Patent Publication Number: US-2009226795-A1

Title: Fuel cell structure with external flow channels

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a fuel cell structure with external flow channels, and more particularly, to a fuel cell structure with external flow channels applicable to fuel cells. 
     2. Description of Related Art 
     A fuel cell is a device for converting chemical energy into electric energy and features continuous generation of electricity as long as the fuel cell is supplied constantly with fuel needed in chemical reactions in the fuel cell. Fuel cells are advantageous in many ways. For example, they are highly efficient in generating electricity, free of pollution and capable of rapid fuel replenishment. As such, fuel cells have been an important technology in developing green energy. Structurally speaking, a fuel cell includes a plurality of cathode and anode flow channels. Fuel is delivered continuously through the flow channels to sustain chemical reactions in the fuel cell and thereby generate electricity. Therefore, the design of flow channels in a fuel cell has direct impact on the efficiency of fuel delivery and is closely related to the fuel cell&#39;s performance. 
     U.S. Pat. No. 6,503,650B1 discloses a fuel cell system comprising a cell multilayer element formed by stacking a plurality of unit cells together, an oxidant channel unit and a fuel channel unit, wherein each of the unit cells has internal oxidant flow channels connected with the oxidant channel unit, and internal fuel flow channels connected with the fuel channel unit. 
     In the aforesaid U.S. Pat. No. 6,503,650B1 the oxidant channel unit is provided on an external surface of the cell multilayer element while the fuel channel unit is formed inside the cell multilayer element by the plurality of unit cells stacked together. Besides, a flow dividing device is required to connect the fuel channel unit with the internal fuel flow channels. 
     In the aforesaid U.S. patent, the oxidant channel unit and the fuel channel unit are particularly designed to prevent blockage of the supplying channels that lowers the efficiency of the fuel cell system. However, the fuel cell system still has the following disadvantages: 
     1. The shape of the fuel supplying channel, which is formed by stacking the plurality of unit cells together, will be affected if one of the unit cells is offset while being stacked. In that case, the efficiency of the entire fuel cell system will be compromised as a result. 
     2. Fuel fed into the unit cell must go through the flow dividing device to be uniformly distributed in the unit cell. In consequence, the fuel enters the unit cell at a reduced speed. 
     BRIEF SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a fuel cell structure with external flow channels, wherein oxygen flow channels, fuel flow channels and coolant flow channels are provided outside a fuel cell stack. As each of the flow channels is independently provided outside the fuel cell stack, it is easier and more convenient to install the external flow channels and connect them with internal flow channels, allowing the internal and external flow channels to be positioned relative to one another with improved precision. 
     Another objective of the present invention is to provide a fuel cell structure with external flow channels, in which the fuel cell structure is capable of simultaneously delivering fuel, oxidant and cooling fluid to a plurality of internal flow channels, thereby increasing the speed of fuel delivery and effectively removing waste heat generated by a fuel cell stack. 
     In order to achieve these objectives, the present invention provides a fuel cell structure with external flow channels, wherein the fuel cell structure comprises: a fuel cell stack formed by stacking a plurality of unit cells together, each of the unit cells having a plurality of internal oxidant flow channels, a plurality of internal fuel flow channels and a plurality of internal coolant flow channels; a first external oxidant flow channel connected with a surface of the fuel cell stack so as to communicate with first ends of all the internal oxidant flow channels; a second external oxidant flow channel connected with a surface of the fuel cell stack so as to communicate with second ends of all the internal oxidant flow channels; a first external fuel flow channel connected with a surface of the fuel cell stack so as to communicate with first ends of all the internal fuel flow channels; a second external fuel flow channel connected with a surface of the fuel cell stack so as to communicate with second ends of all the internal fuel flow channels; a first external coolant flow channel connected with a surface of the fuel cell stack so as to communicate with first ends of all the internal coolant flow channels; and a second external coolant flow channel connected with a surface of the fuel cell stack so as to communicate with second ends of all the internal coolant flow channels. 
     The present invention can be implemented to achieve at least the following advantageous effects: 
     1. The external flow channels are designed to allow precise connection between the internal and external flow channels. 
     2. By omitting the conventional step of forming a common flow channel by stacking a plurality of unit cells together, the production time of the fuel cell can be reduced. 
