WO2013065897A1 - Double-sided superhydrophobic gas diffusion layer for a polymer electrolyte membrane fuel cell, method for preparing same, and polymer electrolyte membrane fuel cell including same - Google Patents

Abstract

The present invention relates to a double-sided superhydrophobic gas diffusion layer for a polymer electrolyte membrane fuel cell, to a method for preparing same, and to a polymer electrolyte membrane fuel cell including same. More particularly, the present invention relates to a double-sided superhydrophobic gas diffusion layer for a polymer electrolyte membrane fuel cell, which not only has stability and durability without any loss in electrical conductivity but also has stable performance in a high-current region in which much moisture is produced due to double-sided superhydrophobicity, and which can maintain ionic conductivity by controlling moisture content to a suitable level in a low-current region, and which can be manufactured economically through a simple process; the present invention also relates to a method for preparing the double-sided superhydrophobic gas diffusion layer and to a polymer electrolyte membrane fuel cell including the double-sided superhydrophobic gas diffusion layer.

Description

Double-sided superhydrophobic gas diffusion layer for polymer electrolyte fuel cell, manufacturing method thereof and polymer electrolyte fuel cell comprising same

The present invention relates to a double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell, a manufacturing method thereof, and a polymer electrolyte fuel cell including the same.

A fuel cell is a power generation device that directly converts chemical energy of fuel into electrical energy by an electrochemical reaction. It is an integrated technology including a fuel cell stack, a fuel converter, a BOP, and a control technology. As demand for portable power is rapidly increasing, it has been spotlighted as a means to sufficiently replace energy systems such as gasoline engines and secondary batteries.

The fuel cell produces water as a product in the process of obtaining electrical energy from the fuel. As the power density increases, the fuel cell stack becomes larger and the smooth drainage and efficient reuse of the generated water become important variables in the system design. . In particular, studies have been conducted to optimize the water drainage characteristics by adding hydrophobic materials in order to properly control the hydrophobicity of the cathode components in which the oxygen reduction reaction occurs, and to supply air and drain the generated water without losing electrical conductivity. Finding the conditions under which is well maintained has been a technically important issue.

Korean Unexamined Patent Publication No. 2010-0132250 discloses a gas diffusion layer carbon substrate having a double structure of a polymer fuel cell membrane electrode assembly and a method of manufacturing the same. Water generated during the power generation process of the battery is introduced into the pore distribution region, and the cohesive force is weakened by the capillary phenomenon so that smooth water repellency is achieved.

In addition, Korean Unexamined Patent Publication No. 2010-0109733 discloses a fuel cell electrode, a manufacturing method thereof, and a fuel cell having the same, and specifically, a gas diffusion layer; Catalyst layer; And a water-repellent material positioned at an interface between the gas diffusion layer and the catalyst layer and having a continuous concentration gradient in the thickness direction and a discontinuous concentration gradient in the plane direction, wherein the water-repellent material includes PTFE, FEP or PFA. Water-repellent polymer such as is used.

However, the above-described inventions require complicated manufacturing processes, such as undergoing separate pore forming operations or varying concentration gradients of water-repellent materials. In addition, the above-described inventions overlook the fact that in order to achieve optimal fuel cell performance, the generated water should be maintained in the low current region, even if the generated water is discharged in the high current region. In other words, in order to preserve the ion conducting performance of the fuel cell, the generated water should not be released, but rather maintained. If the water diffusion treatment is performed only on one surface of the gas diffusion layer or the corresponding water repellent layer, as in the related arts, Moisture retention in the current region is not possible.

On the other hand, Korean Patent Laid-Open Publication No. 2009-0038747 discloses a cathode electrode for a fuel cell having two types of water repellency, a method of manufacturing the same, and a membrane electrode assembly and a fuel cell including the same, and specifically contacting a separator having a flow path formed therein. A cathode electrode for a fuel cell comprising a gas diffusion layer and a catalyst layer interposed between the gas diffusion layer and an electrolyte membrane, the cathode electrode for a fuel cell having a catalyst layer comprising two parts having different water repellency, the electrode not facing the flow path in the catalyst layer. Disclosed is a cathode electrode for a fuel cell, the portion of which is higher in water repellency than the portion facing the flow path.

