Patent Publication Number: US-2005130014-A1

Title: Bipolar plate of fuel cell and fabrication method thereof

Description:
TECHNICAL FIELD  
      The present invention relates to a fuel cell, and in particular to a bipolar plate of a fuel cell and a fabrication method thereof capable of unuiformizing flux distribution, reducing flow resistance of fuel and air respectively flowing into a fuel electrode and an air electrode of a fuel cell and simplifying fabrication thereof.  
     BACKGROUND ART  
      A fuel cell is generally environment-friendly energy, and it has been developed in order to substitute for the conventional fossil energy. As depicted in  FIG. 1 , the fuel cell includes a stack  100  to be combined with at least one unit cell  101  in which electrochemical reaction occurs; a fuel supply pipe  200  connected to the stack  100  so as to supply fuel; an air supply pipe  300  connected to the stack  100  so as to supply air; and discharge pipes  400 ,  500  for discharging by-products of fuel and air passing the reaction respectively. The unit cell  101  includes a fuel electrode (anode) (not shown) in which fuel flows; and an air electrode (cathode) (not shown) in which air flows.  
      The operation of the fuel cell will be described.  
      First, fuel and air are supplied to the fuel electrode and the air electrode of the stack  100  through the fuel supply pipe  200  and the air supply pipe  300  respectively. Fuel supplied to the fuel electrode is ionized into positive ions and electrons (e−) through electrochemical oxidation reaction in the fuel electrode, the ionized positive ions are moved to the air electrode through an electrolyte, and the electrons are moved to the fuel electrode. The positive ions moved to the air electrode perform electrochemical reduction reaction with air supplied to the air electrode and generate by-products such as reaction heat and water, etc. In the process, by the movement of the electrons, electric energy is generated. The fuel through the reaction in the fuel electrode, and water and additional by-products generated in the air electrode are respectively discharged through the discharge pipes  400 ,  500 .  
      The fuel cell can be classified into various types according to electrolyte and fuel, etc. used therein.  
      In the meantime, as depicted in  FIG. 2 , the unit cell  101  constructing the stack  100  includes two bipolar plates  10  having an open channel  11  in which air or fuel flows; and a M.E.A (membrane electrode assembly)  20  arranged between the two bipolar plates  10  so as to have a certain thickness and area. The two bipolar plates  10  and the M.E.A  20  arranged therebetween are combined with each other by additional combining means  30 ,  31 . A channel formed by a channel  11  of the bipolar plate  10  and a side of the M.E.A  20  constructs a fuel electrode, and oxidation reaction occurs while fuel flows through the channel of the fuel electrode. And, a channel formed by a channel  11  of the other bipolar plate  10  and the other side of the M.E.A  20  constructs an air electrode, and reduction reaction occurs while air flows through the channel of the air electrode.  
      A shape of the bipolar plate  10 , in particular, a shape of the channel  11  affects contact resistance generated in flowing of fuel and air and flux distribution, etc., and contact resistance and flux distribution affect power efficiency. And, the bipolar plates  10  have a certain shape appropriate to processing facilitation and mass production.  
      As depicted in  FIG. 3 , in the conventional bipolar plate, through holes  13 ,  14 ,  15 ,  16  are respectively formed at each edge of the plate  12  having a certain thickness and a rectangular shape.  
      And, plural channels  11  are formed on a side of the plate  12  so as to connect the through hole  13  with the diagonally arranged through hole  16 . The channels  11  have a zigzag shape. As depicted in  FIG. 4 , in the section of the channel  11 , the channel  11  has a certain width and depth and an open side. Plural channels  11  are formed on the other side of the plate  12  so as to connect the diagonally arranged two through holes  14 ,  16 , and the channels  11  have the same shape with the channels formed on the opposite side.  
      The operation of the conventional bipolar plate will be described. First, fuel and air respectively flow into the through holes  13 ,  14 , fuel and air passing the through holes  13 ,  14  flow into the channels  11 . Fuel or air in the channels  11  flows zigzag along the channels  11  and is discharged to the outside through the through holes  15 ,  16 . In that process, oxidation reaction occurs in the M.E.A  20  (shown in  FIG. 2 ) in which fuel flows, simultaneously reduction reaction occurs in the M.E.A in which air flows.  
      However, in the conventional bipolar plate, because the channels  11  are formed as zigzag, flux can be distributed evenly to some degree. However, because the channels in which fuel and air flow are complicate and long, flow resistance is increased, and pressure loss for making fuel and air flow is increased. In addition, because processing is complicate and intricate in fabrication, a production cost is high.  
