Fuel cell cathode and fuel cell system including a polymer additive

Abstract

A cathode configured for use in a fuel cell system is provided. The cathode includes a cathode substrate. The cathode also includes a coating disposed on the cathode substrate and including a fluorocarbon polymer additive configured for sintering at a temperature below 200 °C. The fluorocarbon polymer additive can be mixed with a catalyst ink coating or can be applied separately as a topcoat.

Description

[0001] Statement as to Federally Sponsored Research

[0002] This invention was made with government support under Contract No. US; DE- EE0008821 ; HDTruck MEA awarded by the U.S. Department of Energy. The government has certain rights in the invention. TECHNICAL FIELD

[0003] The present disclosure generally relates to a fuel cell cathode and a fuel cell system including a polymeric additive. BACKGROUND

[0004] A fuel cell is an electrochemical device, typically composed of a plurality of anode electrodes that receive hydrogen gas (H2), a plurality of cathode electrodes that receive oxygen gas (O2), and a plurality of electrolytes or electrolyte solutions between each anode and cathode. An electrochemical reaction is initiated to oxidize hydrogen molecules at the anode to produce free protons (H+), which are then reduced at the cathode with an oxidizer, such as oxygen gas, through the electrolyte. This reaction produces electrons at the anode, some of which are redirected through a load, such as a traction motor of a vehicle or a non-vehicle load that requires stationary power generation, and then sent to the cathode. Such a fuel cell can be used in combination with other fuel cells to form a fuel cell stack. Stacks or fuel cell stacks can be electrically connected to each other, for example, in series, such that the voltage supplied by each fuel cell is added to the next, such that the total voltage supplied by the fuel cell stack is the sum of the voltage of each stacked fuel cell.

[0005] Hybrid and all-electric (collectively, "electric drive") powertrains employ various architectures, some of which utilize fuel cell systems to power one or more electric traction motors. SUMMARY

[0006] A cathode configured for use in a fuel cell system is provided. The cathode includes a cathode substrate. The cathode also includes a coating disposed on the cathode substrate and including a fluorocarbon polymer additive configured for sintering at a temperature below 200 °C.

[0007] In some embodiments, the fluorocarbon polymer additive is configured for sintering at a temperature below 150 °C.

[0008] In some embodiments, the coating also includes a catalyst ink. The catalyst ink and the fluorocarbon polymer additive are mixed together and then disposed on the cathode substrate.

[0009] In some embodiments, the coating includes a first coating configured as a face layer. The cathode also includes a second coating including a catalyst ink. The second coating is disposed between the cathode substrate and the first coating.

[0010] In some embodiments, the fluorocarbon polymer additive is an amorphous polytetrafluoroethylene copolymer with fluorinated cycloaliphatic monomers.

[0011] In some embodiments, the amorphous polytetrafluoroethylene copolymer with fluorinated cycloaliphatic monomers is selected from the group comprising tetrafluoroethylene, 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3 dioxole, and 2,2-bistrifluoromethyl-4,5-difluoro-1,3 dioxole.

[0012] In some embodiments, the fluorocarbon polymer additive is a functionalized perfluoropolyether.

[0013] In some embodiments, the functionalized perfluoropolyether is selected from the group comprising a triethoxysilane terminated difunctional perfluoropolyether; a bisphosphate derivative based on a linear perfluoropolyether backbone; and an aqueous dispersion of anionic polyurethane based on a perfluoropolyether backbone.

[0014] In some embodiments, the fluorocarbon polymer additive is a polyvinylidene fluoride semi-crystalline copolymer.

[0015] In some embodiments, the polyvinylidene fluoride semi-crystalline copolymer is selected from the group comprising vinylidene fluoride, polyvinylidene fluoride: hexafluoropropylene copolymer emulsion, and semi-crystalline polyvinylidene fluoride: tetrafluoroethylene copolymer.

[0016] According to one alternative embodiment, a fuel cell system is provided. The fuel cell system includes an anode, a cathode, and a fuel cell membrane disposed between the anode and the cathode. The cathode includes a cathode substrate and a coating disposed on the cathode substrate. The coating includes a fluorocarbon polymer additive configured for sintering at a temperature below 200 °C.

[0017] In some embodiments, the fluorocarbon polymer additive is configured for sintering at a temperature below 150 °C.

[0018] In some embodiments, the coating further includes a catalyst ink. The catalyst ink and the fluorocarbon polymer additive are mixed together and then disposed on the cathode substrate.

[0019] In some embodiments, the coating includes a first coating configured as a face layer. The cathode further includes a second coating including a catalyst ink. The second coating is disposed between the cathode substrate and the first coating.

[0020] In some embodiments, the fluorocarbon polymer additive is an amorphous polytetrafluoroethylene copolymer with fluorinated cycloaliphatic monomers.

