KR102742609B1 - Reinforced composite membrane, membrane-electrode assembly comprising the same and fuel cell - Google Patents

Abstract

A reinforced composite membrane with improved chemical durability and a membrane-electrode assembly including the same are provided. The reinforced composite membrane according to the present invention is a reinforced composite membrane including a first porous support and a second porous support disposed on the first porous support, comprising: a first layer in which pores of the first porous support are filled with a first ion conductor; and a second layer in which pores of the second porous support are filled with a second ion conductor, wherein the first layer includes a first peroxide decomposition promoter, the second layer includes a second peroxide decomposition promoter, and a concentration of the first peroxide decomposition promoter is greater than a concentration of the second peroxide decomposition promoter.

Description

{REINFORCED COMPOSITE MEMBRANE, MEMBRANE-ELECTRODE ASSEMBLY COMPRISING THE SAME AND FUEL CELL}

The present invention relates to a reinforced composite membrane, a membrane-electrode assembly including the same, and a fuel cell. Specifically, the present invention relates to a reinforced composite membrane including layers having different concentrations of a peroxide decomposition accelerator, which prevents the generation of oxygen radicals by decomposing peroxides generated by incomplete oxidation and reduction reactions at each electrode, thereby preventing chemical deterioration of an ion conductor, and a membrane-electrode assembly including the same, and a fuel cell.

A fuel cell is a battery equipped with a power generation system that directly converts chemical reaction energy, such as oxidation/reduction reactions of hydrogen and oxygen contained in hydrocarbon fuels such as methanol, ethanol, and natural gas, into electrical energy. Due to its high energy efficiency and environmentally friendly characteristics of low pollutant emissions, it is attracting attention as a next-generation clean energy source that can replace fossil energy.

These fuel cells have the advantage of being able to produce a wide range of outputs through a stack configuration in which unit cells are laminated, and they are attracting attention as small and portable power sources because they exhibit an energy density that is 4 to 10 times higher than that of small lithium batteries.

The stack that actually generates electricity in a fuel cell has a structure in which several to several dozen unit cells composed of a membrane-electrode assembly (MEA) and a separator (also called a bipolar plate) are laminated. The membrane-electrode assembly generally has an anode (or fuel electrode) and a cathode (or air electrode) formed on both sides of an electrolyte membrane.

Fuel cells can be classified into alkaline electrolyte membrane fuel cells and polymer electrolyte membrane fuel cells (PEMFC) depending on the state and type of electrolyte. Among them, polymer electrolyte membrane fuel cells are attracting attention as portable, vehicle, and home power sources due to their advantages such as low operating temperature of less than 100℃, fast starting and response characteristics, and excellent durability.

Representative examples of polymer electrolyte membrane fuel cells include the Proton Exchange Membrane Fuel Cell (PEMFC), which uses hydrogen gas as fuel, and the Direct Methanol Fuel Cell (DMFC), which uses liquid methanol as fuel.

To summarize the reactions that occur in a polymer electrolyte membrane fuel cell, first, when fuel such as hydrogen gas is supplied to the anode, hydrogen ions (H ⁺ ) and electrons (e ^- ) are generated at the anode through the oxidation reaction of hydrogen gas. The generated hydrogen ions are transferred to the cathode through the polymer electrolyte membrane, and the generated electrons are transferred to the cathode through the external circuit. At the cathode, oxygen gas is supplied, and oxygen combines with hydrogen ions and electrons to generate water through the reduction reaction of oxygen.

Meanwhile, there are still many technical barriers to be overcome in order to commercialize polymer electrolyte membrane fuel cells, and essential improvement factors are the realization of high performance, long life, and low price. The component that has the greatest influence on this is the membrane-electrode assembly, and among them, the polymer electrolyte membrane is one of the key elements that has the greatest influence on the performance and price of the MEA.

The requirements of the polymer electrolyte membrane necessary for the operation of the above polymer electrolyte membrane fuel cell include high hydrogen ion conductivity, chemical stability, low fuel permeability, high mechanical strength, low moisture content, and excellent dimensional stability. Conventional polymer electrolyte membranes tend to have difficulty in normally demonstrating high performance in specific temperature and relative humidity environments, especially in high temperature/low humidity conditions. Due to this, polymer electrolyte membrane fuel cells using conventional polymer electrolyte membranes are limited in their scope of use.

Currently, polymer electrolyte membranes using perfluorinated polymer materials commonly used in transportation fuel cells have the disadvantage of low stability against radicals generated during operation, i.e. low chemical stability. In addition, although the hydrogen ion conductivity is high because the passage for transmitting hydrogen ions is wide, there is the disadvantage of high hydrogen gas permeability used as fuel. In particular, in commercial transportation fuel cells such as buses and trucks that require high long-term stability, a highly durable polymer electrolyte membrane that can overcome these shortcomings is required.

The purpose of the present invention is to provide a reinforced composite membrane including a first layer and a second layer, wherein the concentration of a peroxide decomposition accelerator is high in the first layer adjacent to the cathode electrode, and the concentration of the peroxide decomposition accelerator is relatively low in the second layer adjacent to the anode electrode, thereby preventing the generation of oxygen radicals by decomposing hydrogen peroxide generated when oxygen gas meets hydrogen gas.

Another object of the present invention is to provide a humidified reinforced composite membrane by applying a porous support having different porosities to the reinforced composite membrane, thereby increasing back-diffusion of the generated water generated at the cathode electrode toward the anode electrode during cell operation.

Another object of the present invention is to provide the reinforced composite film, thereby preventing pinholes from being created in an ion conductor by oxygen radicals, thereby improving the chemical durability of the reinforced composite film.

