Electrolyte membrane for fuel cells with improved ion channel continuity and method of manufacturing the same

Abstract

An electrolyte membrane for a fuel cell having improved continuity of ion passage and a method of manufacturing the same are disclosed. The electrolyte membrane can include a solution of an ionomer having different viscosity and a porous carrier having pores, in which continuity of a passage through which a proton moves is improved.

Description

Technical Field

[0001] This invention relates to an electrolyte membrane for fuel cells and a method for manufacturing the same. The electrolyte membrane may comprise an ionomer solution of different viscosities and a porous support with pores, wherein the continuity of the channels through which protons move is improved. Background Technology

[0002] Electrolyte membranes used in fuel cells, such as those comprising Nafion, are essentially configured to transport protons within the fuel cell. In recent years, efforts have been made to develop reinforced membranes in which a porous support, for example, possessing thermal and mechanical stability, is impregnated with an ionomer. In the case of such reinforced membranes, it is difficult to completely impregnate the pores in the reinforced membrane with the ionomer to form continuous proton transport channels.

[0003] For example, ionomers are injected multiple times into the pores formed on the opposing surfaces of a porous carrier in various ways. In this way, air is introduced into the pores along with the ionomers injected in each step, or the air remaining inside cannot completely escape and remains in the porous carrier as bubbles. Summary of the Invention

[0004] In a preferred aspect, a method for suppressing bubble formation in pores contained in a porous carrier is provided.

[0005] In a preferred aspect, an electrolyte membrane with increased proton conductivity is provided.

[0006] The purpose of this invention is not limited to the above aspects. The aspects of this invention can be clearly understood from the following description, and the aspects of this invention can be achieved by the means and combinations thereof described in the claims.

[0007] In one aspect, an electrolyte membrane for a fuel cell is provided. The electrolyte membrane may include: a porous support comprising pores; a first ionomer layer comprising a first ionomer solution permeating from a first surface of the porous support into the pores; and a second ionomer layer comprising a second ionomer solution permeating from a second surface of the porous support opposite to the first surface into the pores. Preferably, the viscosity of the first ionomer solution is different from the viscosity of the second ionomer solution.

[0008] As used herein, "porous carrier" or "porous substrate" refers to a porous material comprising pores (e.g., circular or non-circular), holes, cavities (e.g., microcavities), labyrinths, channels, etc., of various shapes (whether uniformly or irregularly formed). Exemplary porous substrates may include pores (e.g., closed or open pores) within a predetermined size range, said predetermined size being in the submicron to micron dimension and measured by the maximum diameter of the pore.

[0009] As used herein, the term "ionomer" refers to a polymer material or resin comprising ionized groups attached (e.g., covalently bonded) to the polymer backbone as side groups. Preferably, these ionized groups may be functionalized to have ionic properties, such as cationic or anionic properties.

[0010] The ionomer may suitably include one or more polymers selected from fluorinated polymers, polytetrafluoroethylene polymers, perfluorosulfone polymers, benzimidazole polymers, polyimide polymers, polyetherimide polymers, polyphenylene sulfide polymers, polysulfone polymers, polyethersulfone polymers, polyetherketone polymers, polyetheretherketone polymers, polyphenylquinoxaline polymers, and polystyrene polymers.

[0011] The first ionomer in the first ionomer solution and the second ionomer in the second ionomer solution can be of the same or different types. In some respects, the first and second ionomers are different; their physical or chemical properties (e.g., polydispersity index (PDI)) are different. For example, the PDI value of the first ionomer differs from that of the second ionomer by at least 5%, 10%, 20%, 25%, 30%, 35%, 40%, 45%, 60%, 70%, 80%, or 90%.

[0012] The viscosity of the first ionomer solution can be greater than that of the second ionomer solution. A first ionomer layer can be formed by impregnating the first surface of the porous carrier with the first ionomer solution, and a second ionomer layer can be formed by impregnating the second surface of the porous carrier with the second ionomer solution.

[0013] The first ionomer layer can be formed to occupy a portion of the pores from the first surface of the porous carrier, and the second ionomer layer can be formed to occupy a portion of the pores from the second surface of the porous carrier.

