Methods and membranes

Abstract

A fuel cell catalyst-coated membrane comprising a catalyst layer and an ionically conductive membrane, wherein the ionically conductive membrane has a hydrogen permeability constant of less than 1.50010 ‑13 mol s ‑1 cm ‑1 kPa ‑1 , wherein the ionically conductive membrane comprises dispersed platinum group metal-containing nanoparticles, a nanoparticle stabilizer, and an ionically conductive polymer.

Description

Technical Field

[0001] This invention relates to a membrane coated with a fuel cell catalyst, wherein the ion-conducting membrane contains nanoparticles, and to a method for producing the same. Background Technology

[0002] A fuel cell is an electrochemical cell comprising two electrodes separated by an electrolyte. Fuel (e.g., hydrogen, alcohol (such as methanol or ethanol), or formic acid) is supplied to the anode, and an oxidant (e.g., oxygen or air) is supplied to the cathode. Electrochemical reactions occur at the electrodes, and the chemical energy of the fuel and oxidant is converted into electrical energy and heat. Electrocatalysts are used to facilitate the electrochemical oxidation of the fuel at the anode and the electrochemical reduction of oxygen at the cathode.

[0003] Fuel cells are typically classified according to the properties of the electrolyte used. The electrolyte is usually a solid polymer membrane, which is electrically insulating but ionicly conductive. In a proton exchange membrane fuel cell (PEMFC), the membrane is proton-conductive, and protons generated at the anode are transported across the membrane to the cathode, where they combine with oxygen to form water.

[0004] Conventional ion-conducting membranes used in PEMFCs are typically formed from sulfonated perfluorinated polymer materials (generally referred to as perfluorinated sulfonic acid (PFSA) ionomers). As an alternative to PFSA-type ionomers, ion-conducting membranes based on partially fluorinated or non-fluorinated hydrocarbon sulfonated or phosphonic polymers can be used.

[0005] In fuel cells, free radicals can form in the ion-conducting membrane, for example, due to the decomposition of hydrogen peroxide, which can be a byproduct formed during operation. These free radicals decompose the ion-conducting membrane and reduce its durability. Traditionally, such decomposition of the ion-conducting membrane is limited by including free radical scavengers (such as cerium dioxide-based materials disclosed in WO2007 / 120190 of 3M Innovative Properties Co.). Methods to improve the durability of the ion-conducting membrane by preventing free radical activation are desirable, especially in cases where metal cations or oxides are not required.

[0006] Furthermore, high mechanical durability is desired for ion-conducting films. Strong strength is also expected to resist deformation in real-world applications, where the film is subjected to extreme humidity and temperature conditions that could cause deformation and eventual failure.

[0007] The goal is to reduce the thickness of such ion-conducting films to minimize both electronic and ionic resistance. However, it is equally important to minimize any hydrogen permeation through the film to avoid hydrogen mixing with oxygen and the associated safety concerns.

[0008] Proton exchange membranes comprising recombined catalysts are known to catalyze the reaction between hydrogen and oxygen to form water, thereby reducing hydrogen permeation levels. For example, WO2020 / 148545 (Johnson Matthey FuelCells Ltd) describes the introduction of a catalyst containing platinum on a graphene support into a proton exchange membrane. Additionally, CN114874475 (FOSHAN CLEANEST ENERGY TECH CO LTD) describes the use of platinum particles supported on hollow polydopamine microspheres in a proton exchange membrane. In this case, the platinum particles are located within the membrane on the surface of the catalyst support.

[0009] Incorporating platinum nanoparticles into ion-conducting membranes is also known. For example, US10,476,094 (LG Chem Ltd) describes a reinforced membrane comprising a porous polymer support. Platinum nanoparticles are provided on both surfaces of the porous polymer support and on the surfaces within the pores. To prepare this membrane, the porous support is immersed in a solution of a platinum precursor, which is then reduced by adding a reducing agent. This method has several manufacturing drawbacks. For example, the immersion of the porous polymer support in the platinum precursor solution can cause swelling and / or deformation of the support during immersion, and this immersion and drying method is difficult to replicate on a large manufacturing scale. Furthermore, the requirements for co-positioning the reinforcing agent component and the platinum nanoparticles limit the range of options available for optimizing performance by modifying the membrane configuration and limit the ability to disperse the nanoparticles.

[0010] A similar approach involving the local deposition of platinum nanoparticles onto the pores of a PTFE membrane is described in the paper “Reinforced and self-humidifying composite membrane for fuel cell applications”; Liu et al., Journal of Membrane Science, 330 (2009) 357-362. A colloidal dispersion comprising nanoscale noble metal particles and an ionomer component is also described in US2015 / 0236354 (Solvicore GMBH & Co. KG) as being formed by dissolving a suitable noble metal precursor in a liquid acidic ionomer component, followed by a reduction step. This colloidal dispersion contains no other components.

[0011] Incorporating platinum group metal nanoparticles into ion-conducting films remains challenging. It is difficult to reproducibly produce consistent inks containing ion-conducting polymers and platinum group metal nanoparticles that retain their properties during storage. Typically, this means that such inks must be prepared shortly before manufacturing, thus reducing manufacturing flexibility.

[0012] The addition of platinum group metal nanoparticles also increases the cost of the ion-conducting membrane, so it is desirable to maximize the reduction of hydrogen permeation for a given amount of recombinant catalyst.

[0013] Further development is needed to create efficient and scalable methods for producing ion-conducting membranes, and to enhance such membranes to enable efficient operation of thinner membranes with lower gas permeation resistance. Summary of the Invention

[0014] The inventors have surprisingly discovered that stabilized dispersions of platinum group metal nanoparticles can be advantageously combined with ion-conducting polymers to form inks suitable for the manufacture of ion-conducting membranes, and that these inks exhibit nanoparticle size stability over extended time periods. The inventors have also found that these inks can be used to produce ion-conducting membranes exhibiting excellent dispersion of platinum group metal nanoparticles within the membrane layer. Additionally, the inventors have found that the combination of such stabilizers with platinum group metal nanoparticles possesses free radical suppression properties. Furthermore, the inventors have found that ion-conducting membranes containing the combination of such stabilizers with platinum group metal nanoparticles exhibit enhanced hydrogen permeation reduction effects.

[0015] Therefore, in a first aspect, a fuel cell catalyst-coated membrane is provided, the fuel cell catalyst-coated membrane comprising a catalyst layer and an ion-conducting membrane, wherein the ion-conducting membrane has a density of less than 1.500. 10 -13 mol s -1 cm -1 kPa -1 The hydrogen permeation constant, wherein the ion-conducting film comprises dispersed platinum group metal nanoparticles, nanoparticle stabilizers, and ion-conducting polymers.

[0016] In a second aspect, a method for producing an ion-conducting film as defined in the first aspect is provided, the method comprising the following steps:

[0017] (i) Provide a stabilized dispersion containing platinum group metal nanoparticles;

[0018] (ii) The stabilized dispersion is mixed with an ion-conducting polymer to form an ink;

[0019] (iii) An ion-conducting film layer is made from the ink.

[0020] In a third aspect, a method for producing a catalyst-coated membrane as defined in the first aspect is provided, the method comprising the following steps:

[0021] (iv) Producing ion-conducting films by the method of the second aspect;

[0022] (v) Apply the catalyst layer to one or both sides of the ion-conducting membrane prepared in step (iv).

[0023] In the fourth aspect, the use of dispersed platinum group metal nanoparticles combined with nanoparticle stabilizers for preventing the degradation of ion-conducting films by free radicals is provided.

