JP2006120508A - Solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polymer fuel cell improving the diffusion in the surface direction of an MEA in a gas passage and satisfactorily supplying fuel gas to an electrode corresponding to a passage crest part of a separator. <P>SOLUTION: In the solid polymer fuel cell formed by stacking an anode side gas diffusion layer, an anode catalyst layer, a polymer electrolyte membrane, a cathode catalyst layer, and a cathode side gas diffusion layer in this order, a microporous layer comprising a mixture of at least an electron conductive material, water repellent resin, and a pore forming agent is formed on the interface between the catalyst layer and the gas diffusion layer, and a differential pressure ratio in the thickness direction of the gas diffusion layer to a stacking body comprising the gas diffusion layer and the micrroporous layer is prescribed to 20-90. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polymer electrolyte fuel cell, and more particularly to improvement of a polymer electrolyte fuel cell stack MEA (membrane electrode structure).

  The polymer electrolyte fuel cell can generate electricity by electrochemically reacting a fuel gas such as hydrogen and an oxidant gas such as oxygen. Such a polymer electrolyte fuel cell is configured by stacking separators on both sides of a flat stack MEA.

  In this stack MEA, catalyst layers mainly composed of carbon powder carrying a platinum-based metal catalyst are formed in close contact with both surfaces of a polymer electrolyte membrane made of a resin having a sulfone group. Further, in order to smoothly supply the reaction gas to the catalyst layer and discharge the reaction product water, a gas diffusion layer having high gas diffusion and electron conduction is provided outside the catalyst layer.

  In order to mechanically fix the joined body of the polymer electrolyte membrane, the catalyst layer, and the gas diffusion layer, and to electrically connect adjacent joined bodies in series, conductive separator plates are provided on both sides of the joined body. It is arranged. Further, a groove-like flow path for uniformly supplying gas to the gas diffusion layer is provided on the surface of the separator facing the gas diffusion layer. Since the conductivity of the polymer electrolyte membrane is remarkably lowered when water is lost, the fuel gas and the oxidant gas are usually humidified before the reaction and sent into the cell (see, for example, Patent Document 1).

  In addition, as a method for producing a polymer electrolyte fuel cell, an electrolyte membrane and a catalyst layer are first joined to form an electrolyte membrane-catalyst layer stack (CCM), and then a gas diffusion layer is joined to both surfaces thereof. A method of forming a membrane MEA is known. In the MEA produced by this manufacturing method, it is known that the proton conductivity of the electrolyte membrane, the activity of the catalyst, the fuel gas supply property (diffusibility), and the electron conductivity of the electrode / diffusion layer affect the power generation performance. Yes. Further, in the conventional MEA, it is known to improve the performance by reducing the unevenness of the diffusion layer by forming a microporous layer of carbon and water repellent on the diffusion layer and suppressing flooding. (For example, refer to Patent Document 2).

JP-A-7-57742 JP 2004-214173 A

  However, in the conventional MEA in which the mixed layer (microporous layer) of carbon and water repellent is formed on the surface of the diffusion layer as described above, the surface direction is different from the diffusivity in the thickness direction of the MEA in the gas flow path. Since the diffusibility is small and it is difficult for the fuel gas to be supplied to the electrode corresponding to the crest portion of the separator, there is a problem that the power generation performance is lowered. Accordingly, the present invention provides a polymer electrolyte fuel cell that can improve the diffusibility of the MEA in the surface direction in the gas flow path and can satisfactorily supply fuel gas to the electrode corresponding to the flow path peak of the separator. It is an object.

  The electrode for a polymer electrolyte fuel cell of the present invention is a polymer electrolyte fuel cell in which an anode side gas diffusion layer, an anode catalyst layer, a polymer electrolyte membrane, a cathode catalyst layer, and a cathode side gas diffusion layer are laminated in this order. A laminate comprising a gas diffusion layer and a microporous layer, wherein a microporous layer made of a mixture of at least an electron conductive substance, a water repellent resin and a pore former is formed at the interface between the catalyst layer and the gas diffusion layer. The differential pressure ratio in the thickness direction of only the gas diffusion layer is 20 or more and 90 or less.

  In the polymer electrolyte fuel cell of the present invention, it is preferable that the water-repellent resin is polytetrafluoroethylene or a tetrafluoroethylene hexafluoropropylene copolymer.

