Four-fluid bipolar plate for fuel cells

Abstract

The present invention provides a bipolar plate structure for fuel cell bipolar plates that enables improved delivery of humidified reactants and better removal of generated water. [Solution] A bipolar plate 100 for a fuel cell is provided, comprising: a solid subplate including a fluid reactant surface 120, an opposite water management surface 108, and an internal coolant passage between them; and a porous subplate 104 including a fluid reactant surface and an opposite water management surface that is in fluid communication with the water management surface of the solid subplate.

Description

[Technical Field]

[0001] Cross-references to related applications This application references to and claims priority and benefits from U.S. Patent Application No. 17 / 344,377, titled "FOUR-FLUID BIPOLAR PLATE FOR FUEL CELL," filed on 10 June 2021, which is incorporated herein by reference in its entirety. [Background technology]

[0002] This disclosure generally relates to a fuel cell bipolar plate, and more specifically to a bipolar plate structure that provides improved delivery of humidified reactants and better removal of generated water.

[0003] In a proton exchange membrane (PEM) fuel cell, hydrogen fuel is supplied to the anode, where an oxidation reaction occurs: H2 → 2H + +2e - It is catalytically dissociated into a proton and an electron. Proton (H + ) passes through the membrane electrolyte and reaches the positive electrode (cathode), but electrons (e - The current is conducted through an external path, generating a current between the anode and cathode via an external load. At the cathode, the reduction reaction: O2 + 4e - +4H + →According to 2H₂O, protons and electrons recombine in the presence of oxygen to form water. The byproducts of the PEM fuel cell reaction are water and heat, which necessitates cooling the fuel cell to maintain an acceptable internal temperature.

[0004] A single fuel cell includes a membrane electrode assembly (MEA) containing a membrane electrolyte sandwiched between a pair of electrodes (anode and cathode), and conductive plates adjacent to each electrode on the opposite side of the membrane electrolyte, defining the reaction gas flow field. A typical flow field plate guides the reaction gas to each electrode through a gas diffusion layer and a microporous layer. In some designs, the flow field plate can also carry water byproducts out of the cell.

[0005] To increase the electrical output of an electrochemical conversion assembly or fuel cell, multiple fuel cells are typically arranged and connected in a stack. In this arrangement, two adjacent cell units can share a common polar plate, which acts as the anode and cathode for two adjacent cell units connected in series. Such a polar plate is commonly referred to as a "bipolar plate." [Overview of the Initiative] [Means for solving the problem]

[0006] In one embodiment, a bipolar plate for a fuel cell includes a non-porous subplate having at least one water management surface and an internal coolant passage. The bipolar plate further includes a porous subplate having a reactant surface and a water management surface on the opposite side. The reactant surface of the porous subplate includes a first reactant flow field, and the water management surface is fluidly connected to the water management surface of the non-porous subplate.

[0007] In another embodiment, the bipolar plate for the fuel cell includes an oxidizer flow field, a fuel reactant flow field, a dedicated coolant passage, and a water management flow field.

[0008] In yet another embodiment, the bipolar plate for a fuel cell includes a non-porous subplate having a water management surface and a reactant surface. The reactant surface includes a first reactant flow field. The bipolar plate further includes a porous subplate having a reactant surface and a water management surface on the opposite side. The reactant surface includes a second reactant flow field. The water management surface of the porous subplate is fluidly connected to the water management surface of the non-porous subplate.

[0009] The features described herein can be better understood by referring to the drawings described below. The drawings are not necessarily to scale and are intended to illustrate the principles of the present invention. The same numbering is used in the drawings to indicate similar parts throughout the various figures. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 shows a schematic cross-sectional exploded view of a typical fuel cell. [Figure 2] Figure 2 shows a schematic cross-sectional view of a typical fuel cell power plant. [Figure 3] Figure 3 shows an exploded perspective view of the anode side of a bipolar plate according to one embodiment of the present invention. [Figure 4] Figure 4 shows an exploded perspective view of the cathode side of the bipolar plate shown in Figure 3. [Figure 5] Figure 5 shows a further exploded view of the bipolar plate shown in Figure 3. [Figure 6] Figure 6 shows a further exploded view of the bipolar plate shown in Figure 4. [Figure 7] Figure 7 shows a perspective cross-sectional view of the cathode side of the bipolar plate shown in Figure 3. [Figure 8] Figure 8 shows an enlarged cross-sectional view of the bipolar plate shown in Figure 7. [Figure 9] Figure 9 shows another perspective cross-sectional view of the cathode side of the bipolar plate shown in Figure 3. [Figure 10] Figure 10 shows an enlarged cross-sectional view of the bipolar plate shown in Figure 9. [Figure 11] FIG. 11 shows a cross-sectional view of a fuel cell having a bipolar plate according to the first embodiment of the present invention. [Figure 12] FIG. 12 shows a cross-sectional view of a stack of fuel cells having a bipolar plate according to the first embodiment of the present invention. [Figure 13] FIG. 13 shows a schematic cross-sectional view of a fuel cell power plant according to an embodiment of the present invention. [Figure 14] FIG. 14 shows a cross-sectional view of a fuel cell having a bipolar plate according to the second embodiment of the present invention. [Figure 15] FIG. 15 shows a cross-sectional view of a fuel cell having a bipolar plate according to the third embodiment of the present invention. [Figure 16] FIG. 16 shows a cross-sectional view of a fuel cell having a bipolar plate according to the fourth embodiment of the present invention. [Figure 17] FIG. 17 shows a cross-sectional view of a fuel cell having a bipolar plate according to the fifth embodiment of the present invention. [Figure 18] FIG. 18 shows a cross-sectional view of a fuel cell having a bipolar plate according to the sixth embodiment of the present invention. [Figure 19] FIG. 19 shows a cross-sectional view of a fuel cell having a bipolar plate according to the seventh embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] FIG. 1 shows a typical polymer electrolyte membrane (PEM) fuel cell 10, which generally includes an anode 12 and a cathode 14 separated by an ionomer membrane 16. The anode catalyst layer 18 a and the cathode catalyst layer 18 c are formed on respective surfaces of the planar membrane and convert hydrogen and oxygen reaction gases into electricity and water. This assembly is typically referred to as a membrane electrode assembly (MEA) 20. The catalyst layers 18 a and 18 c may be the same for the anode 12 and the cathode 14, but usually they are different. For example, the anode catalyst layer 18a It may have the function of separating hydrogen atoms into hydrogen ions and electrons, while the cathode catalyst layer 18 c It may have the function of reacting oxygen gas with electrons to form water.

