Coating of cation exchange membranes

Abstract

This invention relates to the coating of cation exchange membranes with catalytically active materials. Catalytically coated cation exchange membranes are used in electrochemical cells, particularly fuel cells, specifically proton exchange membrane fuel cells (PEMFCs), or electrolytic devices for water electrolysis, specifically polymer electrolyte membrane water electrolysis (PEMWEs). To overcome the shortcomings of conventional transfer methods, there has been a need for an alternative coating method for cation exchange membranes that enables the transfer of electrocatalysts without using high temperature, high pressure, or PFAS-based substrates. Surprisingly, it was found that treating the catalyst layer with a solvent that swells the cationic conductive polymer immediately before the transfer process significantly simplifies the transfer.

Description

【Technical Field】 【0001】 The present invention relates to the coating of cation exchange membranes with catalytic active substances. The catalytically active coated cation exchange membranes are used in electrochemical cells, particularly fuel cells, specifically proton exchange membrane fuel cells (PEMFCs), or electrolyzers for water electrolysis, specifically polymer electrolyte membrane water electrolysis (PEMWE). In PEMFCs and PEMWEs, the membrane alone conducts the exchange of positively charged hydrogen atoms H + (also called protons). Therefore, in the present invention, the cation exchange membrane is also a proton exchange membrane. 【Background Art】 【0002】 In both water electrolysis and fuel cells, a thin catalyst layer is required on the electrode / membrane surface to enhance efficiency. The catalyst, which promotes the electrochemical reaction in the cell, is also called an electrocatalyst. The production of the catalyst-coated membrane, which is the core of the electrolyzer and fuel cell, has a decisive impact on the cost of both technologies and thus on their economic viability. 【0003】 Today, the standard method for coating cation exchange membranes with electrocatalysts is the so-called "decal method". In this method, first, particulate electrocatalysts are mixed with a thermoplastic adhesion promoter to prepare a coating composition, which is applied to a transfer substrate (usually a film made of PTFE (polytetrafluoroethylene)). Next, the coated transfer substrate is pressed and heated together with the cation exchange membrane. The thermoplastic material melts and bonds the catalyst particles to the membrane. Thereafter, the transfer substrate is peeled off from the membrane like a decal and discarded. Only the coating containing the adhesion promoter and the catalyst particles immobilized thereon remains on the membrane. 【0004】 The decal method enables the production of catalyst coating films (CCMs) using a roll-to-roll process, which is essential for industrial mass production. In this method, the catalyst layer is continuously coated onto a decal film (named "decal") by a printing method, dried, and then transferred to a polymer film by heat pressing. This film is composed solely of cationic conductive polymers. These are typically sulfonated perfluoropolymers, such as Nafion® from The Chemours Company (Wilmington, Delaware, USA). 【0005】 A comprehensive explanation of the decal method is provided in the following paper: KIT Scientific Publishing, 2015. DOI: 10.5445 / KSP / 1000045306 【0006】 However, the decal method requires stringent conditions. Conventional method parameters are transfer temperature: approximately 150°C, pressure: several megapascals, and pressing time: several minutes. 【0007】 Furthermore, in practice, only polyfluoroalkyl compounds (PFAS), particularly polytetrafluoroethylene (PTFE), are used as transfer substrates. These are indispensable because their low surface energy results in good transferability of the electrode layer, and they also have excellent heat resistance. 【0008】 One example of this method is described in Chinese Patent Application Publication No. 113745538, in which a catalyst layer moistened with water is transferred from a PTFE transfer substrate to a proton exchange membrane at a temperature of 180°C and a pressure of 0.1 MPa. 【0009】 U.S. Patent Application Publication No. 2010 / 183804 describes a method for manufacturing a membrane electrode unit (MEA) by applying a Nafion®-containing catalyst ink to a Teflon® transfer substrate and drying it. Subsequently, a swelling agent is applied to the catalyst ink, and the MEA is pressed at a temperature of less than 150°C and a pressure of 0.25 to 3 MPa. The drawbacks of this method are the harsh conditions and the need for a fluorine-containing transfer substrate. 【0010】 While these method parameters allow for a continuous process, the relatively high temperatures (the temperatures required to reach the glass transition temperature of the polymer film), pressure, and residence time make this method inefficient. In addition, PFAS-based substrates are expensive and practically unrecyclable. The use of perfluoropolymers as "disposable" materials is increasingly viewed critically due to potential ecological impacts. [Prior art documents] [Patent Documents] 【0011】 [Patent Document 1] Chinese Patent Application Publication No. 113745538 Specification [Patent Document 2] U.S. Patent Application Publication No. 2010 / 183804 [Overview of the project] [Problems that the invention aims to solve] 【0012】 To overcome the shortcomings of conventional decal methods, there was a need for an alternative coating method for cation exchange membranes that could transfer electrode catalysts without using high temperatures, high pressures, or PFAS-based substrates. 【0013】 European Patent Application No. 23164605, which was unpublished at the time of filing, describes a method for coating an anion exchange membrane. This method deals with positively charged ionomers that naturally repel cations and is therefore unsuitable for the production of cationic conductive membranes. 