KR101534694B1 - Membrane-electrode assembly for fuel cell - Google Patents

Abstract

A membrane-electrode assembly for a fuel cell according to an exemplary embodiment of the present invention includes an anode and a cathode electrode layer formed on both sides of a membrane with a membrane therebetween, and an anode and a cathode gas diffusion layer formed respectively in the anode electrode layer and the cathode electrode layer. And the anode gas diffusion layer is formed to be 5% or more thicker than the cathode gas diffusion layer in order to prevent flooding of the anode.

A fuel cell, an anode, a cathode, an electrode layer, a gas diffusion layer (GDL)

Description

[0001] MEMBRANE-ELECTRODE ASSEMBLY FOR FUEL CELL [0002]

An exemplary embodiment of the present invention relates to a fuel cell, and more particularly, to a membrane-electrode assembly for a fuel cell capable of reducing water moving from the cathode side to the anode side.

As is known, a fuel cell system is a kind of power generation system that converts the chemical energy of a fuel directly into electric energy.

The fuel cell system mainly includes a fuel cell stack that generates electric energy, a fuel supply device that supplies fuel to the fuel cell stack, an air supply device that supplies an oxidant required for the electrochemical reaction to the fuel cell stack, And a heat and water management device that removes the fuel cell stack and controls the operating temperature of the fuel cell stack.

In such a configuration, in the fuel cell system, electricity is generated by an electrochemical reaction between a fuel and an oxidant, and heat and water are discharged as reaction by-products.

In a fuel cell stack applied to a fuel cell vehicle, fuel cells of a unit are arranged in series, and the fuel cell has a membrane-electrode assembly (MEA) located at the innermost part thereof.

The membrane-electrode assembly consists of a membrane capable of transporting hydrogen ions (proton) and an anode catalyst layer and a cathode catalyst layer, respectively applied on both sides of the membrane, so that the fuel and the oxidant can react with each other.

In addition, a gas diffusion layer (GDL) is disposed in the outer portion of the MEA, that is, in each catalyst layer, and a fuel and an oxidant are supplied to the anode electrode layer and the cathode electrode layer on the outer side of each gas diffusion layer A separator having a flow field is disposed to discharge the water generated by the reaction.

Here, the anode gas diffusion layer diffuses the fuel to the anode electrode layer, and the cathode gas diffusion layer diffuses the oxidant to the cathode electrode layer, and the anode and the cathode gas diffusion layers are formed to have substantially the same thickness.

Accordingly, the fuel is supplied to the anode electrode layer through the anode gas diffusion layer, and the oxidant is supplied to the cathode electrode layer through the cathode gas diffusion layer, so that the fuel supplied to the anode electrode layer is separated from hydrogen ions (Proton, H +) by the catalyst of the anode electrode layer (Proton, H +) is selectively passed through the membrane, which is a cation exchange membrane, to the cathode electrode layer, and at the same time, the electrons (e, e) And the cathode electrode layer through the separator.

Thus, in the cathode electrode layer, the hydrogen ion supplied through the membrane and the separately supplied oxidizing agent are brought into contact with each other to generate water. Due to the movement of the hydrogen ions occurring at this time, an electric current is generated by the flow of electrons through the external lead, and the heat is incidentally generated in the water production reaction.

In such a fuel cell, water produced in the cathode electrode layer and water introduced from the outside through a humidifier or the like are reduced in thickness due to back diffusion due to the difference in concentration of water and reduction of the anode (catalyst layer and gas diffusion layer) And moves to the anode side from the cathode side as a heat pipe or the like due to a temperature difference between the cathode (catalyst layer and gas diffusion layer). The principle of the above-mentioned heat pipe will be described more specifically in the embodiment of the present invention.

Therefore, in the prior art, as the water moves from the cathode to the anode due to the temperature difference between the anode and the cathode at a relative humidity of about 100%, the closed loop structure due to the fuel recirculation causes the anode side to be relatively water- And as a result, flooding phenomenon occurs in the anode, so that the performance and durability of the fuel cell are deteriorated.

An exemplary embodiment of the present invention has been made to overcome the above-mentioned problems, and it is an object of the present invention to provide a cathode diffusion layer and a cathode diffusion layer, which are formed by reducing or varying the thicknesses of the anode diffusion layer and the cathode diffusion layer, The membrane-electrode assembly for a fuel cell is provided.

For this, a membrane-electrode assembly for a fuel cell according to an exemplary embodiment of the present invention includes an anode and a cathode electrode layer formed on both sides of a membrane, and an anode and a cathode formed respectively in the anode electrode layer and the cathode electrode layer, The anode diffusion layer is formed to be 5% or more thicker than the cathode diffusion layer in order to prevent flooding of the anode.

