas outlet  11   b.  According to this configuration, the cathode gas supplied from the cathode gas inlet  11   a  is smoothly introduced into the gas diffusion member  31 . The value of (the thickness of the gas diffusion member  31 /the thickness of the gasket  11 ) is, for example, 0.8 to 1.2, and preferably 0.9 to 1.1. 
     As shown in  FIG.  4 C , the accommodating part  12   g  is communicated with the anode gas inlet  12   c  and the anode gas outlet  12   d.  The accommodating part  12   g  accommodates the gas diffusion member  32 . The gas diffusion member  32  diffuses the anode gas supplied from the anode gas inlet  12   c . The gas diffusion member  32  has an overlapping part  32   a  which overlaps the catalyst layers  2   b,    2   c  in a plan view, and the protruding part  32   b  which protrudes from the overlapping part  32   a  towards the anode gas inlet  12   c  and the anode gas outlet  12   d.  According to this configuration, the anode gas supplied from the anode gas inlet  12   c  is smoothly introduced into the gas diffusion member  32 . 
     As shown in  FIG.  5   , the accommodating part  13   g  is communicated with the cooling water inlet  13   e  and the cooling water outlet  13   f.  The accommodating part  13   g  accommodates the cooling water diffusion member  33 . The cooling water diffusion member  33  diffuses the cooling water supplied from the cooling water inlet  13   e,  and for example, is configured of a porous material. The cooling water diffusion member  33  has an overlapping part  33   a  which overlaps the catalyst layers  2   b,    2   c  in a plan view, and the protruding part  33   b  which protrudes from the overlapping part  33   a  towards the cooling water inlet  13   e  and the cooling water outlet  13   f.  According to this configuration, the cooling water supplied from the cooling water inlet  13   e  is smoothly introduced into the cooling water diffusion member  33 . 
     The cathode gas, anode gas, and cooling water are supplied through the cathode gas inlet  3   a  etc., the anode gas inlet  3   c  etc., and the cooling water inlet  3   e  etc., respectively. The cathode gas is supplied to the cathode gas diffusion member  31  and is not supplied to the anode gas diffusion member  32  and the cooling water diffusion member  33 . The cathode gas supplied to the cathode gas diffusion member  31  is emitted through the cathode gas outlet  3   b  etc. The anode gas is supplied to the anode gas diffusion member  32  and is not supplied to the cathode gas diffusion member  31  and the cooling water diffusion member  33 . The anode gas supplied to the anode gas diffusion member  32  is emitted through the anode gas outlet  3   d  etc. The cooling water is supplied to the cooling water diffusion member  33  and is not supplied to the cathode gas diffusion member  31  and the anode gas diffusion member  32 . The cooling water supplied to the cooling water diffusion member  33  is emitted through the cooling water outlet  3   f  etc. 
     The separators  21  and  22  can be formed of metals such as titanium, stainless steel, or composites of a carbon material and a resin. 
     As shown in  FIGS.  6  to  7   , the separator  21  is a flat plate member having first and second principal surfaces  21   i,    21   j.  The principal surface  21   i  is provided with a ridge  21   g,  and the principal surface  21   j  is provided with a ridge  21   h.    
     As shown in  FIG.  1   , the ridge  21   g  faces the gasket  13 , and the ridge  21   g  is pressed against the gasket  13  to form the sealing structure. The ridge  21   g  is provided to form a passage  21   k  that allows the cooling water to flow along the principal surface  21   i.    
     As shown in  FIG.  2   , the ridge  21   h  faces the gasket  11 , and the ridge  21   h  is pressed against the gasket  11  to form the sealing structure. The ridge  21   h  is provided to form a passage  21   i  that allows the cathode gas to flow along the main surface  21   j.    
     As shown in  FIG.  8   , the separator  22  is a flat plate member having first and second principal surfaces  22   i  and  22   j.  The principal surface  22   i  is provided with a ridge  22   g,  and the principal surface  22   j  is provided with a ridge  22   h.  The configuration, manufacturing method and the like of the separator  22  are the same as those of the separator  21 . 
