Bipolar plate structure for fuel cells

Abstract

Bipolar plate structure for a fuel cell, comprising: a cathode bipolar plate (10) having a first flow field portion for forming cathode channels between the first flow field portion and a first gas diffusion layer, and a first land portion for forming coolant channels in a state in which the first land portion communicates with the first gas diffusion layer; and an anode bipolar plate (10) having a second flow field portion for forming anode channels between the second flow field portion and a second gas diffusion layer, and a second land portion for forming coolant channels in a state in which the second land portion communicates with the second gas diffusion layer, wherein the cathode channels have an interlaced channel structure and the anode channels have a parallel channel structure in which flow fields are arranged parallel to each other, wherein an air inlet opening (12) is formed along one of the two long edge portions of a reaction zone (11) in the cathode bipolar plate (10) and the anode bipolar plate (10) in which the first and second flow field portions and the first and second web portions are formed, and an air outlet opening (13) is formed along the other of the two long edge portions of the reaction zone (11), and wherein the longitudinal direction of each of the cathode channels is the width direction of the reaction zone (11), wherein the longitudinal direction of each of the anode channels is the longitudinal direction of the reaction zone (11), so that the longitudinal direction of each of the cathode channels is perpendicular to the longitudinal direction of each of the anode channels, and wherein, when surfaces of the first land portion and the second land portion are respectively connected to the first and second gas diffusion layers of two adjacent fuel cells, coolant channels are formed in an opposite surface of the first and second land portion in the form of a zigzag path so that a longitudinal path and a transverse path of the coolant channels are alternately repeated.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a bipolar plate structure for a fuel cell. More particularly, the present disclosure relates to a bipolar plate structure for a fuel cell capable of uniform power generation throughout the reaction zone, increasing the limiting current density and power density, and improving the performance and efficiency of the fuel cell. BACKGROUND

[0002] A polymer electrolyte membrane fuel cell (PEMFC) generates electrical energy through an electrochemical reaction between hydrogen as the fuel gas and oxygen (or air) as the oxidant gas, the reaction gases.

[0003] The PEMFC exhibits high efficiency, high current density, high power density, short start-up time, and rapid response to load changes compared to other types of fuel cells. Therefore, the PEMFC is used in various applications, such as as a power source for zero-emission vehicles, as a stand-alone power system, and as a power source for military purposes.

[0004] Fuel cells are generally arranged and assembled in a stacked structure to meet the required energy level. Consequently, fuel cells in a vehicle are also installed in a stacked structure, in which several hundred cells are stacked to meet the required high energy level.

[0005] A membrane electrode assembly (MEA) is positioned at the center of each cell unit of the fuel cell stack. The MEA contains a solid polymer electrolyte membrane through which hydrogen cations (protons) migrate, and a catalytic electrode, which is created by depositing catalysts on two surfaces of the electrolyte membrane. The catalytic electrode contains an anode (hydrogen electrode) and a cathode (air electrode).

[0006] Additionally, a gas diffusion layer (GDL), a gasket to prevent gas leakage, and others are stacked on the outside of the MEA, namely at the outer sections where the anode and cathode are located. A bipolar plate has flow fields through which reactant gases, coolant, and water produced by the reaction flow, and is connected to an outer side of the GDL.

[0007] According to the conventional technique described above, an oxidation reaction of hydrogen as fuel takes place in the anode of the fuel cell stack, in which hydrogen ions and - electrons are formed. The hydrogen ions and - electrons migrate through the electrolyte membrane or the bipolar plate to the cathode.

[0008] Thus, electrical energy is generated by the flow of electrons, and water and heat are generated in the cathode by the electrochemical reaction involving the hydrogen ions and electrons from the anode and the oxygen in the air.

[0009] The bipolar plate divides the cell units in the fuel cell stack and simultaneously serves as a current path (a path for transporting the generated electrical energy) between the cell units. The flow fields formed in the bipolar plate serve as a path for conducting the reaction gases to the GDL, for the coolant, and for discharging water produced by the electrochemical reaction through the GDL to the outside.

[0010] Such a bipolar plate consists of a graphite bipolar plate made of a graphite material and a metallic bipolar plate made of a metal material such as stainless steel. A study is currently underway to examine whether the graphite bipolar plate can be replaced by the metallic bipolar plate from the perspective of processability and mass production.

[0011] However, with pressed metal bipolar plates, it is difficult to manufacture complex shapes. To achieve this, a metal bipolar plate uses a thin plate material, which allows for a reduction in the thickness and weight of the bipolar plate, as well as the volume of the cell unit.

[0012] After bipolar plates are manufactured by forming relief / debossed patterns in a metal plate material through compression molding, two bipolar plates are generally bonded together. Coolant flows in a channel space defined by the contact between the bipolar plates, and GDLs are deposited on two sides of the bipolar plates, allowing hydrogen and oxygen to flow in respective channel spaces between the GDLs and the bipolar plates to transport the reactant gases.

[0013] Fig. Figure 1 is a plan view showing a typical metallic bipolar plate structure for a fuel cell. As shown in Fig. As shown in Figure 1, a bipolar plate 10 is generally rectangular in shape. The bipolar plate 10 has a reaction zone 11 with flow fields for air, hydrogen, and coolant. Opposite end portions of the reaction zone 11 have inlet ports 12, 14, and 16 and outlet ports 13, 15, and 17 through which air, hydrogen, and coolant enter and exit, respectively.