【0014】 Surprisingly, it was found that treating the catalyst layer with a solvent that swells the cationic conductive polymer immediately before the transfer process significantly facilitated the transfer. [Means for solving the problem] 【0015】 Therefore, the present invention is a) A step of preparing a flat cation exchange membrane containing a membrane material or containing only a membrane material, b) A step of preparing a first flat transfer substrate coated with the first composition on at least one side, wherein the first composition comprises at least one first polymer and at least one first catalytically active substance or catalytically activatable substance, c) A step of preparing a first swelling agent that is at least partially liquid, d) A step of applying the first swelling agent to the first composition and / or the cation exchange membrane, g) A step of swelling the first polymer with the first swelling agent, e) A step of pressing the first composition onto a cation exchange membrane in the presence of a first transfer substrate, wherein the temperature of the first composition at the time of pressing is -90°C to 100°C. f) A step of peeling the first transfer substrate from the first composition to obtain a cation exchange film on which the first composition is coated on one side. This invention provides a method for coating a cation exchange membrane that has these properties in a non-time-series manner. The present invention provides such a method. 【0016】 Due to swelling, the catalyst layer can be transferred even if the temperature is below the glass transition temperature of the polymer film. The temperature of the first composition and / or the second composition during pressing is preferably -30°C to 80°C, or -15°C to 70°C. The temperature of the first composition is particularly room temperature, i.e., about 10°C to 30°C. 【0017】 Furthermore, the transfer can be performed even at relatively low pressures. The pressure applied during pressing should be between 0.001 MPa and 0.15 MPa. Preferably, pressing is performed at a pressure of 0.01 MPa to 0.1 MPa. 【0018】 Furthermore, by this method, the printed catalyst layer can be transferred onto a conventional non-fluorinated film, such as a PET film, which brings great economic and environmental advantages. 【0019】 A swelling agent is a substance that is at least partially in a liquid state and swells the polymer upon contact with the polymer present in the composition. "Swelling" is understood to mean that the swelling agent penetrates into the polymer and the polymer expands. Thus, while the swelling agent penetrates the polymer, the volume of the polymer continuously increases upon contact with the swelling agent. As a result, swelling is a process that takes a certain amount of time. The swelling agent also includes substances or mixtures of substances that dissolve the polymer. The contact between the polymer and the swelling agent occurs when the swelling agent is applied to the composition or during pressing. Thus, swelling can be carried out simultaneously with application and / or pressing, but it can also be carried out at an earlier or later point. The order of the steps is not important. In particular, swelling does not have to be carried out alone and can also be carried out simultaneously with other steps. The method may also include a waiting stage that gives the swelling agent time to swell the polymer. A chemical reaction between the swelling agent and the polymer is not essential during swelling, but it is not excluded either. In particular, the swelling agent may partially or completely dissolve the polymer. It is important that the swelling agent is at least partially in a liquid state when it comes into contact with the polymer. This promotes swelling. The swelling agent may be partially present in the gas phase, but in that case, the contact efficiency with the polymer decreases and the swelling rate slows down. Therefore, using a liquid swelling agent is important for achieving high process efficiency. 【0020】 As described above, the transfer of the catalyst-containing composition from the transfer substrate to the cation exchange membrane is promoted by performing swelling immediately before pressing. For this reason, the swelling agent is preferably applied at a point before pressing, that is, at a time interval that is sufficient for the swelling operation but does not last for a long time. Thus, the swelling agent is applied as late as possible, but early enough when necessary. 【0021】 In any case, it is too early to prepare the first swelling agent in the composition. This is because there will be an inconvenience that an interaction between the first swelling agent and the first polymer occurs well before pressing, resulting in the possibility that the composition may peel off from the transfer substrate early or the first polymer may dissolve. This is a concern especially when the coated transfer substrate is prepared at a manufacturing site different from pressing. Therefore, according to the present invention, the swelling agent is prepared outside the first composition, that is, separately. The interaction between the first swelling agent and the first polymer can occur only when the first swelling agent is applied to the first composition and / or on the cation exchange membrane. By selecting the application timing, the duration of the interaction between the first swelling agent and the first polymer can be optimally controlled. 【0022】 In the simplest case, the first composition is solid at the time of applying the first swelling agent. When the swelling agent is applied to the dry composition, the solid coating on the transfer substrate softens and transfer becomes easier. 【0023】 Except for the swelling step and the processing temperature, the series of methods according to the present invention is similar to the decal method. However, since a partially liquid swelling agent is used, the method according to the present invention is considered a wet method. Nevertheless, since only a small amount of the swelling agent is used and it evaporates over time under ambient conditions, a drying step that takes a long time and consumes a large amount of energy can be omitted. This is particularly applicable to swelling agents with a low boiling point such as ethanol. 