Proton exchange membrane for energy conversion device

Abstract

A proton exchange membrane for an energy conversion device, a hydrogen fuel cell stack for a vehicle, and a method of forming a proton exchange membrane are provided. The proton exchange membrane includes a first layer of a perfluorosulfonic acid ionomer. In addition, the perfluorosulfonic acid ionomer includes a first methoxynonafluorobutane coated additive. The hydrogen fuel cell stack includes one or more membrane electrode assemblies, each membrane electrode assembly including a proton exchange membrane.

Description

Technical Field

[0001] This disclosure relates to the field of energy conversion, and in particular to a proton exchange membrane for use in energy conversion devices. Background Technology

[0002] Various electrochemical energy conversion devices, such as hydrogen fuel cells for transportation applications and water electrolyzers for hydrogen production, rely on the use of proton exchange membranes (PEM). In a fuel cell, the PEM is positioned between the negative and positive electrodes and functions as a proton-conducting medium, an electrical insulator, and a barrier to gas cross-contamination between the negative and positive electrodes. Fuel, such as hydrogen, is provided at the negative electrode, and an oxidant, such as oxygen from the atmosphere, is provided at the positive electrode. A catalyst at the negative electrode oxidizes the fuel, producing protons and electrons. The membrane allows protons to pass through but prevents electrons and reactants (fuel and oxidant) from passing through. Electrons are transferred from the negative electrode to the positive electrode via an external circuit that generates direct current (DC), which can be used by, for example, an electric motor. Another catalyst at the positive electrode promotes the recombination of protons, electrons, and oxygen to form water. Therefore, a hydrogen fuel cell produces direct current and water as a byproduct.

[0003] As mentioned above, the primary function of the proton exchange membrane (PEM) in a fuel cell is to transport or conduct protons from the negative electrode to the positive electrode. Proton conductivity is measured in Siemens per centimeter (SiM / cm). PEMs are typically composed of ionomers such as perfluorosulfonic acid (PFSA). PFSA-based PEMs exhibit a limited but increasing proton conductivity in the temperature range from near room temperature to approximately 110°C. Although PFSA has a relatively high proton conductivity compared to other ionomers within this temperature window, any further improvement in its conductivity would benefit fuel cell and electrolyzer systems. Increasing the proton conductivity of PFSA-based PEMs reduces resistance and improves the efficiency of the electrochemical energy conversion system.

[0004] In addition, proton exchange membranes (PEMs) contain additives to improve their chemical and mechanical durability and enhance their proton conductivity. One such additive is a composite catalyst, such as platinum, used to address the issue of hydrogen-oxygen cross-contamination, thereby reducing the amount of active hydrogen and oxygen in the electrode. Hydrogen cross-contamination occurs when hydrogen (H2) permeates the PEM and reacts with oxygen on the positive electrode side. A certain amount of hydrogen cross-contamination is unavoidable. PEMs become more susceptible to hydrogen cross-contamination as they degrade due to chemical and mechanical degradation. Hydrogen cross-contamination can degrade the performance of PEMs. Silica is another additive used to enhance PEM performance and is believed to improve the membrane's water retention, thermal stability, mechanical strength, and water retention capacity. Additives based on cerium and manganese salts are used to improve the membrane's chemical durability. Other additives include graphene and carbon nanotubes; graphene can improve selectivity and mitigate reactant cross-contamination.

[0005] Similar to fuel cells, polymer electrolyte membrane (PEM) water electrolyzers also utilize proton exchange membranes. The working principle of a PEM water electrolyzer is the reverse of that of a fuel cell, breaking down molecules such as water into hydrogen and oxygen. Water is fed to the anode of the electrolyzer and then oxidized to form oxygen and protons. The protons pass through the membrane and are reduced at the cathode to form hydrogen. The proton exchange membrane acts as an electrical insulator while allowing protons to pass through and minimizing gas cross-linking between the anode and cathode. The hydrogen can then be used in fuel cells or welding applications. Other applications using proton exchange membranes include direct formic acid fuel cells, direct methanol fuel cells, indirect or reformed methanol fuel cells, and direct ethanol fuel cells, which can be used in a variety of applications, including portable fuel cells, stationary fuel cells, and fuel cells for transportation applications. Further applications of proton exchange membranes include chlor-alkali electrochemical cells for the production of chlorine and caustic soda.

[0006] However, challenges remain. Similarly, increased proton conductivity and improved conductivity will enhance fuel cell efficiency. Additionally, it has been found that fillers introduce voids and alter the weight and density of the polymer system. This may reduce fatigue resistance and increase the membrane's sensitivity to water permeation. This could further negatively impact mechanical stability.

[0007] Therefore, there is still room for improvement in proton exchange membranes, including improvements in proton conductivity. Thus, while existing proton exchange membranes, particularly perfluorosulfonic acid proton exchange membranes, have achieved their intended purpose, new and improved proton exchange membranes are still needed. Summary of the Invention

[0008] According to various aspects, this disclosure relates to a proton exchange membrane for use in energy conversion devices. The proton exchange membrane comprises a first layer of perfluorosulfonic acid ionomer. Additionally, the perfluorosulfonic acid ionomer comprises an additive coated with a first methoxynonafluorobutane.

[0009] In the above embodiments, the first methoxynonfluorobutane-coated additive comprises a composite catalyst. In other embodiments, the first methoxynonfluorobutane-coated additive comprises carbon-supported platinum, and the weight ratio of the perfluorosulfonic acid ionomer to the first methoxynonfluorobutane-coated additive is in the range of 1:10 to 1:2000. Alternatively or additionally, the first methoxynonfluorobutane-coated additive comprises inert particles. Alternatively or additionally, the first methoxynonfluorobutane-coated additive comprises at least one additive selected from the group consisting of silica, carbon black, graphene, and carbon nanotubes.

