Abstract:
The invention is to provide a bipolar plate having keys on at least two sides thereof, with such keys have piercing holes thereon; a bipolar plate, a membrane electrode assembly (“MEA”) and a gasket are formed as a unit in the Bipolar Plate Assembly (“BPA”), and provided any of the MEA in a BPA is damaged and needs to be replaced, keys added on other BPAs enable screw rods to fasten sectionally, thus the BPA containing the damaged MEA can be separated, such that the damaged MEA can be dissembled and replaced. The invention further provides a PEM fuel cell, which comprises a plurality of BPAs, with each of such BPA having a number of bipolar plates having keys, MEAs and gaskets. Moreover, the invention further provides a method for replacing MEAs in a PEM fuel cell, whereby damaged MEAs in a PEM fuel cell can be expediently and safely dissembled, repaired or replaced, and the procedure for re-assembling a PEM fuel cell is thus simplified.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates generally to Proton-Exchange Membrane (“PEM”) fuel cells, more particularly, to a bipolar plate with keys employed in a PEM fuel cell, to a method of expediently and safely disassembling, repairing or replacing damaged Membrane Electrode Assembly (“MEA”) through the use of foregoing keys included in the bipolar plate, and to a procedure of simplifying the MEA re-assembling process.  
           [0003]    2. Description of the Related Art  
           [0004]    A PEM fuel cell is composed of a plurality of cell units, with each cell unit having bipolar plates, MEAs and gaskets.  
           [0005]    The type of membrane employed in such PEM fuel cell is polymer membrane, e.g., and, with the Nafion membrane as the electrolyte and platinum as the catalyst, electricity is generated through chemical reactions between hydrogen and oxygen/air. Such PEM fuel cells can be utilized either in households or in automobiles, for the operational temperature thereof is near 80° C. Certain smaller PEM fuel cells can even be utilized in portable equipment.  
           [0006]    The PEM fuel cell is considered a clean energy source, for the means of generating electricity thereby is through chemical reactions between hydrogen and oxygen/air, and the only waste material discharged during such process is water and heat, without producing any chemical or physical waste that might cause environmental or biological concerns and would require higher costs and complicated processing procedures, as would other types of energy-generating sources. The only noise generated during the operation of the PEM fuel cell is by fans in the system, a problem that is easy to solve, e.g., no noise shall be produced, provided pressurized air tanks are utilized in PEM fuel cells.  
           [0007]    The structure of a conventional PEM fuel cell  7 , shown in FIGS. 13 through 15, comprises a plurality of rectangular (e.g., square) bipolar plates  74  having identical sizes, a pair of current collectors  72  and  73 , and a pair of end plates  70  and  71 . A pair of piercing holes  28  is co-axially installed respectively on each foregoing bipolar plates  74  (please refer to FIG. 16) wherethrough a pair of guiding rods  60  is to pierce, such that the bipolar plates  74  are vertically stacked. The guiding rods  60  are utilized for guiding the plurality of bipolar plates  74  so as to expedite the assembling process of the bipolar plates  74 . Also such pair of guiding rods  60  pierces through the piercing holes  58  of the pair of end plates  70  and  71  respectively with the ends thereof protruding out of the surfaces of the end plates  70  and  71 . The two outer sides of the stacked plurality of bipolar plates  74  are respectively installed with current collectors  72  and  73  utilized as positive and negative electrodes, with the two end plates  70  and  71  installed on the outer sides of the current collectors  72  and  73 . By evenly distributing the locations of the plurality of screw rods  16  on the periphery of the plurality of bipolar plates  74  and the current collectors  72  and  73  to pierce therethrough between the end plates  70  and  71 , along with screw nuts  17  being fastened respectively on the protruding ends of the screw rods  16 , the plurality of bipolar plates  74 , the current collectors  72  and  73  and the metal end plate  70  and  71  are integrally compressed and locked, as shown in FIG. 13. The evenly distributed screw rods  16  assure the balance of pressure.  