【0024】 The method according to the present invention generally uses a cation exchange membrane in a flat shape. In this specification, "flat" is understood to mean that the height (i.e., thickness) of the cation exchange membrane is much smaller than the length and width. Therefore, the cation exchange membrane is substantially two-dimensional. Any embossing on the membrane surface does not change its flat shape. Therefore, the cation exchange membrane is a flat membrane. The transfer substrate is also flat in the same way. 【0025】 In the method according to the present invention, at least one side of the cation exchange membrane is coated with the first composition. Since the cation exchange membrane is typically used in an electrochemical cell having two compartments separated by the membrane, each compartment filled with an electrocatalyst, it is reasonable to coat both sides of the cation exchange membrane. More precisely, the cation exchange membrane is coated on one side with the first composition and on the other side with the second composition. In this case, for example, the first composition contains a catalyst for the cathode reaction, and the second composition contains a catalyst for the anodic reaction. The method according to the present invention makes this possible simultaneously and sequentially. 【0026】 In a preferred advanced form of the present invention, this method is h) A step of preparing a second flat transfer substrate coated with the second composition on at least one side, wherein the second composition comprises at least one second polymer and at least one second catalytically active substance or catalytically activatable substance, i) A step of preparing a second swelling agent that is at least partially liquid, j) A step of applying the second swelling agent to the second composition and / or the cation exchange membrane, k) A step of swelling the second polymer with the second swelling agent, l) A step of pressing the second composition onto a cation exchange membrane in the presence of a second transfer substrate, wherein the temperature of the second composition at the time of pressing is -90°C to 100°C. m) A step of peeling the second transfer substrate from the second composition to obtain a cation exchange film in which the first composition is coated on one side and the second composition is coated on the other side. It also has, in a non-chronological order. 【0027】 Therefore, such a method is intended for double-sided coating of a cation exchange membrane. That is, the first composition is coated on one side and the second composition is applied to the other side. The first and second compositions preferably differ in their formulations, and in particular, they may differ in terms of the catalyst present. However, the two compositions may be substantially identical. 【0028】 It is preferable that the pressing of the first composition against the cation exchange membrane is carried out in the presence of the second transfer substrate, and the pressing of the second composition against the cation exchange membrane is carried out in the presence of the first transfer substrate. Therefore, both compositions are pressed simultaneously with the membrane. This increases the efficiency of the method. 【0029】 The pressure applied during pressing should be between 0.001 MPa and 0.15 MPa. Preferably, pressing is performed at a pressure of 0.01 MPa to 0.1 MPa. The specified pressure range applies to both pressing the first composition against the cation exchange membrane and pressing the second composition against the cation exchange membrane. When both compositions are pressed simultaneously in the presence of their respective transfer substrates, the same pressure is inevitably applied to the entire laminate. In this regard, it should be noted that conventional decal methods are performed at pressures of 0.3 MPa to 10 MPa. Therefore, the method of the present invention applies a much lower pressure. 【0030】 There are various options for applying the first swelling agent. The first swelling agent may be applied to the first composition only, to the cation exchange membrane only, or to both. Similar options are available when using the second swelling agent. The application site is selected based on the swelling behavior of the swelling agent in the relevant polymer. The swelling agent is best applied to the location where the transfer substrate and / or cation exchange membrane are located immediately before pressing. The application time should be selected so that swelling occurs to the desired extent but does not last longer than necessary. 【0031】 Furthermore, a special advantage of the method according to the present invention is that the transfer substrate can be peeled off very easily from the swollen polymer. Therefore, according to the method according to the present invention, a transfer substrate made of a fluorine-free polymer can be used. In known decal methods, a fluoropolymer film, such as PTFE, is generally used as the transfer substrate to reduce adhesion and facilitate peeling. Since the transfer substrate is usually discarded, the use of fluoropolymers is an environmental concern. However, the method according to the present invention can use a transfer substrate made of a harmless and inexpensive fluorine-free polymer, such as polyethylene (PE), polypropylene (PP), or polyethylene terephthalate (PET). Therefore, a particular embodiment of the present invention is characterized in that at least one transfer substrate mainly comprises only a fluorine-free polymer. 【0032】 When coating both sides, one option is to use the same swelling agent on both sides. Thus, the first swelling agent corresponds to the second swelling agent. In its simplest form, "corresponds" is understood to mean that the first and second swelling agents are the same chemical substance. However, in practical application, these swelling agents are used not as pure substances, but at industrial-grade quality. This means that the swelling agents are used with impurities or incidental substances resulting from technical reasons (e.g., 98% ethanol and 2% water, because it is impossible to completely remove water from ethanol at an acceptable cost). If the first swelling agent is used at a different industrial grade than the second swelling agent, but the same substance is present in both, then, in the sense of the terms used herein, the first swelling agent corresponds to the second swelling agent. Therefore, two batches of swelling agents with different water content in ethanol can correspond for the purposes of this invention, even if the two batches are not completely identical. The important thing is that the same substance, e.g., ethanol, is used. In this example, the difference in water content is not important. 