[0012] The reactants (i.e., hydrogen and air) are guided to the MEA 20 by a flow field plate 22, which typically contains reactant flow channels (shown by dashed lines). The flow field plate 22 is shown as a bipolar plate and contains reactant flow channels for both fuel and oxidizer. The reactants are then guided from the channels to the gas diffusion layer (GDL) 24 adjacent to the flow field plate 22. a ,twenty four c It passes through, and then through the GDL and each catalyst layer 18 a , 18 c The microporous layer (MPL) 26 is located between them. a , 26 c The gas diffusion layer (GDL) can serve several functions, including the diffusion of the reaction gas flow into the catalyst layer, the transport of liquid and vapor water byproducts from the catalyst layer to the cathode gas channel (which is carried by the gas flow), the collection of current generated from the electrochemical reaction, and the provision of mechanical strength to support and protect the catalyst coating film. The GDL is typically a highly porous (e.g., 60%–90%) carbon fiber nonwoven or carbon fiber woven fabric, with a thickness of approximately 0.25–0.35 mm and pore sizes on the order of several hundred microns, and may be treated with various proprietary materials to improve performance. The microporous layer (MPL) functions to minimize contact resistance between the GDL and the catalyst layer and helps improve water transport. The MPL typically consists of a thin layer of carbon powder and PTFE particles coated on the GDL and has pore sizes on the order of 1 micron. Some fuel cells assemble the membrane electrode assembly (MEA), microporous layer (MPL), and gas diffusion layer (GDL) to be manufactured as a single unit assembly known as a unitized electrode assembly (UEA)28.

[0013] Figure 2 shows a typical fuel cell power plant 30 using a stack of fuel cells 10 as described in Figure 1. Fuel such as hydrogen (H2) is supplied to the fuel inlet 32, flows through the anode flow field plate, and is distributed to the anode catalyst layer. Unused fuel flows out from the fuel outlet 34, returns to the fuel inlet 32 ​​through a recycling pump (not shown), and may be periodically purged into the ambient environment. An oxidant such as air is supplied to the air inlet 36 by a blower (not shown), flows through the cathode flow field plate, and is distributed to the cathode catalyst layer. Excess process air humidified by water byproducts flows out from the air outlet 38 and may pass through a radiator and / or condenser (not shown) before being discharged into the environment.

[0014] The power plant 30 may further include a coolant loop 40 for removing heat from the fuel cell. In many automotive applications, the coolant is a mixture of water and ethylene glycol to prevent freezing of the coolant in cold climates. A pump 42 supplies the coolant to a coolant inlet 44, where it is guided through a cooling plate or the like (not shown, but typically located between the fuel cells 10) and distributed onto the surface of the plate. The fuel cell 10 transfers sensible heat to the circulating coolant, so the coolant becomes warm, but no phase change occurs. Leaving the stack at the coolant outlet 46, the coolant passes through a heat exchanger 48, where sensible heat is removed before it is circulated back to the inlet 44. In one example, the heat exchanger 48 is a radiator. A flow control valve or orifice 50 may be used to regulate the flow of the coolant.

[0015] As shown in Figure 1, the reactant flow field plate 20 is a bipolar plate. Many bipolar plate designs use solid materials, and a few designs use porous materials on both the anode and cathode sides. Each design has its own advantages and disadvantages. Solid bipolar plates, as their name suggests, are impermeable to hydrogen fuel and are therefore excellent at keeping reaction gases isolated. Furthermore, solid bipolar plates in a stack are relatively easy to seal due to their impermeability. Thus, the power plant stack can be pressurized, which improves cell performance and reduces cell degradation. Another advantage of solid bipolar plates is that, due to their impermeability, antifreeze-type coolants such as water / ethylene glycol mixtures (WEG) can be used in the stack. This antifreeze-type coolant is very beneficial for batteries operating in low-temperature environments, such as in automotive applications. However, since WEG contaminates the membrane electrodes, care must be taken to isolate the WEG from the MEA.

[0016] Solid bipolar plates can be manufactured from metals such as stainless steel or titanium. Metal plates can be mass-produced inexpensively because the flow field shape can be formed by conventional mass production methods such as stamping. Solid bipolar plates may also be manufactured from non-porous carbon or polymer (composite) materials. Solid carbon or composite plates can be mass-produced by molding and other methods, and generally allow for tighter dimensional tolerances than metal molded plates. However, solid carbon or composite plates are more expensive to manufacture than metal plates.

[0017] Solid bipolar plates are useful and may be advantageous in certain applications, but they also have drawbacks. One drawback of metal plates is their susceptibility to corrosion due to the presence of air and water at very high electrochemical potentials. The corroded layer is nonconductive, and as the plate corrodes, the performance of the fuel cell deteriorates. Coatings have been developed and applied to the plates to mitigate corrosion, but this technology also has operational limitations.