[0021] In some embodiments, the fluorocarbon polymer additive is a functionalized perfluoropolyether.

[0022] In some embodiments, the fluorocarbon polymer additive is a polyvinylidene fluoride semi-crystalline copolymer.

[0023] According to one alternative embodiment, a vehicle is provided. The vehicle includes a powertrain and a fuel cell system configured to provide electrical power to the powertrain. The fuel cell system includes an anode, a cathode, and a fuel cell membrane disposed between the anode and the cathode. The cathode includes a cathode substrate and a coating disposed on the cathode substrate. The coating includes a fluorocarbon polymer additive configured to sinter at a temperature below 200 °C.

[0024] In some embodiments, the coating further includes a catalyst ink. The catalyst ink and the fluorocarbon polymer additive are mixed together and then disposed on the cathode substrate.

[0025] In some embodiments, the coating includes a first coating configured as a face layer. The cathode further includes a second coating containing a catalyst ink. The second coating is disposed between the cathode substrate and the first coating.

[0026] The present invention includes the following clauses.

[0027] Clause 1. A cathode configured for use in a fuel cell system, the cathode comprising:

[0028] a cathode substrate; and

[0029] a coating disposed on the cathode substrate and including a fluorocarbon polymer additive configured to sinter at a temperature below 200 °C.

[0030] Clause 2. The cathode of clause 1, wherein the fluorocarbon polymer additive is configured to sinter at a temperature below 150 °C.

[0031] Clause 3. The cathode of clause 1, wherein the coating further includes a catalyst ink; and

[0032] wherein the catalyst ink and the fluorocarbon polymer additive are mixed together and then disposed on the cathode substrate.

[0033] Clause 4. The cathode of clause 1, wherein the coating includes a first coating configured as a face layer;

[0034] wherein the cathode further includes a second coating containing a catalyst ink; and

[0035] wherein the second coating is disposed between the cathode substrate and the first coating.

[0036] Clause 5. The cathode of clause 1, wherein the fluorocarbon polymer additive is an amorphous polytetrafluoroethylene copolymer with a fluorinated cycloaliphatic monomer.

[0037] Scheme 6. The cathode of Scheme 5, wherein the amorphous polytetrafluoroethylene copolymer with the fluorinated aliphatic monomer is selected from the group consisting of tetrafluoroethylene, 4,5-difluoro-2,2-bis(trifluoromethyl)-l,3 dioxole, and 2,2-bistrifluoromethyl-4,5-difluoro-l,3 dioxole.

[0038] Scheme 7. The cathode of Scheme 1, wherein the fluorocarbon polymer additive is a functionalized perfluoropolyether.

[0039] Scheme 8. The cathode of Scheme 7, wherein the functionalized perfluoropolyether is selected from the group consisting of a triethoxysilane terminated difunctional perfluoropolyether; a bisphosphate derivative based on a linear perfluoropolyether backbone; and an aqueous dispersion of an anionic polyurethane based on a perfluoropolyether backbone.

[0040] Scheme 9. The cathode of Scheme 1, wherein the fluorocarbon polymer additive is a polyvinylidene fluoride semi-crystalline copolymer.

[0041] Scheme 10. The cathode of Scheme 9, wherein the polyvinylidene fluoride semi- crystalline copolymer is selected from the group consisting of vinylidene fluoride, polyvinylidene fluoride:hexafluoropropylene copolymer emulsion, and semi-crystalline polyvinylidene fluoride: tetrafluoroethylene copolymer.

[0042] Scheme 11. A fuel cell system comprising:

[0043] an anode;

[0044] a cathode, the cathode comprising: a cathode substrate; and a coating disposed on the cathode substrate and comprising a fluorocarbon polymer additive configured to sinter at a temperature below 200 °C; and

[0045] a fuel cell membrane disposed between the anode and the cathode.

[0046] Scheme 12. The fuel cell system of Scheme 11, wherein the fluorocarbon polymer additive is configured to sinter at a temperature below 150 °C.

[0047] Scheme 13. The fuel cell system of Scheme 11, wherein the coating further comprises a catalyst ink; and wherein the catalyst ink and the fluorocarbon polymer additive are mixed together and then disposed on the cathode substrate.

[0048] Scheme 14. The fuel cell system of Scheme 11, wherein the coating comprises a first coating configured as a face layer;

[0049] wherein the cathode further comprises a second coating comprising a catalyst ink; and wherein the second coating is disposed between the cathode substrate and the first coating.

[0050] Scheme 15. The fuel cell system of Scheme 11, wherein the fluorocarbon polymer additive is an amorphous polytetrafluoroethylene copolymer with a fluorinated cycloaliphatic monomer.

[0051] Scheme 16. The fuel cell system of Scheme 11, wherein the fluorocarbon polymer additive is a functionalized perfluoropolyether.

