Patent Publication Number: US-2007122672-A1

Title: Fuel cell

Description:
CLAIM OF PRIORITY  
      This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C.§119 from an application for FUEL CELL earlier filed in the Korean Intellectual Property Office on 30 Nov. 2005 and there duly assigned Serial No. 10-2005-0115536.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a fuel cell that can generate electric energy using a reaction between fuel and oxygen.  
      2. Description of the Related Art  
      A fuel cell is an electricity generating system for directly converting energy, which is generated by chemical reaction between hydrogen contained in fuel and externally supplied oxygen, into electric energy. The oxygen supplied to unit cells of the fuel cell can be obtained from atmospheric air that flows by natural diffusion or convection.  
      When the fuel cell operates, vaporized moisture generated by a reduction reaction with the air is condensed when the moisture contacts atmospheric air. The condensed moisture or water may block an air flow path provided in the fuel cell. When the atmospheric air is not effectively supplied to the unit cells due to the condensed water that blocks the air flow path, the performance and reliability of the fuel cell are deteriorated. Therefore, it is required that the condensed water should be removed to improve the performance and reliability of a fuel cell.  
     SUMMARY OF THE INVENTION  
      The present invention provides a fuel cell that is designed to absorb moisture generated by an electrochemical reaction between fuel and oxygen. In an exemplary embodiment of the present invention, a fuel cell includes an electricity generation unit including an air supply unit, a fuel supply unit and an membrane electrode assembly (MEA) disposed between the air supply unit and the fuel supply unit, and an absorbing member that is installed on the air supply unit to absorb moisture. The absorbing member can be disposed between the air supply unit and the MEA. The air supply unit can be exposed to the atmospheric air. The absorbing member can closely contact an exposed of the air supply unit to the atmospheric air.  
      The absorbing member can be formed of a porous medium material. The air supply unit can be provided with a plurality of air holes through which the atmospheric air is supplied to the MEA. The absorbing member can be provided with a plurality of holes communicating with the airholes.  
      In another exemplary embodiment of the present invention, a fuel cell includes a medium member having at least one unit region and a manifold along which fuel flows, a fuel supply unit having a first passage along which the fuel flows and mounted on the unit region, MEA closely contacting the fuel supply unit, air supply unit having a second passage along which air flows and closely contacting the MEA, and an absorbing member that is installed on the air supply unit to absorb moisture.  
      The absorbing member can include a porous layer formed of a porous medium material and a moisture absorption layer formed on at least one surface of the porous layer. The moisture absorption layer can be formed of zeolite or phosphoric oxide (P 2 O 5 ). The absorbing member can be disposed between the air supply unit and the MEA such that the moisture absorption layer closely contacts the MEA.  
      The absorbing member can include a porous layer formed of a porous medium material and a moisture absorption layer formed on a surface of the porous layer. At this point, the moisture absorption layer can closely contact an exposed surface of the air supply unit. The air supply unit can be formed of a first current collection plate and the fuel supply units can be formed of a second current collection plate. The first and second current collection plates can differ in polarity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A more complete appreciation of the invention and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
       FIG. 1  is an exploded perspective view of a fuel cell constructed as an exemplary embodiment of the present invention;  
       FIG. 2  is a front view of a medium member shown in  FIG. 1 ;  
       FIG. 3  is an exploded perspective view of a medium member shown in  FIG. 2 ;  
       FIG. 4  is a front view of a fuel supply unit shown in  FIG. 1 ;  
       FIG. 5  is a front view of an air supply unit shown in  FIG. 1 ;  
       FIG. 6  is a sectional view of an electricity generation unit of a fuel cell constructed as an exemplary embodiment of the present invention;  
       FIG. 7  is an exploded perspective view of a fuel cell constructed as another exemplary embodiment of the present invention; and  
       FIG. 8  is a sectional view of an electricity generation unit of a fuel cell constructed as another exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings such that the present invention can be easily put into practice by those skilled in the art. However, the present invention is not limited to the exemplary embodiments, but can be embodied in various forms.  