However, the above-described technology also has a problem in that the manufacturing process is complicated because two parts having different water repellency are formed, and the catalyst efficiency may be adversely affected because the water repellent treatment is performed on the catalyst layer instead of the gas diffusion layer.

Accordingly, the technical problem to be solved by the present invention is stable and durable without loss of electrical conductivity, while exhibiting stable performance in a high current region in which water is generated and maintaining an appropriate level of water content in a low current region, thereby maintaining ion conductivity. It is to provide a double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell that can preserve the, can be produced by an economical and simple manufacturing process, a method of manufacturing the same and a polymer electrolyte fuel cell comprising the same.

The present invention to achieve the first technical problem,

Provided as a gas diffusion layer for a polymer electrolyte fuel cell, a superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell, characterized in that a super water-repellent layer comprising silicon oxide and carbon is deposited on both sides of the gas diffusion layer.

According to one embodiment of the invention, the thickness of the super water-repellent layer may be 1nm to 100nm.

According to another embodiment of the present invention, the gas diffusion layer may be a porous carbon paper, porous carbon fiber or porous carbon felt.

According to another embodiment of the present invention, the gas diffusion layer may further include a carbon powder layer.

According to another embodiment of the present invention, the contact angle of the gas diffusion layer with water may be 150 ° or more.

The present invention to achieve the second technical problem,

Preparing a gas diffusion layer for a polymer precursor and a polymer electrolyte fuel cell including silicon atoms and carbon atoms; And

It provides a method for producing a double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell comprising the step of simultaneously depositing the silicon precursor and the carbon on both sides of the gas diffusion layer by heating the polymer precursor and the gas diffusion layer together in a heating chamber.

According to one embodiment of the invention, the heating step may be performed for 30 minutes to 1 hour at a temperature of 100 ℃ to 400 ℃.

According to another embodiment of the present invention, the heating step may be performed for 30 minutes to 1 hour at a temperature of 150 ℃ to 250 ℃.

According to another embodiment of the present invention, the polymer precursor may be one or more polymers selected from the group consisting of polydiorganosiloxane, organohydrogen polysiloxane and organopolysiloxane.

According to another embodiment of the present invention, the gas diffusion layer may be porous carbon paper, porous carbon fiber or porous carbon felt.

According to another embodiment of the present invention, the gas diffusion layer may further include a carbon powder layer.

The present invention to achieve the third technical problem,

Provided is a polymer electrolyte fuel cell comprising a double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell according to the present invention.

According to the present invention, while maintaining stability and durability without loss of electrical conductivity, due to double-sided super water repellency, it exhibits stable performance in a high current region in which moisture is generated and maintains an appropriate level of water content in a low current region, thereby improving ion conductivity performance. It is possible to provide a double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell that can be preserved and manufactured by an economical and simple manufacturing process, a method of manufacturing the same, and a polymer electrolyte fuel cell including the same.

1 is a view schematically showing how the double-sided water-repellent gas diffusion layer according to the present invention acts in a high current region and a low current region.

2 is a schematic view of a process of heating a polymer precursor and a gas diffusion layer together in a heating chamber in the method of manufacturing a gas diffusion layer for a polymer electrolyte fuel cell according to the present invention.

3a and 3c are electron micrographs for measuring the contact angle with respect to water of the conventional gas diffusion layer (3a: surface without the carbon powder layer; 3c: surface with the carbon powder layer), Figures 3b and 3d are The superhydrophobic gas diffusion layer (3b: surface without carbon powder layer; 3d: surface with carbon powder layer) is an electron micrograph for measuring the contact angle to water.

Figure 4 is a graph showing the measurement of the magnitude of the voltage and power according to the change in current density for the conventional membrane-electrode assembly and the membrane-electrode assembly according to the present invention (membrane-electrode assembly according to the present invention: a square display , Membrane-electrode assembly according to a comparative example: marked with a red circle).

Figure 5 is a graph showing the results of performing the performance evaluation while adjusting the flow rate of the additional air to the membrane-electrode assembly according to the present invention.

6A and 6B are graphs showing SIMS spectra for a gas diffusion layer (FIG. 6A) according to the present invention and a gas diffusion layer (FIG. 6B) according to the prior art.