[0014] On the one hand, the viscosity difference between the first ionomer solution and the second ionomer solution can be from about 10 cP to 490 cP, or the viscosity difference between the first ionomer solution and the second ionomer solution can reach or be at least 10 cP, 20 cP, 30 cP, 40 cP, 50 cP, 100 cP, 150 cP, 200 cP, 250 cP, 300 cP, 350 cP, 400 cP or 450 cP.

[0015] In some respects, the viscosity of the first ionomer solution can be from about 100 cP to 500 cP, and the viscosity of the second ionomer solution can be from about 10 cP to 90 cP.

[0016] The viscosities of the first and second ionomer solutions mentioned herein (and the difference between these viscosities) were determined at the same temperature (e.g., 25°C or 40°C, preferably 25°C).

[0017] On one hand, a method for manufacturing an electrolyte membrane for a fuel cell is provided. This method may include: preparing a porous support comprising pores; preparing a first ionomer solution; preparing a second ionomer solution; first impregnating the pores in the porous support with the first ionomer solution; and second impregnating the pores in the porous support with the second ionomer solution. Preferably, the viscosity of the first ionomer solution is different from the viscosity of the second ionomer solution.

[0018] The viscosity of the first ionomer solution can be greater than that of the second ionomer solution.

[0019] The first impregnation may include impregnating a first surface of the porous carrier with the first ionomer solution, and the second impregnation may include impregnating a second surface of the porous carrier with the second ionomer solution.

[0020] The initial impregnation may include applying a first ionomer solution to a substrate; laminating a first surface of a porous carrier with the first ionomer solution applied to the substrate to form a first ionomer coating on the first surface of the porous carrier; and impregnating the pores in the first surface of the porous carrier with the first ionomer solution.

[0021] In the first impregnation, a portion of the pores in the porous carrier can be impregnated with the first ionomer solution, while in the second impregnation, the remaining portion of the pores in the porous carrier that were not impregnated with the first ionomer solution can be impregnated with the second ionomer solution.

[0022] In some respects, the viscosity of the first ionomer solution can be from about 100 cP to 500 cP, and the viscosity of the second ionomer solution can be from about 10 cP to 90 cP.

[0023] In some respects, the difference between the viscosity of the first ionomer solution and the viscosity of the second ionomer solution can be from about 10 cP to 490 cP.

[0024] The volume of the pores in the porous carrier can be equal to the total volume of the first ionomer solution and the second ionomer solution incorporated into the pores.

[0025] In the first impregnation, a portion of the pores in the porous carrier can be impregnated with the first ionomer solution, while in the second impregnation, the remaining portion of the pores in the porous carrier that were not impregnated with the first ionomer solution can be impregnated with the second ionomer solution.

[0026] The method may further include coating the porous carrier with a first ionomer solution after the first impregnation and the second impregnation.

[0027] Optionally, the first impregnation may include: applying a first ionomer solution to a substrate, laminating a first surface of the porous carrier with the first ionomer solution applied to the substrate to form a first ionomer coating on the first surface of the porous carrier, and impregnating the pores in the first surface of the porous carrier with the first ionomer solution; and the second impregnation may include: applying a second ionomer solution to a second surface of the porous carrier opposite to the first surface to form a second ionomer coating on the second surface of the porous carrier, and impregnating the pores in the second surface of the porous carrier with the second ionomer solution.

[0028] This article also provides a fuel cell that includes the electrolyte membrane described herein.

[0029] According to various exemplary embodiments of the present invention, the proton conductivity in the electrolyte membrane can be effectively increased. Furthermore, discontinuities in the ionomers that serve as proton channels in the porous support can be reduced. Additionally, deformation of the electrolyte membrane can be suppressed, thereby ensuring durability.

[0030] The effects of the present invention are not limited to those described above, but should be understood to include all effects reasonably expected from the following description.