     As shown in  FIG.  1   , the ridge  22   g  faces the gasket  12 , and the ridge  22   g  is pressed against the gasket  12  to form the sealing structure. The ridge  22   g  is provided to form the passage  22   k  that allows the anode gas to flow along the main surface  22   i.    
     As shown in  FIG.  2   , the ridge  22   h  faces the gasket  13 , and the ridge  22   h  is pressed against the gasket  13  to form the sealing structure. The ridge  22   h  is provided to form a passage  22   l  that allows the cooling water to flow along the principal surface  22   j.    
     The gas diffusion member  31  will hereinafter be described in more detail. 
     As shown in  FIG.  9 B , the gas diffusion member  31  comprises a porous material layer  31   c,  a conductive material layer  31   d,  and a microporous layer  31   e.    
     The porous material layer  31   c  is configured of a conductive porous material. The porous material layer  31   c  preferably includes a mixture of a conductive filler and a resin. Binding property of the resin facilitates the formation of grooves  31   c   2  (illustrated in  FIG.  9 A ), which is described later. The conductive filler can be either particulate or fibrous, but in terms of increasing porosity, it is preferably fibrous. The conductive filler is preferably a carbon filler in terms of conductivity. Therefore, the conductive filler is preferably a carbon fiber. The percentage of the conductive filler in the mixture is preferably 70 to 99 mass %, more preferably 80 to 90 mass %. This percentage is, particularly for example, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 mass %, and can be in the range between the two values exemplified herein. The resin preferably does not soften at the operating temperature of the fuel cell, and is preferably thermoplastic resin. 
     The porous material layer  31   c  may also be made of base materials including a conductive and porous sheet-shaped material or the like such as woven fabric of conductive fiber (e.g., carbon fiber), paper body, felt, and nonwoven fabric. More specifically, carbon paper, carbon cloth, and carbon nonwoven fabric are preferably cited as examples of the layer. 
     Porosity of the porous material layer  31   c  is preferably 30 to 85%, more preferably 50 to 85%. Porosity is defined as (the volume of pores in the porous material layer)/(the volume of the porous material layer). The porosity is, particularly for example, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or 85%, and can be in the range between the two values exemplified herein. 
     The thickness of the porous material layer  31   c  is, for example, 0.1 to 1 mm, preferably 0.2 to 0.6 mm. The thickness of the porous material layer  31   c  is, particularly for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.0 mm, and can be in the range between the two values exemplified herein. 
     As shown in  FIG.  9 A , a surface  31   c   1  on the separator  21  side of the porous material layer  31   c  is preferably provided with the groove  31   c   2  as a gas flow path. The uniformity of gas diffusion can be enhanced by providing the groove  31   c   2 . The ratio of the depth of the groove  31   c   2  to the thickness of the porous material layer  31   c  is, for example, 0.1 to 0.9 and preferably 0.1 to 0.7. The ratio of the width of the groove  31   c   2  to the thickness of the porous material layer  31   c  is, for example, 0.1 to 0.9 and preferably 0.1 to 0.7. These ratios are, particularly for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, and can be in the range between the two values exemplified herein. The depth and/or width of the groove  31   c   2  may be constant or variable along the direction in which the groove  31   c   2  extends. The shape of the groove  31   c   2  can be, for example, zigzag, sinusoidal, square wave, or lattice. The number of the groove  31   c   2  may be one or more. The groove  31   c   2  may be provided to extend continuously from the end surface on the cathode gas inlet  3   a  side to the end surface on the cathode gas outlet  3   b  side and may also be provided in a part of the region in between. 
     The surface  31   c   1  of the porous material layer  31   c  on the separator  21  side has many recesses  31   c   3  relating to the pores in the porous material. For this reason, if the porous material layer  31   c  is in direct contact with the separator  21 , the contact surface area becomes smaller by the amount of the recesses  31   c   3 , thereby increasing the contact resistance between the porous material layer  31   c  and the separator  21 . 
