GB2619577A

GB2619577A - Polymeric interconnects in PEM stack

Info

Publication number: GB2619577A
Application number: GB2301242.0A
Authority: GB
Inventors: Belousov Viktor; Nikitin Denis
Original assignee: Zeroavia Ltd
Current assignee: Zeroavia Ltd
Priority date: 2023-01-27
Filing date: 2023-01-27
Publication date: 2023-12-13
Anticipated expiration: 2043-01-27
Also published as: GB2619577B; GB202301242D0

Abstract

A High Temperature Proton Exchange Membrane (HT-PEM) fuel cell 110, comprises: a Membrane Electrode Assembly (MEA) 122 including a Proton Exchange Membrane (PEM) 112; an anode catalyst layer 114 on one surface of the PEM, and a cathode catalyst layer 116 on an opposite surface of the PEM; Gas Diffusion Layers (GDLs) 118,120 on surfaces of the anode and the cathode layers; and Bipolar Plates (BPPs) 124,126 on surfaces of the GDLs; wherein one or more contacting surfaces of the MEA subcomponents are coated, at least in part, with an electrically conductive polymer composite material 130 that softens at or below the operating temperature of the HT-PEM. A method of forming the HT-PEM fuel cell is also disclosed, in which the conductive polymer composite material has a glass transition and/or melting temperature lower than the fuel cell operating temperature, and the subcomponents are pressed together at a temperature above the glass transition temperature of the conductive polymer composite material and cooled while maintaining pressure. A method for maintaining electrical contact between subcomponents of the HT-PEM fuel cell using the conductive polymer composite material to at least partially coat a surface of one or more of the subcomponents is also disclosed.

Description

POLYMERIC INTERCONNECTS IN PEM STACK

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 high temperature proton exchange membrane (HT-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.

1-00031 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 4 21-1++2e-at the anode of the cell, and Equation 1 02+4H++46 42H20 at the cathode of the cell. Equation 2 [0004] Proton Exchange Membrane (PEM) fuel cells are made from several layers of different materials. The heart of a PEM fuel cell 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 fuel cell 10. Fuel cell 10 includes a Proton Exchange Membrane (PEM) 12, typically formed in a specially treated polymer material that conducts only positive charged ions, and blocks 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 sit to the outside of the catalyst layers 14, 16 and facilitate transport of reactants into the catalyst layers, as well as removal of the product water.

[0908] The PEM 12, catalyst layers 14, 16 and the GDLs 18, 20 together make up the so-called Membrane Electrode Assembly (MEA) 22. The MEA 22 is the part of the fuel cell where power is produced.

[0909] Each individual MEA 22 produces less than I V 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 other 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 plates 24, 26, which may be made of metal, carbon, or composites, provide electrical conduction between cells, as well as providing physical strength to the stack. The 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.

r000101 While each MEA 22 in a fuel cell stack is sandwiched between two bipolar plates 24, 26, gaskets (not shown) are added around the edges of the MEA 22 to make a gas-tight seal. These gaskets usually are made of a rubbery polymer.

moon] Efficient operation of a fuel cell 10 requires good mechanical and electrical contact between the subcomponent layers in the fuel cell stack to minimize ohmic resistance. Current High Temperature Proton Exchange Membrane (HT-PEM) fuel cell interlayer contact relies on compression to maintain sufficient contact between layers. However, there are fundamental limitations for interlayer contact based on compression alone. Additionally, over multiple temperature cycles during operation, the fuel cell structure risks irreversible compression set and thermal expansion stresses, leading to poor electrical contact and decreased power output. There is a long felt need to improve the electrical contact without relying solely on compression.

[00012] In accordance with the present disclosure, we coat HT-PEM contacting subcomponent layers with a polymeric composite material that softens at or below the operating temperature of the fuel cell stack. More particularly we employ meltable, conductive polymer composite materials having a glass transition (Tg) and/or a melting temperature (T,,,) lower than the fuel cell operating temperature to tether subcomponent layers of the fuel cell, i.e., the bipolar plates, the gas diffusion layers, the catalyst layers and/or the membrane electrode assembly (MEA).

