Patent Publication Number: US-2021184230-A1

Title: Separator for Fuel Cell

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Korean Patent Application No. 10-2019-0167580, filed in the Korean Intellectual Property Office on Dec. 16, 2019, which application is hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a separator for a fuel cell. 
     BACKGROUND 
     In a polymer electrolyte membrane fuel cell (PEMFC), air and fuel (hydrogen) are supplied to a cathode and an anode of a fuel cell stack as reactant gases. The air or the fuel is supplied to the cathode or the anode after being humidified in a humidifier. Water is produced in a fuel cell reaction. In consideration of this, the degree of humidification by the humidifier is determined. When the air and the fuel flow in opposite directions, the fuel cell reaction occurs more at downstream sides of the reactant gases than at upstream sides thereof. Therefore, at the upstream sides of the reactant gases, an electrolyte membrane is likely to be degraded due to low moisture content of the electrolyte membrane. Because the air is mainly humidified, the aforementioned problem mainly arises at the upstream side of the air flow. To solve this problem, changing the structure of a separator may be considered. However, the difficulty level of development or manufacture may be raised. 
     SUMMARY 
     Embodiments of the present disclosure have been made to solve problems occurring in the prior art while advantages achieved by the prior art are maintained intact. 
     An embodiment of the present disclosure provides a separator for a fuel cell that is capable of solving a problem of degradation in an electrolyte membrane that mainly occurs at upstream sides of reactant gases, in spite of the use of an existing separator without change. 
     The technical problems to be solved by embodiments of the present disclosure are not limited to the aforementioned problems, and any other technical problems not mentioned herein will be clearly understood from the following description by those skilled in the art to which the present disclosure pertains. 
     According to an embodiment of the present disclosure, a separator for a fuel cell includes a main body having an inlet manifold for inflow of a reactant gas, an outlet manifold for outflow of the reactant gas, and a flow area where the reactant gas flows between the inlet manifold and the outlet manifold, and a resistance part that is provided in the flow area of the main body so as to be adjacent to the inlet manifold of the main body and that increases flow resistance to the reactant gas introduced from the inlet manifold and flowing toward the outlet manifold. 
     In an embodiment, the flow area may include a reaction area having a reactant gas guide channel disposed therein, in which the reactant gas guide channel guides the reactant gas to electrodes of a membrane electrode assembly, and a diffusion area located between the reaction area and the inlet manifold and having a diffusion channel disposed therein, in which the diffusion channel diffuses, toward the reaction area, the reactant gas introduced from the inlet manifold. The resistance part may be disposed in the diffusion channel in the diffusion area. 
     In an embodiment, the resistance part may include a diffusion-area porous body that lowers flow speed of the reactant gas passing through the diffusion channel. 
     In an embodiment, the diffusion-area porous body may be formed to be more hydrophilic than a reaction-area porous body that is disposed in the reaction area and that forms the reactant gas guide channel. 
     In an embodiment, the diffusion-area porous body may be integrated with a reaction-area porous body that is disposed in the reaction area and that forms the reactant gas guide channel. 
     In an embodiment, the inlet manifold may include a first inlet manifold for inflow of air and a second inlet manifold for inflow of hydrogen, and the outlet manifold may include a first outlet manifold for outflow of the air and a second outlet manifold for outflow of the hydrogen. The first and second inlet manifolds and the first and second outlet manifolds may be disposed such that the air and the hydrogen flow in opposite directions and a line drawn from the first inlet manifold to the first outlet manifold crosses a line drawn from the second inlet manifold to the second outlet manifold. The flow area may include a first reaction area having a first reactant gas guide channel disposed therein, in which the first reactant gas guide channel guides the air to a cathode of a membrane electrode assembly, and a first diffusion area located between the first reaction area and the first inlet manifold and having a first diffusion channel disposed therein, in which the first diffusion channel diffuses, toward the first reaction area, the air introduced from the first inlet manifold. The resistance part may be disposed in the first diffusion channel in the first diffusion area. 
     In an embodiment, the resistance part may include an upper portion disposed in an area of the first diffusion channel that is adjacent to the first inlet manifold, and a lower portion disposed in an area of the first diffusion channel that is adjacent to the second outlet manifold. The upper portion of the resistance part may be formed to be more hydrophilic than the lower portion of the resistance part. 
     In an embodiment, the inlet manifold may be configured to introduce air as the reactant gas, and the outlet manifold may be configured to release the air. 