     3. The external flow channels are connected and in communication with the internal flow channels of the fuel cell stack to enable simultaneous delivery of oxidant, fuel and cooling fluid into each of the unit cells, thereby increasing the efficiency of the fuel cell stack and rapidly removing waste heat generated by the fuel cell stack. 
     4. The external flow channels are designed to increase a reaction area of electrodes in the fuel cell stack, thereby enabling the fuel cell stack to generate electricity more efficiently. 
     5. The flow channels provided outside the fuel cell stack can be made of materials other than metal to reduce the production cost and weight of the fuel cell. 
     A detailed description of further features and advantages of the present invention is given below, so that a person skilled in the art is allowed to understand and carry out the technical contents of the present invention, and can readily comprehend the objectives and advantages of the present invention by reviewing the contents disclosed herein, the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention as well as a preferred mode of use, further objectives and advantages thereof will be best understood by referring to the following detailed description of illustrative embodiments in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an exploded perspective view of a fuel cell structure with external flow channels according to an embodiment of the present invention; 
         FIG. 2  is an exploded perspective view of a unit cell according to the present invention; 
         FIG. 3A  is a cross-sectional view taken along a line A-A in  FIG. 1 ; 
         FIG. 3B  is a cross-sectional view taken along a line B-B in  FIG. 1 ; 
         FIG. 3C  is a cross-sectional view taken along a line C-C in  FIG. 1 ; and 
         FIG. 4  is an exploded perspective view of a fuel cell structure with external flow channels according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a structure of a fuel cell  10  with external flow channels according to an embodiment of the present invention comprises a fuel cell stack  11 , a first external oxidant flow channel  12 , a second external oxidant flow channel  13 , a first external fuel flow channel  14 , a second external fuel flow channel  15 , a first external coolant flow channel  16  and a second external coolant flow channel  17 . 
     The fuel cell stack  11  is formed by stacking a plurality of unit cells  20  together. Each of the unit cells  20  has a plurality of internal oxidant flow channels  21 , a plurality of internal fuel flow channels  22  and a plurality of internal coolant flow channels  23 . 
     As shown in  FIG. 2 , each of the unit cells  20  comprises an anode flow channel plate  24  having the plurality of internal fuel flow channels  22 , a membrane electrode assembly plate  25 , a cathode flow channel plate  26  having the plurality of internal oxidant flow channels  21 , and a coolant flow channel plate  27  having the plurality of internal coolant flow channels  23 . 
     Each of the internal oxidant flow channels  21  is formed with a first end  211  and a second end  212  provided respectively with openings  213  and  214 . Each of the internal fuel flow channels  22  is formed with a first end  221  and a second end  222  provided respectively with openings  223  and  224 . Each of the internal coolant flow channels  23  is formed with a first end  231  and a second end  232  provided respectively with openings  233  and  234 . In addition, the internal flow channels  22 ,  21  and  23  of the respective flow channel plates  24 ,  26  and  27  can be grate-like flow channels or serpentine flow channels. 
     The membrane electrode assembly plate  25  has at least one membrane electrode assembly. Generally, a membrane electrode assembly plate  25  comprises a gas diffusion layer, a cathode catalyst layer, an anode catalyst layer and an electrolyte layer. When oxidant and fuel flow respectively through the cathode flow channel plate  26  and the anode flow channel plate  24  flanking each membrane electrode assembly plate  25 , electrochemical reactions take place at the cathode and anode of each membrane electrode assembly plate  25  so that electric current is generated in each unit cell  20 . 
     As shown in  FIG. 3A , the first external oxidant flow channel  12  is connected with a surface of the fuel cell stack  11  so as to communicate with the first ends  211  of all the internal oxidant flow channels  21 . The first external oxidant flow channel  12  has at least one first oxidant delivery hole  121  and a first oxidant delivery cavity  122 , wherein the first oxidant delivery hole  121  is in communication with the first oxidant delivery cavity  122 , which in turn is in communication with the first ends  211  of all the internal oxidant flow channels  21 . Hence, the first external oxidant flow channel  12  can be used to supply oxidant, such as oxygen or air, into the fuel cell stack  11 . 