[0052] Scheme 17. The fuel cell system of Scheme 11, wherein the fluorocarbon polymer additive is a polyvinylidene fluoride semi-crystalline copolymer.

[0053] Scheme 18. A vehicle comprising:

[0054] a powertrain; and

[0055] a fuel cell system configured to provide electrical energy to the powertrain, the fuel cell system comprising:

[0056] an anode;

[0057] a cathode comprising: a cathode substrate; and a coating disposed on the cathode substrate and comprising a fluorocarbon polymer additive configured to sinter at a temperature below 200 °C; and

[0058] a fuel cell membrane disposed between the anode and the cathode.

[0059] Scheme 19. The vehicle of Scheme 18, wherein the coating further comprises a catalyst ink; and

[0060] wherein the catalyst ink and the fluorocarbon polymer additive are mixed together and then disposed on the cathode substrate.

[0061] Scheme 20. The vehicle of Scheme 18, wherein the coating comprises a first coating configured as a face layer;

[0062] wherein the cathode further comprises a second coating comprising a catalyst ink; and wherein the second coating is disposed between the cathode substrate and the first coating.

[0063] The above features and advantages and other features and advantages of this disclosure are readily apparent from the following detailed description of the best modes for carrying out the disclosure, when taken in connection with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 schematically illustrates an exemplary fuel cell system comprising a fuel cell according to the present disclosure;

[0065] Figure 2A An exemplary cathode substrate of a fuel cell according to the present disclosure is schematically illustrated as including a catalyst ink layer including a fluorocarbon polymer additive; Figure 1 An exemplary cathode substrate of a fuel cell according to the present disclosure is schematically illustrated as including a catalyst ink layer including a fluorocarbon polymer additive;

[0066] Figure 2B An exemplary cathode substrate of a fuel cell according to the present disclosure is schematically illustrated as including a catalyst ink layer including a fluorocarbon polymer additive; Figure 1 An exemplary cathode substrate of a fuel cell according to the present disclosure is schematically illustrated as including a catalyst ink layer including a fluorocarbon polymer additive;

[0067] Figure 3 Changes in catalyst electrochemical surface area (ECSA) through cyclic testing of both a baseline fuel cell cathode substrate and a fuel cell cathode substrate including the disclosed fluorocarbon polymer additive according to the present disclosure are illustrated in chart form;

[0068] Figure 4 Changes in mass activity through cyclic testing of both a baseline fuel cell cathode substrate and a fuel cell cathode substrate including the disclosed fluorocarbon polymer additive according to the present disclosure are illustrated in chart form;

[0069] Figure 5 An exemplary vehicle equipped with a fuel cell system according to the present disclosure is schematically illustrated as including Figure 1 An exemplary vehicle equipped with a fuel cell system according to the present disclosure is schematically illustrated as including DETAILED DESCRIPTION

[0070] Fuel cell cathode substrates can encounter challenges such as catalyst electrochemical surface area (ECSA) reduction, which can result in mass activity and cell voltage reduction. The present disclosure generally relates to the addition of fluorocarbon polymers to the cathode of a fuel cell system for superior durability, with compositions provided to enable low temperature sintering processes.

[0071] A fuel cell cathode including a polymer additive is disclosed. Some fuel cell cathode substrates can involve a dispersion of carbon-supported platinum / platinum-cobalt catalyst nanoparticles and an ionomer as a binder and proton conductive additive. According to the present disclosure, fluorine-containing polymer materials can be used as an additional component in the cathode substrate structure. In a first example, a fluorocarbon polymer can include a relatively lower sintering temperature (T 熔体 ~ 335 °C) compared to semi-crystalline homopolymers (T 玻璃amorphous polytetrafluoroethylene (PTFE) copolymer with a fluorinated alicyclic monomer having a sintering temperature (T 玻璃 ~90°C or 125°C), which is commercially available from the Solvay Group of Brussels, Belgium, and 2,2-bistrifluoromethyl-4,5-difluoro-l,3 dioxole (BDD)

[0072] In one embodiment, the fluorocarbon polymer additive can be an amorphous fluorocarbon polymer additive. For example, the amorphous fluorocarbon polymer additive can be an amorphous PTFE copolymer with a fluorinated alicyclic monomer. A variety of amorphous PTFE copolymers with a fluorinated alicyclic monomer are provided, which have a sintering temperature (T 熔体 ~335°C) that is lower than that of a semi-crystalline homopolymer (T 玻璃 <200°C). The first amorphous PTFE copolymer includes tetrafluoroethylene (TFE), a semi-crystalline homopolymer having a melting temperature of approximately 335°C. The second amorphous PTFE copolymer includes 4,5-difluoro-2,2-bis(trifluoromethyl)-l,3 dioxole (TTD), which can be embodied as amorphous Hyflon® AD® 40, 40% w / w TTD (T 玻璃 ~90°C), or amorphous Hyflon® AD® 60; 60% w / w TTD (T 玻璃 ~125°C). The third amorphous PTFE copolymer includes 2,2-bistrifluoromethyl-4,5-difluoro-l,3 dioxole (BDD), amorphous Teflon™, AF 1600; 65% w / w BDD (T 玻璃 ~160°C).