Another object of the present invention is to provide a membrane-electrode assembly that prevents chemical deterioration of an ion conductor by arranging the reinforced composite membrane according to the characteristics of the anode electrode and the cathode electrode.

Another object of the present invention is to provide a fuel cell including the membrane electrode assembly.

The purposes of the present invention are not limited to the purposes mentioned above, and other purposes and advantages of the present invention which are not mentioned can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. In addition, it will be easily understood that the purposes and advantages of the present invention can be realized by the means and combinations thereof indicated in the claims.

One embodiment of the present invention for achieving the above object is a reinforced composite membrane including a first porous support and a second porous support disposed on the first porous support, the reinforced composite membrane including a first layer in which pores of the first porous support are filled with a first ion conductor, and a second layer in which pores of the second porous support are filled with a second ion conductor, wherein the first layer includes a first peroxide decomposition promoter, the second layer includes a second peroxide decomposition promoter, and the concentration of the first peroxide decomposition promoter is greater than the concentration of the second peroxide decomposition promoter.

Another embodiment of the present invention for achieving the above object is a membrane-electrode assembly including the reinforced composite membrane, a cathode electrode, and an anode electrode, wherein the reinforced composite membrane is disposed between the cathode electrode and the anode electrode, and the first layer corresponds to a membrane-electrode assembly disposed between the cathode electrode and the second layer.

Another embodiment of the present invention for achieving the above object corresponds to a fuel cell including the membrane electrode assembly.

According to the present invention, by differently configuring the concentration of the peroxide decomposition accelerator in the reinforced composite membrane according to the characteristics of each electrode, it is possible to prevent the generation of oxygen radicals by decomposing hydrogen peroxide generated when oxygen gas meets hydrogen gas. In addition, according to the present invention, by preventing the generation of pinholes in the ion conductor in the reinforced composite membrane by oxygen radicals, it is possible to provide a reinforced composite membrane having improved chemical durability and optimal ion exchange capacity.

According to the present invention, by applying a porous support having different porosities to a reinforced composite membrane, back-diffusion of generated water generated at a cathode electrode during cell operation can be increased to an anode electrode, thereby providing a humidified reinforced composite membrane.

In addition to the effects described above, the specific effects of the present invention are described below together with the specific contents for carrying out the invention.

FIG. 1 is a cross-sectional view showing a reinforced composite membrane according to one embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a membrane electrode assembly according to one embodiment of the present invention.
Figure 3 is a schematic diagram showing a fuel cell according to one embodiment of the present invention.

Hereinafter, each component of the present invention will be described in more detail so that a person with ordinary skill in the art can easily implement the present invention. However, this is only an example, and the scope of the rights of the present invention is not limited by the following contents.

One embodiment of the present invention is a reinforced composite membrane including a first porous support and a second porous support disposed on the first porous support, the reinforced composite membrane including a first layer in which pores of the first porous support are filled with a first ion conductor, and a second layer in which pores of the second porous support are filled with a second ion conductor, wherein the first layer includes a first peroxide decomposition promoter, the second layer includes a second peroxide decomposition promoter, and the concentration of the first peroxide decomposition promoter is greater than the concentration of the second peroxide decomposition promoter.

Below, the configuration of the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a cross-sectional view showing a reinforced composite membrane according to one embodiment of the present invention.

Referring to FIG. 1, the reinforced composite film (100) according to the present invention may include a first layer (20) and a second layer (30) that are sequentially laminated in a first direction (D1). In the present specification, the first direction (D1) may be defined as a thickness direction of the reinforced composite film (100), and the second direction (D2) may correspond to a direction intersecting the first direction (D1). For example, the second direction (D2) may correspond to a direction perpendicular to the first direction (D1).

Specifically, the second layer (30) can be disposed on the first layer (20), and more specifically, the second layer (30) can be disposed directly on the first layer (20). Here, the meaning of 'disposed directly on' corresponds to that no member is interposed between the first layer (20) and the second layer (30). Similarly, the second porous support (12) can be disposed on the first porous support (10).

The first thickness (TH1) of the first layer (20) according to the present invention may correspond to 2 to 80 ㎛ (micrometers), and preferably correspond to 3 to 35 ㎛ (micrometers). If the thickness of the first layer (20) is less than the above numerical range, a problem of reduced mechanical durability reinforcement effect may occur, and if it exceeds the above numerical range, a problem of increased resistance may occur.

The second thickness (TH2) of the second layer (30) according to the present invention may correspond to 2 to 80 ㎛ (micrometers), and preferably correspond to 3 to 35 ㎛ (micrometers). If the thickness of the second layer (30) is less than the above numerical range, a problem of reduced mechanical durability reinforcement effect may occur, and if it exceeds the above numerical range, a problem of increased resistance may occur.

According to one embodiment of the present invention, the first thickness (TH1) of the first layer (20) may be greater than the second thickness (TH2) of the second layer (30). When the porosity of the first layer (20) is greater than the porosity of the second layer (30), the first thickness (TH1) must be greater than the second thickness (TH2) to increase the dimensional stability of the reinforced composite membrane (100).

The thickness ratio of the first layer (20) and the second layer (30) may be 5:95 to 95:5, and preferably 90:10 to 50:50. If the thickness ratio of the first layer (20) and the second layer (30) is outside the numerical range, deformation such as bending of the membrane may occur due to a difference in mechanical stress.

The first layer (20) according to the present invention may include a first porous support (10) and a first ion conductor filling the pores of the first porous support.

The second layer (30) according to the present invention may include a second porous support (12) and a second ion conductor filling the pores of the second porous support (12).