7A and 7B are graphs showing Raman shifts for a gas diffusion layer (FIG. 7A) according to the present invention and a gas diffusion layer (FIG. 7B) according to the prior art.

The present invention provides a double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell, as a gas diffusion layer for a polymer electrolyte fuel cell, wherein a superhydrophobic layer containing silicon oxide and carbon is deposited on both surfaces of the gas diffusion layer.

As will be described in more detail in the following examples, the gas diffusion layer for a polymer electrolyte fuel cell according to the present invention can be produced by a simple manufacturing process, while maintaining a stable performance in a high current region with high moisture generation, while maintaining ion conductivity Excellent performance can be maintained even in low current areas where moisture is required. FIG. 1 schematically illustrates a mechanism of operation of the double-sided water-repellent gas diffusion layer according to the present invention by which mechanism can exhibit stable and excellent performance in the high current region and the low current region, respectively. Referring to FIG. 1, the double-sided superhydrophobic gas diffusion layer according to the present invention performs a self-humidifying function by back diffusion of water toward the catalyst layer and the polymer electrolyte membrane in a low current region. In the high current region, self-discharging is achieved by discharging water forward in the opposite direction. As a result, such self-moisture and self-discharge functions enable the proper amount of water management, which is essential for smooth performance of the fuel cell.

In the present invention, the thickness of the super water-repellent layer is preferably 1nm to 100nm, which may have a problem that the super water-repellent properties are not well implemented when the thickness of the super water-repellent layer is less than 1nm, when the thickness exceeds 100nm This is because there is a problem that the conductivity is lowered, which is not preferable.

In the present invention, as the gas diffusion layer in which the super water repellent layer is formed, a conventional gas diffusion layer for a polymer electrolyte fuel cell may be used without limitation, and in particular, in order to maximize the super water repellency, the surface already has some roughness characteristics. A gas diffusion layer of a porous structure having a large specific surface area, for example, a gas diffusion layer such as porous carbon paper, porous carbon fiber or porous carbon felt may be used.

As described in the following examples, the gas diffusion layer according to the present invention exhibits excellent water repellent properties, so that the contact angle of the gas diffusion layer with water has a minimum value required for superhydrophobic expression, that is, a value of 150 ° or more. . Meanwhile, in some cases, a carbon powder layer may be further laminated on the surface of the gas diffusion layer in order to implement more excellent super water repellency.

The present invention comprises the steps of preparing a gas diffusion layer for a polymer precursor and a polymer electrolyte fuel cell comprising a silicon atom and a carbon atom in order to achieve the second technical problem; And simultaneously depositing silicon oxide and carbon on both sides of the gas diffusion layer by heating the polymer precursor and the gas diffusion layer together in a heating chamber to provide a method for manufacturing a double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell. .

As the polymer precursor, any polymer that includes silicon (Si) atoms and carbon (C) atoms as constituent atoms constituting the polymer may be used without limitation, but is not limited thereto, and polydiorganosiloxanes such as polydimethylsiloxane And one or more polymers selected from the group consisting of organohydrogen polysiloxanes and organopolysiloxanes.

In addition, as described above, the manufacturing method according to the present invention is applicable to various gas diffusion layers such as porous carbon paper, porous carbon fiber or porous carbon felt, such as porous carbon paper, carbon powder to further improve super water repellency Layers may be further stacked.

Figure 2 shows a schematic diagram of a process of heating a polymer precursor and a gas diffusion layer together in a heating chamber in the manufacturing method according to the present invention. As can be seen in Figure 2, in the present invention, by simply putting together the polymer precursor and the gas diffusion layer in the heating chamber, the super water-repellent surface characteristics can be imparted to both sides of the gas diffusion layer. At this time, the polymer precursor placed in the chamber is vaporized by an appropriate heating temperature, and vaporized precursor particles are deposited on the surface of the target gas diffusion layer. Through this process, silicon oxide and carbon are deposited on the surface of the gas diffusion layer to realize super water repellency.

