Process for manufacturing of catalyst coated membranes and membrane electrode units for fuel cells

[0001] [Technical field to which the invention belongs] The present invention relates to a process for producing a catalyst coated membrane for polymer electrolyte membrane fuel cells, which is particularly suitable for continuous production. The present invention also includes the use of these catalyst coated membranes for manufacturing membrane electrode assemblies. [0002] [Conventional technology] Fuel cells convert fuel and oxidants, locally isolated from each other at two electrodes, into electric current, heat and water. The fuel can be hydrogen, methanol, or a hydrogen-rich gas. Oxygen or air acts as an oxidant. The process of energy conversion in fuel cells is characterized by the absence of contaminants and particularly high efficiency. For these reasons, fuel cells are becoming increasingly important for alternative power concepts, household energy supply systems, and portable applications. [0003] Polymer electrolyte fuel cell (PEMFC) and direct methanol fuel cell (direct methanol fuel) Membrane fuel cells, such as cell) (DMFC), are suitable for many applications of movable and stationary regions due to their low operating temperature, small size configuration and power density. [0004] Polymer electrolyte membrane (PEM) fuel cells are constructed as a stack of multiple fuel cell units. These are electrically connected in series to increase the voltage rating. Each fuel cell unit contains a five-layer membrane electrode assembly (MEA) placed between bipolar plates (also called isolation plates) for gas introduction and as current leads. One such five-layer membrane electrode assembly is then assembled into a polymer electrolyte membrane with an electrode layer on each side (three-layer catalyst-coated membrane (CCM)). A so-called gas partitioning layer (GDL or "backing") is then applied to both sides of the CCM, which produces a five-layer membrane electrode assembly. [0005] One of these electrode layers is made as an anode for the oxidation of hydrogen, and the second electrode layer is made as a cathode for the reduction of oxygen. [0006] The gas distribution layer is usually made of carbon fiber paper or carbon fiber cloth. These allow good access of the reactive gas to the reactive layer, as well as good conductivity of the current from the cells and the water produced. [0007] The electrode layer for the anode and cathode contains a polymer that conducts protons and an electrocatalyst, which catalyzically supports a particular reaction (oxidation of hydrogen or reduction of oxygen). Platinum group metals in the periodic table of elements are preferred as catalytically active components. In most cases, so-called supported catalysts (catalytically active platinum group metals applied to the surface of conductive carrier materials such as carbon black) are used. [0008] The polymer electrolyte membrane comprises a polymer material that conducts protons. These materials are also called ionomers. It is preferable to use a tetrafluoroethylene-fluorovinyl ether copolymer having a sulfonic acid group. This material may be obtained, for example, from DuPont under the trade name "Nafion®". However, other ionomer materials, especially those that do not contain fluorine, such as doped sulfonated polyether ketones or doped sulfonated alkyl ketones or sulfinated alkyl ketones, or polybenzimidazoles are also used. obtain. Suitable ionomer materials have been described by the prior art. For use in fuel cells, these membranes generally have a thickness between 10 μm and 200 μm. [0009] Catalytically coated membranes (three-layer CCM) are usually prepared by printing, blade coating, rolling or spraying, using a paste-like preparation, and applying the electrode layer to a polymer electrolyte membrane. .. This paste-like preparation is called an ink or catalytic ink, and these are generally, along with the supported catalysts, proton conductive materials, various solvents, and optionally subdivided hydrophobic materials and pore-forming agents. Contains. Catalytic inks can be distinguished by the nature of the solvent used. There are inks that mainly contain an organic solvent as a solvent and inks that mainly use water as a solvent. For example, prior art discloses catalytic inks containing a mixture of water and a glycol solvent, as well as catalytic inks in which only water is used as the solvent. [0010] The gas partitioning layer (GDL or "backing") usually consists of carbon fiber paper or carbon fiber cloth with coarse pores having a porosity of up to 90%. These materials can be impregnated with a hydrophobic material (eg, a dispersion of polytetrafluoroethylene (PTFE)) to prevent the pore system from overflowing with the reaction water produced at the cathode. In order to improve the electrical contact between the electrode layer and the gas partitioning layer, they often have a carbon black and fluoropolymer "balancing layer" ("microlayer" with a surface facing a particular electrode layer. (Microlayer)) can be coated. Further, the gas partitioning layer itself may be provided with an electrocatalyst layer. This gives a so-called catalyzed GDL. In each case, as already discussed, applying the two GDL layers to the two surfaces of the CCM results in a five-layer membrane electrode assembly. [0011] Commercialization of PEM fuel cell technology requires a process for mass production of catalyst coated membranes (CCMs), and membrane electrode assemblies are available in numerous mobile, static, and portable applications. Need to be. [0012] It is known in the art that polymer electrolyte membranes can be coated using a transfer or decal process. This process involves an ion-exchanged form (eg, Na).