Multilayer sheet bipolar plate

Abstract

A method for forming a bipolar plate (BBP) for use in a fuel cell (FC), comprises: providing a structural base layer, and providing a thermal performance layer (TPL) in contact with the structural bas

Description

FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to fuel cells and methods for making the same. The disclosure has particular utility in the creation of proton exchange membrane (PEM) fuel cells for use in fuel cell powered vehicles including aircraft, and will be described in connection with such utility, although other utilities are contemplated. BACKGROUND AND SUMMARY

[0002] This section provides background information related to the present disclosure which is not necessarily prior art. This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all its features.

[0003] A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. A typical hydrogen fuel cell includes a proton exchange membrane (PEM), that permits only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is reacted to produce hydrogen protons that pass through the PEM. The electrons produced by this reaction travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions are described by the following equations: H2 2H++2e_ at the anode of the cell, and Equation 1 Vi O2+2H++2e_ -^tUO at the cathode of the cell. Equation 2

[0004] PEM fuel cells (FCs) are made from several layers of different materials. The heart of a PEM FC is the membrane electrode assembly (MEA), which includes a PEM membrane, catalyst layers, and gas diffusion layers (GDLs).

[0005] Fig. 1 illustrates a conventional PEM FC 10. FC 10 includes a PEM 12, an ionic conductor typically formed from a specially treated polymer material that conducts positively charged ions while preventing electron transport between electrodes.

[0006] Catalyst layers are provided on both sides of the PEM 12 - an anode catalyst layer 14 on one side, and a cathode catalyst layer 16 on the other.

[0007] Gas Diffusion Layers (GDLs) 18, 20 are provided to the outside of the anode and cathode catalyst layers 14, 16, respectively and facilitate transport of reactants into the catalyst layers, as well as removal of the water by-product.

[0008] The PEM 12, catalyst layers 14, 16 and the GDLs 18, 20 together make up the so-called MEA 22. The MEA 22 is the part of the FC where power is produced.

[0009] Each individual MEA 22 produces less than 1 volt under typical operating condition, but most applications require higher voltages. Therefore, multiple MEAs 22 usually are connected in series by stacking them on top of one another to provide a usable output voltage. Each cell in the stack is sandwiched between two bipolar plates (BPPs) 24, 26 to separate it from neighboring cells. These BPPs 24, 26, which may be made of metal such as stainless steel, carbon, or metal-polymer composites, provide electrical conduction between cells, as well as providing physical strength to the stack. Surfaces of the plates typically contain channels 28, 30 machined or stamped into the plates 24, 26 to allow gases to flow over the MEA 22. Additional channels (not shown) inside each plate may be used to circulate a liquid coolant.

[0010] Each MEA 22 in an FC stack is sandwiched between two bipolar plates 24, 26, and gaskets (not shown) are added around the edges of the MEA 22 to make a gas-tight seal.

[0011] Existing BPP materials for PEM FCs sacrifice the mechanical strength of traditional stainless steel BPPs for the enhanced thermal conductivity of materials such as aluminum, copper, and nickel in order to achieve uniform cooling. However, a risk of cracks and deformations in these materials limits their formability and operational lifetime, while chemical sensitivity limits their corrosion resistance and introduces oxidation issues.

[0012] In accordance with the present disclosure, we optimize a balance of thermal conductivity, corrosion resistance, and mechanical properties of a BPP by providing a multilayer essentially heterostructure comprising a structural base layer (~50 pm), typically made of a stainless steel (SS), a nickel-based alloy, an aluminum alloy, or graphite, and one or more thin sheets of high thermal conductivity metals or metal alloys, or a graphene or a metal-polymer composite material. Providing a multilayer BPP layered structure in accordance with the present disclosure permits us to tune thermal and mechanical performance of BPPs for PEMFCs. Providing a multilayered BPP layered structure in accordance with the present disclosure also enables us to isolate corrosion- or oxidation-prone thermal materials from the hostile FC environment.

