KR102154178B1 - Composite electrolyte membrane with a radical scavenger particle layer, a method for producing the same, and a fuel cell comprising the same - Google Patents

Abstract

The present invention relates to a composite electrolyte membrane including a layer of radical scavenger particles, a method for manufacturing the same, and a fuel cell including the same.
In the composite electrolyte membrane of the present invention, a very thin layer of radical scavenger particles is transferred to both ends of the electrolyte membrane to protect the electrolyte membrane, and heterogeneous particles are added by utilizing the characteristic that the radical scavenger particles are very thinly dispersed on the surface of the electrolyte membrane. Minimize the decrease in hydrogen ion conductivity by

Description

Composite electrolyte membrane with a radical scavenger particle layer, a method for producing the same, and a fuel cell comprising the same}

The present invention relates to a composite electrolyte membrane including a layer of radical scavenger particles, a method for manufacturing the same, and a fuel cell including the same.

Recently, global regulations on the use of fossil fuels and carbon dioxide emissions have been strengthened. Accordingly, interest in fuel cells having high energy efficiency and excellent versatility for the goal of low carbon emission green growth is rapidly increasing. Among various fuel cells, polymer membrane fuel cells are in the spotlight as a portable, vehicle, and power generation energy source based on the advantages of low operating temperature, high performance, fast driving, and various outputs.

Polymer Electrolyte Membrane A fuel cell consists of an anode, a cathode, and a polymer membrane that acts as an electrolyte. In the case of a polymer membrane, a membrane into which a sulfonic acid group (-SO ₃ H) is introduced for conduction of hydrogen ions is used. It may be the company dupont ™ Nafion (Nafion ^®).

Nafion membranes show high hydrogen ion conductivity and have excellent chemical stability and mechanical properties due to fluorine-based properties. However, hydroxy radicals (OH·, OOH·) and hydrogen peroxide generated as by-products of the oxygen reduction reaction of the cathode attack the main chain of the Nafion membrane and the carboxylic acids (carboxylic acids, carboxylic acids) of the terminal groups of the PFSA It causes chemical deterioration. Therefore, removing hydroxy (hydroxy, hydroxyl) radicals generated during fuel cell operation is an important factor enabling long-term operation. Accordingly, studies have been reported in which Cerium Oxide, which is free to move to Ce ⁺² and Ce ⁺³ as a radical scavenger, is mixed and used in the membrane and electrode. However, ceria has a low hydrogen ion conductivity, and has a problem that the ionic conductivity of the polymer electrolyte membrane decreases by interfering with the movement of hydrogen ions due to agglomeration of particles when forming a membrane by mixing with Nafion solution and casting. Actually. There is a need for a technology capable of effectively removing hydroxy radicals while minimizing the decrease in hydrogen ion conductivity.

Korean Patent Registration No. 10-0868308 Korean Patent Registration No. 10-0972525

An object of the present invention is to provide a composite electrolyte membrane for a fuel cell in which layers of radical scavenger particles are transferred to both surfaces of a polymer electrolyte membrane.

In addition, another object of the present invention is to provide a method of manufacturing a composite electrolyte membrane for a fuel cell in which a radical scavenger particle layer is transferred to both surfaces of a polymer electrolyte membrane.

In order to achieve the above object, the present invention provides a composite electrolyte membrane for a fuel cell in which a radical scavenger particle layer is transferred to both surfaces of a polymer electrolyte membrane.

In addition, the present invention 1) preparing a coating solution by dispersing the radical scavenger particles in a polar solvent; 2) forming a radical scavenger particle layer from the coating solution; And 3) thermocompressing the radical scavenger particle layer to a polymer electrolyte membrane to transfer the radical scavenger particle layer to the polymer electrolyte membrane. It provides a method of manufacturing a composite electrolyte membrane for a fuel cell comprising:

In addition, the present invention provides a membrane electrode assembly comprising the composite electrolyte membrane.

In addition, the present invention provides a fuel cell including the membrane electrode assembly.

In addition, the present invention provides a device including the fuel cell, wherein the device is one selected from a transportation means, a household fuel cell, a portable fuel cell, and an energy storage device.