[0018] The automotive industry, in particular, may be aiming for a fuel cell operating life of 5,000 hours. Some coatings on metal plates are said to have achieved this goal. However, the heavy-duty vehicle industry may require an operating life of 30,000 hours. Current automotive coatings and structures are not close to that limit. Therefore, the heavy-duty vehicle industry will likely need to develop fuel cells with a much longer operating limit, perhaps even up to 30,000 hours.

[0019] Another drawback of solid plates is that they lack inherent moisture management capabilities. In the operation of PEM fuel cells, it is crucial to maintain a proper water balance between the rate at which water is generated at the cathode electrode (including water resulting from proton drag through the PEM electrolyte) and the rate at which water is removed from the cathode or supplied to the anode electrode. In PEM fuel cells, if insufficient water is returned to the anode electrode, adjacent portions of the PEM electrolyte will dry out, thereby reducing the rate of hydrogen ion movement through the PEM, causing fluid crossover and localized overheating. Similarly, if water is not removed sufficiently from the cathode, the cathode electrode may become submerged, substantially limiting the supply of oxidizer to the cathode and potentially reducing the current. Furthermore, if too much water is removed from the cathode, the PEM may dry out, limiting the ability of hydrogen ions to pass through the PEM and potentially degrading battery performance. Typically, solid plates require external water management means, such as external humidifiers, to prevent MEA dryout and cracking.

[0020] Porous bipolar plates, also known as water transport plates, are porous separator plates used on both the cathode and anode sides of fuel cell electrodes. Porous bipolar plates precisely control pore size, creating a bubble barrier that allows liquid water to move through these pores into the cavity during fuel cell operation, while preventing the movement of reaction gases. Liquid movement allows for membrane hydration, enabling the removal of generated water on the cathode side resulting from electrochemical reactions within the fuel cell. Preventing the movement of reaction gases prevents fuel and oxidizer gases from leaking into the liquid water cavity.

[0021] Porous plates maintain hydration in the membrane electrode assembly and provide an excellent moisture balance by drawing up excess water in the flow field channels and moving it to areas where moisture is being lost through evaporation. Porous bipolar plates are exposed to the water flow field to maintain the desired operation of the fuel cell. In localized areas of the cell where the reaction gas flows from a low-temperature region to a high-temperature region, water evaporates from the porous plate and the gas flow becomes saturated with water vapor; in areas where the reaction gas flows from a high-temperature region to a low-temperature region, the porous plate can draw up the water produced by the electrochemical reaction and the liquid water condensed from the cooling gas flow. As a result, one advantage of fuel cell systems with porous bipolar plates is that they are extremely durable. Another advantage is that systems with porous bipolar plates can reduce weight and complexity because they do not require the use of an external humidifier.

[0022] Typically, a pump-driven circulating water loop can be used to provide not only a cooling function for the cell but also the driving force to move water through the pores of the water transport plate and remove the generated water.

[0023] Porous bipolar plates have advantages, but also disadvantages. For example, manufacturing plates with specific pore sizes can be difficult, leading to high costs in mass production. Another disadvantage is that porous plates are difficult to seal, which can lead to reliability issues in pressurized systems. Another major drawback is that fuel cells using porous bipolar plates cannot use antifreeze-type coolants such as WEG in the water-cooling loop to avoid the coolant being absorbed into the pores and contaminating the MEA.

[0024] Embodiments of the invention of the present disclosure solve many of the aforementioned problems relating to bipolar plates by using a four-fluid plate structure that provides dedicated coolant passages for a fuel reactant flow field, an oxidizer flow field, a water management flow field, and an antifreeze-type coolant. Embodiments include both a non-porous plate portion and a porous plate portion, which are thoughtfully selected to obtain the best aspects of both designs while reducing or eliminating the associated drawbacks. Four-fluid bipolar plates can be easily manufactured and cost-effective.

[0025] Referring to Figures 3 and 4, the bipolar plate 100 for the fuel cell includes a non-porous subplate 102 and a porous subplate 104. In one embodiment of the present invention, the non-porous subplate 102 includes a reactant surface 106 (shown in Figure 3) and an opposite water management surface 108 (shown in Figure 4). As shown, the reactant surface 106 supplies hydrogen to the anode side of the MEA via a fuel flow field. Non-limiting examples of the flow field include a cavity, a porous substrate, or a fuel flow field channel 110, as shown in the illustrated embodiment. The non-porous subplate 102 further includes an internal coolant passage 112 for separating an antifreeze-type coolant, such as a WEG, from other components in the fuel cell (Figures 8 and 11). Other common features of the non-porous subplate 102 may include internal manifolds 114 for the fuel supply section 114a and fuel return section 114b, for the oxidizer supply section 114c and oxidizer return section 114d, for the water management supply section 114e and water management return section 114f, and for the WEG coolant supply section 114g and WEG coolant return section 114h. Sealing means 116 allow multiple fuel cells to be sealed and operated under pressure.

[0026] Figure 4 shows the opposite side of the bipolar plate 100. The water management surface 108 of the non-porous subplate 102 includes a water flow field. Non-limiting examples of the flow field include cavities, porous substrates, or water channels 118 that form part of an external circulating water management loop 150 (Figure 13), as shown in the illustrated embodiment, and enable proper water management of the cathode flow field, as will be described in detail below. Water enters the plate channel through the water management supply manifold 114e and exits through the water management return manifold 114f.

[0027] The porous subplate 104 includes a reactant surface 120 and a water management surface 122 on the opposite side. The reactant surface 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 a cavity, a porous substrate, or, as shown in the illustrated embodiment, an oxidant flow field channel 124 in this embodiment. In this embodiment, the water management surface 122 (Figure 3) is featureless (e.g., flat) but plays an important role in maintaining optimal cell performance and durability.

