Patent Publication Number: US-2006019129-A1

Title: Planar fuel cell assembly

Description:
FIELD OF THE INVENTION  
      The present invention relates to a planar fuel cell assembly, and more particularly to a planar fuel cell assembly which is easily fabricated and suitable for mass production.  
     BACKGROUND OF THE INVENTION  
      Fuel cells are well known and commonly used to produce electrical energy by means of electrochemical reactions. Comparing to the conventional power generation apparatus, fuel cells have advantages of less pollutant, lower noise generated, increased energy density and higher energy conversion efficiency. Fuel cells can be used in portable electronic products, home-use or plant-use power generation systems, transportation, military equipment, space industry, large-size power generation systems, etc.  
      According to the electrolytes, fuel cells are typically classified into several types, e.g. an alkaline fuel cell (AFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a solid oxide fuel cell (SOFC) and a proton exchange membrane fuel cell (PEMFC). Depending on types of the fuel cells, the operation principles are somewhat different. For example, in the case of a direct methanol fuel cell (DMFC) which has the same structure as the PEMFC but uses liquid methanol instead of hydrogen as a fuel source, methanol is supplied to the anode, an oxidation reaction occurs in the presence of a catalyst, and protons, electrons and carbon dioxide are generated. The protons reach the cathode through the proton exchange membrane. Meanwhile, in the cathode, oxygen molecules take electrons from the anode and are reduced to oxygen ions by reduction. The oxygen ions react with hydrogen ions from the anode and thus produce water.  
      As know, an individual fuel cell unit supplies limited voltage (approximately 0.4 V). For a purpose of offering a sufficient operating voltage to an electronic product, a plurality of fuel cell units are connected in series so as to form a fuel cell assembly. Depending on the arrangement of the fuel cell units, the fuel cell assemblies can be divided into two types, i.e. a stacked fuel cell assembly and a planar fuel cell assembly.  
      Referring to  FIG. 1 , an exploded view of a conventional stacked fuel cell assembly is illustrated. The stacked fuel cell assembly  10  comprises at least two membrane-electrolyte assemblies (MEAs)  11 , a bipolar plate  12  located between two adjacent MEAs  11  and two electrode plates  13  and  14  at opposite ends of the fuel cell assembly. Each MEA  11  includes an anode  111 , a proton exchange membrane  112  and a cathode  113 . The bipolar plate  12  comprises a plurality of channels  121  for flowing fuels and oxygen molecules therethrough. However, since the stacked fuel cell assembly  10  requires a large amount of cell units to be assembled in a stacked form, the thickness and the weight thereof are considerably high. Therefore, the usage of such stacked fuel cell assembly is restricted in some situations.  
      Referring to  FIG. 2 , an exploded view of a conventional planar fuel cell assembly is illustrated. The planar fuel cell assembly  20  comprises a metal frame  21 , a plurality of membrane-electrolyte assemblies (MEAs)  22  and two electrode plates  23  and  24  at opposite ends of the fuel cell assembly. Likewise, each MEA  22  includes an anode, a proton exchange membrane and a cathode (not shown), and is embedded in the corresponding opening  211  of the frame  21 . Furthermore, two current collectors  212  are disposed at one side of the frame  21  as the current output terminals of the planar fuel cell assembly  20 . Each of the electrode plates  23  and  24  comprises channels  231  for flowing fuels and oxygen molecules therethrough. However, the metal frame  21  used in the planar fuel cell assembly  20  is both bulky and weighty. In addition, the procedure of aligning the MEAs  22  in the corresponding openings  211  of the frame  21  is complex and time-consuming. Such planar fuel cell assembly  20  is costly to manufacture, and also contribute a substantial weight and volume to the overall fuel cell assembly. In other words, such planar fuel cell assembly fails to be used in portable electronic products.  
     SUMMARY OF THE INVENTION  
      The present invention provides a planar fuel cell assembly, which is easily fabricated and suitable for mass production.  
      In accordance with the present invention, there is provided a planar fuel cell assembly. The planar fuel cell assembly comprises a plurality of fuel cell units and a first channel-forming plate. The plurality of fuel cell units are connected in series. Each fuel cell unit comprises a meshed metal plate and a membrane-electrolyte assembly. The membrane-electrolyte assembly of each fuel cell unit has a first side in contact with a second portion of the meshed metal plate and a second side in contact with a first portion of the meshed metal plate of an adjacent fuel cell unit. The first channel-forming plate cooperates with the plurality of fuel cell units to define a channel for flowing a fluid fuel therethrough.  