     TECHNICAL GIST OF THE PRESENT INVENTION  
      In order to solve the above-described problems, it is an object of the present invention to provide a bipolar plate of a fuel cell and a fabrication method thereof capable of uniformizing flux distribution, reducing flow resistance of fuel and air respectively flowing into a fuel electrode and an air electrode of a fuel cell and simplifying fabrication thereof.  
      In order to achieve the above-mentioned objects, a bipolar plate of a fuel cell includes a plate having a certain thickness and area; a fluid flowing space formed on both sides of the plate so as to have a certain width, length and depth; a fluid guide mesh installed on the fluid flowing space so as to have a certain shape; an inflow channel formed on the plate so as to be connected with the fluid flowing space and receive a fluid; and an outflow channel formed on the plate so as to be connected with the fluid flowing space and discharge the fluid.  
      In addition, a method for fabricating a bipolar plate of a fuel cell includes fabricating a mold for processing a plate on which a fluid flowing space having a certain area and depth is formed at both sides and an internal channel is formed by a support mesh projected as a mesh shape from the fluid flowing space; forming a plate with the mold; processing an inflow channel on the plate so as to make a fluid flow into the fluid flowing space having the support mesh; and processing an outflow channel on the plate so as to make the flow in the fluid flowing space flow out.  
      In addition, a bipolar plate of a fuel cell includes a plate having a certain thickness and area; a channel region having latticed protrusions by plural latticed grooves formed along a certain area of both sides of the plate; an inflow channel formed at a side of the plate so as to be connected with the latticed grooves in the channel region and receive a fluid; and an outflow channel formed at a side of the plate so as to discharge the fluid passing the latticed grooves of the channel region.  
      In addition, a method for fabricating a bipolar plate of a fuel cell includes fabricating a plate having a certain thickness and area; performing mechanical processing for forming latticed grooves by latticed protrusions formed on both sides of the plate; and processing an inflow channel and an outflow channel on the plate so as to be connected with the latticed grooves.  
      In addition, a bipolar plate of a fuel cell includes a plate having a certain thickness and area in which plural channels consisting of plural ups and downs are formed at both sides on the middle by being pressed so as to have a certain width and length; and a sealing member respectively adhered to the outline of the both sides of the plate so as to form internal channels with the channels of the plate, an inflow channel and an outflow channel in which a fluid flows in/out through the channels.  
      In addition, a method for fabricating a bipolar plate of a fuel cell includes cutting a plate so as to have a certain size; press-processing both sides of the cut plate so as to form plural channels in which a fluid flows; and combining a sealing member with the outline of the press-processed plate. 
    
    
     BRIEF DESCRIPTION OF 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 specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
      In the drawings:  
       FIG. 1  illustrates the conventional fuel cell system;  
       FIG. 2  is an exploded-perspective view illustrating part of a stack of the conventional fuel cell;  
       FIG. 3  is a plane view illustrating a bipolar plate of the conventional fuel cell;  
       FIG. 4  is a sectional view taken along a line A-B in  FIG. 3 ;  
       FIG. 5  is a plane view illustrating a first embodiment of a bipolar plate of a fuel cell in accordance with the present invention;  
       FIG. 6  is an exploded-perspective view illustrating part of the bipolar plate of the fuel cell in accordance with the first embodiment of the present invention;  
       FIG. 7  is a flow chart illustrating a first embodiment of a method for fabricating a bipolar plate of a fuel cell in accordance with the present invention;  
       FIG. 8  is an exploded-perspective view illustrating a stack of the bipolar plate of the fuel cell in accordance with the first embodiment of the present invention;  
       FIG. 9  is a plane view illustrating an operational state of the bipolar plate of the fuel cell in accordance with the first embodiment of the present invention;  
       FIGS. 10 and 11  are a plane view and a front sectional view illustrating a second embodiment of a bipolar plate of a fuel cell in accordance with the present invention;  
       FIG. 12  is a flow chart illustrating a second embodiment of a method for fabricating a bipolar plate of a fuel cell in accordance with the present invention;  
       FIG. 13  is a plane view illustrating an operational state of the bipolar plate of the fuel cell in accordance with the second embodiment of the present invention;  
       FIGS. 14 and 15  are a plane view and a sectional view illustrating a third embodiment of a bipolar plate of a fuel cell in accordance with the present invention; and  
       FIG. 16  is a flow chart illustrating a third embodiment of a method for fabricating a bipolar plate of a fuel cell in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinafter, the preferred embodiments of the present invention will be described with reference to accompanying drawings.  
      First, a first embodiment of a bipolar plate of a fuel cell in accordance with the present invention will be described.  
