Patent Publication Number: US-2022216497-A1

Title: End plate, fastening bar, and fuel cell stack including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims under 35 U.S.C. § 119(a) the benefit of priority to Korean Patent Application No. 10-2021-0000929 filed on Jan. 5, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an end plate, a fastening bar, and a fuel cell stack including the same. 
     BACKGROUND 
     As environmental regulations are strengthened in the vehicle industry, interest in new energy sources that do not emit carbon dioxide (CO 2 ) is increasing. A hydrogen fuel cell that is one of the power sources for vehicles obtains electrical energy through an electrochemical reaction between hydrogen and oxygen. The hydrogen fuel cell has been reported as a clean energy source of the future due to the advantage of not emitting pollutants because it emits only reaction heat and pure water during reaction. Automakers around the world are trying to develop such a hydrogen fuel cell. 
     The hydrogen fuel cell has components such as a separator, a bipolar plate, a gasket, and a current collector stacked to constitute a single cell. And multiple cells are fixed to an end plate to constitute a fuel cell stack. 
     The end plate is a major component that supports the multiple cells constituting the stack. The end plate is a planar component that supports both ends of the stack and is generally made of a thick steel material to maintain structural rigidity and uniform surface pressure of the stack. 
     The steel end plate is thick to maintain uniform surface pressure and secure structural rigidity, which makes the product very heavy. In addition, heat loss to the end plate occurs in cells adjacent to the steel end plate during cold start, thereby decreasing the efficiency of the fuel cell. In addition, there is the disadvantage in that the steel plate is coated with Teflon or an insulating plate is additionally mounted thereon to improve the insulating property. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and accordingly it may include information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY 
     In preferred aspect, provided are components of a fuel cell stack that may secure structural stability and improve fuel cell efficiency while achieving the effect of reducing the weight of a fuel cell. 
     In an aspect, provided is an end plate for a fuel cell stack. The end plate includes: a main body part, and a property forming part disposed in the main body part to exert mechanical properties. Preferably, the end plate can maintain the flatness of a fuel cell stack formed by stacking a plurality of fuel cells so that a uniform surface pressure is maintained, 
     The main body part and the property forming part may include a composite material. 
     The property forming part may include continuous fiber thermoplastic (CFT). 
     The main body part may include long fiber thermoplastic (LFT). 
     Each of the continuous fiber thermoplastic and the long fiber thermoplastic may include: an amount of about 40 to 60 wt % of a reinforced fiber and an amount of 40 to 60 wt % of a thermoplastic resin, respectively, based on the total weight of the continuous fiber thermoplastic and the long fiber thermoplastic. 
     The reinforced fiber can be at least one selected from the group consisting of glass fiber, carbon fiber, and aramid fiber, or the thermoplastic resin may include polypropylene (PP) or polyamide (PA). 
     The property forming part may include: a first property part and a second property part formed to be symmetrical with respect to surfaces in contact with each other. 
     Each of the first property part and the second property part may include: a property main body having a weight reduction groove formed on both ends of a terminal hole in a longitudinal direction, a first rib formed on both ends of the property main body in the longitudinal direction to secure mechanical properties, and a second rib formed on both ends of the property main body in a width direction to secure mechanical properties. 
     The property main body of the first property part and the property main body of the second property part may be in contact with each other, the first rib of the first property part and the first rib of the second property part may face each other at an interval, and the second ribs of the first property part and the second property part may be disposed to face each other at an interval and disposed to be vertically symmetrical with respect to surfaces with which the first property part and the second property part are in contact. 
     The first rib may be formed entirely in the width direction of the property main body and the second rib may be formed at a preset length from a center to both sides in the longitudinal direction of the property main body. 
     For the first property part and the second property part, surfaces in contact with each other may be coupled to each other by thermal fusing by resin heat generated in an injection process. 
     The thickness of the end plate for the fuel cell stack may be about 25 mm to 30 mm. 
     A ratio of the thickness of the property forming part to the thickness of the main body part may be about 15% to 25%. 
