Method and apparatus

Abstract

A method for producing an ion-conductive membrane for a water electrolyzer or a fuel cell is provided. The method includes the step of in-line mixing a first liquid stream containing an ion-conductive polymer and a second liquid stream containing a cerium-containing compound to form a coating composition. Then, the coating composition is deposited on a substrate to form a membrane layer. An apparatus for producing an ion-conductive membrane for a water electrolyzer or a fuel cell is also provided.

Description

【Technical Field】 【0001】 The present invention relates to a method for producing an ion-conductive membrane for an electrochemical device such as a water electrolysis cell or a fuel cell, and an apparatus suitable for manufacturing such an ion-conductive membrane. 【Background Art】 【0002】 Electrolysis of water to produce high-purity hydrogen and oxygen can be carried out in both alkaline and acidic electrolyte systems. An electrolysis cell using a solid proton-conductive polymer membrane or a proton exchange membrane (PEM) is known as a proton exchange membrane water electrolyser (PEMWE). An electrolysis cell using a solid anion-conductive polymer membrane or an anion exchange membrane (AEM) is known as an anion exchange membrane water electrolyser (AEMWE). 【0003】 Ion-conductive membranes such as PEM and AEM are also used in fuel cells. In a proton exchange membrane fuel cell (PEMFC), the membrane is proton-conductive, and protons generated at the anode are transported through the membrane to the cathode, where they combine with oxygen to form water. 【0004】 A catalyst coated membrane (CCM) can be used in an electrochemical device such as an electrolysis cell and a fuel cell. Such a CCM includes an ion-conductive membrane such as a PEM or an AEM, and at least one of an anode catalyst layer and a cathode catalyst layer is applied to the surface of the membrane. 【0005】 In the use of a water electrolyzer, a hydrogen evolution reaction (HER) catalyst, for example, a HER catalyst containing platinum such as platinum on a carbon support, is used for such a cathode catalyst layer. An oxygen evolution reaction (OER) catalyst is utilized in the electrolyzer anode catalyst layer. In the case of PEMWE applications, suitable OER catalysts include iridium or iridium oxide (IrOx), or oxides containing both iridium and ruthenium. In the case of AEMWE applications, non-platinum group metal OER catalysts, such as alloys and oxides of nickel, cobalt, iron, and copper, can also be used. 【0006】 In the use of a fuel cell, an oxygen reduction reaction (ORR) catalyst is used in the cathode catalyst layer, and a hydrogen oxidation reaction (HOR) catalyst is utilized in the anode catalyst layer. In the case of PEMFC applications, suitable cathode and anode catalyst materials include platinum group metals or alloys of platinum group metals and one or more other metals, such as platinum or alloys of platinum and one or more other metals. 【0007】 A separate film layer, typically formed from a non-ion-conductive polymer, is disposed around the edge region of the CCM, for example, on the exposed surface of the ion-conductive membrane where no electrode catalyst is present (however, it often overlaps the edge of the electrode catalyst layer), to provide a seal to prevent leakage of reaction gases and product gases, reinforce and strengthen the edge of the CCM, and provide a suitable surface for supporting subsequent components such as a sub-gasket or an elastomer gasket. An adhesive layer can be present on one or both sides of the seal film layer. 【0008】 The CCM may be incorporated into a membrane electrode assembly (MEA) that is essentially composed of five layers. The central layer is a polymer ion conductive membrane. On either side of the ion conductive membrane, there is an electrode catalyst layer containing an electrode catalyst designed for a specific electrolysis reaction. Finally, adjacent to each electrode catalyst layer, there is a gas diffusion layer or a porous transport layer depending on the final MEA application and stack configuration. Such layers allow reactants to reach the electrode catalyst layer and products to leave. 【0009】 Ion conductive membranes such as PEMs and AEMs are important components of electrochemical devices such as fuel cells and electrolyzers. However, they are subject to significant chemical and mechanical stresses during operation, which can lead to membrane degradation and potentially have an adverse effect on the performance and maintenance costs of fuel cell and electrolyzer stacks. 【0010】 It is known to add cerium-containing compounds to ion conductive membranes. Such additives act as scavengers for reactive oxygen species (ROS) that can cause membrane decomposition. 