JP2006134640A - Polymer electrolyte fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer electrolyte fuel cell capable of stably keeping contact resistance between a metallic separator and a gas diffusion layer in a low value even when repeated load fatigue is added, preventing stay of produced water, and having high power generation performance. <P>SOLUTION: In the polymer electrolyte fuel cell formed by stacking a cathode side separator, an anode side gas diffusion layer, a cathode, a polymer electrolyte membrane, an anode, an anode side gas diffusion layer, and an anode side separator, a high density carbon layer comprising carbon particles and water repellent resin is arranged on the surface of the gas difffusion layer on the contact surface between the separator and the gas diffusion layer. <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 supplying gas uniformly to the gas diffusion layer is provided on the surface of the separator facing the gas diffusion layer.

  In such a polymer electrolyte fuel cell, it is known that the contact resistance of the contact portion between the separator and the gas diffusion layer greatly affects the power generation performance (see, for example, Patent Document 1). That is, the smaller the contact resistance, the smaller the resistance overvoltage that becomes a loss during power generation, and the higher the performance. In addition, a metal separator made by a general press molding process using an inexpensive metal thin plate is expected as a future compact high-performance solid polymer fuel cell. When a metal separator is used as the separator material and a carbon-based nonwoven fabric or woven fabric is used for the gas diffusion layer, the metal surface is usually covered with an oxide film with high resistance. Since resistance tends to increase, it is generally known to form a thin, stable, highly conductive gold or the like on the surface of a metal separator (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 7-22042 JP-A-10-228914

  However, since a polymer electrolyte fuel cell requires a large number of separators to be laminated due to the structure principle of laminating multiple layers, a large amount of expensive noble metals such as gold must be used. It has become an obstacle to cost reduction, which is a major issue for mass diffusion of batteries.

  In addition, the thermal expansion and contraction of the fuel cell due to repeated power generation causes repeated load fatigue on the surface of the metal separator and the surface of the gas diffusion layer, and the contact resistance increases with time by breaking the fibers on the surface of the gas diffusion layer in contact with the separator. Was.

  Therefore, the present invention can maintain the low resistance of the metal separator and the gas diffusion layer stably even when repeated load fatigue is applied, and can prevent the stagnation of generated water. An object of the present invention is to provide a polymer electrolyte fuel cell capable of obtaining performance.

  The electrode for a polymer electrolyte fuel cell according to the present invention comprises a cathode separator, cathode side gas diffusion layer, cathode electrode, polymer electrolyte membrane, anode electrode, anode side gas diffusion layer, and anode side separator. The molecular fuel cell is characterized in that a high-density carbon layer composed of carbon particles and a water-repellent resin is provided on the surface of the gas diffusion layer at the contact surface between the separator and the gas diffusion layer.

  In the polymer electrolyte fuel cell of the present invention, it is preferable that the gas diffusion layer provided with the high-density carbon layer is on the cathode side.

  According to the present invention, since the high-density carbon layer is provided on the surface of the gas diffusion layer at the contact surface between the separator and the gas diffusion layer, contact between the metal separator and the gas diffusion layer can be achieved even when repeated load fatigue is applied. The resistance can be stably kept low, and the high-density carbon layer is composed of carbon particles and a water-repellent resin, so that retention of generated water can be prevented. Excellent power generation performance can be obtained.

  As shown in FIG. 1, a solid polymer fuel cell of the present invention comprises a cathode separator 1, a cathode gas diffusion layer 2, a cathode electrode 3, a polymer electrolyte membrane 4, an anode electrode 5, and an anode gas diffusion layer 6. The anode separator 7 is laminated in this order. Further, carbon particles and a water-repellent resin are formed on the surface of the gas diffusion layer at the contact surface between the separator (1, 7) and the gas diffusion layer (2, 6). The high-density carbon layer (8, 9) made of is provided. In the present invention, constituent elements other than the high-density carbon layer are not particularly limited, and therefore, the high-density carbon layer will be described in detail below.

  The high-density carbon layer in the present invention is provided on the surface of the gas diffusion layer at the contact surface between the separator and the gas diffusion layer, and preferably is embedded in the gas diffusion layer by 1 to 8 μm. In addition, since the gas flow path is formed in the separator, in the present invention, as shown in FIG. 2, the high-density carbon layer 11 is formed on the surface of the gas diffusion layer 10 in accordance with the flow path pattern. . With such a configuration, even when repeated load fatigue is applied due to thermal expansion and contraction of the fuel cell due to repeated power generation, the fibers on the surface of the gas diffusion layer in contact with the separator are not destroyed, and the contact resistance between the separator and the gas diffusion layer is stabilized. Can be kept low.