In the composite electrolyte membrane of the present invention, a very thin layer of radical scavenger particles is transferred to both ends of the electrolyte membrane to protect the electrolyte membrane, and the radical scavenger particles are very thin and well dispersed on the surface of the electrolyte membrane to prevent the addition of heterogeneous particles. It minimizes the decrease in the conductivity of hydrogen ions.

1 is a schematic diagram illustrating a method of manufacturing a composite electrolyte membrane according to Example 1 of the present invention.
2 is a transmission electron microscopy (TEM) photograph showing the size of a radical scavenger particle.
3 is a scanning electron microscope (SEM) photograph showing particle distribution when coating is performed by varying the concentration of the radical scavenger.
4 is an SEM photograph showing the thickness of a particle layer when coating is performed by varying the concentration of the radical scavenger.
5 is a focused ion beam-scanning electron microscope (Focused Ion Beam-Scanning Electron Microscopy) photograph showing a cross section of a composite electrolyte membrane prepared according to Example 1-1 and Example 1-2.
6A is a graph showing the results of a Fenton test for confirming the chemical stability of Example 1-1, Example 1-2, and Comparative Example 1. FIG.
6B is a graph of comparison of ion conductivity before and after the Fenton test of Examples 1-1, 1-2, and Comparative Example 1. FIG.
7 is a graph showing the results of an open circuit voltage test for 72 hours of unit cells manufactured according to Example 2-1, Example 2-2, and Comparative Example 2.
8 is a graph showing performance data of unit cells manufactured according to Example 2-1, Example 2-2, and Comparative Example 2.

The present invention provides a composite electrolyte membrane for a fuel cell in which layers of radical scavenger particles are transferred to both surfaces of a polymer electrolyte membrane.

During operation of the fuel cell, hydroxy radicals and hydrogen peroxide are generated in the cathode as a side reaction of the reduction reaction of oxygen. Hydroxy radicals and hydrogen peroxide attack the main chain of the perfluorinated sulfonic acid-based membrane and the carboxylic acid of the terminal group of PFSA, causing chemical deterioration of the electrolyte membrane. In the composite electrolyte membrane of the present invention, a particle layer having a radical scavenger property is transferred to both surfaces of the electrolyte membrane to protect the electrolyte membrane from radicals and hydrogen peroxide.

In the present invention, unlike the case of manufacturing a composite electrolyte membrane by inserting a radical scavenger into the entire interior of a conventional electrolyte membrane, a radical scavenger particle layer is selectively transferred only to the surface where the electrode where chemical deterioration occurs and the electrolyte membrane abuts. The effect of protecting the membrane can be maximized. The method of transferring the radical scavenger particle layer of the present invention prevents the agglomeration of inorganic particles occurring in a composite electrolyte membrane prepared from a conventional polymer electrolyte and inorganic particle mixture solution, thereby minimizing a decrease in hydrogen ion conductivity. have. In addition, since the radical scavenger layer can be transferred to a commercial electrolyte membrane, there is an advantage that it is not necessary to prepare a separate electrolyte membrane, and the process is also simplified.

The radical scavenger particles may be ceria particles.

The radical scavengers are hindered amines, hydroxylamines, arylamines, phenols, BHT, phosphites, benzofuranones, salicylic acids, azulenyl nitrones and derivatives thereof, tocophenols, DMPO, cyclic and bicyclic nitrates. It may be any one selected from the group consisting of Ron, gold-chitosan nanocomposite, ascorbic acid, and Mn ²⁺ .

The diameter of the radical scavenger particle may be 1 to 50 nm.

Since the thickness and dispersion degree of the layer of the radical scavenger particles generated varies depending on the diameter of the particles, it can be appropriately adjusted within the above range. However, when particles having a diameter less than the above range are used, the effect of reducing the hydrogen ion conductivity due to impurity insertion occurs, and when particles having a diameter exceeding the above range are used, uniform dispersion of the radical scavenger particles cannot be achieved. do.