     In an aspect, provided is a fastening bar for a fuel cell stack includes: a bar main body in contact with an outside of the fuel cell stack, and a coupling part coupled to the end plate by bending one end and the other end of the bar main body in one direction. Preferably, the fastening bar may be fastened to an end plate that maintains the flatness of a fuel cell stack formed by stacking a plurality of fuel cells so that a uniform surface pressure is maintained to fix the fuel cell stack. 
     The bar main body and the coupling part formed integrally may include: a design layer and a property layer connected with the design layer to exert mechanical properties. 
     The design layer and the property layer may include a composite material. 
     The property layer may include continuous fiber thermoplastic (CFT), and the design layer can be made of long fiber thermoplastic (LFT). 
     Each of the continuous fiber thermoplastic and the long fiber thermoplastic may include: an amount of about 20 to 40 wt % of the reinforced fiber and an amount of about 60 to 80 wt % of the thermoplastic resin, respectively, based on the total weight of the continuous fiber thermoplastic and the long fiber thermoplastic. 
     Alternatively, each of the continuous fiber thermoplastic and the long fiber thermoplastic may include: an amount of about 40 to 60 wt % of the reinforced fiber and 40 to 60 wt % of the thermoplastic resin, respectively, based on the total weight of the continuous fiber thermoplastic and the long fiber thermoplastic. 
     The reinforced fiber may include one or more selected from the group consisting of glass fiber, carbon fiber, and aramid fiber, and the thermoplastic resin may include polypropylene (PP) or polyamide (PA). 
     The thicknesses of the bar main body and the coupling part may be about 1 mm to 5 mm. 
     The coupling part may include a through hole through which a fastening means coupled to the end plate passes. 
     A fastening bar for a fuel cell stack includes: a bar main body in contact with an outside of the fuel cell stack, and a coupling part coupled to the end plate by bending one end and the other end of the bar main body in one direction. Preferably, the fastening bar may be fastened to an end plate that maintains the flatness of a fuel cell stack formed by stacking a plurality of fuel cells so that a uniform surface pressure is maintained to fix the fuel cell stack. 
     The bar main body and the coupling part formed integrally may include: a property layer made of a composite material to exert mechanical properties. 
     The property layer may include long fiber thermoplastic (LFT). 
     Each of the long fiber thermoplastic may include an amount of about 20 to 40 wt % of a reinforced fiber and an amount of about 60 to 80 wt % of a thermoplastic resin, based on the total weight of the long fiber thermoplastic; the reinforced fiber may include one or more selected from the group consisting of glass fiber, carbon fiber, and aramid fiber; and the thermoplastic resin may include polypropylene (PP) or polyamide (PA). 
     The long fiber thermoplastic may include: an amount of about 40 to 60 wt % of a reinforced fiber and an amount of about 40 to 60 wt % of a thermoplastic resin, based on the total weight of the long fiber thermoplastic; the reinforced fiber may include one or more selected from the group consisting of glass fiber, carbon fiber, and aramid fiber; and the thermoplastic resin may include polypropylene (PP) or polyamide (PA). 
     The property layer may include a fiber reinforced thermosetting composite material. 
     The fiber reinforced thermosetting composite material may include: an amount of about 20 to 60 wt % of a reinforced fiber and an amount of about 40 to 80 wt % of a thermosetting resin, based on the total weight of the fiber reinforced thermosetting composite material. 
     The reinforced fiber may include one or more selected from the group consisting of glass fiber, carbon fiber, and aramid fiber, and the thermosetting resin can be any one selected from the group consisting of vinyl ester (VE), polyester (UP), epoxy (EPDXY), and polyurethane (PU). 
     In an aspect, provided is a fuel cell stack includes: a plurality of fuel cells, an end plate for the fuel cell stack disposed on both side surfaces of the fuel cell stack to maintain the flatness of the fuel cell stack so that the uniform surface pressure is maintained, and a fastening bar for the fuel cell stack disposed outside the fuel cell stack and having both ends coupled to the end plate for the fuel cell stack. Preferably, the end plate may maintain flatness of the fuel cell stack formed by stacking a plurality of fuel cells so that a uniform surface pressure is maintained. Preferably, the fastening bar may be fastened to the end plate that maintains the flatness of a fuel cell stack formed by stacking a plurality of fuel cells so that a uniform surface pressure is maintained to fix the fuel cell stack. 
     According to various exemplary embodiments of the present invention, as the end plate is made of the composite material other than the steel material, it is possible not only to reduce the weight due to the properties of high specific rigidity and specific strength, but also to improve the efficiency during cold start due to excellent thermal insulation property. 