       FIG. 1  is an exploded perspective view of a fuel cell constructed as an exemplary embodiment of the present invention. Referring to  FIG. 1 , fuel cell  100  is configured as an electricity generation system that is connected to an electronic device or integrally mounted in the electronic device to generate electric energy using an electrochemical reaction between fuel and oxygen, and to output the generated electric energy to the electronic device. Fuel cell  100  is directly supplied with an alcohol-based fuel such as methanol or ethanol and atmospheric air to generate the electric energy using an oxidation reaction of hydrogen contained in the fuel and a reduction reaction of the oxygen contained in atmospheric air.  
      Fuel cell  100  includes fuel cell main body  1 I that is supplied with a fuel from a fuel source (not shown) and atmospheric air that flows by natural diffusion or convection, and that generates electric energy by the oxidation/reduction reaction between the fuel and the atmospheric air. Fuel cell main body  11  is formed in a plate type with two opposite surfaces. Fuel cell  100  is configured to be supplied with the atmospheric air through both surfaces of fuel cell main body  11 .  
      Fuel cell  100  includes medium member  20  and a pair of electricity generation units  30  that are symmetrically disposed to face each other with medium member  20  interposed between the pair of electricity generation units  30 . Medium member  20  functions as a separator for separating electricity generation units  30  from each other. Medium member  20  is formed of an insulation material that allows a fuel to flow through both surfaces thereof. Medium member  20  will be described in more detail later with reference to  FIGS. 2 and 3 .  
      Electricity generation unit  30  is provided as a fuel cell having a plurality of unit cells, which generates electric energy using the reaction between a fuel and atmospheric air. Electricity generation unit  30  includes fuel supply unit  40  closely contacting a surface of medium member  20 , membrane-electrode assembly (MEA)  50  closely contacting fuel supply unit  40 , absorbing member  70  contacting MEA  50 , and air supply units  60  contacting absorbing member  70 .  
      Medium member  20  is formed in a rectangular shape. Medium member  20  includes a plurality of unit regions  21   a,  coupling grooves  21   b,  manifold  22 , outlet  22   a,  and inlet  22   b.  MEA  50  includes first electrode layer  51 , second electrode layer  52 , and electrolyte layers  53 . Air supply units  60  includes second passage  62  and air holes  63 . Absorbing member  70  includes a plurality of holes  75 . The function of each element will be described in detail referring to  FIGS. 2-6 .  
      As shown in  FIG. 2 , each surface of medium member  20  is provided with a plurality of unit regions  21   a  that are disposed on the surface of medium member  20  and are spaced apart from each other. Manifold  22 , which allows a fuel to flow with respect to fuel supply unit  40 , is formed in each unit region  21   a.  Fuel passage  23  communicating with manifold  22  is formed in medium member  20 .  
      Unit region  21   a  is an active area where a unit cell of electricity generation unit  30  is located, and a fuel is supplied to MEA  50  so that the reaction between the fuel and atmospheric air is actually performed in electricity generation unit  30 . Unit region  21   a  is formed extending in a lateral direction (vertical direction as shown in  FIG. 2 ), which is perpendicular to fuel passage  23 , and therefore the plurality of unit regions  21   a  commonly share fuel passage  23 . Unit regions  21   a  are spaced apart from each other in a longitudinal direction (horizontal direction as shown in  FIG. 2 ), which is parallel to fuel passage  23 . Each of unit regions  21  has coupling groove  21   b  to which each of fuel supply units  40  is respectively coupled. Coupling groove  21   b  also can be defined as a space formed between two unit regions  21   a  when unit region  21   a  protrudes outwards. In this case, majority portions of the surface of medium member  20  except coupling groove  21   b  become protruding portions, and coupling groove  21   b  is a space formed between the protruding portions.  
      Fuel passage  23  formed in medium member  20  extends in the longitudinal direction of medium member  20 . Fuel passage  23  includes first passage  23   a  along which a fuel is supplied from a fuel supply device (not shown), and second passage  23   b  along which a fuel from fuel supply unit  40  flows. At this point, first passage  23   a  is formed along a lower edge of medium member  20  while second passage  23   b  is formed along an upper edge of medium member  20 . First and second passages  23   a  and  23   b  are parallel to each other.  
