Patent Publication Number: US-2023163339-A1

Title: Fuel Cell

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2021-00163320, filed on Nov. 24, 2021, which is hereby incorporated by reference as if fully set forth herein. 
     TECHNICAL FIELD 
     The present application relates to a fuel cell. 
     BACKGROUND 
     In general, a fuel cell includes a polymer electrolyte membrane, and generates electrical energy using air supplied to one surface of the polymer electrolyte membrane and hydrogen supplied to the opposite surface of the polymer electrolyte membrane. A fuel cell may be used to supply electrical energy to a vehicle. Such a fuel cell requires reliable airtightness and watertightness. 
     SUMMARY 
     Accordingly, embodiments are directed to a fuel cell that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
     Embodiments provide a fuel cell having improved performance with regard to airtightness and watertightness. 
     A fuel cell according to an embodiment may include a cell stack including a plurality of unit cells stacked in a first direction, an end plate disposed on at least one of both side ends of the cell stack, an enclosure coupled to the end plate to surround a side portion of the cell stack and divided into a plurality of segments, a plate gasket disposed on the end plate, and an enclosure gasket disposed between the plurality of segments. One of the plate gasket and the enclosure gasket may include a protruding portion protruding in the first direction, and the remaining one of the plate gasket and the enclosure gasket may include a depressed portion depressed in the first direction to receive the protruding portion fitted thereinto. 
     For example, the plurality of segments may include a first segment, which includes a first coupling portion and a second coupling portion, and a second segment, which is coupled to the first segment and includes a third coupling portion and a fourth coupling portion, which respectively face the first coupling portion and the second coupling portion. The enclosure gasket may include a first enclosure gasket, disposed on the first coupling portion or the third coupling portion, and a second enclosure gasket, disposed on the second coupling portion or the fourth coupling portion. 
     For example, the first segment may have an “L”-shaped external appearance, and the second segment may have a “¬”-shaped external appearance. 
     For example, the plurality of segments may include a first segment, which includes a first coupling portion and a second coupling portion, a second segment, which is coupled to the first segment and includes a third coupling portion facing the second coupling portion and a fourth coupling portion formed opposite the third coupling portion, a third segment, which is coupled to the second segment and includes a fifth coupling portion facing the fourth coupling portion and a sixth coupling portion formed opposite the fifth coupling portion, and a fourth segment, which is coupled to the first segment and the third segment and includes a seventh coupling portion facing the sixth coupling portion and an eighth coupling portion facing the first coupling portion. The enclosure gasket may include a first enclosure gasket disposed on the first coupling portion or the eighth coupling portion, a second enclosure gasket disposed on the second coupling portion or the third coupling portion, a third enclosure gasket disposed on the fourth coupling portion or the fifth coupling portion, and a fourth enclosure gasket disposed on the sixth coupling portion or the seventh coupling portion. 
     For example, at least one of the first to fourth enclosure gaskets may include a body embodied in a coupling portion of a corresponding segment, among the first to fourth segments, and a coupling protrusion protruding from the body toward a coupling portion facing the coupling portion of the corresponding segment. 
     For example, the enclosure gasket may be disposed so as to extend in the first direction, and may have a length longer than the length of the enclosure in the first direction. 
     For example, the protruding portion may be disposed on the enclosure gasket, and the depressed portion may be disposed in the plate gasket. 
     For example, the protruding portion may be disposed on the plate gasket, and the depressed portion may be disposed in the enclosure gasket. 
     For example, the length that the protruding portion protrudes in the first direction may be less than the depth to which the depressed portion is depressed in the first direction. 
     For example, when the protruding portion is inserted into the depressed portion, the protruding portion and the depressed portion may be elastically coupled to each other such that the protruding portion expands in a second direction, which intersects the first direction, and contracts in the first direction and such that the depressed portion expands in the second direction to the same extent as the protruding portion. 
     For example, the enclosure gasket may include a fixing protrusion protruding in a second direction, which intersects the first direction. 
     For example, the distance that the fixing protrusion is spaced apart from the rear end of the protruding portion in the first direction may be o or more. 
     For example, the height that the fixing protrusion protrudes in the second direction may be proportional to the thickness of the enclosure gasket in the second direction. 
     For example, each of the protruding portion and the depressed portion may have an inclined cross-sectional shape. 
     For example, the width of the front end of the protruding portion in a second direction, which intersects the first direction, may be smaller than the width of an opening of the depressed portion in the second direction. 
     For example, the plate gasket and the enclosure gasket may have the same elasticity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIG.  1    is a coupled perspective view of a fuel cell according to an embodiment; 
         FIG.  2    is an exploded perspective view of the fuel cell shown in  FIG.  1   ; 
         FIG.  3    is a cross-sectional view taken along line A-A′ in the fuel cell shown in  FIG.  1   ; 
         FIG.  4    is a cross-sectional view of the fuel cell shown in  FIG.  1   ; 
         FIG.  5    shows the cross-sectional shape of an embodiment of an enclosure included in the fuel cell; 
         FIG.  6    shows the cross-sectional shape of another embodiment of an enclosure included in the fuel cell; 
         FIG.  7    shows the cross-sectional shape of still another embodiment of an enclosure included in the fuel cell; 
         FIG.  8 A  is an enlarged view of portion ‘A’ in  FIG.  5   ; 
         FIG.  8 B  is a cross-sectional view showing the coupled state of the neighboring segments shown in  FIG.  8 A ; 
         FIG.  9 A  is an enlarged view of portion ‘B’ in  FIG.  6  or  7   ; 
         FIG.  9 B  is a cross-sectional view showing the coupled state of the neighboring segments shown in  FIG.  9 A ; 
         FIG.  10 A  is an exploded perspective view of a portion of a fuel cell according to an embodiment; 
         FIGS.  10 B and  10 C  are, respectively, an exploded cross-sectional view and a coupled cross-sectional view of the fuel cell shown in  FIG.  10 A , taken along line I-I′; 
         FIG.  11 A  is an exploded perspective view of a portion of a fuel cell according to another embodiment; and 
         FIGS.  11 B and  11 C  are, respectively, an exploded cross-sectional view and a coupled cross-sectional view of the fuel cell shown in  FIG.  11 A , taken along line II-II′. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which various embodiments are shown. The examples, however, may be embodied in many different forms, and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will more fully convey the scope of the disclosure to those skilled in the art. 