[0013] While the prior art has proposed metal-polymer composite BPPs (see, for example UK application 2303807.8, filed March 15, 2023) and anticorrosion layers for BPPs (see, for example, US Patent 10,826,078 B2 and CN115000442A), no prior art has suggested forming BPPs from a stack of heterogeneous material sheets in order to optimize thermal performance and mechanical strength.

[0014] In one aspect the present disclosure provides a multilayer BPP composed of a structural base layer and one or more material layers with high thermal conductivity (“thermal performance layers” or TPLs) to promote heat dissipation and equalization across an FC stack. By way of example, but not limitation, the high thermal conductivity material forming the TPLs may be a layer of roughly l-5um, while the structural base layer may be roughly 50um.

[0015] The high thermal conductivity material should have a thermal conductivity greater than that of structural base layer and have a Linear Coefficient of Thermal Expansion (CTE) that closely matches the CTE of the structural base layer. In some embodiments, the structural base layer may be made of SS and have a CTE within about 40% of the high thermal conductivity material. The thermal conductivity of SS varies with the composition of the SS and may range from about 15 to 20 w / (moK). By way of example, SS304 has a thermal conductivity of 16.2 w / (moK) at 100°C. The Linear CTE of SS also varies slightly with the composition of the SS, but generally is around 1.7xe-5 for SS304. In these exemplary embodiments, various metals, and metal alloys, metal-polymer composites, and graphene, may serve as the TPLs, provided they (1) have a thermal conductivity greater than the SS forming structural the base layer of the BPP structure, and (2) are closely matched in Linear CTE to the SS to prevent damage and / or delamination under repeated thermal cycling.

[0016] In one embodiment the TPL is formed on the BPP structural base layer so as to be placed in direct contact with the FC diffusion layer. This BPP architecture exposes the TPL to the corrosive and oxidizing environment of the FC, and is therefore only suitable for materials stable in such an environment. The application of an anti-corrosive layer to the exposed surface of the TPL as taught, for example, by US 10,826,078 B2, the contents of which are incorporated herein in their entirety, may enable the use of otherwise sensitive materials for forming the TPL in this architecture. Alternatively, a carbon-based material with high corrosion resistance, such as graphite or graphene, may be chosen for the TPL.

[0017] In another embodiment, the TPL is formed on the BPP structural base layer so as to be isolated from the FC environment by placing the TPL at the cooling channel sides of the BPP. This mitigates design constraints imposed by the corrosive, oxidizing FC environment and enables TPL materials selection based primarily on thermal conductivity and CTE matching.

[0018] In yet another embodiment, the TPL may be sandwiched between layers forming the BPP structural base layer to function as a high thermal performance “core”. This architecture isolates the TPL from both the cooling channel and FC stack environments, while still permitting thermal contact close to the FC diffusion layer.

[0019] In still yet another embodiment, more than one TPL may be formed on the BPP structural base layer to provide increased control over properties such as mechanical strength, corrosion stability, and thermal conductivity. The use of multiple TPL layers also allows the incorporation of materials with greater total CTE mismatch in the same system, with some embodiments utilizing one or more middle layers to create multiple, smaller CTE mismatches at each interface. This architecture can be extended to each bilayer system discussed above, and also may be applied to the BPP cooling channels as will be discussed below.

[0020] More particularly, in accordance with Aspect A of the disclosure, there is provided a fuel cell comprising a Membrane Electrode Assembly (MEA) sandwiched between a pair of bipolar plates (BPPs), wherein the BPPs are formed at least in part of a structural base layer, and having one or more thermal performance layers (TPLs) in thermal contact with the structural base layer, wherein the TPL is formed of a material having a thermal conductivity greater than that of the material forming the structural base layer.

[0021] In one embodiment of Aspect A, the MEA includes a diffusion layer, wherein the TPL is positioned between and in direct contact with the BPP and the MEA diffusion layer.

[0022] In another embodiment of Aspect A, the BPPs include flow channels, and the TPL is in direct contact with surfaces of the BPP flow channels.