  According to the present invention, the surface of the MEA in the gas flow path is formed by forming a microporous layer comprising at least a mixture of an electron conductive substance, a water repellent resin and a pore former at the interface between the catalyst layer and the gas diffusion layer. It is possible to provide a polymer electrolyte fuel cell with improved directional diffusibility and capable of satisfactorily supplying fuel gas to the electrode corresponding to the crest portion of the separator.

  The solid polymer fuel cell of the present invention has a configuration in which an anode side gas diffusion layer, an anode catalyst layer, a polymer electrolyte membrane, a cathode catalyst layer, and a cathode side gas diffusion layer are laminated in this order. In this configuration, a microporous layer made of a mixture of at least an electron conductive substance, a water repellent resin, and a pore former is formed at the interface with the gas diffusion layer. And the differential pressure ratio of the thickness direction of only the gas diffusion layer with respect to the laminated body which consists of a gas diffusion layer and a microporous layer is controlled to the specific range. In the present invention, components other than the microporous layer are not particularly limited, and therefore the microporous layer will be described in detail below. The polymer electrolyte fuel cell of the present invention can be manufactured using a conventional method.

  The microporous layer in the present invention is limited to those in which the differential pressure ratio in the thickness direction of only the gas diffusion layer with respect to the laminate with the gas diffusion layer is 20 or more and 90 or less. This is the thickness direction of the gas diffusion layer. This is because the differential pressure in the thickness direction of the microporous layer is controlled to be large and the fuel gas can be positively supplied in the plane direction. As a result, the power generation performance is greatly improved by supplying the fuel gas well to the electrodes corresponding to the crest portions of the separator.

  When the differential pressure ratio defined in the present invention is less than 20, the gas is not sufficiently diffused in the MEA plane direction, and the gas supply performance to the electrode corresponding to the channel crest portion of the separator is lowered. . On the other hand, when the differential pressure ratio is more than 70, the gas is relatively easily diffused in the MEA plane direction, but the permeation amount itself is lowered and the gas supply amount to the electrode is reduced.

  Further, the microporous layer in the present invention is composed of a mixture of at least an electron conductive substance, a water repellent resin and a pore former. As the electron conductive material in the present invention, for example, carbon black particles can be used. By using a material made of an electron conductive material as a pore forming agent described later, the electron conductive material and the pore forming agent can be used together. You can also Examples of the water-repellent resin in the present invention include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-ethylene. A copolymer (ETFE) and polyvinylidene fluoride (PVDF) can be used, and among these, PTFE and FEP are preferable. This is because the contact angle with water is large and stable to hot water.

  The pore former in the present invention is preferably a fibrous material having a fiber diameter of 0.4 μm or less. By adding such a fine fibrous material to the catalyst paste as a pore-forming agent, the fibers become pillars and take the load during pressing, and the compression load more than necessary acts on the carbon and the polymer electrolyte membrane. Since the gas channel is held without being crushed, the power generation efficiency is improved. Furthermore, as an advantage of using such a fibrous substance, the porosity of the catalyst layer after the pressing step can be freely controlled by the amount of the fibrous substance added.

Examples of the fibrous material include inorganic fibers such as alumina whiskers and silica whiskers, carbon fibers such as crystalline carbon fibers (also called vapor-grown carbon and carbon whiskers), and polymer fibers such as nylon and polyimide. In the present invention, among these, crystalline carbon fibers are preferably used. This is because crystalline carbon fibers have a large fiber diameter, are easy to control pores, and have high electron conductivity. That is, as described above, the crystalline carbon fiber can be used both as a pore former and an electron conductive material. In the present invention, the crystalline carbon fiber means that the average lattice spacing d _{002 of} [002] plane is less than 0.345 nm, the fiber diameter is 0.1 to 0.5 μm, the fiber length is 10 to 40 μm, and the bulk density is. 0.02 to 0.10 g / cm ³ , true density is 1.8 g / cm ³ or more, specific surface area is 5 to ²⁰ m ² / g, hygroscopicity is less than 0.5%, volatile content is less than 0.3%, An ash content of less than 0.05%, a pH of 7, and an oxidation start temperature of more than 550 ° C.