     According to another embodiment of the present disclosure, a separator for a fuel cell includes a main body having an inlet manifold for inflow of a reactant gas, an outlet manifold for outflow of the reactant gas, and a flow area where the reactant gas flows between the inlet manifold and the outlet manifold, and a resistance part that is provided in the flow area of the main body so as to be adjacent to the inlet manifold of the main body and that allows moisture in the reactant gas introduced from the inlet manifold and flowing toward the outlet manifold to stagnate. 
     In an embodiment, the flow area may include a reaction area in which a reaction-area porous body that forms a reactant gas guide channel that guides the reactant gas to electrodes of a membrane electrode assembly is disposed. The reaction-area porous body may include an upstream portion that is disposed adjacent to the inlet manifold and into which the reactant gas flows, and a downstream portion disposed downstream of the upstream portion. The upstream portion of the reaction-area porous body may be formed to be more hydrophilic than the downstream portion of the reaction-area porous body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of embodiments of the present disclosure will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a plan view illustrating a separator to which an embodiment of the present disclosure is applied; 
         FIG. 2  is a sectional view illustrating part of a fuel cell stack including the separator of  FIG. 1 ; 
         FIG. 3  is a perspective view illustrating a porous structure disposed in a reaction area of the separator of  FIG. 1 ; 
         FIG. 4  is a sectional view illustrating part of a diffusion area of the fuel cell stack including the separator of  FIG. 1 ; 
         FIG. 5  is an enlarged plan view illustrating part of the separator of  FIG. 1 ; and 
         FIG. 6  is a plan view illustrating a porous structure, where the porous structure is able to be disposed in the reaction area of the separator of  FIG. 1  and part of the porous structure functions as a resistance body. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Hereinafter, some embodiments of the present disclosure will be described in detail with reference to the exemplary drawings. In adding the reference numerals to the components of each drawing, it should be noted that the identical or equivalent component is designated by the identical numeral even when they are displayed on other drawings. Further, in describing the embodiments of the present disclosure, a detailed description of well-known features or functions will be omitted in order not to unnecessarily obscure the gist of the present disclosure. 
     The present disclosure relates to a separator for a fuel cell and may be applied to a separator  100  (refer to  FIG. 1 ) that will be described below.  FIG. 1  is a plan view illustrating the separator  100  to which an embodiment of the present disclosure is applied. 
     The separator  100  illustrated in  FIG. 1  may include a main body  110 . The main body no may be formed by stacking a plurality of flat plates. 
     The main body no may have an inlet manifold  120  and an outlet manifold  130 . The inlet manifold  120  may include a first inlet manifold  121  for inflow of air and a second inlet manifold  122  for inflow of hydrogen (fuel). The outlet manifold  130  may include a first outlet manifold  131  for outflow of the air and a second outlet manifold  132  for outflow of the hydrogen. 
     The first and second inlet manifolds  121  and  122  and the first and second outlet manifolds  131  and  132  may be disposed such that the air and the hydrogen flow in opposite directions. For example, as illustrated in  FIG. 1 , the first inlet manifold  121  may be formed at a left distal end of the main body  110 , and the first outlet manifold  131  may be formed at a right distal end of the main body  110 . The second inlet manifold  122  may be formed at the right distal end of the main body  110 , and the second outlet manifold  132  may be formed at the left distal end of the main body  110 . 
     The first and second inlet manifolds  121  and  122  and the first and second outlet manifolds  131  and  132  may be disposed such that a line drawn from the first inlet manifold  121  to the first outlet manifold  131  crosses a line drawn from the second inlet manifold  122  to the second outlet manifold  132 . For example, as illustrated in  FIG. 1 , the first inlet manifold  121  may be formed at an upper left end of the main body  110 , and the first outlet manifold  131  may be formed at a lower right end of the main body  110 . The second inlet manifold  122  may be formed at an upper right end of the main body  110 , and the second outlet manifold  132  may be formed at a lower left end of the main body  110 . 
     As illustrated in  FIG. 1 , the inlet manifold  120  may further include a third inlet manifold  123  for inflow of cooling water. The outlet manifold  130  may further include a third outlet manifold  133  for outflow of the cooling water. 
     The manifolds may be separated from one another by a gasket G. 
     The main body  110  may additionally have a flow area  140 . The flow area  140  is an area where the reactant gases flow between the inlet manifold  120  and the outlet manifold  130 . The separator  100  of a fuel cell stack may form flow passages through which the reactant gases flow. The flow area  140  may be at least part of a flow-passage forming the face of the main body  110 . 