           [0008]    As shown in FIGS.  13  to  15 , the piercing hole  57 A of the end plate  70  is installed with a hydrogen inlet  18 A, whereas the piercing hole  57 B is installed with an oxygen/air inlet  18 B; the piercing hole  157 A (corresponding to the foregoing piercing hole  57 A on the other side) of the other end plate  71  is installed with a hydrogen outlet  19 A, whereas the piercing hole  157 B is installed with an oxygen/air outlet  19 B. S-shaped grooves  743  are installed on the surfaces of the left side  741  and right side  742  for each bipolar plate  74  so as to channel gases, and all bipolar plates  74  are co-axially installed with the piercing holes  57 A so as to channel hydrogen, whereas the piercing holes  57 B are utilized for channeling oxygen/air (please refer to FIGS.  16  to  18 ). Take hydrogen for example, hydrogen is channeled in through the hydrogen inlet  18 A of the end plate  70 , flowing through the piercing holes  57 A and the corresponding gas channel  743  of the bipolar plates  74  and eventually discharged through the hydrogen outlet  19 A.  
           [0009]    As a matter of fact, the PEM fuel cell  7  also includes a plurality of MEAs which are composite components with each of which having two carbon electrodes pressing on each side of the PEM. As shown in FIGS.  16  to  18 , each of these MEAs  45  is interposed between two bipolar plates  74 . Further, in order to avoid gas leaking or any mixture of hydrogen and oxygen/air thus causing ill operation of the PEM fuel cell, gaskets  41  are interposed between each MEA  45  and each bipolar plate  74 , so as to assure normal operation of the PEM fuel cell. The S-shaped groove  743  is installed on one side surface for each bipolar plate  74  (the left side surface  741 ) utilized for channeling hydrogen, as shown in FIG. 16, wherein the arrow of the dotted line indicates the flowing direction of hydrogen within bipolar plates  74  (please also refer to FIG. 17). Oxygen/air then flows in the S-shaped groove  743  on the other side surface (the right side surface  742 ) of the bipolar plates  74 , with the flowing direction indicated by the arrow of the solid line (please also refer to FIG. 18). Therefore, both hydrogen and oxygen/air, flowing on the two sides of each MEA  45 , are incorporated into water through the catalyst applied on the MEAs  45 . FIG. 16 shows the structural diagram of the single MEA  45  and the adjacent bipolar plates  74  and  74 . Yet no MEA is installed on the side surface of the two bipolar plates that adjacent to the current collectors  72  and  73 , so no groove  743  is installed on the surfaces of such two bipolar plates contacting the current collectors  72  and  73 , a design that has already been disclosed by prior arts, thus it is unnecessary to describe here in detail.  
           [0010]    All the MEAs  45 , gaskets  41  and grooves  743  on the surfaces of the bipolar plates  74  are not shown in drawings for the purpose of expediently describing the conventional PEM fuel cell  7 . Please refer to U.S. Pat. No. 5,484,666, No. 6,190,793 and No. 6,207,312 for the detailed composition of the PEM fuel cell, and the bipolar plates and the MEAs thereof.  
           [0011]    The MEAs  45  and the bipolar plates  74  in each cell are all conductive material, with all electric currents in such cell being connected and collected by the current collectors  72  and  73 . The number and area for the bipolar plates  74  in the fuel cell  7  determines the number of Watt output. It is not necessary to go in detail here, for the structure and operational function of the conventional PEM fuel cell have already become extensively known to the public. During the operating process of the conventional PEM fuel cell, it is common to have one or more dysfunctional MEAs  45  that need to be replaced. When such problem occurs, each screw nut  17  on either side of the end plates  70  and  71  needs to be disassembled, thus re-forming the assembled state of the cell to be under the loosening state without being locked, and then both end plates  70  and  71  and both current collectors  72  and  73  are further separated, and then the bipolar plates  74 , the MEAs  45  and the gaskets  41  are respectively pulled out from the guiding rods  60 , until the dysfunctional MEAs are reached and separated. After the dysfunctional MEAs are replaced with new MEAs, the separated MEAs pulled out previously need to be respectively threaded through by the guiding rods  60 , and then the current collectors  72  and  73  and the end plates  70  and  71  are threaded through by the guiding rods  60  in order, eventually fastening the disassembled screw nuts  17  onto the ends of the screw rods  16 , thus completing the re-assembling procedure.  
           [0012]    However, various problems might occur during the processes of disassembling and re-assembling, such as hydrogen leakage due to erroneous re-assembling process of bipolar plates, MEAs and gaskets; further, during the complicated processes of disassembling and re-assembling, intact MEAs that are expensive are prone to percussion and damage. In addition, such process can only be done in manufacturing or maintenance warehouses, thus the whole fuel cell has to be delivered for repair, a procedure that is tremendously inconvenient and time-consuming.  