In particular, in the present invention, the heating temperature for the deposition of the silicon oxide and carbon is very important, preferably, the heating step is 30 at a temperature of 100 ℃ to 400 ℃, more preferably from 150 ℃ to 250 ℃ May be performed for minutes to 1 hour. When the temperature of the heating step is less than 100 ℃ or the heating time is less than 30 minutes there is a problem that it is difficult to deposit silicon oxide and carbon in the gas diffusion layer to be deposited because the precursor is not vaporized, the temperature of the heating step is 400 It is not preferable when the temperature exceeds 1 ° C or the heating time exceeds 1 hour, since the surface structure of silicon oxide and carbon formed on the gas diffusion layer may change and superhydrophobic function may be lost.

Finally, the present invention provides a polymer electrolyte fuel cell comprising a double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell according to the present invention in order to achieve the third technical problem.

The polymer electrolyte fuel cell according to the present invention includes a membrane-electrode assembly composed of a conventional conventional cathode-polymer electrolyte membrane-oxide electrode, in addition to the surface of the cathode that is not in contact with the polymer electrolyte membrane. It has a structure in which a double-sided superhydrophobic gas diffusion layer is laminated on the surface (superhydrophobic gas diffusion layer-reducing electrode-polymer electrolyte membrane-oxide electrode).

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are not intended to limit the scope of the present invention, but are described as to help understanding of the present invention.

<Production of Super Water Repellent Gas Diffusion Layer>

As shown in Fig. 2, polydimethylsiloxane was used as a polymer precursor containing silicon and carbon atoms in a heating chamber to which a power supply was attached, and a commercial carbon paper (SGL Technologies, Germany) was used as a gas diffusion layer. Heating for deposition was performed using a hot wire located within the chamber. Heating was initially continued for 5 minutes at 100V using a voltage controller, and then transformed to 150V to raise the temperature to 200 ° C. The temperature in the chamber was measured in real time through a temperature meter, and the temperature was maintained for 30 minutes so that the polydimethylsiloxane vaporized and deposited on the surface of the carbon paper when the temperature reached 200 ° C.

Contact angle analysis for water

The contact angle with respect to water of the super water-repellent carbon paper prepared by the above example was measured (Phoenix 300 Touch, Futus, Korea), and the measured results are shown in FIG. 3B. Generally, a surface having a contact angle with water of 150 ° or more is referred to as a super water-repellent surface. As shown in FIG. 3B, the contact angle with respect to water of the super water-repellent carbon paper surface prepared by the above embodiment was 150.3 °, and thus It can be seen that it has super water repellent properties. For comparison, FIG. 3A shows the contact angle of water with respect to the conventional carbon paper before the superwater repellent treatment according to the above-described embodiment, and the measured contact angle with respect to the water is 134.7 °. It can be seen that it does not have. Therefore, it can be seen that the silicon oxide and carbon deposited on the surface of the carbon paper by the present invention contribute to the increase in the super water repellency of the carbon paper.

3C and 3D show the gas before the super water repellent treatment (FIG. 3C) and after the super water repellent treatment (FIG. 3D) when the carbon powder layer is additionally laminated on the surface of the gas diffusion layer. It is an electron microscope photograph for measuring the contact angle of the diffusion layer with respect to water. 3C and 3D, the superhydrophobic treatment according to the present invention caused a slight superhydrophobic increase even when including a carbon powder layer for further superhydrophobicity improvement (from 150.6 ° of FIG. 3C, FIG. 3d increased to 150.9 °), the increase in superhydrophobicity is less than in the absence of additional carbon powder layer.

On the other hand, in order to confirm that the gas diffusion layer according to the embodiment contains silicon oxide on the surface, SIMS spectrum for the gas diffusion layer (Fig. 6a) according to the present invention and the gas diffusion layer according to the prior art (Fig. 6b) In order to confirm that the loss of electrical conductivity was minimized even after the superhydrophobic treatment according to the present invention, the gas diffusion layer according to the present invention (FIG. 7A) and the gas diffusion layer according to the prior art (FIG. 7B). Raman shift for was measured. As can be seen from the results of FIGS. 6A and 6B and also FIGS. 7A and 7B, silicon oxide was deposited on the surface of the gas diffusion layer by the superhydrophobic treatment according to the above embodiment, and almost no loss of electrical conductivity occurred after the deposition. You can see that it does not.