[0010] In any of the above embodiments, the proton exchange membrane further includes an expanded polytetrafluoroethylene (ePTFE) membrane comprising a first side and a second side. A first layer of perfluorosulfonic acid ionomer contacts the first side of the ePTFE membrane. In other embodiments, the proton exchange membrane further includes a second layer of perfluorosulfonic acid ionomer contacting the second side of the ePTFE membrane. The second layer of perfluorosulfonic acid ionomer comprises a second methoxynonafluorobutane-coated additive and contacts the second side of the ePTFE membrane. In still other embodiments, the first methoxynonafluorobutane-coated additive and the second methoxynonafluorobutane-coated additive are the same. In additional embodiments, a first thickness of the first layer of perfluorosulfonic acid ionomer is in the range of 4 micrometers to 28 micrometers, and a second thickness of the second layer of perfluorosulfonic acid ionomer is in the range of 2 micrometers to 28 micrometers. In other additional embodiments, a third thickness of the ePTFE membrane is in the range of 1 micrometer to 10 micrometers.

[0011] In the above embodiment, the proton exchange membrane further includes an expanded polytetrafluoroethylene (ePTFE) membrane comprising a first side and a second side. The thickness of the ePTFE membrane is in the range of 1 micrometer to 10 micrometers. The thickness of the first layer of perfluorosulfonic acid ionomer is in the range of 4 micrometers to 15 micrometers, and this first layer contacts the first side of the ePTFE membrane. Additionally, the proton exchange membrane includes a second layer of perfluorosulfonic acid ionomer comprising a second methoxynonafluorobutane-coated additive dispersed in the second layer of the perfluorosulfonic acid ionomer. The thickness of the second layer of the perfluorosulfonic acid ionomer is in the range of 2 micrometers to 6 micrometers, and this second layer contacts the second side of the ePTFE membrane. The first and second methoxynonfluorobutane-coated additives include carbon-supported platinum, the weight ratio of the first layer of perfluorosulfonic acid ionomer to the first methoxynonfluorobutane-coated additive is in the range of 1:10 to 1:2000, and the weight ratio of the second layer of perfluorosulfonic acid ionomer to the second methoxynonfluorobutane-coated additive is in the range of 1:10 to 1:2000.

[0012] Depending on the aspects, this disclosure also relates to hydrogen fuel cell stacks for vehicles. The hydrogen fuel cell stack includes one or more membrane electrode assemblies. Each membrane electrode assembly includes a proton exchange membrane, a negative electrode, and a positive electrode. The negative electrode includes a first gas diffusion layer and a first catalyst disposed on the first gas diffusion layer, the first gas diffusion layer being in contact with a first surface of the proton exchange membrane. The positive electrode includes a second gas diffusion layer and a second catalyst disposed on the second gas diffusion layer, the second gas diffusion layer being in contact with a second surface of the proton exchange membrane. The proton exchange membrane includes a first layer of perfluorosulfonic acid ionomer, and the perfluorosulfonic acid ionomer includes a first methoxynonfluorobutane-coated additive, the additive being present in a weight ratio of perfluorosulfonic acid ionomer to the first methoxynonfluorobutane-coated additive in the range of 1:10 to 1:2000.

[0013] In the above embodiments, the first methoxynonfluorobutane coating additive is a carbon-supported platinum. Alternatively or additionally, the first methoxynonfluorobutane coating additive is an inert particle. Alternatively or additionally, the first methoxynonfluorobutane coating additive includes at least one additive selected from the group consisting of silica, carbon black, graphene, and carbon nanotubes.

[0014] In any of the above embodiments, the proton exchange membrane comprises an expanded polytetrafluoroethylene (ePTFE) membrane including a first side and a second side. A first layer of perfluorosulfonic acid ionomer contacts the first side of the ePTFE membrane. In other embodiments, the proton exchange membrane comprises a second layer of perfluorosulfonic acid ionomer in contact with the second side of the ePTFE membrane. The perfluorosulfonic acid ionomer comprises an additive coated with second methoxynonafluorobutane. In other embodiments, a first thickness of the first layer of perfluorosulfonic acid ionomer is in the range of 4 micrometers to 15 micrometers, a second thickness of the ePTFE membrane is in the range of 2 micrometers to 10 micrometers, and a third thickness of the second layer of perfluorosulfonic acid ionomer is in the range of 2 micrometers to 15 micrometers, wherein the first thickness is greater than the third thickness.

[0015] In any of the above embodiments, the hydrogen fuel cell stack further includes a sealing gasket located on either side of each membrane electrode assembly; a bipolar flow field plate located on either side of the membrane electrode assembly, wherein each sealing gasket is located between the membrane electrode assembly and a bipolar flow field plate; and a current collector plate located outside the membrane electrode assembly and adjacent to each bipolar flow field plate.

[0016] According to various aspects, this disclosure relates to a method for forming a proton exchange membrane. The method includes dispersing an additive in methoxynonfluorobutane and coating the additive with methoxynonfluorobutane. The method further includes separating the coated additive from excess methoxynonfluorobutane and drying the coated additive. The method also includes mixing the coated additive and a perfluorosulfonic acid ionomer solution in a solution of alcohol and water to form an ionomer dispersion, forming the ionomer dispersion into a proton exchange membrane, and drying the proton exchange membrane. Additionally, the method includes verifying the proton conductivity of the dried coated membrane using four-probe electrochemical impedance spectroscopy at one or more relative humidities in the range of 40% to 100%.