[0014] Humidified air and hydrogen are supplied from an external source of a stack through the air and hydrogen inlet ports 12 and 14 as reaction gases for fuel cell operation. Gaseous or liquid water generated in the fuel cell and the supplied reaction gases are exhausted from the stack through the air and hydrogen outlet ports 13 and 15.

[0015] That is, the reaction gases and water generated in the cell are discharged through the air outlet port 13, and the reaction gases and water generated in a cathode and then permeating an electrolyte membrane to an anode are discharged through the hydrogen outlet port 15.

[0016] In each bipolar plate of the fuel cell stack, the reaction gases (air, including hydrogen as fuel gas and oxygen as oxidant gas) and the coolant, supplied through the inlet ports 12, 14, and 16, are distributed to the flow fields (cathode / anode / coolant channels) of each cell for reaction and cooling. Then, the reaction gases and the coolant are combined at the outlet ports 13, 15, and 17 and discharged from the stack as shown in Fig. 2 shown.

[0017] The Fig. 3A and Fig. 3B are sectional views of the fuel cell, showing a cathode channel and an anode channel through which reactant gases flow, as well as a coolant channel. Reference numeral 21 denotes an MEA with a catalytic layer (a catalytic electrode, i.e., a cathode and an anode).

[0018] Here, each section in which the bipolar plate 10 is in contact with the GDL 22 is a land section 10a and each section in which one bipolar plate is in contact with another bipolar plate is a channel section 10b.

[0019] In addition, flow fields formed by the channel portion 10b are channels through which the reaction gases flow, namely a cathode channel (air channel) 11a through which air (oxygen) flows, and an anode channel (hydrogen channel) 11b through which hydrogen flows. A flow field formed by the web portion 10a is a coolant channel 11c through which coolant flows.

[0020] The flow fields of the bipolar plate are divided into the cathode channel 11a, the anode channel 11b, and the coolant channel 11c, in which air, hydrogen, and coolant flow parallel to the flow fields of the bipolar plate. The bipolar plate manufactured by machining a metal material using a press imposes design limitations due to the shape of the bipolar plate itself.

[0021] The flow fields of the metallic bipolar plate are designed in different ways because complex shapes are difficult to realize, but the flow field pattern has the same shape as a typical channel shape.

[0022] That is, the flow fields through which the reaction gases flow have relief and intaglio patterns on the flat and thin plate metal material, and the coolant or other gases flow through the flow fields formed on the opposite surface.

[0023] In addition, the conventional bipolar plate generally has long channels arranged in parallel throughout the reaction zone, or inclined flow fields. The bipolar plate has advantages and disadvantages in terms of performance, pressure characteristics, and discharge characteristics depending on the design of the bipolar plate's flow fields. However, the flow fields are formed with a rectangular cross-section, a trapezoidal cross-section, or a similar cross-section in a section corresponding to the reaction zone of the bipolar plate to allow the supply of the reaction gases.

[0024] The bipolar plate has a section where flow fields are formed and another section where no flow fields are formed. The section where flow fields are formed is a flow field section (with the above channels) containing the flow fields for the reactant gases, and the other section where no flow fields are formed is a land section.

[0025] The flow field section is typically different from the land section of the bipolar plate. The amount of gas diffusion to the GDL varies due to the different flow rates between the flow field section and the land section. This non-uniformity causes a concentration difference between the flow field section and the land section in the MEA where the electrochemical reaction takes place. Therefore, due to the difference in the electrochemical reaction, uniform energy generation across the entire reaction zone is unlikely to be achieved.

[0026] In the conventional bipolar plate, the reaction gases, such as air and hydrogen, are transported perpendicular to the direction in which the substances are transported to the catalytic layer, where the electrochemical reaction takes place. Therefore, the bipolar plate has the disadvantage that the substances are only transported to the catalytic layer depending on the concentration difference and the partial pressure difference between channels 11a and 11b and the MEA 21.

[0027] That is, since the flow direction of the reaction gases is perpendicular to the direction in which the substances are transported to the catalytic layer where the electrochemical reaction takes place, the substances are transported through the GDL 22 to the catalytic layer only by diffusion due to the pressure difference at the inlet and outlet between the flow field channels 11a and 11b for the reaction gas and the concentration difference between the channels 11a and 11b and the catalytic layer.

[0028] This process is a passive transfer process, which involves supplying the reactant gases to a specific location. Therefore, it is difficult to transport the substances to the catalytic layer by the flow in the bipolar plate.

[0029] Therefore, the limiting current density of the fuel cell decreases, which may lead to a deterioration in fuel cell performance. Furthermore, fuel cell performance cannot be improved in a high-energy section, and the water produced as a byproduct of the electrochemical reaction is difficult to remove because water is difficult to remove from GDL.

[0030] Furthermore, since the reaction gas concentration required for the electrochemical reaction is not transferred to the catalytic layer in the rear end portion (the outlet portion) of the flow field channel, a power loss may occur.