      Manifold  22  formed in each unit region  21   a  of medium member  20  includes outlet  22   a  communicating with first passage  23   a  and inlet  22   b  communicating with second passage  23   b.  The fuel flowing along first passage  23   a  is directed to a passage of fuel supply unit  40  through outlet  22   a.  The fuel passing through fuel supply unit  40  is directed to second passage  23   b  through inlet  22   b.  In addition, medium member  20  is provided at a first side portion with fuel injection portion  24  through which a fuel is injected into first passage  23   a  of fuel passage  23 , and at a second side portion with fuel exhaust portion  25  through which the fuel passing through second passage  23   b  is exhausted. At this point, fuel injection portion  24  can be connected to the fuel supply device (not shown) through, for example, a typical pipe line.  
      As shown in  FIG. 3 , medium member  20  includes first and second halves  26  and  27  that face each other and are integrally assembled with each other, thereby forming fuel passage  23  shown in  FIG. 2 . First half  26  is provided at an inner surface with first grooves  26   a  corresponding to first and second passages  23   a  and  23   b.  Second member  27  is also provided at an inner surface with second grooves  27   a  corresponding to first and second passages  23   a  and  23   b.  The inner surfaces of first and second halves  26  and  27  face each other. Therefore, unit regions  21   a  are formed outer surfaces (opposite surfaces of the inner surfaces) of first and second halves  26  and  27 . When first and second halves  26  and  27  are assembled with each other in a manner that the inner surfaces of first and second halves  26  and  27  face each other, fuel passage  23  is formed in medium member  20 .  
      The following paragraphs will describe electricity generation units  30  symmetrically disposed on both opposite surfaces of medium member  20  as shown in  FIG. 1 . Electricity generation unit  30  includes fuel supply unit  40 , membrane-electrode assembly (MEA)  50 , absorbing member  70 , and air supply unit  60 .  
      Membrane-electrode assembly (MEA)  50  includes electrolyte membrane  53 , first electrode layer  51  formed on a first surface of electrolyte membrane  53 , and second electrode layer  52  formed on a second surface of electrolyte membrane  53 . First electrode layer  51  decomposes hydrogen contained in a fuel into electrons and hydrogen ions. Electrolyte membrane  53  moves the hydrogen ions to second electrode layer  52 . Second electrode layer  52  allows the electrons and hydrogen ions supplied from the first electrode layer  51  to react with oxygen contained in the atmospheric air so as to generate moisture and heat. MEA  50  has the same size as fuel supply unit  40  and air supply unit  60 . A typical gasket (not shown) can be provided on an edge of MEA  50 .  
      In the present exemplary embodiment, fuel supply unit  40  closely contacts first electrode layer  51  of MEA  50 , and is mounted on unit regions  21   a.  Fuel supply unit  40  distributes a fuel to first electrode layer  51  of MEA  50 . Fuel supply unit  40  also functions as a conductor for moving electrons, which are extracted from hydrogen contained in a fuel, to air supply unit  60  of electricity generation unit  30 .  
      As shown in  FIG. 4 , fuel supply unit  40  has first passage  42  along which a fuel flows and is mounted in corresponding unit region  21   a.  Fuel supply unit  40  is formed of a conductive metal plate, and designed in a manner that multiple fuel supply units  40  are fit in the size of MEA  50 . Fuel supply unit  40  is designed to be coupled to coupling groove  21   b  defined in unit region  21   a.    
      Since fuel supply unit  40  functions as a conductor for moving electrons to air supply unit  60  of electricity generation unit  30 , fuel supply unit  40  can include current collection plate (or a second current collection plate)  44  having a polarity that is different from that of air supply unit  60 .  
      Fuel supply unit  40  is provided with terminal portion  45  that is electrically connected to air supply unit  60  of electricity generation unit  30  through an electrical connector such as a conductive wire. Terminal portion  45  is integrally formed with fuel supply unit  40 . Terminal portion  45  is formed in protrusion  46  extending out of an edge of medium member  20 . If there are multiple fuel supply units  40 , fuel supply units  40  are arranged in a manner that protrusions of fuel supply units  40  are alternately heading upwards and downwards as shown in  FIG. 1 .  