     According to t various exemplary embodiments of the present invention, for the end plate made of the composite material, a process such as additionally coating the insulating material can be removed due to the insulating property higher than that of the steel material. 
     According to various exemplary embodiments of the present invention, it is possible to use the continuous fiber thermoplastic as the property forming part and to use the long fiber thermoplastic as the main body part surrounding the property forming part, thereby achieving the effect of reducing the weight and at the same time, securing the structural stability and the improvement in the fuel cell efficiency. 
     According to various exemplary embodiments of the present invention, the property forming part made of the continuous fiber thermoplastic has the advantageous effect in terms of securing rigidity because the product is manufactured by the press molding process using the continuous fiber. 
     According to various exemplary embodiments of the present invention, the property forming part made of the continuous fiber thermoplastic can secure various mechanical properties because its vertical symmetrical or asymmetrical structure can be freely designed according to the structural requirement and the height of the core reinforcement part formed along the outer edge of the property main body can be freely changed. In addition, the main body part made of the long fiber thermoplastic can increase the degree of freedom in the product shaping design. 
     According to various exemplary embodiments of the present invention, since the property forming part and the main body part use the same polypropylene or polyamide resin, an interface is bonded using the resin heat in the injection processes and the property forming part and the main body part are coupled by the separate bonding process. 
     The above and other features of the invention are discussed infra. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features of the present invention will now be described in detail with reference to certain exemplary examples thereof illustrated in the accompanying drawings which are given herein below by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  shows an exemplary fuel cell stack according to an exemplary embodiment of the present invention. 
         FIG. 2  shows an exemplary end plate for an exemplary fuel cell stack of  FIG. 1 . 
         FIG. 3  shows an exemplary property forming part of the end plate for the fuel cell stack. 
         FIG. 4  is a cross-sectional diagram taken along line IV-IV of  FIG. 2 . 
         FIG. 5  shows an exemplary embodiment of the end plate for the fuel cell stack of  FIG. 2 . 
         FIG. 6  shows an exemplary property forming part of  FIG. 5 . 
         FIG. 7  is a cross-sectional diagram taken along line VII-VII of  FIG. 5 . 
         FIG. 8  shows an exemplary fastening bar for the fuel cell stack of  FIG. 1 . 
         FIGS. 9A-9F  show exemplary fastening bars for the fuel cell stack of  FIG. 8 . 
         FIG. 10  shows an exemplary embodiment of the fastening bar for the fuel cell stack of  FIG. 8 . 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in section by the particular intended application and use environment. 
     In the figures, reference numbers refer to the same or equivalent sections of the present invention throughout the several figures of the drawing. 
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains can easily carry out the present invention. However, the present invention can be implemented in various different forms and is not limited to the exemplary embodiments described herein. Throughout the specification, similar parts are denoted by the same reference numerals. 
     It is understood that the term “automotive” or “vehicular” or other similar term as used herein is inclusive of motor automotives in general such as passenger automobiles including sports utility automotives (operation SUV), buses, trucks, various commercial automotives, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid automotives, electric automotives, plug-in hybrid electric automotives, hydrogen-powered automotives and other alternative fuel automotives (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid automotive is an automotive that has two or more sources of power, for example both gasoline-powered and electric-powered automotives. 
     Unless otherwise indicated, all numbers, values, and/or expressions referring to quantities of ingredients, reaction conditions, polymer compositions, and formulations used herein are to be understood as modified in all instances by the term “about” as such numbers are inherently approximations that are reflective of, among other things, the various uncertainties of measurement encountered in obtaining such values. 
     Further, unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.” 
     Since an end plate for a fuel cell stack and a fastening bar for the fuel cell stack according to an exemplary embodiment of the present invention can be applied to the fuel cell stack according to the exemplary embodiment of the present invention, hereinafter, the fuel cell stack to which the end plate for the fuel cell stack and the fastening bar for the fuel cell stack are applied will be mainly described. 
