Four-fluid bipolar plate for fuel cell

Abstract

A four-fluid bipolar plate for a fuel cell includes an oxidant flow field, a fuel reactant flow field, a dedicated coolant passage, and a water management flow field. The bipolar plate includes at least one porous layer. A first side of the porous layer is fluidly connected to the water management flow field via a plurality of pores that act as a bubble barrier. An opposite second side of the porous layer includes the fuel reactant flow field or the oxidant flow field. In one example, the dedicated coolant passage is located within the bipolar plate and may be configured to allow an antifreeze-type coolant to flow.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of and incorporates by reference in its entirety U.S. Patent Application Serial No. 17 / 344,377, filed on June 10, 2021, and titled "FOUR - FLUID BIPOLAR PLATE FOR FUEL CELL". Technical field

[0003] This disclosure generally relates to fuel cell bipolar plates, and more particularly, to a bipolar plate structure that provides improved delivery of humidified reactants and better removal of product water. Background art

[0004] In a proton exchange membrane (PEM) fuel cell, hydrogen fuel is supplied to the negative electrode (anode), where the hydrogen fuel catalytically decomposes into protons and electrons according to the oxidation reaction H2 → 2H + + 2e - The protons (H + ) cross the membrane electrolyte to reach the positive electrode (cathode), while the electrons (e - ) conduct through an external path, thereby generating a current through an external load between the anode and the cathode. At the cathode, the protons and electrons recombine in the presence of oxygen to form water according to the following reduction reaction: O2 + 4e - + 4H + → 2H2O. The by - products of the PEM fuel cell reaction are water and heat; this heat requires the fuel cell to be cooled to maintain an acceptable internal temperature.

[0005] A single fuel cell includes a membrane electrode assembly (MEA) that includes: a membrane electrolyte inserted between a pair of electrodes (anode and cathode); and conductive plates adjacent to each electrode, opposite the membrane electrolyte, that define reaction gas flow fields. A typical flow field plate guides the reaction gases through the gas diffusion layer and the microporous layer to their respective electrodes. In some designs, the flow field plate can also transport the by - product water away from the cell.

[0006] Multiple fuel cells are typically arranged and connected in series in a stack to increase the electrical output of the electrochemical conversion components or fuel cells. In such an arrangement, two adjacent cell units can share a common plate that serves as the anode and cathode for two adjacent cell units connected in series. Such a plate is commonly referred to as a "bipolar plate". Summary of the invention

[0007] In one embodiment, a bipolar plate for a fuel cell includes a solid plate having no holes, the solid plate including at least one water management side and an internal coolant passage. The bipolar plate further includes a perforated plate having holes, the perforated plate including a reactant side and an opposite water management side. The reactant side of the perforated plate includes a first reactant flow field, and the water management side is fluidly connected to the water management side of the solid plate.

[0008] In another embodiment, a bipolar plate for a fuel cell includes an oxidant flow field, a fuel reactant flow field, a dedicated coolant passage, and a water management flow field.

[0009] In yet another embodiment, a bipolar plate for a fuel cell includes a solid plate having no holes, the solid plate including a water management side and a reactant side. The reactant side includes a first reactant flow field. The bipolar plate further includes a perforated plate having holes, the perforated plate including a reactant side and an opposite water management side. The reactant side includes a second reactant flow field. The water management side of the perforated plate is fluidly connected to the water management side of the solid plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The features described herein can be better understood with reference to the drawings described below. The drawings are not necessarily to scale, but will generally focus on showing the principles of the invention. In the drawings, like reference numerals are used to indicate like parts in the various views.

[0011] Figure 1 A schematic cross-sectional exploded view of a typical fuel cell is depicted;

[0012] Figure 2 A schematic cross-sectional view of a typical fuel cell power generation device is depicted;

[0013] Figure 3 An exploded perspective view of the anode side of a bipolar plate according to one embodiment of the present invention is depicted;

[0014] Figure 4 Depicts Figure 3 An exploded perspective view of the cathode side of the bipolar plate shown;

[0015] Figure 5 Depicts Figure 3 Another exploded view of the bipolar plate shown;

[0016] Figure 6 Depicts Figure 4 Another exploded view of the bipolar plate shown;

[0017] Figure 7 Depicts Figure 3 A perspective cross-sectional view of the cathode side of the bipolar plate shown;

[0018] Figure 8 DepictsFigure 7 An enlarged cross-sectional view of the bipolar plate shown;

[0019] Figure 9 depicts Figure 3 Another three-dimensional cross-sectional view of the cathode side of the bipolar plate shown;

[0020] Figure 10 depicts Figure 9 An enlarged cross-sectional view of the bipolar plate shown;

[0021] Figure 11 A cross-sectional view of a fuel cell having a bipolar plate according to a first embodiment of the present invention;

[0022] Figure 12 A cross-sectional view of a stack of fuel cells having a bipolar plate according to a first embodiment of the present invention;

[0023] Figure 13 A schematic cross-sectional view of a fuel cell power generation device according to an embodiment of the present invention;

[0024] Figure 14 A cross-sectional view of a fuel cell having a bipolar plate according to a second embodiment of the present invention;

[0025] Figure 15 A cross-sectional view of a fuel cell having a bipolar plate according to a third embodiment of the present invention;

[0026] Figure 16 A cross-sectional view of a fuel cell having a bipolar plate according to a fourth embodiment of the present invention;

[0027] Figure 17 A cross-sectional view of a fuel cell having a bipolar plate according to a fifth embodiment of the present invention;

[0028] Figure 18 A cross-sectional view of a fuel cell having a bipolar plate according to a sixth embodiment of the present invention; and

[0029] Figure 19 A cross-sectional view of a fuel cell having a bipolar plate according to a seventh embodiment of the present invention. Detailed Description

[0030] Figure 1 Shows a typical polymer electrolyte membrane (PEM) fuel cell 10, which generally includes a negative electrode (anode) 12 and a positive electrode (cathode) 14 separated by an ionomer membrane 16. Anode catalyst layer 18 a and cathode catalyst layer 18 cFormed on respective sides of a generally planar membrane to convert hydrogen reaction gas and oxygen reaction gas into electricity and water. This assembly is typically referred to as a membrane electrode assembly (MEA) 20. The catalyst layers 18 a 、18 c For the anode 12 and the cathode 14 can be the same, but typically they are different. For example, the anode catalyst layer 18 a can be used to split hydrogen atoms into hydrogen ions and electrons, while the cathode catalyst layer 18 c can be used to react oxygen and electrons to form water.