【0033】 Similarly, with respect to the first polymer, one option is that it matches the second polymer. The presence of impurities in the polymer for technical reasons is not important. Polymers may match each other if they have the same repeating units but different chain lengths. The first and second polymers preferably have the same repeating units. 【0034】 The polymer swelled with the swelling agent is preferably a cationic conductive polymer, i.e., an ionomer. Therefore, the first polymer and / or the second polymer are cationic conductive. While it is possible to use a nonionic conductive polymer as an adhesion promoter to fix the catalyst onto the film, this is not recommended considering the efficiency of the cells thus produced. 【0035】 In this method, it is preferable, ideally universally, to use a sulfonated perfluoropolymer as the cationic conductive polymer. It is preferable to use the same cationic conductive polymer in the first and / or second composition as the first / second polymer for immobilizing the catalytic active substance. It is particularly preferable to use a cationic conductive polymer having the same repeating units in the composition and as a membrane material. Therefore, the anionic conductivity of the membrane is derived from the intrinsic properties of the cationic polymer. The chain lengths of the cationic polymers having the same repeating units may differ. 【0036】 It is particularly preferable to use the same cationic conductive polymer present in the cation exchange membrane to immobilize the catalyst on the membrane. This reduces the number of materials that need to be used. Therefore, a preferred modification of the present invention is characterized in that the cation exchange membrane contains a cationic conductive polymer or contains only a cationic conductive polymer, and this cationic conductive polymer is identical to the first polymer and / or the second polymer. 【0037】 Using fluorine-free polymers as transfer substrates is particularly advantageous when the transfer substrates are not reused and are discarded after peeling. This is because fluorine-free transfer substrates made of PP, PE, or PET are relatively easy to dispose of or recycle and do not require hydrofluorocarbons in their manufacture. In addition, PP, PE, or PET films are less expensive than conventional PTFE transfer substrates. 【0038】 In a particularly preferred embodiment, the method according to the present invention is carried out as a roll-to-roll method. This means that the starting material is at least partially provided in a ribbon shape on a spool, and the target product is also obtained in a ribbon shape on a spool. The ribbon-shaped material moves continuously from roll to roll during the process. Therefore, this method is particularly productive. Specifically, in the roll-to-roll method according to the present invention, at least one rotating spool is wound up or unwound during operation, and the spool is i) A spool equipped with a ribbon-shaped cation exchange membrane, ii) A spool from which a coated cation exchange membrane is obtained in the shape of a ribbon, iii) A spool on which the transfer substrate is arranged in a ribbon shape. It is selected from the group that includes it. 【0039】 Preferably, two or three of the spools are wound up or unwound. In the roll-to-roll method, each step of the method is performed continuously along the supply direction of the ribbon-like material, but from an overall perspective, since the roll-to-roll method is a continuous method, each step is performed simultaneously. 【0040】 Alternatively, this method may be carried out in a batch manner using non-ribbon-shaped, non-moving material. 【0041】 Advantageously, in a roll-to-roll system, pressing is performed using a pair of rollers whose positions are fixed. At least one of the rollers in the pair rotates or rolls on the aforementioned ribbon-shaped transfer substrate. This allows the compressive force required for pressing to be continuously applied to the transfer substrate, improving manufacturing quality. 【0042】 A particular advantage of this method is that it can be carried out at a lower temperature compared to conventional decal methods. As a result, it is not necessary to heat the rollers individually. In conventional decal methods, heated rollers are generally used to soften the ionomer. In this method, this heating is unnecessary due to the swelling effect. Therefore, in a preferred embodiment of the present invention, the rollers of the roller pair are not heated. 【0043】 In the roll-to-roll method, peeling is performed using at least one fixed peeling roller. The peeling roller rolls or rotates on the aforementioned ribbon-shaped transfer substrate. This results in more stable peeling and improved productivity and quality. 【0044】 In the method according to the present invention, a cation exchange membrane is coated with at least one electrocatalyst-containing composition. An electrocatalyst is a substance that acts as a catalyst in an electrochemical reaction, or can be activated to act as a catalyst. According to current research, the following elements can be used in this method, either in their pure form or as oxides, hydroxides, or hydroxide oxides: iridium (Ir), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), ruthenium (Ru), copper (Cu), molybdenum (Mo), zinc (Zn), lead (Pb), manganese (Mn), tungsten (W), platinum (Pt), sulfur (S), tin (Sn), gold (Au), silver (Ag), palladium (Pd), rhenium (Re), and rhodium (Rh). These elements are useful as electrocatalysts, either individually or in combination, either in their pure form or as oxides, hydroxides, or hydroxide oxides. 【0045】 As an electrocatalyst, it is particularly preferable to use a composition containing platinum or a platinum alloy (Pt / C) supported on carbon, or an iridium-based supported or unsupported catalyst. Preferred supporting materials for iridium-based catalysts are antimond-doped tin oxide (ATO) and niobium or tantalum-doped titanium oxide. 