[00013] In accordance with the present disclosure, fuel cell electrical contact resistance between subcomponent layers of a fuel cell is reduced by coating subcomponent layers of a HTPEM fuel cell with a material having a glass transition (Tg) and/or melting temperature (T,") lower than the fuel cell operating temperature. The coated fuel cell subcomponent layers are assembled, placed under load, and then thermal cycled above and below the Tg of the material. This process of cyclical heating under load creates an interpenetrated structure at the interface between fuel cell subcomponent layers.

moon] Preferably the meltable conductive polymer composite material comprises polyvinylidene fluoride (PVDF) and a polysulfone polymer such as polyethersulfone (PESU). Polyvinylidene fluoride (PVDF) (Tg =170C) promotes deformation and contact with neighboring surfaces, while polyethersulfone (PESU) Tg >225C creates an interconnected structure in the fuel cell stack during assembly. The compressed layer of PVDF softens in the fuel cell operating temperature range creating a patterned, wetted interface that mirrors any microstructure present on the neighboring component. PESU transfers microstructures or patterns present on mating surfaces of subcomponents into the melted PVDF layer during assembly.

[00015] PVDF also has an advantageous property of maintaining good wetted contact between the subcomponent layers during fuel cell operation. PESU contributes to the formation of interconnected structures and helps to maintain the deformation of PVDF. PESU and PVDF enable reduction of contact resistance during assembly, while PVDF enables maintained reduction of contact resistance during operation. This construction can be used to reduce electrical resistance at the interface between the following subcomponent layers: * Bipolar Plate (BPP) * Membrane Electrode Assembly (MEA) * Gas Diffusion Layer (GDL) [00016] In practice, fuel cell subcomponent layers (BPPs, GDLs and MEAs) are coated with a polymeric material having a glass transition temperature (Tg) at or below the desired operating temperature range of the fuel cell. The coated composite fuel cell subcomponent layers (BPPs, GDLs, and MEAs) are first assembled by mechanically pressing the layers together at or above the polymer Tg. These layers deform essentially to match microstructures on the mating surface of fuel cell subcomponent layers, which improves interfacial contact and reduces contact resistance between the layers. The surfaces of the subcomponent layers also may be roughened, e.g., by microscale roughening so that the surface contact of the polymeric materials with the mating surface may be improved.

moon] In other embodiments the subcomponent layers are pressed together by lamination, contact welding, tack welding, hot plate welding, or vacuum deposition under elevated temperatures.

[00018] While the MEA, GDL and BPP are described as the subcomponent layers bonded using this technique, the same method can be applied to other layers of the fuel cell where low electronic resistance is required, e.g., the PEM membrane and the catalyst layers.

[00019] In one embodiment of the disclosure the meltable conductive polymer composite is applied as a single layer of, e.g., 5-10 pm thickness composed of a conductive composite blend. In another embodiment the surface(s) of a subcomponent layer can be coated with multiple conductive polymer materials to create a multilayered structure. This can provide the additional benefit of stronger interlayer penetration and more controlled thermal and conformal behavior over a wider operating temperature range. For example, a three-layered structure may be created on a surface with one polymeric material having a Tg of 150 C, one with a Tg of 170 C, and one with a Tg of 220 C. This tailoring of material interconnect layers ensures that the benefits of contact between subcomponent layers are maintained across a wider operating temperature range.

[00020] Polymeric materials with a Tg ranging from 160 -250 C may be applied to the BPPs, the GDLs, and the MEA by spray coating. Spray coating provides a more consistent coverage of polymeric layers. In other embodiments the polymeric layers can be applied using other application methods such as dipping, brush painting, blade coating, thermal spraying, plasma deposition, flow coating,spin coating, soi-gel, dip coati g powder coating, or surface grafting techniques.

[00021] The melt viscosity of the polymeric layer is an important property of the interconnected structure. Materials with similar melt viscosity values will create a more similar interconnected layer when the temperature is above the Tg. Materials with very low melt viscosity thin more readily to coat the interfacial layer, which can lead to improved cross-contact between subcomponent layers. Materials should be selected with a melt viscosity that can maintain the desired layered thickness within the fuel cell operating temperature range.