     Referring again to  FIG. 3A , the second external oxidant flow channel  13  is connected with a surface of the fuel cell stack  11  so as to communicate with the second ends  212  of all the internal oxidant flow channels  21 . The second external oxidant flow channel  13  has at least one second oxidant delivery hole  131  and a second oxidant delivery cavity  132 , wherein the second oxidant delivery hole  131  is in communication with the second oxidant delivery cavity  132 , which in turn is in communication with the second ends  212  of all the internal oxidant flow channels  21 . Therefore, the second oxidant delivery hole  131  of the second external oxidant flow channel  13  can be used to discharge unreacted oxidant. Alternatively, the second external oxidant flow channel  13  may also serve as an external flow channel for supplying oxidant into the fuel cell stack  11 . 
     Referring now to  FIG. 3B , the first external fuel flow channel  14  is connected with a surface of the fuel cell stack  11  so as to communicate with the first ends  221  of all the internal fuel flow channels  22 . The first external fuel flow channel  14  has at least one first fuel delivery hole  141  and a first fuel delivery cavity  142 , wherein the first fuel delivery hole  141  is in communication with the first fuel delivery cavity  142 , which in turn is in communication with the first ends  221  of all the internal fuel flow channels  22 . Hence, the first external fuel flow channel  14  can be used to supply fuel, such as hydrogen, into the fuel cell stack  11 . 
     Referring again to  FIG. 3B , the second external fuel flow channel  15  is connected with a surface of the fuel cell stack  11  so as to communicate with the second ends  222  of all the internal fuel flow channels  22 . The second external fuel flow channel  15  has at least one second fuel delivery hole  151  and a second fuel delivery cavity  152 , wherein the second fuel delivery hole  151  is in communication with the second fuel delivery cavity  152 , which in turn is in communication with the second ends  222  of all the internal fuel flow channels  22 . Therefore, the second fuel delivery hole  151  of the second external fuel flow channel  15  can be used to discharge unreacted fuel. Alternatively, the second external fuel flow channel  15  may also serve as an external flow channel for supplying fuel into the fuel cell stack  11 . 
     Referring now to  FIG. 3C , the first external coolant flow channel  16  is connected with a surface of the fuel cell stack  11  so as to communicate with the first ends  231  of all the internal coolant flow channels  23 . The first external coolant flow channel  16  has at least one first coolant delivery hole  161  and a first coolant delivery cavity  162 , wherein the first coolant delivery hole  161  is in communication with the first coolant delivery cavity  162 , which in turn is in communication with the first ends  231  of all the internal coolant flow channels  23 . Hence, the first external coolant flow channel  16  can be used to supply cooling fluid, such as a liquid coolant or air, into the fuel cell stack  11 . 
     Referring again to  FIG. 3C , the second external coolant flow channel  17  is connected with a surface of the fuel cell stack  11  so as to communicate with the second ends  232  of all the internal coolant flow channels  23 . The second external coolant flow channel  17  has at least one second coolant delivery hole  171  and a second coolant delivery cavity  172 , wherein the second coolant delivery hole  171  is in communication with the second coolant delivery cavity  172 , which in turn is in communication with the second ends  232  of all the internal coolant flow channels  23 . Therefore, the second coolant delivery hole  171  of the second external coolant flow channel  17  can be used to discharge the cooling fluid. Alternatively, the second external coolant flow channel  17  may also serve as an external flow channel for supplying the cooling fluid to the fuel cell stack  11 . 
     While manufacturing the fuel cell  10  with the external flow channels, all the external flow channels  12 ,  13 ,  14 ,  15 ,  16  and  17  can be made of materials other than metal, such as plastic. Therefore, not only the production cost, but also the overall weight of the fuel cell  10  with the external flow channels can be reduced. 
