KR20230139229A - Composite separator for hydrogen fuel cell comprising stainless powder and manufacturing method thereof - Google Patents

Abstract

It relates to a composite material separator for hydrogen fuel cells and a method of manufacturing the same, mixing graphite, carbon black, binder, and stainless steel metal with sizes within a specific numerical range at a content ratio within a specific numerical range, and then mixing under specific conditions. The composite separator for fuel cells manufactured through the and molding steps not only has excellent mechanical strength, but also has excellent sheet resistance and electrical conductivity.

Description

Composite separator for hydrogen fuel cell comprising stainless powder and manufacturing method thereof}

It relates to a composite separator for hydrogen fuel cells with excellent mechanical strength and electrical conductivity and a method of manufacturing the same.

Polymer electrolyte fuel cells (PEMFC), one of the hydrogen fuel cell fields, are energy production devices expected to play a leading role in the next-generation hydrogen economy along with molten carbonate fuel cells (MCFC) and solid oxide electrolyte fuel cells (SOFC). Compared to the two fuel cells, this is a fuel cell that has been developed to a stage closer to commercialization. In addition, PEMFC is expected to be applied to automotive, home commercial, and portable power sources due to its advantages of being able to operate at low temperatures (below 100°C) and stably achieving low output compared to MCFC or SOFC.

PEMFC is composed of multiple layers of unit cells stacked with a polymer electrolyte in between, an anode that generates protons and electrons, and a cathode where a reaction between oxidizing gas and protons occurs. The separator plate separates the unit cells, serves to separate and supply the supplied hydrogen-containing fuel and oxidizing gas, and secures a flow path, and at the same time serves to electrically connect the unit cells. Therefore, the characteristics required for a separator plate include high flexural strength, high electrical conductivity, bottom resistance, low hydrogen permeability, and high corrosion resistance.

In addition, currently, high-density graphite material processed into gas channels is commonly used for these separators. However, the full-scale commercialization of fuel cells is difficult because the separators are very expensive, accounting for more than 50% of the stack of fuel cells. To achieve this, lowering the price ratio of separator plates is essential, and is currently an area where research is being focused around the world. These studies can be broadly divided into two categories: graphite and metal. Graphite is recognized as a more suitable material than metal in terms of corrosion resistance.

In addition, in order to manufacture a composite material separator considering production costs, there is a problem that natural graphite, which is the cheapest among graphite aggregates, has to be used as the raw material aggregate. Accordingly, even when natural graphite is used, it has high density and high electroconductivity, but There is a need to manufacture composite separators for hydrogen fuel cells with excellent mechanical strength.

Republic of Korea Patent Publication No. 10-2015-0120044

The purpose of solving the above problem is as follows.

A method of manufacturing a separator plate for a hydrogen fuel cell, comprising mixing graphite, carbon black, binder, and stainless steel metal having a size within a specific numerical range at a content ratio within a specific numerical range, followed by a mixing step and a molding step under specific conditions, and The purpose is to provide a composite separator for hydrogen fuel cells manufactured according to this.

According to one embodiment, 81% to 87% by weight of graphite; 3% to 9% by weight of carbon black; 9% to 15% by weight binder; And a composite material separator for a fuel cell can be provided, characterized in that it contains 0.5% by weight to 5% by weight of stainless steel metal.

The composite separator for fuel cells is manufactured by mixing graphite, carbon black, binder, and stainless steel metal with a size within a specific numerical range at a content ratio within a specific numerical range, and then going through the mixing and molding steps under specific conditions. The composite separator for fuel cells has mechanical strength. Not only is it excellent, but it also has excellent sheet resistance and electrical conductivity.

Figure 1 is an image of a mold used to manufacture a composite separator for fuel cells according to an example.
Figure 2 is an image of a composite separator plate before forming a gas channel for a fuel cell manufactured according to an example.

The above objects, other objects, features and advantages will be easily understood through the following preferred embodiments in conjunction with the accompanying drawings. However, it is not limited to the embodiments described here and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed content will be thorough and complete and the technical ideas can be sufficiently conveyed to those skilled in the art.