In the fuel cell membrane-electrode assembly, the anode gas diffusion layer may be a single layer.

In the fuel cell membrane-electrode assembly, the anode gas diffusion layer may be formed of at least two or more layers.

In the membrane-electrode assembly for a fuel cell, the anode and the cathode gas diffusion layer may be formed of a material selected from the group consisting of polytetrafluoroethylene, a copolymer based on the polytetrafluoroethylene, and a mixture of two or more kinds of hydrophobic polymers Polymer blend, and the like.

In the membrane-electrode assembly for a fuel cell, the cathode gas diffusion layer may further contain 1 to 70 parts by weight (WT%) of the hydrophobic substance as compared with the anode gas diffusion layer.

In the fuel cell membrane-electrode assembly, the anode and cathode diffusion layers may be formed of at least one macro-porous substrate and / or a micro-porous layer.

In the above membrane-electrode assembly for a fuel cell, the macropore support may be made of at least one material selected from carbon fiber felt, carbon fiber paper, carbon fiber cloth, metal mesh, and metal foam.

In the membrane-electrode assembly for a fuel cell, the microporous layer may be formed of at least one material selected from carbon powder, carbon fiber, and metal mesh.

According to the exemplary embodiment of the present invention as described above, the thickness of the anode gas diffusion layer and the cathode gas diffusion layer can be made to be two or more in number to reduce the temperature difference between the anode and the cathode, thereby reducing the amount of water moving from the cathode to the anode .

Therefore, in the present embodiment, the current-voltage performance of the fuel cell stack can be improved, and the fuel-cell stack can be prevented from lowering in durability due to insufficient fuel supply by improving the anode- As the control frequency of the valve for discharging the condensed water is reduced, the discharge of the fuel can be minimized and the fuel consumption can be increased by reducing the power of the flow.

In this embodiment, energy loss for thawing the condensed water of the anode can be reduced during cold start of the fuel cell vehicle, and durability of the driving part can be improved as the water contact of the driving part such as the recycle blower is reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

In addition, since the sizes and thicknesses of the respective components shown in the drawings are arbitrarily shown for convenience of explanation, the present invention is not necessarily limited to those shown in the drawings.

In the drawings, the thickness is enlarged to clearly represent the layers and regions.

In the drawings, for the convenience of explanation, the thicknesses of some layers and regions are exaggerated. Whenever a portion such as a layer, film, region, plate, or the like is referred to as being "on" or "on" another portion, it includes not only the case where it is "directly on" another portion but also the case where there is another portion in between.

1 is a schematic view of a fuel cell to which a membrane-electrode assembly according to an exemplary embodiment of the present invention is applied.

Referring to the drawings, a membrane-electrode assembly 100 for a fuel cell according to an exemplary embodiment of the present invention includes a fuel cell 10 composed of a unit cell that generates electric energy by an electrochemical reaction of a fuel and an oxidant will be.

The fuel cell 10 can be classified into a polymer electrolyte fuel cell and a direct oxidation fuel cell depending on the fuel.

Here, the fuel cell 10 is disposed such that the separator 11 is in close contact with both sides of the membrane-electrode assembly 100 according to the present embodiment.

The separator 11 is in the form of a plate having conductivity and forms a channel CH for supplying a fuel and an oxidant to the membrane-electrode assembly 100, respectively.

2 is a cross-sectional view schematically showing a membrane-electrode assembly for a fuel cell according to an exemplary embodiment of the present invention.

Referring to the drawings, a membrane-electrode assembly 100 for a fuel cell according to an exemplary embodiment of the present invention includes an anode electrode layer 30 and a cathode electrode layer 40 formed on both sides of the membrane 20, And an anode gas diffusion layer 50 and a cathode gas diffusion layer 60 formed in the anode electrode layer 30 and the cathode electrode layer 40, respectively.

The anode electrode layer 30 separates the fuel supplied through the channel CH of the separator 11 into an electron and a hydrogen ion through oxidation reaction and the membrane 20 has a function of moving hydrogen ions to the cathode electrode layer 40 .

The cathode electrode layer 40 generates water and heat by reducing the electrons and hydrogen ions received from the anode electrode layer 30 and the oxidant supplied through the channel CH of the separator 11.

The anode gas diffusion layer 50 functions to diffuse the fuel into the anode electrode layer 30 and the cathode gas diffusion layer 60 functions to diffuse the oxidant into the cathode electrode layer 40.

