Abstract:
A flat panel DMFC (direct methanol fuel cell) includes a first electrode plate, a set of membrane assemblies, at least a bonding sheet, a second electrode, and fuel container base. Because of the gap between the first/second electrode plates and the membrane assembly when they are laminated, the present invention provides a method to improve the contact between the first/second electrode plates and the membrane assembly.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to a flat panel fuel cell, and more particularly, to a method of improving the contact between bipolar plates and membrane electrode assembly of a flat panel fuel cell. 
   2. Description of the Prior Art 
   A fuel cell is an electrochemical cell in which a free energy change resulting from a fuel oxidation reaction is converted into electrical energy. Fuel cells utilizing methanol as fuel are typically called Direct Methanol Fuel Cells (DMFCs), which generate electricity by combining gaseous or aqueous methanol with air. DMFC technology has become widely accepted as a viable fuel cell technology that offers itself to many application fields such as electronic apparatuses, vehicles, military equipment, the aerospace industry, and so on. 
   DMFCs, like ordinary batteries, provide DC electricity from two electrochemical reactions. These reactions occur at electrodes (or poles) to which reactants are continuously fed. The negative electrode (anode) is maintained by supplying methanol, whereas the positive electrode (cathode) is maintained by the supply of air. When providing current, methanol is electrochemically oxidized at the anode electrocatalyst to produce electrons, which travel through the external circuit to the cathode electrocatalyst where they are consumed together with oxygen in a reduction reaction. The circuit is maintained within the cell by the conduction of protons in the electrolyte. One molecule of methanol (CH 3 OH) and one molecule of water (H 2 O) together store six atoms of hydrogen. When fed as a mixture into a DMFC, they react to generate one molecule of CO 2 , 6 protons (H+), and 6 electrons to generate a flow of electric current. The protons and electrons generated by methanol and water react with oxygen to generate water. 
   In terms of the amount of electricity generated, a DMFC can generate 300-500 milliwatts per centimeter squared. In general, conventional DMFCs are comprised of numerous basic cells and each cell only carries a limited amount of working voltage. Consequently, the cells need to be stacked together in order to achieve a required level of operational voltage. 
   SUMMARY OF INVENTION 
   It is therefore an objective of the present invention to provide a method of improving the contact between bipolar plates and the membrane electrode assembly of a flat panel fuel cell for solving the above-mentioned problems. 
   According to the preferred embodiment of the present invention, a method of improving the contact between bipolar plates and membrane electrode assembly of a flat panel fuel cell comprises the following steps: providing a first bipolar plate, a membrane electrode assembly, a second bipolar plate, and at least one bonding sheet; the MEA being disposed on the first bipolar plate, an opening being included in the bonding sheet for containing the MEA, and the second bipolar plate being disposed on the MEA; the first bipolar plate including a first MEA surface contacting the MEA and a fuel surface contacting the fuel, and the second bipolar plate including a second MEA surface contacting the MEA and an air surface contacting the air; a first metal layer being disposed on the metal surface, a second metal layer being disposed on the first MEA surface, a third metal layer being disposed on the second MEA surface, and a fourth metal layer being disposed on the air surface; the thickness of the second metal layer being greater than the thickness of the first metal layer and the thickness of the third metal layer being greater than the thickness of the fourth metal layer; and laminating the first bipolar plate, the MEA, the second bipolar plate, and the bonding sheet together for forming a bipolar/MEA assembly. 
   According to the second embodiment of the present invention, a method for improving the contact between bipolar plates and membrane electrode assembly (MEA) of a flat panel fuel cell comprises the following steps: providing a bipolar plate and a membrane electrode assembly (MEA), in which the bipolar plate includes at least one electrode region and the MEA is disposed on the electrode region of the bipolar plate; providing a plurality of conductive bumps on the electrode region; and contacting the membrane electrode assembly with the plurality of conductive bumps. 
   These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective diagram showing a conventional bipolar/MEA assembly of a flat panel fuel cell. 
       FIG. 2  is a perspective diagram showing a conventional bipolar/MEA assembly of a flat panel fuel cell after lamination. 
       FIG. 3  is a perspective diagram showing the bipolar/MEA assembly of a flat panel fuel cell according to the preferred embodiment of the present invention. 
       FIG. 4  is a perspective diagram showing the bipolar/MEA assembly of a flat panel fuel cell after lamination according to the preferred embodiment of the present invention. 
       FIG. 5  is a perspective diagram showing the bipolar/MEA assembly of a flat panel fuel cell according to the second embodiment of the present invention. 
       FIG. 6  is a perspective diagram showing the bipolar/MEA assembly of a flat panel fuel cell after lamination according to the second embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Please refer to  FIG. 1  and  FIG. 2 .  FIG. 1  and  FIG. 2  are perspective diagrams showing the bipolar/MEA assembly of a flat panel fuel cell before and after lamination. As shown in  FIG. 1 , the bipolar/MEA assembly  300  includes a first bipolar plate  320 , at least one bonding sheet  330 , a membrane electrode assembly (MEA)  340 , and a second bipolar plate  350 . The first bipolar plate  320  includes a first substrate  322 , a first metal layer  324  disposed on the upper surface of the first substrate  322 , and a second metal layer  326  disposed on the lower surface of the first substrate  322 . The second bipolar plate  350  includes a second substrate  352 , a third metal layer  354  disposed on the upper surface of second substrate  352 , and a fourth metal layer  356  disposed on the lower surface of the second substrate  352 . The metal layers described previously are equal in thickness and the first metal layer  324 , the second metal layer  326 , the third metal layer  354 , and the fourth metal layer  356  can be comprised of copper metals. 