[0023] In still another embodiment of Aspect A, the FC includes coolant flow channels bounded by the BPPs, wherein the TPL is located on and in thermal contact with surfaces of the BPPs bounding the coolant flow channels.

[0024] In a further embodiment of Aspect A, the BPPs are formed of two or more metallic layers, and wherein the TPL is sandwiched between two of said metallic layers.

[0025] In a still further embodiment of Aspect A, the TPL comprises two or more layers of different materials having different physical properties. In such embodiment, the different materials may have different properties selected from the group consisting of thermal conductivity, mechanical strength, and corrosion resistance.

[0026] In another embodiment of Aspect A, the structural base layer is formed of a stainless steel (SS), and the TPL is formed of a metal or a metal alloy having a thermal conductivity greater than that of SS. In such embodiment, the TPL may be formed of a metal selected from the group consisting of aluminum, copper, silver, nickel, and a metal alloy thereof. Alternatively, the TPL may be formed of a metal-polymer composite material graphite, or graphene.

[0027] In still another embodiment of Aspect A, the TPL is coated at least in part with an anticorrosive layer. In such embodiment, the anticorrosion layer may be selected from the group consisting of tantalum (Ta), chromium (Cr), Niobium (Nb), a Nickel-Silver (Ni-Ag)-based alloy, chromium nitride, titanium nitride, graphite, carbon nanotubes, and nanostructured carbon.

[0028] In yet another embodiment of Aspect A, the TPL has a Linear Coefficient of Thermal Expansion (CTE) within 40% of a linear CTE of the structural base layer to prevent delamination or damage to the BPP under repeated thermal cycling.

[0029] According to Aspect B of the disclosure, there is provided a FC-powered vehicle comprising a FC of Aspect A.

[0030] In one embodiment of Aspect C, the FC-powered vehicle comprises an FC-powered aircraft.

[0031] According to aspect C of the disclosure, there is provided a method for forming a BPP for use in an FC, comprising providing a structural base layer, and providing a TPL in contact with the structural base layer, wherein the TPL is formed of a material having a thermal conductivity greater than that of the structural base layer.

[0032] In one embodiment of Aspect C, the structural base layer is formed of a metal.

[0033] In another embodiment of Aspect C, the structural base layer and the TPL are formed together by co-rolling or by hydroforming.

[0034] In yet another embodiment of Aspect C, the TPL is formed on the structural base layer by an additive process.

[0035] In a further embodiment of Aspect C, the additive process comprises electroforming or physical vapor deposition.

[0036] In still yet another embodiment of Aspect C, the TPL is formed on a non-metal structural base layer by physical vapor deposition.

[0037] In yet another embodiment of Aspect C, the TPL is formed of a metal or a metal alloy, a metal-polymer composite, or graphene.

[0038] According to a first aspect of the present invention there is provided a fuel cell (FC) comprising a Membrane Electrode Assembly (MEA) sandwiched between a pair of bipolar plates (BPPs), wherein the BPPs are formed at least in part of a structural base layer, and having one or more thermal performance layers (TPLs) in thermal contact with the structural base layer, wherein the TPL is formed of a material having a thermal conductivity greater than that of the material forming the structural base layer.

[0039] Preferably the MEA includes a diffusion layer, wherein the TPL is positioned between and in direct contact with the BPP and the MEA diffusion layer.

[0040] Preferably the BPPs include flow channels, and the TPL is in direct contact with surfaces of the BPP flow channels.

[0041] Preferably the fuel cell includes coolant flow channels bounded by the BPPs, wherein the TPL is located on and in thermal contact with surfaces of the BPPs bounding the coolant flow channels.

[0042] Preferably the BPPs are formed of two or more metallic layers, and wherein the TPL is sandwiched between two of said metallic layers.

[0043] Preferably the TPL comprises two or more layers of different materials having different physical properties.

[0044] Preferably the different materials have different properties selected from the group consisting of thermal conductivity, mechanical strength, thermal expansion coefficient, and corrosion resistance.