While describing each drawing, similar reference numerals are used for similar components. In the attached drawings, the dimensions of the structures are enlarged from the actual size for clarity of the present invention. Terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, a first component may be named a second component, and similarly, the second component may also be named a first component without departing from the scope of the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof. Additionally, when a part of a layer, membrane, region, plate, etc. is said to be “on” another part, this includes not only being “directly above” the other part, but also cases where there is another part in between. Conversely, when a part of a layer, membrane, region, plate, etc. is said to be "underneath" another part, this includes not only being "immediately below" the other part, but also cases where there is another part in between.

Unless otherwise specified, all numbers, values, and/or expressions used herein expressing quantities of components, reaction conditions, polymer compositions, and formulations are intended to represent, among other things, how such numbers inherently occur in obtaining such values. Since they are approximations reflecting the various uncertainties of measurement, they should be understood in all cases as being qualified by the term "approximately". Additionally, where a numerical range is disclosed herein, such range is continuous and, unless otherwise indicated, includes all values from the minimum to the maximum of such range inclusively. Furthermore, when such range refers to an integer, all integers from the minimum value up to and including the maximum value are included, unless otherwise indicated.

In this specification, when a range is stated for a variable, the variable will be understood to include all values within the stated range, including the stated endpoints of the range. For example, the range "5 to 10" includes the values 5, 6, 7, 8, 9, and 10, as well as any subranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc. It will be understood that it also includes any values between integers that fall within the scope of the stated range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9, etc. Also, for example, the range "10% to 30%" includes values such as 10%, 11%, 12%, 13%, etc. and all integers up to and including 30%, as well as 10% to 15%, 12% to 12%, etc. It will be understood that it includes any subranges, such as 18%, 20% to 30%, etc., and any value between reasonable integers within the range of the stated range, such as 10.5%, 15.5%, 25.5%, etc.

Conventional separators for fuel cells, preferably polymer electrolyte fuel cells (PEMFC), were manufactured based on graphite containing carbon elements to ensure economic efficiency. Accordingly, there was a need to secure technology to manufacture a composite separator for hydrogen fuel cells with high density and high electrical conductivity while having excellent mechanical strength.

Accordingly, as a result of intensive research to solve the above problem, the present inventors mixed graphite, carbon black, binder, and stainless steel metal with sizes within a specific numerical range at a content ratio within a specific numerical range, and then mixed them under specific conditions. The present invention was completed after discovering that the composite separator for fuel cells manufactured through the forming step not only has excellent mechanical strength but also has excellent sheet resistance and electrical conductivity.

A composite material separator for a hydrogen fuel cell according to one embodiment is characterized by containing graphite, carbon black, binder, and stainless steel metal at a content ratio within a specific numerical range. Preferably, 81% to 87% by weight of graphite; 3% to 9% by weight of carbon black; 9% to 15% by weight binder; And it is characterized in that it contains 0.5% by weight to 5% by weight of stainless steel metal.

In order to manufacture the composite separator for hydrogen fuel cells with high strength and high electrical conductivity, it is desirable to manufacture a high-density separator. At this time, in order to manufacture the separator plate for hydrogen fuel cells at high density, the particles can be arranged so that the packing density of the reference aggregate and auxiliary aggregate is high.

According to one embodiment, the particle arrangement of the reference aggregate of the composite separator for hydrogen fuel cells may be hcp (hexagonal closest packing), and the space occupancy may be 80% to 90%. Accordingly, the reference aggregate may be one or more selected from the group consisting of graphite and metal, and preferably may be impression graphite, which has excellent electrical conductivity.

The graphite may be included in an amount of 81% by weight to 87% by weight, preferably 82% by weight to 83% by weight, to ensure excellent particle arrangement and space occupancy. Outside the above range, if the graphite content is too small, there is a disadvantage of low electrical conductivity, and if the graphite content is too large, there is a disadvantage of high hydrogen permeability.

The particle size of graphite that satisfies the particle arrangement and space occupancy may be greater than 20 μm and less than 440 μm, and preferably, it may be graphite of about 173 μm. Conductive graphite of 20μm and impression graphite of 35μm, which have smaller particle sizes than impression graphite of around 173μm, have the disadvantage of low electrical conductivity, and artificial graphite of 440μm, which has a large particle size, has the disadvantage of low flexural strength.