[0031] Other aspects of the invention are disclosed below. Attached Figure Description

[0032] Figure 1 An exemplary electrolyte membrane according to an exemplary embodiment of the present invention is shown;

[0033] Figure 2 A portion of a cross-section of an exemplary electrolyte membrane according to an exemplary embodiment of the present invention is shown;

[0034] Figure 3 An exemplary electrolyte membrane according to an exemplary embodiment of the present invention is shown; and

[0035] Figure 4 An exemplary manufacturing process for an exemplary electrolyte membrane according to an exemplary embodiment of the present invention is illustrated. Detailed Implementation

[0036] The above and other objects, features, and advantages of the present invention will become clearer from the following preferred embodiments, taken in conjunction with the accompanying drawings. However, the invention is not limited to the embodiments disclosed herein and can be modified in different forms. These embodiments are provided to thoroughly explain the invention and fully convey the spirit of the invention to those skilled in the art.

[0037] Throughout the accompanying drawings, the same reference numerals will refer to the same or similar elements. For clarity of the invention, the dimensions of the structures are described as larger than their actual dimensions. It is to be understood that although terms such as "first," "second," etc., may be used herein to describe various elements, these elements will not be limited by these terms. These terms are used only to distinguish one element from another. For example, an element referred to below as "first" may be referred to as "second" without departing from the scope of the invention. Similarly, a "second" element may also be referred to as "first." As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise.

[0038] It will also be understood that when the terms "comprising," "including," "having," etc., are used in this specification, they indicate the presence of the stated features, values, steps, operations, elements, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or groups thereof. It will be understood that when an element such as a layer, film, region, or sheet is referred to as "on another element," it may be directly on the other element or an intervening element may be present between them. Similarly, when an element such as a layer, film, region, or sheet is referred to as "under another element," it may be directly under the other element or an intervening element may be present between them.

[0039] Unless otherwise stated, all figures, values, and / or representations indicating the amounts of components, reaction conditions, polymer compositions, and mixtures used herein should be considered approximate, including various uncertainties that substantially affect the measurement results at the time of obtaining these values, and should therefore be understood to be modified by the term "about" in all cases. Unless specifically stated or obvious from the context, the term "about" as used herein is understood to mean within the normal tolerances in the field, such as within 2 standard deviations of the mean. "About" can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the specified value. Unless clearly stated from the context, all numerical values ​​provided herein are modified by the term "about".

[0040] Furthermore, when a numerical range is disclosed in this specification, the range is continuous and includes all values ​​from the minimum to the maximum value of the range, unless otherwise stated. Additionally, when such a range involves integer values, it includes all integers from the minimum to the maximum value, unless otherwise indicated.

[0041] In this specification, when describing the range of a variable, it will be understood that the variable includes all values ​​within the range, including the endpoints. For example, the range “5 to 10” should be understood to include any subranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc., and individual values ​​of 5, 6, 7, 8, 9, and 10, and will also be understood to include any values ​​between valid integers within the range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, etc. Similarly, the range “10% to 30%” will be understood to include any subranges such as 10% to 15%, 12% to 18%, 20% to 30%, etc., and all integers, including values ​​not exceeding 30% such as 10%, 11%, 12%, 13%, etc., and will also be understood to include any values ​​between valid integers within the specified range, such as 10.5%, 15.5%, 25.5%, etc.

[0042] This invention relates to an electrolyte membrane for fuel cells and a method for manufacturing the same. Here, an electrolyte membrane for fuel cells, as a product invention, and a method for manufacturing an electrolyte membrane for fuel cells, as a method invention, will be described below.

[0043] Electrolyte membrane for fuel cells

[0044] In one aspect, the electrolyte membrane for a fuel cell may include: a porous carrier including pores; a first ionomer layer including a first ionomer solution permeating from a first surface of the porous carrier into the pores of the porous carrier; and a second ionomer layer including a second ionomer solution permeating from a second surface of the porous carrier opposite to the first surface into the pores of the porous carrier.

[0045] The viscosities of the first ionomer solution and the second ionomer solution are different from each other.

[0046] The first surface of the porous carrier is the bottom side of the porous carrier, while the second surface of the porous carrier is the top side of the porous carrier.

[0047] The porous carrier can be configured to support an electrolyte membrane and a membrane electrode assembly, and the ionomer contained within the pores can serve as a channel to transport protons from an anode disposed on a first surface of the electrolyte membrane to a cathode disposed on a second surface of the electrolyte membrane. The first and second surfaces face opposite directions.