[0045] Preferably the structural base layer is formed of a stainless steel (SS), and the TPL is formed of a metal or a metal alloy having a thermal conductivity greater than that of SS.

[0046] Preferably the TPL is formed of a metal selected from the group consisting of aluminum, copper, silver, nickel, and a metal alloy thereof.

[0047] Preferably the TPL is formed of a metal-polymer composite material, graphite, or graphene.

[0048] Preferably the TPL is coated at least in part with an anticorrosive layer.

[0049] Preferably the anticorrosion layer is selected from the group consisting of tantalum, chromium, niobium, a nickel-silver based alloy, chromium nitride, titanium nitride, graphite, carbon nanotubes, and nanostructured carbon.

[0050] Preferably the TPL has a Linear Coefficient of Thermal Expansion (CTE) within 40% of a Linear CTE of the structural base layer to prevent delamination or damage to the BPP under repeated thermal cycling.

[0051] According to a second aspect of the present invention there is provided a FC powered vehicle comprising a fuel cell according to the first aspect of the present invention

[0052] Preferably the vehicle comprises a FC powered aircraft.

[0053] According to a third aspect of the present invention there is provided a method for forming a bipolar plate (BBP) for use in a fuel cell (FC), comprising: providing a structural base layer, and providing a thermal performance layer (TPL) in contact with the structural base layer, wherein the TPL is formed of a material having a thermal conductivity of greater than that of the structural base layer.

[0054] Preferably the structural base layer is formed of a metal.

[0055] In one alternative the structural base layer and the TPL are formed together by co-rolling or by hydroforming.

[0056] Preferably the TPL is formed on the structural base layer by an additive process.

[0057] Preferably the additive process comprises electroforming or physical vapor deposition.

[0058] In another alternative the TPL is formed on a non-metal structural base layer by physical vapor deposition.

[0059] Preferably the TPL is formed of a metal or a metal alloy, a metal-polymer composite, or graphene.

[0060] According to a fourth aspect of the present invention there is provided a method for forming a bipolar plate (BBP) for use in a fuel cell (FC) according to the first aspect of the present invention, comprising: providing a structural base layer, and providing a thermal performance layer (TPL) in contact with the structural base layer, wherein the TPL is formed of a material having a thermal conductivity of greater than that of the structural base layer.

[0061] Preferably the structural base layer is formed of a metal.

[0062] In one alternative the structural base layer and the TPL are formed together by co-rolling or by hydroforming.

[0063] Preferably the TPL is formed on the structural base layer by an additive process.

[0064] Preferably the additive process comprises electroforming or physical vapor deposition.

[0065] In another alternative the TPL is formed on a non-metal structural base layer by physical vapor deposition.

[0066] Preferably the TPL is formed of a metal or a metal alloy, a metal-polymer composite, or graphene.

[0067]

[0068] In addition to providing improved thermal conductivity, corrosion resistance and mechanical performance, a further feature and advantage of the present disclosure is that the BPP architecture is compatible with scalable manufacturing processes including co-rolling, hydroforming, 3D printing, electroforming, electroplating and physical vapor deposition (PVD).

[0069] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. Brief Description of the Drawings