The thickness of the radical scavenger particle layer may be 10 to 1000 nm.

If the thickness of the particle layer is less than the above range, the radical scavenger particles are not sufficient to protect the electrolyte membrane, and if it exceeds the above range, the hydrogen ion conductivity of the electrolyte membrane decreases, which is not preferable.

The polymer includes Nafion, Flemion, aciflex, a polymer in which polystyrene sulfonic acid is grafted on a polytetrafluoroethylene backbone, a polymer in which polystyrene sulfonic acid is grafted on a polyvinylidenedifluoride backbone, and a polymer having a sulfonic group. It may be any one selected from the group consisting of a block copolymer copolymerized with a hydrogen fluoride-based polymer having no sulfonic group, and preferably Nafion.

Nafion has a form in which a sulfonic acid group is chemically bonded to a fluorinated hydrocarbon. The equivalent weight of the Nafion membrane is 1100-1500, the thickness is 25-175 μm, and has the same hydrogen ion conductivity as a 1 M sulfuric acid solution. Nafion ion exchange membranes are preferred because they have the advantages of high oxygen solubility, high hydrogen ion conductivity, low density, excellent chemical stability and excellent mechanical strength.

The ionic conductivity of the composite electrolyte membrane may range from 60 mS/cm to 400 mS/cm under conditions of 90% relative humidity and 70° C. temperature.

The ionic conductivity of the commercial Nafion NR212 electrolyte membrane has a value of about 70 mS/cm at a relative humidity of 90% and a temperature of 70°C. In the case of the composite electrolyte membrane of the present invention, despite the addition of a radical scavenger, which is a heterogeneous particle, 60 It has an ionic conductivity of mS/cm or more. Compared with the case of the conventional composite electrolyte membrane including a radical scavenger, the decrease in ionic conductivity corresponds to a remarkably small value. This is because a very thin radical scavenger particle layer is transferred to both surfaces of the electrolyte membrane where the electrolyte membrane and the electrode are in contact with each other, thus preventing the aggregation of radical scavenger particles and minimizing the decrease in ionic conductivity.

The composite electrolyte membrane may have a fluorine ion concentration of 6 ppm or less after being immersed in a solution containing 20 wt% hydrogen peroxide and 30 ppm Fe ²⁺ at a temperature of 80° C. for 72 hours.

Fenton's solution is one of the oxidizing reagents, and by measuring the concentration of fluorine ions eluted into the solution from the electrolyte membrane immersed in the Fenton solution, the degree of chemical degradation occurring in the electrolyte membrane can be determined. Metal cations such as Fe ²⁺ contained in the Fenton solution promote the Fenton reaction to generate anionic peroxides and radicals, which attack the electrolyte membrane to elute fluorine ions. In the case of the commercial Nafion NR 212 electrolyte membrane, about 10 ppm of fluorine ions were detected after the Fenton test under the above conditions, but the electrolyte membrane of the present invention has a value of 6 ppm or less because the radical scavenger particle layer protects the electrolyte membrane.

The present invention comprises the steps of 1) preparing a coating solution by dispersing radical scavenger nanoparticles in a polar solvent;

2) forming a radical scavenger layer from the coating solution; And

3) thermocompression bonding the radical scavenger layer to a polymer electrolyte membrane; and a method for manufacturing a composite electrolyte membrane for a fuel cell comprising:

Unlike the conventional method of manufacturing a separate electrolyte membrane by inserting a hydrophilic inorganic material into the electrolyte membrane, the present invention prepares a layer of radical scavenger particles and then transfers it to the surface of the electrolyte membrane, so that a commercial electrolyte membrane is not required to prepare a new membrane. There is an advantage that it can be used as it is.

The radical scavenger may be ceria.

The radical scavengers are hindered amines, hydroxylamines, arylamines, phenols, BHT, phosphites, benzofuranones, salicylic acids, azulenyl nitrones and derivatives thereof, tocophenols, DMPO, cyclic and bicyclic nitrates. It may be any one selected from the group consisting of Ron, gold-chitosan nanocomposite, ascorbic acid, and Mn ²⁺ .