[0048] Porous carriers can be used without particular restrictions, as long as they have pores and can adequately perform their support function. Porous carriers may include expanded polytetrafluoroethylene (e-PTFE).

[0049] The internal porosity of the porous carrier can be in the range of about 5% to about 90%, but the present invention does not particularly limit the thickness of the porous carrier.

[0050] The porous support can be preferably configured such that the pores connect the first surface of the porous support to its second surface and thus pass through the porous support. In this way, when the connectivity between the pores in the porous support is insufficient, the ionomers loaded in the pores will not be discontinuous, and therefore the proton conductivity will not decrease.

[0051] Electrolyte membranes may include a porous support and an ionomer. For example, an electrolyte membrane may have a structure in which the pores of the porous support are impregnated with an ionomer solution. The ionomer solution may suitably include two or more ionomer solutions with different viscosities.

[0052] Ionomers can be used without particular restrictions, as long as they can be used in the field of fuel cells, and preferably include perfluorosulfonic acid (PFSA) ionomers.

[0053] Specifically, the two or more ionomers can be of the same type and differ only in viscosity. Thus, when the pores in the porous support are filled with solutions of two or more ionomers with different viscosities, the decrease in proton conductivity due to the interface between the ionomer solutions can be prevented.

[0054] An ionomer solution may include an ionomer and a solvent, and the solvent may include any of water, alcohol, and combinations thereof.

[0055] The viscosity of an ionomer solution can be controlled by adjusting the ratio of ionomer to solvent. In a high-viscosity ionomer solution, the amount of ionomer is greater than the amount of solvent. If the viscosity of the ionomer solution is low, the amount of ionomer is less than the amount of solvent.

[0056] Furthermore, the viscosity of the ionomer solution can vary depending on the ionomer's equivalent weight (EW) and molecular weight (MW). In particular, viscosity can increase when the ionomer's equivalent weight is low or its molecular weight is high. For example, viscosity can be inversely proportional to the ionomer's equivalent weight and directly proportional to its molecular weight. This increased interaction with the solvent due to the increased number of -SO3 groups in the ionomer leads to the immobilization of solvent molecules.

[0057] The high-viscosity ionomer solution used here is referred to as the first ionomer solution, and the low-viscosity ionomer solution used here is referred to as the second ionomer solution.

[0058] The viscosity difference between the first ionomer solution and the second ionomer solution can be from approximately 10 cP to 490 cP. Here, when the viscosity difference is less than approximately 10 cP, the viscosity of the first ionomer solution may be excessively diluted, thus hindering effective impregnation of the pores in the porous carrier, or failing to adequately maintain the impregnated state after impregnation, which is undesirable. Furthermore, due to the high viscosity of the second ionomer solution, the pores in the porous carrier may not be easily impregnated by it. On the other hand, when the viscosity difference is greater than approximately 490 cP, the viscosity of the first ionomer solution may be too high, making it impossible to impregnate the pores in the porous carrier. Moreover, due to the lower viscosity of the second ionomer solution, an ionomer layer or coating may not be formed after impregnating the pores in the porous carrier, or the processing time may be too long to be economically beneficial.

[0059] The viscosity of the first ionomer solution can suitably be from about 100 cP to 500 cP, and the viscosity of the second ionomer solution can suitably be from about 10 cP to 90 cP.

[0060] A first ionomer solution with high viscosity permeates into the bottom surface of the porous carrier, while a second ionomer solution with low viscosity permeates into the top surface of the porous carrier.

[0061] Figure 1 An electrolyte membrane according to an exemplary embodiment of the present invention is shown. Thus, for example, a porous carrier 10 may be impregnated with a first ionomer solution 20 and a second ionomer solution 30 through its pores. The first ionomer solution 20 and the second ionomer solution 30 may not mix with each other, but rather form a layer within the porous carrier 10.

[0062] The electrolyte membrane may include a first ionomer layer 21 formed by impregnation with a first ionomer solution 20 and a second ionomer layer 31 formed by impregnation with a second ionomer solution 30, wherein the first ionomer layer 21 and the second ionomer layer 31 are formed to be in contact with each other through pores 11 in the porous carrier 10.