[0024] In the fifth aspect, the use of dispersed platinum group metal nanoparticles combined with nanoparticle stabilizers as free radical reducing additives in ion-conducting films is provided.

[0025] In a sixth aspect, a method is provided to prevent the degradation of an ion-conducting membrane by combining dispersed platinum group metal nanoparticles with a nanoparticle stabilizer in the membrane.

[0026] In a seventh aspect, a method is provided for reducing free radicals in an ion-conducting membrane by combining dispersed platinum group metal nanoparticles with a nanoparticle stabilizer in the membrane.

[0027] In aspects four through six, the ion-conducting membrane is suitably an ion-conducting membrane for a fuel cell. Attached Figure Description

[0028] Figure 1A and Figure 1B A schematic diagram of an example arrangement of the catalyst-coated membrane of the present invention is shown.

[0029] Figure 2 The results of stability tests on inks containing PVP-stabilized platinum nanoparticles and ion-conducting polymers are shown.

[0030] Figure 3 The results of scanning electron-energy dispersed X-ray (SEM_EDX) analysis of the membrane, including the platinum-containing film layer, are shown.

[0031] Figure 4 The results of hydrogen permeation tests on the catalyst-coated membrane are shown by curves of average hydrogen permeation current density and permeation test number.

[0032] Figure 5 The results of hydrogen permeation tests on the catalyst-coated membrane are shown by curves comparing the hydrogen permeation constant with the permeation test number.

[0033] Figure 6The graphs showing additive concentration versus Fenton recovery factor for PVP-stabilized platinum nanoparticles and other comparative additives are presented. This graph represents the radical inhibition property. Detailed Implementation

[0034] Preferred and / or optional features will now be described. Unless the context otherwise requires, any aspect may be combined with any other aspect. Unless the context otherwise requires, any preferred and / or optional feature of any aspect may be combined, alone or in combination with any other feature. For the avoidance of ambiguity, any preferred and / or optional features described herein apply not only to the first and second aspects, but also to the fourth through seventh aspects.

[0035] Suitable of the ion-conducting membrane, it is a proton exchange membrane (PEM), such that the catalyst-coated membrane is a PEM fuel cell catalyst-coated membrane. However, those skilled in the art will understand that the ion-conducting membrane can be an anion exchange membrane, such that the catalyst-coated membrane is an anion exchange membrane (AEM) fuel cell catalyst-coated membrane.

[0036] As used herein, the term nanoparticles refer to particles with a size ranging from 1 nm to 100 nm and include particles of 1 nm and 100 nm. The average particle size of particles in an ion-conducting film can be determined by transmission electron microscopy (TEM), for example by analyzing the cross-section of the film by TEM and measuring the size of a group of particles (e.g., 100) by image analysis based on the resulting images, and then calculating the average (mean) value.

[0037] The platinum group metals are platinum, palladium, iridium, rhodium, ruthenium, and osmium. Suitablely, platinum group metal nanoparticles contain platinum group metals, typically platinum or palladium, or are substantially composed of platinum group metals (typically platinum or palladium), i.e., the nanoparticles are platinum group metal nanoparticles (typically platinum nanoparticles or palladium nanoparticles). Alternatively, platinum group metal nanoparticles may be platinum group metals alloyed with one or more of the following elements:

[0038] i) Another platinum group metal;

[0039] ii)gold;

[0040] iii) Base metals, such as iron, nickel, cobalt, or chromium.

[0041] Examples include platinum-palladium alloys, platinum-iridium alloys, platinum-cobalt alloys, or platinum-ruthenium alloys. Platinum group metal nanoparticles are suitably recombinant catalyst nanoparticles, meaning they act as catalysts for the reaction between hydrogen and oxygen to form water.

[0042] Platinum group metal nanoparticles are typically unloaded. The term "unloaded" will be readily understood by those skilled in the art. For example, it should be understood that platinum group metal nanoparticles are not bound or immobilized to a solid catalyst support (such as a carbon support) by physical or chemical bonds (e.g., by ionic or covalent bonds) or by nonspecific interactions (such as van der Waals forces). The use of unloaded nanoparticles provides increased film stability during electrochemical operation, avoids degradation pathways via corrosion of the support or other chemical or electrochemical reactions, and allows for greater dispersion within the film.

[0043] The method described herein includes step (i) providing a stabilized dispersion of nanoparticles. Those skilled in the art will understand that the stabilized nanoparticle dispersion comprises solid nanoparticles in a liquid phase containing at least one nanoparticle stabilizer that interacts with the nanoparticles to prevent agglomeration. Such an agent also acts as a capping agent during synthesis.

[0044] The method described herein involves a first step of forming a stabilized nanoparticle dispersion prior to the subsequent ink-forming step of mixing the stabilized dispersion with an ionically conductive polymer. Therefore, those skilled in the art will understand that the stabilizer used to form the stabilized nanoparticle dispersion, or each stabilizer, is different from the ionically conductive polymer used to form the ink in step (ii). This is also true in ionically conductive films coated with catalysts.

[0045] Suitable platinum group metal nanoparticle stabilizers are selected from those reagents that interact with the nanoparticle surface, prevent nanoparticle aggregation and agglomeration, and enable the formation of nanoparticle dispersions. This stabilization of the nanoparticle surface is typically achieved through interactions between the nanoparticles and the polar functional groups of the stabilizer. Generally, stabilizers contain amide, carboxylic acid, sulfonic acid, amine, alcohol, or ether functional groups. Stabilizers may contain amide or ether functional groups. Stabilizers may suitably contain tertiary amide groups. Suitably, stabilizers do not have acidic functional groups. Suitably, stabilizers do not have sulfonic acid functional groups. Nanoparticle stabilizers can be water-soluble, such as water-soluble polymers. Nanoparticle stabilizers may have a water solubility of at least 1 mg / mL, typically at least 10 mg / mL, and more typically at least 100 mg / mL at 25°C.

[0046] The stabilizer may have a higher hydrophobicity and / or a lower water absorption value than the ion-conductive polymer used in step (ii).

[0047] Suitablely, the stabilized dispersion comprises a polymer nanoparticle stabilizer. The stabilized dispersion may comprise a polymer nanoparticle stabilizer having a higher hydrophobicity and / or lower water absorption value than the ionically conductive polymer used in step (ii). The polymer nanoparticle stabilizer may suitably have a lower weight-average molecular weight than the ionically conductive polymer used in step (ii).

[0048] Suitable polymer stabilizers may contain amide functional groups, such as tertiary amide functional groups, for example pyrrolidone functional groups (such as polyvinylpyrrolidone or copolymers containing vinylpyrrolidone as the first polymerization unit).

[0049] Suitable of the stabilizer is polyvinylpyrrolidone (PVP). It has been found that the use of PVP in the presence of perfluorosulfonic acid (PFSA) polymers provides excellent dispersion stability and greater nanoparticle dispersion stability than nanoparticles containing PFSA alone.

[0050] Suitablely, the stabilizer is a PVP with a weight average molecular weight in the range of 5,000 to 50,000, including 5,000 and 50,000. This range is considered to provide a suitable balance between dispersion stability and ease of polymer processability. The polymer stabilizer can also be a PVP with a weight average molecular weight in the range of 8,000 to 45,000, including 8,000 and 45,000.

[0051] Typically, stabilized dispersions are formed in aqueous media such as water.