[0031] Reactants (i.e., hydrogen and air) are directed to the MEA 20 by the flow field plate 22, which typically includes reactant flow channels (represented by the dashed lines). The flow field plate 22 is shown as a bipolar plate, which includes reactant flow channels for both fuel and oxidant. Reactants pass from these channels through the gas diffusion layers (GDLs) 24 a 、24 c , and then through the microporous layer (MPL) 26 a 、18 c located between the GDL and the respective catalyst layers 18 a 、26 c . The GDL can have several functions, which include diffusing the reaction gas flow to the catalyst layer, transporting liquid and vapor water by-products from the catalyst layer to the cathode gas channel (where the liquid and vapor water by-products are carried away by the gas flow), collecting the current generated by the electrochemical reaction, and providing mechanical strength to support and protect the catalyst-coated membrane. The GDL is typically a highly porous (e.g., 60%-90%) non-woven carbon fiber paper or woven carbon fiber cloth, about 0.25 mm to 0.35 mm thick, with pore sizes on the order of hundreds of microns, and can be treated with various proprietary substances to improve performance. The role of the MPL is to minimize the contact resistance between the GDL and the catalyst layer and to help improve water transport. The MPL is typically composed of a thin layer of carbon powder and PTFE particles coated onto the GDL, with pore sizes on the order of one micron. Some fuel cells are manufactured to produce the membrane electrode assembly (MEA), the microporous layer (MPL), and the gas diffusion layer (GDL) as a one-piece assembly, called a unitized electrode assembly (UEA) 28.

[0032] Figure 2 Shows the use of as Figure 1The general fuel cell power generation device 30 of the stack of the fuel cell 10 described in []. Fuel (such as hydrogen (H2)) is supplied to the fuel inlet 32 and flows through the anode flow field plate to be distributed to the anode catalyst layer. The unconsumed fuel flows out of the fuel outlet 34 and can flow back to the fuel inlet 32 through a recirculation pump (not shown) and can be periodically purged to the environment. The oxidant (such as air) is provided by a blower (not shown) to the air inlet 36 and flows through the cathode flow field plate to be distributed to the cathode catalyst layer. The excess process air that has been humidified by the byproduct water flows out of the air outlet 38 and can pass through a radiator and / or condenser (not shown) before being discharged to the environment.

[0033] The power generation device 30 can further include a coolant circuit 40 for removing heat from the fuel cell. In many automotive applications, the coolant is a mixture of water and ethylene glycol to prevent the coolant from freezing in cold climates. The pump 42 supplies the coolant into the coolant inlet 44, where the coolant is then directed through cooler plates, etc. (not shown, but typically located between the fuel cells 10) and distributed on the surface of the plates. The fuel cell 10 transfers sensible heat to the circulating coolant, so the coolant becomes hotter but does not undergo a phase change. When the coolant leaves the stack at the coolant outlet 46, the coolant passes through the heat exchange device 48, whereby the sensible heat is discharged before circulating back to the inlet 44. In one example, the heat exchange device 48 is a radiator. The coolant flow can be regulated using a flow control valve or orifice 50.

[0034] As Figure 1 shown, the reactant flow field plate 20 is a bipolar plate. Most bipolar plate designs use solid materials, and only a small percentage of designs use porous materials on both the anode side and the cathode side. Each design has its own advantages and disadvantages. As the name implies, solid bipolar plates are impermeable to hydrogen fuel and thus perform excellently in keeping the reaction gases separated. In addition, due to the impermeability of solid bipolar plates, it is relatively simple to seal them in the stack. Therefore, the power generation device stack can be pressurized, which improves battery performance and reduces battery degradation. Another advantage of solid bipolar plates is that their impermeability allows the use of antifreeze coolants, such as water / ethylene glycol mixture (WEG), in the stack. This type of antifreeze coolant is very beneficial for fuel cells operating in cold environments, such as automotive applications. However, WEG can poison the membrane electrode assembly, so care must be taken to isolate WEG from the MEA.

[0035] The solid bipolar plates can be made of metal, such as stainless steel or titanium. Since the flow field geometry can be formed by conventional mass manufacturing methods (such as stamping, etc.), the metal plates can be mass-produced inexpensively. The solid bipolar plates can also be made of non-porous carbon or polymeric (composite) materials. The solid carbon plates or composite plates can be mass-produced by molding, etc., and the dimensional tolerances can generally be maintained more tightly than those of the metal formed plates. However, the solid carbon plates or composite plates are more costly to produce than the metal plates.

[0036] Although the solid bipolar plates may be useful and advantageous for certain applications, they also have disadvantages. One disadvantage of the metal plates is that they are prone to corrosion due to the presence of air and water with very high electrochemical potentials. The corrosion layer is non-conductive, and as the plates continue to corrode, the fuel cell loses performance. Coatings have been developed and applied to the plates to mitigate corrosion, but even this technique has operational limits.

[0037] In particular, the automotive industry may target a service life of 5,000 hours for fuel cells. It is said that some coatings on the metal plates have achieved this goal. However, the heavy vehicle industry may require a service life of 30,000 hours. Current automotive coatings or configurations are not close to this limit. Therefore, the heavy vehicle industry needs to develop fuel cells with longer operational limits, possibly up to 30,000 hours.