As simply illustrated in FIG. 1, the ionomer layer composed of the first ion conductor may be disposed on both surfaces of the first porous support (10), and the ionomer layer composed of the second ion conductor may be disposed on both surfaces of the second porous support (12). The first ion conductor and the second ion conductor may be different. Specifically, the equivalent weight of the first ion conductor and the equivalent weight of the second ion conductor may be different from each other. That is, an ionomer layer may be formed between the first porous support (10) and the second porous support (12).

The first porous support (10) according to one embodiment of the present invention may include a highly fluorinated polymer, preferably a perfluorinated polymer, having excellent resistance to thermal and chemical degradation, and may be, for example, polytetrafluoroethylene (PTFE) or a copolymer of tetrafluoroethylene and CF ₂ =CFC _n F _2n+1 (n is a real number from 1 to 5) or CF ₂ =CFO-(CF ₂ CF(CF ₃ )O) _m C _n F _2n+1 (m is a real number from 0 to 15, n is a real number from 1 to 15).

According to another embodiment of the present invention, the first porous support (10) may correspond to expanded polytetrafluoroethylene (e-PTFE) having a microstructure of polymer fibrils or a microstructure in which nodes are interconnected by fibrils. In addition, a film having a microstructure of polymer fibrils in which nodes do not exist may also be used as the first porous support (10).

A first porous support (10) according to another embodiment of the present invention may include a perfluorinated polymer. The first porous support (10) may correspond to a more porous and stronger porous support by extruding dispersion polymerized PTFE into a tape in the presence of a lubricant and stretching the material obtained thereby.

In addition, the amorphous content of the PTFE can be increased by heat-treating the e-PTFE at a temperature exceeding the melting point of the PTFE (about 342°C). The e-PTFE film manufactured by the above method can have micropores and a porosity having various diameters. The e-PTFE film manufactured by the above method can have a pore of at least 35%, and the diameter of the micropores can be about 0.01 to 1 ㎛ (micrometer).

The first porous support (10) according to one embodiment of the present invention may be a nonwoven fibrous web formed of a plurality of randomly oriented fibers. The nonwoven fibrous web refers to a sheet having a structure of individual fibers or filaments that are interlaid, but not in the same manner as a woven fabric. The nonwoven fibrous web may be manufactured by any one method selected from the group consisting of carding, garneting, air-laying, wet-laying, melt blowing, spunbonding, and stitch bonding.

The fiber may include one or more polymer materials, and any material that is generally used as a fiber-forming polymer material may be used, and specifically, a hydrocarbon-based fiber-forming polymer material may be used. For example, the fiber-forming polymer material may include any one selected from the group consisting of polyolefins such as polybutylene, polypropylene, and polyethylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides (nylon-6 and nylon-6,6), polyurethanes polybutene, polylactic acid, polyvinyl alcohol, polyphenylene sulfide, polysulfone, fluid crystalline polymers, polyethylene-co-vinylacetate, polyacrylonitrile, cyclic polyolefins, polyoxymethylene, polyolefin-based thermoplastic elastomers, and combinations thereof. However, the technical idea of the present invention is not limited thereto.

A first porous support (10) according to one embodiment of the present invention may include a nanoweb in which nanofibers are integrated in a nonwoven form including a plurality of pores.

The above nanofibers exhibit excellent chemical resistance and have hydrophobicity, so that hydrocarbon-based polymers that are free from concerns about shape deformation due to moisture in a high-humidity environment can be preferably used. Specifically, the hydrocarbon-based polymer may be selected from the group consisting of nylon, polyimide, polyaramid, polyetherimide, polyacrylonitrile, polyaniline, polyethylene oxide, polyethylene naphthalate, polybutylene terephthalate, styrene butadiene rubber, polystyrene, polyvinyl chloride, polyvinyl alcohol, polyvinylidene fluoride, polyvinyl butylene, polyurethane, polybenzoxazole, polybenzimidazole, polyamideimide, polyethylene terephthalate, polyphenylene sulfide, polyethylene, polypropylene, copolymers thereof, and mixtures thereof, and among these, polyimide having excellent heat resistance, chemical resistance, and shape stability can be preferably used.

The above nanoweb is a collection of nanofibers in which nanofibers manufactured by electrospinning are randomly arranged. At this time, considering the porosity and thickness of the nanoweb, the nanofibers preferably have an average diameter of 40 to 5000 nm (nanometers) when the diameters of 50 fibers are measured using a scanning electron microscope (JSM6700F, JEOL) and calculated from the average thereof.

If the average diameter of the nanofibers is less than the numerical range, the mechanical strength of the first porous support may be reduced, and if the average diameter of the nanofibers exceeds the numerical range, the porosity may be significantly reduced and the thickness may be increased.

The thickness of the above nonwoven fibrous web may be 10 to 50 ㎛ (micrometers), and specifically 15 to 43 ㎛ (micrometers). If the thickness of the above nonwoven fibrous web is less than the above numerical range, the mechanical strength may be reduced, and if it exceeds the above numerical range, the resistance loss may be increased, and the weight reduction and integration may be reduced.

The nonwoven fibrous web may have a basic weight of 5 to 30 mg/cm ² . If the basic weight of the nonwoven fibrous web is less than the above numerical range, visible pores may be formed, making it difficult to function as a porous support, and if it exceeds the above numerical range, it may be manufactured in the form of paper or fabric in which few pores are formed.

The above porosity can be calculated by the ratio of the air volume in the porous support to the total volume of the porous support according to the following mathematical formula 1. At this time, the total volume is calculated by manufacturing a rectangular sample and measuring the width, length, and thickness, and the air volume can be obtained by measuring the mass of the sample and then subtracting the polymer volume calculated inversely from the density from the total volume.