     It will be understood that when an element is referred to as being “on” or “under” another element, it may be directly on/under the element, or one or more intervening elements may also be present. 
     When an element is referred to as being “on” or “under”, “under the element” as well as “on the element” may be included based on the element. 
     In addition, relational terms, such as “first”, “second”, “on/upper part/above”, and “under/lower part/below”, are used only to distinguish between one subject or element and another subject or element, without necessarily requiring or involving any physical or logical relationship or sequence between the subjects or elements. 
     Hereinafter, a fuel cell  100  according to an embodiment will be described with reference to the accompanying drawings. The fuel cell  100  will be described using the Cartesian coordinate system (x-axis, y-axis, z-axis) for convenience of description, but may also be described using other coordinate systems. In the Cartesian coordinate system, the x-axis, the y-axis, and the z-axis are perpendicular to each other, but the embodiments are not limited thereto. That is, the x-axis, the y-axis, and the z-axis may intersect each other obliquely. 
     Hereinafter, the +x-axis direction and the −x-axis direction will be referred to as a “first direction”, the +y-axis direction and the −y-axis direction will be referred to as a “second direction”, and the +z-axis direction and the −z-axis direction will be referred to as a “third direction”. 
       FIG.  1    is a coupled perspective view of a fuel cell  100  according to an embodiment,  FIG.  2    is an exploded perspective view of the fuel cell  100  shown in  FIG.  1   ,  FIG.  3    is a cross-sectional view taken along line A-A′ in the fuel cell  100  shown in  FIG.  1   , and  FIG.  4    is a cross-sectional view of the fuel cell  100  shown in  FIG.  1   . 
     For convenience of description, illustration of the cell stack  122  shown in  FIG.  4    is omitted from  FIG.  2   , and illustration of the plurality of manifolds (or communication portions) M shown in  FIG.  1    is omitted from  FIGS.  2  and  3   . Also, illustration of an enclosure  300 A is omitted from  FIG.  4   . 
     A fuel cell  100  may be, for example, a polymer electrolyte membrane fuel cell (or a proton exchange membrane fuel cell) (PEMFC), which has been studied most extensively as a power source for driving vehicles. However, the embodiments are not limited to any specific type of fuel cell. 
     The fuel cell  100  may include first and second end plates (pressing plates or compression plates)  112 A and  112 B, outer gaskets (hereinafter referred to as “plate gaskets”)  410  and  412 , a cell stack  122 , and an enclosure  300 A. Although not shown, the fuel cell  100  may further include first and second end cell heaters and current collectors. 
     Referring to  FIG.  4   , the cell stack  122  may include a plurality of unit cells  122 - 1  to  122 -N, which are stacked in the first direction. Here, “N” is a positive integer of  1  or greater, and may range from several tens to several hundreds. However, the embodiments are not limited to any specific value of “N”. Each unit cell  122 - n  may generate, for example, a predetermined magnitude of electrical energy. Here, 1≤n≤N. “N” may be determined depending on the intensity of the power to be supplied from the fuel cell  100  to a load. Here, the term “load” refers to a part of a vehicle that requires power when the fuel cell  100  is used in a vehicle. 
     Each unit cell  122 - n  may include a membrane electrode assembly (MEA)  210 , gas diffusion layers (GDLs)  222  and  224 , first to third inner gaskets  232 ,  234 , and  236 , and first and second separators (or bipolar plates)  242  and  244 . 
     The membrane electrode assembly  210  has a structure in which catalyst electrode layers, in which electrochemical reaction occurs, are attached to both sides of an electrolyte membrane through which hydrogen ions move. Specifically, the membrane electrode assembly  210  may include a polymer electrolyte membrane (or a proton exchange membrane)  212 , a fuel electrode (a hydrogen electrode or an anode)  214 , and an air electrode (an oxygen electrode or a cathode)  216 . 
     The polymer electrolyte membrane  212  is disposed between the fuel electrode  214  and the air electrode  216 . 
     Hydrogen, which is the fuel in the fuel cell  100 , may be supplied to the fuel electrode  214  through the first separator  242 , and air containing oxygen as an oxidizer may be supplied to the air electrode  216  through the second separator  244 . 
     The hydrogen supplied to the fuel electrode  214  is decomposed into hydrogen ions (protons) (H+) and electrons (e−) by the catalyst. Only the hydrogen ions may be selectively transferred to the air electrode  216  through the polymer electrolyte membrane  212 , and at the same time, the electrons may be transferred to the air electrode  216  through the first and second separators  242  and  244 , which are conductors. In order to realize the above operation, a catalyst layer may be applied to each of the fuel electrode  214  and the air electrode  216 . The movement of the electrons described above causes the electrons to flow through an external wire, thus generating current. That is, the fuel cell  100  may generate power due to the electrochemical reaction between hydrogen, which is fuel, and oxygen contained in the air. 
     In the air electrode  216 , the hydrogen ions supplied through the polymer electrolyte membrane  212  and the electrons transferred through the first and second separators  242  and  244  meet oxygen in the air supplied to the air electrode  216 , thus causing a reaction that generates water (“condensate water” or “product water”). 
     In some cases, the fuel electrode  214  may be referred to as an anode, and the air electrode  216  may be referred to as a cathode. Alternatively, the fuel electrode  214  may be referred to as a cathode, and the air electrode  216  may be referred to as an anode. 
     The gas diffusion layers  222  and  224  serve to uniformly distribute hydrogen and oxygen, which are reaction gases, and to transfer the generated electrical energy. To this end, the gas diffusion layers  222  and  224  may be disposed on respective sides of the membrane electrode assembly  210 . That is, the first gas diffusion layer  222  may be disposed on the left side of the fuel electrode  214 , and the second gas diffusion layer  224  may be disposed on the right side of the air electrode  216 . 