           [0013]    The foregoing U.S. Pat. No. 6,190,793 provides a compression assembly and an elongated tension member, so that the fastening and compressing stacks of bipolar plates can be strengthened, a design that fails to improve upon the drawback of complicated disassembling and re-assembling processes for replacing damaged MEAs in fuel cells. The foregoing U.S. Pat. No. 6,207,312 then provides a new internal gas-channel design for PEM fuel cells, a design that also fails to improve upon the drawback of complicated disassembling and re-assembling processes for replacing damaged MEAs in fuel cells.  
           [0014]    As far as the conventional PEM fuel cell is concerned, provided the end plates therein are made of metal, the installment of current collectors is then optional; which is to say, the current collectors are then not necessary for PEM fuel cells having end plates made of metal. On the contrary, provided the end plates therein are not made of metal, the installment of current collectors then becomes mandatory.  
         SUMMARY OF THE INVENTION  
         [0015]    The primary object of the invention is to provide a bipolar plate having keys, and such bipolar plate, installed on two sides with at least one key having at least one piercing hole, is a unit for the whole Bipolar Plate Assembly (“BPA”). Provided one or more of the MEAs in any of the BPAs are damaged and need to be replaced, the keys of the other BPAs enable the screw rods to lock sectionally, thus the BPAs containing the damaged MEAs can be separated, and the damaged MEAs replaced.  
           [0016]    A further object of the invention is to provide a PEM fuel cell having a plurality of BPAs, with each of the BPA comprising bipolar plates having keys, MEAs and gaskets. Each bipolar plate has at least two sides installed with at least one key, on which at least one piercing hole is installed. Provided one or more of the MEAs in any of the BPAs are damaged and need to be replaced, the keys of the other BPAs enable the screw rods to lock sectionally, thus the BPAs containing the damaged MEAs can be separated, and the damaged MEAs replaced.  
           [0017]    Another object of the invention is to provide a method for replacing damaged MEAs in PEM fuel cells. Provided any damaged MEA needs to be replaced, certain amount of pressure is applied, under the means of sectional locking, upon the BPAs adjacent to the BPA containing the damaged MEA, so as to hold still the BPAs that do not contain the damaged MEAs; therefore, the bipolar plates, MEAs and gaskets in good condition are kept in their original places with no need to be moved, and only the BPA containing the damaged MEAs is separated so that the damaged MEAs are replaced, a design that significantly shortens the time needed to disassemble and re-assemble the conventional fuel cell, avoid the serious consequences of hydrogen leakage due to erroneous re-assembling processes, and prevent expensive MEAs in good condition from being damaged due to accidental percussions during the disassembling and re-assembling processes.  
           [0018]    The keys installed on bipolar plates do not adversely affect the function of fuel cells in any way, the keys further provide heat-dispersing function for fuel cells like cooling fins, which increase heat exchange during the operation of fuel cells, thus heat is released out to the surrounding atmosphere, a function that serves to keep the internal temperature of fuel cells under the range of operationability.  
           [0019]    The foregoing method for replacing damaged MEAs in PEM fuel cells saves more replacing time provided the number of BPAs increases.  
           [0020]    The foregoing method for replacing bipolar plates in PEM fuel cells provides the end users on-site maintenance service with no need to bring the whole fuel cell back to the manufacturing factories for maintenance. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings that are provided only for further elaboration without limiting or restricting the present invention, where:  
         [0022]    [0022]FIG. 1 shows a three-dimensional view of the first embodiment for the PEM fuel cell of the invention, mainly manifesting that a plurality of screw rods locking and incorporating the end plates, current collectors and the plurality of BPAs;  
         [0023]    [0023]FIG. 2 shows a right side view of the fuel cell of the invention;  
         [0024]    [0024]FIG. 3 shows a side view of the bipolar plate of the invention;  
         [0025]    [0025]FIG. 4 shows another variation of the position change regarding the keys installed on bipolar plates of the invention;  
         [0026]    [0026]FIG. 5 shows another variation of the position change regarding the keys installed on bipolar plates of the invention;  
         [0027]    [0027]FIG. 6 shows a dissecting view of a BPA containing damaged MEAs based upon the first embodiment of the method for replacing damaged MEAs in fuel cells;  
         [0028]    [0028]FIG. 7 shows a three-dimensional view of the second embodiment of the fuel cell of the invention;  
         [0029]    [0029]FIG. 8 shows a three-dimensional view of the third embodiment of the fuel cell of the invention;  
         [0030]    [0030]FIG. 9 shows a right side view of FIG. 8;  