[00022] The polymeric materials may he blended, filled, doped, or modified by addition of conductive particles to tune the electrical conductivity of the interface layer and can be used to further reduce contact resistance. By way of example but not limitation, the polymeric materials may be blended with carbon particles such as carbon black, carbon nanotubes, or graphene, metallic particles, or other conductive fillers to improve electrical contact at the interface. It is desired to have properties that approach the high conductivity of metal (i.e. gold) without the associated cost and weight of metals. Application may be in consistent and thin layers as a means to lower electrical contact resistance.

[00023] In still other embodiments polymeric materials with high Tg and chemical resistance can be used to add a deformable layer to fuel cell subcomponent layers, including: polyethersulfone (PESU) and polyphenylsulfone (PPSU), polyvinylidene fluoride (PVDF), poi ybenzi midazole (PB1), polyether ether ketone (PEEK), thermoplastic polyimide (TPI), polyethersulfone (PESU), Fluorinated ethylene-propylene (FLIP), polyimide (PI), polyamide (PA), or perfl uoroalk y (PEA). poi yphen yl sulfide (PPS).

[000241 In vet other embodiments, rigid, high melt flow index or high molecular weight ic Is can he added in a pattern to c3 reinforcing struci re to maintainspacing between compressed layers, similar to how rebar is used to reinforce concrete. This adds a benefit of strengthening a fuel cell to better survive a thermal runaway anomaly.

[00025] The material at the interconnect layer can further be modified by blending polymeric materials together to achieve the appropriate Tg, melt viscosity, and electrical conductivity. For example, PESL1 can be blended with PA and conductive fillers to n rt,in chemical resistance and mechanical compliance at interfaces.

[00026] Mok-x:uarweight (M) of the polymeric layer materials can he taken into consideration for forming interconnected structures. High NI, polymers may be blended with low M". polymers to promote more polymeric entanglements at ace, further improving interfacial cont&ct. For example, PFSU (N11,=-45,000 g/mol) can he blended with PESTI (M=8,000 gimol) and applied as an interconnect layer.

[00027] Hysteresis behavior of the polymer interconnect material presents a challenge for maintaining device functionality over a long operating lifetime. Poor interfacial contact and material thickness variation due to thermal cycles or loss of loading is undesirable -this increases the contact resistance. Thus, the polymer contact materials may be selected for their ability to hold shape and maintain contact after repeated heat/cool cycles. And, high Tg polymers can be modified with low Tg polymers to improve the material shape memory after heat cycles.

[00028] Interconnected polymer layers can be imprinted during the initial manufacturing step to control the shape of an interconnected layered structure. For example, polymeric interconnects may be applied to the surfaces of the BPPs, the MEA, and the GDLs. The structure could then be pressed at a temperature above the polymer interconnect material Tg, held to create patterned deformations, then cooled in a controlled manner to ensure that interlayer contact is maintained. This manufacturing step can help to mitigate structural changes during operation.

[00029] Summarizing to this point, in one aspect of the disclosure we provide a High Temperature Proton Exchange Membrane (HT-PEM) fuel cell, comprising, from the inside: a Membrane Electrode Assembly (MEA) including the following subcomponents: a Proton Exchange Membrane (PEM); an anode catalyst layer on one outside surface of the PEM, and a cathode catalyst layer on opposite outside surface of the PEM; Gas Diffusion Layer (GDEs) on outside surfaces of the anode and the cathode layers; and Bipolar Plates (BPPs) on outside surfaces of the GDLs; wherein one or more contacting surfaces of the MEA subcomponents are coated, at least in part, with an electrically conductive polymer composite material that softens at or below the operating temperature of the HT-PEM.

[09030] In one aspect of the disclosure, the HT-PEM fuel cell electrically conductive polymer composite material comprises a material having a glass transition Tg and melting temperature LI below the operating temperature of the HT-PEM.