⁺Form) membranes are used, and a thin catalytic coating with a layer thickness of less than 10 μm is given. This process involves many steps, is lengthy and expensive, and is therefore only suitable for small-scale production. [0013] Continuous processes for coating polymer electrolyte membranes are known in the art. Some prior art literature discloses coating processes for the continuous production of electrode materials, catalyst materials and composite materials of ionomer membranes, where the electrode layer on the carrier provides the electrode material, catalyst material and ionomer material. Manufactured from containing catalyst powder. This electrode layer heats the carrier-free side, softens the ionomer material, and wraps around the ionomer membrane under pressure. This wrapping process can cause damage to the ionomer membrane and electrode layer. [0014] Other prior art documents disclose a continuous process for coating a polymeric electrolyte membrane with an electrode layer, where a ribbon-like ionomer membrane is drawn through a bath of platinum salt solution. The salt to be adhered is then reduced to the noble metal in a gas stream or other bath. Selective coating, i.e. application of the electrode layer to the film in the desired pattern, is not possible using this process. Also, using this process, only a small amount of catalytically active material can be applied to the membrane. [0015] Some prior art literature discloses a process for the continuous production of a material complex, wherein the material complex consists of several functional materials. These complexes can be used in fuel cells, and fluid preparations containing catalytic materials (catalytic inks) can be used to produce catalytic layers. [0016] Other prior art documents disclose processes for manufacturing membrane electrode assemblies, where polymer electrolyte membranes, electrode layers and gases.<u style="single">diffusion</u>The layers are continuously combined in the rolling process. [0017] A continuous process is also used to selectively apply the electrode layer to a ribbon-shaped ionomer film, where the front and back surfaces of the film are printed. For these processes, the polymer electrolyte membrane should have a specific water content (less than 20%). Accurate positioning of front and back prints due to film dimensional changes during the coating process is difficult, especially for thin films (thickness less than 50 μm). [0018] Another continuous process for coating the ionomer membrane involves pre-swelling with an organic solvent and then the use of the coated membrane, and shrinkage during drying is prevented by the clamp. There are many problems with these processes. This is because the pre-swelling of the membrane cannot be precisely controlled. Due to excessive swelling and the resulting swelling of the film, accurate positioning cannot be achieved in subsequent printing. Moreover, the soft, rubber-like ionomer membrane can be easily damaged by the tension of the clamp in its swollen state. [0019] Prior art also discloses a process for producing catalyst-coated ion exchange membranes using a base material, where the membrane is a base material such as polyethylene terephthalate, PTFE, or glass slides. It is fixed on top and then coated. After drying, the base material is stripped. To coat the second surface, this film is fixed to another base material with adhesive tape. Therefore, both the first and second surface coatings require the use of a base material. As the base material, foils made of polymers such as PET and PTFE are disclosed, but slide glass (Pyrex®) is also disclosed. [0020] [Problems to be Solved by the Invention] Based on current state of the art, there is still a need for a process that allows both sides of the ionomer membrane to be continuously catalytically coated, with high positional accuracy and no damage to the membrane. .. There is also a need to process these catalyst coated membranes (three-layer CCM) into a five-layer membrane electrode assembly by combining with a gas partitioning layer. [0021] [0021] [Means for solving problems] The present invention provides a process for coating a polymeric electrolyte membrane, which is described in the following steps: (a) A step of providing a polymer electrolyte membrane, wherein the front surface of the polymer electrolyte membrane is coated with a catalyst and the back surface of the polymer electrolyte membrane has a backing film; (b) The step of removing the backing film from the polymer electrolyte membrane and coating the back surface of the polymer electrolyte membrane with a second catalyst, thereby coating the polymer electrolyte membrane. Including. [0022] In one embodiment, the polymeric electrolyte membrane comprises a polymeric perfluorosulfonic acid compound, a doped polybenzimidazole, a polyetherketone, polysulfone, or an acid or base thereof. [0023] In one embodiment, the backing film on the back