         [0031]    [0031]FIG. 10 shows a dissecting view of a BPA containing damaged MEAs based upon the third embodiment of the method for replacing damaged MEAs in fuel cells;  
         [0032]    [0032]FIG. 11 shows a bipolar plate in hexagonal shape in the embodiment of the invention;  
         [0033]    [0033]FIG. 12 shows a bipolar plate in octagonal shape in the embodiment of the invention;  
         [0034]    [0034]FIG. 13 shows a three-dimensional view of the conventional fuel cell, mainly manifesting that a plurality of screw rods locking and incorporating the end plates, current collectors and the plurality of bipolar plates;  
         [0035]    [0035]FIG. 14 shows a front view of the conventional fuel cell;  
         [0036]    [0036]FIG. 15 shows a right side view of the conventional fuel cell;  
         [0037]    [0037]FIG. 16 shows a dissecting view of the bipolar plates, gaskets and MEAs of the conventional fuel cell, along with the flowing directions of hydrogen and oxygen/air;  
         [0038]    [0038]FIG. 17 shows a structural plane view of the left side surface of a bipolar plate in the conventional fuel cell; and  
         [0039]    [0039]FIG. 18 shows a structural plane view of the right side surface of a bipolar plate in the conventional fuel cell. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0040]    The following is a detailed description of the best presently known modes of carrying out the PEM fuel cell of the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention. Also for better description of the PEM fuel cell of the invention, MEAs, gaskets and grooves installed on the surfaces of bipolar plates are omitted in this specification.  
         [0041]    The first embodiment of the PEM fuel cell  1  of the invention is shown in FIG. 1, comprising end plates  10  and  11 , current collectors  12  and  13 , the first BPA  21 , the second BPA  22 , the third BPA  23 , the fourth BPA  24 , the fifth BPA  25 , the sixth BPA  26 , a plurality of screw rods  16 , a plurality of screw nuts  17 , and a pair of guiding rods  60 . The end plates  10  and  11 , both designed as symmetrical structure, can be made of either metal or non-metal material; in this embodiment, the end plates  10  and  11  are designed to have sixteen piercing holes proportionally distributed thereon for being threaded through by sixteen screw rods  16 , and a pair of piercing holes  58  for being threaded through by the guiding rods  60 . The piercing hole  57 A installed on the end plate  10  is fastened with the hydrogen inlet  18 A by means of screws, whereas the piercing hole  57 B is fastened with the oxygen/air inlet  18 B by means of screws. As for the end plate  11 , the piercing holes  157 A and  157 B installed thereon are fastened respectively with the hydrogen outlet  19 A and the oxygen/air outlet  19 B, please refer to FIG. 2. The foregoing gas inlets  18 A and  18 B and the gas outlets  19 A and  19 B respectively have the identical functions to those of the gas inlets  18 A and  18 B and the gas outlets  19 A and  19 B of the conventional PEM fuel cell  7  shown in FIG. 13.  
         [0042]    Also the foregoing current collector  12  and  13  respectively have the identical functions to those of the current collectors  72  and  73  of the conventional PEM fuel cell  7  shown in FIG. 13.  
         [0043]    In the first embodiment of the invention, each of the BPAs  21 ,  22 ,  23 ,  24 ,  25  and  26  has four bipolar plates  14 ; however, for practical use, designers can alter the number of the BPAs in cells or the number of bipolar plates in BPAs. As mentioned above, the MEAs, the gaskets and the grooves installed on surfaces of bipolar plates are omitted in this specification for better description. Still, the omitted members are necessary for embodying the invention.  
         [0044]    As shown in FIG. 1, the guiding rods  60  are to thread through the piercing holes  28  co-axially installed respectively on the first BPA  21 , the second BPA  22 , the third BPA  23 , the fourth BPA  24 , the fifth BPA  25  and the sixth BPA  26  stacked together, thus threading each BPA together, and then the current collectors  12  and  13 , end plates  10  and  11  are threaded in order on the outside of the threaded BPAs, thus the two ends of the guiding rods  60  are to protrude out of the end plates  10  and  11 .  
         [0045]    The first BPA  21  has four bipolar plates  14  vertically aligned as shown in FIG. 3. The bipolar plates  14 , apart from having the same features of a pair of piercing holes  28 , gas inlets  18 A and  18 B and gas outlets  19 A and  19 B as the conventional PEM fuel cell, mainly have two sets of two keys  33  and  32  in pairs extending correspondently outwards from both the left side and the right side of the square-shaped bipolar plates, with each key  32  having a piercing hole  33  thereon; each bipolar plate  14  having keys  32  thus becomes a composition unit in the first BPA  21 . As for the composition of the third and fifth BPAs  23  and  25 , it is identical to that of the first BPA  21 . Yet the two keys  32  adjacent to one another on the same side of the bipolar plate  14  shown in FIG. 3 can be combined as a single key  32  as shown in FIG. 5.  