【0046】 The swelling agent used in this method is selected to at least swell the polymer or ionomer in the coating composition. Since ionomers used in water electrolysis and water synthesis must, in principle, have high water absorption resistance, aqueous swelling agents are generally unsuitable. Organic swelling agents are more suitable. The following swelling agents have proven particularly suitable: methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), isopropanol (IPA), methanol (MeOH), and ethanol (EtOH). These swelling agents can be used alone or in combination. Dimethyl sulfoxide (DMSO) and / or ethanol (EtOH) are particularly preferred. The last swelling agent mentioned not only fully achieves its purpose but is also relatively safe for the human body, making it easier to handle and process. The swelling agent may be mixed with a substance that does not swell the polymer, or does not swell it sufficiently (e.g., water). 【0047】 Preferably, the swelling agent, its amount used, and its contact time are selected to not only swell each polymer but also to cause initial dissolution. Dissolution is understood to mean neutralizing the intermolecular bonds within the polymer. Swelling is always performed before dissolution of the polymer. Therefore, the transition from polymer swelling to dissolution is often a matter of contact time. In this specification, initial dissolution refers to the dissolution of the polymer in a thin boundary layer in contact with the swelling agent. When the polymer is initially dissolved, the transfer ribbon can be peeled off particularly easily. Therefore, in a preferred development of the present invention, the first swelling agent dissolves the first polymer at least partially, and / or the second swelling agent dissolves the second polymer at least partially. 【0048】 It is particularly preferable to use a combination of a cationic conductive polymer, an organic substance as a swelling agent, namely a sulfonated perfluoropolymer, and dimethyl sulfoxide and / or ethanol as a swelling agent. 【0049】 The mass ratio q / p of the swelling agent to the cationic conductive polymer is preferably 0.01 to 2. In this case, q is understood to mean the mass of the swelling agent applied to the cationic conductive polymer, and p is understood to mean the mass of the cationic conductive polymer. If the ratio amount of swelling agent used is small, the process can be carried out without separate drying. 【0050】 In the method according to the present invention, it is not necessarily required to directly coat the cation exchange membrane with the composition. It is also possible to use a cation exchange membrane that has been pre-coated. The composition is applied to the pre-coating. The pre-coating is then placed between the actual cation exchange membrane and the catalytically active coating. The pre-coating can improve the adhesion of the electrocatalyst to the membrane. Therefore, in one modification of the method according to the present invention, the cation exchange membrane has at least one pre-coating, and the composition is applied to the pre-coating. 【0051】 A cation exchange membrane coated according to the present invention can be attached to an electrochemical cell, particularly a catalytic coating membrane (CCM). The electrochemical cell may be a PEM electrolytic device or a PEM fuel cell. The electrolytic device may be used for the electrolysis of water. A PEM fuel cell is used to convert chemical energy into electrical energy by synthesizing hydrogen and oxygen into water. 【0052】 Exemplary embodiments of the method according to the present invention will be described in more detail with reference to the drawings. The drawings are as follows: [Brief explanation of the drawing] 【0053】 [Figure 1]Figure 1 is a schematic diagram of the roll-to-roll system. [Figure 2] Figure 2 is a photograph of the coating of the transfer substrate with the composition. [Figure 3] Figure 3 is a photograph of a film (transparent film) fixed onto a stainless steel disc. [Figure 4] Figure 4 is a photograph showing the catalyst coating of a coated transfer substrate being wetted with a swelling agent (ethyl alcohol in this specification). [Figure 5] Figure 5 is a photograph of the film before pressing, with the coated transfer substrate attached. [Figure 6] Figure 6 is a photograph of a transfer made by pressing. [Figure 7] Figure 7 shows, on the left, a photograph of the catalyst coating film after successful transfer and removal of the transfer substrate, and on the right, a photograph of the transfer substrate without the catalyst after removal from the catalyst coating film. [Figure 8] Figure 8 shows photographs of transfers that were almost completely unsuccessful without the use of a swelling agent. The left side shows a transfer film that is almost completely coated with the catalyst, while the right side shows a film where the catalyst layer has not been transferred sufficiently. 【0054】 Figure 1 schematically shows the sequence of the method according to the present invention. The illustrated method is a roll-to-roll method. 【0055】 The first spool 1 is equipped with a flat, ribbon-shaped cation exchange membrane 2. The cation exchange membrane 2 is composed solely of a cationic conductive polymer (ionomer). The cation exchange membrane 2 is unwound from the first spool 1. 【0056】 The second spool 3 comprises a first transfer substrate 4. The first transfer substrate 4 is a flat ribbon of polyethylene terephthalate (film) coated on one side thereof with the first composition 5. The coating with the first composition 5 is dry, i.e., solid, at the time of supply. The first composition 5 comprises the same cationic conductive polymer (ionomer) that constitutes the cation exchange membrane 2, and a first electrocatalyst dispersed therein. The electrocatalyst is a substance that catalyzes, for example, the electrolysis or synthesis of water. More precisely, the electrocatalyst present in the first composition 5 catalyzes the cathode reaction in an electrolytic cell or fuel cell. 【0057】 The first transfer substrate 4 is unwound from the second spool 3 and comes into contact with the cation exchange membrane 2 by the first contact roller 6. 