【0011】 WO 2007 / 120190 (3M Innovative Properties Company) describes the addition of cerium oxide compounds to fuel cell membranes, and the examples show that incorporation of cerium oxide in amounts of 0.25 to 1 wt% can result in improved membrane lifetime and reduced fluoride ion generation (and an indicator of membrane degradation). 【0012】 The use of doped cerium-containing compounds is known. For example, Baker, A.M. et al, July 2017, Journal of Materials Chemistry A 5(29) reports on Ce 0.85 Zr 0.15It has been described that O2 exhibits excellent radical scavenging activity. Venkateshkumar Prabhakaran and Vijay Ramani 2014 J.Electrochem.Soc.161 F1 describe that nitrogen-doped CeO2 has high ROS scavenging activity. 【0013】 Including a cerium-containing compound can pose significant difficulties in achieving the high quality control standards required for ion-conductive membranes during their manufacture, particularly for ion-conductive membranes used in fuel cell and electrolyzer applications, due to the non-uniform distribution of the cerium-containing compound in the formed membrane and / or due to precipitation of particles of the cerium-containing compound during membrane manufacture. 【0014】 There is still a need to further improve and develop methods for producing ion-conductive electrolyte membranes for fuel cells and electrolyzers, as well as devices that facilitate the reproducible production of high-quality membranes and CCMs for electrochemical devices. 【Summary of the Invention】 【0015】 The inventors have confirmed that in-line mixing of a liquid stream containing a cerium-containing compound and an ion-conductive polymer can be advantageously used during the production of ion-conductive membranes for fuel cells and electrolyzers, and that this provides a solution to one or more of the aforementioned problems. 【0016】 Accordingly, in a first aspect of the present invention, there is provided a method for producing an ion-conductive membrane such as a PEM or AEM for a water electrolyzer or a fuel cell, the ion-conductive membrane comprising at least one membrane layer, the method comprising: a) in-line mixing a first liquid stream containing an ion-conductive polymer and a second liquid stream containing a cerium-containing compound to form a coating composition; b) depositing the coating composition onto a substrate to form a membrane layer. 【0017】 The use of in-line mixing provides an improvement in the reproducible quality of the resulting membrane and a reduction in quality control issues associated with the formation of crystalline particles of the cerium-containing compound during manufacture. 【0018】 The methods described herein may be particularly useful for the production of catalytically coated membranes. Thus, according to a second aspect of the invention, there is provided a method of manufacturing a catalytically coated membrane, the method comprising: (i) providing an ion-conductive membrane produced using the method according to the first aspect, the membrane comprising a first surface and a second surface; (ii) forming a catalyst layer on the first surface and / or the second surface of the membrane. 【0019】 Advantageously, the membranes produced by the method of the first aspect and the catalytically coated membranes produced by the method of the second aspect are suitable for use in a water electrolysis cell or a fuel cell. 【0020】 In a third aspect of the invention, there is provided an apparatus for producing an ion-conductive membrane for a water electrolysis cell or a fuel cell, such as a PEM or an AEM, the apparatus comprising: (i) a first source for providing a first liquid stream comprising an ion-conductive polymer; (ii) a second source for providing a second liquid stream comprising a cerium-containing compound; (iii) an in-line mixing device in fluid communication with the first source and the second source, the in-line mixing device being configured to mix the first liquid stream and the second liquid stream to form a coating composition; (iv) a coating device configured to receive the coating composition from the in-line mixing device and coat a substrate with the coating composition to form an ion-conductive membrane layer. 【0021】 The use of such a device can provide an improvement in reproducible film quality and can be used to facilitate the operation of a film production line, in particular, it enables such a line to be easily stopped and started without causing film quality control problems, and thus reduces waste. 【Brief Description of the Drawings】 【0022】 【Figure 1】 A schematic diagram of an embodiment of the device described herein is shown. 