[0031] From GB 2 509 319 A, a bipolar plate structure for a fuel cell is known, comprising: a cathode bipolar plate having a first flow field portion for forming cathode channels between the first flow field portion and a first gas diffusion layer, and a first land portion for forming coolant channels in a state in which the first land portion communicates with the first gas diffusion layer; and an anode bipolar plate having a second flow field portion for forming anode channels between the second flow field portion and a second gas diffusion layer, and a second land portion for forming coolant channels in a state in which the second land portion communicates with the second gas diffusion layer, wherein the cathode channels have an interlaced channel structure and the anode channels have a parallel channel structure in which flow fields are arranged parallel to one another.

[0032] DE 11 2007 000 134 T5 discloses a method for manufacturing a fuel cell component provided with a first porous body having a first porosity and a second porous body having a second porosity higher than the first porosity, the method comprising: laminating the first porous body containing conductive material onto a membrane electrode assembly; performing a porosity adjustment process that forms at least a portion (15) in a vicinity of a periphery of the second porous body with a porosity lower than the second porosity; laminating the second porous body onto the first porous body laminated onto the membrane electrode assembly;Injection-molding a sealing member comprising at least one of a thermosetting material and a thermoplastic resin on a periphery of the membrane electrode assembly on which the first porous body and the second porous body are laminated, to unite the membrane electrode assembly, the second porous body, and the sealing member by injection molding;

[0033] WO 2002 / 069 424 A1 describes a bipolar plate for a fuel cell or a chemical reactor. It has a distribution component on each side of a metal layer for distributing a gas over the surface of a cathode and the surface of an anode. The distribution components are formed by rectangular gas distribution layers that are firmly soldered to the center of the metal layer. Gas flow channels for crossflow are arranged along opposite edges of the gas distribution layer. This achieves a compact design with particularly low flow resistance.

[0034] US 6 884 536 B1 provides a polymer electrolyte fuel cell comprising a hydrogen ion-conducting polymer electrolyte membrane, an anode and a cathode sandwiching the hydrogen ion-conducting polymer electrolyte membrane, an anode-side conductive separator plate having gas flow channels for supplying a fuel gas to the node, and a cathode-side conductive separator plate having gas flow channels for supplying an oxidant gas to the cathode, wherein the anode-side and cathode-side conductive separator plates have a substantially rectangular part in contact with the anode or the cathode, in which the length of a longer side is equal to or more than twice the length of a shorter side, and the oxidant gas flow channels have a linear part formed along the longer side of the rectangular part.

[0035] Furthermore, WO 2008 / 142557 A2 shows separators that are alternately stacked with power generation modules, each including a power generation body, to form a fuel cell. Each separator has oxidizing gas outlet manifold holes for discharging an oxidizing gas and a power generation region that overlaps with the power generation body in the stacking direction when stacked, and that includes at least a portion positioned on one side of the oxidizing gas outlet manifold hole and a portion positioned on another side of the oxidizing gas outlet manifold hole opposite the aforementioned side thereof.

[0036] The above statements in this background section are intended only to provide a better understanding of the background of the invention and may therefore contain information that is not part of the prior art already known to the average person skilled in the art in this country. OVERVIEW OF REVELATION

[0037] The present disclosure has been made in an effort to solve the above-described problems in the prior art.

[0038] It is an object of the present disclosure to provide a bipolar plate structure for a fuel cell that is capable of uniform energy generation throughout the reaction zone, increases the limiting current density and power density, and improves the performance and efficiency of the fuel cell.

[0039] In another aspect, the present disclosure provides a bipolar plate structure for a fuel cell that can improve the ability of water removal from a gas diffusion layer (GDL) and thermal efficiency by increasing the contact area with the coolant.

[0040] The object is achieved by a bipolar plate structure having the features of claim 1. Advantageous further developments can be found in the subclaims.

[0041] According to one embodiment, a bipolar plate structure for a fuel cell includes a cathode bipolar plate having a first flow field portion forming cathode channels between the first flow field portion and a first gas diffusion layer, and a first land portion forming coolant channels in a state where the first land portion communicates with the first gas diffusion layer. An anode bipolar plate has a second flow field portion forming anode channels between the second flow field portion and a second gas diffusion layer, and a second land portion forming coolant channels in a state where the second land portion communicates with the second gas diffusion layer. The cathode channels have an interlaced channel structure, and the anode channels have a parallel channel structure in which flow springs are arranged parallel to each other.An air inlet port is formed along one of the two long edge portions of a reaction zone in the cathode bipolar plate and the anode bipolar plate in which the first and second flow field portions and the first and second land portions are formed. An air outlet port is formed along the other of the two long edge portions of the reaction zone. The longitudinal direction of each of the cathode channels is the width direction of the reaction zone, and the longitudinal direction of each of the anode channels is the longitudinal direction of the reaction zone such that the longitudinal direction of each of the cathode channels is perpendicular to the longitudinal direction of each of the anode channels.Then, when surfaces of the first land portion and the second land portion are respectively connected to the first and second gas diffusion layers of two adjacent fuel cells, coolant channels in the form of a zigzag path are formed in an opposite surface of the first and second land portion such that a longitudinal path and a transverse path of the coolant channels are alternately repeated.