【0058】 Similarly, the second transfer substrate 7 is unwound from the third spool 8 and comes into contact with the cation exchange membrane 2 by the second contact roller 9. The second transfer substrate 7 supports a second composition 10 which contains the same ionomer but a different electrocatalyst. This different electrocatalyst catalyzes the anodic reaction. 【0059】 The first transfer substrate 4 is in contact with the upper surface of the cation exchange membrane 2, while the second transfer substrate 7 is in contact with the lower surface of the cation exchange membrane 2. The two rollers 6 and 9 are in contact simultaneously at the same point in the passage path of the cation exchange membrane. 【0060】 Immediately before the two transfer substrates 4 and 7 come into contact with the cation exchange membrane 2, the two compositions 5 and 10 are sprayed with the swelling agent 11, respectively. The swelling agent 11 is a liquid organic substance that swells the ionomer. The same swelling agent 11 is used for both compositions 5 and 10. It is also conceivable to use different swelling agents for the two compositions, namely the first swelling agent for the first composition 5 and the second swelling agent for the second composition 10. However, since both compositions contain the same cationic conductive polymer, it is reasonable to use the same swelling agent 11 for both compositions 5 and 10. 【0061】 The two compositions 5 and 10 swell after the liquid swelling agent 11 is sprayed onto them. More precisely, the swelling agent 11 penetrates the ionomers, causing the ionomers present in both compositions to swell. 【0062】 Using a pair of rollers 12 and 13 with fixed positions, a first transfer substrate 4 having the first composition 5 and a second transfer substrate 7 having the second composition 10 are pressed against the cation exchange membrane 2. The two rollers 12 and 13 roll over a layered structure consisting of the two transfer substrates 4 and 7 and the cation exchange membrane 2 positioned between them. During this process, the two rollers 12 and 13 press against each other with a force F that presses the two swelling compositions 5 and 10 against the cation exchange membrane 2. The pressing force F acts perpendicular to the plane on which the cation exchange membrane 2 extends. This force acts through the two transfer substrates 4 and 7. The two transfer substrates 4 and 7 isolate the two rollers of the roller pair 12 and 13 from the compositions 5 and 10, preventing contamination. 【0063】 The pressing of the two compositions 5 and 10 onto the cation exchange membrane 2 is performed at room temperature. The rollers of roller pairs 12 and 13 are not heated. 【0064】 As a result of pressing, a ribbon-shaped sandwich body 14 having the following layer structure (from top to bottom) is obtained. - First transfer substrate 4 -First composition 5 - Cation exchange membrane 2 -Second composition 10 - Second transfer substrate 7 【0065】 Since the same ionomer is used in both compositions 5 and 10 and in the cation exchange membrane 2, the movement from the first composition 5 to the cation exchange membrane 2 and then to the second composition 10 is fluid. In principle, the first electrocatalyst accumulates on the upper surface of the cation exchange membrane 2, and the second electrocatalyst accumulates on the lower surface of the cation exchange membrane 2. The ionomer fixes catalyst particles on both sides of the membrane 2 while simultaneously establishing cation conduction connections between catalyst particles and through the membrane 2. 【0066】 After pressing the two compositions 5 and 10 onto the cation exchange membrane 2, the two transfer substrates 4 and 7 become unnecessary. The transfer substrates 4 and 7 are peeled off from the sandwich body 14 using two peeling rollers 15 and 16, leaving a cation exchange membrane 17 coated with electrocatalyst on both sides. This is the target product of this method. The coated cation exchange membrane 17 is wound onto the fourth spool 18. 【0067】 The two transfer substrates 4 and 7, after peeling, are also wound onto the 5th and 6th spools 19 and 20. 【0068】 When the first spool 1 is empty, the method is stopped and the two spools 19 and 20 containing the peeled transfer substrates 4 and 7 are discarded. Since these are PET films, they can be easily discarded. The fourth spool 18 containing the coated cation exchange membrane 17 is the target material in the container. A protective film (not shown) may be provided on the coated cation exchange membrane 17 when winding it onto the fourth spool 18, if necessary. The protective film prevents damage to the coating. One option is to use one or both of the peeled transfer substrates 4 and 7 as a protective film, thereby saving material and reducing waste generation. For example, if the peeled second transfer substrate 7 is used as a protective film, it is not wound onto the sixth spool 20, but rather wound onto the fourth spool 18 together with the coated cation exchange membrane 17. 【0069】 Next, a new first spool 1 equipped with an uncoated cation exchange membrane 2, a new second spool 3 equipped with a new first transfer substrate 4 and a new first composition 5, and a new third spool 8 equipped with a new second transfer substrate 7 and a new second composition 10 are prepared. The method is then started anew. 【0070】 By using the roll-to-roll method described in this way, an electrocatalyst is efficiently coated on both sides of a flat, ribbon-shaped cation exchange membrane 2, thereby obtaining a flat, ribbon-shaped cation exchange membrane 17 with coatings on both sides. 【0071】 This is cut to a predetermined size and placed in an electrolytic cell / fuel cell such that the anodic reaction catalyst surface of the coated cation exchange membrane 17 faces the anode and the other surface faces the cathode (not shown). The resulting electrolytic cell is used for PEM-type electrochemical decomposition of water into oxygen and hydrogen (PEMWE). Meanwhile, a fuel cell (PEMFC) manufactured in the same manner is used to convert the chemical energy stored in hydrogen and oxygen into electrical energy. [Examples] 【0072】 The transfer process for PEM applications is described below, using a platinum / carbon-based catalyst layer as an example. The effects obtained by the present invention will be experimentally demonstrated. The cationic conductive polymer or proton conductive (anionic) polymer used is Nafion®. Nafion® was used as both a membrane (Nafion N115) and an ionomer (D2021 Nafion® solution). 