     Therefore, in the present embodiment, the conductive material layer  31   d  is placed on the surface  31   c   1  of the porous material layer  31   c  on the separator  21  side. The conductive material layer  31   d  is constituted of a conductive material and is provided so that the pores of the porous material that constitutes the porous material layer  31   c  (in other words, the recesses  31   c   3  relating to the pores of the porous material) are filled with the conductive material. Consequently, as shown in  FIG.  9 B , the surface  31   c   1  is planarized, thereby reducing the contact resistance between the porous material layer  31   c  and the separator  21 . 
     The porosity of the conductive material layer  31   d  is lower than that of the portion of the porous material layer  31   c  other than the conductive material layer  31   d,  and is, for example, 0 to 20% and preferably 0 to 10%. This porosity is, particularly for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20%, and can be in the range between the two values exemplified herein. 
     The thickness of the conductive material layer  31   d  is, for example, 1 to 100 μm, preferably 1 to 60 μm, and further preferably 5 to 30 μm. If the conductive material layer  31   d  is too thin, the contact resistance reduction effect may be insufficient, and if it is too thick, gas diffusion may be inhibited. The thickness of conductive material layer  31   d  is, particularly for example, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, or 100 μm, and can be in the range between the two values exemplified herein. 
     Defining that the thickness of the part of the conductive material layer  31   d  formed inside the porous material layer  31   c  is T1 and the thickness of the part formed outside the porous material layer  31   c  is T2, the value of T2/T1 is preferably 0.5 or less, more preferably 0.3 or less, and even more preferably 0.1 or less. This is because if T2 is large, the resistance of the conductive material layer  31   d  may lead to the increased internal resistance. The value of T2/T1 is, particularly for example, 0, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, or 0.5, and can be in the range between the two values exemplified herein. 
     The conductive material layer  31   d  can be formed by applying the conductive material to the surface  31   c   1  of the porous material layer  31   c  and curing it. It is preferable to press the flat surface of the separator  21  or another member against the surface of the porous material layer  31   c  in curing the conductive material. This can flatten the surface of the conductive material layer  31   d    
     If the conductive material is an adhesive material, a cathode gas diffusion unit  41 , which is unitized by adhering the separator  21  to the gas diffusion member  31  via the conductive material, can be obtained, as shown in  FIG.  9 C , by pressing the separator  21  against the surface  31   c   1  of the porous material layer  31   c  after the application of the conductive material and by curing the conductive material under such a condition. Adhesion of the separator  21  to the gas diffusion member  31  can reduce the contact resistance drastically as well as the number of components of the fuel cell, thereby reducing time required for the assembly step. The gasket  11  can be fixed to the separator  21  of the gas diffusion unit  41 , thereby further reducing the number of components. 
     The conductive material has conductivity and can fill the pores of the porous material constituting the porous material layer  31   c.  For example, the conductive material is formed of a resin in which conductive particles are dispersed. The diameter of the conductive particles is preferably ½ or less of the pore diameter of the porous material. This is because the pores of the porous material can be easily filled with the conductive particles in this case. It is preferable that the resin can be cured after the conductive material is applied to the porous material layer  31   c.  The curing method may be heat curing, light curing, or room temperature curing. When the gas diffusion unit is obtained by adhering the separator  21  to the gas diffusion member  31  via the conductive material, it is preferable to cure the resin at a temperature of 100° C. or lower. If the curing temperature is too high, the gas diffusion unit may be warped due to the difference in linear expansion coefficient between the gas member  31  and the separator  21 . The curing temperature is, for example, 0 to 100° C., and particularly for example, 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100° C., and can be in the range between the two values exemplified herein. The conductive particles are preferably carbon particles and more preferably carbon black, in terms of conductivity and availability. 
     The conductive material may also be constituted of conductive polymers. In this case, the addition of the conductive particles is not necessary. 
     The microporous layer  31   e  is provided on a surface  31   c   4  on the catalyst layer  2   b  side of the porous material layer  31   c.  The microporous layer  31   e  has conductivity and finer pores than those of the porous material layer  31   c.  The microporous layer  31   e  facilitates the removal of water generated by the reaction in the catalyst layer  2   b.  The microporous layer  31   e  has higher permeability than the conductive material layer  31   d.  The permeability can be measured in accordance with JIS P 8117:2009. The porosity of the microporous layer  31   e  is preferably higher than that of the conductive material layer  31   d.  The microporous layer  31   e  preferably contains a mixture of the conductive filler and the resin. The permeability and porosity of the microporous layer  31   e  can be adjusted by varying the proportion of the resin in the mixture or the size of the conductive filler. The microporous layer  31   e  can be omitted if it is not needed. 