     The first gas diffusion layer  222  may serve to diffuse and uniformly distribute hydrogen supplied as a reactant gas through the first separator  242 , and may be electrically conductive. The second gas diffusion layer  224  may serve to diffuse and uniformly distribute air supplied as a reactant gas through the second separator  244 , and may be electrically conductive. 
     The first, second, and third inner gaskets  232 ,  234 , and  236  may serve to maintain airtightness and clamping pressure of the cell stack at an appropriate level with respect to the reactant gases and the coolant, to disperse the stress when the first and second separators  242  and  244  are stacked, and to independently seal the flow paths. As such, since airtightness and watertightness are maintained by the first, second, and third inner gaskets  232 ,  234 , and  236 , the flatness of the surfaces that are adjacent to the cell stack  122 , which generates power, may be secured, and thus surface pressure may be distributed uniformly over the reaction surface of the cell stack  122 . 
     The first and second separators  242  and  244  may serve to move the reactant gases and the cooling medium and to separate each of the unit cells from the other unit cells. In addition, the first and second separators  242  and  244  may serve to structurally support the membrane electrode assembly  210  and the gas diffusion layers  222  and  224  and to collect the generated current and transfer the collected current to the current collectors. 
     The first and second separators  242  and  244  may be respectively disposed outside the first and second gas diffusion layers  222  and  224 . That is, the first separator  242  may be disposed on the left side of the first gas diffusion layer  222 , and the second separator  244  may be disposed on the right side of the second gas diffusion layer  224 . 
     The first separator  242  serves to supply hydrogen as a reactant gas to the fuel electrode  214  through the first gas diffusion layer  222 . The second separator  244  serves to supply air as a reactant gas to the air electrode  216  through the second gas diffusion layer  224 . In addition, each of the first and second separators  242  and  244  may form a channel through which a cooling medium (e.g. coolant) flows. Further, the separators  242  and  244  may be formed of a graphite-based material, a composite graphite-based material, or a metal-based material. However, the embodiments are not limited to any specific material of the separators  242  and  244 . 
     The first and second end plates  112 A and  112 B shown in  FIGS.  1  to  4    may be disposed at respective ends of the cell stack  122 , and may support and fix the cell stack  122  in which the multiple unit cells are stacked. That is, the first end plate  112 A may be disposed at one end of the cell stack  122 , and the second end plate  110 B may be disposed at the opposite end of the cell stack  122 . 
     Further, each of the first and second end plates  112 A and  112 B may be formed by combining multiple plates. 
     Further, at least one of the first end plate  112 A or the second end plate  112 B may include a plurality of manifolds M. Further, each of the first and second separators  242  and  244  may include manifolds that are formed in the same shape at the same positions as the manifolds M formed in at least one of the first end plate  112 A or the second end plate  112 B. The manifolds M may include inlet manifolds MI 1 , MI 2 , and MI 3  and outlet manifolds MO 1 , MO 2 , and MO 3 . Hydrogen and oxygen, which are reactant gases necessary in the membrane electrode assembly  210 , may be introduced into the cell stack  122  from outside through the inlet manifolds MI 1  and MI 2 . Gas or liquid, in which the reactant gases humidified and supplied to the cell and the condensate water generated in the cell are combined, may be discharged to the outside of the fuel cell  100  through the outlet manifolds MO 1  and MO 2 . The cooling medium may flow from the outside into the cell stack  122  through the inlet manifold MI 3 , and may flow to the outside through the outlet manifold MO 3 . As described above, the manifolds M (MI 1  to MI 3  and MO 1  to MO 3 ) allow the fluid to flow into and out of the membrane electrode assembly  210 . 
     For example, as shown in  FIG.  1   , some (e.g. MI 1 , MI 2 , MO 1 , and MO 2 ) of the manifolds M (MI 1  to MI 3  and MO 1  to MO 3 ) may be formed in the second end plate  112 B (or the first end plate  112 A), and the remaining ones MI 3  and MO 3  of the manifolds M (MI 1  to MI 3  and MO 1  to MO 3 ) may be formed in the first end plate  112 A (or the second end plate  112 B). Alternatively, unlike what is illustrated in  FIG.  1   , the manifolds M (MI 1  to MI 3  and MO 1  to MO 3 ) may be formed in the first end plate  112 A or the second end plate  112 B. 
     The enclosure  300 A may be coupled to at least one of the first end plate  112 A or the second end plate  112 B to surround the side portion of the cell stack  122 . 
     As shown in  FIGS.  1  to  3   , the enclosure  300 A may be disposed between the first end plate  112 A and the second end plate  112 B, and may be coupled to the first end plate  112 A and the second end plate  112 B to surround the side portion of the cell stack  122 , which is disposed between the first end plate  112 A and the second end plate  112 B. 
     Alternatively, unlike what is illustrated in  FIGS.  1  to  3   , the enclosure  300 A may be coupled to the second end plate  112 B, rather than being coupled to the first end plate  112 A, so as to surround the side portion of the cell stack  122 , or may be coupled to the first end plate  112 A, rather than being coupled to the second end plate  112 B, so as to surround the side portion of the cell stack  122 . 
     The enclosure  300 A may be coupled to at least one of the first end plate  112 A or the second end plate  112 B, and may thus serve as a clamping member for clamping the plurality of unit cells in the first direction. For example, the clamping pressure of the cell stack  122  may be maintained by the first and second end plates  112 A and  112 B, which have rigid body structures, and the enclosure  300 A. 
     The following description may also apply to the case in which only one of the first and second end plates  112 A and  112 B is coupled to the enclosure  300 A and the other one thereof is surrounded by the enclosure  300 A. 
       FIGS.  5  to  7    show various cross-sectional shapes of enclosures  300 A,  300 B, and  300 C included in the fuel cell  100  according to the embodiment.  FIG.  5    shows the cross-sectional shape of the enclosure  300 A shown in  FIGS.  1 ,  2 , and  3   . 