[Mathematical formula 1]

Porosity (%) = (air volume in porous support / total volume of porous support) X 100

The first porosity of the first porous support (10) according to the present invention may be 30 to 90%, and preferably 60 to 85%. If the first porosity of the first porous support (10) is less than the above numerical range, the problem of reduced impregnation of the ion conductor may occur, and if it exceeds the above numerical range, the shape stability may be reduced, and thus the post-process may not proceed smoothly.

The second porous support (12) according to the present invention may be the same as or different from the first porous support (10). The second porosity of the second porous support (12) may correspond to 30 to 90%, and is preferably 60 to 85%. If the second porosity of the second porous support (12) exceeds the above numerical range, shape stability may deteriorate, and thus subsequent processes may not proceed smoothly.

The reason why the porosity of the first porous support (10) is adjusted to be greater than the porosity of the second porous support (12) is to effectively back-diffuse the generated water from the cathode electrode side, which will be described later, toward the anode electrode side, which will be described later, when the cell is operated, and to improve the humidifying performance of the reinforced composite membrane adjacent to the relatively insufficient anode electrode.

As a result, the first porosity of the first porous support (10) according to the present invention may be greater than the second porosity of the second porous support (12). Specifically, the difference between the first porosity and the second porosity may correspond to 5% to 60%, and preferably correspond to 10 to 25%.

If the difference between the first porosity and the second porosity is less than the above numerical range, a problem may arise in which the reverse diffusion effect of water from the cathode electrode to the anode electrode, which will be described later, cannot be significantly exerted, and if it exceeds the above numerical range, a problem may arise in which durability decreases due to a difference in mechanical stress or in which electrical resistance by the support increases.

The equivalent weight (EW) of the first ion conductor according to the present invention may be 400 to 1500 g/eq, and preferably 450 to 1200 g/eq. If the equivalent weight range of the first ion conductor is less than the above numerical range, a problem of reduced dimensional stability may occur, and if it exceeds the above numerical range, a problem of reduced ionic conductivity may occur.

In addition, the ion exchange capacity (IEC) of the first ion conductor may be 0.6 to 2.5 meq/g, and preferably 0.83 to 2.30 meq/g. When the ion exchange capacity of the first ion conductor is less than the above numerical range, the hydrogen ion conductivity may decrease, and when it exceeds the above numerical range, the mechanical durability may be weakened.

The equivalent weight (EW) of the second ion conductor according to the present invention may be 400 to 1500 g/eq, and preferably 450 to 1200 g/eq. If the equivalent weight range of the second ion conductor is less than the above numerical range, a problem of deterioration in dimensional stability may occur, and if it exceeds the above numerical range, a problem of deterioration in ionic conductivity may occur.

In addition, the ion exchange capacity (IEC) of the second ion conductor may be 0.6 to 2.5 meq/g, and preferably 0.83 to 2.30 meq/g. When the ion exchange capacity of the second ion conductor is less than the above numerical range, the hydrogen ion conductivity may decrease, and when it exceeds the above numerical range, the mechanical durability may be weakened.

According to one embodiment of the present invention, the equivalent weight of the first ion conductor may be greater than the equivalent weight of the second ion conductor. Through this, it is possible to compensate for the possibility of reduced durability when the porosity of the first porous support (10) filled with the first ion conductor is greater than the porosity of the second porous support (12).

The first ion conductor and the second ion conductor according to the present invention may each independently be a cation conductor having a cation exchange functional group such as a hydrogen ion, or an anion conductor having an anion exchange functional group such as a hydroxy ion, a carbonate or a bicarbonate. The cation exchange functional group may be any one selected from the group consisting of a sulfonic acid group, a carboxyl group, a boronic acid group, a phosphoric acid group, an imide group, a sulfonimide group, a sulfonamide group, a sulfonic acid fluoride group and combinations thereof, and may generally be a sulfonic acid group or a carboxyl group.

The above cation conductor includes the cation exchange functional group, and may include hydrocarbon polymers such as fluorine-containing polymers in the main chain, benzimidazole, polyamide, polyamideimide, polyimide, polyacetal, polyethylene, polypropylene, acrylic resin, polyester, polysulfone, polyether, polyetherimide, polyester, polyethersulfone, polyetherimide, polycarbonate, polystyrene, polyphenylene sulfide, polyetheretherketone, polyetherketone, polyarylethersulfone, polyphosphazene or polyphenylquinoxaline, partially fluorinated polymers such as polystyrene-graft-ethylenetetrafluoroethylene copolymer or polystyrene-graft-polytetrafluoroethylene copolymer, sulfone imide or mixtures thereof.

More specifically, when the cation conductor is a hydrogen ion cation conductor, the polymers may include a cation exchange group selected from the group consisting of a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a phosphonic acid group and derivatives thereof in the side chain, and specific examples thereof include poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), a copolymer of tetrafluoroethylene and fluorovinyl ether containing a sulfonic acid group, a fluorine-based polymer including a defluorinated sulfated polyether ketone or a mixture thereof, sulfonated polyimide (S-PI), sulfonated polyarylethersulfone (S-PAES), sulfonated polyetheretherketone (S-PEEK), sulfonated polybenzimidazole (S-PBI), sulfonated polysulfone (S-PSU), Sulfonated polystyrene (S-PS), sulfonated polyphosphazene, sulfonated polyquinoxaline, sulfonated polyketone, sulfonated polyphenylene oxide, sulfonated polyether sulfone, sulfonated polyether ketone, sulfonated polyphenylene sulfone, sulfonated polyphenylene sulfide, sulfonated polyphenylene sulfide sulfone, sulfonated polyphenylene sulfide sulfone nitrile, sulfonated polyarylene ether, Examples of hydrocarbon polymers include sulfonated polyarylene ether nitrile, sulfonated polyarylene ether ether nitrile, sulfonated polyarylene ether sulfone ketone, and mixtures thereof, but the technical idea of the present invention is not limited thereto.