      First passage  42  includes a plurality of flow paths that connect outlet  22   a  of manifold  22  to inlet  22   b  of the manifold  22  in order to distribute the fuel injected into first passage  23   a  of medium member  20  to first electrode layer  51  of the MEA  50 .  
      First passage  42  is made by forming a predetermined pattern on the plate of fuel supply unit  40 . For example, first passage  42  can have a plurality of straight lines that are spaced apart from each other, and are formed into a square wave shape (meander shape) as shown in  FIG. 4 . One end of first passage  42  is connected to outlet  22   a  of manifold  22 , and the other end is connected to inlet  22   b  of manifold  22 .  
      In the current exemplary embodiment, air supply unit  60  are arranged in close contact with absorbing member  70  which is in close contact with second electrode layer  52  of MEAs  50 . Air supply unit  60  functions to distribute air to second electrode layer  52  of MEA  50  by natural diffusion or a process of convection. Air supply unit  60  also functions as a conductor for receiving electrons from fuel supply unit  40 .  
      As shown in  FIG. 5 , air supply unit  60  has second passage  62  along which air is distributed to second electrode layer  52  of MEA  50 . Air supply unit  60  is formed of a conductive metal plate. Air supply unit  60  has a size corresponding to the size of fuel supply unit  40 . Second passage  62  includes a plurality of air holes  63  formed on a plane of air supply unit  60 .  
      Since air supply unit  60  functions as a conductor for receiving electrons from fuel supply unit  40 , air supply unit  60  can include a current collection plate (or a first current collection plate)  64  having a polarity that is different from that of fuel supply unit  40 .  
      Air supply unit  60  is provided with terminal portion  65  that is electrically connected to terminal portion  45  of fuel supply unit  40  of electricity generation unit  30  through an electrical connector such as a conductive wire. Terminal portion  65  is integrally formed with air supply unit  60 . That is, the terminal portion  65  is formed by a protrusion  66  extending out of an edge of medium member  20 . If there are multiple air supply units  60 , air supply units  60  are arranged in a manner that protrusions  66  of air supply units  60  are alternately heading upwards and downwards as shown in  FIG. 1 .  
      When above described fuel cell  100  operates, first electrode  51  of MEA  50  decomposes hydrogen contained in a fuel supplied through first passage  42  of fuel supply unit  40  into electrons and hydrogen ions by an oxidation reaction of the fuel. At this point, the hydrogen ions move to second electrode layer  52  through electrolyte layer  53 . The electrons cannot pass through electrolyte layer  53  but move to second electrode layer  52  of MEA  50  through the electrical connector that connects protrusion  66  of air supply unit  60  to protrusion  46  of fuel supply unit  40   
      At the same time, second electrode layer  52  generates vaporized moisture through a reduction reaction between the hydrogen ions supplied through electrolyte layer  53 , the electrons supplied through the electrical connector that connects air supply unit  60  to fuel supply unit  40 , and the oxygen contained in atmospheric air supplied through air holes  63  of air supply unit  60 .  
      During the above process, since air supply unit  60  is exposed to atmospheric air, the vaporized moisture generated in second electrode layer  52  is condensed in air holes  63  of air supply unit  60  as it contacts relatively low temperature atmospheric air. Therefore, the condensed water coheres with air holes  63  to block air holes  63  and thus atmospheric air cannot be effectively supplied to second electrode layer  52  through air holes  63 . In order to solve this problem, the present exemplary embodiment includes absorbing member  70  formed between air supply unit  60  and MEA  50 . Absorbing member  70  functions as a filter for absorbing the condensed water generated from second electrode layer  52 .  