[00031] In another aspect of the disclosure the electrically conductive polymer composite material comprise a plurality of layers, each layer having a different Tg and Tm.

[00032] In yet another aspect of the disclosure the polymeric material has a Tg and T., in the range of 160-2500 [00033] In a further aspect of the disclosure the conductive polymer composite material includes conductive carbon particles selected from the group consisting of carbon black, graphitized carbon particles, amorphous carbon particles, carbon nanotubes, graphene and a mixture thereof.

[000341 In yet another aspect of the disclosure the conductive polymer composite material includes metal particles selected from the group consisting of gold, tungsten, silver, titanium, zirconium, vanadium, niobium, tantalum, aluminum, magnesium, and an alloy thereof.

r000351 In a further aspect of the disclosure the conductive polymeric composite material layer comprises one or more layers including a layer formed of polyvinylidene fluoride, containing conductive particles, and a layer formed of a polysulfone polymer selected of the group consisting of polyphenylsultbne, polyethersulfone, and a mixture thereof, containing conductive particles.

[00036] In another aspect of the disclosure the polymeric composite material includes a polymeric material selected from the group consisting of polythiophene, poly(3,4-ethylenedioxythiophene) (PEDOT), poly(pyrrole), polyphenylsulfone (PPSU), and polyaniline (PANT).

[000371 In a further aspect of the disclosure the conductive polymeric composite material includes a polymer material selected from the group consisting of polybenzimidazole, polyether ether ketone, thermoplastic polyimide, polyethersulfone, fluorinated ethylene-propylene, and perfluoroalkoxy.

[00038] The disclosure also provides a fuel cell powered vehicle comprising a HT-PEM fuel cell as above described.

[000391 In one aspect of the disclosure the vehicle comprises a HT-PEM fuel cell powered aircraft.

[000401 The disclosure also provides a method for maintaining electrical contact between subcomponents of a High Temperature Proton Exchange Membrane (HT-PEM) fuel cell, comprising: coating at least in part a surface of at least some of the subcomponents with an electrically conductive polymer composite material that softens at or below an operating temperature of the IT-PEM.

[00041] The disclosure additionally provides a method of forming a HT-PEM fuel cell as above described, which comprises coating at least in part surface of one or more of the subcomponents of a HT-PEM fuel cell with a conductive polymer composite material having a glass transition Tg and/or melting temperature T. lower than the fuel cell operating temperature, pressing the subcomponents assembled together at a temperature above the Tg of the conductive polymer composite material, and subsequently cooling the assembled subcomponents while maintaining pressure on the assembled components.

[00042] In one aspect of the above method the fuel cell subcomponents are assembled, placed under pressure and thermal cycled above and below the Tg of the conductive polymer composite materi al. [00043] In another aspect of the method the electrically conductive polymer composite material comprises a material having a glass transition Tg and melting temperature T. below the operating temperature of the HT-PEM.

[00044] In still another aspect of the method the electrically conductive polymer composite material comprise a plurality of layers, each layer having a different Tg and T. [00045] In yet another aspect of the method the polymeric material has a Tg and T. in the range of 160-2500 [00046] In a further aspect of the method the conductive polymer composite material includes conductive carbon particles selected from the group consisting of carbon black, graphitized carbon particles, amorphous carbon particles, carbon nanotubes, graphene and a mixture thereof.

1-000471 In yet another aspect of the method the conductive polymer composite material includes metal particles selected from the group consisting of gold, tungsten, silver, titanium, zirconium, vanadium, niobium, tantalum, aluminum, magnesium, and an alloy thereof.

[000481 In still yet another aspect of the disclsoure the conductive polymeric composite material layer comprises one or more layers including a layer formed of polyvinylidene fluoride, containing conductive particles, and a layer formed of a polysulfone polymer selected of the group consisting of polyphenylsultbne, polyethersultbne, and a mixture thereof, containing conductive particles.