     As illustrated in  FIG. 2 , the main body  110  of the separator loo may be formed by stacking a cathode separator  114  and an anode separator  115 .  FIG. 2  is a sectional view illustrating part of the fuel cell stack including the separator of  FIG. 1 . An air guide channel  150   a  for a flow of the air may be provided between the cathode separator  114  and a membrane electrode assembly (MEA) in opposite thereto. A fuel guide channel  150   b  for a flow of the fuel may be formed between the anode separator  115  and an MEA  111  opposite thereto. As described above, the channels  150   a  and  150   b  for the flow of the reactant gases may be provided on one surface and an opposite surface of the main body  110 . The portion of the main body  110  in which the channels  150   a  and  150   b  are provided may be the flow area  140  of  FIG. 1 . “W” in  FIG. 2  denotes a cooling water guide channel. 
     Each of the MEAs  111  may include an electrolyte membrane, and a cathode and an anode formed on opposite surfaces of the electrolyte membrane. Gas diffusion layers (GDLs) may be disposed on the opposite surfaces of the MEA  111 . In  FIG. 2 , reference numeral  112  denotes a cathode gas diffusion layer, and reference numeral  113  denotes an anode gas diffusion layer. 
     As illustrated in  FIG. 1 , the flow area  140  may include a reaction area  141 . The reaction area  141  is an area where reactant gas guide channels  150  (refer to  FIG. 2 ) that guide the reactant gases to the electrodes of the MEA  111  are disposed. The reactant gas guide channels  150  may include the first reactant gas guide channel  150   a  for guiding the air to the cathode of the MEA  111  and the second reactant gas guide channel  150   b  for guiding the fuel to the anode of the MEA  111 . The first reactant gas guide channel  150   a  corresponds to the air guide channel described above, and the second reactant gas guide channel  150   b  corresponds to the fuel guide channel described above. The reaction area  141  may include a first reaction area  141   a  where the first reactant gas guide channel  150   a  is disposed and a second reaction area (not illustrated) where the second reactant gas guide channel  150   b  is disposed. The second reaction area may be provided on a rear surface of the main body  110  of  FIG. 1 . 
     A reaction-area porous body  190  illustrated in  FIGS. 2 and 3  may be disposed in the reaction area  141 . In  FIG. 2 , a porous structure disposed between the cathode separator  114  and the MEA  111  opposite thereto is illustrated as the reaction-area porous body  190 . The reaction-area porous body  190 , together with the cathode separator  114 , may form the air guide channel. Due to the reaction-area porous body  190 , the air may be more smoothly guided to the cathode in the air guide channel. For reference, in the reaction area  141 , a general reactant gas flow passage formed by the separators may be provided instead of the reaction-area porous body  190 . 
     As illustrated in  FIG. 1 , the flow area  140  may further include a diffusion area  142 . The diffusion area  142  is located between the reaction area  141  and the inlet manifold  120 . A diffusion channel  160  for diffusing, toward the reaction area  141 , the reactant gases introduced from the inlet manifold  120  is disposed in the diffusion area  142 . The reactant gases in the inlet manifold  120  may be moved to the diffusion channel  160  through holes H and thereafter diffused into the reaction area  141  through the diffusion channel  160 . The diffusion channel  160  (refer to  FIG. 5 ) may be formed between lands  161 . 
     The diffusion area  142  may include a first diffusion area  142   a  located between the first reaction area  141   a  and the first inlet manifold  121 . The first diffusion area  142   a  is an area where a first diffusion channel  160   a  (refer to  FIG. 4 ) that diffuses, toward the first reaction area  141   a,  the air introduced from the first inlet manifold  121  is disposed. 
     As illustrated in  FIG. 1 , the flow area  140  may further include a recovery area  143 . The recovery area  143  is located between the reaction area  141  and the outlet manifold  130 . The recovery area  143  is an area where a recovery channel (not illustrated) that guides the reactant gases in the reaction area  141  to the outlet manifold  130  is disposed. The recovery channel may have substantially the same structure as the diffusion channel  160 . 
     Embodiment 1 
     A separator according to embodiment 1 of the present disclosure may include a main body  110  and a resistance part  180 . The main body  110  of this embodiment may be the main body  110  described above. 
     The resistance part  180  (refer to  FIG. 4 ) of this embodiment is configured to increase flow resistance to a reactant gas that is introduced from the inlet manifold  120  and that flows toward the outlet manifold  130 . The flow resistance refers to a force against the flow of the fluid. The flow resistance is mainly determined by the diameter and length of a pipe through which the fluid flows, the viscosity of the fluid, and the like. The resistance part  180  of this embodiment may increase the flow resistance in such a manner as to decrease the diameter of the pipe. 