  The high-density carbon layer in the present invention can be provided on both the cathode-side and anode-side gas diffusion layer surfaces. In particular, by providing the high-density carbon layer on the cathode-side gas diffusion layer surface, In addition to the effect, the water produced at the cathode electrode can be well controlled to prevent the produced water from staying.

  Furthermore, the high-density carbon layer in the present invention is composed of carbon particles and a water-repellent resin, and the weight ratio of carbon in the high-density carbon layer is preferably 16 to 50 wt% or more. When the carbon content is less than 16 wt%, the electron conductivity is hindered, the resistance overvoltage (IR) increases, and the power generation performance decreases. On the other hand, when the carbon content exceeds 50 wt%, the gas diffusivity in the surface direction is hindered, the concentration overvoltage increases, and the power generation performance decreases.

  As the carbon particles 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.

  Further, the polymer electrolyte fuel cell of the present invention is impregnated with a coating made of carbon particles and a water-repellent resin so as to form a pattern corresponding to the portion in contact with the separator on the surface of the gas diffusion layer. Produced suitably by the method for producing a polymer electrolyte fuel cell of the present invention, wherein a density carbon layer is provided, and the portion of the separator that contacts the surface of the gas diffusion layer is overlapped with the high-density carbon layer. can do. In the production method of the present invention, patterned screen printing or the like is used as a method for impregnating the carbon particles and the water-repellent resin.

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>
20 g of platinum-supporting carbon (trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) and 179 g of ion conductive polymer solution (trade name: Nafion DE2020, manufactured by Dupont) were ball milled to prepare a catalyst paste.

Next, this catalyst paste is applied on a polytetrafluoroethylene (PTFE) sheet by screen printing so that the weight of platinum is 0.5 mg / cm ^2, and then dried by heat treatment at 120 ° C. for 60 minutes. Cathode and anode electrocatalyst sheets were prepared. Next, the cathode and anode electrode catalyst sheets were transferred to both surfaces of a polymer electrolyte membrane (trade name: Nafion 112, manufactured by Dupont) by a decal method to form an electrolytic catalyst 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.

  Carbon paper (trade name: TGP-H-060, manufactured by Toray Industries, Inc.) is impregnated with a 10 wt% solution of tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and then heat treated at 380 ° C. for 30 minutes. Was dried, and a gas diffusion layer was produced by subjecting the carbon paper to a water repellent treatment.

  On the other hand, 10 g of granular carbon (trade name: Vulcan XC72, manufactured by Cabot) having both electronic conductivity and pore-forming property, 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 mixed and stirred by a ball mill to prepare a high-density carbon layer paste. Next, the high-density carbon layer paste is applied by screen printing on the portion where the separator of the gas diffusion layer subjected to the water repellent treatment contacts, and then impregnated in the gas diffusion layer, and then 380 ° C. for 30 minutes. A high-density carbon layer was produced in a pattern corresponding to the portion in contact with the separator.

Next, the carbon paper on which the high-density carbon 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. Subsequently, the linear groove formed in the carbon separator and the high-density carbon layer were brought into contact with each other, and the carbon separator was sandwiched between both surfaces of the above-described stack MEA, whereby a polymer electrolyte fuel cell of Example 1 was produced.

<Example 2>
In the formation process of the high-density carbon layer of Example 1, the composition of the high-density carbon layer paste is 5 g of granular carbon (trade name: Vulcan XC72, manufactured by Cabot), water-repellent resin (trade name: PTFE powder full-on L170J, Asahi Glass. A polymer electrolyte fuel cell of Example 2 was produced in the same manner as in Example 1, except that 10 g and 180 g of ethylene glycol were used.

<Example 3>
In the formation process of the high-density carbon layer of Example 1, the composition of the high-density carbon layer paste is as follows. A polymer electrolyte fuel cell of Example 3 was produced in the same manner as in Example 1, except that 10 g and 180 g of ethylene glycol were used.

<Comparative Example 1>
A solid polymer type fuel cell of Comparative Example 1 was produced in the same manner as in Example 1 except that the high density carbon layer was not formed in the production of the solid polymer type fuel cell of Example 1.