[00049] According to aspect A of the present invention there is provided a High Temperature Proton Exchange Membrane (HT-PEM) fuel cell, comprising, from the inside: a Membrane Electrode Assembly (MEA) including the following subcomponents: a Proton Exchange Membrane (PEM); an anode catalyst layer on one outside surface of the PEM, and a cathode catalyst layer on opposite outside surface of the PEM; Gas Diffusion Layers (GDLs) on outside surfaces of the anode and the cathode layers; and Bipolar Plates (BPPs) on outside surfaces of the GDLs; wherein one or more contacting surfaces of the MEA subcomponents are coated, at least in part, with an electrically conductive polymer composite material that softens at or below the operating temperature of the HT-PEM fuel cell.

r000501 Preferably the electrically conductive polymer composite material comprises a material having a glass transition Tg and melting temperature T", below the operating temperature of the HT-PEM.

[000511 Preferably the electrically conductive polymer composite material comprises a plurality of layers, each layer having a different Tg and T.,.

[00052] Preferably the polymeric material has a Tg and T., in the range of 160-2500 [000531 Preferably the conductive polymer composite material includes conductive carbon particles selected from the group consisting of carbon black, graphitized carbon particles, amorphous carbon particles, carbon nanotubes, graphene and a mixture thereof.

[00054] Preferably the conductive polymer composite material includes metal particles selected from the group consisting of gold, tungsten, silver, titanium, zirconium, vanadium, niobium, tantalum, aluminum, magnesium, and an alloy thereof.

[00055] Preferably the conductive polymeric composite material layer comprises one or more layers including a layer formed of polyvinylidene fluoride, containing conductive particles, and a layer formed of a polysultbne polymer selected of the group consisting of polyphenylsulfone, polyethersulfone, and a mixture thereof, containing conductive particles.

[00056] Preferably the polymeric composite material includes a polymeric material selected from the group consisting of polythiophene, poly(3,4-ethylenedioxythiophene) (PEDOT), poly(pyrrole), polyphenylsulfone (PPSU), and polyaniline (PANI).

[00057] Preferably the conductive polymeric composite material includes a polymer material selected from the group consisting of a polyurethane, a cyanate ester, an epoxy, a silicone, polybenzimidazole polyether ether ketone, thermoplastic polyimide, polyethersulfone, fluorinated ethylene-propylene, and perfluoroalkoxv.

[000581 According to aspect B of the present invention there is provided a fuel cell powered vehicle comprising a HT-PEM fuel cell according to aspect A of the present invention.

[00059] Preferably the vehicle comprises a HT-PEM fuel cell powered aircraft.

[000601 According to aspect C of the present invention there is provided a method for maintaining electrical contact between subcomponents of a High Temperature Proton Exchange Membrane (HT-PEM) fuel cell, comprising: coating surface of at least some of the subcomponents at least in part with an electrically conductive polymer composite material that softens at or below an operating temperature of the HT-PEM.

[00061] According to aspect D of the present invention there is provided a method for maintaining electrical contact between subcomponents of a High Temperature Proton Exchange Membrane (HT-PEM) fuel cell according to aspect A of the present invention, comprising: [00062] coating surface of at least some of the subcomponents at least in part with an electrically conductive polymer composite material that softens at or below an operating temperature of the IT-PEM.

[000631 According to aspect E of the present invention there is provided a method of forming a HT-PEM fuel cell according to aspect A of the present invention, which comprises coating at least in part a surface of one or more of the subcomponents with a conductive polymer composite material having a glass transition Tg and/or melting temperature T", lower than the fuel cell operating temperature, pressing the subcomponents assembled together at a temperature above the Tg of the conductive polymer composite material, and subsequently cooling the assembled subcomponents while maintaining pressure on the assembled components.

[00064] Preferably the fuel cell subcomponents are assembled, placed under pressure and thermal cycled above and below the Tg of the conductive polymer composite material.

[000651 Preferably the electrically conductive polymer composite material comprises a material having a glass transition Tg and melting temperature T", below the operating temperature of the HT-PEM.

[000661 Preferably the electrically conductive polymer composite material comprises a plurality of layers, each layer having a different Tg and T,-g.

