JP2004207231A - Electrolyte membrane-electrode junction body for fuel cell and fuel cell operating method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte membrane-electrode junction body suitable for operation in high humidity, by smoothening the surface of a carbon fabric non-woven fabric used for a gas diffusing base material of a high polymer electrolyte fuel cell, and by optimizing it so that paint for forming a water-repellent layer is inhibited from unevenly infiltrating into it. <P>SOLUTION: This electrolyte membrane-electrode junction body is composed of a high polymer electrolyte membrane and a pair of electrodes holding the high polymer electrolyte membrane between them, and the electrode is composed of a catalyst layer in contact with the high polymer electrolyte membrane and a gas diffusing layer having a water-repellent layer in contact with the catalyst layer. A cloth-like carbon fabric woven fabric woven by warps and wefts of electron conducting carbon fabrics is used for the base material of the gas diffusing layer, and openings are formed at the crossing points of the warps and wefts. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an electrolyte membrane-electrode assembly for a polymer electrolyte fuel cell using a proton conductive polymer electrolyte membrane, and a method for operating a fuel cell using the electrolyte membrane-electrode assembly.

  Generally, an electrolyte membrane-electrode assembly (hereinafter, referred to as MEA) of a polymer electrolyte fuel cell (hereinafter, referred to as PEFC) includes a polymer electrolyte membrane and a pair of electrodes sandwiching the polymer electrolyte membrane. . These electrodes include a catalyst layer in contact with the polymer electrolyte membrane and a gas diffusion layer having a water-repellent layer in contact with the catalyst layer. The MEA is sandwiched between separator plates provided with gas flow paths from both outer surfaces thereof and fastened together with a sealing material for preventing gas leakage under a certain pressure to form a PEFC cell.

  A groove (gas flow path) is formed in the separator plate from the supply port of the reaction gas (fuel gas or oxidant gas) to the discharge port, and the reaction gas flows through the gas flow path. The function required of the gas diffusion layer is to diffuse the reaction gas supplied through the gas flow path and supply the reaction gas to the entire surface of the catalyst layer. Further, as a function of the gas diffusion layer, it is important to discharge excess water so that the water generated in the cathode-side catalyst layer in the reaction during the operation of the PEFC does not inhibit the diffusibility of the reaction gas. That is, it is an important function of the gas diffusion layer to allow the generated water to pass through the pores in the gas diffusion layer without stagnation and to smoothly reach the gas flow path of the separator plate. The gas diffusion layer is in contact with the protrusions (ribs) formed on both sides of the gas flow path of the separator plate and is electrically connected to the separator plate, and serves to conduct current generated in the MEA to the separator plate. Have.

  Generally, a water-repellent layer is formed on the gas diffusion layer in contact with the catalyst layer, and a fluorine-based resin is used as a water-repellent material for the water-repellent layer. The water-repellent layer contains a conductive material such as carbon together with the water-repellent material. In the conventional general technology, the gas diffusion ability is secured by making the base material of the gas diffusion layer a porous structure, and the water permeation ability is controlled by forming the water-repellent layer on the gas diffusion layer, Furthermore, the electronic conductivity is ensured by using an electron conductive material made of carbon fiber, metal fiber, or the like as a base material of the gas diffusion layer. As a base material of a general gas diffusion layer, carbon paper, carbon felt, carbon fiber woven fabric, or the like is used.

  Although carbon paper and carbon felt have differences in properties such as gas diffusivity and water permeability depending on the basis weight and thickness, the carbon paper and carbon felt are composed of randomly arranged carbon fibers. The difference in characteristics is small. On the other hand, since the carbon fiber woven fabric is woven so that the carbon fibers are regularly arranged, the weaving method of the carbon fiber woven fabric is an important controlling factor of the above-described characteristics, in addition to the basis weight and the thickness. In other words, unlike carbon paper and carbon felt, carbon fiber woven fabric may provide a material having optimal properties as a gas diffusion layer substrate depending on the weaving method, but on the other hand, depending on the weaving method, the opposite result may occur. It has the uniqueness of being easy. However, if the specificity of such a carbon fiber woven fabric is utilized, it may be possible to control the characteristics to be optimal for a gas diffusion layer substrate.

  An ordinary gas diffusion layer forms a water-repellent conductive layer (hereinafter, referred to as a water-repellent layer) by applying a water-repellent layer forming paint in which, for example, carbon black and a fluororesin are dispersed in water, on one surface of a substrate. It is produced by doing. In this case, the state of formation of the water-repellent layer is largely controlled by the properties of the surface of the base material other than the properties of the paint and the method of applying the paint to the base material.