     The enclosure according to the embodiment may be divided into a plurality of segments. 
     According to one embodiment, the enclosure may be divided into two segments. 
     In one example, as shown in  FIGS.  1  to  3  and  5   , the enclosure  300 A may be divided into two segments, namely first and second segments  300 U and  300 L. The first segment  300 U may have a “¬”-shaped external appearance, and the second segment  300 L may have an “L”-shaped external appearance. Alternatively, the first segment  300 U may have an “L”-shaped external appearance, and the second segment  300 L may have a “¬”-shaped external appearance. 
     In another example, as shown in  FIG.  6   , the enclosure  300 B may be divided into two segments, namely first and second segments  310  and  312 . The first segment  310  may have a “[”-shaped external appearance, and the second segment  312  may have a “|”-shaped external appearance. Alternatively, although not shown, the first segment  310  may have a “|”-shaped external appearance, and the second segment  312  may have a “[”-shaped external appearance. Alternatively, the first segment  310  may have a “-”-shaped (or “U”-shaped) external appearance, and the second segment  312  may have a “U”-shaped (or “-”-shaped) external appearance. 
     In the case in which the enclosure is a five-surface enclosure that surrounds five surfaces of the cell stack and exposes one surface thereof, only one of the first and second end plates may be coupled to the enclosure. 
     The embodiment will be described below with reference to the case in which both the first and second end plates are coupled to the enclosure. The following description may also apply to the case in which the enclosure is a five-surface enclosure and only one of the first and second end plates is coupled to the enclosure. 
     As shown in  FIG.  5   , in the case in which the enclosure  300 A is divided into two segments, the first segment  300 U may include first and second coupling portions (or joining portions) C 11  and C 12 , and the second segment  300 L, which is coupled (or joined) to the first segment  300 U, may include a third coupling portion C 13 , which faces the first coupling portion C 11 , and a fourth coupling portion C 14 , which faces the second coupling portion C 12 . 
     As shown in  FIG.  6   , in the case in which the enclosure  300 B is divided into two segments, the first segment  310  may include first and second coupling portions C 21  and C 22 , and the second segment  312 , which is coupled to the first segment  310 , may include a third coupling portion C 23 , which faces the first coupling portion C 21 , and a fourth coupling portion C 24 , which faces the second coupling portion C 22 . 
     In another example, the enclosure may be divided into three or four segments. 
     For example, as shown in  FIG.  7   , the enclosure  300 C may be divided into four segments, namely first to fourth segments  322 ,  324 ,  326 , and  328 . In the case in which the enclosure  300 C is divided into four segments, the first segment  322  may include first and second coupling portions C 31  and C 32 . The second segment  324  may be coupled to the first segment  322 , and may include a third coupling portion C 33 , which faces the second coupling portion C 32 , and a fourth coupling portion C 34 , which is formed opposite the third coupling portion C 33 . The third segment  326  may be coupled to the second segment  324 , and may include a fifth coupling portion C 35 , which faces the fourth coupling portion C 34 , and a sixth coupling portion C 36 , which is formed opposite the fifth coupling portion C 35 . The fourth segment  328  may be coupled to the first and third segments  322  and  326 , and may include a seventh coupling portion C 37 , which faces the sixth coupling portion C 36 , and an eighth coupling portion C 38 , which faces the first coupling portion C 31 . 
     In still another example, the enclosure may have an external appearance that is divided into two segments such that, among the six surfaces of the enclosure, five surfaces thereof correspond to a first segment and the one remaining surface thereof corresponds to a second segment. However, the embodiments are not limited as to the specific shape of segments or the specific number of segments into which the enclosure is divided. 
     Further, when the enclosure is divided into a plurality of segments, the segments may be coupled to each other in various ways. For example, the segments may be coupled to each other using a fastener in the form of a bolt or a rivet. However, the embodiments are not limited as to the specific form in which the segments are coupled to each other. 
     Hereinafter, the fuel cell  100  according to the embodiment will be described as including the enclosure  300 A having the shape shown in  FIGS.  1  to  3  and  5   . However, the following description may also apply to the case in which the fuel cell  100  includes an enclosure having a different shape from the enclosure  300 A, e.g. any one of the enclosures  300 B and  300 C having the shapes shown in  FIGS.  6  and  7   . 
     The plate gaskets may be disposed on at least one of the first end plate  112 A or the second end plate  112 B. For example, as shown in  FIGS.  2  to  4   , the fuel cell  100  may include first and second plate gaskets  410  and  420 , which are respectively disposed on the first and second end plates  112 A and  112 B. 
     The first and second plate gaskets  410  and  420  may be respectively embedded in grooves EH 1  and EH 2  that are respectively formed in the inner surfaces  112 AI and  112 BI of the first and second end plates  112 A and  112 B. The following description of the plate gaskets  410  and  420  may also apply to the case in which the fuel cell  100  includes only one of the plate gaskets  410  and  420 . 
     The first plate gasket  410  may be disposed between the inner surface  112 AI of the first end plate  112 A and the enclosure  300 A, and the second plate gasket  420  may be disposed between the inner surface  112 BI of the second end plate  112 B and the enclosure  300 A. 
     In addition, enclosure gaskets may be disposed between the segments. 
     According to one embodiment, when the enclosure  300 A is divided into two segments  300 U and  300 L, as shown in  FIGS.  1  to  3  and  5   , the fuel cell  100  may include first and second enclosure gaskets  510  and  512 . The first enclosure gasket may be disposed on the first or third coupling portion C 11  or C 13 . For example, as shown in  FIG.  5   , the first enclosure gasket  510  may be disposed on the third coupling portion C 13 . The second enclosure gasket may be disposed on the second or fourth coupling portion C 12  or C 14 . For example, as shown in  FIG.  5   , the second enclosure gasket  512  may be disposed on the fourth coupling portion C 14 . 