[0052] Appropriately, platinum group metal nanoparticles are prepared at a concentration of 0.5 g L. -1 Up to 10g L -1 Within the range and including 0.5g L -1 and 10g L -1 The amount present in the dispersion, for example, in the case where the platinum group metal nanoparticles are platinum particles, such particles are typically present in quantities of 0.5g. Pt L -1 Up to 10g Pt L -1 Within the range and including 0.5g Pt L -1 and 10g Pt L -1 The amount of [particles] present. The concentration of nanoparticles can be adjusted using techniques known to those skilled in the art, such as evaporation or cross-flow filtration.

[0053] Appropriately, the dispersion formed in step (i) has a zeta potential that is more positive than +25 mV or more negative than -25 mV. The zeta potential can be measured using electrophoretic light scattering, for example, using a Zetasizer Ultra (Malvern Panalytical).

[0054] Those skilled in the art will recognize methods for producing suitable platinum group metal nanoparticle dispersions. For example, the dispersions can be produced by continuous flow hydrothermal synthesis. Suitablely, such synthesis can be carried out in a mixing reactor, such as the mixing reactor described in WO2015075439A1 (University of Nottingham), which is incorporated herein by reference.

[0055] Platinum group metal nanoparticle dispersions can also be produced by mixing a suitable platinum group metal precursor with a stabilizer in a solvent (such as water), followed by in-situ formation of nanoparticles. For example, in the case of platinum nanoparticles, the dispersion can be produced by mixing a platinum precursor (such as chloroplatinic acid (H₂PtCl₆), platinum nitrate, or platinum acetylacetonate) with a stabilizer in a solvent (such as water), followed by reduction of the platinum precursor, for example, using sodium borohydride or formaldehyde. An example of this preparation is described in Du, YK, Journal of Applied Polymer Science, Vol. 99, 23–36 (2006), which is incorporated herein by reference.

[0056] The method includes step (ii) mixing a stabilized dispersion with an ion-conducting polymer to form an ink. Typically, this is achieved by forming a dispersion of the ion-conducting polymer and then mixing that dispersion with a stabilized dispersion of nanoparticles.

[0057] Those skilled in the art will recognize suitable ion-conducting polymers for use in ion-conducting membranes. Ion-conducting polymers can be proton-conducting polymers or anion-conducting polymers, such as hydroxyl anion-conducting polymers. Examples of suitable proton-conducting polymers include PFSA ionomers (e.g., Nafion). ® (Chemours), Aciplex ® (Asahi Kasei), Aquivion ™ (Synesqo), Flemion ® (Asahi Glass Co.), or ionomers based on sulfonated hydrocarbons, i.e., sulfonated hydrocarbon ionomers, which, as is known in the art, are ionomers without fluorine groups, such as those available from FuMA-Tech GmbH as fumapem ®Those obtained from P, E, or K series products (JSR Corporation, Toyobo Corporation, etc.), or Pemion sulfonated hydrocarbon ionomers from IonomrInnovations. ™ Examples of suitable anionic conductive polymers include A901 and A201 manufactured by Tokuyama Corporation, Fumasep FAA from FuMA-Tech GmbH, and Aemion polymer from Ionomr Innovations.

[0058] When the ion-conducting membrane is a PEM ion-conducting membrane, the ion-conducting polymer is suitably a proton-conducting polymer, and particularly a partially fluorinated or fully fluorinated sulfonic acid polymer. Examples of suitable proton-conducting polymers include PFSA polymers. Suitably, the ion-conducting polymer can be a PFSA polymer and have an equivalent mass (EW) greater than 700 EW, greater than 750 EW, greater than 760 EW, greater than 770 EW, or greater than 790 EW. The ion-conducting polymer can suitably be a PFSA polymer having an equivalent mass in the range of 700 EW to 1200 EW and including 700 EW and 1200 EW (such as in the range of 750 EW to 1200 EW and including 750 EW and 1200 EW, such as in the range of 770 EW to 1000 EW and including 770 EW and 1000 EW, or in the range of 800 EW to 900 EW and including 800 EW and 900 EW). Suitably, the PFSA polymer may have an equivalent mass in the range of 700 EW to 900 EW and including 700 EW and 900 EW (such as in the range of 750 EW to 850 EW and including 750 EW and 850 EW). The EW of the PFSA polymer may suitably be less than 750 EW. The EW of the PFSA polymer may suitably be greater than or equal to 650 EW, or greater than or equal to 700 EW. Therefore, the EW of the PFSA polymer may be at least 650 EW and less than 750 EW, or at least 700 EW and less than 750 EW. Alternatively, the ion-conducting polymer may be a sulfonated hydrocarbon ionomer that may suitably have an ion exchange capacity (IEC) greater than 0.5 mmol / g or greater than 1.0 mmol / g. The sulfonated hydrocarbon ionomer may suitably have an IEC less than or equal to 3.5 mmol / g, or less than or equal to 3.0 mmol / g. IEC can be in the range of 0.5 mmol / g to 3.5 mmol / g and including 0.5 mmol / g and 3.5 mmol / g, or in the range of 1.0 mmol / g to 3.0 mmol / g and including 1.0 mmol / g and 3.0 mmol / g.

[0059] Ionically conductive polymers are typically dispersed in a mixture of an organic solvent and water. For example, the solvent can be a mixture of an alcohol (such as ethanol or propanol) and water. The volume ratio of the organic solvent (such as ethanol) to water can range from 95:5 to 60:40, including 95:5 and 60:40, such as from 90:10 to 70:30, including 90:10 and 70:30. The solvent is formulated to achieve desired dispersion, coating, and drying characteristics.

[0060] The ink may also contain radical reducing additives (e.g., peroxide radical reducing additives, such as cerium dioxide), which are additional additives to a combination of platinum group metal nanoparticles and nanoparticle stabilizers, i.e., the combination does not contain the additive. For example, the radical reducing additive (such as cerium dioxide) may be provided in the dispersion at a weight percentage ranging from 0.15 wt% to 0.35 wt% and including 0.15 wt% and 0.35 wt%, such as in the range of 0.20 wt% to 0.30 wt% and including 0.20 wt% and 0.30 wt%. The radical reducing agent is typically added to the ink once the stabilized dispersion is mixed with the ion-conducting polymer. It may be suitable that the ink does not contain such radical reducing additives, such as cerium dioxide, for example because the combination of platinum group metal nanoparticles and nanoparticle stabilizers acts as a radical reducing agent. In other words, in this case, the only additive with radical reducing properties is the combination of platinum group metal nanoparticles and nanoparticle stabilizers. Therefore, it may be suitable for the ink to be free of cerium (including cerium dioxide) or manganese. This reduces the amount of metallic substances present in the ion-conductive membrane, and consequently reduces the potential adverse effects of these substances on the performance of the catalyst-coated membrane.

[0061] The resulting ink typically contains or is essentially composed of the following substances:

[0062] (i) Ionically conductive polymers, such as protonally conductive polymers, for example, PFSA ionomers or sulfonated hydrocarbon ionomers. The ionically conductive polymers are typically provided in the ink at a weight percentage ranging from 5% to 25% by weight, and including both 5% and 25% by weight, such as ranging from 10% to 20% by weight, and including both 10% and 20% by weight, relative to the total weight of the ink components;

[0063] (ii) Platinum group metal nanoparticles, such as palladium or platinum nanoparticles. Typically, the nanoparticles, such as palladium or platinum nanoparticles, are present in the ink in an amount ranging from 0.01 wt% to 0.40 wt% and including 0.01 wt% and 0.40 wt% relative to the total weight of the ink components.