[0073] In the second example, the fluoropolymer may include Fluorolink® oligomers, including functionalized perfluoropolyethers (PFPEs), which are commercially available from Solvay Group in Brussels, Belgium. Examples include Fluorolink® S10 (triethoxysilane-terminated bifunctional PFPE), Fluorolink® F10 (a diphosphate derivative based on a linear PFPE backbone), and Fluorolink® P56 (an aqueous dispersion of anionic polyurethane based on a PFPE backbone).

[0074] A variety of PFPE oligomers are provided. The first oligomer includes Fluorolink® oligomers that embody modified PFPE oligomers as represented by the following formula (1).

[0075]

[0076] The second oligomer comprises Fluorolink® S10 trisiloxane-terminated, which can be represented by the following formula (2).

[0077]

[0078] The third oligomer includes Fluorolink® E10 ethoxylate end-capped polymer, which can be represented by the following formula (3).

[0079]

[0080] The fourth oligomer includes Fluorolink® F10 phosphate-capped oligomer.

[0081] In the third example, the fluoropolymer may include a homopolymer with a specific ratio (T 熔体 The relatively low sintering temperature (T ~160℃) 熔体 A PVDF semi-crystalline copolymer (<150℃). One example includes T 熔体 Solef® XPH-883 or 884 PVDF-HFP copolymer latex, commercially available from Solef Group in Brussels, Belgium, is a highly non-reactive, semi-crystalline thermoplastic fluoropolymer, operating at ~100°C or 140°C. The disclosed polymer additives are provided as alternatives to achieve the same or similar benefits for the fuel cell cathode. The polymer additives can provide excellent durability to the fuel cell, including enhanced ECSA retention and / or mass activity.

[0082] Provides homopolymers with higher specificity (T 熔体 Low sintering temperature (T ~160℃) 熔体<150°C) polyvinylidene fluoride (PVDF) semi-crystalline copolymers. The first PVDF semi-crystalline copolymer includes a semi-crystalline homopolymer of vinylidene fluoride (VDF) with a melting temperature of approximately 160°C. The second PVDF semi-crystalline copolymer includes hexafluoropropylene, a semi-crystalline PVDF:HFP copolymer (5-20% HFP w / w polymer) with a lower melting temperature of 100°C to 150°C. The third PVDF semi-crystalline copolymer includes tetrafluoroethylene (TFE), a semi-crystalline PVDF:TFE copolymer (5-20% TFE w / w polymer) with a lower melting temperature of 130°C to 150°C. In accordance with the present disclosure, a variety of exemplary fluorocarbon polymeric additive materials are provided herein, and the cathode substrate can be modified with any one or more of the provided materials.

[0083] Fluorocarbons can be used as an additive in phosphoric acid fuel cell cathode substrate technology based on the Teflon™ structure with the chemical name polytetrafluoroethylene (PTFE). While PTFE acts as a mechanical binder and provides acceptable moisture barrier functionality for the cathode substrate structure, PTFE is incompatible with some manufacturing of proton exchange membrane fuel cell (PEMFC) cathode substrates. Specifically, T 熔体 PTFE additives at ~335°C include a thermal sintering process at temperatures in the range of 350°C-400°C, at which temperatures the ionomer in the PEMFC cathode substrate chemically degrades. In addition, PTFE-based additives do not improve the performance and durability of the fuel cell. The fluorine-containing polymeric additives disclosed herein utilize a thermal sintering process at temperatures less than 200°C and in some embodiments less than 150°C, which thus facilitates processing with PEMFC cathode substrate coating technology.

[0084] The disclosed polymeric additives can be disposed on the cathode by direct addition to the catalyst ink and then applied to the cathode substrate coating. In another embodiment, the disclosed polymeric additives can be added to the cathode substrate as a topcoat after the catalyst ink is applied. Regardless of the method used, the polymer is dissolved or dispersed in a solvent that is compatible with the catalyst ink ingredients. When delivered by direct addition to the catalyst ink, the polymeric additive can be added to the ionomer premix solution and then mixed with the dry catalyst powder, or dispersed on the catalyst powder in solvent. When delivered as a topcoat, the polymeric additive can be delivered as a topcoat onto the dry cathode substrate surface. The amount of polymer delivered using either of these two methods can be less than 0.4 milligrams per centimeter squared of cathode substrate. 2

[0085] ​A cathode configured for use in a fuel cell system is provided having a carbon-fluoropolymer additive configured for sintering at temperatures below 200°C and in some embodiments below 150°C. The carbon-fluoropolymer additive can be added directly to a catalyst ink prior to a cathode coating. In other embodiments, a dry cathode coating is layered separately with a carbon-fluoropolymer additive layer.