[0038] Another disadvantage of the solid plates is that they do not have inherent water management capabilities. In the operation of a PEM fuel cell, it is crucial to maintain an appropriate water balance between the rate of water generation at the cathode electrode (including water generated by proton traction through the PEM electrolyte) and the rate of water removal from the cathode electrode or water supply to the anode electrode. For a PEM fuel cell, if insufficient water returns to the anode electrode, adjacent parts of the PEM electrolyte will dry out, reducing the rate at which hydrogen ions can transfer through the PEM and also causing crossover of the reducing fluid, resulting in local overheating. Similarly, if insufficient water is removed from the cathode, the cathode electrode may be flooded, effectively limiting the supply of oxidant to the cathode and thus reducing the current. In addition, if too much water is removed from the cathode, the PEM may dry out, limiting the ability of hydrogen ions to cross the PEM and thus reducing the cell performance. Solid plates typically require external water management means, such as an external humidifier to prevent the MEA from drying out and cracking.

[0039] A porous bipolar plate (sometimes referred to as a water transport plate) is a porous separator used on the cathode and anode sides of the electrodes in a fuel cell. The porous bipolar plate strictly controls the pore size to form a bubble barrier that allows liquid to be transported through the pores to a liquid water chamber during fuel cell operation, but prevents the transport of reactant gases. Liquid transport allows membrane hydration and enables the removal of product water generated by the electrochemical reaction within the fuel cell on the cathode side. Preventing reactant gas transport stops the fuel gas and oxidant gas from escaping into the liquid water chamber.

[0040] The porous plate provides excellent water balance to wick excess water in the flow field channels through capillary action and migrate it to areas where water is lost due to evaporation, while maintaining the hydration of the membrane electrode assembly. The porous bipolar plate is exposed to the water flow field to maintain the desired operation of the fuel cell. In local regions of the cell (where the reactant gases flow from a cooler region to a hotter region), water evaporates from the porous plate, filling the gas flow with water vapor; in regions where the reactant gases move from a higher temperature to a lower temperature, the product water formed in the electrochemical reaction and the liquid water condensed from the cooling gas flow can be wicked away by the porous plate. As a result, one advantage of fuel cell systems with porous bipolar plates is that they exhibit very high durability. Another advantage is that systems with porous bipolar plates do not require the use of an external humidifier, which can reduce weight and complexity.

[0041] Typically, a pump-driven recirculating water loop can be utilized to provide the cell cooling function as well as the driving force to move water through the pores of the water transport plate to remove the product water.

[0042] Although porous bipolar plates have advantages, they also have disadvantages. For example, due to the difficulty in manufacturing plates with specific pore sizes, porous bipolar plates can be costly to produce on a large scale. Another disadvantage is that porous plates are difficult to seal, which can cause reliability issues in pressurized systems. Another significant disadvantage is that fuel cell systems utilizing porous bipolar plates cannot use antifreeze coolants (such as WEG) in the water cooling loop because the coolant will be absorbed into the pores of the plate and poison the MEA.

[0043] Embodiments of the disclosed invention address many of the aforementioned problems of bipolar plates by utilizing a four-fluid plate configuration that provides a fuel reactant flow field, an oxidant flow field, a water management flow field, and a dedicated coolant passage for an antifreeze coolant. The embodiments include a non-porous plate portion and a porous plate portion, which are wisely selected to capture the best aspects of both designs while reducing or eliminating the associated disadvantages. The four-fluid bipolar plate can be easily manufactured to reduce costs.

[0044] Refer to Figure 3 and Figure 4, the bipolar plate 100 for a fuel cell includes a non-porous plate 102 and a porous plate 104. In one embodiment of the present invention, the non-porous plate 102 includes a reactant side 106 (as Figure 3 shown) and an opposite water management side 108 (as Figure 4 shown). As shown, the reactant side 106 supplies hydrogen to the anode side of the MEA via a fuel flow field. Non-limiting examples of the flow field include cavities, porous substrates, or fuel flow field channels 110 as shown in the illustrated embodiment. The non-porous plate 102 further includes an internal coolant passage 112 ( Figure 8 and Figure 11 ), which isolates the antifreeze coolant (such as WEG) from other components in the fuel cell. Other general features of the non-porous plate 102 may include internal manifolds 114 for a fuel supply section 114a and a return section 114b, an oxidant supply section 114c and a return section 114d, a water management supply section 114e and a return section 114f, and a WEG coolant supply section 114g and a return section 114h. The sealing device 116 allows multiple fuel cells to be sealed and operated under pressure.

[0045] Figure 4 shows the opposite side of the bipolar plate 100. The water management side 108 of the non-porous plate 102 includes a water flow field. Non-limiting examples of the flow field include cavities, porous substrates, or water channels 118 as shown in the illustrated embodiment, which form part of an external circulating water management circuit 150 ( Figure 13 ), which allows for proper water management of the cathode flow field, as discussed in detail below. Water enters the plate channels through the water management supply manifold 114e and exits through the water management return manifold 114f.

[0046] The porous plate 104 includes a reactant side 120 and an opposite water management side 122. The reactant side 120 supplies an oxidant (e.g., air) to the cathode side of the MEA via an oxidant flow field. Non-limiting examples of the flow field include cavities, porous substrates, or oxidant flow field channels 124 as shown in the illustrated embodiment. The water management side 122 ( Figure 3 ) has no features (e.g., flat) in this embodiment, but plays a crucial role in maintaining optimal cell performance and durability.

[0047] The porous plate 104 can be made of graphite or other carbon-based materials and can also be made of metals (such as titanium or stainless steel). Features such as channels can be formed by hydroforming, casting, thermoforming, 3D printing / additive manufacturing, or milling / machining.

[0048] As described above, the pore sizes in the multi-Confucius plate 104 are designed to create a bubble barrier during fuel cell operation. The pore sizes are determined by the specific fuel cell operating conditions and pressure. For graphite or other carbon-based materials, pores can be formed in the plate by known processes. For example, U.S. Patent No. 6,197,442 details a manufacturing process in which graphite powder, reinforcing fibers, cellulose fibers, and a thermosetting resin are mixed with a liquid to form a slurry and the slurry is sprayed onto a mesh to form a planar sheet, and the sheet is dried to form a paper. The paper is cut to the desired size and laminated. The laminate is laminated, carbonized, and graphitized by pressure and heat to form a water-transporting plate for subsequent machining as needed. The finished porous plate exhibits excellent physical properties in terms of bubble pressure, water permeability, median pore size, porosity, through-plane resistivity, and compressive yield strength. For metal porous plates, pores can be formed by, for example, a stamping press or laser drilling.