[0064] (iii) Nanoparticle stabilizers, such as polymeric nanoparticle stabilizers, for example, PVP. Typically, the nanoparticle stabilizer is present in the ink in an amount ranging from 0.05 wt% to 2 wt% and including 0.05 wt% and 2 wt%, such as in an amount ranging from 0.05 wt% to 0.50 wt% and including 0.05 wt% and 0.50 wt%, relative to the total weight of the ink components;

[0065] (iv) Optionally, the amount of the free radical reducing additive, such as cerium dioxide (CeO2), relative to the total weight of the ink components, is typically in the range of 0.15 wt% to 0.35 wt%, and includes both 0.15 wt% and 0.35 wt%. Alternatively, the ion-conducting film is free of cerium (including cerium dioxide) or manganese.

[0066] Components (i) to (iv) are dispersed in a solvent, such as a mixture of alcohol (e.g., ethanol or 1-propanol) and water, for example, in a volume ratio of alcohol:water:95:5 to 60:40.

[0067] The method includes step (iii) fabricating an ion-conducting film layer from the ink. The ion-conducting film layer is typically formed by depositing ink onto a substrate to form a layer.

[0068] Coating compositions can be deposited using slot die coating processes (whereby the dispersion is extruded onto the substrate via a slot by gravity or under pressure), doctor blade coating, bar coating, inkjet printing, curtain coating, spraying, or casting processes. Suitablely, slot die coating, bar coating, or inkjet printing can be used to deposit the coating composition. Deposition using slot die coating is preferred.

[0069] A coating composition is deposited onto a substrate to form an ion-conducting film layer. In some cases, the ion-conducting film is formed from a single layer. Alternatively, the ion-conducting film may be formed from two or more layers (such as two or three layers, typically two layers). The number of layers will be determined by, for example, the desired thickness of the ion-conducting film and the desired degree of variation of the composition throughout the film.

[0070] Typically, the substrate is a backing sheet, an ion-conducting layer, a catalyst layer on the backing sheet, or a catalyst layer on a gas diffusion electrode. Those skilled in the art will understand that the choice of substrate will depend on the structure of the ion-conducting film and the manufacturing stage.

[0071] In cases where the ion-conducting membrane is formed from a single layer or at the start of the production of a multilayer membrane, the substrate is typically a backing layer. The backing layer provides support for the ion-conducting membrane during manufacturing and, if not immediately removed, can provide support and strength during any subsequent storage and / or transport. The material used to make the backing layer should provide the necessary carrier, is generally compatible with inks, is typically ink-impermeable, can withstand the process conditions involved in the production of the ion-conducting membrane, and can be easily removed without damaging the ion-conducting membrane. Examples of suitable materials include fluoropolymers (such as polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), perfluoroalkoxy polymers (PFA), fluorinated ethylene propylene (FEP - a copolymer of hexafluoropropylene and tetrafluoroethylene)) and polyolefins (such as biaxially oriented polypropylene (BOPP)).

[0072] When producing a catalyst-coated membrane, a catalyst layer is provided on a backing layer, for example, by printing or using known coating techniques. A coating composition can then be deposited onto the catalyst layer, such that the catalyst layer is positioned between the backing layer and an ion-conducting film layer formed by depositing ink.

[0073] In some cases, the substrate is a previously formed ion-conducting film layer. It should be understood that ion-conducting films can be formed by sequential deposition of layers. As an example, an ion-conducting film can be formed as follows: In a first step, an ink containing an ion-conducting polymer can be deposited onto a backing layer to form a first ion-conducting polymer layer, which is then dried. In a second step, ink is deposited onto the first ion-conducting polymer layer to form a second ion-conducting polymer layer. Subsequently, the second ion-conducting polymer layer is dried. This sequence of application and drying continues to produce additional ion-conducting polymer layers as needed, thereby forming the desired film structure. Those skilled in the art will understand that the platinum group metal nanoparticle-containing ink, as described above, can be used in one or more coating steps in the coating process, depending on the requirements of the final film structure.

[0074] The ion-conducting membrane formed by the method described herein can be used to produce catalyst-coated membranes. In this case, the method includes the step of forming a catalyst layer on a first and / or second surface of the ion-conducting membrane to form an anode and / or cathode. Those skilled in the art will understand that the specific type of catalyst used for the cathode and anode is selected based on, for example, whether the membrane is used for a PEM or AEM fuel cell as previously described. Furthermore, the deposition method can be varied; for example, the catalyst layer can be transferred from a decal to the membrane by, for example, hot pressing, or the catalyst ink can be printed directly onto the membrane.

[0075] In the membrane coated with fuel cell catalyst, the ion-conducting membrane has a density of less than 1.500. 10 -13 mol s -1 cm -1 kPa -1 Appropriately less than 1.300 10 -13 mol s -1 cm -1 kPa -1 Typically less than 1.200 10 -13 mol s -1 cm -1 kPa -1 The hydrogen permeation constant is determined by the process described in the Examples section. This permeation constant is typically a value calculated after permeation test 1 according to the process described in the Examples section. That is, it corresponds to the inherent level of hydrogen permeation observed for the ion-conducting membrane. However, the ion-conducting membrane will typically have such a hydrogen permeation constant after permeation test 2, appropriately after permeation test 4, for example after permeation test 6. That is, the ion-conducting membrane will maintain its inherent level of hydrogen permeation after multiple cycles under harsh operating conditions. Referring to the detailed process described in the Examples section, in order to calculate the hydrogen permeation constant based on the measurement of the hydrogen permeation current density, the catalyst-coated membrane undergoes an initial conditioning step, which is conventional in the art. The hydrogen permeation current density is measured during permeation test 1 by performing a linear sweep voltammetry in which hydrogen is supplied to the anode and nitrogen is supplied to the cathode. The measurement is repeated three times. The hydrogen permeation current density is obtained by averaging the current densities between 0.3V and 0.35V. A lower hydrogen permeation current density means less hydrogen permeation.

[0076] Prior to the second hydrogen permeation current density measurement, the catalyst-coated membrane was subjected to an open-circuit voltage hold for 25 hours. Then, a second hydrogen permeation current density measurement was performed to obtain the permeation current density for transmission test 2. This cycle of open-circuit voltage hold followed by permeation current density measurement was repeated to obtain transmission tests 3, 4, 5, etc., until the hydrogen permeation current density exceeded 20 mA cm⁻¹. -2 .

[0077] The hydrogen permeability constant for a specific permeability test number is calculated using the formulas described in the Examples section.

[0078] Typically, ion-conducting films may have a thickness of less than or equal to 50 μm. Suitably, ion-conducting films may have a thickness of less than or equal to 40 μm, 30 μm, 20 μm, 15 μm, or less than 10 μm. Ion-conducting films may suitably have a thickness of at least 1 μm (such as at least 5 μm). Ion-conducting films may suitably have a thickness in the range of 1 μm to 50 μm and including 1 μm and 50 μm, such as 1 μm to 40 μm, 1 μm to 30 μm, 1 μm to 20 μm, 1 μm to 15 μm, or for example, greater than or equal to 1 μm and less than 10 μm. Ion-conducting films may suitably have a thickness in the range of 5 μm to 50 μm and including 5 μm and 50 μm, such as 5 μm to 40 μm, 5 μm to 30 μm, 5 μm to 20 μm, 5 μm to 15 μm, or for example, greater than or equal to 5 μm and less than 10 μm. The benefit of the low level of hydrogen permeation exhibited by the ion-conducting membranes described in this article is that very thin membranes can be produced, thereby promoting higher performance in CCMs without exacerbating the harmful effects of hydrogen permeation.