[0028] The porous subplate 104 may be manufactured from graphite or other carbon-based materials, or from a metal such as titanium or stainless steel. Features such as channels may be formed by hydroforming, casting, thermoforming, 3D printing / additive manufacturing, or milling / machining.

[0029] As mentioned above, the pores in the porous subplate 104 are made to a size that forms a bubble barrier during fuel cell operation. The pore size is determined by the specific fuel cell operating conditions and pressure. For graphite or other carbon-based materials, pores may be formed in the plate by known methods. For example, U.S. Patent No. 6,197,442 details a manufacturing process in which graphite powder, reinforcing fibers, cellulosic fibers, and thermosetting resin are mixed with a liquid to form a slurry, which is showered onto a screen to form a planar sheet, which is then dried to form paper. Such paper is cut to the desired size and laid up. The layups are laminated under pressure and heat, carbonized, and graphitized to form a water transport plate for later machining as needed. The finished porous plate exhibits excellent physical properties with respect to bubble pressure, water permeability, median pore diameter, porosity, in-plane resistivity, and compression yield strength. In the case of metallic porous plates, pores may be formed, for example, by punch press or laser drilling.

[0030] Figures 5 and 6 show further exploded views of a non-porous subplate 102 according to a first embodiment of the present invention. The non-porous subplate 102 may be formed from two half-plates 102A and 102B that are easily manufactured and joined together. For example, the half-plates may be manufactured from a metal such as stainless steel or titanium, and flow channels and other features may be formed by metal stamping or the like, and these two half-plates may be joined together by welding.

[0031] Other non-limiting examples of joining methods include, for example, laser welding, brazing, thermoplastic bonding, or adhesives. In the illustrated embodiment, half plate 102A includes a fuel flow field channel 110 on the side facing the reactants (Figure 5) and a WEG coolant half channel 126A on the opposite side (Figure 6). Half plate 102B includes a water channel 118 on the water management surface 108 (Figure 6) and a WEG coolant half channel 126B on the opposite side (Figure 5).

[0032] Further details can be found by referring to Figures 7 and 8, where Figure 7 shows a cross-sectional view of the cathode side of the bipolar plate 100 along approximately the position shown in Figure 4, and Figure 8 shows an enlarged view of the plate shown in Figure 7. Referring to Figure 8, the non-porous subplate 102 and the porous subplate 104 are shown in more detail. The half plates 102A and 102B are shown separately for clarity (e.g., before joining). Each half plate may include rows of raised surfaces 128 and valleys 130, 132 between them, which can define fluid flow channels on the outer surface of the non-porous plate. The raised surface 128 on one side of the plate defines a recess 134 on the opposite side of the same plate. This recess can define an internal cavity 136 when the two half plates 102A and 102B are joined together. 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 antifreeze coolant passage.

[0033] The reactant surface 120 of the porous subplate 104 includes an oxidant flow field channel 124 for supplying air to the MEA. In one example, the channel 124 is transverse to the fuel flow field channel 110. The water management surface 122 of the porous subplate 104 is positioned relative to the flat raised surface 128 of the halfplate 102B. In this way, as desalination (DI) water is circulated through the water channel 118, the pores in the porous subplate 104 are in fluid communication with the DI water, and the subplate 104 is completely saturated with liquid and maintains that state.

[0034] The desired porosity in the porous subplate 104 may be achieved by any suitable method known in the field of fuel cell technology. For example, the porous subplate 104 may be assembled as a water transport plate (WTP), formed into a net shape from a slurry having an appropriate particle size, or laser-perforated to achieve a desired pore size.

[0035] Figure 9 shows another cross-sectional view of the bipolar plate 100, a portion of which is enlarged in Figure 10 to illustrate one possible structure. Looking at Figure 10, the cross-sectional view includes a half-plate 102A, a half-plate 102B, and a porous subplate 104. Similar to Figure 8, the half-plates 102A and 102B are shown somewhat separated for clarity. Also shown is a recess 134 in the half-plate 102A that forms a WEG coolant half-channel 126A.

[0036] The porous subplate 104 may be sealed to the non-porous subplate 102 by conventional means to prevent gas or water leakage. For example, the sealing means 116 may include adhesive, nesting, interference fit, or grooves for receiving molded compression seals, gaskets, or O-rings. In one example, the porous subplate 104 may be nested in a recess 138 formed in the water management surface 108 of the non-porous subplate 102. The recess 138 extends across the entire plane of the porous subplate 104, effectively capturing the plate and ensuring proper alignment during assembly. In some examples, the porous subplate 104 is substantially embedded within the thickness of the other plate, and the increase in overall thickness dimension is minimal, so the recess 138 can reduce the overall thickness of the bipolar plate 100.

[0037] Figure 11 shows a cross-sectional view of a proton exchange membrane (PEM) fuel cell 140 with a bipolar plate 100 according to a first embodiment of the present invention, Figure 12 shows a stack of such a fuel cell, and Figure 13 shows a cross-sectional view of a fuel cell power plant 144 with the disclosed bipolar plate 100. In the illustrated example, the oxidizer flow field channel 124 is shown to be parallel to the fuel flow field channel 110, but this is for illustrative purposes and is similar in other embodiments. The fuel cell 140 includes a bipolar plate 100 between upper and lower unitized electrode assemblies 28 (UEAs). The bipolar plate 100 is in contact with each UEA 28.