[0017] In any of the above embodiments, the dispersing additive comprises a dispersing composite catalyst. In other embodiments, the dispersing inert support particles comprise a dispersing platinum-supported carbon catalyst. Additionally or alternatively, the dispersing additive comprises dispersing inert particles, wherein the amount of the coated additive added is such that the weight ratio of the perfluorosulfonic acid ionomer to the first methoxynonafluorobutane-coated additive is in the range of 1:10 to 1:2000. Additionally or alternatively, the dispersing additive comprises at least one of dispersing silica, carbon black, graphene, and carbon nanotubes.

[0018] In any of the above embodiments, dispersing the additive in methoxynonfluorobutane includes a period of 1 hour to 48 hours by wet milling. In other embodiments, the method includes separating the coated additive with a vacuum filter and drying the coated additive at a temperature of 50°C to 150°C for 5 minutes to 60 minutes.

[0019] In any of the above embodiments, dispersing the additive in methoxynonfluorobutane includes dispersing the additive in an alcoholic solution of methoxynonfluorobutane.

[0020] In any of the above embodiments, the alcohol and water solution comprises an alcohol present in the range of 30% to 50% by volume and water present in the range of 50% to 70% by volume.

[0021] In the above embodiments, forming a proton exchange membrane from an ionomer dispersion further includes coating a first side of an expanded polytetrafluoroethylene (ePTFE) membrane with the ionomer dispersion. In other embodiments, the method includes coating a second side of the ePTFE membrane and drying the coated ePTFE membrane. Attached Figure Description

[0022] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of this disclosure in any way.

[0023] Figure 1 An embodiment of a vehicle including a fuel cell according to an embodiment of the present disclosure is shown;

[0024] Figure 2 A fuel cell stack according to an embodiment of this disclosure is shown;

[0025] Figure 3 A proton exchange membrane according to an embodiment of this disclosure is shown;

[0026] Figure 4 A method for forming a proton exchange membrane according to an embodiment of the present disclosure is shown;

[0027] Figure 5 The proton conductivity (measured in millisiemens per centimeter on the vertical y-axis) is shown as measured over a relative humidity percentage range (shown on the horizontal x-axis). Detailed Implementation

[0028] The following description is merely exemplary in nature and is not intended to limit this disclosure, its application, or its uses. Furthermore, it is not intended to be bound by any express or implied theory presented in the foregoing background, summary of the invention, or the following detailed description. It should be understood that throughout the drawings, corresponding reference numerals denote similar or corresponding parts and features.

[0029] Reference will now be made in detail to several embodiments of this disclosure illustrated in the accompanying drawings. Wherever possible, the same or similar reference numerals are used in the drawings and description to refer to the same or similar parts or steps. The drawings are simplified and not drawn to scale.

[0030] This disclosure relates to a methoxynonfluorobutane coating on an additive for a perfluorosulfonic acid proton exchange membrane, and to a perfluorosulfonic acid proton exchange membrane comprising an additive coated with methoxynonfluorobutane. This disclosure also relates to energy conversion devices, particularly fuel cells and electrolyzers, comprising a perfluorosulfonic acid proton exchange membrane including an additive coated with methoxynonfluorobutane. This disclosure further relates to a method of forming a perfluorosulfonic acid proton exchange membrane comprising an additive coated with methoxynonfluorobutane. The aforementioned proton exchange membranes are incorporated into energy conversion devices (e.g., hydrogen fuel cells used in vehicles).

[0031] As used herein, the term "vehicle" is not limited to automobiles. While this document primarily describes the technology in the context of hydrogen fuel cell vehicles, the technology is not limited to hydrogen fuel cell vehicles. These concepts can be used in fuel cells for a wide range of applications, such as those related to components used in motorcycles, mopeds, locomotives, aircraft, ships, and other vehicles, as well as generators and other power solutions. Furthermore, the proton exchange membrane described herein can be used in other electrochemical conversion devices, including electrolyzers, direct formic acid fuel cells, direct methanol fuel cells, indirect or reformed methanol fuel cells, and direct ethanol fuel cells, chlor-alkali batteries, and other related electrochemical devices that require solid proton-conducting membrane materials.

[0032] Figure 1 A vehicle 100 is shown, including a propulsion system 102 powered by a fuel cell. As further described herein, the propulsion system 102 typically includes one or more hydrogen fuel cell stacks 104 that power a power module 106. The power module 106 then powers an electric motor 108, which is connected to a transmission (drive unit) 110 and a drivetrain 112 that transmits mechanical power and rotation to the vehicle's wheels 114. The power module 106 includes a controller 116 programmed to control and manage the operation of the electric motor 108 and associated hardware. The controller 116 includes one or more processors and tangible non-transitory memory 126. The power module 106 also includes a DC / DC converter 118 that regulates the current from the fuel cell stack 104. Additionally, a traction battery 120 is provided to store the electricity generated by the fuel cell stack 104, and a DC / DC converter 122 is provided in the power module 106 to regulate the charging and discharging of the traction battery 120. Furthermore, a 12V DC / DC converter 124 can be provided to power additional electrical systems (such as infotainment systems) associated with the vehicle 100.