Next, the effects of the present invention will be described in detail by way of specific examples.
1. Preparation of polymer electrolyte fuel cell <Example 1>
9 g of platinum-supporting carbon (trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) and 35 g of ion conductive polymer solution (trade name: Nafion DE2020, manufactured by Dupont) were ball-milled to prepare a cathode catalyst paste. Further, 10 g of platinum-ruthenium-supported carbon (trade name: TEC61E54, manufactured by Tanaka Kikinzoku) and 40 g of ion-conducting polymer solution (trade name: Nafion DE2021, manufactured by Dupont) were ball-milled to prepare an anode catalyst paste. did.

Next, each of these catalyst pastes was applied onto a polytetrafluoroethylene (PTFE) sheet by screen printing so that the platinum weight was 0.5 mg / cm ^2, and then heat-treated at 120 ° C. for 60 minutes. To prepare cathode and anode electrocatalyst sheets. Next, the cathode and anode electrode catalyst sheets were transferred to respective surfaces of a polymer electrolyte membrane (trade name: Nafion 112, manufactured by Dupont) by a decal method to form an electrocatalyst layer on the polymer electrolyte. . The transfer by the decal method means that the PTFE sheet is peeled after the catalyst layer side of the electrocatalyst sheet is thermocompression bonded to the polymer electrolyte membrane.

  Moreover, as shown in Table 1, carbon paper (trade name: TGP-H-060, manufactured by Toray Industries, Inc.) was impregnated with a 10 wt% solution of tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Then, it dried by heat processing for 30 minutes at 380 degreeC, and produced the gas diffusion layer which water-repellent-treated carbon paper.

On the other hand, as shown in Table 1, 10 g of crystalline carbon fiber (trade name: VGCF, manufactured by Showa Denko KK) having both electronic conductivity and pore-forming property, and water-repellent resin (trade name: PTFE powder fullon L170J, Asahi Glass Co., Ltd. 10 g) and ethylene glycol 180 g were mixed and stirred by a ball mill to prepare a microporous layer paste. Next, this microporous layer paste is applied on the gas diffusion layer subjected to the water repellent treatment by screen printing so that the dry weight becomes 2 mg / cm ^2, and then again by screen printing under the same conditions. The porous layer paste was applied, and then dried by heat treatment at 380 ° C. for 30 minutes to produce a microporous layer.

Next, the carbon paper on which the microporous layer was formed and the ion exchange membrane to which the electrocatalyst layer was transferred were thermocompression bonded at 140 ° C. and a surface pressure of 30 kgf / cm ² to produce a stack MEA. Next, a solid polymer fuel cell of Example 1 was produced by sandwiching carbon separators with straight grooves formed on both sides of the above-described stack MEA.

<Example 2>
In the gas diffusion layer forming step of Example 1, as shown in Table 1, Example 2 was performed in the same manner as Example 1 except that carbon paper (trade name: GDL20AA, manufactured by SGL Carbon Co.) was used. A polymer electrolyte fuel cell was produced.

<Example 3>
In the formation process of the microporous layer of Example 1, the composition of the microporous layer paste was as shown in Table 1. : Vulcan XC-72, manufactured by Cabot) 4 g, water-repellent resin (trade name: PTFE powder full-on L170J, manufactured by Asahi Glass Co., Ltd.) 10 g, and ethylene glycol 180 g Example 3 A solid polymer fuel cell was prepared.

<Example 4>
In the microporous layer forming step of Example 1, the composition of the microporous layer paste was as shown in Table 1, 3 g of crystalline carbon fiber (trade name: VGCF, manufactured by Showa Denko KK), granular carbon (trade name) Example 4 in the same manner as in Example 1 except that 7 g of Vulcan XC-72, manufactured by Cabot), 10 g of water-repellent resin (trade name: PTFE powder full-on L170J, manufactured by Asahi Glass Co., Ltd.), and 180 g of ethylene glycol were used. A solid polymer fuel cell was prepared.

<Example 5>
In the microporous layer forming step of Example 1, the composition of the microporous layer paste was as shown in Table 1, with 10 g of crystalline carbon fiber (trade name: VGCF, manufactured by Showa Denko KK), water repellent resin (product) Name: PTFE powder fulon L170J, manufactured by Asahi Glass Co., Ltd.) A solid polymer fuel cell of Example 5 was produced in the same manner as in Example 1 except that 3 g and 180 g of ethylene glycol were used.

<Comparative Example 1>
In the step of forming the gas diffusion layer of Example 1, as shown in Table 1, except that carbon paper (trade name: MFG070, manufactured by Mitsubishi Rayon Co., Ltd.) was used, Comparative Example 1 was the same as Example 1. A polymer electrolyte fuel cell was produced.