[0086] In some embodiments, the carbon-fluoropolymer additive includes an amorphous copolymer of tetrafluoroethylene-co-2,2,4-trifluoro-5-trifluoromethoxy-l,3-dioxole composition (TFE-TTD).

[0087] In some embodiments, the carbon-fluoropolymer additive includes a functionalized perfluoropolyether. In some embodiments, the functionalized oligomer includes a triethoxysilane terminated perfluoropolyether, a diphosphate terminated perfluoropolyether, or an aqueous dispersion of anionic polyurethane based on a perfluoropolyether backbone.

[0088] In some embodiments, the carbon-fluoropolymer additive includes a semi-crystalline carbon-fluoropolymer additive including a thermoplastic fluoropolymer containing polyvinylidene fluoride: hexafluoropropylene copolymer (PVDF:HFP).

[0089] According to one alternative embodiment, a fuel cell system is provided. The fuel cell system includes an anode and a cathode. The cathode includes a cathode substrate and a coating disposed on the cathode substrate including a carbon-fluoropolymer additive configured for sintering at temperatures below 200°C and in some embodiments below 150°C. The fuel cell system further includes a fuel cell membrane disposed between the anode and the cathode.

[0090] Throughout the disclosure, hydrogen is provided as an exemplary fuel for use by the fuel cell system. In other embodiments, other fuels can be used as reactants in the fuel cell reaction, and references to hydrogen and hydrogen gas throughout the disclosure can be replaced by any fuel that can be used as a reactant in a fuel cell.

[0091] Reference will now be made to the drawings wherein like numerals refer to like features throughout. Figure 1An exemplary fuel cell system is schematically illustrated. Fuel cell system 10 is provided for context related to the exemplary fuel cell system and illustrates includes a fuel cell stack 50, a hydrogen storage tank 20, a fuel injector 32, and a fuel injector 34 that supplies a hydrogen gas stream to the injector device 30. For simplicity, a single fuel cell is illustrated as including an anode 52 and a cathode 54 separated by a fuel cell membrane 56. Fuel cell system 10 can include a plurality of fuel cell stacks 50 that include a plurality of pairs of anodes 52 and cathodes 54. An anode gas loop 70 including a hydrogen gas stream is provided to the anode 52. A cathode gas subsystem 60 including a compressed air stream is provided to the cathode 54. As described herein, the fuel cell stack 50 utilizes the hydrogen gas stream at the anode 52 and the compressed air at the cathode 54 to generate electrical energy used by the vehicle 300 or system equipped with the fuel cell stack 50. Figure 5

[0092] Hydrogen gas is supplied by the hydrogen storage tank 20 at a high pressure. A shut-off valve 22 is provided and can selectively allow or not allow hydrogen gas to flow from the hydrogen storage tank 20 to the remainder of the fuel cell system 10. A pressure regulator 24 is provided that controls and reduces the high pressure delivered from the hydrogen storage tank 20 to a medium pressure hydrogen gas pressure delivered to the fuel injector 32 and the fuel injector 34. A pressure sensor 26 is provided between the pressure regulator 24 and the two fuel injectors 32, 34.

[0093] The fuel injector 32 and the fuel injector 34 are operable to selectively open and supply hydrogen gas to the anode gas loop 70 and to selectively close and prohibit hydrogen gas flow into the anode gas loop 70. Hydrogen gas is delivered to the fuel injector 32 and the fuel injector 34 at a medium pressure. The fuel injector 32 and the fuel injector 34 supply hydrogen gas to the anode gas loop 70 at a low pressure by cycling between an open state and a closed state, open to increase the pressure to a maximum desired anode gas loop pressure, close when the pressure within the anode gas loop 70 reaches the maximum desired anode gas loop pressure, and open again when the pressure within the anode gas loop 70 reaches a minimum desired anode gas loop pressure. The fuel injector 32 and the fuel injector 34 are operable to maintain the pressure within the anode gas loop 70 within a desired low pressure range by opening the fuel injector 32 and the fuel injector 34 when the pressure within the anode gas loop 70 reaches the minimum desired anode gas loop pressure and by closing the fuel injector 32 and the fuel injector 34 when the pressure within the anode gas loop 70 reaches the maximum desired anode gas loop pressure.