     As shown in  FIG. 4 , if the first ends  221  of all the internal fuel flow channels  22  and the first ends  231  of all the internal coolant flow channels  23  are located on a same surface of the fuel cell stack  11 , the first external fuel flow channel  14  and the first external coolant flow channel  16  may have an integrally formed structure divided by a partition  18 . Similarly, if the second ends  222  of all the internal fuel flow channels  22  and the second ends  232  of all the internal coolant flow channels  23  are located on a same surface of the fuel cell stack  11 , the second external fuel flow channel  15  and the second external coolant flow channel  17  may have an integrally formed structure divided by a partition  18 . 
     According to the structure of the fuel cell  10  with the external flow channels, oxidant and fuel can be fed in, for example, through the first oxidant delivery hole  121  and the first fuel delivery hole  141 , respectively. 
     Thereafter, the oxidant and fuel flow through the first external oxidant flow channel  12  and the first external fuel flow channel  14 , respectively. Since the first oxidant delivery cavity  122  and the first fuel delivery cavity  142  are respectively in communication with the first ends  211  and  221  of all the internal oxidant flow channels  21  and internal fuel flow channels  22 , the oxidant and the fuel are allowed to flow uniformly and simultaneously into the internal flow channels of each unit cell  20  via the openings  213  and  214  of all the internal oxidant flow channels  21  and all the internal fuel flow channels  22 , respectively, without the help of an additional flow dividing device. Thus, the oxidant and the fuel can enter each unit cell  20  more speedily while the external flow channels increase a reaction area of the electrodes in the fuel cell stack  11 , thereby enhancing the efficiency of the fuel cell stack  11 . 
     After entering each unit cell  20 , the oxidant and the fuel flow along the internal oxidant flow channels  21  of the cathode flow channel plate  26  and the internal fuel flow channels  22  of the anode flow channel plate  24 , respectively, so that the membrane electrode assembly plate  25  is supplied with the oxidant and the fuel and starts electrochemical reactions to generate electricity. Finally, unreacted oxidant flows through the openings  214  of the internal oxidant flow channels  21  and exits via the second oxidant delivery hole  131 , while unreacted fuel flows through the openings  224  of the internal fuel flow channels  22  and exits via the second fuel delivery hole  151 . 
     The structure of the fuel cell  10  with the external flow channels also allows an alternative way of oxidant and fuel delivery, in which oxidant and fuel are fed in through the second oxidant delivery hole  131  and the second fuel delivery hole  151 , respectively, whereas unreacted oxidant and fuel are discharged through the first oxidant delivery hole  121  and the first fuel delivery hole  141 , respectively. 
     The structure of the fuel cell  10  with the external flow channels may comprise a liquid-cooled fuel cell stack or a gas-cooled fuel cell stack. When the structure of the fuel cell  10  with the external flow channels comprises a liquid-cooled fuel cell stack, the first external coolant flow channel  16  and the second external coolant flow channel  17  are liquid-cooling external flow channels. Similarly, when the structure of the fuel cell  10  with the external flow channels comprises a gas-cooled fuel cell stack, the first external coolant flow channel  16  and the second external coolant flow channel  17  are gas-cooling external flow channels. 
     The structure of the fuel cell  10  with the external flow channels is cooled by a cooling liquid or gas entering through the first coolant delivery hole  161  of the first external coolant flow channel  16  and exiting through the second coolant delivery hole  171  of the second external coolant flow channel  17 . Alternatively, the cooling liquid or gas may be fed in through the second coolant delivery hole  171  and discharged through the first coolant delivery hole  161 . 
     Since the first coolant delivery cavity  162  of the first external coolant flow channel  16  and the second coolant delivery cavity  172  of the second external coolant flow channel  17  are respectively in communication with the first ends  231  and the second ends  232  of all the internal coolant flow channels  23 , the cooling liquid or gas will circulate through all the internal coolant flow channels  23  and thus remove waste heat generated from the electrochemical reactions in the fuel cell stack  11 , thereby protecting the fuel cell stack  11  from overheating. 
     The disclosed embodiments are intended to illustrate features of the present invention so as to enable a person skilled in the art to understand and implement the contents of the present invention. The embodiments, however, are not intended to limit the scope of the present invention. Therefore, all equivalent modifications or changes which do not depart from the spirit of the present invention should be encompassed by the appended claims.