         [0046]    Please refer to FIG. 4. The second BPA  22  is similar to the first BPA  21 , except that the keys  32  of the second BPA  22  are staggeredly installed without overlapping with the keys  32  of the first BPA  21 . As for the composition of the fourth and sixth BPAs  24  and  26 , it is identical to that of the second BPA  22 .  
         [0047]    For each threaded BPA, the piercing hole  33  of the keys  32  on the identical direction are co-axially positioned and aligned with the piercing holes on the end plates  10  and  11 , therefore each screw rod  16  is to thread through the end plates  10  and  11  and every key  32  of each BPA, eventually the end plates  10  and  11 , current collectors  12  and  13  and each BPA are compressed and locked together through fastening the screw nuts  17  on two protruding ends for each screw rod  16 , as shown in FIG. 1.  
         [0048]    After connecting the gas inlet  18 A with the hydrogen providing source, and connecting the gas inlet  18 B with the oxygen/air providing source, the PEM fuel cell  1  of the invention is to operate through reactions from the foregoing gases to produce water and electricity, a principle that is identical to that of the conventional fuel cell and thus it is no need to describe in detail here.  
         [0049]    The method of replacing damaged MEAs through utilizing keys of the invention is described in detail as follows in accordance with FIG. 1, FIG. 3, FIG. 4 and FIG. 6.  
         [0050]    Suppose it is found that the MEA interposed between two bipolar plates  14 A and  14 B in the second BPA  22  is damaged and needs to be replaced, the key  32  of the invention is utilized for the screw rods  16 A and  16 B having proper lengths to thread through, so as to lock the BPAs  21  and  23  to  26 , thus separating the second BPA  22  containing the damaged MEA (as shown in FIG. 6) for replacement or repair. Therefore the damaged MEA can be replaced and the PEM fuel cell re-assembled easily and expediently, so that the proper operation of the PEM fuel cell can be maintained.  
         [0051]    The second embodiment of the invention is elaborated as follows.  
         [0052]    The PEM fuel cell  1  shown in FIG. 7 is not identical to the first embodiment in that, the bipolar plate in FIG. 7 is the bipolar plate  14  shown in FIG. 4 and FIG. 5, and the keys of the bipolar plate are installed in both left-and-right directions, as well as up-and-down directions. According to FIG. 7, numerous variations can be developed out of the invention.  
         [0053]    The third embodiment of the invention is further elaborated as follows.  
         [0054]    Another type of PEM fuel cell  2  is shown in FIG. 8 in accordance with FIG. 9. Such type of PEM fuel cell  2  is not identical to the PEM fuel cell  1  in that, in the fuel cell  2  shown in FIG. 8, a plurality of screw rods  16  is to directly thread through the end plate  10 , the first to sixth BPAs  21  to  26  (including MEAs and gaskets) and the end plate  11 , and then the screw nuts  17  having the corresponding numbers are to lock the whole fuel cell  2  together. Since the metal screw rods  16  are to directly thread through the end plates  10  and  11  and each BPA, insulating material (not shown in figures) must be utilized to cover the exterior of the screw rods  16 , so as to avoid short circuit. Furthermore, provided the end plates  10  and  11  are made of metal, screw holes  80  and  81  can be added respectively on one side of the end plates  10  and  11  for connecting the current output guide wire, thus no current collectors  12  and  13  are needed for such type of fuel cell  2 .  
         [0055]    Further, the PEM fuel cell  2  in FIG. 8 has guiding rods  60  that thread through the co-axial piercing holes  29  of the stacked first BPA  21 , second BPA  22 , third BPA  23 , fourth BPA  24 , fifth BPA  25 , and sixth BPA  26  (shown in FIG. 10), thus threading each BPA together, and then the end plates  10  and  11  are threaded through in order, leaving the two ends of the guiding rods  60  protruding out of the end plates  10  and  11 . Each screw rod  16  can then thread through the corresponding piercing holes installed on the end plates  10  and  11 , and eventually the screw nuts  17  are fastened on the two ends for each screw rod  16 , thus compressing and locking the end plates  10  and  11  and each BPA together.  