[0038] During operation, hydrogen is introduced at inlet 114a and flows through the fuel flow field channel 110 in the non-porous subplate 102 to reach the anode side of the UEA 28. Air is introduced at inlet 114c and flows through the oxidizer flow field channel 124 in the porous subplate 104 to reach the cathode side of the UEA 28. The water pump 146 circulates water through the desalination unit 148 in the water management loop 150. Desalination water, or deionized (DI) water, flows through the water management supply unit 114e and into the stack 144 through the channel 118 formed by the non-porous subplate 102 and the porous subplate 104. The pores of the porous subplate 104 are filled with water, and the subplate functions as a sponge that retains water and maintains the water content of the UEA 28. The porous subplate 104 can either directly transport the liquid to the UEA 28 or evaporate the water and transfer the water vapor to the UEA through the airflow. The porous subplate 104 can also remove the water product formed by the reaction at the cathode from the UEA 28. The water product in liquid form can also be directly introduced into the pores of the porous subplate 104 by maintaining the pressure in the water management loop 150 lower than the pressure of the reactants. If the water product is in vapor form, it can be condensed on the porous subplate, absorbed there, and returned to the circulating water loop.

[0039] Thermal management is primarily controlled by a dedicated, isolated coolant loop 152. A coolant pump 154 ​​flows the coolant into the stack 144 through a coolant supply section 114g and out of the stack 144 through a coolant return section 114h. In the meantime, in some configurations, the coolant is distributed across the entire surface of the cell 140. In the illustrated embodiment, the coolant flows through an internal passage 112 formed by joining half plates 102A and 102B (Figure 10). Leaving the stack at the coolant return section 114h, the coolant passes through a heat exchanger 156, where sensible heat is discharged, before being circulated back to the supply section 114g. In one example, the heat exchanger 156 is a radiator. A flow control valve or orifice 158 may be used to regulate the coolant flow.

[0040] The impermeability of the non-porous subplate 102 eliminates the need for separate coolant tubes, allowing the coolant passages to be located inside the subplate 102, thus saving space compared to some designs that add separate cooling plates. As mentioned earlier, this design allows the use of antifreeze-type coolants such as water / ethylene glycol mixtures (WEG), which is beneficial for fuel cells operating in low-temperature environments.

[0041] In the illustrated embodiment, the coolant flows through an internal passage formed by joining half plates 102A and 102B. However, other means of distributing the coolant are also conceivable within the scope of the present invention. For example, the internal coolant passage can be defined by a cavity containing a porous substrate for distributing the coolant.

[0042] In most circumstances, an external humidifier is not necessary in the disclosed embodiments, but there are scenarios in which adding an external humidifier may be beneficial to the system. For example, if the bipolar plate 100 uses only passive water management functions and is operated particularly in hot, dry environments, water may evaporate from the porous subplate faster than the fuel cell can produce water. In such environments, it may be advantageous to add an external humidifier 159 (Figure 13) to the system than to incorporate an active cooling function as detailed in other embodiments of this specification.

[0043] In the illustrated embodiment, there is no porous medium in the anode channel 110. Under certain operating conditions, such as the presence of locally cold regions, moisture may condense and accumulate in the anode channel. To prevent degradation of the anode electrode performance, the water needs to be removed periodically. Conventional solutions to this problem include attempts to blow the water away, but this requires extra operating procedures and consumes parasitic power. In one embodiment, as shown in Figures 11 and 12, one or more small drainage holes 142 can be drilled from the bottom of the hydrogen channel to communicate with the DI water cavity 118. The drainage holes 142 can be sized to act as a bubble barrier to transport excess water from the fuel channel 110 to the water channel 118 without allowing reaction gases to escape. The pressure in the DI water loop can be kept lower than the pressures in the anode and cathode. In this way, the pressure difference forces the accumulated water through the drainage holes 142 into the cavity 118, where the water is returned to the DI water loop.

[0044] As described above, under typical operating conditions, thermal management of a fuel cell power plant is primarily controlled by the antifreeze coolant loop 152, with sensible heat being transferred to the circulating coolant passing through the coolant flow field. To a lesser extent, some cell cooling can also be provided by evaporative cooling as generated water in the pores evaporates, but evaporative cooling is not typically considered a control parameter in the sensible heat coolant flow system.

[0045] Evaporative cooling, compared to sensible heat coolant flow methods, utilizes the heat of vaporization to improve the cooling effect per unit volume of water by up to 100 to 1. The inventors of this disclosure have confirmed that enhanced cooling can be achieved by evaporation under certain conditions. Therefore, in one aspect of the present invention, a thermal boost mode or a water recovery / storage mode can be operated by utilizing the independent operation of the water management loop and the coolant loop.

[0046] In thermal boost mode, additional cooling is required for a finite duration, such as when the stack is demanding a large amount of power. In fuel cell vehicles (especially trucks), thermal boost mode can be useful when climbing steep inclines or long roads, operating at high power on hot days, or in any other scenario where the radiator is not large enough to adequately handle the cooling requirements. In thermal boost mode, the thermal management method shifts from sensible cooling to evaporative cooling, providing greater cooling capacity. Evaporative cooling can account for the majority of the total cooling function in thermal boost mode, and in some design scenarios, it can account for more than 90%.

[0047] If additional cooling is needed or calculated to be needed during operation, in the first step, the coolant flow rate (i.e., WEG) is reduced, thereby decreasing the sensible heat cooling capacity. As a result, the stack temperature begins to rise, increasing the rate of water evaporation from the pores, resulting in significant evaporative cooling. Next, in the second step, the fuel cell temperature is increased or maintained to further enhance the degree of evaporative cooling. In the third step, to compensate for the increased water evaporation and prevent the pores from drying out and the bubble barrier from being lost, the flow rate of water through the water management flow field can be increased. In one example, the increase in water flow rate is achieved by providing a pump-driven circulating water management loop that fluid-communicates with the water management flow field and increasing the water flow rate by the pump.