[0094] ​Ejector device 30 is a device for providing hydrogen gas from fuel injector 32 and from fuel injector 34 into anode gas circuit 70. Ejector device 30 includes a venturi configuration. Hydrogen gas flowing through ejector device 30 flows through a venturi within ejector device 30. Anode gas circuit 70 includes an upstream portion 72 upstream of anode 52 and a downstream portion 74 downstream of anode 52. Upstream portion 72 includes a high concentration of hydrogen gas. As hydrogen gas passes through anode 52, anode 52 can consume a substantial portion of the hydrogen gas. However, a lower concentration of hydrogen gas can remain in downstream portion 74. Downstream portion 74 is connected to the venturi of ejector device 30 such that the movement of hydrogen gas from fuel injector 32 and fuel injector 34 through ejector device 30 and into upstream portion 72 flows through the venturi device and draws gas from downstream portion 74 into the gas flowing into upstream portion 72. In this way, gas from downstream portion 74 is recirculated through anode 52. Pressure sensor 76 is provided to monitor the pressure within upstream portion 72.

[0095] Water, as a byproduct of the chemical reactions of the fuel cell stack, can exit anode 52. Downstream portion 74 can include an anode water separator and an anode drain valve for draining water from downstream portion 74.

[0096] Air is provided to cathode 54 for use in the oxygen of the fuel cell stack reactions. An air compressor 66 is provided, drawing in ambient air and providing a pressurized flow of air through cathode gas subsystem 60. Cathode gas subsystem 60 includes a cathode reactant portion 62 and a cathode bypass portion 64. Cathode reactant portion 62 provides a flow of air to cathode 54. A bypass valve 61 is connected to cathode bypass portion 64, and control of bypass valve 61 can be used to control how much air flows through cathode bypass portion 64 and how much air flows through cathode reactant portion 62. Such control of how much air flows through cathode reactant portion 62 can be important for controlling the reactions of fuel cell stack 50. Air exits through air expander device 68.

[0097] Figure 2A An exemplary cathode substrate 54 of a fuel cell is schematically illustrated, including a catalyst ink layer 55 including a fluorocarbon polymer additive. The fluorocarbon polymer additive can be added to the catalyst ink, which is then applied to the cathode substrate 54.

[0098] Figure 2B An exemplary cathode substrate 54 of a fuel cell is schematically illustrated, including a catalyst ink layer 57 and a face layer 59, the catalyst ink layer 57 and face layer 59 including a fluorocarbon polymer additive. The catalyst ink layer 57 can be applied to the cathode substrate 54 and can be allowed to dry or cure, then the face layer 59 is added.

[0099] Figure 3A graph illustrating the change in catalyst electrochemical surface area (ECSA) through cyclic testing of both a baseline fuel cell cathode substrate compared to a fuel cell cathode substrate including the disclosed fluorocarbon polymer additive is illustrated. Specifically, the test samples used direct addition of two fluorocarbon polymers to the ionomer premix solution used for the cathode coating. Specifically, amorphous Hyflon® AD40 copolymer was received as a 9% w / w solution in a PFPE solvent and dispersed in the PFSA ionomer premix solution using a Thinky® ARE-310 centrifugal mixer to yield an oil emulsion of 1.5% w / w PFSA. Fluorolink® P56 was received as a 25% w / w solid dispersion in an aqueous solvent and added directly to the ionomer premix solution for another additive loading of 1.5% w / w PFSA. The resulting cathode substrate coating was dried at 40°C under an IR lamp and then sintered at 150°C for 10 minutes in a convection oven purged with inert N2 gas.

[0100] Figure 3 The graph of FIG. 1 illustrates includes a vertical axis 104 illustrating the ECSA values of the cathode substrate in meters 2 / gram. The horizontal axis includes four different samples: sample 110, an initial comparative baseline sample; sample 112, the comparative baseline sample after cyclic testing; sample 120, an initial sample including an amorphous fluorocarbon polymer additive; and sample 122, a sample including the fluorocarbon polymer additive after cyclic testing. Comparing sample 110 to sample 112, it can be seen that the cathode substrate degraded from an initial ECSA value of 69.7 meters 2 / gram to 30.3 meters 2 / gram. Comparing sample 120 to sample 122, it can be seen that the cathode substrate degraded from an initial ECSA value of 69.7 meters 2 / gram to 37.2 meters 2 / gram. The addition of the fluorocarbon polymer additive improved the durability and performance of the cathode substrate by providing excellent electrochemical surface area retention.