[0079] The thickness of the ion-conductive film (and the thickness of the film layers) can be measured using scanning electron microscopy (SEM) at 0% relative humidity. SEM analysis is performed on a cross-section of the ion-conductive film, and the film and / or layer thickness is measured at multiple (e.g., 10) points. The thickness value is then determined by calculating the arithmetic mean of the measurements. Typically, SEM measurements are performed on a cross-section of the ion-conductive film embedded in resin, milled, and polished.

[0080] Platinum group metal nanoparticles are dispersed in an ion-conducting film layer. The film layer also contains an ion-conducting polymer and a nanoparticle stabilizer, each suitably as described above regarding the method. "Dispersed in an ion-conducting film layer" means herein that the nanoparticles are uniformly distributed throughout some or all of the film. Those skilled in the art will understand that the term "dispersed" does not exclude the aggregation of nanoparticles, but in this case, the clusters themselves are distributed throughout the film layer. The platinum group metal nanoparticles and nanoparticle stabilizers may be dispersed throughout the entire plane of the ion-conducting film, adjacent to a catalyst layer (typically a cathode). This means that a portion of the film thickness adjacent to a catalyst layer (typically a cathode) contains the platinum group metal nanoparticles and nanoparticle stabilizers dispersed therein, while the remaining thickness of the ion-conducting film adjacent to another catalyst layer (typically an anode) does not. In this case, when the film is a two- or three-layer film, a sublayer, i.e., the sublayer adjacent (i.e., in contact) to the desired catalyst layer (typically a cathode), will contain the platinum group metal nanoparticles and nanoparticle stabilizers dispersed therein.

[0081] When two sublayers exist in an ion-conducting membrane, one of the ion-conducting polymer sublayers may be appropriately thicker than the other. The ratio of the thicker to the thinner ion-conducting polymer sublayer may appropriately be greater than 1:1. The ratio may appropriately not exceed 10:1, or 5:1, and appropriately not exceed 3:1, for example, not exceed 2:1. The thickness of the ion-conducting membrane layers can be determined by SEM analysis of the cross-section of the membrane as described above.

[0082] Suitablely, the platinum group metal nanoparticles have an average particle size of less than 50 nm, such as in the range of 1 nm to 50 nm and including 1 nm and 50 nm. Suitablely, the nanoparticles have an average particle size in the range of 1 nm to 40 nm and including 1 nm and 40 nm, in the range of 1 nm to 30 nm and including 1 nm and 30 nm, in the range of 1 nm to 20 nm and including 1 nm and 20 nm, or in the range of 1 nm to 10 nm and including 1 nm and 10 nm. The average particle size of the platinum group metal nanoparticles in the ion-conducting film can be determined by transmission electron microscopy (TEM), for example by analyzing the cross-section of the film by TEM and measuring the size of the particle group (e.g., 100 particles) by image analysis based on the obtained image, and then calculating the average (mean) value.

[0083] Typically, platinum group metal nanoparticles exist primarily as discrete nanoparticle clusters. In this case, the nanoparticles exist as individual nanoparticles that are co-located in clusters rather than as nanoparticle aggregates or clusters, where the nanoparticles are bonded together by nanoparticle surface-to-surface interactions. Unbound by theory, this arrangement of nanoparticles is proposed to provide benefits related to greater accessibility of hydrogen to the catalytic site. Typically, the clusters have an average size in the range of 100 nm to 500 nm, including both 100 nm and 500 nm. The average particle size of the platinum group metal nanoparticle clusters in the ion-conducting film can be determined by transmission electron microscopy (TEM), for example by analyzing the cross-section of the film using TEM and measuring the size of the clusters (e.g., 100 clusters) based on the resulting images, and then calculating the average (mean) value.

[0084] The ion-conducting film contains nanoparticle stabilizers as described above, such as polymeric nanoparticle stabilizers, for example, PVP. Typically, platinum group metal nanoparticles are at least partially coated with nanoparticle stabilizers.

[0085] As described above, nanoparticle stabilizers can possess higher hydrophobicity and / or lower water absorption values ​​than ion-conducting polymers used in ion-conducting membranes. Unbound by theory, it is possible to improve the efficiency of platinum group metal nanoparticles as recombination catalysts by using nanoparticle stabilizers with higher hydrophobicity and / or lower water absorption values ​​than ion-conducting polymers, thereby increasing the rate at which hydrogen approaches the surface of platinum group metal nanoparticles and promoting the removal of water formed from the catalyst surface. This provides a higher hydrogen and oxygen recombination rate and thus enhanced protection against hydrogen permeation for a given catalyst loading in the ion-conducting membrane. The water absorption values ​​of ion-conducting polymers and nanoparticle stabilizers can be determined by drying the material sample and then measuring the weight of the sample before and after immersion in water (e.g., for 24 hours at 23°C). For example, water absorption can be measured by: (i) drying the sample in an oven until the weight stabilizes; (ii) cooling the sample in a desiccator; (iii) weighing the sample; (iv) immersing the sample in water (e.g., at 23°C for 24 hours); (iv) removing the sample and gently patting it dry with a lint-free cloth; and (v) reweighing the sample.

[0086] The ion-conducting membrane may appropriately have a concentration of at least 1 μg / cm. 2 Appropriately, at least 5 μg / cm 2 The loading of platinum group metal nanoparticles (e.g., platinum or palladium) is appropriate. The ion-conducting film can suitably have a loading of up to 30 μg / cm³. 2 Appropriately, up to 25 μg / cm 2 Appropriately, up to 15 μg / cm 2For example, at most 10 μg / cm 2 The loading of platinum group metal nanoparticles (e.g., platinum or palladium) is considered. It has been found that this range of nanoparticle loadings provides a suitable balance between reducing hydrogen permeation levels during use and the cost associated with containing nanoparticles in an ion-conducting membrane. It is also advantageous that hydrogen permeation can be effectively reduced with such low amounts of platinum group metal nanoparticles. Such low amounts offer benefits in terms of, for example, lower cost and lower risk of side effects. The loading can be determined by inductively coupled plasma mass spectrometry (ICP-MS). Suitablely, the molar ratio of nanoparticle stabilizer to platinum group metal nanoparticles will be at most 60:1, suitablely at most 50:1, suitablely at most 40:1, and typically at most 30:1. Suitablely, the molar ratio of nanoparticle stabilizer to platinum group metal nanoparticles will be at least 10:1.

[0087] Ion-conductive films can be suitably formed by methods that do not require a lamination step, such as by depositing multiple layers of ion-conductive polymers on top of each other via liquid phase deposition processes such as printing, spraying, or coating.

[0088] An ion-conducting membrane may suitably be a single, coherent polymer membrane comprising one or more ion-conducting polymer layers as defined above. The term "adhesion" as used herein refers to a membrane without internal lamination interfaces.

[0089] The lamination of ion-conducting membranes involves pressing and / or bonding together at least two solid ion-conducting membranes, which may optionally be coated with a catalyst layer. A lamination interface is formed between the two membranes, wherein the solid surfaces of the individual membranes are pressed and / or bonded together. The lamination interface includes physical defects. Furthermore, the structure and / or chemical properties of the lamination interface differ from those of the host polymer material. This is because when a solid membrane is formed, the outer surface of the solid membrane has surface features that differ from those in the host material. For example, a hydrophobic surface layer is formed on the membrane surface at an air interface. Raman spectroscopy can detect this difference. Therefore, when two solid membranes are pressed together, the lamination interface formed by the two solid surfaces is chemically and / or structurally different from the host ion-conducting polymer material. Thus, microscopy and spectroscopic techniques can distinguish the lamination interface between ion-conducting polymer layers from interfaces formed via liquid-phase deposition processes such as printing, spraying, or coating to construct multilayer structures. That is, non-laminated interfaces differ structurally and / or chemically from laminated interfaces, and this difference is not merely a characteristic of the manufacturing method. Furthermore, in the absence of prior knowledge of the manufacturing process, a non-laminated interface can be identified as being non-laminated within the film. Examples of analytical techniques used to detect laminated interfaces include cross-sectional SEM. Changes in crystallinity at the interface can be detected using cross-sectional TEM. Other techniques used to detect laminated interfaces include 13C / 1H / 19F solid-state NMR, neutron diffraction, and / or combinations of two or more of the above techniques.