  The water repellency required for the water repellent layer also depends on the operating conditions of the fuel cell, and when operated under high humidification conditions, it is preferable that the water repellency of the outermost surface of the gas diffusion layer in contact with the catalyst layer is not so high, Conversely, when operated under low humidification conditions, the above water repellency is preferably higher. That is, when the outermost surface of the gas diffusion layer in contact with the catalyst layer has high water repellency, the effect of confining water inside the electrode works even when the polymer electrolyte membrane is sufficiently humidified.

  In a high humidification operation in which a large amount of moisture is supplied from the outside, the above water repellency may be low because the effect of confining water is not so required. On the other hand, in a low humidification operation in which little water is supplied from the outside, it is preferable to increase the water repellency. Especially when operating under high humidification conditions, in addition to controlling the strength of the water repellency of the outermost surface, the water repellency is applied from the outermost surface of the gas diffusion layer in contact with the catalyst layer to the side in contact with the separator plate. It is important to form a water-repellent layer (hereinafter, referred to as a uniform water-repellent layer) that attenuates with a continuous slope. Thereby, surplus water continuously generated by the battery reaction during operation can be smoothly discharged to the gas flow path side without staying in the pores in the gas diffusion layer.

  As a method of changing the water repellency of the water repellent layer, a method of changing the weight ratio of the carbon black and the fluororesin in the water repellent layer, and the same weight ratio is used to form the thickness of the water repellent layer and the formation of the water repellent layer. In general, a method of changing the coating amount of a paint for business is used. However, in these cases, when the coating material for forming the water-repellent layer is directly applied to the carbon fiber woven fabric, the coating material is preferentially soaked into the portion where the fiber density of the base material is low, so that the coating material can be applied uniformly. Have difficulty.

  When such a non-uniform penetration of the paint occurs, a non-uniform water-repellent layer is formed in the gas diffusion layer in which portions having high and low water repellency are randomly scattered. Moisture is easily taken into the gaps between the parts having high water repellency, and the taken-in moisture is not easily discharged. In other words, when the above-described non-uniform penetration of the paint occurs, a uniform water-repellent layer cannot be formed, and the excess water cannot be efficiently discharged. As described above, the uneven penetration of the coating material into the base material significantly impairs the moisture permeability of the gas diffusion layer. In particular, in the case of a fuel cell operated under high humidification conditions, the uniform penetration of the water repellent layer is suppressed. Is an important issue.

  As a countermeasure, a method of transferring a water-repellent layer formed by applying a paint to another sheet in advance to a carbon gas diffusion layer base material has been studied. However, this transfer method has a disadvantage that the number of processing steps increases. In addition, although suppression of the above-mentioned permeation by using a water-repellent layer forming paint prepared to have a moderately high viscosity has been studied, a sufficient suppression effect cannot be obtained.

  Further, in the conventional carbon fiber woven fabric used as the gas diffusion layer base material, there are uneven portions having large steps on the surface, so that a large number of gaps are formed at the junction between the catalyst layer and the gas diffusion layer, and PEFC During operation, there is a problem that water stays in the gaps and the drainage of water is reduced. As described above, in PEFC operated under high humidification conditions, the use of carbon fiber woven fabric as the base material for the gas diffusion layer may control the properties to be optimal for the gas diffusion layer base material. At present, the optimization has not been performed.

  The present invention solves the problem of the gas diffusion layer in the conventional PEFC, in particular, by smoothing the surface of a carbon fiber woven fabric used as a gas diffusion layer base material, It is an object of the present invention to provide an MEA that is optimized so as to form a uniform water-repellent layer in which an excellent permeation is suppressed, and thereby is suitable for a high humidification operation.

The fuel cell electrolyte membrane-electrode assembly of the present invention comprises a polymer electrolyte membrane and a pair of electrodes sandwiching the polymer electrolyte membrane, wherein the electrode is in contact with the catalyst layer and the catalyst layer in contact with the polymer electrolyte membrane. A gas diffusion layer having a water-repellent layer, wherein the base material of the gas diffusion layer is a cloth-like carbon fiber woven fabric woven with warp yarns and weft yarns made of electron conductive carbon fibers, and between the intersections of the warp yarns and the weft yarns. Alternatively, an opening is formed in the vicinity thereof.
When the warp density of the carbon fiber woven fabric is Z yarns / cm, the weft yarn density is W yarns / cm, the warp yarn thickness is X mm, and the weft yarn thickness is Y mm, 1/1500 ≦ (10 / W− Y) It is preferable to satisfy the relationship of ((10 / ZX) / XY ≦ １ ／).