【Modes for Carrying Out the Invention】 【0023】 Next, the preferred and / or optional features of the present invention are described. Any of the preferred and / or optional features of any aspect can be combined, either singly or in combination, with any other preferred and / or optional features of any aspect of the present invention, unless otherwise required by the context. 【0024】 The present invention provides a method for producing an ion-conductive membrane, such as a proton exchange membrane or an anion exchange membrane, for use in an electrolytic cell or a fuel cell. The membrane may preferably be a proton exchange membrane for an electrolytic cell or a fuel cell. 【0025】 The method includes the step of in-line mixing a first liquid stream containing an ion-conductive polymer and a second liquid stream containing a cerium-containing compound to form a coating composition. 【0026】 The first liquid stream contains an ion-conductive polymer. Those skilled in the art are aware of suitable ion-conductive polymers for the preparation of ion-conductive membranes. The ion-conductive polymer can be a proton-conductive polymer or an anion-conductive polymer such as a hydroxyl anion-conductive polymer. Examples of suitable proton-conductive polymers include perfluorosulfonic acid ionomers (e.g., Nafion® (E.I. DuPont de Nemours and Co.), Aciplex® (Asahi Kasei), Aquivion™ (Solvay Speciality Polymers), Flemion® (Asahi Glass Co.)), or sulfonated hydrocarbon-based ionomers such as those available from FuMA-Tech GmbH as fumapem® P, E or K series products, and from JSR Corporation, Toyobo Corporation, etc. Examples of suitable anion-conductive polymers include A901 manufactured by Tokuyama Corporation and Fumasep FAA of FuMA-Tech GmbH. 【0027】 Preferably, the first liquid stream contains an ion-conductive polymer dispersed in a mixture of water and a polar solvent other than water. The polar solvent can be a polar protic solvent. Preferably, the polar solvent is an alcohol such as methanol, ethanol, propan-1-ol, propan-2-ol, n-butanol, isobutanol, butan-2-ol, and tert-butyl alcohol, or a mixture thereof. Preferably, the alcohol is ethanol and / or propan-1-ol. In some preferred cases, the first liquid stream contains (or consists essentially of) at least one ion-conductive polymer, water, and an alcohol (such as at least one of ethanol or propan-1-ol). 【0028】 Typically, the weight ratio of water to a polar solvent, such as ethanol and / or propan-1-ol, is in the range of 9:1 to 1:1, for example, 9:1 to 7:3 (including both end values). Those skilled in the art will understand that the solvent ratio can vary depending on the characteristics of the selected ion-conductive polymer. 【0029】 Typically, the first liquid stream contains the ion-conductive polymer in an amount in the range of 5 to 80% by weight, preferably 10 to 50% by weight, preferably 15 to 30% by weight, and most preferably 15 to 20% by weight (including both end values) based on the total weight of the components of the first liquid stream. 【0030】 The second liquid stream contains a cerium-containing compound. Such a compound is selected as a cerium-containing scavenger for reactive oxygen species. Preferably, the cerium-containing compound is a doped or undoped oxide of cerium, or a doped or undoped cerium salt. In some preferred cases, the cerium-containing compound is a doped or undoped oxide of cerium such as doped or undoped cerium(IV) oxide (CeO2). Suitable dopants may be selected from, for example, one or more transition metals such as zirconium, or nitrogen. In some even more preferred cases, the cerium-containing compound is cerium oxide (CeO2). 【0031】 Preferably, the second liquid stream contains the cerium-containing compound in a solvent such as water, or in a mixture of water and a polar solvent other than water, such as a mixture of water and an alcohol, for example, a mixture of water and ethanol and / or propan-1-ol. In some preferred cases, the solvents used in the first and second liquid streams are the same. In some preferred cases, the second liquid stream contains the cerium-containing compound in the form of a colloidal sol. Using the cerium-containing compound in the form of a colloidal sol facilitates dispersion during mixing. Such a colloidal sol can contain additives such as acetic acid and / or nitric acid. 【0032】 Typically, the cerium-containing compound (e.g., doped or undoped cerium oxide) is present in the second liquid stream in an amount of less than 1 wt%, e.g., less than 0.1 wt%, or less than 0.01 wt%, based on the total weight of the components of the second liquid stream. Preferably, the cerium-containing compound (e.g., doped or undoped cerium oxide) is present in the second liquid stream in the range of 0.001 to 0.1 wt% (including both end values), e.g., in an amount of 0.001 to 0.01 wt%, based on the total weight of the components of the second liquid stream. 