The filling density can be increased by filling the voids created by the particle arrangement of the reference aggregate with auxiliary aggregate. The auxiliary aggregate may have an auxiliary particle size according to Equation 1 below.

[Equation 1]

Radius of auxiliary aggregate (r) < Radius of reference aggregate (R) x 0.155

There is an advantage in obtaining a high-density separator plate for hydrogen fuel cells by controlling the size of the auxiliary aggregate according to the relationship in Equation 1 above.

The auxiliary aggregate is not particularly limited as long as it is a material that can secure electrical conductivity that may be lowered due to excellent mechanical strength and formability of composite separators for fuel cells to be manufactured in the future, and is preferably carbon black, binder, and stainless steel metal.

The carbon black can be used to improve electrical conductivity, which can be reduced to secure mechanical strength or formability.

According to one embodiment, carbon black may be included in an amount of 3% to 9% by weight, preferably 4% to 5% by weight. Outside the above range, if the carbon black content is too low, there is a disadvantage of low electrical conductivity, and if the carbon black content is too high, there is a disadvantage of high hydrogen permeability.

The stainless steel metal may be included to ensure mechanical strength as well as corrosion resistance.

According to one embodiment, the stainless steel metal may be one or more types selected from the group consisting of STS316L, STS304L, and 17-4PH, and is preferably STS316L, which ensures corrosion resistance and mechanical strength.

The stainless steel metal may be included in an amount of 0.5% by weight to 5% by weight, preferably 1% by weight to 2% by weight. Outside the above range, if the content of stainless steel is too low, there is a disadvantage of low corrosion resistance and low flexural strength, and if the content of stainless metal is too high, there is a disadvantage of low electrical conductivity.

The binder may be included to ensure formability when manufacturing composite separator plates for fuel cells.

According to one embodiment, the binder is selected from the group consisting of polyvinylidene fluoride (PVDF), fluorinated ethylene propylene copolymer (FEP), and polytetrafluoroethylene (PTFE). There may be more than one type.

The binder may be included in an amount of 9% to 15% by weight, preferably 10% to 11% by weight. Outside the above range, if the binder content is too low, there is a disadvantage of low flexural strength, and if the binder content is too high, there is a disadvantage of low electrical conductivity.

The binder is preferably comprised of PVDF, FEP, and PTFE in descending order of content due to its melting point. More preferably, it is polyvinylidene fluoride (PVDF): fluorinated ethylene propylene copolymer (FEP): polytetrafluoroethylene (PTFE) in an amount of 7 to 10% by weight: 1.5 to 3% by weight: 0.5 to 2% by weight. It may be included in an amount of %, and more preferably, it may be included in an amount of 7 to 8% by weight: 1.5 to 2% by weight: 0.5 to 1% by weight. If the PTFE content is too high outside the above range, there is a disadvantage in that it is difficult to proceed with the firing process.

According to one embodiment, a composite separator plate for fuel cells that satisfies the above characteristics may be manufactured in a plate shape. The thickness of the composite separator plate for fuel cells that satisfies the plate shape may be 2.5 mm to 3.5 mm, preferably 2.5 mm to 3.0 mm. Outside the above range, if the thickness is too thin, there is a disadvantage of low flexural strength, and if the thickness is too thick, there is a disadvantage of low electrical conductivity.

A method of manufacturing a composite material separator for a fuel cell according to another embodiment includes 81% to 87% by weight of graphite, 3% to 9% by weight of carbon black, 9% to 15% by weight of binder, and 0.5% by weight of stainless steel metal. A mixing step of making a mixture by mixing % to 5% by weight; A repeated pressing step of repeatedly pressing and stopping the mixture with a hot press machine; and a molding step of molding the repeatedly pressed result. At this time, among the content related to the manufacturing method of the composite material separator for fuel cells according to another embodiment, the content that is the same as the content of the composite material separator for fuel cells according to one embodiment may be omitted.

The mixing step is a step of mixing graphite, which is a reference aggregate, and carbon black, a binder, and stainless steel metal, which are auxiliary aggregates.

The mixing method may be performed using one method selected from the group consisting of a grinding mixer capable of grinding and mixing. At this time, mixing and kneading conditions may be room temperature (15-25'C), grinding time of 1 minute, and kneading time of 1 minute.