[0070] Further features and advantages of the disclosure will be seen in the following detailed description, taken in conjunction with the accompanying drawings, wherein like numerals depict like parts. The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure. In the drawings: Fig. 1 is a cross-sectional view of a conventional Proton Exchange Membrane (PEM) fuel cell (FC) in accordance with the prior art; Fig. 2 is a cross-sectional view of a PEM FC in accordance with an embodiment of present disclosure; Fig. 3 is a view similar to Fig. 2, of another embodiment of a PEM FC in accordance with the present disclosure; Fig. 4 is a view similar to Fig. 2, of still yet another embodiment of a PEM FC in accordance with the present disclosure; Fig. 5 is a view similar to Fig. 2, of still yet another embodiment of a PEM FC in accordance with the present disclosure; Fig. 6 is a graph comparing thermal conductivity of SS to various materials; Fig. 7 is a table listing the Linear CTEs of SS and several common metals and metal alloys; Fig. 8 diagrammatically illustrates forming an FC BPP in accordance with one embodiment of the present disclosure; Fig. 9 diagrammatically illustrates forming an FC BPP in accordance with another embodiment of the present disclosure; Fig. 10 diagrammatically illustrates forming an FC BPP in accordance with yet another embodiment of the present disclosure; Fig. 11 diagrammatically illustrates forming an FC BPP in still yet another embodiment of the present disclosure; and Fig. 12 is a schematic depiction of a hydrogen FC-powered aircraft powered by FCs made in accordance with the present disclosure. Detailed Description

[0071] Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms, and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0072] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, components, and / or groups, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0073] When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” “formed on”, “formed over” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0074] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another element, component, region, layer, or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the example embodiments.

[0075] Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0076] As used herein the terms “component” and “subcomponent” are employed interchangeably to describe the several elements forming our Proton Exchange (PEM) fuel cell.

[0077] As used herein the term “thermal performance layer” or “TPL” means a material layer having a thermal conductivity greater than that of an underlying structural base layer, and a Linear CTE that closely matches, i.e., is within about 40% of the Linear CTE of the underlying structural base layer.

[0078] As used herein the term PEM fuel cells mean PEM fuel cells generally as well as high temperature PEM fuel cells.

[0079] Referring to Fig. 2, a PEM FC 110 in accordance with the present disclosure is similar to the prior art PEM described above in Fig. 1, and includes a PEM 112, an ionic conductor typically formed from a specially treated polymer material that conducts only positively charged ions, while preventing electron transport between electrodes. Catalyst layers are provided on both sides of the PEM 112 - an anode catalyst layer 114 on one side, and a cathode catalyst layer 116 on the other. GDLs 118, 120 sit to the outside of the catalyst layers 114, 116 and facilitate transport of reactants into the catalyst layers, as well as removal of the water by-product. The PEM 112, catalyst layers 114, 116 and the GDLs 118, 120 together make up the MEA 122. As in the case of the prior art PEM of Fig. 1, multiple MEAs 122 usually are connected in series by stacking them on top of one other to provide a usable output voltage. Accordingly, each cell in the stack is sandwiched between two BPPs 124, 126 to separate it from neighboring cells. Also, as before, the surfaces of the plates typically contain channels 128, 130 machined or stamped into the BPPs 124, 126, respectively to allow gases to flow over the MEA 122. Additional channels (not shown) may be provided inside each plate to circulate a liquid coolant.

[0080] As distinguished from the prior art PEM of Fig. 1 as described above, in accordance with the present disclosure, a thermal performance layer, TPL 132 is formed covering the surfaces of the channels 128 on the anode and cathode sides of the MEA 122 and in direct contact with the FC GDL 118. This geometry exposes the TPL 132 to the corrosive and oxidizing environment of the PEM FC 110. Accordingly, the material forming the TPL 132 should be formed of a material stable to such environment. By way of example, but not limitation, the material forming the TPL 132 may comprise a metal such as aluminum, nickel or silver, or a metal alloy thereof. Other metals such as copper and metal alloys thereof may be used for forming the TPL, provided the exposed metal surfaces are coated with an anti-corrosive layer as mentioned above or include dopants such as Mn that improve corrosion resistance. The TPL 132 also may be formed of a metal-polymer composite material, or carbon-based materials such as graphite and graphene, all of which have been previously shown to have acceptable corrosion resistance.

[0081] Alternatively, as illustrated in Fig. 3, a PEM FC 110 in accordance with the another embodiment of the present disclosure, wherein a TPL 150 may be formed on the surfaces of the cooling channels 152 of the PEM FC 110. This architecture isolates the TPLs from the FC environment, which mitigates design constraints imposed by the corrosive, oxidizing FC environments, and enables materials selections for the TPL based primarily on thermal conductivity and CTE matching.