【0073】 1. Preparation of the composition A screw-cap jar was filled to one-third capacity with yttrium-stabilized zirconium oxide pulverized balls (5 mm in diameter). Next, 9 parts by weight of ionomer solution (D2021 Nafion® solution) was added to the screw-cap jar and diluted with 82 parts by weight of 1-propanol. Finally, 9 parts by weight of platinum-supported carbon catalyst (Pt / C=1 / 1) was added in the absence of oxygen and pre-dispersed using a shaker. The ink was then dispersed in the screw-cap jar using a roller mixer for 72 hours. 【0074】 2. Coating of the transfer substrate with the composition The composition prepared in step 1 was applied to a commercially available fluoroethylene propylene film (FEP-S1833-16, manufactured by Bola). A photograph of this is shown in Figure 2. Figure 2: Coating of transfer substrate with composition An applicator frame with a coating gap of 50 μm was selected. The layer thickness after drying (at 20°C for 16 hours) was approximately 7 μm. 【0075】 3. Transcription process To selectively control the geometric shape of the proton exchange membrane during coating, potentially saving catalyst, this shape may be separated from the coated substrate and transferred to the membrane. In this example, a 2cm x 2cm square was cut from a substrate coated the previous day, and this catalyst layer was transferred to a larger rectangular membrane piece. To facilitate handling, the edges of the membrane piece were secured to a stainless steel disc with transparent adhesive tape. A photograph of this is shown in Figure 3. Figure 3: Film (transparent film) fixed onto a stainless steel disc. 【0076】 A piece of coated FEP film, cut to a predetermined size, was immersed in a container of ethyl alcohol for approximately 2 seconds. Next, the swelling agent remaining on the transfer film was drained from the corner of the container. A photograph of this process is shown in Figure 4. Figure 4: Photograph showing the catalyst coating of a coated transfer substrate being wetted with a swelling agent (ethyl alcohol in this specification). 【0077】 A coated transfer substrate immersed in ethyl alcohol was attached to a film cut to a predetermined size, with its catalyst layer facing the film (photograph in Figure 5). Figure 5: Film before pressing, with coated transfer substrate attached. 【0078】 In this example, a contact pressure of approximately 0.07 MPa was achieved by the weight of a flat stainless steel disc placed on top of the assembly of the film and transfer substrate (photograph in Figure 6). An absorbent cloth (more precisely, a cleanroom cloth) was used to absorb excess swelling agent. In this example, the transfer was achieved within 60 seconds at 20°C. The combination of the swelling agent and contact pressure ensures that the catalyst layer is completely transferred to the film. Figure 6: Transfer by pressure 【0079】 As shown in Figure 7, after transferring the catalyst layer to the film, the FEP film was removed, but the catalyst layer remained on the film. Figure 7: Left side - Catalyst coating film successfully transferred and with the transfer substrate removed. Right side: Transfer substrate without catalyst after removal from the catalyst coating film. 【0080】 4. Comparative example: Transfer without a swelling agent (not according to the present invention) When the catalyst layer was not wetted with a swelling agent, no transfer of the catalyst layer occurred, even when extremely high pressure (60 MPa for 2 minutes) was applied with a platen press. Figure 8: Transfer without the use of a swelling agent, which was almost always unsuccessful. Left: Transfer film almost completely coated with catalyst. Without the swelling agent, over 95% of the catalyst remained on the transfer film and was not transferred to the film. Right side: Film with insufficient transfer of the catalyst layer. 【0081】 5. Conclusion A comparison of the transfers shown in Figures 7 and 8 clearly demonstrates that the use of the swelling agent according to the present invention significantly improves the transfer efficiency of the catalyst layer at low temperatures. [Explanation of Symbols] 【0082】 1. First spool 2. Cation exchange membrane 3. Second spool 4. First Transfer Substrate 5 First composition 6. First contact roller 7. Second Transfer Substrate 8. Third spool 9. Second contact roller 10 Second composition 11. Swelling agent 12 Laura vs. 13 Laura vs. 14 Sandwich body 15. First peeling roller 16. Second peeling roller 17. Coated cation exchange membrane 18. Fourth spool 19. Fifth spool 20. 6th spool F force

Claims

[Claim 1] a) A step of preparing a flat cation exchange membrane containing a membrane material or containing only a membrane material, b) A step of preparing a first flat transfer substrate coated with the first composition on at least one side, wherein the first composition comprises at least one first polymer and at least one first catalytically active substance or catalytically activatable substance, c) A step of preparing a first swelling agent that is at least partially liquid, d) A step of applying the first swelling agent to the first composition and / or the cation exchange membrane, e) A step of pressing the first composition onto the cation exchange membrane in the presence of the first transfer substrate, f) A step of peeling the first transfer substrate from the first composition to obtain a cation exchange film on which the first composition is coated on one side. This is a coating method for a cation exchange membrane that has a non-time-series relationship. The temperature of the first composition at the time of pressing is -90°C to 100°C. g) A method comprising the step of swelling the first polymer with the first swelling agent. [Claim 2] h) A step of preparing a second flat transfer substrate coated with the second composition on at least one side, wherein the second composition comprises at least one second polymer and at least one second catalytically active substance or catalytically activatable substance, i) A step of preparing a second swelling agent that is at least partially liquid, j) A step of applying the second swelling agent