[0033] Hydrogen H2 (fuel) is stored under pressure in tank 130 and supplied to fuel cell stack 104 via supply line 136. Pressure regulator 132 and metering valve 134 are integrated in the supply line and used to regulate the pressure and quantity of hydrogen supplied to fuel cell stack 104. Excess hydrogen H2 not consumed by fuel cell stack 104 is recovered via recovery line 140 and transported by recirculation fan 142. Contaminant gases and excess water are removed via drain line 144 through valve 146, which is periodically or otherwise actuated.

[0034] Oxygen is supplied from ambient air A, which is introduced through air intake line 150 and compressed by air compressor 152 in air intake line 150 before being introduced under pressure into fuel cell stack 104. The pressure in fuel cell stack 104 is regulated downstream of fuel cell stack 104 in exhaust line 154 by dynamic pressure control valve 156. A water management system 158 may also be provided to supply moisture, which may be derived from exhaust gas passing through exhaust line 154 or introduced by injecting condensate into recirculation line 160. The humid air wets the proton exchange membrane to maintain the required relative humidity level. Additionally, a coolant system 166 may be provided for fuel cell stack 104. The coolant system may include one or more radiators, one or more fans, and one or more coolant pumps that guide non-conductive coolant through fuel cell stack 104.

[0035] Turn now Figure 2 , Figure 2 A hydrogen fuel cell stack 104 including a membrane electrode assembly 202 is shown. The membrane electrode assembly 202 typically includes a proton exchange membrane 204 and two electrodes, a negative electrode 206 and a positive electrode 208, disposed on either side 210, 212 of the proton exchange membrane 204. It should be understood that although only one membrane electrode assembly 202 is shown, multiple membrane electrode assemblies 202 may exist in a single fuel cell stack 104. Sealing gaskets 224, 226 are disposed on or around either side 220, 222 of the membrane electrode assembly 202, forming a seal between the membrane electrode assembly 202 and bipolar flow field plates 228, 230, which supply fuel (e.g., hydrogen, carbon dioxide, carbon monoxide, and methanol) to the negative electrode 206 and an oxidant, such as oxygen, to the positive electrode 208. Current collectors 238 and 240 are disposed outside the sealing gaskets 224 and 226 and the membrane electrode assembly 202, adjacent to the bipolar flow field plates 228 and 230. Additionally, end plates 244 and 246 are disposed outside the current collectors 238 and 240, which are used to hold the components of the fuel cell stack 104 together.

[0036] Now for reference Figure 3This illustrates an embodiment of a proton exchange membrane 204. The proton exchange membrane 204 transports ions (e.g., hydrogen protons H+) from the negative electrode to the positive electrode through the membrane. + This membrane blocks electrons or reactant molecules (e.g., hydrogen (H2) and oxygen (O2) from passing through. In one embodiment, the proton exchange membrane 204 is formed of an ionomer 302 comprising an additive 330 coated with methoxynonfluorobutane dispersed throughout the ionomer 302. In other embodiments, an expanded polytetrafluoroethylene membrane 312 is used to support the ionomer 302.

[0037] Ionomer 302 is understood to be a copolymer containing both ionic and nonionic repeating units. In embodiments, the ionomer comprises a perfluorosulfonic acid ionomer, such as NAFION from DuPont or AQUIVION from Synesqo in Brussels, Belgium. In a particular embodiment, the perfluorosulfonic acid ionomer comprises perfluorovinyl ether groups terminated with sulfonate esters dangling from the tetrafluoroethylene backbone. In other embodiments, the ionomer has the chemical formula C7HF. 13 O5SC2F4.

[0038] The methoxynonfluorobutane-coated additive 330 is dispersed in the ionomer 302. In an embodiment, the methoxynonfluorobutane-coated additive 330 is present in a weight ratio of perfluorosulfonic acid ionomer to the coated additive in the range of 1:10 to 1:2000 (inclusive), and preferably in the range of 1:100 to 1:300. Additionally or alternatively, the methoxynonfluorobutane-coated additive is present with an areal density in the range of 5 μg / cm² to 1000 μg / cm² (inclusive, and preferably 5 μg / cm² to 200 μg / cm², more preferably 5 μg / cm² to 100 μg / cm²).

[0039] In one embodiment, the coated additive 304 comprises a composite catalyst, such as carbon-supported platinum, platinum-transition metal alloys (e.g., platinum-cobalt), platinum, platinum-ruthenium, ruthenium oxide, palladium, and combinations thereof. In other embodiments, the composite catalyst is carbon-supported platinum. In additional or alternative embodiments, additive 304 comprises at least one of silica, carbon black, graphene, and carbon nanotubes. In other additional or alternative embodiments, additive 304 comprises inert particles, i.e., particles that do not chemically react with the components forming the proton exchange membrane 204 or with ions passing through the membrane. However, inert particles can improve the mechanical properties of the proton exchange membrane 204. Inert particles include, but are not limited to, carbon black, talc, barium sulfate, calcium carbonate, glass fiber, glass beads, α-alumina, alumina, silica, titanium dioxide, and zirconium oxide. In one embodiment, the particle size of additive 304 is from 20 nanometers to 1 micrometer, including all values ​​and increments thereof. In other embodiments, the specific surface area of ​​additive 304 is in the range of 10 m². 2 / g to 1000m 2 The range is within / g, including all values ​​and ranges therein. Particle size can be measured using a microscope, and surface area can be measured using Brunauer, Emmett, and Teller theories.