[0090] Such interfaces can increase the resistance of multilayer ion-conducting films due to physical defects and / or chemical changes at the lamination interfaces between ion-conducting polymer films. Therefore, it has been found advantageous to construct multilayer film structures by depositing ion-conducting polymer layers dispersed in a liquid solvent, rather than by laminating individual solid layers / films of ion-conducting polymers.

[0091] The ion-conducting membrane may suitably include a planar reinforcing component, such as a porous reinforcing polymer sheet impregnated with an ion-conducting polymer. Since typical reinforcing polymer materials do not conduct ions, or conduct ions only adequately, a porous reinforcing polymer is used to form a reinforcing layer. This porous reinforcing polymer is impregnated through the pores of the material using the ion-conducting polymer to provide an ion conduction path from one side of the layer to the other. The ion-conducting membrane may suitably contain a reinforcing polymer, such as expanded polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI). PBI is typically in the form of PBI nanofibers. The reinforcing component may suitably constitute at least 5% of the volume fraction of the ion-conducting membrane, typically at least 10%. The reinforcing component may suitably constitute at most 50% of the volume fraction of the ion-conducting membrane, typically at most 40%, more typically at most 30%, for example at most 20%. For example, the reinforcing component may suitably comprise between 5% and 50% of the volume fraction of the ion-conducting film, typically between 10% and 40%, more typically between 10% and 30%, for example between 10% and 20% of the volume fraction. The thickness of the reinforcing component may suitably be distributed across at least 50% of the thickness of the ion-conducting film, typically at least 60%, for example at least 70%.

[0092] The ion-conducting membrane may contain a radical reducing additive (e.g., a peroxide radical reducing additive, such as cerium dioxide), which is an additional additive in the combination of platinum group metal nanoparticles and nanoparticle stabilizers, i.e., the combination does not contain this additive. It should be noted that peroxides can decompose to form a series of free radicals (O, OH, OOH), and the radical reducing additive can reduce the amount of one, several, or all of these free radicals. The radical reducing additive can be dispersed in the membrane. It is suitable that the ion-conducting membrane does not contain such radical reducing additives, such as cerium dioxide, for example, because the combination of platinum group metal nanoparticles and nanoparticle stabilizers acts as a radical reducing agent. In other words, in this case, the only additive with radical reducing properties is the combination of platinum group metal nanoparticles and nanoparticle stabilizers. Therefore, it may be suitable that the ion-conducting membrane does not contain cerium (including cerium dioxide) or manganese. This reduces the amount of metallic substances that will be present in the ion-conducting membrane, and consequently reduces the potential detrimental effects of these substances on the performance of the catalyst-coated membrane.

[0093] Figure 1A and Figure 1B The configuration shown illustrates a fuel cell catalyst-coated membrane 1 in which platinum group metal nanoparticles and nanoparticle stabilizers are dispersed throughout the ion-conducting membrane (A) and in one sublayer of a two-layer ion-conducting membrane (B). Reference Figure 1AAn ion-conducting membrane 4 is disposed between the cathode catalyst layer 2 and the anode catalyst layer 3. Platinum group metal nanoparticles are distributed throughout the ion-conducting membrane, and the planar reinforcement component 5 is distributed across at least 50% of the thickness of the ion-conducting membrane. (Reference) Figure 1B There are two ion-conducting sublayers, 6 and 7, where sublayer 6 is thicker than sublayer 7. Sublayer 6 contains platinum group metal nanoparticles and is positioned adjacent to the cathode catalyst layer 2. Similar to... Figure 1A The planar reinforcement component shown and bridging the two sublayers is not shown here.

[0094] The catalyst-coated membrane described herein has an anodic catalyst layer and / or a cathode catalyst layer applied to the surface of an ion-conducting membrane. Therefore, this document provides a method for producing a catalyst-coated membrane as defined herein, the method comprising the following steps:

[0095] (iv) Production of ion-conducting films using the methods described herein;

[0096] (v) Apply the catalyst layer to one or both sides of the ion-conducting membrane prepared in step (iv).

[0097] In a fuel cell catalyst-coated membrane, a cathode catalyst layer can be applied to the surface of an ion-conducting membrane containing a catalyst for catalyzing the oxygen reduction reaction. In a PEM fuel cell, the cathode catalyst layer may contain a platinum group metal catalyst, such as platinum, as a reducing metal or in alloy form, for example with another platinum group metal or base metal (such as iron, nickel, cobalt, or chromium), such as a carbon-supported platinum catalyst / or a carbon-supported platinum alloy catalyst. The catalyst material can be formulated as an ink, non-in-situ printed onto a PTFE sheet, and transferred onto the membrane by hot pressing. Alternatively, the ink can be directly coated onto the membrane.

[0098] In a fuel cell catalyst-coated membrane, an anode catalyst layer can be applied to the surface of an ion-conducting membrane containing a catalyst for catalyzing the hydrogenation reaction. In a PEM fuel cell, the anode catalyst layer may contain platinum (such as a carbon-supported platinum catalyst).

[0099] The anode material can be formulated into an ink, appropriately incorporated into an ion-conducting polymer, and non-in-situ printed onto a PTFE sheet, and then transferred to an ion-conducting membrane via hot pressing. Alternatively, the ink can be directly coated onto the ion-conducting membrane.

[0100] The present invention will now be described with reference to the following embodiments. These embodiments are provided to aid in understanding the invention and not to limit its scope.

[0101] Example

[0102] Example 1 - Formation of a stabilized dispersion of platinum nanoparticles using PVP

[0103] A PVP-stabilized dispersion of platinum nanoparticles in water was prepared using a continuous flow hydrothermal reactor operated at elevated temperature and pressure, consisting of an aqueous solution of platinum nitrate and an aqueous solution of 2 w / v% PVP (MW 10,000). The platinum loading in the dispersion was 3.93 g / L, as measured by ICP.

[0104] Dynamic light scattering (DLS) analysis showed that the z-average value of the PVP-Pt clusters in the dispersion was 280 nm, while small-angle X-ray scattering (SAXS) analysis showed that the size of the platinum nanoparticles ranged from 1 nm to 10 nm.

[0105] Example 2 - Formation of an ink containing PVP-stabilized platinum nanoparticles and an ion-conducting polymer

[0106] The aqueous dispersion prepared in Example 1 was mixed with additional water and EtOH to produce an ethanol-containing aqueous mixture (weight % ratio 4:1). A dried PFSA ionomer (3M Corporation, EW-800) was added to produce approximately 17 wt% ionomer and 0.08 wt% platinum ink. The ink was mixed using a roller mixer.

[0107] Dynamic light scattering (DLS) analysis showed that the z-average diameter of the Pt-PVP clusters in the dispersion was 1200 nm.

[0108] The stability of the ink during storage was evaluated by measuring the z-mean diameter after 1 day and 3 months. The results showed... Figure 2 The results showed no change in the DLS analysis curve, indicating high stability and anti-aggregation properties.