[000671 Preferably the polymeric material has a Tg and Tin in the range of 160-2500 [00068] Preferably the conductive polymer composite material includes conductive carbon particles selected from the group consisting of carbon black, graphitized carbon particles, amorphous carbon particles, carbon nanotubes, graphene and a mixture thereof.

[00069] Preferably the conductive polymer composite material includes metal particles selected from the group consisting of gold, tungsten, silver, titanium, zirconium, vanadium, niobium, tantalum, aluminum, magnesium, and an alloy thereof.

[000701 Preferably the conductive polymeric composite material layer comprises one or more layers including a layer formed of polyvinylidene fluoride, containing conductive particles, and a layer formed of a polysulfone polymer selected of the group consisting of polyphenylsulfone, polyethersulfone, and a mixture thereof, containing conductive particles.

[00071] While the foregoing disclosure describes primarily the use of thermoplastic polymers in forming the interconnect layers, thermoset materials such as cross-linked polyurethanes, cyanate esters, epoxies, or silicones also can be used to maintain the shape of the interconnected layers while coatings on the material maintain low contact resistance. For example, a silicone layer can be patterned and cured on the surface of a fuel cell subcomponent. For example high Tg silicone filled with carbon nanotubes can be stamped or overmolded to create a conformal layer within the fuel cell structure.

[000721 In other embodiments thermoset polymeric precursors can be applied to connected layers and then further converted to a network structure by a thermal, UV, or microwave curing step. For example, a layer of low molecular weight silicone precursors can be coated to the surface of the polymer material and then vulcanized to create a thermoset interconnect layer. Using low viscosity thermoset precursors also enables alternative manufacturing methods to apply patterned polymeric structures for fuel cell stacks.

[00073] Further areas of applicability will become apparent form 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 di mei os ure.

Brief Description of the Drawings

[000741 Further features and advantages of the disclosure will be seen in the following detailed description, taken in conjunction with the accompanying drawings. 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 High Temperature Proton Exchange Membrane (HT-PEM) fuel cell; Fig. 2 is a cross sectional view of a HT-PEM fuel cell in accordance with the present disclosure; Fig. 3 is a flow diagram illustrating a process for forming a HT-PEM fuel cell in accordance with the present disclosure; and Fig. 4 is a schematic depiction of a hydrogen fuel cell powered aircraft in accordance with the present disclosure.

Detailed Description

[09075] Example embodiments will now he 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.

[00076] 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, and/or components, 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.

[09077] When an element or layer is referred to as being "on," "engaged to, "connected to 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,-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.

[00078] 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 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.

[00079] 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.

[000801 As used herein the terms component" and "subcomponent are employed interchangeably to describe the several elements forming our High Temperature Proton Exchange (HT-PEM fuel) cell.

[00081] Referring to Figs 2, a High Temperature Proton Exchange Membrane (HT-PEM) fuel cell 110 in accordance with the present disclosure is similar to the prior art HT-PEM described above in Fig. I, and includes a Proton Exchange Membrane (PEM) I 12, typically formed in a specially treated polymer material that conducts only positive charged ions, and blocks 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. Gas Diffusion Layers (GDLs) 118, 120 sit to the outside the catalyst layers 114, 116 and facilitate transport of reactants into the catalyst layers, as well as removal of the product water. The PEM 112, catalyst layers 114, 116 and the GDLs 118, 120 together make up the so-called Membrane Electrode Assembly (MEA) 122. As in the case of the prior art HT-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 bipolar plates (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 plates I 24, 126 to allow gases to flow over the MEA 122. And, as before additional channels (not shown) may be provided inside each plate to circulate a liquid coolant.

[000821 As distinguished from the prior art HT-PEM as described above, in accordance with the present disclosure one or more of the contacting surfaces of the MEA 122, i.e., surfaces of the PEM 112, the anode and cathode catalyst layers 114, 116, the GDLs 118, 120 and/or the BPPs are coated, at least in part with an electrically conductive composite material 130 that softens at or below the operating temperature of the HT-PEM. Electrically conductive composite material may comprise one or a plurality of layers 130A, 130B (see Fig. 3). The layers each may have a different Tg and Tm.