The above anion conductor is a polymer capable of transporting anions such as hydroxyl ions, carbonates or bicarbonates. The anion conductor is commercially available in the form of hydroxide or halide (typically chloride), and the anion conductor can be used in industrial water purification, metal separation or catalytic processes.

As the above anion conductor, a polymer doped with metal hydroxide can generally be used, and specifically, poly(ethersulfone), polystyrene, vinyl polymer, poly(vinyl chloride), poly(vinylidene fluoride), poly(tetrafluoroethylene), poly(benzimidazole), or poly(ethylene glycol) doped with metal hydroxide can be used.

As illustrated in FIG. 1, the first layer (20) according to the present invention may include a first peroxide decomposition accelerator (1). In addition, the second layer (30) according to the present invention may include a second peroxide decomposition accelerator.

In this specification, the concentration of the peroxide decomposition promoter (mmol/cm ³ ) is defined as moles (mmol) of the peroxide decomposition promoter per unit volume (cm ³ ).

The concentration of the first peroxide decomposition accelerator (1) according to the present invention may be greater than the concentration of the second peroxide decomposition accelerator (2). Specifically, the concentration of the first peroxide decomposition accelerator (1) may correspond to 0.001 to 0.6 mmol/cm ³ , and preferably correspond to 0.01 to 0.2 mmol/cm ³ . When the concentration of the first peroxide decomposition accelerator (1) is less than the above numerical range, it may be difficult to sufficiently see the peroxide decomposition effect, and when it exceeds the above numerical range, it may be difficult to reduce ion conductivity.

The concentration of the second peroxide decomposition accelerator (2) may be 0.001 to 0.6 mmol/cm ³ , and preferably 0.01 to 0.2 mmol/cm ³ . If the concentration of the second peroxide decomposition accelerator (2) is less than the above numerical range, it may be difficult to sufficiently see the peroxide decomposition effect, and if it exceeds the above numerical range, it may be difficult to reduce ion conductivity.

As a result, the difference in the concentration of the first peroxide decomposition promoter (1) and the concentration of the second peroxide decomposition promoter (2) may be 0.01 to 0.45 mmol/cm ³ , and is preferably 0.05 to 0.2 mmol/cm ³ . If the difference in the concentration of the first peroxide decomposition promoter (1) and the concentration of the second peroxide decomposition promoter (2) is outside the numerical range, the overall efficiency of peroxide decomposition may decrease.

The average particle size of the first peroxide decomposition accelerator (1) according to the present invention may be 0.1 to 100 nm (nanometers), and preferably 1 to 50 nm (nanometers). If the average particle size of the first peroxide decomposition accelerator (1) is less than the above numerical range, a problem of leakage during fuel cell operation may occur, and if it exceeds the above numerical range, a problem of not being effectively introduced into pores and interfering with ion conduction channels may occur.

The average particle size of the second peroxide decomposition accelerator (2) according to the present invention may be 0.1 to 100 nm (nanometers), and preferably 1 to 50 nm (nanometers). If the average particle size of the second peroxide decomposition accelerator (2) is less than the above numerical range, a problem of leakage during fuel cell operation may occur, and if it exceeds the above numerical range, a problem of not being effectively introduced into pores and interfering with ion conducting channels may occur.

The above first peroxide decomposition accelerator (1) and the above second peroxide decomposition accelerator (2) may each independently include at least one selected from the group consisting of a metal-based peroxide decomposition accelerator, an organic peroxide decomposition accelerator, and a peroxide decomposition accelerator salt compound.

The above metal peroxide decomposition accelerator may include at least one selected from the group consisting of cerium ions, nickel ions, tungsten ions, cobalt ions, chromium ions, zirconium ions, yttrium ions, manganese ions, iron ions, titanium ions, vanadium ions, molybdenum ions, lanthanum ions, neodymium ions, silver ions, platinum ions, ruthenium ions, palladium ions, and rhodium ions.

The above metal peroxide decomposition accelerator may include an oxide of a metal or a noble metal. The oxide of the metal or noble metal may include at least one selected from the group consisting of cerium oxide, nickel oxide, tungsten oxide, cobalt oxide, chromium oxide, zirconium oxide, yttrium oxide, manganese oxide, iron oxide, titanium oxide, vanadium oxide, molybdenum oxide, lanthanum oxide, and neodymium oxide.

The above organic peroxide decomposition accelerator may correspond to at least one selected from the group consisting of syringic acid, vanillic acid, protocatechuic acid, coumaric acid, caffeic acid, ferulic acid, chlorogenic acid, cynarine, gallic acid, and mixtures thereof.

The above peroxide decomposition promoting salt compound may include a salt of a metal including a transition metal or a noble metal. It may be any one selected from the group consisting of a carbonate, an acetate, a chloride, a fluoride, a sulfate, a phosphate, a tungstate, a hydroxide, an ammonium acetate, an ammonium sulfate, an acetylacetonate salt, a permanganate salt of the metal, and specifically, examples of cerium include cerium carbonate, cerium acetate, cerium chloride, cerium acetate, cerium sulfate, cerium ammonium acetate, cerium ammonium sulfate, and the like, and examples of the organometallic complex salt include cerium acetylacetonate.

The method for manufacturing a reinforced composite membrane (100) according to the present invention may include a step of laminating a second layer (30) on a first layer (20). Specifically, when manufacturing the first porous support (10), the content and porosity of the peroxide decomposition accelerator may be controlled. In addition, when manufacturing the second porous support (12), the content and porosity of the peroxide decomposition accelerator may be controlled differently from the first porous support (10).