【0033】 It will be understood that the second liquid stream may contain two or more cerium-containing compounds, e.g., a doped cerium-containing compound and an undoped cerium-containing compound, two doped cerium-containing compounds having different dopants, or a doped or undoped oxide and a doped or undoped salt of cerium. It will also be understood that the second liquid stream may contain two or more forms of cerium-containing compounds, such as dissolved cerium-containing compounds and cerium-containing compounds in the form of colloidal sols. 【0034】 The first and second liquid streams are mixed in-line. Typically, such in-line mixing involves adding the second liquid stream to the flowing first liquid stream. Preferably, the second liquid stream is added at a controlled flow rate in order to achieve the desired amount of the cerium-containing compound in the resulting coating composition. Such controlled addition can be provided, for example, by a metering pump. 【0035】 In-line mixing can be carried out using a static mixer such as a pipe mixer or a plate static mixer. It will be understood that the static mixer may be provided with inlets for the first and second liquid streams, or the first and second liquid streams may be combined and then the combined stream may flow through the static mixer for mixing the components. 【0036】 Those skilled in the art will understand that in-line mixing of the first and second liquid streams is carried out so that sufficient mixing is completed before the coating composition reaches the coating apparatus or other apparatus used in film preparation. 【0037】 Preferably, the ratio of the flow rate of the first liquid stream to the flow rate of the second liquid stream at the time of in-line mixing is in the range of 5:1 to 15:1 (including both end values), for example, in the range of 7:1 to 10:1 (including both end values). 【0038】 After in-line mixing the first and second liquid streams to form a coating composition, the method includes step (b) of depositing the coating composition on a substrate to form a film layer. 【0039】 The coating composition can be deposited using a slot-die coating method (wherein the dispersion is extruded onto the substrate by gravity or under pressure through a slot), a knife coating method, a bar coating method, an inkjet printing method, a gravure printing method, a curtain coating method, a spray coating method, or a casting method. Preferably, the coating composition can be deposited using slot-die coating, bar coating, inkjet printing, or gravure printing. Deposition using slot-die coating may be particularly preferred in some cases. 【0040】 The coating composition is deposited on a substrate to form a film layer. In some cases, the ion-conductive membrane is formed from a single film layer. Alternatively, the ion-conductive membrane may be formed from two or more layers, such as 2 to 7 layers. The number of layers is determined, for example, by the desired thickness of the film and the degree of variation in the desired composition across the entire film (for example, the film may contain one or more layers containing a reinforcing polymer such as ePTFE or an additive such as a recombination catalyst). 【0041】 Typically, the substrate is a backing sheet, a second membrane layer, a catalyst layer on the backing sheet, or a catalyst layer on the gas diffusion electrode. One skilled in the art will understand that the choice of substrate depends on the membrane structure and the production stage. 【0042】 When the membrane is formed from a single membrane 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-conductive membrane during production and can provide support and strength during subsequent storage and / or transportation if not removed immediately. The material used to make the backing layer must provide the necessary support, be preferably compatible with the coating composition, be preferably impermeable to the coating composition, be able to withstand the process conditions associated with the production of the ion-conductive membrane, and be easily removable without damaging the ion-conductive membrane. Examples of suitable materials for use include fluoropolymers such as polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), perfluoroalkoxy polymer (PFA), fluorinated ethylene propylene (FEP - a copolymer of hexafluoropropylene and tetrafluoroethylene), and polyolefins such as biaxially oriented polypropylene (BOPP). 