[0048] The disclosed evaporative cooling method offers a superior short-term thermal management control strategy due to its greater ability to handle large, short-term thermal demands. The coolant flow rate can be adjusted to a low value to achieve an appropriate level of evaporative cooling and the desired stack temperature.

[0049] The disclosed thermal boost mode depletes the amount of water in the water management loop by more than can be simultaneously replenished by the formation of generated water. Therefore, the thermal boost mode is intended to be relatively short in duration. However, in another aspect of the invention, the independent operation of the water management loop and the coolant loop may be utilized to operate a water recovery / storage mode. In the water recovery / storage mode, the coolant flow rate (i.e., WEG) is increased beyond the normal rate, reducing evaporative cooling and generating excess water in the cell by condensation. The excess generated water can be collected and retained for use in a future thermal boost mode.

[0050] In one embodiment, the water recovery / storage mode can also be operated during a portion of the cycle when stacking is not required and the airflow through the radiator provides sufficient cooling, such as when the vehicle is traveling on level ground. In the first step, when additional generated 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 decreases, the amount of generated water evaporating from the pores decreases, and condensed water is formed instead. In the second step, the fuel cell temperature is lowered but maintained to condense the excess generated water. In the third step, to compensate for the reduction in water evaporation and prevent self-rudding, the flow rate of water through the water management flow field may be reduced. In one example, the reduction in water flow rate may be achieved by providing a pump-driven circulating water management loop that is in fluid communication with the water management flow field, and using the pump to reduce the water flow rate.

[0051] In another embodiment, the fuel cell controller may receive sensor inputs or environmental inputs to determine whether a thermal boost mode or a water recovery / storage mode is guaranteed, and if so, to what extent. Non-limiting examples of sensor inputs may include air flow rate, cathode exhaust temperature, cathode exhaust pressure, total storage capacity, water stock, water temperature, ambient temperature, coolant return temperature, and water loop outlet pressure. The controller may command flow rate settings for the coolant pump and / or water pump in response to the sensor input values.

[0052] The fuel cell controller may also receive input from external environmental factors. Non-limiting examples include payload timing, vehicle route, GPS coordinates, road gradient, weather forecast, time of day, and driver behavior. For example, the controller may receive GPS route data indicating that a steep or extended road gradient is approaching. The controller may instruct the stack well in advance to activate water recovery / storage mode, allowing it to collect generated water and store it in a reservoir. Then, when the vehicle encounters a gradient, the controller may instruct the stack to activate thermal boost mode.

[0053] The operation of the thermal boost mode and the water recovery / storage mode is not limited to the disclosed hybrid bipolar plate. The inventors assume that the disclosed operating method may be possible and beneficial in any four-fluid fuel cell power plant where an antifreeze type coolant loop operates independently of the water management loop, as disclosed in U.S. Patent No. 7,135,247. The 247 patent discloses separate individual coolant plates arranged between all the other fuel cells.

[0054] The disclosed thermal boost mode and water recovery / storage mode offer several advantages over conventional three-fluid stacks. One advantage is that the thermal boost mode reduces parasitic power because, at high power levels, it actually tunes down the radiators and fans instead of increasing them. In conventional stacks, running the radiators and fans hard reduces efficiency. Conversely, tuning down the radiators increases efficiency.

[0055] Another advantage of the disclosed thermal boost mode is that the radiator size can be reduced because there are alternative cooling methods that can be achieved within the fuel cell. Conventional three-fluid designs use much larger radiators, which are more expensive and increase the vehicle's weight, thus reducing performance. This is especially true for fuel cell trucks.

[0056] Figure 14 shows 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. The half-plate 102A may have the same structure as shown in Figure 11, but the half-plate 102B is replaced with a simple flat plate 202B. The flat plate may be formed from the same material as the half-plate 102A. In this embodiment, the porous subplate 204 includes an oxidizer flow field channel 224 on a first side of the plate and a DI water channel 218 on a second side opposite it. In this structure, the non-porous subplate 102 does not have water channels. One advantage of this embodiment is that it is thin, reducing the 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.

[0057] Figure 15 shows 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, the DI water does not circulate throughout the entire stack, but only within the cell 340. The half-plate 102A may have the same structure as shown in Figure 11, but the half-plate 102B is replaced with a simple flat plate 302B. The flat plate may be formed from the same material as the half-plate 102A. A sub-plate 304, which may be constructed as a water transport plate, functions as a porous substrate for the DI water and is effectively a DI water "sponge": it collects generated water and humidified water from the air, circulates it back to the inlet of the cell reactant channel 324, and humidifies the UEA 28. Intra-cell circulation occurs by pore wicking, such that as water in the pores evaporates at the inlet of the reactant channel, new water is drawn up from further downstream of 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 is not overly complex, saves on the cost of external pumps and piping, and offers the advantages of passive water management, as it does not consume parasitic power.

[0058] Figure 16 shows 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 configuration is essentially the same as that shown in Figure 11, except that an additional separator plate 460 divides the internal WEG coolant passage into two separate channels (indicated as WEG1 and WEG2). The separate channels can be used to equalize the heat distribution throughout the cell, i.e., higher cooling capacity can be added where needed. In one example, the two separate channels can carry coolants of different compositions or completely different fluids.

[0059] Figure 17 shows 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 passages are essentially the same as those shown in Figure 9, except that the anode side uses a porous subplate 562 to supply hydrogen to the UEA 28. The non-porous subplate 102 remains unchanged, but in this embodiment, instead of the valleys 132 of subplate 102A defining the fuel reactant channels (Figure 8), these define water channels 518 to maintain hydration of the porous anode subplate 562. Similar to the cathode side, the porous anode subplate 562 includes a fuel flow field channel 510 adjacent to the UEA 28.