       FIG. 5  is a plane view illustrating a first embodiment of a bipolar plate of a fuel cell in accordance with the present invention, and  FIG. 6  is an exploded-perspective view illustrating part of the bipolar plate of the fuel cell in accordance with the first embodiment of the present invention.  
      As depicted in  FIGS. 5 and 6 , the first embodiment of the bipolar plate of the fuel cell in accordance with the present invention includes a plate  40  having a certain thickness and area; a fluid flowing space  41  formed on both sides of the plate  40  so as to have a certain width, length and depth; a fluid guide mesh  42  installed in the fluid flowing space  41  so as to have a certain shape; an inflow path  43  formed on the plate  40  to be connected to the fluid flowing space  41  for introducing a fluid; and an outflow path  44  formed on the plate  40  to be connected to the fluid flowing space  41  for discharging the fluid.  
      The plate  40  has a rectangular shape and has a certain thickness, the fluid flowing space  41  is respectively formed on both sides of the rectangular plate  40 , and it has a rectangular shape and has a certain depth. The plate  40  is made of a stainless steel material. The plate  40  and the fluid flowing space  41  can have other shapes besides the rectangular shape.  
      The fluid guide mesh  42  has a rectangular shape smaller than the fluid flowing space  41  so as to be inserted into the fluid flowing space  41  of the plate  40 , and it has a thickness not greater than the depth of the fluid flowing space  41 .  
      The inflow path  43  is constructed as at least one through hole and is formed at a side of the plate  40 . The outflow path  43  is constructed as at least one through hole and is formed at the opposite side of the inflow path  43  so as to be diagonal to the inflow path  43 .  
      Next, a first embodiment of a method for fabricating a bipolar plate of a fuel cell in accordance with the present invention will be described.  
       FIG. 7  is a flow chart illustrating a first embodiment of a method for fabricating a bipolar plate of a fuel cell in accordance with the present invention.  
      As depicted in  FIG. 7 , in the first embodiment of the method for fabricating the bipolar plate of the fuel cell in accordance with the present invention, a mold for processing a plate on which a fluid flowing space having a certain area and depth is formed at both sides and a mesh is formed to be projected in the fluid flowing space is fabricated. And, a plate is processed with the mold. Herein, in the plate, a rectangular fluid flowing space having a certain depth is formed at both sides of the rectangular plate having a certain depth, and a mesh shape is formed in the fluid flowing space so as to form a channel. The mesh can be formed as various shapes.  
      Next, an inflow path is processed on the plate so as to make a fluid flow into the fluid flowing space having the mesh, and an outflow path is processed so as to make the fluid in the fluid flowing space flow out. The inflow path and the outflow path are respectively processed as at least one through hole or open groove.  
      Hereinafter, the operation of the bipolar plate of the fuel cell and the fabrication method thereof in accordance with the first embodiment of the present invention will be described.  
      First, the bipolar plates of the fuel cell construct a stack. In more detail, as depicted in  FIG. 8 , a M.E.A (M) is arranged between the bipolar plates (BP), and they are combined with each other by combining means (not shown). Herein, by the fluid flowing space  41  formed on the side of the bipolar plate (BP), the fluid guide mesh  42  formed in the fluid flowing space  41  and a side of the M.E.A (M), a path in which fuel flows is formed. By the other side of the M.E.A (M), the fluid flowing space  41  formed on a side of the other bipolar plate (BP) facing the bipolar plate (BP) and the fluid guide mesh  42  formed in the fluid flowing space  41 , a path in which air flows is formed.  
      In that structure, when fuel flows into the inflow path  43  of the bipolar plate (BP), as depicted in  FIG. 9 , the fuel in the inflow path  43  flows into the fluid flowing space  41 . And, the fuel in the fluid flowing space  41  spreads all over the fluid flowing space  41  by the fluid guide mesh  42  positioned in the fluid flowing space  41 , and the fuel is discharged to the outside through the outflow path  44 .  
      In that process, the fluid guide mesh  42  in the fluid flowing space  41  performs not only a guide function by spreading the fuel in the fluid flowing space  41  evenly but also a diffusion function by adjusting flux appropriately. Herein, distribution and pressure can be adjusted by a mesh size of the fluid guide mesh  42 . In the meantime, by forming the fluid guide mesh  42  as a mesh, contact area with the M.E.A (M) contacted to the bipolar plate (BP) is comparatively reduced, and accordingly effective area of the fuel and the M.E.A (M) is increased.  
      In addition, air flows by passing the above-described process.  