【0043】 In some cases where a catalyst-coated membrane is produced, the catalyst layer is provided on the backing layer, for example, by printing or using known coating techniques. Then, the coating composition can be deposited on the catalyst layer such that the catalyst layer is disposed between the backing layer and the membrane layer formed by depositing the coating composition. The use of the methods and apparatus described herein can be particularly advantageous when the membrane layer is formed on the catalyst layer and can provide a high-quality membrane layer at the interface between the catalyst layer and the ion-conductive membrane. 【0044】 In some cases, typically when the thickness of the ion-conductive membrane is such that multiple steps are required to build the membrane structure, the substrate is a pre-formed membrane layer. It will be understood that the ion-conductive membrane may be formed by successive deposition of layers. By way of example, the ion-conductive membrane can be formed as follows. In a first step, the aforementioned coating composition can be deposited on the backing layer to form a first ion-conductive polymer layer, which is then dried. In a second step, the coating composition is deposited on the first ion-conductive polymer layer to form a second ion-conductive polymer layer. The second ion-conductive polymer layer is then dried. This sequence of application and drying is continued to produce further ion-conductive polymer layers required to form the desired membrane structure. 【0045】 Typically, each layer of the ion-conductive membrane contains a cerium-containing compound, although in some cases it may be desirable to include a membrane layer that does not contain (or has a reduced level of) the cerium-containing compound. In such cases, the use of the devices and methods described herein is beneficial as it allows the operator to simply reduce or stop the flow of the second liquid stream during a particular deposition step. 【0046】 The membranes formed by the methods described herein can be used to produce catalytically coated membranes. In such cases, the method can include the step of forming a catalytic layer on the first and / or second surface of the membrane to form an anode and / or a cathode. Those skilled in the art will understand that the specific type of catalyst for the cathode and anode will be selected depending on, for example, whether the membrane is for a fuel cell or an electrolyzer, and whether the membrane is a PEM or an AEM as described above. Further, the deposition method can be changed, for example, the catalytic layer can be transferred to the membrane from a decal, for example by hot pressing, or the catalytic ink can be printed directly onto the membrane. 【0047】 The present invention also provides an apparatus for the production of ion-conductive membranes. 【0048】 The device comprises a first supply source in fluid communication with an in-line mixing device. The first supply source provides a first liquid stream containing an ion-conductive polymer. Typically, the first supply source is a container containing a dispersion of at least one ion-conductive polymer in a solvent or a mixture of solvents. Preferably, the container is configured to stir the contents, for example, by agitation or shaking. 【0049】 Preferably, the device comprises a first pump configured to transfer the contents of the first supply source to the in-line mixing device as a first liquid stream at a controlled flow rate. Preferably, the device further comprises a filter configured such that the first liquid stream passes through the filter before reaching the in-line mixing device. 【0050】 The device comprises a second supply source in fluid communication with the in-line mixing device. The second supply source provides a second liquid stream containing a cerium-containing compound. Typically, the second supply source is a container containing a cerium-containing compound in a solvent such as water or a mixture of solvents. Preferably, the container is configured to stir the contents, for example, by agitation or shaking. 【0051】 Preferably, the device comprises a second pump configured to transfer the contents of the second supply source to the in-line mixing device as a second liquid stream at a controlled flow rate. Preferably, the device further comprises a filter configured such that the second liquid stream passes through the filter before reaching the in-line mixing device. 【0052】 The device comprises an in-line mixing device configured to mix the first liquid stream and the second liquid stream to form a coating composition. Preferably, the in-line mixing device is configured such that the second liquid stream is added to the flowing first liquid stream. 