surface of the polymeric electrolyte membrane comprises polyester, polyethylene, polypropylene, polycarbonate, polyimide, or a similar polymeric material. [0024] In one embodiment, the catalyst on the front surface of the polymer electrolyte membrane until step (a) reaches a solvent content of less than 5% by weight based on the weight of the polymer electrolyte membrane coated on the front surface. Further includes the step of drying. [0025] In one embodiment, the catalyst is dried in a continuous process using hot air, infrared, microwave, plasma, or a combination thereof. [0026] In one embodiment, the drying temperature is 50-150 ° C, and the drying time is 1-30 minutes. [0027] In one embodiment, step (b) further comprises treating the coated polymer electrolyte membrane in deionized water at a temperature of 20-90 ° C. [0028] In another aspect, the invention provides a process for producing polymer electrolyte membranes coated on the front and back surfaces, the process of which is: (a) A step of coating a polymer electrolyte membrane with a catalyst on the front surface, wherein the polymer electrolyte membrane has a backing film on the back surface; (b) A step of removing the backing film from the polymer electrolyte membrane and coating the back surface of the polymer electrolyte membrane with a second catalyst, wherein the coating of the second catalyst is carried out without the backing film. Includes the process of producing polymer electrolyte membranes, thereby coating the front and back surfaces. [0029] In one embodiment, step (a) is such that the residual solvent content after drying is less than 5% by weight based on the weight of the polymer electrolyte membrane coated on the front surface. It further includes the step of drying the catalyst on the front surface of the electrolyte membrane. [0030] In another aspect, the present invention provides a process for producing a ribbon-shaped polymer electrolyte membrane for fuel cells, the front and back surfaces of which are coated with a catalyst, the process of which is: (a) A step of providing a backing film on the back surface of the polymer electrode film; (b) The step of coating the front surface of the polymer electrolyte membrane with a first electrode layer using catalytic ink, and drying the coating on the front surface of the polymer electrolyte membrane at a high temperature; (c) Step of removing this backing film from the back surface of this polymer electrolyte membrane; (d) The step of coating the back surface of this polymer electrolyte membrane with a second electrode layer and drying at high temperature; (e) A step of treating a polymer electrolyte membrane having a catalyst coated on the front surface and the rear surface with hot water. Including. [0031] In one embodiment, the first electrode layer on the front surface of the polymer electrolyte membrane has a residual solvent content after drying of 5% by weight based on the weight of the polymer electrolyte membrane coated on the front surface. Dry to less than. [0032] In one embodiment, the coating is applied by screen printing, offset printing, stencil printing, halftone printing, knife coating, or spraying. [0033] In one embodiment, the polymeric electrolyte membrane comprises a polymeric perfluorosulfonic acid compound, a doped polybenzimidazole, a polyetherketone, polysulfone, or an acid or base thereof. [0034] In one embodiment, the backing film on the back surface of the polymeric electrolyte membrane comprises a polymer selected from the group consisting of polyester, polyethylene, polypropylene, polycarbonate, polyimide, or polymeric derivatives thereof. [0035] In one embodiment, the electrode layer is dried in a continuous process using hot air, infrared, microwave, plasma, or a combination thereof. [0036] In one embodiment, the drying temperature is 50-150 ° C, and the drying time is 1-30 minutes. [0037] In one embodiment, the treatment of the coated membrane is performed in deionized water at a temperature of 20-90 ° C. [0038] In one embodiment, the first electrode layer is applied to the front surface of the polymer electrolyte membrane in a desired pattern, and the back surface of the polymer electrolyte membrane is coated with a second electrode layer, while Maintain accurate positioning with respect to the front pattern. [0039] In another aspect, the invention provides a method of using the polymer electrolyte membrane produced by the process for a polymer electrolyte fuel cell, in which the front surface of the polymer electrolyte membrane coated with the catalyst. And a gas partitioning layer is provided on the back surface, which is then bonded to the front and back surfaces under suitable pressure and temperature conditions. [0040] In one embodiment, the catalyst-coated polymer electrolyte membrane having the two gas partitioning layers is produced at a pressure of 10-100 bar and a temperature of 50-150 ° C. [0041] In another aspect, the present invention provides a method of using a polymer electrolyte membrane produced by the above process in a PEM fuel cell or a direct methanol fuel cell. [0042] In one embodiment, the polymer electrolyte membrane is partially or completely coated with the catalyst. [0043] The present invention provides a process that allows both sides of a polymer electrolyte membrane to be continuously catalytically