      In an embodiment, the meshed metal plate of each fuel cell unit is fabricated by punching a plurality holes in a metal piece.  
      In an embodiment, the first channel-forming plate is integrally formed of a plastic material by an injection molding process.  
      In an embodiment, each membrane-electrolyte assembly includes an anode, a proton exchange membrane and a cathode.  
      Preferably, the fluid fuel is in a gaseous or liquid state.  
      In an embodiment, the first portion and the second portion of the meshed metal plate are disposed at different levels by a gap.  
      In an embodiment, an edge of the membrane-electrolyte assembly is bonded to a connection portion between the first portion and the second portion of the meshed metal plate.  
      In an embodiment, the edge of the membrane-electrolyte assembly is bonded to the connection portion via an adhesive material.  
      In an embodiment, the second side of the membrane-electrolyte assembly is in contact with the first portion of the meshed metal plate of the adjacent fuel cell unit such that the top surface of the first portion of the adjacent fuel cell unit is substantially at the same level as that of the fuel cell unit.  
      In an embodiment, the first channel-forming plate comprises a depression portion enclosed by protruding edges thereof and a plurality of raised rods provided on the depression portion, wherein the raised rods along with the depression portion and the protruding edges define the channel for flowing the fluid fuel therethrough.  
      In an embodiment, a plurality of supporting blocks are disposed beside the protruding edges and the raised rods for supporting the plurality of fuel cell units.  
      In an embodiment, the plurality of fuel cell units are connected with the supporting blocks via an adhesive material.  
      In an embodiment, the planar fuel cell assembly further comprises a decorative plate disposed on the plurality of fuel cell units and the first channel-forming plate.  
      In an embodiment, the decorative plate and the first channel-forming plate are bonded together by means of an ultrasonic welding technique.  
      In an embodiment, the decorative plate is secured to the first channel-forming plate by tenons, screws or resilience sheets.  
      In an embodiment, the decorative plate is made of a plastic material.  
      In an embodiment, the first channel-forming plate further comprises weld lines corresponding to the periphery of the plurality of fuel cell units so as to facilitate sealing the fuel cell units and prevent leakage of the fluid fuel.  
      In an embodiment, the planar fuel cell assembly further comprises a second channel-forming plate disposed on the plurality of fuel cell units and the first channel-forming plate, the structures of the second channel-forming plate and the first channel-forming plate being substantially identical.  
      In an embodiment, the planar fuel cell assembly further comprises a blower disposed at an inlet of the second channel-forming plate for enhancing the flow rate of the air flowing through the second channel-forming plate.  
      In an embodiment, the planar fuel cell assembly further comprises two current collectors connected to the two terminal fuel cell units and acting as the current output terminals of the planar fuel cell assembly.  