     The gas diffusion member  32  can be constituted in the same way as the gas diffusion member  31 . The contact resistance between the gas diffusion member  32  and the separator  22  can be reduced by providing a conductive material layer in the gas diffusion member  32 . Further, the gas diffusion member  32  may be adhered to the separator  22  via the conductive material to obtain an anode gas diffusion unit. The gasket  12  may be fixed to the separator  22  of the anode gas diffusion unit. 
     2. Other Embodiments 
     In the first embodiment, the cooling layer  5  is provided for each single cell  4 , but the cooling layer  5  may be provided for each of a plurality of single cells  4 . In this case, an anode/cathode separator is provided between two single cells  4 . Since the gas diffusion members  31 ,  32  are brought into contact with the anode-cathode separator, the contact resistance can be reduced by the same configuration as in the first embodiment. The anode/cathode separator is a cathode-side separator when viewed from the gas diffusion member  31  side and is an anode-side separator when viewed from the gas diffusion member  32  side. 
     In the above embodiment, the sealing structure is realized by pressing the ridge provided on the separator against the gasket, but the sealing structure may be realized by other methods. For example, the sealing structure may be realized by placing the gasket (sealing material such as packing, O-ring, or the like) inside a groove provided on the separator. 
     EXPLANATION OF SYMBOLS 
       1 : fuel cell,  2 : catalyst-coated membrane,  2   a : electrolyte membrane,  2   b : cathode catalyst layer,  2   c : anode catalyst layer,  2   d : periphery,  3 : support frame,  3   a : cathode gas inlet,  3   b : cathode gas outlet,  3   c : anode gas inlet,  3   d : anode gas outlet,  3   e : cooling water inlet,  3   f : cooling water outlet,  4 : single cell,  5 : cooling layer,  11 : cathode gasket,  11   a : cathode gas inlet,  11   b : cathode gas outlet,  11   c : anode gas inlet,  11   d : anode gas outlet,  11   e : cooling water inlet,  11   f : cooling water outlet,  11   g : accommodating part,  12 : anode gasket,  12   a : cathode gas inlet,  12   b : cathode gas outlet,  12   c : anode gas inlet,  12   d : anode gas outlet,  12   e : cooling water inlet,  12   f : cooling water outlet,  12   g : accommodating part,  13 : cooling water gasket,  13   a : cathode gas inlet,  13   b : cathode gas outlet,  13   c : anode gas inlet,  13   d : anode gas outlet,  13   e : cooling water inlet,  13   f : cooling water outlet,  13   g : accommodating part,  21 : cathode separator,  21   a : cathode gas inlet,  21   b : cathode gas outlet,  21   c : anode gas inlet,  21   d : anode gas outlet,  21   e : cooling water inlet,  21   f : cooling water outlet,  21   g : ridge,  21   h : ridge,  21   i : first principal surface,  21   j : second principal surface,  21   k : passage,  21   l : passage,  22 : cooling water separator,  22   a : cathode gas inlet,  22   b : cathode gas outlet,  22   c : anode gas inlet,  22   d : anode gas outlet,  22   e : cooling water inlet,  22   f : cooling water outlet,  22   g : ridge,  22   h : ridge,  22   i : first principal surface,  22   j : second principal surface,  22   k : passage,  22   i : passage,  31 : cathode gas diffusion member,  31   a : overlapping part,  31   b : protruding part,  31   c : porous material layer,  31   c   1 : surface,  31   c   2 : groove,  31   c   3 : recess,  31   c   4 : surface,  31   d : conductive material layer,  31   e : microporous layer,  32 : anode gas diffusion member,  32   a : overlapping part,  32   b : protruding part,  33 : cooling water diffusion member,  33   a : overlapping part,  33   b : ridge,  41 : cathode gas diffusion unit, B: area, C: area