coated. This process is highly accurate in position and does not damage the membrane. These polymer electrolyte membranes can be easily combined with the gas partitioning layer. [0044] In one embodiment, the present invention provides a process for coating a polymeric electrolyte membrane, the process of providing a polymeric electrolyte membrane, wherein the front surface of the polymeric electrolyte membrane is coated with a catalytic layer. , And the back surface of the polymer electrolyte film has a backing film; and the process of removing the backing film from the polymer electrolyte film and coating the back surface of the polymer electrolyte film with a second catalyst layer. Thereby, the step of coating the polymer electrolyte membrane is included. [0045] In another embodiment, the present invention provides a process for producing a polymer electrolyte membrane coated with front and back surfaces, the process of coating the front surface of the polymer electrolyte membrane with a catalyst. A step in which the polymer electrolyte membrane has a backing film on its back surface; as well as a step of removing the backing film from the polymer electrolyte membrane and coating the back surface of the polymer electrolyte membrane with a second catalyst, wherein the polymer electrolyte membrane has a backing film on the back surface. This second catalytic coating is carried out without a backing film, which comprises the step of producing a polymer electrolyte membrane coated on the front and back surfaces. [0046] In a further embodiment, the invention provides a process for producing a polymeric electrolyte membrane for fuel cells, both sides coated with a catalyst, the process providing a polymeric electrode membrane having a backing film on the back surface. Steps; The front surface of the polymer electrolyte membrane is coated with a catalytic ink in the first electrode layer, and the coating on the front surface of the polymer electrolyte membrane is dried at high temperature; the backing film is coated on the back surface of the polymer electrolyte membrane. Includes a step of removing from the polymer electrolyte membrane; a step of coating the back surface of the polymer electrolyte membrane with a second electrode layer; and a step of treating the polymer electrolyte membrane, both sides coated with a catalyst, at high temperature with water. [0047] To further understand the present invention, along with other and additional advantages and embodiments, the following description will be referred to in consideration of the examples. The scope of the present invention is described in the scope of the accompanying patent description. [0048] BEST MODE FOR CARRYING OUT THE INVENTION Here, the present invention will be described in relation to preferred embodiments. These embodiments are presented to aid in the understanding of the invention, and are not intended and should not be considered limiting in any way. All alternatives, modifications and equivalents that may be apparent to those skilled in the art by reading this disclosure are included within the intent and scope of the invention. [0049] The basic concepts known to those of skill in the art are not described in detail as this disclosure is not an introduction to the process for producing polymer electrolytes or for catalytically coating polymer electrolyte membranes. [0050] According to one aspect of the invention, an ionomer membrane with a polymer backing film on the back is used. The front surface of this supported film is coated with a first electrode layer. After the first electrode layer has dried, the polymer backing film is removed and the back surface of the film is coated. After subsequent drying, the catalyst coated membrane is post-treated, rinsed and rolled in a water bath. Various processes can coat the anterior and / or posterior surfaces either partially or completely. Examples include screen printing, stencils, halftone printing, blade coating, or spraying. The two gas partitioning layers are then applied to the two surfaces of the three-layer CCM to produce a five-layer membrane electrode assembly. [0051] The process can preferably handle polymeric electrolyte membranes of polymeric perfluorosulfonic acid compounds, doped polybenzimidazoles, polyetherketones or polysulfones in acidic or basic form. Polymer films of polyester, polyethylene, polypropylene, polycarbonate, polyimide or similar polymeric materials or derivatives thereof are suitable for use as backing films on the back surface of polymer electrolyte films. [0052] The use of an ionomer film, which is supported by a polymer film on the back surface, causes the film to expand in length and width (x and y directions) during the initial coating process, especially during contact with the solvent for the ink. It has been shown to reduce. Especially large print formats (ie 200 cm²In the case of CCM) with a larger working area) and a thin ionomer membrane (thickness less than 50 μm), bulge and wrinkle formation do not occur. [0053] Surprisingly, after removing the backing film, the back surface of the already coated ionomer film was subjected to a preceding drying process so that the ionomer film coated on one side contained the least amount of residual solvent possible. It has also been found that, when implemented, it can be printed with high position