      The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an exploded view of a stacked fuel cell assembly according to prior art;  
       FIG. 2  is an exploded view of a planar fuel cell assembly according to prior art;  
       FIG. 3 (A) is an exploded view of a fuel cell unit according to a preferred embodiment of the present invention;  
       FIG. 3 (B) is a perspective view of the fuel cell unit in  FIG. 3 (A);  
       FIG. 4 (A) is an exploded view illustrating a plurality of fuel cell units of  FIG. 3 (B) connected in series;  
       FIG. 4 (B) is a perspective view of the series-connected fuel cell units in  FIG. 4 (A);  
       FIG. 5 (A) is an exploded view illustrating a planar fuel cell assembly according to a first preferred embodiment-of the present invention;  
       FIG. 5 (B) is a perspective view of the planar fuel cell assembly in  FIG. 5 (A);  
       FIG. 6 (A) is an exploded view illustrating a planar fuel cell assembly according to a second preferred embodiment of the present invention;  
       FIG. 6 (B) is a perspective view of the planar fuel cell assembly in  FIG. 6 (A);  
       FIG. 6 (C) is a cross-sectional view of the channel-forming plate of  FIG. 6 (A) along the line AA;  
       FIG. 7 (A) is an exploded view illustrating a planar fuel cell assembly according to a third preferred embodiment of the present invention; and  
       FIG. 7 (B) is a perspective view of the planar fuel cell assembly in  FIG. 7 (A). 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring to FIGS.  3 (A) and  3 (B), a fuel cell unit according to a preferred embodiment of the present invention is shown. In this embodiment, the fuel cell unit  31  comprises a meshed metal plate  311  and a membrane-electrolyte assembly (MEA)  312 . The meshed metal plate  311  can be made by punching a plurality holes in a metal piece. Alternatively, the common metallic mesh can be used as the meshed metal plate  311 . For a purpose of reducing cost, the meshed metal plate  311  can be made of an ignoble metal (for example iron or copper), and the surface of the meshed metal plate  311  can be coated with a noble metal (for example gold or silver) for corrosion protection. The meshed metal plate  311  comprises a first portion  3111  and a second portion  3112  disposed at different levels by a gap of “d”. The MEA  312  is disposed on the second portion  3112 , and includes an anode, a proton exchange membrane and a cathode (not shown). The first side  3121  of the MEA  312  is in contact with the top surface  31121  of the second portion  3112 . The edge of the MEA  312  is bonded to the connection portion  3113  between the first portion  3111  and the second portion  3112  by an adhesive dispensing machine (not shown). The second side  3122  of the MEA  312  is either an anode or a cathode to be electrically connected to the adjacent fuel cell unit.  
      For a purpose of offering a sufficient operating voltage to an electronic product, a plurality of fuel cell units shown in  FIG. 3 (B) can be connected in series so as to form a fuel cell assembly. Please refer to FIGS.  4 (A) and  4 (B), which illustrate a plurality of fuel cell units connected in series. For neat drawings, however, only three fuel cell units  31  are shown in the drawing. Each fuel cell unit  31  is electrically connected to the previous one via the bottom surface  31112  of the first portion  3111 , and electrically connected to the next one via the second side  3122  of the MEA  312 . In such way, the top surfaces  31111  of the first portions  3111  of all fuel cell units  31  are substantially at the same level. Depending on the required operating voltage, the number of the fuel cell units  31  is varied.  
      Since fuels are essentials for the fuel cell, the fuel cell assembly provided by the present invention further comprises a channel-forming plate  32 , as is illustrated in FIGS.  5 (A) and  5 (B). The channel-forming plate  32  is integrally formed of a plastic material by an injection molding process. The channel-forming plate  32  comprises a depression portion  321  enclosed by the protruding edges  320  thereof. Several raised rods  322  are provided on the depression portion  321 . The raised rods  322 , along with the depression portion  321  and the protruding edges  320 , define a channel  323  for flowing a fluid fuel therethrough. The channel-forming plate  32  is further provided with a fuel inlet  324  and a fuel outlet  326  on opposite edges thereof for introducing and discharging the fluid fuel, respectively. There are many supporting blocks  325  disposed beside the protruding edges  320  and the raised rods  322  for supporting the fuel cell units  31 .  
      The fuel cell units  31  connected in series can be arranged in a line. Alternatively, the arrangement of the series-connected fuel cell units  31  can be changed as required. For example, as shown in FIGS.  5 (A) and  5 (B), the series-connected fuel cell units  31  comprises two type-A series-connected groups, three type-B series-connected groups and two current collectors C 1  and C 2 . Each type-A series-connected group comprises one fuel cell unit arranged in the vertical direction. Whereas, each type-B series-connected group comprises three fuel cell units connected in the horizontal direction. For clarification, the designations A 1 ˜A 2  and B 1 ˜B 9  denote the first portions  3111  of the meshed metal plates  311  of the fuel cell units  31  for the type-A and type-B series-connected groups, respectively. The current collectors C 1  and C 2  act as the current output terminals of the planar fuel cell assembly  3 .  