[0040] Next, additive 304 is treated with methoxynonfluorobutane to produce a methoxynonfluorobutane coating 306 on additive surface 308. Coating 306 covers at least a portion of additive surface 308, and in other embodiments, coating 306 covers the entire additive surface 308. Therefore, it should be understood that in some embodiments, the entire additive surface 308 is not covered by coating 306. Additionally, in some embodiments, the methoxynonfluorobutane forms coating 306 at a weight percentage (inclusive of all values ​​and ranges) relative to the weight load of the additive. In other embodiments, the methoxynonfluorobutane coating 306 is present in an amount of 1% to 2% by weight of the total weight of methoxynonfluorobutane and the additive. A non-limiting example of methoxynonfluorobutane is NOVEC 7100 engineering fluid, available from 3M.

[0041] In one embodiment, a perfluorosulfonic acid ionomer 302 comprising an additive 330 coated with methoxynonfluorobutane is formed as a layer with a thickness ranging from 1 micrometer to 20 micrometers (inclusive) to provide a proton exchange membrane 204.

[0042] In other embodiments, the perfluorosulfonic acid ionomer 302, including the methoxynonfluorobutane-coated additive 330, is reinforced or supported by an expanded polytetrafluoroethylene (ePTFE) membrane 312. The ePTFE membrane 312 includes a plurality of micropores 310 dispersed throughout its entire volume (including at surfaces 314, 316). The perfluorosulfonic acid ionomer 302 permeates at least a portion of the micropores 310 at surfaces 314, 316, and in some embodiments, the perfluorosulfonic acid ionomer 302 permeates the entire thickness 318 of the ePTFE membrane 312. In embodiments, the thickness of the ePTFE membrane 312 is in the range of 1 micrometer to 10 micrometers, including all values ​​and ranges therein. The ePTFE membrane 312 may be extruded or electrospun.

[0043] In one embodiment, a first layer 322 of perfluorosulfonic acid ionomer 302, comprising a first methoxynonfluorobutane-coated additive 330, is applied to a first surface 314 of an expanded polytetrafluoroethylene film 312. The thickness 324 of the first layer 322 of perfluorosulfonic acid ionomer 302 is in the range of 4 micrometers to 28 micrometers, including all values ​​and ranges therein. In another embodiment, a second layer 326 of perfluorosulfonic acid ionomer 302, comprising a second methoxynonfluorobutane-coated additive 330, is applied to a second surface 316 of the expanded polytetrafluoroethylene film 312. The first and second methoxynonfluorobutane-coated additives 330 each comprise an additive 304 selected individually from the additives described above. In one embodiment, the additive 304 of the first and second methoxynonfluorobutane-coated additives 330 is the same. The thickness 328 of the second layer 326 of perfluorosulfonic acid ionomer 302 is in the range of 2 micrometers to 28 micrometers, including all values ​​and ranges therein. In some further embodiments, the thickness of the first layer of the perfluorosulfonic acid ionomer is greater than the thickness of the second layer of the perfluorosulfonic acid ionomer. The total thickness of the proton exchange membrane 204 is in the range of 6 micrometers to 30 micrometers, including all values ​​and ranges therein. Further, the weight ratio of the first layer of the perfluorosulfonic acid ionomer to the first methoxynonafluorobutane coating additive is in the range of 1:10 to 1:2000, and the weight ratio of the second layer of the perfluorosulfonic acid ionomer to the second methoxynonafluorobutane coating additive is in the range of 1:10 to 1:2000.

[0044] Return to reference Figure 2The negative electrode 206 includes a porous gas diffusion layer 248 to allow hydrogen fuel gas to flow through. The gas diffusion layer material includes, but is not limited to, one or more of the following: carbon paper, carbon cloth, woven carbon fabric, nonwoven carbon fabric, graphite sheet, titanium mesh, and titanium felt. Further, in an embodiment, the gas diffusion layer 248 may be impregnated with polytetrafluoroethylene or other fluoropolymers to modify the hydrophobicity of the gas diffusion layer 248. In an embodiment, the thickness of the gas diffusion layer 248 is in the range of 50 micrometers to 300 micrometers, including all values ​​and ranges therein. A negative electrode electrocatalyst 250 is disposed on the gas diffusion layer 248 and, in an embodiment, is impregnated within the gas diffusion layer 248. The negative electrode electrocatalyst 250 includes one or more catalysts selected from platinum, platinum-transition metal alloys (e.g., platinum-ruthenium and platinum-cobalt), platinum supported on carbon black (Pt / C), iridium black, and iridium oxide. The particle size (maximum cross-sectional length) of the negative electrode electrocatalyst 250 is in the range of 5 nanometers to 50 nanometers, including all values ​​and ranges therein. In the embodiment, the negative electrode electrocatalyst 250 is present with an areal density ranging from 0.05 mg to 0.5 mg platinum per square centimeter, including all values ​​and ranges therein. The negative electrode electrocatalyst 250 contacts the first side 210 of the proton exchange membrane 204.

[0045] The positive electrode 208 also includes a porous gas diffusion layer 252 to allow oxygen to flow through it. The gas diffusion layer 252 includes, but is not limited to, one or more of the following: carbon paper, carbon cloth, woven carbon fabric, nonwoven carbon fabric, graphite sheet, titanium mesh, and titanium felt. Further, in an embodiment, the gas diffusion layer 252 may be impregnated with polytetrafluoroethylene or other fluoropolymers to modify the hydrophobicity of the support material 348. The thickness of the gas diffusion layer 252 is in the range of 50 micrometers to 300 micrometers, including all values ​​and ranges therein. A positive electrode electrocatalyst 254 is disposed on the gas diffusion layer 252, and in an embodiment, is impregnated within the gas diffusion layer 252. The positive electrode electrocatalyst 254 includes one or more catalysts selected from platinum, platinum-transition metal alloys (e.g., platinum-ruthenium and platinum-cobalt), platinum supported on carbon black (Pt / C), iridium black, and iridium oxide. The particle size (maximum cross-sectional length) of the positive electrode electrocatalyst 254 is in the range of 2 nanometers to 50 nanometers, including all values ​​and ranges therein. In this embodiment, the positive electrode catalyst 254 is present at an areal density in the range of 0.05 mg to 0.5 mg platinum per square centimeter (inclusive). The positive electrode catalyst 254 contacts a second side 212 of the proton exchange membrane 204, which is opposite to a first side 210 of the proton exchange membrane 204.