     For example, the resistance part  180  of this embodiment may increase the flow resistance in such a manner as to block part of a channel through which the reactant gas flows. More specifically, the resistance part  180  of this embodiment may include a porous body. The flow resistance to the reactant gas may be increased by filling the channel for the flow of the reactant gas with the porous body. The porous body of this embodiment may be any one of porous materials. For example, the porous body may be metal foam. Alternatively, the porous body may be formed in a shape similar to a gas diffusion layer (GDL) that is formed by agglomeration of graphite fiber. 
     The reactant gas may flow slower as the flow resistance is increased. The degree to which moisture remains in the reactant gas may be raised when the velocity of the reactant gas is lowered. Due to the increase in the flow resistance by the resistance part  180 , the separator of this embodiment may allow the moisture in the reactant gas to further remain in the area where the resistance part  180  is disposed, and may allow the remaining moisture to be left for a longer period of time in the area where the resistance part  180  is disposed. 
     The separator of this embodiment may improve a problem of degradation in an electrolyte membrane by disposing the resistance part  180  in a place where the electrolyte membrane is likely to be degraded. Furthermore, even in a downstream area of the resistance part  180  that is disposed adjacent to the area where the resistance part  180  is disposed, the separator of this embodiment may improve a problem of degradation in an electrolyte membrane due to an increase in moisture in the area where the resistance part  180  is disposed. 
     The resistance part  180  of this embodiment may be disposed in the flow area  140  (refer to  FIG. 2 ) of the main body no and may be disposed adjacent to the inlet manifold  120  of the main body  110 . A region of the flow area  140  that is located adjacent to the inlet manifold  120  is a region where a moisture content of an electrolyte membrane located to correspond to the relevant region is likely to be lowered. Accordingly, the resistance part  180  of this embodiment may be disposed adjacent to the inlet manifold  120  to raise the moisture content of the electrolyte membrane in the region located adjacent to the inlet manifold  120 . 
     As illustrated in  FIG. 4 , the resistance part  180  of this embodiment may be disposed in the diffusion channel  160  in the diffusion area  142  (refer to  FIG. 5 ).  FIG. 4  is a sectional view illustrating part of the diffusion area of the fuel cell stack including the separator of  FIG. 1 . The diffusion channel  160  for diffusing, toward the reaction area  141 , the reactant gas introduced from the inlet manifold  120  is disposed between the lands  161  in the diffusion area  142  (refer to  FIG. 5 ). The resistance part  180  of this embodiment may be disposed in the diffusion channel  160  (refer to  FIG. 4 ). 
     The moisture content of the electrolyte membrane may be mainly lowered in an area located adjacent to the first inlet manifold  121  for inflow of air. Accordingly, the resistance part  180  of this embodiment may be provided in the first diffusion channel  160   a  disposed in the first diffusion area  142   a  (refer to  FIG. 5 ). 
     As illustrated in  FIG. 5 , the first diffusion channel  160   a  may include an upper area A 1  adjacent to the first inlet manifold  121  and a lower area A 2  adjacent to the second outlet manifold  132 . The resistance part  180  of this embodiment may include an upper portion disposed in the upper area A 1  and a lower portion disposed in the lower area A 2 . 
     In the reaction area  141 , water is produced by a fuel cell reaction. The lower area A 2  is an area disposed adjacent to the second outlet manifold  132  through which the reactant gas is released. Accordingly, moisture exchange may more actively occur in the lower area A 2  than in the upper area A 1 . Due to this, the need for moisture stagnation is greater in the upper area A 1  than in the lower area A 2 . In view of that, the upper portion of the resistance part  180  may be formed to be more hydrophilic than the lower portion of the resistance part  180 . The higher the hydrophilic property, the higher the degree to which moisture remains. Furthermore, in the lower area A 2 , release of moisture may be more important than stagnation of moisture. This is because water introduced from the first inlet manifold  121  is easily gathered in the lower area A 2 . This phenomenon may be induced by the following two causes. First, the water is heavier than the reactant gas. Second, the flow speed of the reactant gas is lowered when the reactant gas flows into the diffusion channel from the manifold. Accordingly, the water flowing into the diffusion channel from the manifold together with the reactant gas is easily gathered in the lower area A 2 . 
     Meanwhile, a diffusion-area porous body  181  may be formed to be more hydrophilic than the reaction-area porous body  190 . Accordingly, the degree to which moisture remains in the diffusion area  142  may be further raised. For reference, methods for raising the hydrophilic or hydrophobic property of a target by specifically treating the surface of the target have been known. For example, methods such as plasma treatment, chemical treatment, coating treatment, and the like have been known. The hydrophilic property of the diffusion-area porous body  181  may be raised by these treatments. 