[0063] The bottom of the porous carrier (e.g., the first surface of the porous carrier) can be impregnated with a first ionomer solution to form a first ionomer layer, and the top of the porous carrier (e.g., the second surface of the porous carrier) can be impregnated with a second ionomer solution to form a second ionomer layer. For example, the first ionomer layer 21 can be formed to occupy a portion of the pore 11 from the first surface of the porous carrier 10, and the second ionomer layer 31 can be formed to occupy a portion of the pore 11 from the second surface of the porous carrier 10 opposite to the first surface, wherein the first ionomer layer 21 and the second ionomer layer 31 loaded in the pore 11 do not contain air bubbles.

[0064] Ultimately, the volume of the pores 11 in the porous carrier 10 can be the same as the total volume of the first ionomer solution and the second ionomer solution incorporated into the pores.

[0065] Furthermore, the first ionomer solution 20 and the second ionomer solution 30 can be coated onto the two surfaces of the porous carrier 10 impregnated with the first ionomer solution 20 and the second ionomer solution 30 to form a coating. For example, the ionomer solution included in the electrolyte membrane can be present in the pores 11 of the porous carrier 10, and can also be present on the surface of the porous carrier 10.

[0066] like Figure 2 As shown, a portion of the first ionomer solution 20 can be incorporated into the pores of the porous carrier 10, and the remaining portion of the first ionomer solution 20 can remain on the surface of the porous carrier 10 to form a layer. This layer is referred to as the first ionomer coating 22, and the coating formed by the second ionomer solution is referred to as the second ionomer coating.

[0067] Depending on the end use, the first ionomer coating and the second ionomer coating can be excluded.

[0068] The first ionomer solution 20 can be applied to the surface of the second ionomer layer 31 to form a third ionomer layer 51. The resulting electrolyte membrane... Figure 3 As shown in the figure. For example, a first ionomer solution 20 with high viscosity can be applied onto a second ionomer layer 31 formed from a second ionomer solution 30 with low viscosity to provide a third ionomer layer 51. This process can optionally be performed to control the thickness of the electrolyte membrane and improve processing efficiency.

[0069] Method for manufacturing electrolyte membranes for fuel cells

[0070] In one aspect, a method for manufacturing an electrolyte membrane for a fuel cell may include: preparing a porous support comprising pores; preparing a first ionomer solution; preparing a second ionomer solution; and impregnating the pores in the porous support with the first ionomer solution and the second ionomer solution.

[0071] The porous support, the first ionomer solution, and the second ionomer solution are the same as those described above for the electrolyte membrane used in fuel cells, so descriptions that are repeated will be omitted.

[0072] Preparation of porous supports

[0073] Porous supports used as carriers, frameworks, and proton transport channels for electrolyte membranes and membrane electrode assemblies preferably include porous expanded polytetrafluoroethylene (e-PTFE).

[0074] Preparation of the first ionomer solution

[0075] A first ionomer solution can be prepared, which is the first ionomer solution used to impregnate the pores in a porous support, and the first ionomer solution may include a first ionomer and a first solvent. Here, the first solvent may suitably include any one selected from water, alcohols, and combinations thereof.

[0076] The viscosity of the first ionomer solution can be from about 100 cP to 500 cP, or particularly from about 100 cP to 250 cP. When the viscosity of the first ionomer solution is less than about 100 cP, it may not be possible to properly impregnate the pores in the porous carrier with the first ionomer solution, or it may be difficult to form a first ionomer coating 22 with the desired thickness after impregnation. On the other hand, when the viscosity of the first ionomer solution is greater than about 500 cP, the first ionomer solution may not be able to completely penetrate into the pores of the porous carrier, making it impossible to impregnate the interior of the carrier with the first ionomer solution.

[0077] Preparation of the second ionomer solution

[0078] After impregnating a portion of the pores in the porous carrier with a first ionomer solution, a second ionomer solution can be prepared, which is an ionomer solution incorporated into the remaining portion of the pores that were not impregnated by the first ionomer solution.