[0060] Figure 18 shows a cross-sectional view of a fuel cell 640 having a bipolar plate 600 according to a sixth embodiment of the present invention. This embodiment is a three-fluid system because it does not include an internal coolant passage for the WEG coolant. The bipolar plate includes a non-porous subplate 602 and a porous subplate 104. The porous subplate is essentially the same as that shown in Figure 11. The non-porous subplate 602 differs from the previous embodiment in that it includes a single plate and there is no flat plate welded or otherwise joined to it. Thus, the subplate 602 includes a water management surface defining a water channel 618 and, on the opposite side, a reactant surface defining a fuel flow field channel 610.

[0061] Figure 19 shows 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. In this embodiment, the bipolar plate 700 includes a porous subplate 704 on the cathode side and a hybrid subplate 766 on the anode side. Subplate 704 is essentially the same as subplate 204 (Figure 14) and has an oxidizer flow field 724 on one side and a water flow field 718 on the opposite side. The hybrid subplate 766 includes a porous portion and a non-porous portion. The non-porous portion defines an internal coolant passage 712 that isolates the coolant from exposure to other cell components. The coolant may 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 pores 768 are sized to act as bubble barriers for transporting excess water from the fuel flow field 710 to the water flow field 718 without allowing hydrogen gas to escape into the water cavities.

[0062] In one example, the subplate 766 may include a halfplate 766A (similar to 102A in Figure 8) joined to a halfplate 766B (similar to 202B in Figure 14) for forming an internal coolant passage 712. The flatplate 766B may be formed from the same material as the halfplate 766A. The halfplates 766A and 766B may be joined by any of the aforementioned techniques, such as welding, laser welding, brazing, thermoplastic bonding, or adhesive bonding. After joining, pores 768 may be formed by any suitable technique, such as laser drilling.

[0063] Further embodiments can be realized by swapping the fuel and oxidizer reactants. For example, in the previous embodiment, it was described that air flows through the channels of the porous subplate 104 and hydrogen flows through the channels of the non-porous subplate 102. Swapping the positions, i.e., hydrogen flows through the channels of the porous subplate 104 and air flows through the channels of the non-porous subplate 102, is also considered to be within the scope of the present invention.

[0064] One of the improvements to the disclosed fuel cell system is the prevention of electrolytic corrosion on the non-porous metal subplate. Electrolytic corrosion can occur at the interface 164 (Figures 11 and 13) between the porous carbon subplate and the metal subplate due to their potential difference. As the metal begins to oxidize, the cell begins to degrade in performance as the oxide layer becomes non-conductive. A prior art solution to this problem (when the system contains non-porous carbon) is to apply a coating to the metal plate to prevent corrosion. While the disclosed fuel cell system could still benefit from a coating, it may not need to utilize one because a desalination / deionized water loop sweeps the interface 164 between the metal and carbon, removing any corrosion products that would normally accumulate and make the interface non-conductive. In fact, the water circulating over the interface prevents oxide buildup.

[0065] Examples of the methods described herein are as follows:

[0066] (1) A method for preventing corrosion of a carbon / metal interface in a fuel cell, the method comprising the following steps:

[0067] A bipolar plate comprising a metal subplate and a porous subplate, wherein the metal subplate has at least one water management surface, the porous subplate has a water management surface opposite to the reactant surface, and the water management surface of the porous subplate is adjacent to the water management surface of the metal subplate so as to form an interface;

[0068] A step of providing a unitized electrode assembly adjacent to the bipolar plate;

[0069] A step of initiating an electrochemical reaction by flowing the fuel and oxidizer reactants from the reactant flow field on the bipolar plate to the unitized electrode assembly;

[0070] The steps include: flowing water through a water management loop to the water management surfaces of the metal subplate and porous subplate in order to remove corrosion products formed at the interface; and,

[0071] A step of deionizing and dechlorinating water flowing within a water management loop.

[0072] (2) A method for preventing corrosion at the carbon / metal interface in a fuel cell as described in (1) above, further comprising the step of forming an internal coolant passage in a bipolar plate and flowing an antifreeze-type coolant through the internal coolant passage.

[0073] (10) A method for operating a four-fluid fuel cell in thermal boost mode, including the following steps:

[0074] A step of providing a four-fluid fuel cell comprising an oxidizer flow field, a fuel reactant flow field, a water management flow field, and an independent circulating coolant loop capable of removing sensible heat, wherein the coolant loop is in fluid communication with the coolant flow field;

[0075] A step of reducing the flow rate of the coolant in the coolant loop and thereby reducing the sensible heat cooling capacity; and

[0076] A step of maintaining or increasing the temperature of the fuel cell in order to increase evaporative cooling.

[0077] (11) A method for operating the four-fluid fuel cell described in (10) above, wherein the coolant is an antifreeze type coolant.

[0078] (12) A method for operating the four-fluid fuel cell described in (10) above, wherein at least one of the oxidizer flow field and the fuel reactant flow field includes a plurality of pores fluidly connected to a water management flow field, the pores being configured as a bubble barrier.

[0079] (13) A method for operating the four-fluid fuel cell described in (10) above, wherein the step of providing the four-fluid fuel cell includes providing a hybrid bipolar plate comprising an oxidizer flow field, a fuel reactant flow field, an internal coolant passage, and a water management flow field.

[0080] (14) A method for operating the four-fluid fuel cell described in (10) above, further comprising the step of increasing the flow rate of water through a water management flow field in order to compensate for the increase in evaporation.

[0081] (15) A method for operating the four-fluid fuel cell described in (14) above, wherein the step of providing the four-fluid fuel cell further comprises providing a circulating water management loop that is in fluid communication with a water management flow field.