  The thickness of the carbon fiber woven fabric is preferably in the range of 0.05 to 0.30 mm. The density of the carbon fiber woven fabric is preferably in the range of 0.32 to 0.42 g / cc. Further, it is preferable that one of the warp yarn density and the weft yarn density of the carbon fiber woven fabric is in the range of 16 to 45 yarns / cm, and the other is in the range of 12 to 40 yarns / cm.

  A method of operating a fuel cell according to the present invention includes the fuel cell electrolyte membrane-electrode assembly according to the present invention, and supplies a humidified fuel gas to an anode, and supplies a humidified oxidant gas to a cathode. A method for operating a fuel cell for generating power, wherein the dew point of a fuel gas and the dew point of an oxidizing gas are set to the same temperature as the operating temperature of the electrolyte membrane-electrode assembly or to a lower temperature within a range of 5 ° C. It is characterized by controlling and driving.

  According to the present invention, it is possible to provide an electrolyte membrane-electrode assembly for a polymer electrolyte fuel cell, which has excellent anti-flooding characteristics in a high humidification operation and can obtain a high operating voltage.

The present invention provides a woven fabric of carbon fiber woven fabric that can optimize the surface condition of the carbon fiber woven fabric used as the base material of the gas diffusion layer of PEFC and the application state of the water-repellent layer forming paint to the carbon fiber woven fabric. , It is possible to provide an MEA suitable for high humidification operation.
The base material of the gas diffusion layer in the present invention is a cloth-like carbon fiber woven fabric woven with warp yarns and weft yarns made of electron conductive carbon fibers, wherein openings are formed at intersections of the warp yarns and the weft yarns. And When the warp yarn density is Z yarns / cm, the weft yarn density is W yarns / cm, the warp yarn thickness is X mm, and the weft yarn thickness is Y mm, the carbon fiber woven fabric is 1/1500 ≦ (10 / W−Y) (10 / Z−X) / XY ≦ １ ／.

In the above relational expression, XYmm ² corresponds to an area of a portion where the warp and the weft intersect (hereinafter, referred to as an intersecting portion), and (10 / W−Y) (10 / Z−X) mm ² corresponds to the warp. It corresponds to the area of an opening (gap) portion where none of the weft yarns exist (hereinafter, referred to as a gap portion). That is, in the carbon fiber woven fabric of the present invention, an opening is provided at the intersection of the warp and the weft, and the area ratio (10 / WY) (10 / ZX) / XY of the intersecting portion and the gap portion is 1 /. It is not less than 1500 and not more than 1/5.

  In the present invention, the carbon fiber woven fabric used as the base material of the gas diffusion layer is made of carbon fiber yarn as a constituent material, and a plain woven fabric is most commonly used as a woven fabric structure. In addition to plain weave, oblique weave and satin weave carbon fiber woven fabrics can also be used. In these carbon fiber woven fabrics, warp yarns and weft yarns are combined in a regular geometric pattern. That is, the carbon fiber woven fabric is a carbon fiber yarn (weft or weft) belonging to the second group in a direction perpendicular to the direction of one group of carbon fiber yarns (warp or weft) arranged in parallel. (Warp yarns) in a predetermined manner. At this time, the cloth is configured such that the second group of carbon fiber yarns also maintain a parallel relationship with each other.

  Next, the fabric structure of the carbon fiber woven fabric will be described by taking a plain woven carbon fiber woven fabric as an example. FIG. 1 is a plan view of a plain-woven carbon fiber woven fabric, in which weft yarns 2 are intersected at equal intervals in a direction perpendicular to warp yarns 1 arranged at equal intervals. The warp yarn 1 and the weft yarn 2 of the carbon fiber woven fabric may be composed of a plurality of yarns such as a twin yarn composed of two yarns, in addition to a single yarn composed of a single yarn. Therefore, since the cross section of the warp 1 or the weft 2 is not necessarily circular, in the present invention, the thickness of the warp and the width of the weft are, for convenience, the width of the warp and the width of the weft as viewed from a plan view of the carbon fiber woven fabric. It shall represent the width.

  In the carbon fiber woven fabric according to the present invention, the area of the gap portion 4 where neither the warp yarn 1 nor the weft yarn 2 is present is set to 1/1500 to 1/1 / the area of the intersecting portion 3 where the warp yarn 1 and the weft yarn 2 intersect. By predominantly reducing the ratio by a factor of 5, when the paint for forming a water-repellent layer is applied to a carbon fiber woven fabric, preferential penetration of the paint from the gap portion 4 is suppressed, and a uniform water-repellent layer is formed. Can be formed. As a result, a gas diffusion layer having the characteristic that the water repellency attenuates with a gentle slope from the surface in contact with the catalyst layer to the surface on the gas flow path side is obtained. By using the MEA having the gas diffusion layer, even during high humidification operation, excess water can be smoothly discharged to the gas flow path without taking water into the pores in the gas diffusion layer.