[0079] Like the first ionomer solution, the second ionomer solution may include a second ionomer and a second solvent, and the second ionomer may preferably be of the same type as the first ionomer contained in the first ionomer solution. However, the second ionomer solution is characterized by having a lower viscosity compared to the first ionomer solution, and the viscosity can be controlled by adjusting the amounts of the second ionomer and the second solvent. The viscosity of the second ionomer solution can be from about 10 cP to 90 cP. When the viscosity of the second ionomer solution is less than about 10 cP, the solution may be over-diluted, and therefore the ionomer layer or ionomer coating may not form as desired, or bubbles may form in the pores of the porous carrier after drying. On the other hand, when the viscosity of the second ionomer solution is greater than about 90 cP, the pores in the porous carrier may not be properly impregnated with the second ionomer solution.

[0080] Immersion

[0081] The porous carrier prepared as described above can be impregnated with a first ionomer solution and a second ionomer solution.

[0082] Impregnation may include: first impregnating the porous carrier 10 with a first ionomer solution 20, and second impregnating the porous carrier 10 with a second ionomer solution 30.

[0083] Figure 4An exemplary impregnation method is shown for impregnating an exemplary porous carrier with an exemplary ionomer solution. For example, S1 is the step of preparing a porous carrier 10 to be impregnated with a first ionomer solution 20, wherein the first ionomer solution 20 can be prepared by applying the first ionomer solution 20 onto a substrate 1. The porous carrier 10 thus prepared includes pores 11, and in particular, the porous carrier 10 may include pores 11 passing through a first surface to a second surface of the porous carrier 10.

[0084] The impregnation of the first ionomer solution can be carried out by directly applying the first ionomer solution 20 to the porous carrier 10, or by applying the first ionomer solution 20 to the prepared substrate 1, and then laminating the porous carrier 10 and the surface of the substrate 1 to which the first ionomer solution 20 has been applied.

[0085] The subsequent impregnation process Figure 4 As shown in the figure. For example, S2 to S4 are steps of impregnating the porous carrier 10 with the first ionomer solution 20 and the second ionomer solution 30, and specifically include: first impregnating the bottom of the porous carrier 10 with the first ionomer solution, and second impregnating the top of the porous carrier 10 with the second ionomer solution.

[0086] S2 and S3 correspond to the first impregnation of the present invention. For example, S2 is the step of laminating the prepared porous carrier 10 to the surface of the substrate 1 to which the first ionomer solution 20 has been applied, wherein a portion of the pores 11 in the porous carrier 10 is impregnated by the first ionomer solution 20 applied to the substrate 1. S3 is the step of separating the substrate 1 from the first surface of the porous carrier 10 after sufficient impregnation with the first ionomer solution 20.

[0087] The first ionomer solution 20 can remain not only in the pores 11 of the porous carrier 10, but also on its surface. For example, the first ionomer solution 20 can be applied to the first surface of the porous carrier 10, so that a portion of the first ionomer solution 20 can remain on the first surface of the porous carrier 10 to form a first ionomer coating, and the remaining portion of the first ionomer solution 20 can penetrate into the pores 11 of the porous carrier 10 to impregnate the porous carrier.

[0088] S4 corresponds to secondary impregnation. For example, S4 can be used to completely impregnate the remaining portions of the pores 11 in the porous carrier 10 that were not impregnated by the first ionomer solution 20. In particular, the second ionomer solution 30 can be used to directly coat and impregnate the surfaces of the porous carrier 10 that were not impregnated by the first ionomer solution 20. Because the second ionomer solution 30 has a low viscosity, the pores 11 in the porous carrier 10 can be easily impregnated and filled by the second ionomer solution 30 due to gravity. Thus, when the second ionomer solution 30 is impregnated in the pores 11, the second ionomer solution 30 comes into contact with the first ionomer solution 20 that has been incorporated into the pores 11. Therefore, the first ionomer solution 20 and the second ionomer solution 30 can be used to fill all the pores 11 in the porous carrier 10 formed in the opposing surfaces of the porous carrier 10 without leaving any voids (bubbles).

[0089] According to various exemplary embodiments of the present invention, the viscosity of the second ionomer solution 30 may be less than the viscosity of the first ionomer solution 20. When the second ionomer solution 30 has a high viscosity like the first ionomer solution 20, the pressure on the remaining pores 11 in the porous carrier 10 may increase excessively, making it impossible to completely impregnate the pores 11 in the porous carrier 10 with the second ionomer solution 30.