The diameter of the radical scavenger particle may be 1 to 50 nm.

Since the thickness and dispersion degree of the layer of the radical scavenger particles generated varies depending on the diameter of the particles, it can be appropriately adjusted within the above range. However, when particles having a diameter less than the above range are used, the effect of reducing the hydrogen ion conductivity due to impurity insertion occurs, and when particles having a diameter exceeding the above range are used, uniform dispersion of the radical scavenger particles cannot be achieved. do.

The thickness of the radical scavenger layer may be 10 to 1000 nm.

If the thickness of the particle layer is less than the above range, the radical scavenger particles are not sufficient to protect the electrolyte membrane, and if it exceeds the above range, the hydrogen ion conductivity of the electrolyte membrane decreases, which is not preferable.

The polymer includes Nafion, Flemion, aciflex, a polymer in which polystyrene sulfonic acid is grafted on a polytetrafluoroethylene backbone, a polymer in which polystyrene sulfonic acid is grafted on a polyvinylidenedifluoride backbone, and a polymer having a sulfonic group. It may be any one selected from the group consisting of a block copolymer copolymerized with a hydrogen fluoride-based polymer having no sulfonic group, and preferably Nafion.

The step 2) may be performed by spin coating or blading.

It is possible to form a very thin and evenly dispersed radical scavenger particle layer by spin coating or blading method, and by applying a mixed solution of polymer electrolyte and inorganic particles to prevent agglomeration between particles that occur when manufacturing a composite electrolyte membrane. I can.

The thermocompression bonding in step 3) may be performed at a temperature of 130 to 300° C. at a pressure of 1 to 10 MPa.

In general, the glass transition temperature of the polymer electrolyte membrane is 120°C, and the surface of the polymer electrolyte membrane exhibits viscous behavior above the glass transition temperature, and bonds with the radical scavenger particle layer. When compression is performed below the above temperature range, the viscosity of the polymer electrolyte membrane may not be sufficient, and thus the bonding strength with the hydrophilic radical scavenger particle layer may be insufficient. When the temperature is lowered to 90° C. or less after the thermocompression bonding is completed, a composite electrolyte membrane in which the radical scavenger particle layer is transferred can be obtained.

In particular, although not explicitly described in the following Examples or Comparative Examples, etc., in the method of manufacturing a composite electrolyte membrane for a fuel cell according to the present invention, various types of polar solvents, radical scavengers, and thickness of radical scavengers layers, A composite electrolyte membrane for a fuel cell was prepared by changing the temperature and pressure conditions of the polymer electrolyte membrane and thermocompression bonding, and its shape was confirmed through a scanning electron microscope (SEM) and a focused ion beam-scanning electron microscope (FIB-SEM). In addition, a unit cell including the prepared composite electrolyte membrane was manufactured and a performance test was performed.

As a result, unlike in other conditions and other numerical ranges, when all of the following conditions were satisfied, the electrolyte membrane was not exposed and completely transferred by the radical scavenger particle layer.

(I) the organic solvent is water, (ii) the radical scavenger is ceria (CeO ₂ ) having a particle diameter of 15 to 35 nm, (iii) the radical scavenger particle layer has a thickness of 60 to 80 nm, (iv) The polymer electrolyte membrane is Nafion, (v) forming a radical scavenger particle layer by spin coating (vi) transfer by thermocompression bonding at a temperature of 150 to 180 °C at a pressure of 1 to 5 MPa.

However, when any of the above conditions was not satisfied, it was confirmed that some defects occurred in the radical scavenger particle layer, and the electrolyte membrane was not completely transferred by the radical scavenger particle layer, but was exposed.

The present invention provides a membrane electrode assembly comprising the composite electrolyte membrane according to the above.

The present invention provides a fuel cell including the membrane electrode assembly according to the above.

The present invention provides a device comprising the fuel cell according to the above, wherein the device is one selected from a vehicle, a household fuel cell, a portable fuel cell, and an energy storage device.