[0042] A hydrogen inlet port may be formed along one of the two short edge portions of the reaction zone in the cathode bipolar plate and the anode bipolar plate, and a hydrogen outlet port may be formed along the other of the two short edge portions.

[0043] The longitudinal direction of each of the cathode channels may intersect with the longitudinal direction of each of the anode channels.

[0044] The first web section can have a zigzag shape in which a longitudinal and a transverse section are repeated alternately.

[0045] At least a portion of the first land portion may have a closed shape to form a plurality of enclosed flow field portions enclosing the entire circumference of each enclosed flow field portion in the state where the first land portion is in communication with the first gas diffusion layer.

[0046] Coolant inlet and outlet ports may be formed in corner portions of the reaction zone.

[0047] An air inlet opening may be formed along one of the two long edge portions of the cathode bipolar plate and the anode bipolar plate in the longitudinal direction of the cathode and anode bipolar plates. An air outlet opening may be formed along the other of the long edge portions in the longitudinal direction of the cathode and anode bipolar plates. A hydrogen inlet opening may be formed at one of the two short edge portions of the cathode bipolar plate and the anode bipolar plate in the width direction of the cathode and anode bipolar plates. A hydrogen outlet opening may be formed at the other short edge portion in the width direction of the cathode and anode bipolar plates. A reaction zone in which the first and second flow field portions are formed may be surrounded by the air inlet and outlet openings and the hydrogen inlet and outlet openings.

[0048] Each of the cathode bipolar plates and the anode bipolar plates may be a metallic bipolar plate in which the first and second web portions and the first and second flow field portions are formed by pressing.

[0049] Other aspects and embodiments of the invention are described below.

[0050] It is understood that the term "vehicle" or "vehicular" or other similar terms used herein generally refer to motor vehicles, such as passenger cars, including sports utility vehicles (SUVs), buses, trucks, various commercial vehicles, personal watercraft including various boats and ships, aircraft, and the like, and also includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles (chargeable from a wall outlet), hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As used herein, a hybrid vehicle is a vehicle with two or more power sources, e.g., vehicles with both gasoline and electric power.

[0051] The above and other features of the invention are described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The above and other features of the present invention will now be described in detail below with reference to specific embodiments shown by way of example only in the accompanying drawings and thus do not limit the present disclosure. Fig. Figure 1 is a plan view of a conventional bipolar plate for a fuel cell stack. Fig. Figure 2 shows a perspective view of the conventional bipolar plate for a fuel cell stack and the direction of a fluid flow. Fig. 3A and Fig. 3B are sectional views of a cell showing a cathode channel and an anode channel through which reactant gases flow, and a coolant channel in the conventional fuel cell stack. Fig. 4 is a plan view of a bipolar plate for a fuel cell according to an embodiment of the present inventive concept. Fig. 5A to 5C are plan views showing cathode channels, anode channels, and coolant channels in the bipolar plate according to the embodiment of the present inventive concept, respectively. Fig. 6A to 6D are plan views of a bipolar plate for a fuel cell and a flow field structure thereof according to another embodiment of the present inventive concept. Fig. 7A to 7D are plan views of a bipolar plate for fuel cell and a flow field structure thereof according to another embodiment of the present inventive concept. Fig. 8A to 8D are plan views showing various examples in which the positions of the coolant inlet and outlet ports in the bipolar plate are changed according to the present inventive concept.

[0053] It should be understood that the accompanying drawings are not necessarily to scale, presenting a somewhat simplified representation of the various features illustrative of the principles of the invention. The specific design features of the present invention disclosed herein, including, for example, particular dimensions, orientations, locations, and shapes, will be determined in part by the particular intended application and the environmental conditions at the site of use.

[0054] In the figures, identical reference numerals designate the same or equivalent parts of the present invention in the different figures of the drawing. DETAILED DESCRIPTION

[0055] In the following, various embodiments of the present inventive concept will be explained in detail, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it should be understood that the present description of the invention is not intended to be limited to these exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents, and other embodiments included within the spirit and scope of the invention as defined by the appended claims.

[0056] Since the conventional bipolar plate for a fuel cell as described above only transports the substances to the catalytic layer by diffusion of the reaction gases, uniform energy generation in the entire reaction zone is difficult due to the uneven gas concentration between the flow field section and the land section, the limiting current density is low, and the ability of water removal from the GDL and the performance in the high-energy section can hardly be improved.

[0057] In contrast, since the bipolar plate of the present disclosure has an interlaced channel structure, the above disadvantages can be overcome. Furthermore, the space required for uniformly distributing the reaction gases and coolant from the inlet ports can be minimized by the novel channel structure, contributing to improving fuel cell efficiency and power density.

[0058] Fig. 4 is a plan view of a bipolar plate for a fuel cell according to an embodiment of the present inventive concept. As shown in the drawing, a bipolar plate 10 according to the present disclosure may be a metallic bipolar plate formed into a rectangular shape by compression molding (stamping). The bipolar plate (a cathode bipolar plate and an anode bipolar plate to be described later) 10 includes an air inlet port 12 extending longitudinally of the bipolar plate 10 along a central portion thereof for supplying air to cathode channels in a corresponding reaction zone 11. An air outlet port 13 extends longitudinally of the bipolar plate 10 along each of two long edge portions thereof and discharges the air passing through the cathode channels.