[0101] Figure 4A graph illustrates the change in mass activity through cyclic testing of both a comparative baseline fuel cell cathode substrate and a fuel cell cathode substrate including the disclosed fluorocarbon polymer additive. Mass activity can be described as current per unit mass or current density at a specific voltage normalized to active material mass loading. Specifically, the test sample including the amorphous fluorocarbon polymer additive includes a mixture of Hyflon® and Fluorolink® P56 additives. A graph 200 is illustrated, which includes a vertical axis 204, which illustrates mass activity values for the cathode substrate in amperes / milligrams platinum. The horizontal axis includes four different samples from the testing: sample 210, an initial comparative baseline sample; sample 212, the comparative baseline sample after cyclic testing; sample 220, an initial sample including the fluorocarbon polymer additive; and sample 222, a sample including the fluorocarbon polymer additive after cyclic testing. Comparing sample 210 to sample 212, one can see that the initial mass activity value decreases from 35 amperes / milligrams platinum to 0.26 amperes / milligrams platinum. Comparing sample 220 to sample 222, one can see that the initial mass activity value decreases from 0.37 amperes / milligrams platinum to 0.34 amperes / milligrams platinum. The addition of the fluorocarbon polymer additive improves the durability and performance of the cathode substrate by providing excellent mass activity retention.

[0102] Benefits of the disclosed additive include a lower less of the catalyst electrochemical surface area, which results in improved mass activity, and cell voltage performance throughout the life.

[0103] The disclosed Figure 1 Fuel cell system 10 can be used for a wide variety of applications. Figure 1 Fuel cell system 10 can be employed in a power system for producing an output torque on an output shaft. Figure 5 An exemplary vehicle 300 is schematically illustrated equipped with Figure 1 Fuel cell system 10. Vehicle 300 is illustrated, which includes hydrogen storage tank 20, fuel cell system 10, power system 310, and output shaft 320. Hydrogen fuel is supplied from hydrogen storage tank 20 to fuel cell system 10. Fuel cell system 10 includes a cathode comprising a coating including an amorphous fluorocarbon polymer additive as disclosed herein. Fuel cell system 10 generates electrical energy that is supplied to power system 310. Power system 310 can include a battery or other energy storage device for storing electrical energy supplied by fuel cell system 10. Power system 310 utilizes the electrical energy to produce an output torque on output shaft 320, which can be used to power vehicle 300.

[0104] A cathode configured for use in a fuel cell system is provided. The cathode includes a cathode substrate. The cathode also includes a coating disposed on the cathode substrate and including a fluorocarbon polymer additive configured to sinter at a temperature below 200 °C.

[0105] The fluorocarbon polymer additive can be configured to sinter at a temperature below 150 °C.

[0106] The coating can also include a catalyst ink. The catalyst ink and the fluorocarbon polymer additive can be mixed together and then disposed on the cathode substrate.

[0107] The coating can include a first coating configured as a face layer. The cathode can also include a second coating including a catalyst ink. The second coating can be disposed between the cathode substrate and the first coating. That is, the second coating can be disposed between and in contact with the cathode substrate and the first coating.

[0108] The fluorocarbon polymer additive can be an amorphous polytetrafluoroethylene copolymer with a fluorinated cycloaliphatic monomer.

[0109] The amorphous polytetrafluoroethylene copolymer with a fluorinated cycloaliphatic monomer can be selected from the group including tetrafluoroethylene, 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3 dioxole, and 2,2-bistrifluoromethyl-4,5-difluoro-1,3 dioxole.

[0110] The fluorocarbon polymer additive can be a functionalized perfluoropolyether.

[0111] The functionalized perfluoropolyether is selected from the group including a triethoxysilane-terminated difunctional perfluoropolyether; a bisphosphate derivative based on a linear perfluoropolyether backbone; and an aqueous dispersion of an anionic polyurethane based on a perfluoropolyether backbone.

[0112] The fluorocarbon polymer additive can be a polyvinylidene fluoride semi-crystalline copolymer.

[0113] The polyvinylidene fluoride semi-crystalline copolymer can be selected from the group including vinylidene fluoride, polyvinylidene fluoride:hexafluoropropylene copolymer emulsion, and semi-crystalline polyvinylidene fluoride:tetrafluoroethylene copolymer.

[0114] According to one alternative embodiment, a fuel cell system is provided. The fuel cell system includes an anode, a cathode, and a fuel cell membrane disposed between the anode and the cathode. The cathode includes a cathode substrate and a coating disposed on the cathode substrate. The coating includes a fluorocarbon polymer additive configured to sinter at a temperature below 200 °C.

[0115] The fluorocarbon polymer additive can be configured to sinter at a temperature below 150 °C.

[0116] The coating can further include a catalyst ink. The catalyst ink and the fluorocarbon polymer additive can be mixed together and then disposed on the cathode substrate.

[0117] The coating can include a first coating configured as a face layer. The cathode can further include a second coating including a catalyst ink. The second coating can be disposed between the cathode substrate and the first coating.

[0118] The fluorocarbon polymer additive can be an amorphous polytetrafluoroethylene copolymer with a fluorinated cycloaliphatic monomer.

[0119] The fluorocarbon polymer additive can be a functionalized perfluoropolyether.