[0082] Referring to Fig. 4, a PEM FC 110 in accordance with yet another embodiment of the disclosure, the TPLs 160 may be sandwiched between structural layers forming the BPPs 124, 126 to function as a “high performance core” of the BPPs 124, 126. This BPP architecture isolates the TPLs 160 from both the cooling channel 152 and the FC stack environments while still permitting high conductivity material thermal contact close to the FC diffusion layers.

[0083] Referring to Fig. 5, a PEM FC 110 in accordance with yet another embodiment, multiple TPLs 160, 162 may be formed over the BPP base to provide increased control over properties such as mechanical strength, operational stability and thermal conductivity. For example, a first TPL 160 may be formed of high thermal conductivity Cu, in direct contact with the BPPs 124, 126 forming the cooling channels 166, while a second TPL 162, formed of for example a corrosion resistant aluminum alloy containing Mn, may be formed over the first TPL 160. In other embodiments, the TPL 160 layer or layers may be formed at a combination of the cooling channel, GDLs 118, 120 , or as a BPP 124, 126 core.

[0084] Fig. 6 plots thermal conductivity of various common materials, and Fig. 7 provides Linear CTEs of various materials.

[0085] Several exemplary materials suitable for use as a TPL in accordance with the present disclosure are listed in Fig. 6. Metals such as aluminum, copper, silver, and gold offer upwards of a tenfold or more improvement in thermal conductivity compared to SS, a common material in the prior art, such that incorporating these TPL materials at a relative thickness of even <10% to the thickness of a structural base layer provides significant thermal dissipation improvement. Beyond elemental metals, alloys may be used to achieve a desired blend of CTE, thermal transport, and operational environment stability. One particularly preferred group of alloys for forming the TPL are AlSiCs, which have a marginally lower thermal conductivity than elemental Al, but can be designed to closely match the CTE of the structural base layer.

[0086] In some embodiments, thermal transport materials such as metal-polymer composites and graphene may be used as the TPL. As shown in Fig. 7, the metals discussed above are closely matched in CTE to SS. In particular, copper and silver metals offer very small CTE mismatches that will mitigate damage and delamination risks during thermal cycling. Aluminum and its alloys are less well suited in CTE, but over typical FC operational environment range of 0°C - 250°C are practical solutions. The same CTE considerations may be extended to embodiments implementing metal-polymer composites, or other material systems as the TPL.

[0087] A feature and advantage of the present disclosure is that TLPs readily may be incorporated into BPP structures using established processing techniques for BPP synthesis. For example, referring to Fig. 8, in one embodiment, TPLs may be formed on BPPs by co-rolling a layer of a selected TPL roll material 204 on a metallic base layer roll material 206. In such embodiment, TPL roll material 204 and metallic base layer roll material 206 after cleaning in a cleaning step 207 are pressed between a set of cylindrical rollers 208, 210. Cylindrical rollers 208, 210 have contoured channels 212 on their surfaces to provide a desired BPP flow field pattern. Layer lamination is achieved by either post-process heat treatment in a heat treatment step 214 or by applying sufficient pressure between the rollers 208, 210 to roll bond the TPL roll material 204 and the metallic base layer roll material 206, expanding on the teachings of Bauer et al. “Manufacturing of Metallic Bipolar Plate Channels by Rolling” in J. Manuf. Mater. Process 201, 3, 48, www.mdpi.com / journal / jnimp, the contents of which are incorporated herein by reference. The resulting laminated structure may then be cut the size in a cutting step 215.

[0088] A BPP structure in accordance with the present disclosure also may be formed by co-rolling a TPL 204 and a metallic base layer 206 having an adhesive layer applied either to the TPL 204 or the metallic base layer 206 similar to the teachings of our co-pending application no. 18 / 212,492 filed June 21, 2023 “High Temperature Proton Exchange Membrane and Direct Cell Deposition and Manufacturing Process”, the contents of which are incorporated herein by reference.