For example, when the first porous support (10) and the second porous support (12) are expanded polytetrafluoroethylene (e-PTFE), the content and porosity of the peroxide decomposition accelerator can be controlled in the step of stretching the polytetrafluoroethylene.

Fig. 2 is a cross-sectional view showing a membrane electrode assembly according to one embodiment of the present invention. Parts that have been described above and are repeated are briefly described or omitted.

Referring to FIG. 2, the membrane-electrode assembly (150) according to the present invention may include the reinforced composite membrane (100), the cathode electrode (50), and the anode electrode (40).

The above-described reinforced composite film (100) may be placed between the cathode electrode (50) and the anode electrode (40). The first layer (20) of the above-described reinforced composite film (100) may be placed between the cathode electrode (50) and the second layer (30). In other words, the second layer (30) of the above-described reinforced composite film (100) may be placed between the first layer (20) and the anode electrode (40).

In general, oxygen gas may meet hydrogen gas passing through the anode electrode (40) interface to generate hydrogen peroxide, which may cause chemical deterioration. A bigger problem is that hydrogen gas may permeate through the cathode electrode (50), causing an incomplete oxygen reduction reaction at the cathode electrode (50), thereby weakening the chemical durability of the reinforced composite membrane. In particular, the ion conductor at the interface between the reinforced composite membrane and the cathode electrode may undergo chemical deterioration.

Specifically, the reaction mechanism by which chemical deterioration occurs in the above-mentioned reinforced composite film is as follows.

[Reaction Formula 1]

H ₂ →2H·

The above reaction formula 1 corresponds to a reaction formula in which hydrogen gas is converted into two hydrogen radicals.

[Reaction Formula 2]

H·+O ₂ →HO ₂ ·

The above reaction formula 2 corresponds to a reaction formula in which hydrogen radicals meet with oxygen gas to generate oxygen radicals. The oxygen radicals can deteriorate the ion conductor of the reinforced composite membrane.

[Reaction Formula 3]

HO ₂ ·+H·→H ₂ O ₂

The above reaction formula 3 corresponds to a reaction formula in which the oxygen radical reacts with a hydrogen radical to produce hydrogen peroxide.

The above oxygen radicals can attack the polar bonds of the reinforced composite membrane, such as C-F, S-O, and C-O. In particular, the mechanical strength of the reinforced composite membrane decreases due to the breakage of the C-F bond, and pinholes may occur. This may increase the amount of hydrogen gas passing through the membrane. Meanwhile, the ion exchange capacity (IEC) of the reinforced composite membrane may decrease due to the breakage of the S-O and C-O bonds.

To solve this problem, the first layer (20) according to the present invention can prevent chemical deterioration of the first ion conductor by including a peroxide decomposition accelerator at a relatively higher concentration than the second layer (30). Accordingly, it is possible to solve the problem of hydrogen gas permeating and reacting with the interface of the cathode electrode, thereby causing an incomplete oxidation-reduction reaction of oxygen gas at the cathode electrode.

Another embodiment of the present invention may correspond to a fuel cell comprising the membrane-electrode assembly.

Figure 3 is a schematic diagram showing a fuel cell according to one embodiment of the present invention.

Referring to FIG. 3, a fuel cell (200) according to the present invention may include a fuel supply unit (210) that supplies a mixed fuel in which fuel and water are mixed, a reforming unit (220) that reforms the mixed fuel to generate a reformed gas containing hydrogen gas, a stack (230) that generates electrical energy by causing an electrochemical reaction between the reformed gas containing hydrogen gas supplied from the reforming unit (220) and an oxidizer, and an oxidizer supply unit (240) that supplies an oxidizer to the reforming unit (220) and the stack (230).

The above stack (230) may be equipped with a plurality of unit cells that generate electrical energy by inducing an oxidation/reduction reaction of a reforming gas containing hydrogen gas supplied from the reforming unit (220) and an oxidizing agent supplied from the oxidizing agent supply unit (240).

Each unit cell means a unit cell that generates electricity, and may include the membrane electrode assembly that oxidizes/reduces oxygen in a reforming gas containing hydrogen gas and an oxidizing agent, and a separator (also called a bipolar plate, hereinafter referred to as a 'separator') for supplying the reforming gas containing hydrogen gas and the oxidizing agent to the membrane electrode assembly. The separator is arranged on both sides of the membrane electrode assembly with the membrane electrode assembly at the center. At this time, the separator plates each positioned at the outermost side of the stack are specifically referred to as end plates.

Among the above separators, the end plate may be provided with a first supply pipe (231) in the shape of a pipe for injecting a reformed gas containing hydrogen gas supplied from the reforming unit (220), and a second supply pipe (232) in the shape of a pipe for injecting oxygen gas. Another end plate may be provided with a first discharge pipe (233) for discharging a reformed gas containing hydrogen gas that is ultimately unreacted and remaining in a plurality of unit cells to the outside, and a second discharge pipe (234) for discharging an oxidizing agent that is ultimately unreacted and remaining in the unit cells to the outside.

In the above fuel cell, the separator, fuel supply unit, and oxidizer supply unit constituting the electricity generating unit are those used in a typical fuel cell, and therefore, a detailed description thereof is omitted in this specification.

Hereinafter, embodiments of the present invention will be described in detail so that a person having ordinary skill in the art to which the present invention pertains can easily implement the present invention, but this is only an example, and the scope of the rights of the present invention is not limited by the following contents.

[Manufacturing example: reinforced composite membrane]

As shown in Table 1 below, reinforced composite membranes were manufactured according to examples and comparative examples.