     The fuel cell stack according to the exemplary embodiment of the present invention will be described with reference to  FIG. 1 . 
       FIG. 1  shows an exemplary fuel cell stack according to an exemplary embodiment of the present invention. 
     For example, a fuel cell stack  100  according to an exemplary embodiment includes a fuel cell  4 , an end plate  1  for a fuel cell stack (hereinafter referred to as an end plate), and a fastening bar  3  for the fuel cell stack (hereinafter referred to as a fastening bar). 
     The fuel cell  4  uses hydrogen as a fuel to produce a direct current, and a plurality of them are stacked to form one unit. Here, since a detailed configuration of the fuel cell  4  is the same as that of the fuel cell of the known configuration, a detailed description thereof will be omitted. The end plates  1  are disposed on one surface and the other surface of the fuel cell  4 . The end plate  1  is fixed to the fuel cell  4  by the fastening bar  3 . 
     The end plate will be described with further reference to  FIGS. 2 to 4 . 
       FIG. 2  shows an enlarged diagram of the end plate for the fuel cell stack of  FIG. 1 ,  FIG. 3  is an enlarged diagram of a property forming part of the end plate for the fuel cell stack, and  FIG. 4  is a cross-sectional diagram taken along line IV-IV of  FIG. 2 . 
     As shown in  FIGS. 2 to 4 , the end plate  1  is disposed on each of the upper and lower surfaces of the fuel cell  4  to maintain the flatness of the stacked fuel cells  4  so that a uniform surface pressure may be maintained. The end plate  1  includes a property forming part  10  and a main body part  20  and may be designed to structurally withstand a high load. The end plate  1  may be manufactured in an insert overmolding method in which the property forming part  10  is applied as an insert to fill its outside with the main body part  20 . The property of the property forming part  10  may be insulation, shape maintenance, weight reduction, securing rigidity, free design of the structure, insulation due to very low heat conduction, as well as a mechanical property indicating the correlation between deformation and stress. 
     The property forming part  10  maintains the rigidity of the end plate  1 , and the main body part  20  forms the outer shape of the end plate  1  while surrounding and protecting the property forming part  10 . To reduce the weight of the end plate  1 , a part of the main body part  20  is recessed to form a weight reduction groove  23 . A plurality of weight reduction grooves  23  are formed. Due to the weight reduction groove  23 , the end plate  1  can maintain strength while having the reduced weight. 
     The property forming part  10  and the main body part  20  may include a composite material. 
     The property forming part  10  may include a continuous fiber thermoplastic (CFT), and the main body part  20  can be made of a long fiber thermoplastic (LFT). 
     Each of the continuous fiber thermoplastic and the long fiber thermoplastic can include an amount of about 40 to 60 wt % of a reinforced fiber and an amount of about 40 to 60 wt % of a thermoplastic resin, respectively, based on the total weight of the continuous fiber thermoplastic and the long fiber thermoplastic. Here, the reinforced fiber may include one or more selected from the group consisting of glass fiber, carbon fiber, and aramid fiber, and the thermoplastic resin may include polypropylene or polyamide. 
     When the content of the reinforced fiber is greater than about 60 wt %, the uniformity of structural performance may be reduced due to the occurrence of fiber concentration phenomenon and a problem in that delamination occurs in a fiber concentration part, and when the content of the reinforced fiber is less than about 40 wt %, structural rigidity is not satisfied. 
     Since the property forming part  10  is manufactured in a press molding process using the continuous fiber, it is advantageous in terms of securing rigidity. The main body part  20  may include the long fiber, thereby increasing the degree of freedom in a shape design. Since the property forming part  10  and the main body part  20  include the same resin (PP or PA), an interface is bonded by the resin heat in an injection process, and therefore, the property forming part  10  and the main body part  20  can be coupled. Therefore, a separate bonding process for coupling the property forming part  10  and the main body part  20  does not occur. 
     The end plate  1  in which the property forming part  10  and the main body part  20  may include a composite material having specific strength and specific rigidity greater than those of a steel has a very high weight reduction effect. In addition, the structural design of the property forming part  10  can be varied, thereby maximizing the rigidity of the end plate  1 . 
     In addition, it can be seen that the resin made of PP or PA has very low thermal conductivity compared to steel and aluminum as shown in Table 1 below. Therefore, the end plate  1  has the improved efficiency during cold start due to high thermal insulation property. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Material 
                 Thermal conductivity(W/mK) 
               