【0053】 The in-line mixing device may preferably be a static mixer such as a pipe mixer or a plate static mixer. The static mixer can comprise a first inlet for receiving a first liquid stream and a second inlet for receiving a second liquid stream. Alternatively, the device may be configured such that the second liquid stream is added to the first liquid stream and then the combined first and second liquid streams pass through a static mixer. 【0054】 The device comprises a coating device configured to coat a substrate with a coating composition to form an ion-conductive membrane. To avoid misunderstanding, the device is configured such that the outlet of the in-line mixing device is in fluid communication with the inlet of the coating device. The coating device may be any device suitable for forming an ion-conductive membrane on a substrate. Such devices are known to those skilled in the art and include slot die coaters, bar coaters, knife over roll coaters, inkjet printers or gravure printers. 【0055】 The in-line mixing device is preferably disposed in proximity to the inlet of the coating device. The device may preferably be configured such that the transit time of the coating composition between the outlet of the in-line mixing device and the inlet of the coating device is less than 60 seconds, such as less than 30 seconds, less than 15 seconds, or less than 10 seconds. The device may preferably be configured such that the transit time of the coating composition between the outlet of the in-line mixing device and the inlet of the coating device is within the range of 1 to 60 seconds (including both end values), preferably within the range of 1 to 30 seconds (including both end values), or within the range of 1 to 10 seconds (including both end values). 【0056】 Typically, the device comprises a device for drying the membrane layer after formation by the coating device. Such devices are known to those skilled in the art and include ovens and infrared dryers. 【0057】 The device may preferably comprise an analytical device for analyzing the chemical composition of the film layer after formation, in particular the cerium content in the film when the film is produced. Suitably, the device is an X-ray fluorescence (XRF) detector. Advantageously, the device is configured such that the flow rate of the second liquid stream is automatically adjusted based on the cerium content detected in the film by the analytical device. 【0058】 Preferably, the device further comprises a purge line configured to enable removal of the coating composition from a portion of the device downstream of the static mixer (and upstream of the coating device). This enables the coating composition to be discharged from the device when the device is stopped or during the coating operation, avoiding the problem that cerium-containing compounds may crystallize during periods when the device is not being operated. 【0059】 Figure 1 shows an embodiment of an apparatus (1) for the production of an ion-conductive membrane. The apparatus (1) comprises a first tank (2) that functions as a source of a dispersion of an ion-conductive polymer in a solvent (e.g., a mixture of water and ethanol), and a second tank (3) that functions as a source of cerium oxide in a solvent (such as a mixture of water and ethanol). A first pump (4) pumps the dispersion of the ion-conductive polymer from the tank (2), optionally through an in-line filter (5), towards a static mixer (6). A second pump (7) pumps the cerium-containing stream, optionally through an in-line filter (8), towards the static mixer (6). The first pump (4) and the second pump (7) are preferably controlled by a human-machine interface (9) that can be used, for example, to adjust the flow rate. The apparatus may include means (10) for diverting the flow of the dispersion of the ion-conductive polymer back to the tank (2). The static mixer (6) mixes the two liquid feeds to form a coating composition, which proceeds to a coating head (11) of a coating device such as a slot die coater, and this coating head deposits the coating composition onto a substrate to form a membrane, for example, on a backing layer. The membrane is dried after formation by passing it, for example, through a heater (not shown in Figure 1) at a temperature of 80 °C to remove the solvent. The apparatus comprises a valve (12) connected to a purge line that enables purging of the line between the static mixer and the coating head, and it is preferred that when the coating line stops, the mixed composition can be discarded before the apparatus is restarted. The formed membrane is analyzed in situ by an X-ray fluorescence analyzer (13) that determines the cerium content of the membrane. Advantageously, the apparatus (1) is configured such that the speed of the first pump (7) is automatically adjusted based on data from the X-ray fluorescence analyzer (13).