[0059] The air inlet port 12 and the air outlet port 13 form communicating air paths, which are an air inlet and an air outlet, through which air is supplied to and discharged from each bipolar plate 10 in a state where the fuel cell stack is assembled by stacking cells with the bipolar plate 10.

[0060] In addition, hydrogen inlet and outlet ports 14 and 15 and coolant inlet and outlet ports 16 and 17 are formed in both short edge portions of the bipolar plate 10. The hydrogen inlet ports 14 and the coolant inlet ports 16 are formed in one of the short edge portions to supply hydrogen and coolant to the anode channels and coolant channels in the respective reaction zones 11. The hydrogen outlet ports 15 and the coolant outlet ports 17 are formed in the other of the short edge portions to discharge the hydrogen and coolant passing through the respective anode channels and coolant channels.

[0061] The hydrogen inlet port 14 and the hydrogen outlet port 15 extend in the width direction of each reaction zone 11 along each short edge portion. In this case, the coolant inlet port 16 and the coolant outlet port 17 are located in corner portions on the periphery of each reaction zone 11.

[0062] Similar to the air inlet and outlet ports 12 and 13, the hydrogen inlet port 14 and the hydrogen outlet port 15 form communicating hydrogen paths, which are a hydrogen inlet and a hydrogen outlet, through which hydrogen is supplied to and discharged from each bipolar plate 10 in the state where the bipolar plates 10 of the fuel cell stack are stacked.

[0063] In addition, the coolant inlet port 16 and the coolant outlet port 17 form communicating coolant paths, which are a coolant inlet and a coolant outlet port, through which coolant is supplied to and discharged from each bipolar plate 10 in the state in which the bipolar plates 10 of the fuel cell stack are stacked.

[0064] Accordingly, in the bipolar plate 10 of the present disclosure, the distance between the air inlet port 12 and each of the air outlet ports 13 is shorter than the distance between the hydrogen inlet port 14 and the hydrogen outlet port 15, as shown in Fig. 4. Therefore, each of the cathode channels that transport the air from the central portion of the bipolar plate 10 to the long edge portion of the bipolar plate 10 is shorter than each of the anode channels that move the hydrogen from one of the short edge portions to the other.

[0065] In addition, since the air inlet opening 12 is located in the central portion of the bipolar plate 10, the air entering through the air inlet opening 12 in the central portion is divided in both directions and then flows through the cathode channels in the associated reaction zone 11 to the air outlet openings 13, which are each formed in the two short edge portions of the bipolar plate 10.

[0066] Thus, the reaction zone 11, in which an electrochemical reaction of the fuel cells takes place, is divided into two zones with respect to the air inlet opening 12 in the central section of the bipolar plate 10.

[0067] Since the inlet and outlet openings 12, 13, 14, and 15 are located at the edge sections of the reaction zone 11, the air and hydrogen flow in mutually perpendicular directions. The coolant flows in different directions, such as longitudinal and transverse.

[0068] Furthermore, the bipolar plate 10 of the present disclosure includes two types of bipolar plates 10 for forming the cathode channels as air flow fields, the anode channels as hydrogen flow fields, and the coolant channels as coolant flow fields in the fuel cell stack. That is, the bipolar plate 10 includes a cathode bipolar plate forming the cathode channels and the coolant channels, and an anode bipolar plate forming the anode channels and the coolant channels.

[0069] The cathode bipolar plate has the same configuration as the anode bipolar plate with respect to the positions and shapes of the air inlet and outlet ports 12 and 13, the hydrogen inlet and outlet ports 14 and 15, and the coolant inlet and outlet ports 16 and 17.

[0070] In the embodiment, however, the cathode bipolar plate has an interlaced channel structure and the anode bipolar plate has a parallel channel structure in which the anode channels are arranged parallel to each other.

[0071] The Fig. 5A to 5C are plan views of section “A” in Fig. 4, which illustrate the cathode channels, the anode channels, and the coolant channels, respectively, in the bipolar plate according to the present disclosure.

[0072] As in Fig. As shown in Figure 5A, the cathode bipolar plate with the interlaced channel structure includes a flow field section provided with relief and intaglio patterns that form flow fields, and a land section that communicates with a GDL. The flow field section in the fuel cell stack forms air flow fields, i.e., the cathode channels, so that air flows as an oxidant gas between the flow field section and the GDL.

[0073] In a particular embodiment, the web portion has a zigzag path in which a longitudinal and transverse portion alternately repeat continuously. When the cathode bipolar plate is bonded to the anode bipolar plate in the fuel cell stack in a state where one surface of the web portion is bonded to the GDL, the coolant channels are formed in another surface of the web portion of the cathode bipolar plate.

[0074] As in Fig. As shown in Figure 5B, the anode bipolar plate with the parallel channel structure also includes a flow field section provided with relief and intaglio patterns to form flow fields, and a land section connected to the GDL. In this case, the flow field section and the land section extend parallel to each other.