[0049] Figure 5 and Figure 6 FIG. depicts another exploded view of the non-porous plate 102 according to the first embodiment of the present invention. The non-porous plate 102 can be formed from two half-plates 102A and 102B that are easy to manufacture and then joined together. For example, the half-plates can be made of metal (such as stainless steel or titanium), the flow channels and other features can be formed by metal stamping, etc., and the two half-plates are joined together by welding. Other non-limiting examples of joining methods include, for example, laser welding, brazing, thermoplastic bonding, or adhesives. The half-plate 102A in the illustrated embodiment includes a fuel flow field channel 110 ( Figure 5 ) located on the reactant-facing side and a WEG coolant half-channel 126A ( Figure 6 ) located on the opposite side. The half-plate 102B includes a water channel 118 ( Figure 6 ) located on the water management side 108 and a WEG coolant half-channel 126B ( Figure 5 ) located on the opposite side.

[0050] Reference Figure 7 and Figure 8 for more details, where, Figure 7 depicts a cross-sectional view of the cathode side of the bipolar plate 100 taken approximately at the location shown in Figure 4 , and Figure 8 depicts an enlarged view of the plate shown in Figure 7 . Refer to Figure 8, which more particularly shows the unperforated plate 102 and the multi-perforated plate 104. For clarity, the half-plates 102A, 102B are shown separated (e.g., prior to joining). Each half-plate may include rows of raised surfaces 128, and the valleys 130, 132 between these raised surfaces may define fluid flow channels on the outer surface of the unperforated plate. The raised surfaces 128 on one side of the plate define recesses 134 on the opposite side of the same plate. When the two half-plates 102A, 102B are joined together, the recesses may define an internal cavity 136. In one example, the valley 130 on the half-plate 102B defines a water management channel 118, the valley 132 on the half-plate 102A defines a fuel flow field channel 110, and the internal cavity 136 defines an internal anti-freeze coolant passage 112.

[0051] The reactant side 120 of the multi-perforated plate 104 includes an oxidant flow field channel 124 to supply air to the MEA. In one example, the channel 124 is transverse to the fuel flow field channel 110. The water management side 122 of the multi-perforated plate 104 is positioned against the flat raised surface 128 of the half-plate 102B. In this way, when deionized (DI) water circulates through the water channel 118, the pores within the multi-perforated plate 104 are in fluid communication with the deionized water, allowing the sub-plate 104 to become and remain fully filled with liquid.

[0052] The desired porosity in the multi-perforated plate 104 can be achieved by any suitable method known in the fuel cell art. For example, the multi-perforated plate 104 can be constructed as a water transport plate (WTP), a net shape molded from a slurry with an appropriate particle size, or laser drilled to achieve the desired pore size.

[0053] Figure 9 An alternative cross-sectional view of the bipolar plate 100 is depicted; Figure 10 A portion of the view is enlarged to show a possible configuration. Turning Figure 10 , the cross-sectional view includes the half-plate 102A, the half-plate 102B, and the multi-perforated plate 104. Similar to Figure 8 , for clarity, the half-plates 102A and 102B are shown slightly separated. Also shown are the recesses 134 in the half-plate 102A, which form the WEG coolant half-channels 126A.

[0054] The multi-perforated plate 104 can be sealed to the non-perforated plate 102 by conventional means to prevent gas or water leakage. For example, the sealing device 116 can include adhesives, nesting, interference fits, or grooves for receiving molded compression seals, gaskets, or O-rings. In one example, the multi-perforated plate 104 can be nested into a recess 138 formed in the water management side 108 of the non-perforated plate 102. The recess 138 spans the entire planar form of the multi-perforated plate 104 to effectively capture the plate and ensure proper alignment during assembly. In some examples, the recess 138 can reduce the overall thickness of the bipolar plate 100 because the multi-perforated plate 104 is substantially recessed into the thickness of the other plate and only minimally increases the overall thickness dimension.

[0055] Figure 11 A cross-sectional view of a proton exchange membrane (PEM) fuel cell 140 having a bipolar plate 100 according to a first embodiment of the present invention is depicted, Figure 12 a stack of such fuel cells is depicted, and Figure 13 a cross-section of a fuel cell power generation device 144 having the disclosed bipolar plate 100 is depicted. In the example shown, the oxidant flow field channels 124 are shown parallel to the fuel flow field channels 110, but this is for illustrative purposes and the convention will be followed for other embodiments. The fuel cell 140 includes a bipolar plate 100 located between an upper unitized electrode assembly 28 (UEA) and a lower unitized electrode assembly (UEA). The bipolar plate 100 abuts each UEA 28.

[0056] In operation, hydrogen is introduced at inlet 114a and reaches the anode side of the UEA 28 by flowing through the fuel flow field channels 110 in the non-perforated plate 102. Air is introduced at inlet 114c and reaches the cathode side of the UEA 28 by flowing through the oxidant flow field channels 124 in the multi-perforated plate 104. The water pump 146 circulates water through the desalinator 148 in the water management loop 150. Softened water, or deionized (DI) water, passes through the water management supply 114e and flows into the stack 144 through the channels 118 formed by the non-perforated plate 102 and the multi-perforated plate 104. The pores in the multi-perforated plate 104 are filled with water, and the sub-plate acts as a sponge to hold water and keep the UEA 28 hydrated. The multi-perforated plate 104 can directly transport the liquid to the UEA 28, or the multi-perforated plate can evaporate the water and the water vapor can migrate to the UEA through the air flow. The multi-perforated plate 104 can also remove the product water formed by the reaction at the cathode from the UEA 28. By maintaining the pressure in the water management loop 150 below the pressure of the reactants, the product water in liquid form can be directly driven into the pores of the multi-perforated plate 104. If the product water is in vapor form, it will condense on the multi-perforated plate and be absorbed back into the circulating water loop.