               
                   
                   
               
             
            
               
                   
                 Steel 
                  50 
               
               
                   
                 Aluminum 
                 235 
               
               
                   
                 Polypropylene (PP) 
                 0.1 to 0.2 
               
               
                   
                 Polyamide (PA) 
                 0.24 to 0.28 
               
               
                   
                   
               
            
           
         
       
     
     In addition, as shown in Table 2 below, since the resin has excellent insulating property compared to the steel material, a process of adding a Teflon coating or an insulating plate formed on the steel material does not occur. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Material 
                 Electric resistivity(Ω ○ cm) 
               
               
                   
                   
               
             
            
               
                   
                 Steel 
                 7.2 × 10 −5   
               
               
                   
                 Aluminum 
                 2.7 × 10 −6   
               
               
                   
                 Polypropylene (PP) 
                 1.6 × 10 16   
               
               
                   
                 Polyamide (PA) 
                 1.4 × 10 16   
               
               
                   
                   
               
            
           
         
       
     
     The property forming part  10  includes a first property part  11  and a second property part  12 . 
     The first property part  11  includes a property main body  111 , a first rib  112 , and a second rib  113 . 
     The property main body  111  is formed in a plane and has a preset width and length. For example, a terminal hole  114  through which a terminal passes vertically penetrates a center of the property main body  111 . 
     The first rib  112  is formed by bending both ends  111 L of the property main body  111  in a longitudinal direction upward. The first rib  112  is formed entirely in a width direction Y of the property main body  111 . The first rib  112  is formed in a curved shape. 
     The second rib  113  is formed by bending both ends  111 W of the property main body  111  in a width direction upward. The second rib  113  is formed in the longitudinal direction from the longitudinal center of the property main body  111  and has a planar portion. The first rib  112  and the second rib  113  are not connected. 
     The second property part  12  includes a property main body  121 , a first rib  122 , and a second rib  123 . In addition, a terminal hole  124  and a weight reduction groove  125  are formed in the property main body  121 . Since the property main body  121 , the first rib  122 , and the second rib  123  of the second property part  12  are the same as the property main body, the first rib, and the second rib of the first property part  11 , a duplicated description will be omitted. 
     The first property part  11  and the second property part  12  are manufactured by compression molding by stacking several sheets of continuous fiber thermoplastic manufactured, respectively in a molding device (not shown). Therefore, the first property part  11  and the second property part  12  are formed in the same shape. 
     Meanwhile, the first property part  11  is located on the top and the second property part  12  is located under the first property part  11  in an inverted state, and therefore, one surface of the property main body  111  of the first property part  11  and one surface of the property main body  121  of the second property part  12  are in contact with each other. In addition, the first ribs  112 ,  122  of the first property part  11  and the second property part  12  face each other at an interval. The second ribs  113 ,  123  of the first property part  11  and the second property part  12  also face each other at an interval. Therefore, the property forming part  10  forms a vertically symmetrical shape with respect to surfaces with which the property main bodies  111 ,  121  are in contact. 
     A space  115  is formed between the first ribs  112 ,  122  and the second ribs  113 ,  123  as the property forming part  10  has a vertical symmetrical structure with respect to a vertical virtual center line CL. 
     The main body part  20  is disposed outside the property forming part  10 . Since the property forming part  10  is formed to be vertically symmetric, the main body part  20  is formed to be vertically symmetrical with respect to the vertical virtual center line CL. 
     Meanwhile, since the resins of the composite material constituting the property forming part  10  and the main body part  20  are the same, the property forming part  10  and the main body part  20  are coupled without separate adhesive by the resin heat generated in the injection process in an injection device in which the property forming part  10  is located. 