<Comparative example 2>
In the microporous layer forming step of Example 1, the composition of the microporous layer paste was as shown in Table 1, 10 g of granular carbon (trade name: BP3500, manufactured by Cabot), water repellent resin (trade name: PTFE). A polymer electrolyte fuel cell of Comparative Example 2 was produced in the same manner as in Example 1 except that 10 g of Powder Fullon L170J (manufactured by Asahi Glass Co., Ltd.) and 180 g of ethylene glycol were used.

<Comparative Example 3>
In the microporous layer forming step of Example 1, the composition of the microporous layer paste was as shown in Table 1 and 10 g of granular carbon (trade name: Vulcan XC-72, manufactured by Cabot), water-repellent resin (product) Name: PTFE powder full-on L170J, manufactured by Asahi Glass Co., Ltd.) A polymer electrolyte fuel cell of Comparative Example 3 was produced in the same manner as in Example 1 except that 10 g and ethylene glycol 180 g were used.

<Comparative example 4>
In the gas diffusion layer forming process of Example 1, as shown in Table 1, comparison was made in the same manner as in Example 1 except that carbon paper (trade name: TGP-H-030, manufactured by Toray Industries, Inc.) was used. The polymer electrolyte fuel cell of Example 4 was produced.

2. Differential pressure ratio In the above process, only the gas diffusion layer used in the polymer electrolyte fuel cells of Examples 1 to 5 and Comparative Examples 1 to 4, and the constituent parts of the laminate composed of the gas diffusion layer and the microporous layer These were measured for differential pressure, and the differential pressure ratio of only the gas diffusion layer to the laminate comprising the gas diffusion layer and the microporous layer was determined. The differential pressure is a restricted surface pressure from the thickness direction on a pressing plate provided with a gas flow path having a permeation area of 2.2 cm ^{2 in} a laminate composed of only a gas diffusion layer or a gas diffusion layer and a microporous layer. The measurement was performed by sandwiching at 12 kgf / cm ² and passing nitrogen gas through the gas flow path at a flow rate of 500 cc / min / cm ² . These results are shown in Table 2.

3. Electricity generation performance evaluation For the polymer electrolyte fuel cells of Examples 1 to 5 and Comparative Examples 1 to 4 produced as described above, hydrogen gas was supplied to the anode side and air was supplied to the cathode side, and the cell temperature : 72 ° C, Stoich: Anode 5.7 / Cathode 7.3, Relative humidity: Anode / Cathode = 50/50% RH, current density: 1 A / cm ² , and terminal voltage at this time Was measured. The area of the MEA electrode part was 36 cm ² . These results are shown in Table 2 and FIG.

  As shown in Table 2 and FIG. 1, for the polymer electrolyte fuel cells of Examples 1 to 5, the differential pressure ratio of only the gas diffusion layer to the laminate composed of the gas diffusion layer and the microporous layer is 20 or more and 90 or less. In the electrode, it was shown that the diffusibility in the surface direction in the microporous layer was improved, the terminal voltage was high, and the power generation performance was excellent. On the other hand, in Comparative Examples 1 to 4 where the differential pressure ratio deviates from the scope of the present invention, it is shown that the diffusibility in the surface direction in the microporous layer is very low, the terminal voltage is low, and the power generation performance is inferior. It was.

It is a diagram which shows the correlation with the differential pressure ratio of only the gas diffusion layer with respect to the laminated body which consists of a gas diffusion layer and a microporous layer, and a terminal voltage.

Claims (2)

  In a polymer electrolyte fuel cell in which an anode side gas diffusion layer, an anode catalyst layer, a polymer electrolyte membrane, a cathode catalyst layer, and a cathode side gas diffusion layer are laminated in this order, at the interface between the catalyst layer and the gas diffusion layer A microporous layer made of a mixture of at least an electron conductive substance, a water repellent resin, and a pore former is formed, and the differential pressure ratio in the thickness direction of only the gas diffusion layer with respect to the laminate composed of the gas diffusion layer and the microporous layer is 20 A solid polymer fuel cell characterized by being 90 or less.   2. The polymer electrolyte fuel cell according to claim 1, wherein the water-repellent resin is polytetrafluoroethylene or a tetrafluoroethylene hexafluoropropylene copolymer.

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