<Comparative example 2>
In the formation process of the high-density carbon layer of Example 1, the composition of the high-density carbon layer paste was changed to 10 g of granular carbon (trade name: Vulcan XC72, manufactured by Cabot) and 180 g of ethylene glycol. In the same manner, a polymer electrolyte fuel cell of Comparative Example 2 was produced.

<Comparative Example 3>
In the formation process of the high-density carbon layer of Example 1, the composition of the high-density carbon layer paste is 10 g of granular carbon (trade name: Vulcan XC72, manufactured by Cabot), polyethylene resin (trade name: NUCG-4953, Nihon Unicar). (Manufactured) A polymer electrolyte fuel cell of Comparative Example 3 was produced in the same manner as in Example 1 except that 10 g and 180 g of ethylene glycol were used.

2. Evaluation (1) Power generation performance For the polymer electrolyte fuel cells of Examples 1 to 3 and Comparative Examples 1 to 3 produced as described above, hydrogen gas was supplied to the anode side and air was supplied to the cathode side. , Cell temperature: 72 ° C., stoic: anode 5.7 / cathode 7.3, relative humidity: anode / cathode = 50/50% RH, current density: 1 A / cm ^2. The terminal voltage and IR were measured. IR free was calculated | required from these values. The area of the MEA electrode part was 36 cm ² . These results are shown in Table 1 and FIG.

(2) Penetration resistance In the production of the stack MEA in the polymer electrolyte fuel cells of Examples 1 to 3 and Comparative Examples 1 to 3, the gas diffusion layers of the cathode and the anode are directly used without using the polymer electrolyte membrane. A stack MEA having a structure in which the layers are stacked so as to come into contact with each other is manufactured, and the stack MEA is sandwiched between a carbon separator having a linear groove and a SUS plate, and a load of 20 kgf / cm ² is repeatedly applied. Then, the surface pressure was maintained at 10 kgf / cm ² , and the penetration resistance between the separator SUS plates was measured with a resistance meter, and the change in penetration resistance due to stack expansion and contraction was evaluated. These results are shown in Table 1 and FIG.

  As shown in Table 1 and FIG. 3, Comparative Examples 2 and 3 in which a high-density carbon layer composed of carbon particles and a water-repellent resin is not provided are inferior in initial power generation performance and cannot be put to practical use. It was shown that. Further, as shown in Table 1 and FIG. 4, in Comparative Example 1 in which the high-density carbon layer is not provided, although the initial power generation performance is excellent, the penetration resistance is remarkably increased in the state where the stack expansion and contraction is repeated, and the power generation Inferior performance. On the other hand, in Examples 1 to 3 provided with a high-density carbon layer composed of carbon particles and a water-repellent resin, not only the initial power generation performance is excellent, but also in a state where stack expansion and contraction is repeated, The increase in penetration resistance was slight, indicating that the polymer electrolyte fuel cell was excellent.

It is sectional drawing which showed typically one Embodiment of the polymer electrolyte fuel cell of this invention. It is the top view which showed typically one Embodiment of the polymer electrolyte fuel cell of this invention. It is a diagram which shows IR free electric power generation performance and IR. It is a diagram which shows the penetration resistance with respect to the frequency | count of repetition.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cathode side separator, 2 ... Cathode side gas diffusion layer, 3 ... Cathode electrode,
4 ... polymer electrolyte membrane, 5 ... anode electrode, 6 ... anode side gas diffusion layer,
7 ... anode-side separator, 8, 9, 11 ... high density carbon layer, 10 ... gas diffusion layer.

Claims (3)

  In a polymer electrolyte fuel cell in which a cathode side separator, a cathode side gas diffusion layer, a cathode electrode, a polymer electrolyte membrane, an anode electrode, an anode side gas diffusion layer, and an anode side separator are laminated, the separator and the gas diffusion layer A solid polymer fuel cell, characterized in that a high-density carbon layer comprising carbon particles and a water-repellent resin is provided on the gas diffusion layer surface on the contact surface.   2. The polymer electrolyte fuel cell according to claim 1, wherein the gas diffusion layer provided with the high-density carbon layer is on the cathode side.   On the surface of the gas diffusion layer, a high-density carbon layer is provided by impregnating a paint composed of carbon particles and a water-repellent resin so as to form a pattern corresponding to a portion in contact with the separator, and the gas diffusion layer of the separator is provided. A method for producing a polymer electrolyte fuel cell, wherein a portion in contact with a surface and the high-density carbon layer are overlapped.

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