       FIG. 6  is a sectional view of electricity generation unit  30  of fuel cell  100  to show arrangement of fuel supply unit  40 , MEA  50 , absorbing member  70 , and air supply unit  60 . As shown in  FIGS. 1 and 6 , absorbing member  70  is provided in the form of a sheet interposed between the air supply unit  60  and the MEA  50 . Absorbing member  70  includes porous layer  71  formed of a porous medium material and moisture absorption layer  73  integrally formed on at least one surface of porous layer  71 . Porous layer  71  can be formed of porous carbon paper or porous carbon cloth. That is, porous layer  71  functions as a storage unit for storing absorbed moisture. In addition, moisture absorption layer  73  formed on at least one surface of porous layer  71  can be formed of zeolite or phosphoric oxide (P 2 O 5 ).  
      Absorbing member  70  is interposed between air supply unit  60  and MEA  50 . That is, absorbing member  70  is disposed in close contact with second electrode layer  52  of MEA  50 . Absorbing member  70  is provided with a plurality of holes  75  communicating with air holes  63  of air supply unit  60  in order to effectively supply atmospheric air to second electrode layer  52  of MEA  50  through air holes  63  of air supply unit  60 . In other words, positions of holes  75  of absorbing member  70  is aligned to the positions of air holes  63  of air supply unit  60 .  
      The following will describe the operation of the above described fuel cell constructed as an exemplary embodiment of the present invention. Two electricity generation unit  30  are symmetrically disposed on both opposite surfaces of medium member  20 , and therefore, operation of one electricity generation unit  30  will be described. Fuel cell  100  is connected to an electronic device through a cable, or is integrally mounted in the electronic device. Air supply units  60  of electricity generation units  30  are exposed to atmospheric air through a surface of fuel cell main body  11 . In this state, a fuel supply device (not shown) supplies a fuel to first passage  23   a  of the medium member  20  through fuel injection portion  24 . Then, the fuel passing through first passage  23   a  is discharged through outlets  22   a  of manifolds  22 , and is distributed to first electrode layer  51  of MEA  50  through first passages  42  of fuel supply units  40 . At this point, the fuel that cannot be directed to first electrode layers  51  of MEAs  50  is directed to second passage  23   b  of medium member  20  through inlets  22   b  of second passage  23   b,  and is then exhausted through fuel exhaust portion  25 .  
      During the above process, since air supply unit  60  of the electricity generation unit  30  are exposed to atmospheric air, air is distributed to second electrode layer  52  of the MEA  50  through air holes  63  of air supply unit  60  by natural diffusion or convention thereof. Then, first electrode layer  51  of MEA  50  decompose hydrogen contained in a fuel into electrons and hydrogen ions (protons) through an oxidation reaction between the fuel and atmospheric air. The hydrogen ions (protons) move to second electrode layers  52  through electrolyte layers  53  of MEAs  50 . The electrons cannot pass through electrolyte layers  53 , but are directed to air supply units  60  of electricity generation units  30  through an electrical connector that connects protrusion  66  of air supply unit  60  to protrusion  46  of fuel supply unit  40 .  
      By the movement of the electrons, fuel cell  100  generates current, and thus fuel supply unit  40  and air supply unit  60 , which include current collection plates  44  and  64 , respectively, output electric energy having a predetermined potential difference to an electronic device.  
      Meanwhile, second electrode layer  52  generates heat and vaporized moisture through a reduction reaction between the hydrogen ions supplied through the electrolyte layers  53 , the electrons supplied through fuel supply unit  40  and air supply unit  60 , and atmospheric air supplied through air holes  63  of air supply units  60 .  
      The moisture generated from second electrode layer  52  of MEA  50  is absorbed by absorbing member  70  interposed between MEA  50  and air supply unit  60 . Since moisture absorption layer  73  of absorbing member  70  closely contacts second electrode layer  52  of MEA  50 , the moisture is absorbed by moisture absorption layer  73  and is then stored in porous layer  71 . The moisture stored in porous layer  71  is vaporized by the heat generated in second electrode layer  52  of MEA  50 .  
      Since the moisture generated from second electrode layer  52  of MEA  50  is effectively absorbed by absorbing member  70 , the blocking of the air holes  63  of air supply units  60  by the moisture can be prevented.  