Claims

[Claim 1] A method for producing an ion-conducting membrane for a water electrolytic cell or fuel cell, wherein the ion-conducting membrane comprises at least one membrane layer, and the method is (a) A step of mixing in-line a first liquid stream containing an ion-conducting polymer and a second liquid stream containing a cerium-containing compound to form a coating composition, (b) A method for producing an ion-conducting membrane for a water electrolytic cell or fuel cell, comprising the step of depositing the coating composition onto a substrate to form a film layer. [Claim 2] The method according to claim 1, wherein the first liquid stream comprises a dispersion of an ion-conducting polymer in a mixture of water and a polar solvent other than water. [Claim 3] The method according to claim 1, wherein the second liquid stream contains the cerium-containing compound in the form of a colloidal sol. [Claim 4] The method according to claim 1, wherein the cerium-containing compound is a cerium-doped or undoped oxide. [Claim 5] The method according to claim 1, wherein the substrate is selected from a backing sheet, a second film layer, or a catalyst layer on a backing sheet. [Claim 6] The method according to claim 1, wherein the in-line mixing in step (a) is performed using a static mixer. [Claim 7] The method according to claim 1, wherein the ratio of the flow rate of the first liquid flow to the flow rate of the second liquid flow is within the range of 7:1 to 15:1 (including both endpoints). [Claim 8] (c) The method according to claim 1, further comprising the step of drying the film layer. [Claim 9] (d) A step of depositing the coating composition on the film layer to form an additional film layer, (e) The method according to claim 1, further comprising the step of drying the additional film layer. [Claim 10] The method according to claim 9, wherein steps (d) and (e) are repeated 1 to 6 times. [Claim 11] The method according to claim 1, wherein the ion-conducting membrane is a proton exchange membrane. [Claim 12] A method for producing a catalyst-coated film, (i) Providing an ion-conductive film produced according to any one of claims 1 to 11, wherein the film includes a first surface and a second surface; (ii) A method comprising the step of forming a catalyst layer on the first surface and / or the second surface of the film. [Claim 13] The method according to claim 12, further comprising the step of applying a sealing material to the first surface and / or the second surface of the catalyst-coated film. [Claim 14] The method according to claim 12, further comprising the step of applying a gas diffusion layer and / or a porous transport layer to the first surface and / or the second surface of the catalyst-coated film. [Claim 15] An apparatus for generating ion-conducting membranes for fuel cells or electrolytic cells, (i) A first source for providing a first liquid flow containing an ion-conducting polymer, (ii) A second source for providing a second liquid stream containing a cerium-containing compound, (iii) an in-line mixing device configured to be in fluid communication with the first supply source and the second supply source, and to mix the first liquid flow and the second liquid flow to form a coating composition, (iv) A coating apparatus configured to receive the coating composition from the inline mixing device and to coat a substrate with the coating composition to form an ion-conductive film layer. [Claim 16] The apparatus according to claim 15, wherein the in-line mixing device is a static mixer. [Claim 17] The apparatus according to claim 15 or 16, wherein the coating apparatus is a slot die coater, a bar coater, an inkjet printer, or a gravure printer. [Claim 18] The apparatus according to claim 15 or 16, further comprising an analytical device for analyzing the cerium content in the film layer when the film layer is formed. [Claim 19] The apparatus according to claim 18, wherein the apparatus is configured such that the flow rate of the second liquid flow is automatically adjusted based on the cerium content detected in the film layer by the analytical device. [Claim 20] The apparatus according to claim 15 or 16, wherein the apparatus is configured such that the passage time of the coating composition between the outlet of the inline mixing device and the inlet of the coating apparatus is less than 60 seconds, for example, less than 30 seconds or less than 10 seconds.

Images