to the second composition and / or the cation exchange membrane, k) A step of swelling the second polymer with the second swelling agent, l) A step of pressing the second composition onto the cation exchange membrane in the presence of the second transfer substrate, wherein the temperature of the second composition at the time of pressing is -90°C to 100°C. m) A step of peeling the second transfer substrate from the second composition to obtain a cation exchange film in which the first composition is coated on one side and the second composition is coated on the other side. The method according to claim 1, further comprising the following in a non-chronological order. [Claim 3] The method according to claim 2, wherein the pressing of the first composition with the cation exchange membrane is performed in the presence of the second transfer substrate, and the pressing of the second composition with the cation exchange membrane is performed in the presence of the first transfer substrate. [Claim 4] The method according to any one of claims 1 to 3, wherein the first swelling agent is applied only to the first composition, or the first swelling agent is applied only to the cation exchange membrane, or the first swelling agent is applied to both the first composition and the cation exchange membrane. [Claim 5] The method according to any one of claims 1 to 4, wherein the first swelling agent is provided on the outside of the first composition. [Claim 6] The method according to any one of claims 1 to 5, wherein the first composition is solid when the first swelling agent is applied. [Claim 7] The method according to any one of claims 1 to 6, wherein at least one of the transfer substrates mainly comprises only a polymer that does not contain fluorine. [Claim 8] The method according to any one of claims 2 to 7, wherein the first swelling agent is the same as the second swelling agent. [Claim 9] The method according to any one of claims 2 to 8, wherein the first polymer and the second polymer include the same repeating unit. [Claim 10] The method according to any one of claims 1 to 9, wherein the first polymer and / or the second polymer is cationic conductive. [Claim 11] - The aforementioned film material, - The first polymer, - The second polymer The method according to any one of claims 1 to 10, wherein at least one of them is a sulfonated perfluoropolymer. [Claim 12] The method according to any one of claims 1 to 11, wherein at least one of the swelling agents is an organic substance, or the swelling agent is selected from the group consisting only of methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), isopropanol (IPA), methanol (MeOH), and ethanol (EtOH). [Claim 13] The method according to claim 11 or claim 12, wherein the mass of the sulfonated perfluoropolymer is p, the mass of the swelling agent applied to the sulfonated perfluoropolymer is q, and the q / p ratio is greater than 0.01 and less than 2. [Claim 14] The method according to any one of claims 1 to 13, wherein the first swelling agent dissolves the first polymer at least partially, and / or the second swelling agent dissolves the second polymer at least partially. [Claim 15] The method according to any one of claims 1 to 14, wherein at least one of the swelling agents is present in the mixture. [Claim 16] The method according to any one of claims 7 to 15, wherein at least one of the transfer substrates is discarded after peeling or used as a protective film for the coated cation exchange membrane. [Claim 17] At least one rotating spool is wound up or unwound during the operation of this method, and the spool is i) A spool in which the cation exchange membrane is arranged in a ribbon shape, ii) A spool in which the coated cation exchange membrane is obtained in the shape of a ribbon, iii) A spool on which the transfer substrate is arranged in a ribbon shape. A method according to any one of claims 1 to 16, selected from the group including the group. [Claim 18] The method according to claim 17, wherein the pressing is performed using a pair of rollers whose positions are fixed, and at least one of the rollers of the pair of rollers rotates or rolls on the ribbon-shaped transfer substrate. [Claim 19] The method according to claim 18, wherein the rollers of the roller pair are not heated. [Claim 20] The method according to any one of claims 17 to 19, wherein the peeling is performed using a peeling roller whose position is fixed at least one, and the peeling roller rolls or rotates on the ribbon-shaped transfer substrate. [Claim 21] The at least one catalytically active or catalytically activatable substance comprises at least one element selected from the group consisting only of iridium (Ir), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), ruthenium (Ru), copper (Cu), molybdenum (Mo), zinc (Zn), lead (Pb), manganese (Mn), tungsten (W), platinum (Pt), sulfur (S), tin (Sn), gold (Au), silver (Ag), palladium (Pd), rhenium (Re), and rhodium (Rh). The method according to any one of claims 1 to 20, wherein the element exists in a pure form or as an oxide, hydroxide or hydroxide oxide. [Claim 22] The method according to claim 21, wherein the catalytically active substance or catalytically activatable substance is platinum or a platinum alloy (Pt / C) supported on carbon, or an iridium-based supported or unsupported catalyst, particularly antimond-doped tin oxide (ATO), or niobium or tantalum-doped titanium (oxide). [Claim 23] The method according to any one of claims 1 to 22, wherein the temperature of the first composition and / or the second composition at the time of pressing is -30°C to 80°C, the temperature of the first composition and / or the second composition at the time of pressing is -15°C to 70°C, or the temperature of the first composition and / or the second composition at the time of pressing is 15°C to 30°C. [Claim 24] The method according to any one of claims 1 to 23, wherein the cation exchange membrane has at least one pre-coat layer, and the composition is applied on the pre-coat layer. [Claim 25] The method according to any one of claims 1 to 24, wherein the pressing is performed at a pressure of 0.001 MPa to 0.15 MPa, or the pressing is performed at a pressure of 0.01 MPa to 0.1 MPa.

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