The fuel cell 10 generates electricity in the cathode electrode layer 40 during the process of generating electrical energy as an electrochemical reaction between the fuel and the oxidant. The fuel cell 10 flows into the fuel cell 10 from the outside through the water and the humidifier Water is supplied to the heat pipe by the back diffusion due to the difference in the concentration of water and the temperature difference between the anode (catalyst layer and gas diffusion layer) and the cathode (catalyst layer and gas diffusion layer) The cathode is moved from the cathode to the anode.

In this case, the above-mentioned heat pipe phenomenon occurs when the temperature of the membrane-electrode assembly 100 of the fuel cell 10 is lowered near the relative humidity of 100% by an amount proportional to the temperature difference between the anode and the cathode, .

The difference in temperature means a value obtained by dividing the temperature difference between the anode and the cathode by the thickness in each of these lamination directions. Generally, the temperature difference between the cathode electrode layer 40 and the anode gas diffusion layer 50 is larger than the difference between the cathode electrode layer 40 and the cathode Which is larger than the temperature difference of the gas diffusion layer 60, so that the water moves from the cathode to the anode. At this time, the temperature distribution between the anode and the cathode shows the highest temperature in the cathode electrode layer 40 where an electrochemical reaction occurs.

Accordingly, the membrane-electrode assembly 100 according to the exemplary embodiment of the present invention is configured as a structure capable of reducing the amount of water moving from the cathode electrode layer 40 to the anode electrode layer 30.

Specifically, the thickness of the anode gas diffusion layer 50 and the thickness of the cathode diffusion layer 60 are reduced to reduce the temperature difference between the anode and the cathode, thereby reducing the amount of water moving from the cathode electrode layer 40 to the anode electrode layer 30 As shown in FIG.

For this, in the membrane-electrode assembly 100, the anode gas diffusion layer 50 and the cathode gas diffusion layer 60 are formed to have different thicknesses. In this embodiment, the anode gas diffusion layer 50 is formed as a single layer, And is formed to be approximately 5% or more thicker than the gas diffusion layer 60.

That is, in the present embodiment, by increasing the thickness of the anode gas diffusion layer 50 to a certain ratio and reducing the thickness of the cathode gas diffusion layer 60 to a certain ratio, the total thickness of the gas diffusion layers 50, Lt; RTI ID = 0.0 > a < / RTI > cathode diffusion layer.

The reason why the total thickness of the anode gas diffusion layer 50 and the cathode gas diffusion layer 60 according to the present embodiment is formed to be similar to the combined thickness of the anode gas diffusion layer and the cathode gas diffusion layer according to the prior art, So as not to affect the electrical resistance and current-voltage performance of the device.

In the membrane-electrode assembly 100 as described above, the anode gas diffusion layer 50 and the cathode gas diffusion layer 60 are formed in the same manner as in the membrane-electrode assembly 100 in order to smoothly discharge the water generated by the electrochemical reaction of the fuel and the oxidizer, Polytetrafluoroethylene, a copolymer based on the polytetrafluoroethylene, or a polymer blend in which two or more of these hydrophobic polymers are mixed.

Here, the cathode gas diffusion layer 60 promotes the discharge of the reaction-generated water remaining in the cathode gas diffusion layer 60 without water being back-diffused toward the anode gas diffusion layer 50, and water flooding It is preferable that 1 to 70 parts by weight (WT%) of the above-mentioned hydrophobic substance is further contained in comparison with the anode gas diffusion layer 50 in order to minimize the phenomenon of "flooding" for convenience.

The anode gas diffusion layer 50 and the cathode gas diffusion layer 60 are formed as one or two or more macro-porous substrates and / or micro-porous layers.

In this case, the macro pore scaffold is composed of one or more materials selected from carbon fiber felt, carbon fiber paper, carbon fiber cloth, metal mesh, and metal foam, either singly or in combination.

The microporous layer may be formed of one or more materials selected from carbon powder, carbon fiber, and metal mesh, either singly or in combination.

Accordingly, the membrane-electrode assembly 100 for a fuel cell according to the exemplary embodiment of the present invention configured as described above can reduce the thickness of the anode gas diffusion layer 50 and the cathode gas diffusion layer 60 so that the temperature difference between the anode and the cathode The amount of water moving from the cathode electrode layer 40 to the anode electrode layer 30 can be reduced.

FIG. 3 is a graph showing the ratio of the anode and cathode condensed water to the generated water according to the prior art and the present embodiment. In this graph, AWT represents the ratio of the condensate of the anode to the generated water according to the prior art, AWT2 represents the ratio of the condensate of the anode to the produced water according to the present embodiment, and CWT2 represents the ratio of the condensate of the cathode to the produced water according to this embodiment.

Referring to the drawings, when the thicknesses of the anode gas diffusion layer and the cathode gas diffusion layer are the same in the prior art, the ratio of the anode to cathode condensed water with respect to the produced water shows a tendency of AWT and CWT.