     At this time, the surfaces with which the first property part  11  and the second property part  12  are in contact are also coupled to each other. Therefore, the property forming part  10  and the main body part  20  are integrally formed. In addition, the same terminal hole and weight reduction groove are formed in the portion of the main body part  20  that matches with the terminal hole  114  and the weight reduction groove  115  of the property forming part  10 . 
     The thickness of the end plate  1  may be 25 mm to 30 mm. When the thickness of the end plate  1  is less than about 25 mm, the required performance of the finished vehicle cannot be satisfied, and when it is greater than about 30 mm, a manufacturing cost increases along with an increase in the weight. The thickness of the end plate  1  may be 30 mm. In addition, a ratio of the thickness of the property forming part  10  to the thickness of the main body part  20  (total thickness of the end plate) may be about 15% to 25%. When the thickness of the property forming part  10  is less than 15% of the total thickness of the main body part  20 , the mechanical property efficiency can be reduced, and when it is greater than about 25%, the mechanical property is improved but the weight of the end plate  1  can increase. Therefore, this can lead to an increase in vehicle weight, which can reduce fuel efficiency. 
     Additional exemplary embodiment of the end plate will be described with reference to  FIGS. 5 to 7 . 
       FIG. 5  shows another exemplary embodiment of the end plate for the fuel cell stack of  FIG. 2 ,  FIG. 6  is a schematic diagram showing the property forming part of  FIG. 5 , and  FIG. 7  is a cross-sectional diagram taken along line VII-VII of  FIG. 5 . 
     It has been described in the exemplary embodiment of  FIGS. 2 to 4  that the property forming part  10  includes the first property part  11  and the second property part  12 . 
     However, as in the exemplary embodiment described with reference to  FIGS. 5 to 7 , for a property forming part  10   a , the second property part may be omitted. Therefore, for the property forming part  10   a , only the first property part  11  is formed. Therefore, the property forming part  10   a  is formed in a vertical asymmetrical structure with respect to the vertical virtual center line CL. A main body part  20  may also be formed to be vertically asymmetric. The vertical symmetry or asymmetry of an end plate  2  may be determined according to design requirements of the fuel cell stack. The end plate  2  may derive various mechanical properties vertically symmetrically or asymmetrically. The thickness of the end plate  2  can be 25 mm to 30 mm. Many features described in the exemplary embodiment described with reference to  FIGS. 2 to 4  can be applied to the present exemplary embodiment. 
     Next, the fastening bar will be described with reference to  FIGS. 8 and 9 , 
       FIG. 8  is a schematic diagram showing a fastening bar for the fuel cell stack of  FIG. 1 , and  FIGS. 9A-9F  is a schematic diagram showing an exemplary embodiment of the fastening bar for the fuel cell stack of  FIG. 8 . 
     First, further referring to  FIG. 8 , for the end plate according to the present exemplary embodiment, the fastening bar  3  may be formed in the thickness of 1 mm to 5 mm. The fastening bar  3  includes a bar main body  3   a  and a coupling part  3   b.    
     The coupling part  3   b  is formed by bending one side and the other side of the bar main body  3   a  in a longitudinal direction at right angles in one direction, and therefore the bar main body  3   a  and the coupling part  3   b  are integrally formed. 
     The bar main body  3   a  and the coupling part  3   b  include a design layer  32  and a property layer  31 , respectively. The bar main body  3   a  and the coupling part  3   b  are manufactured in an insert overmolding method and are formed in different types of structures. 
     Here, the thickness of the design layer  32  is formed to be greater than the thickness of the property layer  31 . However, the thicknesses of the property layer  31  and the design layer  32  can be the same. 
     One surface of the property layer  31  is in contact with the fuel cell, and the other surface thereof is not in contact with the fuel cell. For example, the property layer of the coupling part  3   b  is in contact with the end plate  1 . A seating groove  21  (see  FIG. 2 ) is formed in the portion of the end plate  1 . The coupling part  3   b  is located in the seating groove  21  and fixed by a fastening means (not shown) such as a screw and a rivet. Therefore, a through hole (h) through which the fastening means passes is formed in the coupling part  3   b.    
     The design layer  32  is disposed along at least three surfaces of the property layer  31  and is not in contact with the fuel cell. However, the property layer  31  can surround all surfaces of the property layer  31 . 
     The property layer  31  may include continuous fiber thermoplastic (CFT). The design layer  32  may include long fiber thermoplastic (LFT). 