     According to another embodiment, when the enclosure  300 B is divided into two segments  310  and  312 , as shown in  FIG.  6   , the fuel cell  100  may include first and second enclosure gaskets  520  and  522 . The first enclosure gasket may be disposed on the first or third coupling portion C 21  or C 23 . For example, as shown in  FIG.  6   , the first enclosure gasket  520  may be disposed on the third coupling portion C 23 . The second enclosure gasket may be disposed on the second or fourth coupling portion C 22  or C 24 . For example, as shown in  FIG.  6   , the second enclosure gasket  522  may be disposed on the second coupling portion C 22 . 
     According to still another embodiment, when the enclosure  300 C is divided into four segments  322  to  328 , as shown in  FIG.  7   , the fuel cell  100  may include first to fourth enclosure gaskets  530 ,  532 ,  534 , and  536 . The first enclosure gasket may be disposed on the first or eighth coupling portion C 31  or C 38 . For example, as shown in  FIG.  7   , the first enclosure gasket  530  may be disposed on the first coupling portion C 31 . The second enclosure gasket may be disposed on the second or third coupling portion C 32  or C 33 . For example, as shown in  FIG.  7   , the second enclosure gasket  532  may be disposed on the third coupling portion C 33 . The third enclosure gasket may be disposed on the fourth or fifth coupling portion C 34  or C 35 . For example, as shown in  FIG.  7   , the third enclosure gasket  534  may be disposed on the fifth coupling portion C 35 . The fourth enclosure gasket may be disposed on the sixth or seventh coupling portion C 36  or C 37 . For example, as shown in  FIG.  7   , the fourth enclosure gasket  536  may be disposed on the seventh coupling portion C 37 . 
     As shown in  FIGS.  5  to  7   , the enclosure gasket provided between neighboring segments is disposed only on either one of two coupling portions facing each other. The reason for this is that, if the enclosure gasket were disposed on both the coupling portions facing each other, the coupling force between neighboring segments would decrease. For example, unlike what is illustrated in  FIG.  7   , if the enclosure gasket  532  provided between the neighboring first and second segments  322  and  324  were disposed on both the second and third coupling portions C 32  and C 33 , which face each other, the coupling force between the neighboring first and second segments  322  and  324  would decrease. 
       FIG.  8 A  is an enlarged and exploded cross-sectional view of portion ‘A’ in  FIG.  5   , and  FIG.  8 B  is a cross-sectional view showing the coupled state of the neighboring segments  300 U and  300 L shown in  FIG.  8 A . 
       FIG.  9 A  is an enlarged and exploded cross-sectional view of portion ‘B’ in  FIG.  6  or  7   , and  FIG.  9 B  is a cross-sectional view showing the coupled state of the neighboring segments shown in  FIG.  9 A . 
     At least one of the first to fourth enclosure gaskets may include a body, which is embedded in the coupling portion of a corresponding segment, among the first to fourth segments, and a coupling protrusion, which protrudes from the body toward a coupling portion, which the coupling portion of the corresponding segment faces. 
     For example, referring to  FIG.  8 A , the first enclosure gasket  510  may include a body B 1 , which is embedded in the third coupling portion C 13  of the second segment  300 L, among the first and second segments  300 U and  300 L, and a coupling protrusion P 1 , which protrudes from the body B 1  toward the first coupling portion C 11 , which the third coupling portion C 13  of the second segment  300 L faces. In this case, the coupling protrusion may have a cross-sectional shape that protrudes further than the upper surface of the coupling portion of the corresponding segment toward a coupling portion, which the coupling portion of the corresponding segment faces. For example, referring to  FIG.  8 A , the coupling protrusion P 1  may have a cross-sectional shape that protrudes further than the top surface  300 LS of the third coupling portion C 13  of the second segment  300 L toward the first coupling portion C 11 , which the third coupling portion C 13  of the second segment  300 L faces. Due to this structure, when the first and second segments  300 U and  300 L, which are adjacent to each other, are coupled to each other, as shown in  FIG.  8 B , the coupling protrusion P 1  is pressed by the first coupling portion C 11  of the first segment  300 U, and thus completely fills a receiving groove  300 H in which the body B 1  is received, thereby increasing the coupling force between the neighboring first and second segments  300 U and  300 L. 
     Also, referring to  FIGS.  6  and  9 A , the first enclosure gasket  522  may include a body B 2 , which is embedded in the second coupling portion C 22  of the first segment  310 , among the first and second segments  310  and  312 , and a coupling protrusion P 2 , which protrudes from the body B 2  toward the fourth coupling portion C 24 , which the second coupling portion C 22  of the first segment  310  faces. In this case, the coupling protrusion may have a cross-sectional shape that protrudes further than the top surface of the coupling portion of the corresponding segment toward a coupling portion, which the coupling portion of the corresponding segment faces. For example, referring to  FIG.  9 A , the coupling protrusion P 2  may have a cross-sectional shape that protrudes further than the upper surface  310 S of the second coupling portion C 22  of the first segment  310  toward the fourth coupling portion C 24 , which the second coupling portion C 22  of the first segment  310  faces. Due to this structure, when the first and second segments  310  and  312 , which are adjacent to each other, are coupled to each other, as shown in  FIG.  9 B , the coupling protrusion P 2  is pressed by the fourth coupling portion C 24  of the second segment  312 , and thus completely fills a receiving groove  310 H in which the body B 2  is received, thereby increasing the coupling force between the neighboring first and second segments  310  and  312 . 
     Also, referring to  FIGS.  7  and  9 A , the fourth enclosure gasket  536  may include a body B 2 , which is embedded in the seventh coupling portion C 37  of the fourth segment  328 , among the first to fourth segments  322 ,  324 ,  326 , and  328 , and a coupling protrusion P 2 , which protrudes from the body B 2  toward the sixth coupling portion C 36 , which the seventh coupling portion C 37  of the fourth segment  328  faces. In this case, the coupling protrusion may have a cross-sectional shape that protrudes further than the top surface of the coupling portion of the corresponding segment toward a coupling portion, which the coupling portion of the corresponding segment faces. For example, referring to  FIG.  9 A , the coupling protrusion P 2  may have a cross-sectional shape that protrudes further than the top surface  310 S of the seventh coupling portion C 37  of the fourth segment  328  toward the sixth coupling portion C 36 , which the seventh coupling portion C 37  of the fourth segment  328  faces. Due to this structure, when the third and fourth segments  326  and  328 , which are adjacent to each other, are coupled to each other, as shown in  FIG.  9 B , the coupling protrusion P 2  is pressed by the sixth coupling portion C 36  of the third segment  326 , and thus completely fills a receiving groove  310 H in which the body B 2  is received, thereby increasing the coupling force between the neighboring third and fourth segments  326  and  328 . 