[0109] Example 3 - Preparation of membranes including platinum-containing film layers

[0110] An ion-conducting film containing a platinum film layer was prepared by coating an ink layer prepared according to the method of Example 2 onto a 15 μm thick PFSA film and drying it at room temperature.

[0111] The cross-section of the formed film was analyzed by scanning electron microscopy with energy-dispersive X-ray diffraction (SEM-EDX). This showed that the platinum-containing film layer had a thickness of approximately 30 μm. A magnified portion of the SEM-EDX image of the platinum-containing film layer is shown in... Figure 3 This indicates that platinum nanoparticles are distributed throughout the entire film layer.

[0112] Example 4 - Preparation of a film containing a platinum film layer and analysis by low-temperature TEM

[0113] The ink prepared according to Example 2 was frozen in a cryostat using liquid nitrogen and sliced ​​using a diamond blade. One slice was placed on a copper grid and thawed to form a film <100 nm thick.

[0114] The ion-conducting film was analyzed by cryogenic transmission electron microscopy (cryoTEM). This analysis showed that the platinum nanoparticles in the film have an average particle size in the range of 1 nm to 10 nm and are in the form of discrete clusters of platinum nanoparticles.

[0115] The average nearest neighbor distance between platinum particles was measured using a cryogenic TEM image obtained from an algorithm. This data was compared with the analysis of a contrasting ion-conducting film, which incorporates a platinum-containing layer with the same platinum loading but prepared from an ink containing platinum particles from a platinum black source without any stabilizers. This indicates that when a film is formed from a stabilized nanoparticle dispersion, the interparticle distance is significantly reduced, thus increasing the dispersion of platinum in the film.

[0116] Example 5 - Formation of CCM with a platinum-containing membrane and hydrogen permeation test.

[0117] By containing 13µg / cm 2 An ion-conducting film with a thickness of approximately 25 μm was prepared by casting a 10 μm layer of platinum (measured using XRF) and PVP (using the method described in Example 3) onto a 15 μm ePTFE-reinforced PFSA film. This was achieved by casting a 10 μm layer of platinum (measured using XRF) and PVP onto a 15 μm ePTFE-reinforced PFSA film. -2 (platinum loading) and Pt / C anode catalyst layer (with 0.08 mg cm⁻¹) -2 CCM (Cathode Matrix Composite) is obtained by laminating platinum-loaded layers onto either side of the composite membrane. The platinum-loaded membrane sublayer is adjacent to the cathode catalyst layer. Lamination is achieved by hot-pressing at 80°C and 800 PSI for 2 minutes.

[0118] For comparison, blank CCMs with a thickness of ~25 μm were also prepared using the exact same method, but the dispersions cast onto 15 μm ePTFE-reinforced PFSA films were platinum-free.

[0119] Hydrogen permeation and hydrogen permeability constant

[0120] The CCMs prepared in Example 5 were subjected to an initial conditioning step in which they were operated under the following conditions: anode: H2, cathode: air, relative humidity (RH) 100%, 80°C, 100 kPag pressure, 500 mA cm -2 Current density, maintained for 54 hours.

[0121] To determine the hydrogen permeation current density, a linear sweep voltammetry was performed with hydrogen supplied to the anode and nitrogen to the cathode. A lower hydrogen permeation current density implies less hydrogen permeation. Specifically, the linear sweep voltammetry was performed under the following conditions: anode: H2, cathode: N2, 100% RH, 80°C, 13.8 kPag pressure, swept from 0.1 V to 0.5 V RH at 1 mV / s. The hydrogen permeation current density was obtained by averaging the current densities between 0.3 V and 0.35 V. The test was repeated three times. This is through test 1. Figure 4 The relationship between the average permeation current density and the permeation test number is plotted in the figure.

[0122] Prior to the second hydrogen permeation current density measurement, the CCM was subjected to harsh open-circuit voltage (OCV) conditions. Specifically, the OCV was maintained under the following conditions: anode: H2, cathode: air, RH 30%, 90°C, 50 kPag pressure, 0 mA cm⁻¹. -2 The current density was maintained for 25 hours. Then, a second hydrogen permeation current density measurement was performed to obtain the permeation test result 2, which was plotted on... Figure 4 Repeat this combination of measurements to give transmission tests 3, 4, 5, etc., until the hydrogen permeation current density exceeds 20 mA / cm². -2 Therefore, under each pass test number, CCM has undergone additional stringent conditions.

[0123] like Figure 4 As can be seen, CCMs with platinum and PVP sublayers exhibit lower initial hydrogen permeation current densities and maintain lower hydrogen permeation current densities for further permeation, meaning they are resistant to hydrogen permeation for a greater number of OCV cycles. Therefore, in real-world applications, CCMs will inherently be more resistant to degradation caused by the hydrogen permeation pathway and will maintain this resistance for a longer period.

[0124] Osmotic current density (A·cm) -2 The relationship between the hydrogen permeability constant (P) and the hydrogen permeability constant (P) is as follows: [i] As shown:

[0125] A·cm -2 = P(mol·cm -1 ·s -1 ·cm -2 ·kPa -1 )·P H2 (kPa)·F(C·mol -1 )·2e·t(cm -1 )

[0126] After rearranging, the equation becomes:

[0127] P(mol·cm-1 ·s -1 ·cm -2 ·kPa -1 ) = A·cm -2 ·P H2 (kPa) -1 ·F(C·mol -1 ) -1 ·2e -1 ·t(cm)

[0128] Where F is Faraday's constant, "e" is the number of electrons (two) in the hydrogen oxidation reaction, and the partial pressure of hydrogen is obtained by subtracting the partial pressure of water vapor from the measured cell pressure. [ii] To determine this, a micrometer is used to measure the film thickness (t). The values ​​used in these calculations are shown below.

[0129]

[0130] Figure 5 It shows the use of Figure 4 The curve shown is a result of calculating the hydrogen permeation constant from the permeation current density data and comparing it with the permeation test number.

[0131] Free radical inhibition

[0132] Three dilutions containing 10 ppm, 20 ppm, and 30 ppm solids in 1 M H₂SO₄ were prepared using a dispersion with a solid content of 0.1 wt% as prepared in Example 1. These three dilutions were used to measure free radical inhibition capacity by a method defined below.

[0133] Comparative aqueous dispersions containing platinum but without PVP were prepared using three dilutions of 5 ppm, 20 ppm, and 30 ppm solids in 1 M H₂SO₄. These three dilutions were also used to measure free radical inhibition capacity using a method defined below.

[0134] Comparative aqueous dispersions containing cerium dioxide and free of PVP were prepared using three dilutions of 20 ppm, 25 ppm, and 45 ppm solids in H₂SO₄ 1M. These three dilutions were also used to measure free radical inhibition capacity using the method defined below.

[0135] A dispersion containing only PVP was also prepared, which was diluted to 20 ppm solids in 1 M H₂SO₄. This dispersion was also used to measure the free radical inhibition capacity by the method defined below.