[00083] Referring to Fig. 3, an HT-PEM in accordance with the present disclosure is formed as follows: A surface of one or more of the subcomponents of a fuel cell, such as a BPP 124 is coated at least in part with a layer of an electrically conductive polymer composite that softens at or below the operating temperature of the fuel cell in a coating step 150. In the illustrated case the electrically conductive polymer composite comprises two layers that are sequentially applied, a first layer 130A comprising a composite polymer material formed of PVDF containing 3-70% by volume conductive media, comprising a polymeric material formed of PESU containing 3-70% by volume conductive media. Conductive media may comprise one or more of 0 to 55% by volume carbon black and 0 to 30% carbon nanotubes. In other embodiments non-carbon conductive media may be used, e.g., conductive polymers (e.g., polyaniline, etc.), metals, and conductive metal oxides particles (e.g., RexOy). The coated BPP 124 subcomponent is then assembled with an MEA 122 subcomponent by pressing the two subcomponents together at a pressure of 0.1 to 100 kg/cm2 in a pressure step 152. The step 152 may last for as little as one second or as long as practical, though structure is usually formed within the first several seconds. In some embodiments step 152 may be a heating and pressure step above the polymer interconnect Tg, e.g., at a temperature of 100 to 400 "C. In some embodiments, only one composite polymer layer is used (i.e., 124, 130A, 122) and in other embodiments more than two composite polymer layers are used (i.e., 124, I 30A, I 30B, ... 130n, 122). The polymer composite material layers 130A, 130B deform to match microstructures 154 on the mating surface(s) of the subcomponent(s), which improves interfacial contact and reduces contact resistance between layers. The assembly is allowed to cool, and the assembly may then be subjected to one or more additional heat and pressure cycles (step 156). Other subcomponents may similarly be assembled and joined together.

[00084] Fig. 4 illustrates an aircraft 140 including two electric motors 142, 14 which are powered by two parallel HT-PEIV1 hydrogen fuel cells 146, 148 in accordance with the present disclosure.

1-000851 While the foregoing disclosure focuses on using polymeric materials to maintain a conformal interface coating which lower fuel cell contact resistance, other functional benefits can be incorporated into polymeric interconnect layers. For example, chemically resistant materials can he embedded in the stack to increase robustness against other media such as alkaline or acidic materials.

1-000861 Also, while the foregoing disclosure is focused primarily on HT-PEM fuel cell applications, the composition of matter and manufacturing process disclosed can be adapted for use in electronic devices, battery manufacturing, or other areas where a high degree of interfacial electrical contact is desired, such as, for example press-fit or gas-tight electric connectors, sockets, pins and the like, particularly those designed for high temperature environments.

1-000871 The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to he 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.