     Also, referring to  FIG.  3   , the enclosure gasket (e.g.  510 ) has a length X 2  extending in the first direction, and the enclosure  300 A has a length X 1  extending in the first direction. In this case, X 2  may be longer than X 1 . The reason why the length X 2  of the enclosure gasket (e.g.  510 ) is longer than the length X 1  of the enclosure  300 A is to couple (or join) the enclosure gasket (e.g.  510 ) to the plate gaskets  410  and  420 , which will be described later. 
     One of the plate gasket and the enclosure gasket may include a protruding portion that protrudes in the first direction, and the other one thereof may include a depressed portion that is depressed in the first direction to receive the protruding portion fitted thereinto. In this way, the plate gasket and the enclosure gasket may be coupled to each other by coupling (or female-male engagement) between the protruding portion and the depressed portion. 
     Hereinafter, various embodiments in which the protruding portion and the depressed portion are coupled to each other will be described with reference to  FIGS.  10  and  11   . 
       FIG.  10 A  is an exploded perspective view of a portion of a fuel cell according to an embodiment, and  FIGS.  10 B and  10 C  are, respectively, an exploded cross-sectional view and a coupled cross-sectional view of the fuel cell shown in  FIG.  10 A , taken along line I-I′. 
     According to an embodiment, the fuel cell shown in  FIGS.  10 A to  10 C  may include an end plate  600 , a plate gasket  700 A, an enclosure gasket  800 A, and an enclosure  900 . Here, the end plate  600 , the plate gasket  700 A, the enclosure gasket  800 A, and the enclosure  900  may respectively correspond to the first end plates  112 A and  112 B, the plate gaskets  410  and  420 , the enclosure gaskets  510 ,  512 ,  520 ,  522 ,  530 ,  532 ,  534 , and  536 , and the enclosures  300 A,  300 B, and  300 C described above. 
     The plate gasket  700 A is embedded in a groove portion EH 1  in the end plate  600 , and protrudes a predetermined thickness above the inner surface  600 S of the end plate  600  toward the enclosure  900  before the enclosure  900  and the end plate  600  are coupled to each other, as shown in  FIG.  10 B . Thereafter, when the enclosure  900  and the end plate  600  are coupled to each other, the portion of the plate gasket  700 A that protrudes above the inner surface  600 S is tightly fitted into the groove portion EH 1 , as shown in  FIG.  10 C , and accordingly, the upper surface  700 S of the plate gasket  700 A becomes coplanar with the inner surface  600 S. 
     According to an embodiment, the enclosure gasket  800 A may include a protruding portion  810 , which protrudes in the first direction, and the plate gasket  700 A may include a depressed portion  710 , which is depressed in the first direction to receive the protruding portion  810  fitted thereinto. In this way, the plate gasket  700 A and the enclosure gasket  800 A may be coupled to each other by female-male engagement between the protruding portion  810  and the depressed portion  710 . 
     In the case shown in  FIG.  10 B , the depth of the depressed portion  710  is greater than D 1 . However, as shown in  FIG.  10 C , when the plate gasket  700 A is completely fitted into the groove portion EH 1 , the depth D 1  corresponds to the actual length of the depressed portion  710 . 
     If the length L 1  that the protruding portion  810  protrudes in the first direction is not less than the depth D 1  to which the depressed portion  710  is depressed in the first direction, when the enclosure  900  and the end plate  600  are coupled to each other, the protruding portion  810  is not capable of being completely inserted into the depressed portion  710 , thus leading to erroneous assembly, or the protruding portion  8 w may become separated from the depressed portion  710 , thus leading to unreliable female-male engagement. In order to prevent this, according to the embodiment, the length L 1  of the protruding portion  810  may be less than the depth D 1  of the depressed portion  710 . 
     The width W 4  of the front end EF 1  of the protruding portion  810  in the second direction may be smaller than the width W 3  of the rear end EB 1  of the protruding portion  810  in the second direction, and the width W 1  of the opening OP 1  of the depressed portion  710  may be larger than the width W 2  of the bottom BS 1  of the depressed portion  710 . 
     Also, the width W 4  of the front end EF 1  of the protruding portion  810  in the second direction may be smaller than the width W 1  of the opening OP 1  of the depressed portion  710  in the second direction. 
     In this case, each of the protruding portion  810  and the depressed portion  710  may have an inclined cross-sectional shape. Accordingly, the protruding portion  810  may be easily inserted into the depressed portion  710 . 
     Referring to  FIG.  10 C , when the protruding portion  810  is inserted into the depressed portion  710 , the protruding portion  810  and the depressed portion  710  may be elastically coupled to each other such that the protruding portion  810  expands in the second direction and contracts in the first direction and such that the depressed portion  710  expands in the second direction to the same extent as the protruding portion  810 . That is, the width of the rear end EB 1  of the protruding portion  810  may increase in the second direction from W 3  to W 31 , the length that the protruding portion  810  protrudes may decrease from L 1  to L 11 , and the width of the opening OP 1  of the depressed portion  710  may increase in the second direction from W 1  by the width by which the protruding portion  810  expands. 
     In order to allow the depressed portion  710  to expand to the same extent as the protruding portion  810 , the plate gasket  700 A and the enclosure gasket  800 A may have the same elasticity. If the plate gasket  700 A and the enclosure gasket  800 A do not have the same elasticity, the expansion rates thereof differ from each other, and accordingly, the depressed portion  710  is not capable of expanding to the same extent as the protruding portion  810 . 