The repeated pressing step is a step of first forming by repeatedly pressing and stopping with a hot press machine.

According to one embodiment, the repeated pressurization step is performed by pressing the mixture in a hot press machine (cylinder diameter 280 mm to 320 mm) at a gauge pressure of 100 kgf/cm ² to 200 kgf/cm ² at a temperature of 230°C to 270°C for 1 second to 2 seconds. The step and pause of 3 to 5 seconds can be repeated 10 to 15 times. If the pressure is outside the above range and is too low or high, it is difficult to obtain the desired packing density between aggregates. Additionally, if the pressurization time is too short or too long, it is difficult to arrange the particles so that the packing density between aggregates is high. Additionally, if the stopping time is too short or too long, air and gas that may be generated during molding may not escape smoothly, making molding difficult.

The molding step is a step of performing secondary molding that varies the pressure holding time while maintaining the temperature after the first molding step.

According to one embodiment, the molding step is performed by molding the resultant using a hot press machine (cylinder diameter 280mm to 320mm) at a temperature of 230°C to 270°C for 30 to 37 minutes at a gauge pressure of 100kgf/cm ² to 200kgf/cm ² can do. Preferably, the process of pressurizing at a temperature of 230°C to 270°C for 25 to 30 minutes and then maintaining the pressure for 5 to 7 minutes may be repeated 5 to 6 times.

Through this molding process, the packing density between aggregates can be increased, and air and gas that may be generated during molding can be sufficiently discharged, which can affect the resulting product's characteristics of high flexural strength.

That is, the composite material separator for fuel cells according to one embodiment is made by mixing graphite, carbon black, binder, and stainless steel metal with sizes within a specific numerical range at a content ratio within a specific numerical range, followed by a mixing step and molding under specific conditions. Since it is manufactured through several steps, it not only has excellent mechanical strength, but also has excellent sheet resistance and electrical conductivity.

The present invention will be described in more detail through examples below. The following examples are merely examples to aid understanding of the present invention, and the scope of the present invention is not limited thereto.

Examples and Comparative Examples: Manufacturing of composite material separator for fuel cells

Conductivity, graphite, carbon black, binder, and stainless steel metal are mixed according to the tables below, and the molding powder material is mixed at room temperature. The molding powder material is ground to an average particle size of 1 to 20 μm with a grinding mixer, and the crushed powder material is kneaded to form a mixture. manufacture.

The mixture was placed in a mold as shown in Figure 1 preheated to 250°C, and the pressure step of 1 to 2 ^seconds and the stop step of 3 to 5 seconds were repeated at a pressure of 100 kgf/cm 2 to 200 kgf/cm ² on the gauge of a hot press machine (cylinder diameter 300 mm). It goes through a pressurization step.

Next, through the forming steps shown in the table below, a composite separator plate before forming a gas channel for a fuel cell as shown in FIG. 2 was finally manufactured.

How to measure physical properties

- Electrical conductivity: Measured using a surface resistance meter using the 4-Point Probe technique (evaluation method ASTM D991)

- Flexural strength: Use a universal material testing machine with specimen size of 80mm

and measured at a constant strain rate (1 mm/min) (evaluation method ASTM D790)

Experimental Example 1: Examination of graphite particle size and carbon black content

The content of conductive graphite or impression graphite used as graphite was fixed at 83% by weight for effective particle arrangement and space occupancy, and the binder content was varied according to changes in the particle size of conductive graphite or impression graphite and the content of carbon black. After manufacturing the composite separator for fuel cells according to the examples and comparative examples, the physical properties were measured using the above-described physical property measurement method, and the results are shown in Table 1 (conductive graphite; 20 μm) and Table 2 (impressive graphite; 173 μm).

* unit

Sheet resistance: Ω/sq, measured thickness: mm, electrical conductivity: S/cm

Referring to Tables 1 and 2 above, the sheet resistance and electrical conductivity are relatively higher in the composite separator for fuel cells manufactured with a conductive graphite size of 173 μm than in the composite separator for fuel cells manufactured with a conductive graphite size of 20 μm. I was able to confirm that it was excellent. In addition, among composite separators for fuel cells manufactured with a graphite size of 173 μm, it was confirmed that when the carbon black content was 5% by weight, sheet resistance was the lowest and electrical conductivity was excellent.