[0057] Thermal management is primarily controlled by a dedicated and isolated coolant circuit 152. A coolant pump 154 causes coolant to flow through a coolant supply section 114g into the stack 144 and out of the stack 144 through a coolant return section 114h. Between the coolant supply section and the coolant return section, in some configurations, the coolant is distributed over the surface of the cells 140. In the illustrated embodiment, the coolant flows through an internal passage 112 formed by the mating of half-plates 102A and 102B ( Figure 10 ). When the coolant exits the stack at the coolant return section 114h, the coolant passes through a heat exchange device 156, whereby sensible heat is removed before cycling back to the supply section 114g. In one example, the heat exchange device 156 is a radiator. The coolant flow can be regulated using a flow control valve or an orifice 158.

[0058] The impermeable nature of the non-porous orifice plate 102 eliminates the need for separate coolant tubing and allows the coolant passage to be located within the sub-plate 102, saving space compared to some designs that add separate cooler plates. As previously mentioned, this design allows the use of an antifreeze coolant, such as a water / ethylene glycol mixture (WEG), which is beneficial for fuel cells operating in cold environments.

[0059] In the illustrated embodiment, the coolant flows through an internal passage formed by the mating of half-plates 102A and 102B. However, other means of distributing the coolant are also within the scope of the present invention. For example, the internal coolant passage can be defined by a cavity that includes a porous substrate for distributing the coolant.

[0060] In most cases, an external humidifier is not required in the disclosed embodiments, but there are situations where adding an external humidifier may be beneficial to the system. For example, if the bipolar plates 100 use only passive water management features and operate in a particularly hot and dry environment, water can evaporate from the porous orifice plate faster than the product water produced by the fuel cell. In such an environment, adding an external humidifier 159 ( Figure 13 ) to the system, rather than incorporating active cooling features as detailed in other embodiments herein, may be advantageous.

[0061] In the illustrated embodiment, there is no porous medium in the anode channels 110. Under certain operating conditions, such as when there are local cooling regions, moisture can condense in the anode channels, causing water accumulation. The water must be removed periodically to prevent performance degradation at the anode electrode. Prior art solutions to this problem include attempts to blow the water out, which involve additional operating steps and consume parasitic power. In one embodiment, as Figure 11 and Figure 12As shown, one or more small drain holes 142 can be drilled from the bottom of the hydrogen channel to communicate with the DI water chamber 118. The size of the drain holes 142 can be designed as a bubble barrier to convey excess water from the fuel channel 110 to the water channel 118 without allowing the reaction gases to escape. The DI water circuit pressure can be maintained lower than the pressures at the anode and cathode. In this way, the pressure difference will drive the accumulated water through the drain holes 142 into the chamber 118, where the water returns to the DI water circuit.

[0062] As described above, under typical operating conditions, the thermal management of the fuel cell power generation device is mainly controlled by the antifreeze coolant circuit 152, where sensible heat is transferred to the circulating coolant passing through the coolant flow field. To a lesser extent, when the product water in the pores evaporates, some cell cooling can be provided by evaporative cooling, but the evaporative cooling function is typically not considered a control parameter in the sensible heat coolant flow system.

[0063] Compared with the sensible heat coolant flow method, evaporative cooling utilizes the latent heat of vaporization to increase the cooling efficiency per volume of water by up to one hundred-fold. The inventors of the present disclosure have determined that enhanced cooling can be achieved via evaporation in certain cases. Thus, in one aspect of the present invention, the independent operation of the water management circuit and the coolant circuit can be used to operate in a heat boost mode or a water recovery / accumulation mode.

[0064] In the heat boost mode, additional cooling is required for a limited duration, such as when the stack requires a large amount of power. In fuel cell vehicles, especially trucks, the heat boost mode can be beneficial when climbing steep or long road gradients, or operating at high power on a hot day, or in any other situation where the radiator is not large enough to handle the cooling requirements. In the heat boost mode, the thermal management strategy switches from sensible heat cooling to evaporative cooling to provide greater cooling capacity. In the heat boost mode, evaporative cooling can account for a larger portion of the total cooling function and may account for 90% or more in some design scenarios.

[0065] In operation, when additional cooling is needed or calculated to be needed, in the first step, the coolant flow rate (i.e., WEG) is reduced, which decreases the sensible heat cooling capacity. As a result, the stack temperature begins to rise, the rate of water evaporation from the pores increases, and significant evaporative cooling is achieved. Then, in the second step, the fuel cell is allowed to warm up or the temperature is maintained to increase the degree of evaporative cooling. To compensate for the increased water evaporation and prevent the pores from drying out and losing their bubble barriers, in the third step, the flow rate of water through the water management flow field can be increased. In one example, the increase in the water flow rate can be achieved by providing a pump-driven circulating water management circuit in fluid communication with the water management flow field and using the pump to increase the water flow rate.

[0066] Because the disclosed evaporative cooling scheme has a greater ability to handle large, short-duration heat demands, it provides a better short-term thermal management control strategy. The coolant flow rate can be adjusted to a reduced value to achieve an appropriate level of evaporative cooling and a desired stack temperature.

[0067] The disclosed heat boost mode consumes more water in the water management loop than can be simultaneously replenished through product water formation. Therefore, the heat boost mode is intended to last for a relatively short duration. However, in another aspect of the present invention, independent operation of the water management loop and the coolant loop can be used to operate the water recovery / accumulation mode. In the water recovery / accumulation mode, the coolant flow (i.e., WEG) is increased to a rate higher than its normal rate to reduce evaporative cooling and generate excess water through condensation within the cell. The excess product water can be collected and retained for future use in the heat boost mode.