[0082] (20) A method for storing and retaining generated water in a four-fluid fuel cell, comprising the following steps:

[0083] A step of providing a four-fluid fuel cell comprising an oxidizer flow field, a fuel reactant flow field, a water management flow field, and an independent circulating coolant loop capable of removing sensible heat, wherein the coolant loop is in fluid communication with the coolant flow field;

[0084] A step of increasing the flow rate of the coolant in the coolant loop to increase the sensible heat cooling capacity; and

[0085] A step of maintaining or lowering the temperature in order to condense the excess generated water.

[0086] (21) A method for storing and retaining generated water in a four-fluid fuel cell as described in (20) above, further comprising the step of providing a reservoir for storing excess generated water, wherein the reservoir is in fluid communication with a water management loop.

[0087] (22) A method for storing and retaining generated water in a four-fluid fuel cell as described in (20) above, further comprising the steps of reducing the flow rate of water through a water management flow field, storing excess generated water, and compensating for reduced evaporation.

[0088] (23) A method for storing and retaining generated water in a four-fluid fuel cell as described in (22) above, wherein the step of providing the four-fluid fuel cell further includes providing a circulating water management loop that is in fluid communication with a water management flow field.

[0089] (24) A method according to either (10) or (20) above, wherein a controller commands flow rate settings for a coolant pump and a water pump in accordance with sensor data, the sensor data including at least one of air flow rate, cathode exhaust temperature, cathode exhaust pressure, total reservoir capacity, water stock, water temperature, ambient temperature, coolant return temperature, and water loop outlet pressure.

[0090] (25) A method according to either (10) or (20) above, wherein a controller commands the flow rate settings of a coolant pump and a water pump in response to environmental factors, the environmental factors include at least one of payload timing, vehicle route, GPS coordinates, road gradient, weather forecast, time of day, and driver behavior.

Claims

1. below: A non-porous subplate comprising a first water management surface and a second water management surface opposite to the first water management surface, hereafter: Fuel supply internal manifold through-passage and fuel return internal manifold through-passage; Oxidizer supply internal manifold through-passage and oxidizer return internal manifold through-passage; Water management supply internal manifold through-passage and water management return internal manifold through-passage; Coolant supply internal manifold through-passage and coolant return internal manifold through-passage; and An internal coolant passage having fluid communication with the coolant supply internal manifold passage at one end and with the coolant return internal manifold passage at the other end, wherein the internal coolant passage extends across the region between the fuel supply internal manifold passage and the fuel return internal manifold passage and the oxidizer supply internal manifold passage and the oxidizer return internal manifold passage. A non-porous subplate that defines the area; A first porous subplate comprising a reactant surface and a water management surface on the opposite side, wherein the reactant surface includes a first reactant flow field that is in fluid communication with one of the fuel supply internal manifold through-passage and the oxidizer supply internal manifold through-passage, and the water management surface is in fluid communication with the first water management surface of the non-porous subplate; and A second porous subplate comprising a reactant surface and a water management surface on the opposite side, wherein the reactant surface includes a second reactant flow field that is in fluid communication with the other of the fuel supply internal manifold through-passage and the oxidizer supply internal manifold through-passage, and the water management surface is in fluid communication with the second water management surface of the non-porous subplate. A bipolar plate for fuel cells, including [the specified component].

2. The bipolar plate according to claim 1, wherein at least one of the first porous subplate and the second porous subplate forms a nested seal within the recessed peripheral of the non-porous subplate.

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

4. The bipolar plate according to claim 3, wherein the water management flow field includes a water flow field channel.

5. The bipolar plate according to claim 1, wherein the non-porous subplate includes a first halfplate bonded to a second halfplate.

6. The bipolar plate according to claim 5, wherein 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 antifreeze type coolant.

8. The bipolar plate according to claim 1, wherein at least one of the first porous subplate and the second porous subplate includes a bubble barrier pore structure suitable for enabling the transfer of liquids through the pore structure and preventing the transfer of reaction gases through the pore structure.

9. The bipolar plate according to claim 8, wherein both the first porous subplate and the second porous subplate include a bubble barrier pore structure that enables the transfer of liquid through the pore structure and prevents the transfer of reaction gas through the pore structure.

10. A non-porous subplate for fuel cell bipolar plate assemblies, It includes a first water management surface and a second water management surface opposite to the first water management surface, The non-porous subplate is as follows: Fuel supply internal manifold through-passage and fuel return internal manifold through-passage; Oxidizer supply internal manifold through-passage and oxidizer return internal manifold through-passage; Water management supply internal manifold through-passage and water management return internal manifold through-passage; Coolant supply internal manifold through-passage and coolant return internal manifold through-passage; and An internal coolant passage having fluid communication with the coolant supply internal manifold passage at one end and with the coolant return internal manifold passage at the other end, wherein the internal coolant passage extends across the region between the fuel supply internal manifold passage and the fuel return internal manifold passage and the oxidizer supply internal manifold passage and the oxidizer return internal manifold passage. A non-porous subplate that defines the area.

11. The non-porous subplate according to claim 10, wherein the first water management surface includes a first recessed periphery suitable for receiving the first porous subplate.

12. The non-porous subplate according to claim 11, wherein the first recessed peripheral portion is further suitable for providing a nested seal together with the first porous subplate.

13. The non-porous subplate according to claim 11, wherein the second water management surface includes a second recessed periphery suitable for receiving the second porous subplate.

14. The non-porous subplate according to claim 13, wherein the second recessed peripheral portion is further suitable for providing a nested seal together with the second porous subplate.

15. The non-porous subplate according to claim 10, further comprising a first half plate bonded to a second half plate, thereby defining an internal coolant passage.

Images