      In the method for fabricating the bipolar plate of the fuel cell in accordance with the first embodiment of the present invention, by fabricating a plate with a mold, it can be mass-produced easily. In more detail, by fabricating a plate having a support mesh and processing an inflow path and an outflow path, a bipolar plate can be simply and easily fabricated.  
      Next, a bipolar plate of a fuel cell in accordance with a second embodiment of the present invention will be described.  
       FIGS. 10 and 11  are a plane view and a front sectional view illustrating a second embodiment of a bipolar plate of a fuel cell in accordance with the present invention.  
      As depicted in  FIGS. 10 and 11 , the bipolar plate of the fuel cell in accordance with the second embodiment of the present invention includes a plate  50  having a certain thickness and area; a channel region  53  having latticed protrusions  52  by plural latticed grooves  51  formed along a certain area of both sides of the plate  50 ; an inflow path  54  formed at a side of the plate  50  so as to be connected to the latticed grooves  51  of the channel region  53  for introducing a fluid; and an outflow path  55  formed at a side of the plate  50  so as to discharge the fluid passing the latticed grooves  51  of the channel region  53 .  
      The plate  50  has a rectangular shape and has a certain thickness. The channel region  53  is respectively formed at both sides of the plate  50  so as to have a rectangular shape. The plate  50  and the channel region  53  can be formed as various shapes besides the rectangular shape.  
      The latticed protrusions  52  are formed as a rectangular cone shape, and each latticed groove  51  is formed between the latticed protrusions  52  having the rectangular cone shape. The latticed protrusion  52  can be formed so as to have a triangular cone shape.  
      The latticed protrusions  52  are regularly arranged. In modification, the latticed protrusions  52  can be irregularly arranged.  
      The inflow path  54  and the outflow path  55  are respectively formed at a side of the plate  50  as an open shape having a certain width and depth. In addition, the inflow path  54  and the outflow path  55  can be respectively formed as at least one through hole.  
      The bipolar plate of the fuel cell in accordance with the second embodiment of the present invention is made of a stainless steel material.  
       FIG. 12  is a flow chart illustrating a second embodiment of a method for fabricating a bipolar plate of a fuel cell in accordance with the present invention.  
      As depicted in  FIG. 12 , in the method for fabricating bipolar plate of the fuel cell in accordance with the second embodiment of the present invention, a first step is for fabricating a plate having a certain thickness and area. And, a second step as a mechanical processing for forming latticed grooves by latticed protrusions on both sides of the plate is performed. The second step includes the sub-steps of scratching both sides of the plate to form latticed protrusions; and grinding the scratched both sides of the plate. The latticed protrusions formed by the scratching have a rectangular-cone shape, and they can be formed as other shapes besides the rectangular-cone shape. By the scratching, latticed grooves are formed among the latticed protrusions, and the latticed grooves form channels in which fluid flows. By performing the grinding, it is possible to remove burr occurred by the scratching and process the sharp end of the latticed protrusions so as to be dull.  
      And, a third step is for processing an inflow path and an outflow path on the plate so as to be connected to the latticed grooves.  
      Hereinafter, the operation of the bipolar plate of the fuel cell and the fabrication method thereof in accordance with the second embodiment of the present invention will be described.  
      The bipolar plates of the fuel cell construct a stack. Herein, by the channel region  53  formed at a side of the bipolar plate (BP) and a side of the M.E.A (M), a path in which fuel flows is formed. By the other side of the M.E.A (M) and a side of the other bipolar plate (BP) facing the bipolar plate (BP), a path in which air flows is formed.  
      In that structure, when fuel flows into the inflow path  54  of the bipolar plate (BP), as depicted in  FIG. 13 , fuel in the inflow path  54  flows all over the channel region  53  through the path formed by the latticed grooves  51  in the channel region  53 , and the fuel is discharged to the outside through the outflow path  55 .  
      In the process, by a small and uniform shape like the mesh formed by the latticed grooves  51  formed by the latticed protrusions  52  in the channel region  53 , the fluid can be not only spread out evenly but also diffused. Herein, by the latticed protrusions  52  formed in the channel region  53 , contact area of the bipolar plate (BP) and the M.E.A (M) is relatively reduced, and effective contact area of the fuel and the M.E.A (M) is increased.  
      In addition, air flows through the above-described process.  
      In the method for fabricating the bipolar plate of the fuel cell in accordance with the second embodiment of the present invention, by processing an inflow path and an outflow path mechanically at both sides of a rectangular plate having a certain thickness with a roller, etc., fabrication is simple and easy.  
       FIGS. 14 and 15  are a plane view and a sectional view respectively illustrating a third embodiment of a bipolar plate of a fuel cell in accordance with the present invention.  