     In addition, the enclosure gasket  800 A may include a fixing protrusion  812 , which protrudes in the second direction, which intersects the first direction. 
     The distance L 2  that the fixing protrusion  812  is spaced apart from the rear end EB 1  of the protruding portion  810  in the first direction may be zero (0) or more. If the distance L 2  is zero, burrs may be generated during the manufacturing process. Therefore, when the distance L 2  is greater than zero, the process of manufacturing the enclosure gasket  800 A may be more reliably performed than when the distance L 2  is zero. Also, if the portion indicated by “L 2 ” is inserted into the depressed portion  710  together with the protruding portion  810 , watertightness may be degraded. Therefore, the enclosure gasket  800 A may be formed such that only the protruding portion  810  is inserted into the depressed portion  710 . 
     The height H that the fixing protrusion  812  protrudes in the second direction may be proportional to the thickness T of the enclosure gasket  800 A in the second direction. 
       FIG.  11 A  is an exploded perspective view of a portion of a fuel cell according to another embodiment, and  FIGS.  11 B and  11 C  are, respectively, an exploded cross-sectional view and a coupled cross-sectional view of the fuel cell shown in  FIG.  11 A , taken along line II-II′. 
     According to another embodiment, the fuel cell shown in  FIGS.  11 A to  11 C  may include an end plate  600 , a plate gasket  700 B, an enclosure gasket  800 B, and an enclosure  900 . Here, the end plate  600 , the plate gasket  700 B, the enclosure gasket  800 B, and the enclosure  900  may respectively correspond to the first end plates  112 A and  112 B, the plate gaskets  410  and  420 , the enclosure gaskets  510 ,  512 ,  520 ,  522 ,  530 ,  532 ,  534 , and  536 , and the enclosures  300 A,  300 B, and  300 C described above. 
     The plate gasket  700 B is embedded in a groove portion EH 1  in the end plate  600 , and protrudes a predetermined thickness above the inner surface  600 S of the end plate  600  toward the enclosure  900  before the enclosure  900  and the end plate  600  are coupled to each other, as shown in  FIG.  11 B . Thereafter, when the enclosure  900  and the end plate  600  are coupled to each other, the portion of the plate gasket  700 B that protrudes above the inner surface  600 S is tightly fitted into the groove portion EH 1 , as shown in  FIG.  11 C , and accordingly, the upper surface  700 S of the plate gasket  700 B becomes coplanar with the inner surface  600 S. 
     According to this embodiment, the plate gasket  700 B may include a protruding portion  720 , which protrudes in the first direction, and the enclosure gasket  800 B may include a depressed portion  820 , which is depressed in the first direction to receive the protruding portion  720  fitted thereinto. In this way, the plate gasket  700 B and the enclosure gasket  800 B may be coupled to each other by female-male engagement between the protruding portion  720  and the depressed portion  820 . 
     In the case shown in  FIG.  11 B , the length that the protruding portion  720  protrudes is greater than L 3 . However, as shown in  FIG.  11 C , when the plate gasket  700 B is completely fitted into the groove portion EH 1 , the protruding length L 3  corresponds to the actual length of the protruding portion  720 . 
     If the length L 3  that the protruding portion  720  protrudes in the first direction is not less than the depth D 2  to which the depressed portion  820  is depressed in the first direction, when the enclosure  900  and the end plate  600  are coupled to each other, the protruding portion  720  is not capable of being completely inserted into the depressed portion  820 , thus leading to erroneous assembly, or the protruding portion  720  may become separated from the depressed portion  820 , thus leading to unreliable female-male engagement. In order to prevent this, according to the embodiment, the length L 3  of the protruding portion  720  may be less than the depth D 2  of the depressed portion  820 . 
     The width W 6  of the front end EF 2  of the protruding portion  720  in the second direction may be smaller than the width W 5  of the rear end EB 2  of the protruding portion  720  in the second direction, and the width W 7  of the opening OP 2  of the depressed portion  820  may be larger than the width W 8  of the bottom BS 2  of the depressed portion  820 . 
     Also, the width W 6  of the front end EF 2  of the protruding portion  720  in the second direction may be smaller than the width W 7  of the opening OP 2  of the depressed portion  820  in the second direction. 
     In this case, each of the protruding portion  720  and the depressed portion  820  may have an inclined cross-sectional shape. Accordingly, the protruding portion  720  may be easily inserted into the depressed portion  820 . 
     Referring to  FIG.  11 C , when the protruding portion  720  is inserted into the depressed portion  820 , the protruding portion  720  and the depressed portion  820  may be elastically coupled to each other such that the protruding portion  720  expands in the second direction and contracts in the first direction and such that the depressed portion  820  expands in the second direction to the same extent as the protruding portion  720 . That is, the width of the rear end EB 2  of the protruding portion  720  may increase in the second direction from W 5  to W 51 , the length that the protruding portion  720  protrudes may decrease from L 3  to L 31 , and the width of the opening OP 2  of the depressed portion  820  may increase in the second direction from W 7  by the width by which the protruding portion  720  expands. 
     In order to allow the depressed portion  820  to expand to the same extent as the protruding portion  720 , the plate gasket  700 B and the enclosure gasket  800 B may have the same elasticity. 
     If the plate gasket  700 B and the enclosure gasket  800 B do not have the same elasticity, the expansion rates thereof differ from each other, and accordingly, the depressed portion  820  is not capable of expanding to the same extent as the protruding portion  720 . 
     The plate gaskets  700 A and  700 B and the enclosure gaskets  800 A and  800 B described above may be made of the same material, for example, rubber or plastic. However, the embodiments are not limited to any specific material of the plate gaskets  700 A and  700 B or the enclosure gaskets  800 A and  800 B. 
     Hereinafter, a fuel cell according to a comparative example and the fuel cell according to the embodiment will be described. 