[0075] The flow field portion of the anode bipolar plate in the fuel cell stack forms hydrogen flow fields, i.e., the anode channels, so that hydrogen as the fuel gas flows between the flow field portion and the GDL. When the cathode bipolar plate is connected to the anode bipolar plate in the fuel cell stack in a state where one surface of the land portion is connected to the GDL, the coolant channels are formed in the other surface of the land portion of the anode bipolar plate.

[0076] Accordingly, the coolant channels in the fuel cell stack have a multidirectional flow field structure, where longitudinal flow fields intersect with transverse flow fields, as shown in Fig. 5C is shown.

[0077] Furthermore, when the cathode bipolar plate is connected to the anode bipolar plate in the fuel cell stack, the cathode channels are formed as air flow fields in one surface of the flow field portion of the cathode bipolar plate, and the anode channels are formed as hydrogen flow fields in one surface of the flow field portion of the anode bipolar plate. Here, other surfaces of the flow field portions of the two bipolar plates are connected to each other.

[0078] In addition, the cathode bipolar plate with the entangled channel structure as described above has an inlet and an outlet separated from each other, and air as a reaction gas flows across the GDL between the channels (flow field section).

[0079] When the cathode bipolar plate is connected to the anode bipolar plate in the fuel cell stack, the flow field section of the cathode bipolar plate extends perpendicular to the flow field section of the anode bipolar plate. Accordingly, the longitudinal direction of each cathode channel (the width direction of each bipolar plate and reaction zone) and the longitudinal direction of each anode channel (the longitudinal direction of each bipolar plate and reaction zone), formed by the flow field sections of the respective bipolar plates, are perpendicular to each other. The flow directions of air and hydrogen between the GDL and the MEA are also perpendicular to each other.

[0080] Since the web sections of the two bipolar plates extend perpendicular to each other when the cathode bipolar plate is connected to the anode bipolar plate in the fuel cell stack, the coolant flows between the bipolar plates 10 in any possible longitudinal and transverse direction. In this case, the coolant can flow along a zigzag path configured such that a longitudinal and transverse path alternately repeat continuously.

[0081] In the bipolar plate 10 described above, the reaction zone 11 is divided into two zones with respect to the air inlet opening 12 in the central portion of a cell, and the inlet and outlet openings 12, 13, 14, 15, 16 and 17 are located along the edge portions of the respective reaction zones 11, as shown in Fig. 4. Therefore, it is not necessary to form a separate branch channel section for uniform distribution of the channels, and thus the power density can be improved.

[0082] The cell unit can include two reaction zones 11 by forming the air inlet opening 12 in the central portion of the bipolar plate 10. The positions and shapes of the reaction zones 11 and the air inlet and outlet openings 12 and 13 can be changed in various ways.

[0083] In addition, the coolant inlet and outlet ports 16 and 17 are located in corner portions relative to the respective rectangular reaction zones 11. The hydrogen inlet and outlet ports 14 and 15 are each located in the short sides of the corresponding reaction zone 11, and the air inlet and outlet ports 12 and 13 are each located in the long sides of the corresponding reaction zone 11.

[0084] Accordingly, the coolant is supplied through the corner portions on one side of the reaction zone 11, that is, the coolant is supplied through the coolant inlet ports 16 on both sides of each hydrogen inlet port 14, and then passes through the coolant flow fields (channels) of zigzag shape between the bipolar plates 10. Then, the coolant is discharged through the corner portions on the other side of the reaction zone 11, that is, the coolant is discharged through the coolant outlet ports 17 on both sides of each hydrogen outlet port 15.

[0085] In the interlaced channel structure of the present disclosure, the hydrogen flow fields (hydrogen channels or anode channels) and the air flow fields (air channels or cathode channels) are perpendicular to each other rather than in the same direction. The length of each air flow field in the interlaced channel structure is so short that it approximately corresponds to the width of the reaction zone of the bipolar plate 10.

[0086] As the channel length of the interlaced channel structure increases, the pressure difference between the inlet and outlet for the reactant gases in the bipolar plate 10 increases, and the flow effect of the reactant gases traversing the GDL between the channels is weakened. Thus, the performance of the interlaced channels is reduced.

[0087] Especially when the channel length of the interlaced channel structure is long, the performance is similar to that of the conventional parallel channel structure, and the limiting current density and the ability of water discharge from the GDL are difficult to increase or improve.

[0088] On the other hand, if the channel length of the entangled channel structure is short, the power and power density increase.

[0089] With shorter channel lengths in the interlaced channel structure, the convection effect of the GDL between the channels increases. Therefore, the limiting current density can be maximized.

[0090] In this regard, if interlaced channels of the bipolar plate 10 are provided toward the short side of the rectangular reaction zone 11 of the bipolar plate 10 for the fuel cell with the reaction zone 11 having long and short sides, the limiting current density can be significantly increased compared to that of the conventional parallel channel. Consequently, the power density is also increased, and therefore the performance of the stack can be improved and the stack size reduced.

[0091] Accordingly, in the present disclosure, the air inlet port 12 and the air outlet ports 13 are formed along the long edge portions of the reaction zone 11 of the bipolar plate 10. The air flow fields have interlaced channels, and the air flow direction is set perpendicular (the width direction of the reaction zone) to the hydrogen flow direction (the longitudinal direction of the reaction zone). The length of each air channel of the interlaced channel structure is so short that it approximately corresponds to the width of the reaction zone 11.