   As shown in  FIG. 2 , a laminating process is then performed to contact the second metal layer  326  and the third metal layer  354  to the MEA  340 . However, the stress induced by metal layers will often cause problems such as extra spacing and poor adhesion between the second metal layer  326 , the third metal layer  354 , and the MEA  340 . In addition, a change in amount of pressure exerted on the MEA  340  may also cause the MEA  340  to produce an uneven thickness and corrugated surface, and a change in temperature may cause a separation to the bipolar plates as a result of expansion or shrinkage. Consequently, various effects caused after the lamination will bring an increase in cost and decrease in manufacture efficiency for the bipolar/MEA assembly  300 . 
   Please refer to  FIG. 3  and  FIG. 4 .  FIG. 3  and  FIG. 4  are perspective diagrams showing a method for improving the contact between the bipolar plates and the MEA of a flat panel fuel cell according to the preferred embodiment of the present invention. As shown in  FIG. 3 , the bipolar/MEA assembly  400  includes a first bipolar plate  420 , at least one bonding sheet  430 , a membrane electrode assembly (MEA)  440 , and a second bipolar plate  450 . The first bipolar plate  420  includes a first substrate  422 , a first metal layer  424  disposed on the upper surface of the first substrate  422 , and a second metal layer  426  disposed on the lower surface of the first substrate  422 . The second bipolar plate  450  includes a second substrate  452 , a third metal layer  454  disposed on the upper surface of second substrate  452 , and a fourth metal layer  456  disposed on the lower surface of the second substrate  452 . The first metal layer  424 , the second metal layer  426 , the third metal layer  454 , and the fourth metal layer  456  can be comprised of copper metals. The thickness of the second metal layer  426  is greater than the thickness of the first metal layer  424  and the thickness of the third metal layer  454  is greater than the thickness of the fourth metal layer  456 . In addition, the first substrate  422  and the second substrate  452  can be comprised of glass fiber reinforced polymeric materials, such as FR-1, FR-2, FR-3, FR-4, FR-5, CEM-1, or CEM-3 ANSI grade. The MEA can be Nafion membrane electrode assembly from DuPont Corp., or any other solid state membrane electrode assembly with similar functions, whereas the bonding sheet can be made of prepreg B-stage resin commonly utilized in printed circuit board (PCB) fabrication. 
   As shown in  FIG. 4 , a laminating process is performed next to bind the first bipolar plate  420 , the MEA  440 , the second bipolar plate  450 , and the bonding sheet  430  together for forming a bipolar/MEA assembly  400 . 
   Please refer to  FIG. 5  and  FIG. 6 .  FIG. 5  and  FIG. 6  are perspective diagrams showing another embodiment for improving the contact between the bipolar plates and the MEA of a flat panel fuel cell according to the present invention. As shown in  FIG. 5 , the bipolar/MEA assembly  500  includes a first bipolar plate  520 , at least one bonding sheet  530 , a membrane electrode assembly (MEA)  540 , and a second bipolar plate  550 . The first bipolar plate  520  includes a first substrate  522  and at least one electrode region  524 , in which a plurality of conductive bumps  528  is disposed on the lower surface  526  of the electrode region  524 . The second bipolar plate  550  includes a second substrate  552  and at least one electrode region  554 , in which a plurality of conductive bumps  558  is disposed on the upper surface  556  of the electrode region  554 . The conductive bumps  528 ,  558  can be comprised of tin, lead, tin-lead alloy, or copper, the outmost layer of the conductive bumps  528 ,  558  may include an Au-plating layer disposed thereon, and the thickness of the conductive bumps  528 ,  558  can be greater than 0.1 mm. 
   In addition, the first substrate  522  and the second substrate  552  can be comprised of glass fiber reinforced polymeric materials, such as FR-1, FR-2, FR-3, FR-4, FR-5, CEM-1, or CEM-3 ANSI grade and the MEA can be Nafion membrane electrode assembly from DuPont Corp., or any other solid state membrane electrode assembly with similar functions, whereas the bonding sheet can be made of prepreg B-stage resin commonly utilized in PCB fabrication. 
   As shown in  FIG. 6 , a laminating process is then performed to bind the first bipolar plate  520 , the MEA  540 , the second bipolar plate  550 , and the bonding sheet  530  together for forming a bipolar/MEA assembly  500 . 
   In contrast to the conventional method, the disclosed method for improving the contact between bipolar plates and membrane electrode assembly of a flat panel fuel cell provides numerous advantages. By utilizing upper and lower metal layers having different thickness and the conductive bumps on the surface of the electrode region of the MEA, the present invention is able to effectively reduce the contact inability problem between the bipolar plates and the MEA, which is caused by the uneven thickness and decrease in thickness of the MEA after lamination. Moreover, an increase in electric power can also be achieved by applying an appropriate amount of pressure to the MEA. 
   Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.