     Each of the continuous fiber thermoplastic and the long fiber thermoplastic may include an amount of about 20 to 40 wt % of a reinforced fiber and an amount of about 60 to 80 wt % of a thermoplastic resin, respectively, based on the total weight of the continuous fiber thermoplastic and the long fiber thermoplastic. 
     Alternatively, each the continuous fiber thermoplastic and the long fiber thermoplastic may include 40 to 60 wt % of a reinforced fiber and 40 to 60 wt % of a thermoplastic resin, respectively based on the total weight of the continuous fiber thermoplastic and the long fiber thermoplastic. 
     The reinforced fiber may include one or more selected from the group consisting of glass fiber, carbon fiber, and aramid fiber, and the thermoplastic resin may include polypropylene (PP) or polyamide (PA). 
     When the content of the reinforced fiber is greater than about 60 wt %, the uniformity of the structural performance may be reduced due to the occurrence of fiber concentration, and a problem in that delamination occurs in the fiber concentration part, and when the content of the reinforced fiber is less than 20 wt %, the structural rigidity is not satisfied. 
     In addition, when the content of the thermoplastic resin is greater than about 80 wt %, a manufacturing cost may increase, and when the content of the thermoplastic resin is less than about 60 wt %, a coupling force between the design layer and the property layer can be reduced. 
     The property layer  31  and the design layer  32  of the fastening bar  3  according to the present exemplary embodiment may have the features of the property forming part and the main body part of the end plate according to the exemplary embodiment described with reference to  FIGS. 2 to 7 . Therefore, a duplicated description will be omitted. 
     In addition, the bar main body  3   a  and the coupling part  3   b  are connected by an inclined surface  3   c  as shown in  FIG. 9A . The length of the inclined surface  3   c  can be the same as the length of the coupling part  3   b . Although not shown in the drawings, an inclined surface can be formed between the seating groove  21  and the side surface of the end plate  1  in contact with the inclined surface  3   c.    
     As shown in  FIG. 9B , the coupling part  3   b  is formed by bending the bar main body  3   a  at a right angle, and the bent portion is formed as a curved surface  3   d . It is possible to minimize the stress concentration in the bent portion by the curved surface. 
     As shown in  FIG. 9C , the coupling part  3   b  is formed by bending the bar main body  3   a  at a right angle, and a reinforced projection  3   e  is formed on the bent inner portion. A groove (not shown) in which the reinforced projection  3   d  is seated can be formed in the end plate  1 . 
     As shown in  FIG. 9D , the coupling part  3   b  is formed by bending the bar main body  3   a  at a right angle, and the bent inner portion is processed as a chamfering  3   f.    
     As shown in  FIG. 9E , the coupling part  3   b  is formed by bending the bar main body  3   a  at a right angle, and a part of the bent portion is formed as the inclined surface  3   c  and a part thereof is formed as the curved surface  3   d . It is possible to minimize the stress concentration in the bent portion by the curved surface  3   d  and the inclined surface  3   c.    
     As shown in  FIG. 9F , the coupling part  3   b  is formed by bending the bar main body  3   a  at a right angle, and the inside and outside of the bent portion are processed as a chamfering  3   g.    
     Next, another exemplary embodiment of the fastening bar for the fuel cell stack will be described with reference to  FIG. 10 . 
       FIG. 10  shows an exemplary embodiment of the fastening bar for the fuel cell stack of  FIG. 8 . 
     As shows in  FIG. 10 , for the fastening bar  5  for the fuel cell stack according to the present exemplary embodiment, the design layer of the fastening bar  3  according to the exemplary embodiments described with reference to  FIGS. 8 and 9  is omitted and the fastening bar  5  is composed of only the property layer. 
     The fastening bar  5  according to the present exemplary embodiment may include a single layer including a bar main body  51  and a coupling part  52 , in which the design layer is omitted and the fastening bar  5  is composed of only the property layer. Therefore, the fastening bar  5  according to the present exemplary embodiment is formed in a single structure, and the property layer can be made of a long fiber thermoplastic. 
     The long fiber thermoplastic may include an amount of about 20 to 40 wt % of a reinforced fiber and an amount of about 60 to 80 wt % of a thermoplastic resin based on the total weight of the long fiber thermoplastic. Alternatively, the long fiber thermoplastic may include an amount of about 40 to 60 wt % of the reinforced fiber and an amount of about 40 to 60 wt % of the thermoplastic resin, based on the total weight of the continuous fiber thermoplastic and the long fiber thermoplastic. 
     The reinforced fiber may include one or more selected from the group consisting of glass fiber, carbon fiber, and aramid fiber, and the thermoplastic resin can be polypropylene or polyamide. For other configurations, the configuration of the exemplary embodiment described with reference to  FIGS. 8 and 9  can be applied as it is. 