[0092] Furthermore, since pronounced hydrogen diffusion occurs even within the hydrogen flow fields, there is no difference between the interlaced channel structure and the parallel channel structure. Therefore, the hydrogen flow fields are designed with parallel channels with a low pressure difference.

[0093] The coolant flow fields have the zigzag channel structure by means of the web sections of the cathode bipolar plate and the anode bipolar plate instead of the simple parallel structure as in the related art, which increases the contact area with water.

[0094] This allows the cooling capacity of the fuel cell to be increased and the entire reaction zone to be regulated to a uniform temperature by reducing the temperature difference through heat transfer, since the flow itself inevitably exhibits turbulent properties. Therefore, the fuel cell can be operated more efficiently in terms of heat management.

[0095] The Fig. 6A to 6D are plan views of a bipolar plate for a fuel cell and a flow field structure thereof according to another embodiment of the present inventive concept, and show examples in which the bipolar plate 10 has a reaction zone 11.

[0096] As in the Fig. As shown in Figures 6A to 6D, an air inlet opening 12 extends along one of the long edge portions of the bipolar plate 10 rather than in a central portion thereof in the longitudinal direction of the bipolar plate 10. An air outlet opening 13 extends along the other long edge portion in the longitudinal direction of the bipolar plate 10.

[0097] The reaction zone 11 is a rectangular zone arranged in the center except for the long and short edge sections of the bipolar plate 10. An interlaced channel structure of a cathode bipolar plate and a parallel channel structure of an anode bipolar plate are identical to those of the embodiment in Fig. 4.

[0098] In addition, there is no difference in the structure of the air flow fields (cathode channels or air channels) and the hydrogen flow fields (anode channels or hydrogen channels), the structure of the coolant flow fields (coolant channels) formed by a web section, the flow direction of hydrogen as a fuel gas and the flow direction of air including oxygen as an oxidant gas.

[0099] However, the design differs from Fig. 6A from the above embodiment in Fig. 4, in which two reaction zones 11 are formed, but only one reaction zone 11 in the embodiment of Fig. 6A. Furthermore, the air supplied through the air inlet opening 12 in the central section is distributed to both sides and discharged from the two air outlet openings 13 in the embodiment of Fig. 4, but the air supplied through the air inlet opening 12 on one long side is transported in the width direction of the bipolar plate 10 (in the width direction of the reaction zone) and then through the air outlet opening 13 on the other long side of the embodiment of Fig. 6A diverted.

[0100] The Fig. 7A to 7D are plan views of a bipolar plate for a fuel cell and a flow field structure thereof according to another embodiment of the present inventive concept. The present embodiment of the Fig. 7A to 7D differs from the above embodiment of the Fig. 6A to 6D with respect to the air flow field structure of a cathode bipolar plate, that is, the shapes of the interlaced channels and the shapes of the coolant channels formed by a land portion as shapes of the cathode channels (air flow fields) vary.

[0101] The other configurations of the embodiment in the Fig. 7A to 7D are identical to those of the embodiment in the Fig. 6A to 6D.

[0102] The cathode channels of the cathode bipolar plate of the embodiment in the Fig. 7A to 7D have an interlaced channel base structure in which an inlet and an outlet for air as a reaction gas are provided separately, and air traverses the GDL, coming into contact with the land portion between the flow fields (channels). The shape of the land portion of the embodiment of Fig. 7A to 7D differs from that of the embodiments of the Fig. 4 to 6D.

[0103] The flow direction of the air is perpendicular to the flow direction of the hydrogen in the embodiments of the Fig. 4 to 6D. In the embodiment of the Fig. However, in Figures 7A to D, at least a portion of the land portion communicating with the GDL has a closed shape in the cathode bipolar plate, and therefore, a plurality of enclosed flow field portions are formed. The entire perimeter of each enclosed flow field portion is enclosed by the closed land portion between the cathode bipolar plate and the GDL.

[0104] In this case, the land section is designed so that the enclosed flow field sections are arranged laterally. The air introduced into the air inlet section in the side channels traverses the GDL, coming into contact with the land section, then successively passes through adjacent enclosed flow field sections, and then flows to the air outlet sections in the channels.

[0105] The Fig. 8A to 8D are plan views showing various examples in which the positions of the coolant inlet and outlet ports in the bipolar plate are changed according to the present disclosure. The configurations of the embodiment are identical to those of the above embodiments, except that the positions of the coolant inlet and outlet ports 16 and 17 are changed.

[0106] As in the Fig. 8A to 8D, the temperature distribution in the reaction zone 11 can vary depending on the positions of the coolant inlet and outlet openings 16 and 17. If, as in Fig. 8A, the coolant inlet ports 16 are located in corners of the reaction zone 11 of the short edge portions, each being an end portion of the long side in the longitudinal direction thereof, and the coolant outlet ports 17 are located in corners of the reaction zone 11 in the short edge portions, each being a different end portion of the long side in the longitudinal direction thereof, a side portion in which the coolant outlet ports 17 are located in the reaction zone 11 is a high-temperature zone.