accuracy. According to the present invention, the parameters of the drying process are such that the residual solvent content of the coated film prior to the second coating step is between 0% and 5% by weight, preferably 0% by weight. Set to be between 3% by weight. If the content of the residual solvent is higher, excessive bulging and wrinkling will occur in the second coating process. The content of the residual solvent is determined by determining the mass loss of the coated sample after drying in a circulating air drying oven at 120 ° C. [0054] Suitable continuous drying processes include, among other things, hot air drying, infrared drying, and / or a combination of these two processes. The drying profile (time and temperature) is set to achieve the lowest possible residual solvent content. Suitable temperatures are 40-150 ° C, more preferably 50-150 ° C, and suitable times are 1-30 minutes. [0055] The position accuracy between before and after printing that can be achieved using this process ranges from 0.05 to 0.2 mm. Due to this, the first electrode layer is applied to the anterior surface of the polymer electrolyte membrane in the desired pattern, and the second electrode layer is applied to the posterior surface of the polymer electrolyte membrane with respect to the anterior pattern. It is possible to coat with a position accuracy of 0.05 to 0.2 mm. [0056] The electrode layers on both sides of the membrane can be different from each other. These are different catalyst inks, and catalyst and precious metal loading (mg Pt / cm)²) Can be produced in different proportions. [0057] Different electrocatalysts (supported catalysts containing noble metals, supported catalysts free of noble metals, and unsupported metal blacks) can be used. [0058] [0058] The first coating step (using a film supported by a backing film) can be performed in a single or multiple coating processes, while printing on the back surface (after removing the backing film) is preferably simple. It is carried out as a one-step coating process. However, other combinations of processes are also possible. [0059] Now that the invention has been generally described, the invention can be more easily understood by reference to the following examples. These examples are provided for illustrative purposes and are not intended to limit the invention unless specifically stated. [0060] [Example] (Example 1) Membrane electrode assemblies were manufactured by the process according to the invention using catalytic inks with the following composition: Catalytic ink composition (anode and cathode): 15.0g Platinum-supported catalyst (40% by weight platinum supported on carbon black, made by OMG) 44.0g Nafion® solution (11.4% by weight in water) 41.0g dipropylene glycol (100g in total). [0061] The catalyst was suspended in an aqueous Nafion® solution with a dispersant. [0062] Polymer electrolyte membranes 30 cm wide and 100 m long, supported by a polyester film laminated on one side (Nafion® 112, DuPont; H⁺A morphology, 50 μth thick ribbon was first coated on the front with catalytic ink by a screen printing process in a roll-to-roll coating system (constructed as described in EP1037295). The coating area is 100 cm²(Form size 10 x 10 cm). After printing, the coated film was dried with hot air in a continuous ribbon dryer. A slowly increasing drying profile was used with a high flow of hot air, and this profile was adjusted to a residual solvent content of the coated film after drying to 2.3% by weight (maximum temperature: 95 °). C; Total drying time: 8 minutes). After drying, these membranes were rolled with a coiling machine. Before printing on the back surface, the film was spread, turned inside out, rewound, and then returned to the coating system. Before coating the back surface, the backing film was stripped and wrapped around a second roll. The back surface of the unsupported film was coated with the same catalyst in a single printing step. The drying profile was adjusted to a maximum temperature of 75 ° C and a total drying time of 5 minutes. [0063] After printing the back surface, the catalyst coated film (CCM) was rinsed in deionized water at 80 ° C. This CCM is 0.4mg Pt / cm²(0.2 mg on each side Pt / cm²) Had total platinum loading. [0064] 50 cm for electrochemical testing²The working area of was cut out from this CCM and processed into a 5-layer membrane electrode assembly (MEA). This was done by applying hydrophobic treated carbon fiber paper (Toray TGPH-060 type, 200 μm thick) to both sides of the CCM and making composites by hot pressing at 130 ° C and 70 bar. [0065] MEAs prepared in this manner were incorporated into a suitable single PEMFC battery. Output test is H₂Was used as the anode gas and air was used as the cathode gas. The temperature of this battery was 80 ° C. The anode was humidified at 80 ° C and the cathode was humidified at 65 ° C. The pressure of the working gas was 1.5 bar (absolute pressure). The gas stoichiometry was 1.1 (hydrogen) and 1.5 (cathode gas). Battery voltage is 600mA / cm²It was 670 mV when measured with the current of. This is about 0.4 W / cm²Is equivalent to the power of. [0066] (Example 2) MEA was manufactured for use with a modified gas containing hydrogen. A 30 μm thick ionomer film on a polyester backing film was used. The printed format is 15 x 15 cm (working area 225 cm).