[0090] A portion of the second ionomer solution 30 can be used for impregnation, and the remaining portion of the second ionomer solution 30 can be retained or left on the surface of the porous carrier 10, thereby forming a second ionomer coating.

[0091] Because the viscosity of the second ionomer solution 30 is low, a second ionomer coating of appropriate thickness cannot be formed. Therefore, a third ionomer layer can be formed by further applying the first ionomer solution 20, which has a high viscosity, onto the second ionomer coating or the second ionomer layer.

[0092] The coating step to form the third ionomer layer is performed to improve processing efficiency, but it can also be omitted if necessary.

[0093] S5 is a step of drying the electrolyte membrane comprising the porous support 10, the first ionomer solution 20, and the second ionomer solution 30. The drying process removes solvent from the first ionomer solution 20 and the second ionomer solution 30. Since the ionomers remaining in the first ionomer solution 20 and the second ionomer solution 30 are of the same type, continuous proton channels can be formed, containing a single type of ionomer that passes through all surfaces of the electrolyte membrane.

[0094] Although various exemplary embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various modifications may be made without departing from the scope and spirit of the invention as disclosed in the appended claims, and such modifications should not be understood separately from the technical concept or essential features of the invention.

Claims

1. A method of manufacturing an electrolyte membrane, the method comprising: preparing a porous support comprising pores that penetrate a bottom surface and a top surface of the porous support; preparing a first ionomer solution; preparing a second ionomer solution; first impregnating the bottom surface of the porous support with the first ionomer solution such that a portion of the pores in the porous support are impregnated with the first ionomer solution; then second impregnating the top surface of the porous support with the second ionomer solution such that a remaining portion of the pores in the porous support that were not impregnated with the first ionomer solution are impregnated with the second ionomer solution; wherein the viscosity of the first ionomer solution is higher than the viscosity of the second ionomer solution.

2. The method of manufacturing an electrolyte membrane according to claim 1, wherein, the first impregnating comprises applying the first ionomer solution on a substrate, laminating the bottom surface of the porous support with the layer of the first ionomer solution applied on the substrate to form a first ionomer coating on the bottom surface of the porous support, and impregnating the pores in the bottom surface of the porous support with the first ionomer solution.

3. The method of manufacturing an electrolyte membrane according to claim 1, wherein, the viscosity of the first ionomer solution is from 100 cP to 500 cP and the viscosity of the second ionomer solution is from 10 cP to 90 cP.

4. The method of manufacturing an electrolyte membrane according to claim 1, wherein, the difference between the viscosity of the first ionomer solution and the viscosity of the second ionomer solution is from 10 cP to 490 cP.

5. The method of manufacturing an electrolyte membrane according to claim 1, wherein, the volume of the pores in the porous support is equal to the total volume of the first ionomer solution and the second ionomer solution incorporated into the pores.

6. The method of manufacturing an electrolyte membrane according to claim 1, wherein, the method further comprises coating the porous support with the first ionomer solution after the first impregnating and the second impregnating.

7. The method of manufacturing an electrolyte membrane according to claim 1, wherein, the first impregnating comprises applying the first ionomer solution on a substrate, laminating the bottom surface of the porous support with the layer of the first ionomer solution applied on the substrate to form a first ionomer coating on the bottom surface of the porous support, and impregnating the pores in the bottom surface of the porous support with the first ionomer solution, and the second impregnating comprises applying the second ionomer solution on the top surface of the porous support opposite the bottom surface to form a second ionomer coating on the top surface of the porous support, and impregnating the pores in the top surface of the porous support with the second ionomer solution.

8. An electrolyte membrane prepared by the method of any one of claims 1 to 7, comprising: a porous support comprising pores; a first ionomer layer comprising the first ionomer solution impregnated into the pores from a bottom surface of the porous support; and a second ionomer layer comprising the second ionomer solution impregnated into the pores from a top surface of the porous support opposite the bottom surface; wherein the viscosity of the first ionomer solution is higher than the viscosity of the second ionomer solution.

9. A fuel cell comprising the electrolyte membrane of claim 8.

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