     In the case of a fuel cell according to the comparative example, a plate gasket and an enclosure gasket are in surface contact with each other, rather than being coupled to each other in a female-male engagement manner. In this case, a path through which moisture or air can permeate may be formed at a triple point at which an enclosure, the enclosure gasket, which is disposed between divided segments of the enclosure, and the plate gasket meet, thus leading to degradation of watertightness and airtightness. Although the gasket of the end plate and the gasket of the enclosure are provided, a sufficient amount of surface pressure is not formed at the triple point at which the aforementioned three components meet due to the engagement structure thereof, thus failing to prevent permeation of moisture. 
     In contrast, in the case of the embodiment, the enclosure gasket  510 ,  512 ,  520 ,  522 ,  530 ,  532 ,  534 ,  536 ,  800 A, or  800 B and the plate gasket  410 ,  420 ,  700 A, or  700 B are coupled to each other in a female-male engagement manner, rather than being in surface contact with each other. Accordingly, a triple point at which the enclosure  300 A,  300 B,  300 C, or  900 , the enclosure gasket  510 ,  512 ,  520 ,  522 ,  530 ,  532 ,  534 ,  536 ,  800 A, or  800 B, which is disposed between the divided segments of the enclosure  300 A,  300 B,  300 C, or  900 , and the plate gasket  410 ,  420 ,  700 A, or  700 B meet is more reliably sealed, thereby blocking a path through which moisture or air can permeate, thus improving performance with regard to watertightness and airtightness. As a result, it is possible to meet a waterproof criterion for a vehicle that uses a fuel cell. 
     In addition, in the fuel cell according to the embodiment, when the end plate  112 A,  112 B, or  600  and the enclosure  300 A,  300 B,  300 C, or  900  are coupled to each other, a sufficient amount of surface pressure may be formed at a point at which the plate gasket  410 ,  420 ,  700 A, or  700 B and the enclosure gasket  510 ,  512 ,  520 ,  522 ,  530 ,  532 ,  534 ,  536 ,  800 A, or  800 B meet. The reason for this is that the force by which the segment adjacent thereto presses the plate gasket, the force by which the plate adjacent thereto presses the enclosure gasket, and the force by which the protruding portion  810  (or  720 ) presses the depressed portion  710  (or  820 ) increase. To this end, as shown in  FIGS.  10 B and  11 B , the plate gasket  700 A or  700 B may protrude a predetermined thickness above the inner surface  600 S of the end plate  600  toward the enclosure  900  before the enclosure  900  and the end plate  600  are coupled to each other. 
     Further, as shown in  FIG.  10 C , the width of the protruding portion  810  in the second direction increases from W 3  to W 31 , and as shown in  FIG.  11 C , the width of the protruding portion  720  in the second direction increases from W 5  to W 51 . Accordingly, the clamping pressure may increase as indicated by the arrows. 
     The position of the enclosure gasket may not be fixed, but may be misaligned for various reasons. For example, the position of the enclosure gasket may be misaligned by the pressure generated when the segments are coupled to each other or when the enclosure gasket is coupled to the plate gasket. In order to prevent this, the enclosure gasket  800 A includes the fixing protrusion  812 . For example, if the height H of the fixing protrusion  812  satisfies Equation 1 below, the fixing protrusion  812  may perform the function thereof more reliably. However, the embodiments are not limited to any specific value of height H. 
         H&gt;T/ 2   [Equation 1]
 
     Therefore, according to the embodiment, due to the presence of the fixing protrusion  812 , the position of the enclosure gasket  510 ,  512 ,  520 ,  522 ,  530 ,  532 ,  534 ,  536 , or  800 A is fixed without being misaligned even under various situations. Accordingly, when the plate gasket  410 ,  420 , or  700 A and the enclosure gasket  510 ,  512 ,  520 ,  522 ,  530 ,  532 ,  534 ,  536 , or  800 A are coupled to each other, the position of the protruding portion  810  that is inserted into the depressed portion  710  is fixed without being misaligned. Accordingly, the plate gasket  410 ,  420 , or  700 A and the enclosure gasket  510 ,  512 ,  520 ,  522 ,  530 ,  532 ,  534 ,  536 , or  800 A are stably coupled to each other at the triple point, and thus the coupling force therebetween increases. As a result, the fuel cell according to the embodiment has improved performance with regard to watertightness and airtightness. 
     In the process of manufacturing the fuel cell, the first end plate  112 A (or the second end plate  112 B) is placed below stacking equipment. Thereafter, the unit cells are sequentially stacked on the first end plate  112 A (or the second end plate  112 B) in order from the first unit cell  122 - 1  to the last unit cell  122 -N, and then the second end plate  112 B (or the first end plate  112 A) is stacked on the last unit cell  122 -N. Thereafter, the segments and the end plates  112 A and  112 B are coupled to each other by pressing the same using a press. In the case in which the protruding portion  810  and the depressed portion  710  are formed as shown in  FIGS.  10 A to  10 C , it is possible to insert the protruding portion  810  into the depressed portion  710  while visually checking the same during the above process. Accordingly, workability is improved. 
     As is apparent from the above description, according to a fuel cell according to the embodiment, coupling pressure between gaskets increases, thereby improving performance with regard to watertightness and airtightness, thus meeting a waterproof criterion for a vehicle that uses a fuel cell. In addition, workability is improved. 
     However, the effects achievable through the embodiments are not limited to the above-mentioned effects, and other effects not mentioned herein will be clearly understood by those skilled in the art from the above description. 
     The above-described various embodiments may be combined with each other without departing from the scope of the present disclosure unless they are incompatible with each other. 
     In addition, for any element or process that is not described in detail in any of the various embodiments, reference may be made to the description of an element or a process having the same reference numeral in another embodiment, unless otherwise specified. 
     While the present disclosure has been particularly shown and described with reference to exemplary embodiments thereof, these embodiments are only proposed for illustrative purposes, and do not restrict the present disclosure, and it will be apparent to those skilled in the art that various changes in form and detail may be made without departing from the essential characteristics of the embodiments set forth herein. For example, respective configurations set forth in the embodiments may be modified and applied. Further, differences in such modifications and applications should be construed as falling within the scope of the present disclosure as defined by the appended claims.