      In the embodiment described above, a pair of electricity generation units  30  is provided on both opposite surfaces of medium member  20 , and air supply unit  60  of electricity generation unit  30  is exposed to atmospheric air through fuel cell main body  11 . However, the present invention is not limited to this structure. The fuel cell can be formed in a mono-polarity type, in which electricity generation unit  30  is a planar fuel cell main body and atmospheric air is supplied to one surface of the planar fuel cell main body.  
       FIG. 7  is an exploded perspective view of a fuel cell constructed as another exemplary embodiment of the present invention, and  FIG. 8  is an electricity generation unit of the fuel cell constructed as another exemplary embodiment of the present invention.  
      Referring to  FIGS. 7 and 8 , the structure of the fuel cell of this exemplary embodiment is basically identical to that of the fuel cell described referring to  FIG. 1 , except that relative positions of absorbing member  170  and air supply unit  160  are switched. Electricity generation unit  130  of this embodiment is designed to include absorbing member  170  disposed in close contact with an exposed (or outer) surface of air supply unit  160 . That is, absorbing member  170  of the present exemplary embodiment has a structure identical to that of fuel cell  100  described referring to  FIG. 1 , but a moisture absorption layer  173  contacts the exposed (or outer) surface of air supply unit  160 . Herein, the exposed or outer surface of an air supply unit is defined as a surface of the air supply unit that is exposed to atmospheric air or faces toward atmospheric air.  
      Since other structures and operation of the fuel cell of this embodiment are identical to those of the embodiment referring to  FIG. 1 , a detailed description thereof will be omitted herein.  
      Meanwhile, when absorbing member  170  is arranged on an exposed surface of air supply unit  160 , absorbing member  170  is able to absorb moisture generated outside the fuel cell main body (inside outer case of the fuel cell) as well as the moisture generated from the electricity generation unit. As a final product, an outer case is provided to enclose the fuel cell main body. Therefore, when the fuel cell operates, moisture may be generated inside the outer case due to a temperature difference between an interior and exterior of the outer case. The temperature of the interior of the outer case is relatively high due to the heat generated from the fuel cell main body.  
      When moisture remains in the outer case, a device coupled to the fuel cell can be adversely affected. Therefore, when the absorbing member is provided on the exposed surface of the air supply unit, the absorbing member absorbs moisture generated inside the outer case. Therefore, the damage of the device coupled to the fuel cell can be prevented.  
      In this case, the absorbing member may be formed of a material including melamine. The absorbing member may be substantially provided in the form of a sheet with an opening corresponding to the opening (for the airflow) of the outer case. Furthermore, the absorbing member can be formed in a multi-layer structure. At this point, a layer facing the outer case may be colored with a color corresponding to a color of the outer case.  
      In the embodiments described above, the absorbing member of the exemplary embodiment of the present invention is applied to a passive type fuel cell where the atmospheric air is directly supplied to the fuel cell main body. However, the present invention is not limited to this type of fuel cell. For example, the absorbing member may be applied to all of other types of fuel cells as well as the above described fuel cell.  
      According to the present invention, since the electricity generation unit has an absorbing member that can absorb moisture generated by the electrochemical reaction between the fuel and the oxygen, the blocking of the air holes of the air supply unit by the moisture can be prevented. Therefore, atmospheric air can be effectively supplied through the air holes of the air supply units and thus the performance efficiency and reliability of the fuel cell can be further improved. In addition, since the air supply units of the electricity generation unit are exposed to atmospheric air through the both opposite surface of the fuel cell main body, the air can be effectively supplied to the air supply units regardless of the user environment. Furthermore, the heat generated from the air supply units can be effectively dissipated. As a result, the output of the electric energy can be maximized and the hazard that may be caused by the increase of the temperature of the fuel cell main body can be avoided, thereby further improving the performance and reliability of the fuel cell.  
      Although the exemplary embodiments and the modified examples of the present invention have been described, the present invention is not limited to the embodiments and examples, but may be modified in various forms without departing from the scope of the appended claims, the detailed description, and the accompanying drawings of the present invention. Therefore, it is natural that such modifications belong to the scope of the present invention.