Claims

What is Claimed: I. A High Temperature Proton Exchange Membrane (HT-PEM) fuel cell, comprising, from the inside: a Membrane Electrode Assembly (MEA) including the following subcomponents: a Proton Exchange Membrane (PEM); an anode catalyst layer on one outside surface of the PEM, and a cathode catalyst layer on opposite outside surface of the PEM; Gas Diffusion Layers (GDLs) on outside surfaces of the anode and the cathode layers; and Bipolar Plates (BPPs) on outside surfaces of the GDLs; wherein CO one or more contacting surfaces of the MEA subcomponents are coated, at least in part, with an electrically conductive polymer composite material that softens at or below the operating temperature of the HT-PEM fuel cell.
2. The HT-PEM fuel cell of claim I, wherein the electrically conductive polymer composite 0 material comprises a material having a glass transition Tg and melting temperature T,,, below the operating temperature of the HT-PEM.
3. The HT-PEM fuel cell of claim I or 2, wherein the electrically conductive polymer composite material comprises a plurality of layers, each layer having a different Tg and Tim
4. The HT-PEM fuel cell of any of claims 1 to 3, wherein the polymeric material has a Tg and T", in the range of 160-250°.
5. The HT-PEM fuel cell of any preceding claim, wherein the conductive polymer composite material includes conductive carbon particles selected from the group consisting of carbon black, graphitized carbon particles, amorphous carbon particles, carbon nanotubes, graphene and a mixture thereof.
6. The HT-PEM fuel cell of any preceding claim, wherein the conductive polymer composite material includes metal particles selected from the group consisting of gold, tungsten, silver, titanium, zirconium, vanadium, niobium. tantalum, aluminum, magnesium, and an alloy thereof.
7. The HT-PEM fuel cell of any preceding claim, wherein the conductive polymeric composite material layer comprises one or more layers including a layer formed of polyvinylidene fluoride, containing conductive particles, and a layer formed of a polysultbne polymer selected of the group consisting of polyphenylsulfone, polyethersulfone, and a mixture CO thereof, containing conductive particles.C\I
8. The HT-PEM fuel cell of any preceding claim, wherein the polymeric composite material includes a polymeric material selected from the group consisting of polythiophene, poly(3,4-N ethylenedioxythiophene) (PEDOT), poly(pyrrole), polyphenylsulfone (PPSU), and polyaniline (PAN!).
9. The HT-PEM fuel cell of any preceding claim, wherein the conductive polymeric composite material includes a polymer material selected from the group consisting of a polyurethane, a cyanate ester, an epoxy, a silicone, polybenzimidazole, polyether ether ketone, thermoplastic polyimide, polyethersulfone, fluorinated ethylene-propylene and perfluoroallcoxy.
10. A fuel cell powered vehicle comprising a HT-PEM fuel cell as claimed in any of claims 1 to 9.
11. The fuel cell powered vehicle as claimed in claim 10, wherein the vehicle comprises a HT-PEM fuel cell powered aircraft.
12. A method for maintaining electrical contact between subcomponents of a High Temperature Proton Exchange Membrane (HT-PEM) fuel cell, comprising: coating surface of at least some of the subcomponents at least in part with an electrically conductive polymer composite material that softens at or below an operating temperature of the HT-PEM.
13. A method for maintaining electrical contact between subcomponents of a High Temperature Proton Exchange Membrane (HT-PEM) fuel cell as claimed in any of claims I to 9, comprising: coating surface of at least some of the subcomponents at least in part with an electrically conductive polymer composite material that softens at or below an operating temperature of the CO HT-PEM.C\I
14. A method of forming a HT-PEM fuel cell as claimed in any of claims I to 9, which 0 comprises coating at least in part a surface of one or more of the subcomponents with a conductive polymer composite material having a glass transition Tg and/or melting temperature Tr, lower than the fuel cell operating temperature, pressing the subcomponents assembled together at a temperature above the Tg of the conductive polymer composite material, and subsequently cooling the assembled subcomponents while maintaining pressure on the assembled components.
15. The method of claim 14, wherein the fuel cell subcomponents are assembled, placed under pressure and thermal cycled above and below the Tg of the conductive polymer composite material.
16. The method of claim 14 or claim 15, wherein the electrically conductive polymer composite material comprises a material having a glass transition Tg and melting temperature Till below the operating temperature of the HT-PEM.
17. The method of any of claims 14 to 16, wherein the electrically conductive polymer composite material comprises a plurality of layers, each layer having a different Tg and Trn.
18. The method of any of claims 14 to 17, wherein the polymeric material has a Tg and Tn, in the range of I 60-250°.
19. The method of any of claims 14 to 18, wherein the conductive polymer composite material includes conductive carbon particles selected from the group consisting of carbon black, graphitized carbon particles, amorphous carbon particles, carbon nanotubes, graphene and a CO mixture thereof.C\I
20. The method of any of claims 14 to 19, wherein the conductive polymer composite material includes metal particles selected from the group consisting of gold, tungsten, silver, titanium, zirconium, vanadium, niobium, tantalum, aluminum, magnesium, and an alloy thereof.
21. The method of any of claims 14 to 20, wherein the conductive polymeric composite material layer comprises one or more layers including a layer formed of polyvinylidene fluoride, containing conductive particles, and a layer formed of a polysultbne polymer selected of the group consisting of polyphenylsulfone, polyethersulfone, and a mixture thereof, containing conductive particles.