<Comparative Example 1>

Hydrophilically treated polytetrafluoroethylene having an average pore size of 0.1 ㎛ (micrometer) and a thickness of 4 ㎛ (micrometer) is placed in a reaction vessel containing isopropyl alcohol at room temperature and pretreated for 5 minutes, and then the pretreated porous support is stretched so that the porosity becomes 80% to obtain expanded polytetrafluoroethylene. In the stretching step, 0.05 mmol/cm ³ of cerium oxide is added in powder form. The expanded polytetrafluoroethylene (or first porous support) is continuously injected into a 10 wt.% Nafion solution (product name: Nafion D1021) dispersed in an emulsion state at room temperature and impregnated for 5 minutes, and then dried at 60° C. for 4 hours to produce a first layer. The second layer was manufactured in the same manner as the first layer, but the porosity of the second porous support was adjusted to 80% through a stretching step, and 0.05 mmol/cm ³ of cerium oxide was added in powder form. The second layer was laminated on the first layer to manufacture a final reinforced composite membrane.

<Comparative Example 2>

A reinforced composite membrane was manufactured using the same method as Comparative Example 1, but in the step of stretching the first porous support, the porosity was adjusted to 60%, and 0.05 mmol/cm ³ of cerium oxide was added. Thereafter, when manufacturing the second porous support, in the step of stretching, the porosity was adjusted to 80%, and 0.15 mmol/cm ³ of cerium oxide was added in powder form.

<Comparative Example 3>

A reinforced composite membrane was manufactured using the same method as Comparative Example 1, but in the step of stretching the first porous support, the porosity was adjusted to 80%, and 0.059 mmol/cm ³ of cerium oxide was added. Thereafter, when manufacturing the second porous support, in the step of stretching, the porosity was adjusted to 60%, and 0.05 mmol/cm ³ of cerium oxide was added in powder form.

<Comparative Example 4>

A reinforced composite membrane was manufactured using the same method as Comparative Example 1, but in the step of stretching the first porous support, the porosity was adjusted to 80%, and 0.56 mmol/cm ³ of cerium oxide was added. Thereafter, when manufacturing the second porous support, in the step of stretching, the porosity was adjusted to 60%, and 0.1 mmol/cm ³ of cerium oxide was added in powder form.

<Comparative Example 5>

A reinforced composite membrane was manufactured using the same method as Comparative Example 1, but in the step of stretching the first porous support, the porosity was adjusted to 90%, and 0.1 mmol/cm ³ of cerium oxide was added. Thereafter, when manufacturing the second porous support, in the step of stretching, the porosity was adjusted to 29%, and 0.05 mmol/cm ³ of cerium oxide was added in powder form.

<Comparative Example 6>

A reinforced composite membrane was manufactured using the same method as Comparative Example 1, but in the step of stretching the first porous support, the porosity was adjusted to 80%, and 0.1 mmol/cm ³ of cerium oxide was added. Thereafter, when manufacturing the second porous support, in the step of stretching, the porosity was adjusted to 76%, and 0.05 mmol/cm ³ of cerium oxide was added in powder form.

<Example 1>

A reinforced composite membrane was manufactured using the same method as Comparative Example 1, but in the step of stretching the first porous support, the porosity was adjusted to 80%, and 0.15 mmol/cm ³ of cerium oxide was added. Thereafter, when manufacturing the second porous support, in the step of stretching, the porosity was adjusted to 60%, and 0.05 mmol/cm ³ of cerium oxide was added in powder form.

<Example 2>

A reinforced composite membrane was manufactured using the same method as Comparative Example 1, but in the step of stretching the first porous support, the porosity was adjusted to 80%, and 0.1 mmol/cm ³ of cerium oxide was added. Thereafter, when manufacturing the second porous support, in the step of stretching, the porosity was adjusted to 60%, and 0.05 mmol/cm ³ of cerium oxide was added in powder form.

<Example 3>

A reinforced composite membrane was manufactured using the same method as Comparative Example 1, but in the step of stretching the first porous support, the porosity was adjusted to 80%, and 0.1 mmol/cm ³ of cerium oxide was added. Thereafter, when manufacturing the second porous support, in the step of stretching, the porosity was adjusted to 55%, and 0.05 mmol/cm ³ of cerium oxide was added in powder form.

<Example 4>

A reinforced composite membrane was manufactured using the same method as Comparative Example 1, but in the step of stretching the first porous support, the porosity was adjusted to 80%, and 0.1 mmol/cm ³ of cerium oxide was added. Thereafter, when manufacturing the second porous support, in the step of stretching, the porosity was adjusted to 65%, and 0.05 mmol/cm ³ of cerium oxide was added in powder form.

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Example 1 Example 2 Example 3 Example 4 Porosity of the first porous support A1(%) 80 60 80 80 90 80 80 80 80 80 Second porous support porosity A2(%) 80 80 60 60 29 76 60 60 55 65 A1-A2(%) 0 -20 20 20 61 4 20 20 25 15 Concentration of first peroxide decomposition accelerator B1 (mmol/cm ³ ) 0.05 0.05 0.059 0.56 0.1 0.1 0.15 0.1 0.1 0.1 Secondary peroxide decomposition accelerator concentration B2 (mmol/cm ³ ) 0.05 0.15 0.05 0.1 0.05 0.05 0.05 0.05 0.05 0.05 B1-B2 mmol/cm ³ ) 0 -0.1 0.009 0.46 0.05 0.05 0.1 0.05 0.05 0.05 1) First porous support and second porous support: ePTFE
2) First peroxide decomposition accelerator and second peroxide decomposition accelerator: Cerium oxide (powder)

[Experimental example: OCV hold test and I-V polarization curve measurement experiment]

The OCV hold test and I-V polarization curve were measured for the membrane-electrode assembly including the reinforced composite membrane according to the above examples and comparative examples. The results of the OCV hold test are shown in Table 2 below, and the results of the I-V polarization curve are shown in Table 3 below. The respective measurement methods are as follows.