[0136] The experimental procedure for measuring free radical inhibition ability followed that of Fei et al. (Fei Yu, Da Xu, Rong Lei, Na Li) and Ke'an Li (Journal of Agricultural and Food Chemistry, 2008, 56, 730-735); and Mei-Fang et al. (Mei-Fang Hou, Lin Liao, Wei-De Zhang, Xiao-Yan Tang, Hong-Fu Wan) and Guang-Cai Yin (Chemosphere, 2011, 83, 9, 1279-1283), in which the Fenton reaction was performed:

[0137] (Reaction 1)

[0138] (Reaction 2)

[0139] This process generates free radicals that degrade Rhodamine B (RhB) dye. UV-vis spectroscopy was used to track this degradation to determine if the presence of different additives could prevent this degradation through a free radical inhibition mechanism. For UV-vis spectroscopy, an Agilent Cary 5000 UV-vis-NIR was used with a 1 cm QS colorimetric tube. The abs peak at 554 nm was tracked. To simulate the low pH environment formed by PFSA ionomers in fuel cells, tests were conducted in 1 M H₂SO₄. Each test was performed at the following concentrations for each chemical:

[0140] • 14 ppm of RhB

[0141] • 35ppm Fe 2+

[0142] • Add 10 μL of 3% H2O2 and mix for 10 minutes, then measure the UV-Vis spectrum.

[0143] In the absence of any additives, only reaction 1 occurs, and the addition of H2O2 leads to a decrease in the UV-vis peak height at 554 nm by Δb. In the presence of a radical-reducing additive, both reactions 1 and 2 occur, resulting in a smaller decrease in the UV-vis peak height at 554 nm by Δa. For each additive at a given concentration, the "recovery" factor R can be calculated via the following equation:

[0144]

[0145] Figure 6The recovery factor (R) for each additive is shown; the higher the value of R, the stronger the free radical inhibition ability.

[0146] Clearly, dispersions containing platinum stabilized with PVP exhibit superior free radical suppression activity (higher R value) compared to platinum alone, and are particularly useful as free radical reducing additives for existing cerium dioxide-based membranes. Therefore, it is surprising that Pt stabilized with PVP will be useful as a free radical reducing agent in ion-conducting membranes.

[0147] Table 1 provides the recovery factor for each additive, including PVP alone, diluted 20 ppm solid in 1 M H₂SO₄. Clearly, PVP alone does not exhibit radical suppression, and the combination of platinum and PVP demonstrates stronger radical suppression than platinum alone.

[0148]

[0149] Table 1

[0150] Example 6 - Stabilized dispersion of platinum nanoparticles formed using a simple wet synthesis technique with PVP and formaldehyde body.

[0151] Add Pt(NO3)4 (equivalent to 1 g of platinum) to water (500 mL) and stir. Add PVP10 (average molecular weight 10,000, 8.5 g), followed by formaldehyde (37% in water, 20.8 g). Heat the mixture to 68 °C, then cool to room temperature and stir overnight to form a dispersion.

[0152] Example 7 - Formation of an ion-conducting polymer ink containing PVP-stabilized nanoparticles

[0153] A stabilized aqueous dispersion of platinum nanoparticles (formed according to a method similar to Example 6) was mixed with ethanol and water to produce a mixture with an ethanol:water weight ratio of 80:20. A dried ionomer (3M Corp, 800EW) was added to the mixture to produce a dispersion, wherein the ionomer solids were approximately 17% wt.

Claims

1. A membrane coated with a fuel cell catalyst, the membrane comprising a catalyst layer and an ion-conducting membrane, wherein the ion-conducting membrane has a density of less than 1.

500. 10 -13 mol s -1 cm -1 kPa -1 The hydrogen permeation constant, wherein the ion-conducting membrane comprises dispersed platinum group metal nanoparticles, nanoparticle stabilizers, and ion-conducting polymers.

2. The catalyst-coated membrane according to claim 1, wherein the ion-conducting membrane has a thickness of less than or equal to 50 μm.

3. The catalyst-coated film according to claim 1 or claim 2, wherein the ion-conducting polymer has an EW in the range of 700 to 1200 and including 700 and 1200.

4. A catalyst-coated membrane according to any of the preceding claims, wherein the ion-conducting membrane comprises a planar reinforcement component.

5. The catalyst-coated membrane according to claim 4, wherein the reinforcing component comprises expanded polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI).

6. The catalyst-coated membrane according to claim 4 or claim 5, wherein the reinforcing component accounts for 5% to 50% of the volume fraction of the ion-conducting membrane.

7. The catalyst-coated membrane according to any one of claims 4 to 6, wherein the thickness of the reinforcing component is distributed across at least 50% of the thickness of the ion-conducting membrane.

8. A catalyst-coated membrane according to any of the preceding claims, wherein the ion-conducting membrane is free of cerium or manganese.

9. A catalyst-coated film according to any of the preceding claims, wherein the nanoparticle stabilizer has higher hydrophobicity and / or lower water absorption value than the ion-conducting polymer.

10. A catalyst-coated film according to any of the preceding claims, wherein the platinum group metal nanoparticles are in the form of discrete nanoparticle clusters.

11. A catalyst-coated film according to any of the preceding claims, wherein the nanoparticle stabilizer is a polymer, such as polyvinylpyrrolidone.

12. A catalyst-coated film according to any of the preceding claims, wherein the platinum group metal nanoparticles are at least partially coated with the nanoparticle stabilizer.

13. A catalyst-coated film according to any of the preceding claims, wherein the average particle size of the nanoparticles is less than 50 nm.

14. A catalyst-coated membrane according to any of the preceding claims, wherein the ion-conducting membrane is a single coherent polymer membrane comprising two ion-conducting polymer sublayers.

15. The catalyst-coated membrane according to claim 14, wherein one of the ion-conducting polymer sublayers is thicker than the other ion-conducting polymer sublayer.

16. The catalyst-coated film according to claim 15, wherein the thickness ratio of the thicker ion-conducting polymer sublayer to the thinner ion-conducting polymer sublayer is greater than 1:1 and does not exceed 10:

1.

17. The catalyst-coated membrane according to any one of claims 14 to 16, wherein the platinum group metal nanoparticles and the stabilizer are present in a sublayer of the ion-conducting membrane.

18. A catalyst-coated membrane according to any of the preceding claims, wherein the platinum group metal nanoparticles are present adjacent to the cathode catalyst layer of the catalyst-coated membrane.

19. A fuel cell membrane electrode assembly, the fuel cell membrane electrode assembly comprising a catalyst-coated membrane according to any of the preceding claims and a gas diffusion layer in contact with the catalyst layer.

20. A method for producing an ion-conducting film as defined in any one of claims 1 to 18, the method comprising the following steps: (i) Provide a stabilized dispersion containing platinum group metal nanoparticles; (ii) The stabilized dispersion is mixed with an ion-conducting polymer to form an ink; (iii) An ion-conducting film layer is manufactured from the ink.

21. An ion-conducting membrane produced by the method according to claim 20.

22. A method for producing a catalyst-coated membrane according to any one of claims 1 to 18, the method comprising the following steps: (iv) Producing an ion-conducting membrane by the method of claim 20; (v) Apply the catalyst layer to one or both sides of the ion-conducting membrane prepared in step (iv).

23. The use of dispersed platinum group metal nanoparticles combined with nanoparticle stabilizers to prevent ion-conducting films from being degraded by free radicals.

24. The use of dispersed platinum group metal nanoparticles combined with nanoparticle stabilizers as free radical reducing additives in ion-conducting films.

25. The use according to claim 23 or claim 24, wherein the ion-conducting membrane is a fuel cell ion-conducting membrane.

26. A method for preventing the ion-conducting membrane from being degraded by free radicals by combining dispersed platinum group metal nanoparticles with a nanoparticle stabilizer in an ion-conducting membrane.

27. A method for reducing free radicals in an ion-conducting membrane by combining dispersed platinum group metal nanoparticles with a nanoparticle stabilizer in the membrane.

28. The method according to claim 26 or claim 27, wherein the ion-conducting membrane is a fuel cell ion-conducting membrane.

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