Experimental Example 2: Review of binder and stainless steel content

As in Experimental Example 1, the content ranges of conductivity, graphite, and carbon black were determined, and the content ranges were varied to find the optimal binder and stainless metal content ranges to manufacture composite separator plates for fuel cells, and then measure the physical properties. It was measured using this method and the results are shown in Table 3 below.

Referring to Table 3 above, a composite material separator for a fuel cell manufactured by fixing graphite and carbon black and manufacturing 10% to 12% by weight of binder and 0% to 2% by weight of stainless steel has a satisfactory sheet resistance while providing electrical power. It was confirmed that conductivity and flexural strength were excellent.

Experimental Example 3: Review of content according to binder type

After determining the content ranges of conductivity, graphite, carbon black, binder, and stainless steel as in Experimental Examples 1 and 2 above, in order to check the physical properties according to the content range of the binder types included in the same binder content range, After manufacturing the composite separator plate for fuel cells under the same conditions as the molding step in Table 3, the physical properties were measured using the above measurement method, and the results are shown in Table 4 below.

Referring to Table 4, as in Experimental Example 1 and Experimental Example 2, among the content ranges of conductive, graphite, carbon black, binder, and stainless steel metal, the binder content is polyvinylidene fluoride (PVDF): fluorinated ethylene propylene. Copolymer (FEP): Polytetrafluoroethylene (PTFE) has low sheet resistance in the composite separator for fuel cells manufactured by including 7 to 10% by weight: 1.5 to 3% by weight: 0.5 to 2% by weight. It was confirmed that electrical conductivity and flexural strength were excellent.

That is, according to one embodiment, the fuel is manufactured by mixing graphite, carbon black, binder, and stainless steel metal with sizes within a specific numerical range at a content ratio within a specific numerical range, and then going through a mixing step and forming step under specific conditions. It was confirmed that the composite separator for batteries not only has excellent mechanical strength, but also has excellent sheet resistance and electrical conductivity.

Claims (9)

81% to 87% by weight of graphite;
3% to 9% by weight of carbon black;
9% to 15% by weight binder; and
A composite material separator for fuel cells, characterized in that it contains 0.5% by weight to 5% by weight of stainless steel metal. According to paragraph 1,
A composite material separator for a fuel cell, wherein the particle size of the graphite is greater than 20 μm and less than 440 μm. According to paragraph 1,
The binder includes one or more selected from the group consisting of polyvinylidene fluoride (PVDF), fluorinated ethylene propylene copolymer (FEP), and polytetrafluoroethylene (PTFE). Composite separator for fuel cells. According to paragraph 1,
A composite material separator for a fuel cell, wherein the stainless steel metal may be one or more types selected from the group consisting of STS316L, STS304L, and 17-4PH. According to paragraph 1,
A composite separator plate for fuel cells having a thickness of 2.5mm to 3.5mm. A mixing step of mixing 81% to 87% by weight of graphite, 3% to 9% by weight of carbon black, 9% to 15% by weight of binder, and 0.5% to 5% by weight of stainless steel metal to form a mixture;
A repeated pressing step of repeatedly pressing and stopping the mixture with a hot press machine; and
A method of manufacturing a composite separator plate for a fuel cell comprising a molding step of molding the repeatedly pressed result. According to clause 6,
The repeated pressing step is
A method of manufacturing a composite material separator for a fuel cell, wherein the mixture is pressed at a pressure of 100 kgf/cm ² to 200 kgf/cm ² on the gauge of a hot press machine for 1 to 2 seconds and a stop step for 3 to 5 seconds is repeated. In clause 7,
A method of manufacturing a composite material separator for a fuel cell, wherein the number of repetitions is 10 to 15 times. According to clause 6,
The forming step is
A method of manufacturing a composite separator plate for a fuel cell, wherein the repeatedly pressed result is molded at a temperature of 230°C to 270°C for 30 to 37 minutes at a pressure of 100 kgf/cm ² to 200 kgf/cm ² on a hot press gauge.