²)Met. [0067] Anode ink composition: 15.0g PtRu-supported catalyst (40% by weight PtRu supported on carbon black: 26.4% by weight Pt, 13.6% by weight Ru; catalyst equivalent to US Pat. No. 6,007,934) 60.0g Nafion® solution (10% by weight in water) 15.0g deionized water 10.0g Propylene glycol (100g in total). [0068] A 30 μm thick polymer electrolyte membrane was first coated with anode ink on the front surface in a single printing step. Subsequent drying was performed so that the residual solvent content of the film coated on one side was 1.2% by weight. This required a drying profile with a maximum temperature of 105 ° C and a residence time of 5 minutes in a continuous hot air dryer. After removing the backing film, the back surface was printed in a single step using the catalytic ink formulated in Example 1 and dried again as in Example 1. Finally, the CCM was rinsed with 80 ° C deionized water. Precious metal loading of this catalyst coated membrane is 0.4 mg PtRu / cm at the anode²And 0.3 mg Pt / cm at the cathode²Met. [0069] 50cm²A sample having the working area of was cut out from this CCM. Two gas partitioning layers (consisting of hydrophobized carbon fiber paper (Toray TGPH-060)) are applied to the front and back of this CCM, and the composite is heated at 130 ° C, 70 bar pressure. Made by press. [0070] MEAs manufactured in this manner were studied on a fuel cell test bench. Output test is 45% H₂, 30% by volume N₂, 23% CO₂A modified gas mixture containing 50 ppm CO and 50 ppm CO was used with air bleed of 2% by volume air. Air was used as the cathode gas. The temperature of the battery was 70 ° C. The anode was humidified at 85 ° C and the cathode was humidified at 55 ° C. The working gas pressure was 1 bar (absolute pressure). The gas stoichiometry was 1.1 (anode gas) and 2.0 (cathode gas). Battery voltage is 600mA / cm²At the current of, it was 620 mV (output density 0.37 W / cm)²). [0071] (Example 3) A MEA was prepared for use directly in a direct methanol fuel cell (DMFC). [0072] An 87.5 μm thick ionomer film laminated on a backing polyester film was used. The print format was 5 x 5 cm (working area 25 cm)²). The anterior surface of the polymer electrolyte membrane was first coated with a stencil printing process (stencil thickness 100 μm) with an anode ink compatible with that described in Example 2. However, instead of 40% by weight PtRu-supported catalyst, 60% by weight PtRu-supported catalyst was used. Final drying was performed so that the residual solvent content of the film coated on one side was 3.2% by weight. This required a drying profile with a maximum temperature of 105 ° C and a residence time of 7 minutes in the dryer. After removal of the backing film, the back surface was also printed in a stencil process using the catalytic ink described in Example 1 and dried. Finally, the CCM thus prepared was rinsed with 80 ° C deionized water. Precious metal loading of this catalyst coated membrane is 1 mg PtRu / cm relative to the anode²And 0.6 mg Pt / cm relative to the cathode²Met. [0073] Two gas partitioning layers (consisting of hydrophobized carbon fiber paper) are applied to the front and back surfaces of this CCM to produce five layers of MEA, and the composite is applied at a pressure of 140 ° C, 60 bar. It was produced by a hot press of. MEAs manufactured in this manner were studied on a DMFC fuel cell test bench. The working area of the battery is 25 cm²Met. This power test used a 2 molar aqueous solution of methanol. The flow rate of methanol was 4 ml / min. The battery temperature was 60 ° C. Air was used as the cathode gas. The maximum output density measured for this battery is 65mW / cm²Met. [0074] The present invention provides a continuous process for producing catalyst coated polymer electrolyte membranes and membrane electrode assemblies for fuel cells. The process of the present invention uses an ionomer membrane with a polymer backing film on the back. After the first coating step, the film is dried and the residual solvent can be removed almost completely during this drying. After this, the polymer backing film is removed and the back surface of the film is coated in a second step. The front and back surfaces of this film can be coated by a variety of methods (eg, screen printing or stencil printing). Two gas partitioning layers are applied to the two surfaces of the catalyst coated membrane to produce a five-layer membrane electrode assembly. This membrane electrode assembly is used in polymer electrolyte membrane fuel cells and direct methanol fuel cells. [0075] Although the present invention has been described for a particular embodiment thereof, further modifications are possible, and the present application is known or customary in the art to which the invention belongs, from the principles of the invention and the disclosure. Any of the present invention, as practiced in, and generally subject to deviations as applicable to the essential features set forth herein and in accordance with the scope of the appended claims. It is understood that it is intended to cover variations, uses, or adaptations. [0076] [Effect of the invention] INDUSTRIAL APPLICABILITY According to the present invention, there is provided a process that enables continuous catalytic coating of both sides of an ionomer membrane with high positional accuracy and without damage to the membrane.