[0089] Referring to Fig. 9, in another embodiment, hydroforming press system 220 may be used to press-form a TPL foil 222 and a metallic base layer 224 together in a hydroforming press system 220, following the teachings of Sheet Metal Hydroforming: The Ultimate Guide for Engineers and Manufacturers by EngineeringCheatSheet.com, April 22, 2023, the contents of which are incorporated herein by reference. Layer lamination may then be achieved in a post-process heat treatment step 226.

[0090] In yet another embodiment, a TPL may be formed on a metallic base layer by electroforming. Referring to Fig. 10, in order to form a TPL by electroforming, a preformed metallic base layer 236 is submerged in an electrolytic solution 238 containing a sacrificial electrode 240 formed of the metal to be deposited as the TPLs. A DC bias applied across the system causes the reduction of the sacrificial electrode 240 sending metal ions into solution, where the ions plate onto the metallic base layer 236 which acts as a cathode, forming a thin film of the TPL metal electrolytically bonded to the metallic base layer 236. This process enables geometry agnostic synthesis of the TPL, while avoiding the introduction of internal stresses which may be formed in cold working such as described in the Fig. 8 and the Fig. 9 embodiments. This electroforming technique is particularly useful for thermal transport materials with poor workability, and is applicable to elemental metal TPL systems.

[0091] Referring to Fig. 11, in still yet another embodiment, a TPL may be formed on a BPP using a Physical Vapor Deposition (PVD) process. In a PVD process a preformed BPP base layer target 280 is placed under vacuum conditions, and a material 282 selected for forming the TPL is evaporated, transported, and deposited onto the surface of a preformed BPP base layer target 280. The TPL material 282 is deposited as a uniform densified film, offering improved corrosion resistance compared to TPLs formed by electroplating. Some metal alloys also may be deposited via PVD.

[0092] Still other manufacturing processes may be employed for forming a TPL on a base layer. By way of example, a desired BPP geometry may be formed using an additive process by stacking preformed metallic base layer sheets and a top sheet of a TPL, and applying heat to bond the plurality of sheets together as described in US Published Appln. 2024 / 0043956 Al, the contents of which are incorporated herein in their entirety. Alternatively, a desired BPP geometry may be produced using a multi-nozzle or a multi-slurry 3D printer laying down a metallic base layer and a top layer of a TPL, following the teachings of US Published Appln. 2021 / 0252780 Al, the contents of which are incorporated herein in their entirety.

[0093] Fig. 12 illustrates an aircraft 250 including two electric motors 252, 254 which are powered by two parallel PEM hydrogen fuel cells 256, 258 having BPPs incorporating TPLs in accordance with the present disclosure.

[0094] While the foregoing disclosure focuses on using TPLs to provide enhanced thermal conductivity, other functional benefits can be incorporated into TPLs. For example, chemically resistant materials can be incorporated into the TPLs to increase robustness against corrosion and oxidation.

[0095] As can be seen from the foregoing, the present disclosure provides several advantages over prior art BPPs including: • the ability to “tune” or optimize the thermal and physical properties of the BPP for specific applications; • the ability to isolate corrosion or oxidation prone thermal materials away from hostile FC environments; and • the ability to promote heat dissipation and heat equalization across an FC stack.

[0096] Also, while the foregoing disclosure is focused primarily on PEM FC applications, the composition of matter and manufacturing process disclosed can be adapted for use in electronic devices, battery manufacturing, or other area where a high degree of interfacial heat transfer is desired.