      After the fuel cell units  31  are connected in series and supported on the supporting blocks  325  of the channel-forming plate  32  as shown in  FIG. 5 (B), the connection portions between the supporting blocks  325  and the fuel cell units  31  are then sealed by the adhesive dispensing machine as described above. By the way, the top surface of the resulting planar fuel cell assembly  3  is exposed to the ambient air. Take a direct methanol fuel cell (DMFC) for example. During operation of such planar fuel cell assembly  3 , methanol is supplied into the channel  323  of the channel-forming plate  32  via the fuel inlet  324 . In the anode, an oxidation reaction occurs in the presence of a catalyst, and thus protons, electrons and carbon dioxide are generated. The protons reach the cathode through the proton exchange membrane to the cathode. The oxygen molecules containing in the air will flow through the meshed metal plate of the individual fuel cell unit to the cathode. Meanwhile, in the cathode, oxygen molecules take electrons from the anode and are reduced to oxygen ions by reduction. The oxygen ions react with hydrogen ions from the anode and thus produce water.  
      A further embodiment of a planar fuel cell assembly is illustrated in FIGS.  6 (A)- 6 (C). In this embodiment, the arrangement of the series-connected fuel cell units  31  and the channel-forming plate  32  included therein are similar to those shown in  FIG. 5 , and are not to be redundantly described herein. However, a decorative plate  33  is further provided on the fuel cell units  31  and the channel-forming plate  32 . The decorative plate  33  is made of plastic and comprises a plurality of hollow regions  330  for exposing the first portion  3111  of the individual meshed metal plate  311 . The decorative plate  33  is preferably bonded to the channel-forming plate  32  by means of a well-known ultrasonic welding technique. Alternatively, the decorative plate  33  is secured to the channel-forming plate  32  by other means such as tenons, screws or resilience sheets. In addition, the supporting blocks  325  beside the raised rods  322  of the channel-forming plate  32  can be provided with weld lines  326 , as shown in  FIG. 6 (C). When the ultrasonic welding technique is performed, the weld lines  326  will be melted and flow to the periphery of the fuel cell units  31  so as to facilitate sealing the fuel cell units  31  and prevent leakage of the fuel. When comparing with the conventional technology using the adhesive dispensing machine, the process of fixing the respective components of the planar fuel cell assembly  3  by using the ultrasonic welding technique is more convenient and simpler.  
      A further embodiment of a planar fuel cell assembly is illustrated in FIGS.  7 (A) and  7 (B). In this embodiment, the arrangement of the series-connected fuel cell units  31  and the channel-forming plate  32  included therein are similar to those shown in  FIG. 5 , and are not to be redundantly described herein. However, another channel-forming plate  34  is provided on the fuel cell units  31  and the channel-forming plate  32 . The structure of the channel-forming plate  34  is substantially the same as that of the channel-forming plate  32 . The arrangement of the channel-forming plate  34  facilitates preventing the fuel cell units from exposing to the ambient dust and moisture when the fuel cell assembly is used outdoors. For a purpose of enhancing amount of the supplied oxygen molecules and thus increasing the reaction in the cathode, a blower  35  is provided at the inlet  341  of the channel-forming plate  34 . The flow pressure of the supplied air can be also further increased if the diameter of the outlet  346  of the channel-forming plate  34  is smaller that of the inlet  341 . By the way, some marks, pictures, slogans or warning phrases can be printed on the outer surface of the channel-forming plate  34 , depending on the requirement.  
      From the above description, the planar fuel cell assembly of the present invention is assembled by a plurality of fuel cell units connected in series and at least one channel-forming plate. For the individual fuel cell unit, the specific structures of the meshed metal plate  311  and the membrane-electrolyte assembly (MEA)  312  are advantageous for mass production of the planar fuel cell assembly. In addition, the arrangement of the decorative plate  33  facilitates sealing the fuel cell units and prevents leakage of the fuel, and the process of fixing the respective components of the planar fuel cell assembly  3  is more convenient and simpler when using the ultrasonic welding technique. Alternatively, the arrangement of the additional channel-forming plate  34  facilitates preventing the fuel cell units from exposing to the ambient dust and moisture and thus the pot life of the planar fuel cell assembly  3  is increased. Since the bulky metal frame and the bipolar plate used in the conventional fuel cell assembly are omitted, the overall weight of the present planar fuel cell assembly is reduced. Furthermore, the meshed metal plate  311  is rigid enough for supporting and fixing the membrane-electrolyte assembly (MEA)  312 , and the fuel cell units  31  can be effectively secured on the supporting blocks  325  of the channel-forming plate  32 .  
      While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.