[0068] In one implementation, the water recovery / accumulation mode can be operated during a portion of the cycle when the stack is not demanded (such as when the vehicle is traveling on a level ground), and the airflow through the radiator provides sufficient cooling. In the first step, when additional product water is needed or calculated to be needed, the coolant flow rate (i.e., WEG) in the coolant loop is increased to increase sensible heat cooling. As a result, the stack temperature drops, less product water evaporates via the pores, and instead condensate is formed. In the second step, the fuel cell is allowed to cool down or the temperature is maintained to condense the surplus product water. To compensate for the reduced water evaporation and prevent flooding of the cell, in the third step, the flow rate of water through the water management flow field can be reduced. In one example, the reduction in the water flow rate can be achieved by providing a pump-driven recirculating water management loop in fluid communication with the water management flow field and using the pump to reduce the water flow rate.

[0069] In another implementation, the fuel cell controller can receive sensor inputs or environmental inputs to determine whether the heat boost mode or the water recovery / accumulation mode is warranted and, if so, to what extent. Non-limiting examples of sensor inputs can include air flow rate, cathode exhaust temperature, cathode exhaust pressure, total water reservoir capacity, water inventory, water temperature, ambient temperature, coolant return temperature, and water loop outlet pressure. The controller can command the coolant pump and / or water pump flow rate settings in response to the sensor input values.

[0070] The fuel cell controller can also receive inputs from external environmental factors. Non-limiting examples include payload timing, vehicle route, GPS coordinates, road grade, weather forecast, time of day, and driver behavior. In one example, the controller can receive GPS route data indicating that a steep or extended road grade is approaching. The controller can command the stack to operate in a water recovery / accumulation mode well in advance to collect product water and retain it in a reservoir. Then, when the vehicle encounters the grade, the controller can command the stack to operate in a heat boost mode.

[0071] The operation of the heat boost mode and the water recovery / accumulation mode is not limited to the disclosed hybrid bipolar plates. The inventors envision that the disclosed operating methods are possible and beneficial in any four-fluid fuel cell power generation device in which an antifreeze coolant loop operates independently of a water management loop, such as that disclosed in U.S. Patent No. 7,135,247. The '247 patent discloses separate individual cooler plates disposed between every other fuel cell.

[0072] The disclosed heat boost mode and water recovery / accumulation mode provide several benefits and advantages over prior art 3-fluid stacks. One benefit of the heat boost mode is reduced parasitic power because the radiator and fan are actually turned down rather than increased during high power surges. In prior art stacks, operating the radiator and fan severely penalizes efficiency. Instead, turning down the temperature of the radiator increases efficiency.

[0073] Another advantage of the disclosed heat boost mode is that the size of the radiator can be reduced because there are available alternative cooling means that can be implemented within the fuel cell. Prior art 3-fluid designs utilize larger radiators that are more costly and increase the weight of the vehicle, resulting in a performance penalty. This is especially true for fuel cell trucks.

[0074] Figure 14 A cross-sectional view of a fuel cell 240 having a four-fluid bipolar plate 200 according to a second embodiment of the present invention is depicted. The half plate 102A can have the same construction as that Figure 11 depicted, but the half plate 102B is replaced by a simple flat plate 202B. The flat plate can be formed of the same material as the half plate 102A. The perforated plate 204 in this embodiment includes an oxidant flow field channel 224 on the first side of the plate and a DI water channel 218 on the opposite second side. In this configuration, the non-perforated plate 102 does not have a water channel. One advantage of this embodiment is its lower profile, which reduces stack height and weight. The size of the WEG coolant passage 212 is also reduced by half, but this can be compensated for by increasing the coolant flow rate.

[0075] Figure 15Depicts a cross-sectional view of a fuel cell 340 having a four-fluid bipolar plate 300 according to a third embodiment of the present invention. In this embodiment, DI water does not circulate throughout the stack, and water only circulates within the cell 340. The half plate 102A may have the same structure as that Figure 1 depicted, but the half plate 102B is replaced by a simple flat plate 302B. The flat plate may be formed of the same material as the half plate 102A. The sub-plate 304 may be configured as a water delivery plate and serve as a porous substrate for DI water; in effect, a DI water "sponge": the sub-plate collects product water and humidification water from the air, circulates them back to the inlet of the cell reactant channels 324, and hydrates the UEA 28. In-cell circulation occurs by capillary wicking, and when the water in the pores evaporates at the reactant channel inlet, fresh water is wicked from further below in the channel 324 where the pores are still saturated. This cycle continues passively, with evaporation occurring at the channel inlet and condensation occurring at the channel outlet. This embodiment provides the advantages of passive water management, which is less complex, saves the cost of external pumps and piping, and does not consume parasitic power.

[0076] ​ Depicts a cross-sectional view of a fuel cell 440 having a four-fluid bipolar plate 400 according to a fourth embodiment of the present invention. In this embodiment, the structure is substantially the same as that ​ depicted, except that an additional partition 460 divides the internal WEG coolant passage into two separate channels (shown as WEG1, WEG2). The separate channels can be used to evenly distribute heat on the cell, i.e., to increase more cooling capacity when needed. In one example, the two separate channels can carry different components of the coolant or completely different fluids.

[0077] ​ Depicts a cross-sectional view of a fuel cell 540 having a four-fluid bipolar plate 500 according to a fifth embodiment of the present invention. In this embodiment, the cathode-side structure and the WEG internal coolant passage are substantially the same as those ​ depicted, but the anode side utilizes a porous sub-plate 562 to supply hydrogen to the UEA 28. The non-porous plate 102 remains unchanged, but instead of the valleys 132 in the sub-plate 102A defining the fuel reactant channels ( ​ ), in this embodiment, these valleys define water channels 518 to keep the porous anode sub-plate 562 hydrated. Similar to the cathode side, the porous anode sub-plate 562 includes fuel flow field channels 510 adjacent to the UEA 28.