         [0056]    The method of replacing damaged MEAs by utilizing keys of the invention is further elaborated in accordance with FIG. 8, FIG. 9 and FIG. 10.  
         [0057]    Suppose it is found that the MEA interposed between two bipolar plates  14 A and  14 B in the third BPA  23  is damaged and needs to be replaced, the key  32  of the invention is utilized for the screw rods  16 C and  16 D having proper lengths to thread through, so as to lock the BPAs  21  and  22  and  24  to  26 , thus separating the third BPA  23  containing the damaged MEA (as shown in FIG. 10) for replacement or repair. Therefore the damaged MEA can be replaced and the PEM fuel cell re-assembled easily and expediently, so that the proper operation of the PEM fuel cell can be maintained.  
         [0058]    According to the first and second embodiment utilizing keys of the invention to disassemble BPAs of fuel cells, procedures for replacing damaged MEAs are deducted as follows:  
         [0059]    1. Disassemble the screw rods that thread through keys of BPAs set to be locked.  
         [0060]    2. Fasten BPAs set to be locked by using screw rods having proper lengths and screw nuts.  
         [0061]    3. Disassemble the remaining screw rods and screw nuts and separate the BPA containing the damaged MEA.  
         [0062]    4. Replace the damaged MEA.  
         [0063]    The foregoing procedures can be adjusted according to particular needs without being limited by the invention. After completing the replacement of the damaged MEA, the procedures are reversed so as to re-assemble the PEM fuel cell.  
         [0064]    According to the third embodiment utilizing keys of the invention to disassemble BPAs of fuel cells, procedures for replacing damaged MEAs are deducted as follows:  
         [0065]    1. Fasten BPAs that do not contain the damaged MEA by using screw rods having proper lengths and screw nuts.  
         [0066]    2. Disassemble the existing screw rods and screw nuts and separate the BPA containing the damaged MEA.  
         [0067]    3. Replace the damaged MEA.  
         [0068]    The foregoing procedures can be adjusted according to particular needs without being limited by the invention. After completing the replacement of the damaged MEA, the procedures are reversed so as to re-assemble the PEM fuel cell.  
         [0069]    The number of bipolar plates in each BPA can be various according to different needs for the number of Watt output. As the number of bipolar plates in a BPA becomes larger, the pressure taken by the screw rods and screw nuts becomes greater, thus the BPAs are compressed further by higher pressure.  
         [0070]    The positions for keys installing on the bipolar plates are important in that, through the design of a plurality of keys, pressure is to be distributed to the whole bipolar plate without concentrating on areas adjacent to a single key. Therefore, the shape, size, installing position and number of a key on each bipolar plate can vary according to different needs. For example, the bipolar plate  14  can further be hexagonal, with at least two outwardly extending keys  32  being installed thereon; such key is installed with at least one piercing hole  33 . Or the bipolar plate  14  can further be octagonal, with at least two outwardly extending keys  32  being installed thereon; such key is installed with at least one piercing hole  33 .  
         [0071]    The positions for keys of bipolar plates of all types are functioned as pressure-balancing mechanisms; during the replacement of a damaged bipolar plate, the greater the pressure applies on the keys, more securely fastened the bipolar plate is.  
         [0072]    The keys installed on bipolar plates do not adversely affect the function of fuel cells in any way, the keys further provide heat-dispersing function for fuel cells like cooling fins, which increase heat exchange during the operation of fuel cells, thus heat is to be released out to the surrounding atmosphere, thus serving to keep the internal temperature of fuel cells under the range of operationability.  
         [0073]    The foregoing method for replacing damaged MEAs in PEM fuel cells saves more replacing time provided the number of BPAs increases.  
         [0074]    The foregoing method for replacing bipolar plates in PEM fuel cells provides the end users on-site maintenance service with no need to bring the whole fuel cell back to the manufacturing factories for maintenance.  
         [0075]    The material for end plates is not limited by the invention. When end plates are made of metal, current collectors can be installed, but not mandatory when end plates are not made of metal, current collectors then become necessary members in such PEM fuel cell. It is also not limited by the invention as to the number of keys on bipolar plates or shapes of bipolar plates. It is no need to elaborate the order for detailed disassembling of the screw rods or screw nuts as long as the method of sectional locking is followed within the spirit and scope of the invention. The foregoing drawings and elaboration are not to be taken in a limiting sense, but are made merely for the purpose of illustrating the general principles of the invention.