1) OCV (Open Circuit Voltage) hold test

The evaluation cell is placed in the OCV state, and the cell voltage is measured at regular time intervals to calculate the decrease rate compared to the initial OCV. Measurements were made using the Scribner 850 fuel cell test system (evaluated under the conditions of 90℃, 30%RH, and 50kPa). Specifically, OCV(V)/initial OCV(V) over time (hr) was measured.

2) I-V polarization curve

The evaluation cell is connected and the electrical load is applied step-by-step, and the cell voltage is measured after stabilization. The Scribner 850 fuel cell test system is used (measured under 50%RH, 100%RH, and normal pressure conditions at 65℃). Table 3 below compares the current density (mA/cm ² ) at 0.6 V on the IV polarization curve.

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Example 1 Example 2 Example 3 Example 4 40hr 0.941 0.933 0.940 0.954 0.923 0.944 0.947 0.944 0.942 0.945 80hr 0.907 0.885 0.915 0.931 0.858 0.925 0.920 0.919 0.911 0.922 120hr 0.806 0.774 0.811 0.902 0.712 0.854 0.876 0.858 0.831 0.843

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Example 1 Example 2 Example 3 Example 4 50% RH 673 624 716 577 741 663 731 726 737 685 100%RH 1094 1112 1105 913 1129 1102 1110 1115 1124 1113

Referring to Tables 2 and 3 above, Examples 1 to 4 showed a relatively low degree of OCV reduction overall compared to the comparative examples, and exhibited a relatively high cell current density under conditions of 50% RH with a low relative humidity, indicating improved chemical durability and performance under low humidity conditions.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

1: First peroxide decomposition accelerator 2: Second peroxide decomposition accelerator
10: First porous support 12: Second porous support
20: 1st floor 30: 2nd floor
100: Reinforced composite membrane TH1: First thickness
TH2: Second thickness D1: First direction
D2: Second direction 150: Membrane-electrode assembly
40: Anode electrode 50: Cathode electrode
200: Fuel cell 210: Fuel supply unit
220: Modified part 230: Stack
231: 1st supply pipe 232: 2nd supply pipe
233: First discharge pipe 234: Second discharge pipe
240: Oxidizer supply unit

Claims (14)

A reinforced composite membrane comprising a first porous support; and a second porous support disposed on the first porous support;
A first layer in which a first ion conductor is filled in the pores of the first porous support; and
A second layer in which a second ion conductor is filled in the pores of the second porous support; including:
The first layer comprises a first peroxide decomposition accelerator,
The second layer comprises a second peroxide decomposition accelerator,
The concentration of the first peroxide decomposition accelerator is greater than the concentration of the second peroxide decomposition accelerator,
The first porosity of the first porous support is greater than the second porosity of the second porous support.
Reinforced composite membrane. In the first paragraph,
A reinforced composite membrane wherein the difference in the concentration of the first peroxide decomposition accelerator and the concentration of the second peroxide decomposition accelerator is 0.01 to 0.45 mmol/cm ³ . In the first paragraph,
A reinforced composite membrane having a thickness ratio of the first layer and the second layer of 5:95 to 95:5. In the first paragraph,
A reinforced composite membrane, wherein the first peroxide decomposition accelerator and the second peroxide decomposition accelerator each independently include at least one selected from the group consisting of a metal-based peroxide decomposition accelerator, an organic peroxide decomposition accelerator, and a peroxide decomposition accelerator salt compound. In paragraph 4,
The above metal peroxide decomposition accelerator is,
A reinforced composite membrane comprising any one selected from the group consisting of cerium ions, nickel ions, tungsten ions, cobalt ions, chromium ions, zirconium ions, yttrium ions, manganese ions, iron ions, titanium ions, vanadium ions, molybdenum ions, lanthanum ions, neodymium ions, silver ions, platinum ions, ruthenium ions, palladium ions, rhodium ions, cerium oxide, nickel oxide, tungsten oxide, cobalt oxide, chromium oxide, zirconium oxide, yttrium oxide, manganese oxide, iron oxide, titanium oxide, vanadium oxide, molybdenum oxide, lanthanum oxide, and neodymium oxide. In paragraph 4,
The above organic peroxide decomposition accelerator is,
A reinforced composite membrane comprising any one selected from the group consisting of syringic acid, vanillic acid, protocatechuic acid, coumaric acid, caffeic acid, ferulic acid, chlorogenic acid, cynarine, gallic acid, and mixtures thereof. In paragraph 4,
The above peroxide decomposition promoting salt compound is,
A reinforced composite membrane comprising one selected from the group consisting of metal carbonates, acetates, chlorides, fluorides, sulfates, phosphates, tungstates, hydroxides, ammonium acetates, ammonium sulfates, acetylacetonates and permanganates. In the first paragraph,
A reinforced composite membrane wherein the average particle sizes of the first peroxide decomposition accelerator and the second peroxide decomposition accelerator are each independently 0.1 to 100 nm (nanometers). delete In the first paragraph,
A reinforced composite membrane having a difference between the first porosity and the second porosity of 5 to 60%. In the first paragraph,
A reinforced composite membrane, wherein the equivalent weights (EW) of the first and second ion conductors are each independently 400 to 1500 g/eq. In Article 11,
A reinforced composite membrane, wherein the equivalent weight of the first ion conductor is greater than the equivalent weight of the second ion conductor. A membrane-electrode assembly comprising a reinforced composite membrane according to claim 1; a cathode electrode; and an anode electrode,
The above reinforced composite film is placed between the cathode electrode and the anode electrode,
The first layer is a membrane-electrode assembly disposed between the cathode electrode and the second layer. A fuel cell comprising a membrane electrode assembly according to claim 13.