[0107] In Fig. 8, the coolant inlet ports 16 are located at one end portion of the reaction zone in the width direction thereof, and the coolant outlet ports 17 are located at another end portion. The side portion where the coolant outlet ports 17 are located in the reaction zone 11 is also a high-temperature zone.

[0108] As opposed to Fig. 8A, the positions of the coolant inlet openings 16 and the coolant outlet openings 17 in Fig. 8C reversed. In contrast to Fig. 8B, the positions of the coolant inlet openings 16 and the coolant outlet openings 17 in Fig. 8D reversed.

[0109] In the Fig. 8C and Fig. 8D, the side section in which the coolant outlet openings 17 are located in the reaction zone 11 is a high-temperature zone.

[0110] According to the present disclosure, since the inlet and outlet ports extend along the edge portions of the reaction zone in the bipolar plate for the fuel cell, it is not necessary to form a separate branch channel portion for uniformly distributing the channels, and thus the power density can be improved.

[0111] In addition, since interlaced channels of the bipolar plate are used toward the short side of the rectangular reaction zone with long and short sides in the bipolar plate for the fuel cell with the reaction zone, the limiting current density and power density of the fuel cell stack can be significantly increased, the performance of the stack can be improved, and the size of the stack can be reduced.

[0112] In addition, since the reaction gases between the channels cross the GDL due to the entangled channel structure, the ability of water removal from the GDL can be improved.

[0113] Furthermore, since the coolant flow fields feature a zigzag channel structure with the web sections of the cathode bipolar plate and the anode bipolar plate instead of the simple parallel structure as in related technology, the contact area with water can be increased. This can increase the cooling efficiency and control the entire reaction zone to a uniform temperature, since the flow itself inevitably exhibits turbulent characteristics.

Claims

[1] Bipolar plate structure for a fuel cell, comprising: a cathode bipolar plate (10) having a first flow field portion for forming cathode channels between the first flow field portion and a first gas diffusion layer, and a first land portion for forming coolant channels in a state in which the first land portion communicates with the first gas diffusion layer; and an anode bipolar plate (10) having a second flow field portion for forming anode channels between the second flow field portion and a second gas diffusion layer, and a second land portion for forming coolant channels in a state in which the second land portion communicates with the second gas diffusion layer, wherein the cathode channels have an interlaced channel structure and the anode channels have a parallel channel structure in which flow fields are arranged parallel to each other, wherein an air inlet opening (12) is formed along one of the two long edge sections of a reaction zone (11) in the cathode bipolar plate (10) and the anode bipolar plate (10) in which the first and second flow field sections and the first and second web sections are formed, and an air outlet opening (13) is formed along the other of the two long edge sections of the reaction zone (11), and wherein the longitudinal direction of each of the cathode channels is the width direction of the reaction zone (11), wherein the longitudinal direction of each of the anode channels is the longitudinal direction of the reaction zone (11), so that the longitudinal direction of each of the cathode channels is perpendicular to the longitudinal direction of each of the anode channels, and wherein, when surfaces of the first land portion and the second land portion are respectively connected to the first and second gas diffusion layers of two adjacent fuel cells, coolant channels are formed in an opposite surface of the first and second land portion in the form of a zigzag path so that a longitudinal path and a transverse path of the coolant channels are alternately repeated. [2] The bipolar plate structure according to claim 1, wherein a hydrogen inlet port (14) is formed along one of the two short edge portions of the reaction zone (11) in each of the cathode bipolar plate (10) and the anode bipolar plate (10), and a hydrogen outlet port (15) is formed along the other of the two short edge portions. [3] The bipolar plate structure of claim 1, wherein the longitudinal direction of each of the cathode channels intersects the longitudinal direction of each of the anode channels. [4] The bipolar plate structure according to claim 1, wherein the first web portion has a zigzag path such that a longitudinal portion and a transverse portion thereof are alternately repeated. [5] The bipolar plate structure according to claim 1, wherein at least a portion of the first land portion has a closed shape to form a plurality of enclosed first flow field portions to close the entire circumference of each enclosed first flow field portion in the state where the first land portion is in communication with the first gas diffusion layer. [6] A bipolar plate structure according to claim 1, wherein coolant inlet and outlet openings (16, 17) are formed in corner portions of the reaction zone (11). [7] The bipolar plate structure of claim 1, wherein: an air inlet opening (12) is formed in one of the two long edge portions of the cathode bipolar plate and the anode bipolar plate in the longitudinal direction of the cathode and anode bipolar plates, and an air outlet opening (13) is formed in the other of the long edge portions in the longitudinal direction of the cathode and anode bipolar plates; a hydrogen inlet opening (14) is formed in one of the two short edge portions of the cathode bipolar plate and the anode bipolar plate in the width direction of the cathode and anode bipolar plates, and a hydrogen outlet opening (15) extends in the other of the short edge portions in the width direction of the cathode and anode bipolar plates; and a reaction zone (11) in which the first and second flow field sections and the first and second web sections are formed, surrounded by the air inlet and outlet openings (12, 13) and the hydrogen inlet and outlet openings (14, 15). [8] The bipolar plate structure of claim 1, wherein each of the cathode bipolar plate (10) and the anode bipolar plate (10) is a metallic bipolar plate pressed to form the first and second land portions and the first and second flow field portions.

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