[0120] The fluorocarbon polymer additive can be a polyvinylidene fluoride semi-crystalline copolymer.

[0121] According to one alternative embodiment, a vehicle is provided. The vehicle includes a powertrain and a fuel cell system configured to provide electrical power to the powertrain. The fuel cell system includes an anode, a cathode, and a fuel cell membrane disposed between the anode and the cathode. The cathode includes a cathode substrate and a coating disposed on the cathode substrate. The coating includes a fluorocarbon polymer additive configured for sintering at a temperature below 200 °C.

[0122] The coating can further include a catalyst ink. The catalyst ink and the fluorocarbon polymer additive can be mixed together and then disposed on the cathode substrate.

[0123] The coating can include a first coating configured as a face layer. The cathode can further include a second coating including a catalyst ink. The second coating can be disposed between the cathode substrate and the first coating.

[0124] While the best mode for carrying out the disclosure has been described in detail, those familiar with the art to which this disclosure relates will recognize various alternative designs and embodiments in which the disclosure can be practiced within the scope of the appended claims.

Claims

1. A cathode configured for use in a fuel cell system, the cathode comprising: Cathode substrate; and A coating is disposed on the cathode substrate and includes a fluoropolymer additive configured for sintering at a temperature below 200°C. The coating includes a first coating configured as a top layer; The cathode further includes a second coating comprising catalyst ink; and The second coating is disposed between the cathode substrate and the first coating.

2. The cathode according to claim 1, wherein the fluoropolymer additive is configured for sintering at a temperature below 150°C.

3. The cathode according to claim 1, wherein the coating further comprises catalyst ink; and The catalyst ink and the fluoropolymer additive are mixed together and then disposed on the cathode substrate.

4. The cathode according to claim 1, wherein the fluoropolymer additive is an amorphous polytetrafluoroethylene copolymer with a fluorinated alicyclic monomer.

5. The cathode according to claim 4, wherein the amorphous polytetrafluoroethylene copolymer with the fluorinated alicyclic monomer is selected from the group consisting of tetrafluoroethylene, 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxacyclopentene and 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxacyclopentene.

6. The cathode according to claim 1, wherein the fluoropolymer additive is a functionalized perfluoropolyether.

7. The cathode according to claim 6, wherein the functionalized perfluoropolyether is selected from the group consisting of: triethoxysilane-terminated bifunctional perfluoropolyethers; diphosphate derivatives based on linear perfluoropolyether backbones; and aqueous dispersions of anionic polyurethanes based on perfluoropolyether backbones.

8. The cathode according to claim 1, wherein the fluoropolymer additive is a polyvinylidene fluoride semi-crystalline copolymer.

9. The cathode according to claim 8, wherein the polyvinylidene fluoride semi-crystalline copolymer is selected from the group consisting of: vinylidene fluoride, polyvinylidene fluoride:hexafluoropropylene copolymer latex and semi-crystalline polyvinylidene fluoride:tetrafluoroethylene copolymer.

10. A fuel cell system comprising: anode; A cathode, comprising: a cathode substrate; and a coating disposed on the cathode substrate and including a fluoropolymer additive configured for sintering at a temperature below 200°C; and A fuel cell membrane disposed between the anode and the cathode; The coating includes a first coating configured as a top layer; The cathode further includes a second coating containing catalyst ink; and the second coating is disposed between the cathode substrate and the first coating.

11. The fuel cell system of claim 10, wherein the fluoropolymer additive is configured for sintering at a temperature below 150°C.

12. The fuel cell system of claim 10, wherein the coating further comprises catalyst ink; and wherein the catalyst ink and the fluoropolymer additive are mixed together and then disposed on the cathode substrate.

13. The fuel cell system according to claim 10, wherein the fluoropolymer additive is an amorphous polytetrafluoroethylene copolymer with a fluorinated alicyclic monomer.

14. The fuel cell system according to claim 10, wherein the fluoropolymer additive is a functionalized perfluoropolyether.

15. The fuel cell system according to claim 10, wherein the fluoropolymer additive is a polyvinylidene fluoride semi-crystalline copolymer.

16. A vehicle comprising: Power system; and A fuel cell system configured to provide electrical energy to the power system, the fuel cell system comprising: anode; A cathode, comprising: a cathode substrate; and a coating disposed on the cathode substrate and including a fluoropolymer additive configured for sintering at a temperature below 200°C; and A fuel cell membrane disposed between the anode and the cathode; The coating includes a first coating configured as a top layer; The cathode further includes a second coating containing catalyst ink; and the second coating is disposed between the cathode substrate and the first coating.

17. The vehicle of claim 16, wherein the coating further comprises catalyst ink; and The catalyst ink and the fluoropolymer additive are mixed together and then disposed on the cathode substrate.

Images