[0078] ​A cross-sectional view of a fuel cell 640 having a bipolar plate 600 according to a sixth embodiment of the present invention is depicted. This embodiment is a 3-fluid system because it does not include internal coolant passages for WEG coolant. The bipolar plate includes a non-porous sub-plate 602 and a porous sub-plate 104. The porous sub-plate is ​ . The non-porous daughter plate 602 differs from the previous embodiment in that it comprises a single plate and has no flat plates welded or otherwise joined thereto. Accordingly, the daughter plate 602 includes a water management side defining water channels 618 and an opposing reactant side defining fuel flow field channels 610.

[0079] ​ A cross-sectional view of a fuel cell 740 having a four-fluid bipolar plate 700 according to a seventh embodiment of the present invention is depicted. In this embodiment, the bipolar plate 700 includes a porous sub-plate 704 on the cathode side and a mixing sub-plate 766 on the anode side. The sub-plate 704 can be coupled to the sub-plate 204 ( ​ ) are substantially the same, having an oxidant flow field 724 on one side and a water flow field 718 on the opposite side. The mixing sub-plate 766 includes a porous portion and a non-porous portion. The non-porous portion defines internal coolant passages 712 that isolate the coolant from exposure to other cell components. The coolant can be an antifreeze type coolant, such as WEG. The porous portion defines a plurality of pores 768 that fluidly connect the fuel reactant flow field 710 to the water flow field 718. The size of the pores 768 is designed to be a bubble barrier to transport excess water from the fuel flow field 710 to the water flow field 718 without allowing hydrogen to escape into the water cavity.

[0080] In one example, the daughter board 766 may include a half board 766A (similar to ​ 102A in FIG), which is joined to half-plate 766B (similar to ​ 202B in the middle) to form the internal coolant passage 712. Flat plate 766B can be formed from the same material as half plate 766A. Half plates 766A and 766B can be joined by any of the aforementioned techniques, such as welding, laser welding, brazing, thermoplastic bonding, or adhesives. After joining, apertures 768 can be formed by any suitable technique, such as laser drilling.

[0081] Further embodiments can be implemented by swapping the fuel reactants and the oxidant reactants. For example, the previous embodiment described air flowing through the channels in the porous daughter plate 104 and hydrogen flowing through the channels in the non-porous daughter plate 102. It is contemplated within the scope of the present invention that the positions are swapped, meaning that hydrogen flows through the channels in the porous daughter plate 104 and air flows through the channels in the non-porous daughter plate 102.

[0082] One of the improvements to the disclosed fuel cell system is to prevent galvanic corrosion on the non-porous metal subplate. Due to the potential difference between the porous carbon subplate and the metal subplate, galvanic corrosion may occur at the interface 164 between the porous carbon subplate and the metal subplate ( ​ and ​ ). When the metal begins to oxidize, the cell begins to lose performance because the oxide layer is non-conductive. Existing technology solutions to this problem (where the system includes non-porous carbon) include applying a coating on the metal plate to prevent corrosion. Although the disclosed fuel cell system may still benefit from coatings, the system may not need to utilize them because the demineralized water loop / deionized water loop sweeps across the interface 164 between the metal and carbon and carries away any corrosion products that might otherwise accumulate and render the interface non-conductive. In fact, the water circulating at this interface prevents oxide buildup.

[0083] Examples of the method described herein are as follows:

[0084] (1) A method for preventing corrosion at the carbon / metal interface in a fuel cell, the method comprising the steps of:

[0085] Providing a bipolar plate comprising a metal subplate and a porous subplate, the metal subplate having at least one water management side, and the porous subplate having a reactant side and an opposing water management side, the water management side of the porous subplate being adjacent to the water management side of the metal subplate to form an interface;

[0086] Providing a combined electrode assembly adjacent to the bipolar plate;

[0087] Flowing fuel reactants and oxidant reactants from the reactant flow field on the bipolar plate to the combined electrode assembly to initiate an electrochemical reaction; [[ID=2,1]]

[0088] Flowing water through a water management circuit to the water management sides of the metal subplate and the porous subplate to sweep away corrosion products formed at the interface; and

[0089] Deionizing and desalting the water flowing in the water management circuit.

[0090] (2) The method for preventing corrosion at the carbon / metal interface in a fuel cell as described in (1) above, the method further comprising the steps of: forming an internal coolant passage within the bipolar plate and flowing an anti-freeze coolant through the internal coolant passage.

[0091] (10) A method for operating a four-fluid fuel cell in a thermal boost mode, the method comprising the steps of:

[0092] Providing a four-fluid fuel cell comprising an oxidant flow field, a fuel reactant flow field, a water management flow field, and an independent circulation coolant loop operable to remove sensible heat, the coolant loop being in fluid communication with a coolant flow field;

[0093] Reducing the flow rate of the coolant in the coolant circuit to reduce the sensible heat cooling capacity; and

[0094] Allowing the fuel cell to maintain or increase the temperature to increase evaporative cooling.

[0095] (11) The method of operating a four-fluid fuel cell as described in (10) above, wherein the coolant is an anti-freeze coolant.

[0096] (12) The method of operating a four-fluid fuel cell as described in (10) above, wherein at least one of the oxidant flow field and the fuel reactant flow field includes a plurality of pores fluidly connected to the water management flow field, and these pores are configured as bubble barriers.

[0097] (13) The method of operating a four-fluid fuel cell as described in (10) above, wherein the step of providing the four-fluid fuel cell includes providing a hybrid bipolar plate that includes an oxidant flow field, a fuel reactant flow field, an internal coolant passage, and a water management flow field.

[0098] (14) The method of operating a four-fluid fuel cell as described in (10) above, the method further comprising the step of: increasing the flow rate of water through the water management flow field to compensate for increased evaporation.

[0099] (15) The method of operating a four-fluid fuel cell as described in (14) above, wherein the step of providing the four-fluid fuel cell further includes providing a circulating water management circuit fluidly connected to the water management flow field.