Generally, although the amount of AWT in the CWT is relatively small, the water discharge on the anode side is relatively difficult due to the closed loop structure using the fuel recirculation method, so that the anode side is flooded, The endurance is adversely affected.

However, in the present embodiment, when the thickness of the anode gas diffusion layer 50 is increased by 30% and the thickness of the cathode gas diffusion layer 60 is reduced by 30%, that is, when the thicknesses of the anode gas diffusion layer 50 and the cathode gas diffusion layer 60 ) If there is no change in the sum of the thicknesses, the ratio of anode to cathode condensate to product water represents the trend of AWT2 and CWT2.

That is, as can be seen from the graph of this embodiment, the condensed water of the anode is remarkably improved compared to the conventional one, and the condensed water of the cathode is further increased compared with the conventional one. This is because the air flow control and the hydrophobic treatment of the cathode gas diffusion layer And the water discharge treatment is relatively easy compared with the anode side due to strengthening or the like.

As a result, the membrane-electrode assembly 100 for a fuel cell according to the exemplary embodiment of the present invention can reduce the amount of water moving from the cathode side to the anode side, thereby reducing the anode's condensed water by approximately 34 to 44% The condensate of the cathode is increased by approximately 8 to 37%.

As described above, in this embodiment, the current-voltage performance of the stack in which a plurality of fuel cells 10 are stacked can be improved, and the durability of the stack is lowered due to the shortage of fuel due to the floding on the anode side As the control frequency of the valve for discharging the condensed water on the anode side is reduced, the discharge of the fuel can be minimized, and the fuel consumption can be increased due to the reduced power of the flow.

Further, in the present embodiment, it is possible to reduce the energy loss for thawing the condensed water of the anode when the fuel cell vehicle is cold-started, and as the water contact of the driving unit such as the recycle blower decreases, the durability of the driving unit can be improved do.

4 is a cross-sectional view schematically showing a membrane-electrode assembly for a fuel cell according to another exemplary embodiment of the present invention.

Referring to the drawings, a membrane-electrode assembly 200 for a fuel cell according to another exemplary embodiment of the present invention includes a plurality of anode gas diffusion layers 150 and a cathode gas diffusion layer 160, .

In the present embodiment, the anode gas diffusion layer 150 is thicker than the cathode diffusion layer 160 by a predetermined ratio, and at least two or more layers are attached.

The rest of the configuration and operation of the membrane-electrode assembly 200 for a fuel cell according to another exemplary embodiment of the present invention are the same as those in the first embodiment, and thus a detailed description thereof will be omitted herein.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, And it goes without saying that the invention belongs to the scope of the invention.

These drawings are for the purpose of describing an exemplary embodiment of the present invention, and therefore the technical idea of the present invention should not be construed as being limited to the accompanying drawings.

1 is a schematic view of a fuel cell to which a membrane-electrode assembly according to an exemplary embodiment of the present invention is applied.

2 is a cross-sectional view schematically showing a membrane-electrode assembly for a fuel cell according to an exemplary embodiment of the present invention.

3 is a graph for explaining the operation of a membrane-electrode assembly for a fuel cell according to an exemplary embodiment of the present invention.

4 is a cross-sectional view schematically showing a membrane-electrode assembly for a fuel cell according to another exemplary embodiment of the present invention.

Claims (8)

An anode and a cathode electrode layer formed on both sides of the membrane with the membrane therebetween; and a microporous layer formed on the anode electrode layer and the cathode electrode layer, the macro-porous substrate and the microporous layer An anode and a cathode gas diffusion layer, A membrane-electrode assembly for a fuel cell in which water is moved from the cathode electrode layer to the anode electrode layer, and a closed separator is closely attached to the anode and the cathode gas diffusion layer, In order to prevent flooding of the anode, the anode gas diffusion layer is formed to be 5% or more thicker than the cathode gas diffusion layer, and the anode gas diffusion layer is composed of two or more layers, Wherein the anode and the cathode gas diffusion layers contain a hydrophobic substance selected from polytetrafluoroethylene, a copolymer based on the polytetrafluoroethylene, and a polymer blend comprising two or more kinds of hydrophobic polymers, Wherein the cathode gas diffusion layer comprises 1 to 70 parts by weight (WT%) of the hydrophobic substance as compared to the anode gas diffusion layer. delete delete delete delete delete The method according to claim 1, Wherein the macropore support is made of at least one material selected from carbon fiber felt, carbon fiber paper, carbon fiber cloth, metal mesh, and metal foam. The method according to claim 1, Wherein the microporous layer is made of at least one material selected from carbon powder, carbon fiber, and metal mesh.

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