Hereinafter, the present invention will be described in more detail with reference to preferred examples. However, these examples are intended to describe the present invention in more detail, and it will be apparent to those of ordinary skill in the art that the scope and contents of the present invention are reduced or limited and cannot be interpreted. In addition, if it is based on the disclosure of the present invention including the following examples, it is obvious that a person skilled in the art can easily implement the present invention for which no experimental results are presented, and such modifications and modifications are attached to the patent. It is natural to fall within the scope of the claims.

Example 1. Preparation of a composite electrolyte membrane having a ceria particle layer

Example 1-1

Ceria (CeO ₂ ) nanoparticles were mixed with 1.0 wt% DI water and ultrasonically dispersed. After applying the dispersed solution on the PI film, coating was performed using a spin coater. DI water was removed by drying in an oven at 80° C. for 10 minutes. Between the two PI films coated with ceria particles, a Nafion (NR 212) electrolyte membrane was disposed in a sandwich shape. Imprinting was performed for 5 minutes at a temperature of 130° C. and a pressure of 5 MPa using a thermocompression bonding equipment. After lowering the temperature of the thermocompression equipment to 90 ℃, the PI film adhered to both sides of the Nafion electrolyte membrane was removed to complete a composite electrolyte membrane in which a thin and evenly dispersed ceria particle layer was transferred.

Example 1-2

A composite electrolyte membrane was prepared in the same manner as in Example 1-1, except that the ceria nanoparticles were mixed in DI water at 2.5 wt%.

Example 2. Unit cell comprising a composite electrolyte membrane having a ceria particle layer

Example 2-1

The composite electrolyte membrane prepared in Example 1-1 was inserted between two sheets of carbon paper serving as a gas diffusion layer and a gasket, and then inserted between the two carbon plates on which gas flow channels of a certain shape were formed to form a membrane electrode assembly. Formed. And this was fastened using a graphite end plate to prepare a unit cell.

Example 2-2

A unit cell was manufactured in the same manner as in Example 2-1, except that the composite electrolyte membrane prepared according to Example 1-2 was used.

Comparative Example 1. Nafion electrolyte membrane

For comparison with the above example, a DuPont Nafion electrolyte membrane (NR212) without any treatment was used.

Comparative Example 2. Unit cell including Nafion electrolyte membrane

A unit cell was manufactured in the same manner as in Example 2, except that the Nafion electrolyte membrane of Comparative Example 1 was used.

Test Example 1. Transmission electron microscope observation of ceria particles

Fig. 2 shows a photograph of ceria particles observed through a Transmission Electron Microscope (TEM). It was confirmed that the diameter of the particles used through FIG. 2 was about 25 nm.

Test Example 2. Scanning electron microscope observation of ceria particle layer

The photographs of the surfaces of the composite electrolyte membranes prepared according to Example 1-1 and Example 1-2 were observed using a Scanning Electron Microscope (SEM) are shown in FIG. 3. In FIG. 3, it was confirmed that as the concentration of ceria increases, the amount of ceria coated on the surface also increases proportionally. In addition, a photograph of the cross section of each composite electrolyte membrane observed using a scanning electron microscope is shown in FIG. 4. Through the cross-sectional analysis of FIG. 4, in the case of the thickness, there was no significant difference depending on the concentration, and it was confirmed that the average ceria particles were coated with 2 to 3 layers to have a thickness of 60 to 80 nm.

Test Example 3. Focused ion beam-scanning electron microscope observation of composite electrolyte membrane

The cross-section of the composite electrolyte membrane prepared according to Example 1-1 and Example 1-2 is shown in FIG. 5 as a photograph observed through a focused ion beam-scanning electron microscope (FIB-SEM; Focused Ion Beam-Scanning Electron Microscopy) image. Done. Through the focused ion beam-scanning electron microscope image, it was confirmed that the ceria particles were inserted in the completed composite electrolyte membrane, and it was confirmed that the distribution of ceria before transfer was similar.