[0046] Sealing gaskets 224 and 226 are formed of an elastomeric material, and in embodiments include one or more of the following materials: natural rubber, styrene-butadiene rubber, cis-butadiene rubber, polyurethane, and thermoplastic elastomers. As described above, sealing gaskets 224 and 226 are disposed around each membrane electrode assembly 202 or between either side of the membrane electrode assembly 202 and bipolar flow field plates 228 and 230, wherein one of the bipolar flow field plates 228 and 230 is located on either side of the membrane electrode assembly 202. Each bipolar flow field plate 228 and 230 includes a plurality of channels or grooves defined therein, which form a flow field to supply fuel or oxidant in a relatively uniform manner on the surface of adjacent electrodes (negative electrode 206 or positive electrode 208). In embodiments, bipolar flow field plates 228 and 230 are conductive. For each additional membrane electrode assembly provided, an additional bipolar flow field plate (and sealing gasket) is provided. In such embodiments, bipolar flow field plates 228 and 230 are arranged alternately with the membrane electrode assembly 202. Therefore, it should be understood that, in the implementation, a single bipolar flow field plate 228, 230 can provide a flow field for a separate membrane electrode assembly 202 on each side 232, 234 of the bipolar flow field plate 228, 230.

[0047] In one embodiment, current collectors 238 and 240 are disposed on either side of bipolar flow field plates 228 and 230, sandwiching the bipolar flow field plates 228 and 230 and the membrane electrode assembly 202. Current collectors 238 and 240 are connected to circuit 242, which connects the fuel cell stack 104 to a load, such as power module 106 or traction battery 120. Current collectors 238 and 240 may be formed of at least one of gold, nickel, aluminum, graphite, or other conductive materials. In another embodiment, bipolar flow field plates 228 and 230 also provide current collectors 238 and 240, and separate current collectors 238 and 240 are not required. The membrane electrode assembly 202, gaskets 224 and 226, bipolar flow field plates 228 and 230, and current collectors 238 and 240 are sandwiched between end plates 244 and 246, which are placed adjacent to current collector 238 and outside current collectors 238 and 240.

[0048] Figure 4An embodiment of the method 400 for forming the proton exchange membrane 204 described herein is shown. At block 402, an additive 304 for the proton exchange membrane 204 is dispersed in methoxy-nonfluorobutane. The additive 304 is added to the methoxy-nonfluorobutane at a concentration ranging from 1 gram to 20 grams per 100 mL of methoxy-nonfluorobutane. In other embodiments, the methoxy-nonfluorobutane is combined with an alcohol (e.g., isopropanol, n-butanol, n-propanol, ethanol, and methanol) in a molar mass ranging from 32 g / mol to 75 g / mol. When the alcoholic solution of methoxy-nonfluorobutane is provided, the methoxy-nonfluorobutane is present in the alcohol at a concentration ranging from 1% to 60% (inclusive of all values ​​and increments). The alcohol constitutes the remainder of the solution. The additive 304 is provided in the alcoholic solution of methoxy-nonfluorobutane at a concentration ranging from 1 gram to 20 grams per 100 mL of methoxy-nonfluorobutane and alcohol. In an embodiment, wet milling is used to disperse the additive 304. Wet milling includes at least one of the following processes: ball milling, roller milling, bead milling, and high-shear mixing. In one embodiment, wet milling is performed using a ball mill with, for example, 5 mm zirconium beads or other abrasive media. In alternative or additional embodiments, additive 304 is dispersed with methoxynonfluorobutane using a mixer, with or without alcohol. The additive is dispersed in alcohol-free methoxynonfluorobutane for a period ranging from 1 hour to 72 hours (inclusive of all values ​​and ranges, such as 24 hours). During dispersion, additive 304 is coated with methoxynonfluorobutane. In embodiments, the dispersion facilitates the depolymerization of individual particles of the additive, thereby increasing the availability of methoxynonfluorobutane on the additive surface.

[0049] At box 404, excess methoxynonfluorobutane and alcohol (if present) are separated from the methoxynonfluorobutane-coated additive. In an embodiment, a filter is used to separate the coated additive 330, and in a particular embodiment, a vacuum filter is used. In an alternative embodiment, the coated additive 330 is separated by a centrifuge or by an inline filter. At box 406, the coated additive 330 is dried at a temperature ranging from 50°C to 100°C for a period of time ranging from 5 minutes to 30 minutes. In an embodiment, the coated additive 330 is dried in an oven, or alternatively in a vacuum dryer or a drum dryer.