     The first diffusion channel  160   a  in the first diffusion area  142   a  of the main body  110  may be filled with the resistance part  180  of this embodiment without a change in the structure of the main body  110 . Accordingly, the resistance part  180  of this embodiment may be applied to a main body in the related art without change to solve a problem of deterioration in moisture content. 
     The first diffusion channel  160   a  is provided between the lands  161  (refer to  FIG. 4 ). The lands  161  serve as conductors. Accordingly, the resistance part  180  with which the first diffusion channel  160   a  is filled may be selected in consideration of only a flow resistance increase without considering conductivity. 
     Embodiment 2 
     A separator according to embodiment 2 of the present disclosure includes a main body  110  and a resistance part  280 . The separator of embodiment 2 differs from the separator of embodiment 1 in terms of the resistance part. The following description will be focused on the resistance part  280 . 
     The resistance part  280  of this embodiment is configured to allow moisture in a reactant gas introduced from the inlet manifold  120  and flowing toward the outlet manifold  130  to stagnate. When the moisture in the reactant gas further stagnates due to the resistance part  280 , the moisture in the reactant gas may further remain in the area where the resistance part  280  is disposed. 
     In this embodiment, part of a reaction-area porous body  290  (refer to  FIG. 6 ) may serve as the resistance part  280 . Likewise to the reaction-area porous body  190  of embodiment 1 described above, the reaction-area porous body  290  of  FIG. 6  may be disposed in the reaction area  141  (refer to  FIG. 1 ) and may form a reactant gas guide channel for guiding the reactant gas to the electrodes of the MEA  111 . The reaction-area porous body  290  of this embodiment may be substantially the same as the reaction-area porous body  190  of embodiment 1 in terms of the basic structure. 
     The reaction-area porous body  290  may include an upstream portion  290   a  that is disposed adjacent to the inlet manifold  120  and into which the reactant gas flows, and a downstream portion  290   b  disposed downstream of the upstream portion  290   a.  The upstream portion  290   a  may be formed to be more hydrophilic than the downstream portion  290   b.  The moisture in the reactant gas may easily stagnate when the hydrophilic property is raised. 
     The separator of this embodiment may raise the hydrophilic property of the upstream portion  290   a  of the reaction-area porous body  290 , thereby raising a moisture content of an electrolyte membrane disposed to correspond to the upstream portion  290   a.  The upstream portion  290   a  of the reaction-area porous body  290  may be the resistance part  280  for allowing the moisture in the reactant gas to stagnate. 
     Even in the related art, there is an example in which a porous body is used in the reaction area  141 . However, in the related art, the porous body is configured such that the same characteristic appears in the entire reaction area  141 . In contrast, the reaction-area porous body  290  of this embodiment is configured such that the characteristics of the upstream portion  290   a  and the downstream portion  290   b  differ from each other. Accordingly, the moisture content of the electrolyte membrane in the upstream portion  290   a  where a problem of degradation in the electrolyte membrane is likely to occur may be raised. 
     The upstream portion  290   a  of the reaction-area porous body  290  may be appropriately selected in consideration of an area where degradation in the electrolyte membrane is likely to occur. 
     To raise the hydrophilic property of the upstream portion  290   a,  a contact angle of the upstream portion  290   a  may be formed to be smaller than a contact angle of the downstream portion  290   b.  The contact angle may be used to represent the degree of hydrophilicity or hydrophobicity. The smaller the contact angle, the higher the degree of hydrophilicity. This is an ordinary matter, and therefore detailed description thereabout is omitted. 
     According to embodiments of the present disclosure, the resistance part may be disposed in a partial area of an existing separator to increase flow resistance in the area where the resistance part is disposed, thereby enabling moisture in a reactant gas to further remain in the area where the resistance part is disposed and enabling the remaining moisture to be left for a longer period of time in the area where the resistance part is disposed, which in turn raises moisture content of an electrolyte membrane in the area where the resistance part is disposed and an area downstream thereof. 
     Hereinabove, although the present disclosure has been described with reference to exemplary embodiments and the accompanying drawings, the present disclosure is not limited thereto, but may be variously modified and altered by those skilled in the art to which the present disclosure pertains without departing from the spirit and scope of the present disclosure claimed in the following claims. Therefore, the exemplary embodiments of the present disclosure are provided to explain the spirit and scope of the present disclosure, but not to limit them, so that the spirit and scope of the present disclosure is not limited by the embodiments. The scope of the present disclosure should be construed on the basis of the accompanying claims, and all the technical ideas within the scope equivalent to the claims should be included in the scope of the present disclosure.