<Production of membrane-electrode assembly>

Comparative example. Preparation of membrane-electrode assembly according to the prior art

In order to produce a cathode, a metal catalyst layer was formed by supporting a platinum supported catalyst on a carbon paper in a content of about 0.5 mg / cm ² using a spray method (ionomer: 30% of the supported catalyst amount). Subsequently, the prepared cathode, polymer electrolyte membrane (Nafion membrane, Dupont) and an anode (platinum supported catalyst: 0.3 mg / cm ² , ionomer: 30% of the amount of supported catalyst) were laminated, and at a temperature of 140 ° C. , Under pressure of 10 MPa, for 5 minutes to prepare a membrane-electrode assembly.

Example. Preparation of the membrane-electrode assembly according to the present invention

A membrane-electrode assembly was manufactured by the same method as the comparative example, except that the prepared superhydrophobic gas diffusion layer was further stacked on the surface not in contact with the polymer electrolyte membrane of the cathode.

<Performance evaluation>

In order to compare the performance of the membrane-electrode assembly according to the comparative example and the membrane-electrode assembly according to the present invention, the magnitude of voltage and power according to the change of the current density for each membrane-electrode assembly was measured. Voltage measurements were performed at a temperature of 70 ° C., 100% relative humidity, and under conditions of supplying hydrogen fuel and air. 4 shows the measured voltage (membrane-electrode assembly according to the present invention: a square display, a membrane-electrode assembly according to a comparative example: a red circle), and referring to FIG. 4, a membrane-electrode assembly according to the present invention. It can be seen that shows a stable performance in the high current region with the most water generation, and excellent performance compared to the membrane-electrode assembly according to the comparative example even in a low current region that requires some moisture for ion conductivity.

In addition, in order to evaluate the stability of the performance according to the proper water drainage performance evaluation was performed by adjusting the flow rate of the additional air, the results are shown in FIG. In the description of FIG. 5, lambda 1.0 means the amount of oxygen theoretically required to generate a constant current, and it is possible to produce a stable current at a surplus oxygen, that is, a lambda value of 2.5 or more.

 Referring to FIG. 5, the membrane-electrode assembly according to the present invention is capable of producing a stable current even under a lambda value of 1.5 or 2.0, which shows that the membrane-electrode assembly according to the present invention exhibits stable performance even at 60% of a conventional flow rate. In particular, considering that the performance evaluation condition is 100% relative humidity, it can be seen that the effect of stability is very large.

Claims (12)

1. A gas diffusion layer for a polymer electrolyte fuel cell, wherein a super water-repellent layer including silicon oxide and carbon is deposited on both surfaces of the gas diffusion layer.
2. The double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell according to claim 1, wherein the superhydrophobic layer has a thickness of 1 nm to 100 nm.
3. The double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell according to claim 1, wherein the gas diffusion layer is a porous carbon paper, a porous carbon fiber or a porous carbon felt.
4. The double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell according to claim 1, further comprising a carbon powder layer on a surface of the gas diffusion layer.
5. The double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell according to claim 1, wherein a contact angle with water of the gas diffusion layer is 150 ° or more.
6. Preparing a gas diffusion layer for a polymer precursor and a polymer electrolyte fuel cell including silicon atoms and carbon atoms; And

   And simultaneously depositing silicon oxide and carbon on both sides of the gas diffusion layer by heating the polymer precursor and the gas diffusion layer together in a heating chamber.
7. The method of claim 6, wherein the heating is performed for 30 minutes to 1 hour at a temperature of 100 ° C. to 400 ° C. 7.
8. The method of claim 6, wherein the heating is performed at a temperature of 150 ° C. to 250 ° C. for 30 minutes to 1 hour.
9. The method of claim 6, wherein the polymer precursor is at least one polymer selected from the group consisting of polydiorganosiloxane, organohydrogen polysiloxane, and organopolysiloxane.
10. The method of claim 6, wherein the gas diffusion layer is a porous carbon paper, a porous carbon fiber, or a porous carbon felt.
11. The method of manufacturing a double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell according to claim 6, further comprising a carbon powder layer on the surface of the gas diffusion layer.
12. A polymer electrolyte fuel cell comprising a double-sided superhydrophobic gas diffusion layer for a polymer electrolyte fuel cell according to any one of claims 1 to 5.

Images