[0100] (20) A method of accumulating and retaining product water in a four-fluid fuel cell, the method comprising the steps of:

[0101] Providing a four-fluid fuel cell that includes an oxidant flow field, a fuel reactant flow field, a water management flow field, and an independent circulating coolant circuit operable to remove sensible heat, the coolant circuit being fluidly connected to the coolant flow field;

[0102] Increasing the flow rate of the coolant in the coolant circuit to increase sensible heat cooling; and

[0103] Allowing the fuel cell to maintain or reduce the temperature to condense the surplus product water.

[0104] (21) The method of accumulating and retaining product water in a four-fluid fuel cell as described in (20) above, the method further comprising the step of providing a water reservoir to store the surplus product water, the water reservoir being fluidly connected to the water management circuit.

[0105] (22) The method for accumulating and retaining product water in a four-fluid fuel cell as described in (20) above, the method further comprising the steps of: reducing the flow rate of water through the water management flow field to accumulate surplus product water and compensate for reduced evaporation.

[0106] (23) The method for accumulating and retaining product water in a four-fluid fuel cell as described in (22) above, wherein the step of providing the four-fluid fuel cell further comprises providing a circulating water management circuit in fluid communication with the water management flow field.

[0107] (24) The method as described in (10) or (20) above, wherein the controller commands coolant pump and water pump flow rate settings in response to sensor data, the sensor data including at least one of air flow rate, cathode exhaust temperature, cathode exhaust pressure, total water reservoir capacity, water inventory, water temperature, ambient temperature, coolant return temperature, and water loop outlet pressure.

[0108] (25) The method as described in (10) or (20) above, wherein the controller commands coolant pump and water pump flow rate settings in response to environmental factors, the environmental factors including at least one of payload timing, vehicle route, GPS coordinates, road grade, weather forecast, time of day, and driver behavior.

Claims

1. A bipolar plate for a fuel cell, comprising: A non-porous plate, comprising: A first water management side and a second water management side opposite to the first water management side; The non-porous plate defines: A fuel supply internal manifold through-passage and a fuel return internal manifold through-passage; An oxidant supply internal manifold through-passage and an oxidant return internal manifold through-passage; A water management supply internal manifold through-passage and a water management return internal manifold through-passage; A coolant supply internal manifold through-passage and a coolant return internal manifold through-passage; and An internal coolant passage that is in fluid communication with the coolant supply internal manifold through-passage at one end and in fluid communication with the coolant return internal manifold through-passage at the other end, the internal coolant passage extending over an area between the fuel supply internal manifold through-passage and the fuel return internal manifold through-passage, and an area between the oxidant supply internal manifold through-passage and the oxidant return internal manifold through-passage; A first multi-porous plate, the first multi-porous plate comprising a reactant side and an opposite water management side, the reactant side comprising a first reactant flow field in fluid communication with one of the fuel supply internal manifold through-passage and the oxidant supply internal manifold through-passage, the water management side being in fluid communication with the first water management side of the non-porous plate; And A second multi-porous plate, the second multi-porous plate comprising a reactant side and an opposite water management side, the reactant side comprising a second reactant flow field in fluid communication with the other of the fuel supply internal manifold through-passage and the oxidant supply internal manifold through-passage, the water management side being in fluid communication with the second water management side of the non-porous plate.

2. The bipolar plate according to claim 1, characterized in that, At least one of the first multi-porous plate and the second multi-porous plate forms a nested seal within the recessed perimeter of the non-porous plate.

3. The bipolar plate according to claim 1, wherein At least one side of the non-porous plate defines a water management flow field.

4. The bipolar plate according to claim 3, characterized in that, The water management flow field includes water flow field channels.

5. The bipolar plate according to claim 1, wherein The non-porous plate includes a first half plate joined to a second half plate.

6. The bipolar plate according to claim 5, characterized in that, The internal coolant passage is defined by the joined first half plate and second half plate.

7. The bipolar plate according to claim 1, wherein The internal coolant passage is compatible with an anti-freeze coolant.

8. The bipolar plate according to claim 1, characterized in that, At least one of the first multi-porous plate and the second multi-porous plate includes a bubble barrier pore structure adapted to allow liquid to be transported through the pore structure and prevent reaction gas from being transported through the pore structure.

9. The bipolar plate according to claim 8, wherein Both the first multi-porous plate and the second multi-porous plate include a bubble barrier pore structure adapted to allow liquid to be transported through the pore structure and prevent reaction gas from being transported through the pore structure.

10. A non-porous plate for a fuel cell bipolar plate assembly, comprising: The non-porous plate includes a first half-plate and a second half-plate; the second half-plate is disposed opposite to the first half-plate; the first half-plate and the second half-plate each have rows of raised surfaces and valleys; the valleys of the first half-plate and the second half-plate provide a first water management side and a second water management side; the second water management side is opposite to the first water management side; The non-porous plate defines: a fuel supply internal manifold through-passage and a fuel return internal manifold through-passage; an oxidant supply internal manifold through-passage and an oxidant return internal manifold through-passage; a water management supply internal manifold through-passage and a water management return internal manifold through-passage; a coolant supply internal manifold through-passage and a coolant return internal manifold through-passage; and an internal coolant passage that is in fluid communication with the coolant supply internal manifold through-passage at one end and in fluid communication with the coolant return internal manifold through-passage at the other end, the internal coolant passage extending over an area between the fuel supply internal manifold through-passage and the fuel return internal manifold through-passage, and an area between the oxidant supply internal manifold through-passage and the oxidant return internal manifold through-passage.

11. The non-porous plate according to claim 10, wherein, The first water management side includes a first recessed perimeter adapted to receive a first perforated sub-plate.

12. The non-porous plate according to claim 11, wherein The first recessed perimeter is further adapted to provide a nested seal for the first perforated sub-plate.

13. The non-porous plate according to claim 11, characterized in that, The second water management side includes a second recessed perimeter adapted to receive a second perforated sub-plate.

14. The non-porous plate according to claim 13, wherein The second recessed perimeter is further adapted to provide a nested seal for the second perforated sub-plate.

15. The non-porous plate according to claim 10, wherein Further included is the first half-plate joined to the second half-plate, thereby defining the internal coolant passage.

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