[0097] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. Various changes and advantages may be made in the above disclosure without departing from the spirit and scope thereof. List of References: 10 fuel cell 12 PEM 14 anode catalyst layer 16 cathode catalyst layer 18, 20 GDL 22 MEA 24, 26 BPPs 28, 30 channels 110 FC 112 PEM 114 anode catalyst layer 116 cathode catalyst layer 118,120 GDLs 122 MEA 124, 126 BPP 128, 130 channels 132 TPL 150 TPL 152 cooling channels 160, 162 TPL 166 cooling channels 180 base target 182 material 204 TPL roll material 206 metallic base layer roll material 207 cleaning step 208,210 cylindrical rollers 212 contoured channels 214 heat treating step 215 cutting step 220 hydroforming press system 222 TPL foil 224 metallic base layer 226 post-process heat treatment step 236 metallic base 238 electrolyte solution 240 sacrificial electrode 250 aircraft 252, 254 electric motors 256, 258 PEM hydrogen FC 280 BPP base layer target 282 TPL material

Claims

1. A fuel cell (FC) comprising a Membrane Electrode Assembly (MEA) sandwiched between a pair of bipolar plates (BPPs), wherein the BPPs are formed at least in part of a structural base layer, and having one or more thermal performance layers (TPLs) in thermal contact with the structural base layer, wherein the TPL is formed of a material having a thermal conductivity greater than that of the material forming the structural base layer.

2. The FC of claim 1, wherein the MEA includes a diffusion layer, wherein the TPL is positioned between and in direct contact with the BPP and the MEA diffusion layer.

3. The FC of claim 1 or claim 2, wherein the BPPs include flow channels, and the TPL is in direct contact with surfaces of the BPP flow channels.

4. The FC of any preceding claim, wherein the fuel cell includes coolant flow channels bounded by the BPPs, wherein the TPL is located on and in thermal contact with surfaces of the BPPs bounding the coolant flow channels.

5. The FC of any preceding claim, wherein the BPPs are formed of two or more metallic layers, and wherein the TPL is sandwiched between two of said metallic layers.

6. The FC of any preceding claim, wherein the TPL comprises two or more layers of different materials having different physical properties.

7. The FC of claim 6, wherein the different materials have different properties selected from the group consisting of thermal conductivity, mechanical strength, thermal expansion coefficient, and corrosion resistance.

8. The FC of any preceding claim, wherein the structural base layer is formed of a stainless steel (SS), and the TPL is formed of a metal or a metal alloy having a thermal conductivity greater than that of SS.

9. The FC of claim 8, wherein the TPL is formed of a metal selected from the group consisting of aluminum, copper, silver, nickel, and a metal alloy thereof.

10. The FC of any preceding claim, wherein the TPL is formed of a metal-polymer composite material, graphite, or graphene.

11. The FC of any preceding claim, wherein the TPL is coated at least in part with an anticorrosive layer.

12. The FC of claim 11, wherein the anticorrosion layer is selected from the group consisting of tantalum, chromium, niobium, a nickel-silver based alloy, chromium nitride, titanium nitride, graphite, carbon nanotubes, and nanostructured carbon.

13. The FC of any preceding claim, wherein the TPL has a Linear Coefficient of Thermal Expansion (CTE) within 40% of a Linear CTE of the structural base layer to prevent delamination or damage to the BPP under repeated thermal cycling.

14. A FC powered vehicle comprising a fuel cell as claimed in any preceding claim.

15. The FC powered vehicle as claimed in claim 14, wherein the vehicle comprises a FC powered aircraft.

16. A method for forming a bipolar plate (BBP) for use in a fuel cell (FC), comprising: providing a structural base layer, andproviding a thermal performance layer (TPL) in contact with the structural base layer, wherein the TPL is formed of a material having a thermal conductivity of greater than that of the structural base layer.

17. The method of claim 16, wherein the structural base layer is formed of a metal.

18. The method of claim 17, wherein the structural base layer and the TPL are formed together by co-rolling or by hydroforming.

19. The method of claim 17, wherein the TPL is formed on the structural base layer by an additive process.

20. The method of claim 19, wherein the additive process comprises electroforming or physical vapor deposition.

21. The method of claim 16, wherein the TPL is formed on a non-metal structural base layer by physical vapor deposition.

22. The method of any one of claims 16 to 21, wherein the TPL is formed of a metal or a metal alloy, a metal-polymer composite, or graphene.

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