      As depicted in  FIGS. 14 and 15 , the bipolar plate of the fuel cell in accordance with the third embodiment of the present invention includes a plate  60  having a certain thickness and area in which plural channels  61  consisting of plural ups and downs are formed at both sides on the middle by being pressed so as to have a certain width and length; and a sealing member  65  respectively adhered to the outline of the both sides of the plate  60  so as to form channels  62   a ,  62   b ,  62   c  with the channels  61  of the plate  60 , an inflow channel  63  and an outflow channel  64  in which a fluid flows in/out.  
      The plate  60  is constructed as a rectangular metal plate, and the channels  61  are formed in a certain internal region of the rectangular metal plate. The channels  61  consisting of plural ups and downs are formed on both sides of the plate  60  at regular intervals. By pressing the plate  60 , the channels  61  are respectively formed at both sides of the plate  60 , and the channels  61  have the uniform depth.  
      The sealing member  65  has a rectangular shape and has a certain width, it has the same thickness with a height of the ups of the channel  61  and has the same size with the plate  60 . Height of the ups of the channel  61  is approximately 2.5 mm.  
      The inflow channel  63  in which a fluid flows is formed at a side of the sealing member  65 , and the outflow channel  64  is formed so as to be opposite to the inflow channel  63 .  
      An internal channel formed by the sealing member  65  includes an inflow buffer channel  62   a  for distributing a fluid to the channels  61  of the plate  60 ; an outflow buffer channel  62   b  for making the fluid passing the channels  61  of the plate  60  flow into the outflow channel  64 ; and a connection channel  62   c  for connecting the inflow buffer channel  62   a  and the outflow buffer channel  62   b.    
      And, a method for fabricating a bipolar plate of a fuel cell in accordance with a third embodiment of the present invention will be described.  
       FIG. 16  is a flow chart illustrating a method for fabricating a bipolar plate of a fuel cell in accordance with a third embodiment of the present invention.  
      As depicted in  FIG. 16 , in the method for fabricating the bipolar plate of the fuel cell in accordance with the third embodiment of the present invention, a first step is for processing the plate  60  by cutting a metal plate having a certain thickness and area as a certain size, and a second steps if for press-processing the plate  60  in order to form plural channels  61  on both sides of the plate  60 . The metal plate  60  has a rectangular shape.  
      The channels  61  of the plate  60  are fabricated as straight and have a certain length, height of ups of the channels  61  are uniform. The channel  61  of the plate  60  can have various section shape such as waveform or rectangular form.  
      A third step is for combining the sealing member  65  with the outline of the press-processed plate  60 . The sealing member  65  is formed as a rectangular ring shape having a certain width and thickness, the sealing member  65  is combined with the outline of the plate  60  so as to encompassed the internal area of the plate  60 , and accordingly the channels  62   a ,  62   b ,  62   c  are formed. The inflow channel  63  and the outflow channel  64  are formed on the sealing member  65 . The inflow channel  63  and the outflow channel  64  can be formed by cutting part of the sealing member  65 .  
      Hereinafter, the operation of the bipolar plate of the fuel cell in accordance with the present invention will be described.  
      As described-above in the first embodiment of the present invention, a stack of a fuel cell is constructed. Herein, by the ups of the straight channel  61  formed on a side of the bipolar plate (BP) and a side of the M.E.A (M), a path in which fuel flows is formed. By the other side of the M.E.A (M) and downs of the straight channels  61  formed at a side of the other bipolar plate (BP) facing the bipolar plate (BP), a path in which air flows is formed.  
      In that structure, when fuel flows into the inflow channel  63  of the bipolar plate (BP), the fuel in the inflow channel  63  flows through the path, namely, the inflow buffer channel  62   a , the connection channel  62   c , the channel  61  and the outflow buffer channel  62   b . After that, the fuel is discharged to the outside through the outflow channel  64 . In addition, air flows by passing the above-described process.  
      And, in the present invention, by fabricating a metal plate by press-processing, fabrication is simple and easy. In addition, by reducing a thickness of the bipolar plate, size and weight of the stack can be reduced.  
     INDUSTRIAL APPLICABILITY  
      As described-above, in the bipolar plate of the fuel cell and the fabrication method thereof in accordance with the present invention, by uniformizing flux distribution of fuel and air respectively flowing into a fuel electrode and an air electrode of a fuel cell, increasing an reaction effective area with the M.E.A and increasing diffusion zone, power efficiency can be improved. By reducing flow resistance of fuel and air, pressure loss generating flow of the fuel and air, namely, pumping force can be reduced. In addition, by simplifying and facilitating fabrication, a production cost can be sharply reduced, and accordingly mass production is possible.