     Still another exemplary embodiment of the present invention has most of the components of the exemplary embodiment described with reference to  FIG. 10 . However, a property layer of the present exemplary embodiment can be made of a fiber reinforced thermosetting composite material. The fiber reinforced thermosetting composite material may include an amount of about 20 to 60 wt % of the reinforced fiber and an amount of about 40 to 80 wt % of the thermosetting resin based on the total weight of the fiber reinforced thermosetting composite material. 
     The reinforced fiber may include one or more selected from the group consisting of glass fiber, carbon fiber and aramid fiber. The thermosetting resin can be made of any one selected from the group consisting of vinyl ester (VE), polyester (UP), epoxy (EPDXY), and polyurethane (PU). The fastening bar has excellent effects of heat resistance, solvent resistance, chemical resistance, mechanical properties, and electrical insulation by the thermosetting resin. 
     EXAMPLE 
     Experimental Example 1 
     The end plate having the property forming part and the main body part made of the composite material was manufactured. 
     For the end plate  1 , the required performance of the finished vehicle should be satisfied. In this regard, analysis was conducted to verify the performance of the end plate to which the composite material was applied, and the test specifications and the required performance were as follows. 
     Test method: 3-point bending test 
     Example 1 
     To form the property forming part  10  constituting the end plate  1 , the continuous fiber thermoplastic (CFT) including 60 wt % of the glass fiber and 40 wt % of the polypropylene was used. In the manufacturing process, after manufacturing the continuous fiber thermoplastic, several sheets were stacked and subjected to compression molding to form the property forming part  10  composed of the property main body, the first rib, and the second rib. 
     To form the main body  20  outside the property forming part  10 , the long fiber thermoplastic (LFT) including 60 wt % of the glass fiber and 40 wt % of the polypropylene was used. 
     First, the property forming part  10  was formed into the first property part and the second property part and disposed in the mold to form vertical symmetry. In addition, the long fiber thermoplastic was cut by a regular length, and then put into the mold in which the property forming part  10  was disposed. The end plate was manufactured using a one-shot overmolding method formed in the single mold. The cross-sectional shape of the end plate finally completed through the insert one-shot overmolding process had a vertically symmetrical structure according to the design of the property forming part. The thickness of the property forming part  10  in the manufactured end plate  1  was 30 mm. 
     Example 2 
     The second property part of the property forming part  10  is omitted and composed of only the first property part, and therefore, the cross-sectional shape of the end plate has the vertically asymmetrical structure according to the design of the property forming part composed of only the first property part. The end plate was manufactured in the same manner as in Example 1, except that the thickness of the property forming part  10  was 25 mm. 
     Comparative Example 1 
     The end plate was manufactured in the same manner as in Example 1 while the property forming part  10  was vertically symmetrical and had the thickness of 25 mm. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Thickness (mm) 
                 Performance 
                   
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Example 1 
                 30 
                 159 
               
               
                   
                 Example 2 
                 25 
                 105 
               
               
                   
                 Comparative Example 1 
                 25 
                 91 
               
               
                   
                   
               
            
           
         
       
     
     Referring to Table 3, the three-point bending test was performed using the end plates of Examples 1 and 2 and Comparative Example 1. 
     For Comparative Example 1, the property forming part was designed to have the vertically symmetrical structure, and the required performance was not satisfied at the thickness of 25 mm. 
     For Example 1, the property forming part was designed to have the vertically symmetrical structure, and the required performance was satisfied at the thickness of 30 mm. 
     For Example 2, the property forming part was designed to have the vertically asymmetrical structure, and the thickness was formed at 25 mm in the same manner as in Comparative Example 1, and the required performance was satisfied. 
     Although the preferred exemplary embodiments of the present invention have been specifically described above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention defined by the appended claims also fall within the scope of the present invention.