[0050] At frame 408, an ionomer dispersion is formed by mixing an additive 330 coated with methoxynonfluorobutane and a perfluorosulfonic acid ionomer solution in a solution of alcohol and water. The perfluorosulfonic acid ionomer solution comprises perfluorosulfonic acid ionomer dispersed in a solvent. The perfluorosulfonic acid ionomer solution is present in the range of 1% to 25% by weight (inclusive) of the total weight of the perfluorosulfonic acid ionomer solution, and the solvent is present in the range of 75% to 99% by weight (inclusive) of the total weight of the perfluorosulfonic acid ionomer solution, wherein the total weight percentage is 100% by weight. The solvent comprises an alcohol, and in a preferred embodiment, the solvent comprises an alcohol and water. Water is present in the range of 35% to 65% by weight of the total weight of the solvent, and alcohol is present in the range of 35% to 65% by weight of the total weight of the solvent, wherein the total weight of the solvent is 100% by weight. Furthermore, alcohols include alcohols with a molar mass ranging from 32 g / mol to 75 g / mol, such as isopropanol, n-butanol, n-propanol, ethanol, and methanol.

[0051] In the embodiment, in the solution of alcohol and water, the alcohol is present in the range of 35% to 50% by weight of the total solution weight, and the water is present in the range of 50% to 65% by weight of the total solution weight. The total weight percentage of the solution is 100%. The alcohol may be isopropanol, n-butanol, n-propanol, ethanol, and methanol.

[0052] A perfluorosulfonic acid ionomer solution is added to the ionomer dispersion at a rate ranging from 5% to 20% by weight (inclusive of all values ​​and ranges) of the total weight of the ionomer dispersion. A coated additive is added to the ionomer dispersion at a rate ranging from 0.1% to 10% by weight (inclusive of all values ​​and ranges) of the total weight of the ionomer dispersion. A dispersion medium is added to the ionomer dispersion at a mass ratio ranging from 1% to 16% by weight (inclusive of all values ​​and ranges, where the total weight percentage is 100% by weight). In an embodiment, the ionomer dispersion is mixed by wet milling. In an embodiment, wet milling is used to disperse additive 304. Wet milling includes at least one of the following processes: ball milling, roller milling, medial milling, bead milling, and high-shear mixing. In one embodiment, wet milling is performed using a ball mill with, for example, 5 mm zirconium beads or other abrasive media. In an alternative embodiment, the ionomer dispersion is mixed in a mixer. Additionally, the time period for mixing the ionomer dispersion is within the range of 1 hour to 72 hours (inclusive of all values ​​and ranges).

[0053] In one embodiment, the ionomer dispersion is formed into a proton exchange membrane by casting or extruding the membrane into the desired shape, and then the ionomer dispersion is dried to provide the proton exchange membrane.

[0054] In other embodiments, the proton exchange membrane is formed by coating an ionomer dispersion onto a carrier (e.g., an expanded polytetrafluoroethylene membrane). At frame 410, the first side of the expanded polytetrafluoroethylene membrane is coated with an ionomer dispersion to form a first layer 322 comprising a perfluorosulfonic acid ionomer including a coated additive 330 dispersed therein. The ionomer dispersion is coated onto the expanded polytetrafluoroethylene membrane using one or more coating techniques, including but not limited to roll casting, spin coating, dip coating, slot die coating, and spray coating. As described above, after the coating dispersion dries, a sufficient amount of the ionomer dispersion is deposited on the expanded polytetrafluoroethylene membrane to form a layer with a thickness ranging from 4 micrometers to 15 micrometers (inclusive). Further, in an embodiment, the coated additive is present with an areal density in the range of 5 micrograms per square centimeter to 1000 micrograms per square centimeter (inclusive), and preferably 5 micrograms per square centimeter to 200 micrograms per square centimeter, more preferably 5 micrograms per square centimeter to 100 micrograms per square centimeter. At box 412, the coated film is dried at a temperature in the range of 60°C to 180°C (inclusive) for a period of 10 minutes to 60 minutes (inclusive). In an embodiment, the ionomer-coated film is dried in an oven.

[0055] Optionally, at frame 414, an ionomer dispersion is coated onto the second side of the expanded polytetrafluoroethylene (ePTFE) membrane to form a second layer 326 comprising a perfluorosulfonic acid ionomer including the coated additive 330 dispersed therein. The ionomer dispersion is coated onto the ePTFE membrane using one or more coating techniques, including but not limited to roll casting, spin coating, dip coating, slot die coating, and spray coating. As described above, a sufficient amount of the ionomer dispersion is deposited on the ePTFE membrane to form a layer with a thickness ranging from 2 micrometers to 14 micrometers (inclusive). Further, in embodiments, the coated additive is present with an areal density ranging from 5 micrograms / cm² to 1000 micrograms / cm² (inclusive), and preferably from 5 micrograms / cm² to 200 micrograms / cm², more preferably from 5 micrograms / cm² to 100 micrograms / cm². At frame 416, the second layer of the coated film is dried at a temperature ranging from 60°C to 180°C (inclusive) for a period of 10 to 60 minutes (inclusive). In an embodiment, the ionomer-coated film is dried in an oven.

[0056] Additionally, optionally, at box 418, the proton conductivity of the proton exchange membrane is verified. Proton conductivity can be measured at various relative humidities (e.g., within the range of 30% to 100% relative humidity, including all values ​​and ranges therein). Furthermore, proton conductivity can be measured at various temperatures (e.g., within the range of 10°C to 150°C). The method for testing in-plane and through-plane proton conductivity is performed by electrochemical impedance spectroscopy (EIS) using a four-probe or two-probe setup.

[0057] Figure 5 A comparative measurement of in-plane proton conductivity (mSv / cm, shown on the vertical y-axis) as a function of relative humidity (perfluorosulfonic acid ionomer proton exchange membranes including a methoxynonfluorobutane modified additive (in this case, a platinum catalyst (line A)) and a perfluorosulfonic acid ionomer proton exchange membrane with an unmodified platinum catalyst (line B) is shown using a four-probe EIS setup from BekkTech conductive cells. The membranes were measured over a range of 40% to 100% relative humidity. As shown, at 50% or greater relative humidity, the proton conductivity of the proton exchange membrane including the methoxynonfluorobutane modified additive is generally higher.