Test Example 4. Evaluation of the chemical stability of the membrane using the Fenton test

The composite electrolyte membranes prepared according to Example 1-1, Example 1-2, and Comparative Example 1 were immersed in 100 g of Fenton's solution (20 wt% hydrogen peroxide, 30 ppm Fe ²⁺ (Iron Sulfate)), and then 80 It was left for 72 hours at a temperature of °C. Next, the fluorine ion concentration of the Fenton solution was measured, and the results are shown in FIG. 6A. In the case of the composite electrolyte membrane of Example 1-2 using 2.5 wt% of ceria particles, it was confirmed that the eluted fluorine ion concentration was lower than that of Example 1-1 using 1.0 wt%, and in the case of the commercial electrolyte membrane of Comparative Example 1, fluorine It was confirmed that the amount of ions eluted was the highest at 9.96 ppm.

In addition, ionic conductivity was measured before and after the Fenton test of Example 1-1, Example 1-2, and Comparative Example 1, and the results are shown in FIG. 6B. The ion conductivity measurement was performed under the condition of a temperature of 70° C. and a relative humidity of 90%, and it was confirmed that the change in ionic conductivity was also significantly reduced in the commercial electrolyte membrane of Comparative Example 1. In the case of the composite electrolyte membrane having a high ceria concentration, the It was confirmed that the reduction was not large.

Test Example 5. Open circuit voltage test

An open circuit voltage (OCV) test was performed using the unit cells prepared according to Example 2 and Comparative Example 2, and the results are shown in FIG. 7. The test was conducted for 72 hours under conditions of hydrogen flow rate of 300 ccm, oxygen flow rate of 300 ccm, unit cell temperature of 90° C., and relative humidity of 30%. After 72 hours, it was confirmed that the unit cell of Comparative Example 2 including a commercial electrolyte membrane had a greater decrease in open-circuit voltage compared to Example 2-1 and Example 2-2. In addition, it was confirmed that Example 2-2 using ceria particles having a high concentration had a smaller reduction in open circuit voltage than Example 2-1 using ceria particles having a low concentration.

Test Example 6. Unit cell cell performance test

Performance evaluation of the unit cells was performed using the unit cells prepared according to Example 2 and Comparative Example 2, and the results are shown in FIG. 8. Performance evaluation was performed under conditions of a hydrogen flow rate of 150 ccm, an air flow rate of 800 ccm, a unit cell temperature of 70° C., a relative humidity of 100%, and an active area of 5 cm 2. At this time, it was confirmed that the performance of Comparative Example 2 in which the ceria particles were not transferred was the best, and the composite membrane having a high ceria concentration showed a slightly lower performance than this. This is a result showing that the hydrogen ion conductivity is reduced to some extent even though the thin and well-dispersed ceria layer was transferred.

However, as a result of measuring the performance after conducting the open circuit voltage test of Test Example 5, in the case of Comparative Example 2 using a commercial film, the performance decrease was the largest, and in the case of Example 2 in which the ceria particles were transferred, the performance decrease was small. Showed reversed performance.

Claims (20)

delete delete delete delete delete delete delete delete 1) preparing a coating solution by dispersing radical scavenger particles in a polar solvent;
2) forming a radical scavenger particle layer from the coating solution; And
3) transferring the radical scavenger particle layer to the polymer electrolyte membrane by thermocompressing the radical scavenger particle layer to a polymer electrolyte membrane, comprising:
The polar solvent is water;
The radical scavenger particle is ceria (CeO ₂ ), and the particle diameter is 15 to 35 nm;
The thickness of the radical scavenger particle layer is 60 to 80 nm;
The polymer electrolyte membrane is Nafion;
Step 2) is performed by spin coating;
The method of manufacturing a composite electrolyte membrane for a fuel cell, wherein the thermocompression bonding in step 3) is performed at a temperature of 150 to 180° C. and a pressure of 1 to 5 MPa. delete delete delete delete delete delete delete delete A membrane electrode assembly comprising a composite electrolyte membrane manufactured according to the manufacturing method of claim 9. A fuel cell comprising the membrane electrode assembly according to claim 18. An apparatus comprising the fuel cell of claim 19,
The device, characterized in that one selected from a vehicle, a domestic fuel cell, a portable fuel cell and an energy storage device.

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