[0058] The proton exchange membrane, hydrogen fuel cell, and method described in this paper offer numerous advantages. These advantages include, for example, improved proton conductivity. They also include, for example, improvements in the coating of methoxynonfluorobutane-modified additives with ionomers and the dispersion of methoxynonfluorobutane-modified additives in ionomers, which are believed to improve proton conductivity. Unbound from any particular theory, it is also believed that perfluorosulfonic acid ionomers have enhanced affinity for fluorocarbon molecules on the surface of catalysts treated with methoxynonfluorobutane, orienting sulfonate ion clusters to improve conductivity.

[0059] As used herein, the term "power module" refers to an assembly containing several interconnected components for performing energy conversion and regulation functions. These components include, but are not limited to, controllers, transformers, rectifiers, inverters, converters, and other devices for regulating and distributing power.

[0060] As used herein, the term "controller" and related terms (e.g., microcontroller, control module, module, control, control unit, processor, and similar terms) refer to application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), electronic circuits, central processing units (e.g., microprocessors), and related non-transitory memory components in the form of memory and storage devices (read-only, programmable read-only, random access, hard disk drives, etc.). Controller 116 may also consist of multiple controllers electrically connected to each other. Controller 116 may interconnect with additional systems and / or controllers of vehicle 100, allowing controller 116 to access data such as the speed, acceleration, braking, and steering angle of vehicle 100.

[0061] The processor may be a custom or commercially available processor, a central processing unit (CPU), a graphics processing unit (GPU), an auxiliary processor among a plurality of processors associated with controller 116, a microprocessor based on semiconductor composite conductors (in the form of a microchip or chipset), a macroprocessor, a combination thereof, or a device typically used to execute instructions.

[0062] The tangible non-transitory memory 126 may include volatile and non-volatile storage devices such as read-only memory (ROM), random access memory (RAM), and keep-alive memory (KAM). KAM is a persistent or non-volatile memory that can be used to store various operational variables when the processor is powered off. The tangible non-transitory memory 126 may be implemented using many memory devices, such as programmable read-only memory (PROM), electrical PROM (EPROM), electrically erasable PROM (EEPROM), flash memory, or other electrical, magnetic, optical, or combined memory devices capable of storing data, some of which represents executable instructions used by the controller 116 to control various systems of the vehicle 100.

[0063] The descriptions in this disclosure are merely exemplary in nature, and changes that do not depart from the spirit and scope of this disclosure are intended to fall within its scope. Such changes should not be considered as departing from the spirit and scope of this disclosure.

Claims

1. A proton exchange membrane for use in an energy conversion device, comprising: The first layer of perfluorosulfonic acid ionomer, The perfluorosulfonic acid ionomer includes an additive coated with first methoxynonafluorobutane.

2. The proton exchange membrane according to claim 1, wherein, The first methoxynonfluorobutane-coated additive includes a composite catalyst.

3. The proton exchange membrane according to claim 2, wherein, The first methoxynonfluorobutane-coated additive comprises carbon-supported platinum, and the weight ratio of the perfluorosulfonic acid ionomer to the first methoxynonfluorobutane-coated additive is in the range of 1:10 to 1:2000.

4. The proton exchange membrane according to claim 1, wherein, The first methoxynonfluorobutane-coated additive includes inert particles.

5. The proton exchange membrane according to claim 1, wherein, The additives used in the first methoxynonfluorobutane coating include at least one additive selected from the group consisting of silica, carbon black, graphene, and carbon nanotubes.

6. The proton exchange membrane according to claim 1 further comprises an expanded polytetrafluoroethylene (ePTFE) membrane, wherein the ePTFE membrane includes a first side and a second side, wherein, The first layer of the perfluorosulfonic acid ionomer contacts the first side of the expanded polytetrafluoroethylene film.

7. The proton exchange membrane according to claim 6, further comprising a second layer of the perfluorosulfonic acid ionomer in contact with the second side of the expanded polytetrafluoroethylene membrane, wherein, The second layer of the perfluorosulfonic acid ionomer includes an additive coated with second methoxynonafluorobutane and is in contact with the second side of the expanded polytetrafluoroethylene film.

8. The proton exchange membrane according to claim 7, wherein, The additive coated with the first methoxynonfluorobutane is the same as the additive coated with the second methoxynonfluorobutane.

9. The proton exchange membrane according to claim 7, wherein, The first thickness of the first layer of the perfluorosulfonic acid ionomer is in the range of 4 micrometers to 28 micrometers, and the second thickness of the second layer of the perfluorosulfonic acid ionomer is in the range of 2 micrometers to 28 micrometers.

10. A method for forming a proton exchange membrane, comprising: The additives were dispersed in methoxynonfluorobutane; The additive was coated with methoxynonfluorobutane during dispersion; The coated additive is separated from excess methoxynonfluorobutane; Dry the coated additive; The coated additive and the perfluorosulfonic acid ionomer solution are mixed in a solution of alcohol and water to form an ionomer dispersion; The ionomer dispersion is used to form the proton exchange membrane; Dry the proton exchange membrane; as well as The proton conductivity of the proton exchange membrane was verified using four-probe electrochemical impedance spectroscopy at one or more relative humidities ranging from 40% to 100%.

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