  As a conventional problem, when a plurality of MEAs are stacked and fastened to form a PEFC, if the fastening pressure is increased to reduce the contact resistance between the components, the components will bend. Therefore, it is necessary to keep the fastening pressure low within a range in which gas does not leak. If the fastening pressure is low, a gap is formed along the unevenness of the substrate at the interface between the catalyst layer and the gas diffusion layer, so that water tends to stay, and surplus water is not discharged to the outside of the MEA.

  By increasing the area ratio of the intersecting portion 3 of the carbon fiber woven fabric according to the present invention, the level difference between the convex portion and the concave portion on the surface is reduced, and the surface is smoothed. This solves the above problem. That is, in the carbon fiber woven fabric according to the present invention, since the intersecting portion 3 having a large thickness is 5 to 1500 times as large as the gap portion 4 having a small thickness, the step between the concave portion and the convex portion on the surface is small. By using this carbon fiber woven fabric, the formation of a gap at the interface between the catalyst layer and the gas diffusion layer is suppressed, and the problem of excess water remaining is eliminated.

  As described above, in the PEFC using the MEA according to the present invention provided with the gas diffusion layer in which the uniform water-repellent layer is formed on the carbon fiber woven fabric having a smooth surface state, the excess water discharge capacity of the gas diffusion layer is particularly high. In the required high humidification operation, high performance can be exhibited.

  In the carbon fiber woven fabric as the gas diffusion layer base material, if the area ratio of the gap portion to the intersecting portion exceeds 1/5, the surface smoothness becomes insufficient, and the uneven paint penetration is sufficiently suppressed. You can't do that. When the area ratio is less than 1/1500, the voids in the gas diffusion layer are insufficient, and the gas diffusion capacity and the moisture permeability are insufficient.

  The thickness of the carbon fiber woven fabric used for the MEA of the present invention is preferably in the range of 0.05 to 0.30 mm, and more preferably in the range of 0.05 to 0.20 mm. By reducing the thickness of the carbon fiber woven fabric, it is possible to further reduce the level difference between the concave portion and the convex portion on the surface of the carbon fiber woven fabric and to smooth the surface. Accordingly, it is possible to provide an MEA that can more effectively prevent water from staying at the junction between the gas diffusion layer and the catalyst layer, and can more effectively prevent the occurrence of a flooding phenomenon in a high humidification operation. It becomes possible.

  The thinner the carbon fiber woven fabric, the smaller the void volume in the gas diffusion layer and the smaller the amount of water retained in the gas diffusion layer, so that it can be easily discharged. However, carbon fiber woven fabrics thinner than 0.05 mm are often difficult to handle or cannot be woven due to insufficient tensile strength of the raw carbon fiber yarns. On the other hand, in a carbon fiber woven fabric having a thickness of more than 0.30 mm, an adverse effect such that water stays at the joint between the gas diffusion layer and the catalyst layer is likely to occur due to a large step between the concave portion and the convex portion on the surface.

  The carbon fiber woven fabric used for the MEA of the present invention preferably has a density in the range of 0.32 to 0.42 g / cc. By suppressing the fiber density of the carbon fiber woven fabric to a low level, the pressure at the time of fastening the fuel cell stack causes the carbon fiber woven fabric to be easily compressed and smoothed.

  As described above, when the carbon fiber woven fabric is compressed and smoothed, the step between the concave portion and the convex portion on the surface becomes smaller, and the gap where water stays at the junction between the gas diffusion layer and the catalyst layer is eliminated. Can be. As a result, it is possible to provide an MEA that can more effectively prevent the occurrence of the flooding phenomenon in the high humidification operation. The lower the density of the carbon fiber woven fabric, the greater the above-mentioned effect. However, if the density of the carbon fiber woven fabric is less than 0.32 g / cc, the mechanical strength of the carbon fiber woven fabric is insufficient. Handling becomes difficult. On the other hand, if the density of the carbon fiber woven fabric exceeds 0.42 g / cc, the pressure at the time of fastening does not sufficiently smooth the carbon fiber woven fabric, and the above effects cannot be obtained sufficiently.

  In the carbon fiber woven fabric used for the MEA of the present invention, one of the warp yarn density and the weft yarn density is in the range of 16 to 45 yarns / cm, and the other is in the range of 12 to 40 yarns / cm. preferable. By increasing the yarn density (the number of carbon fiber woven fabric yarns per unit length or width), the thickness of each yarn becomes thinner, so that the thickness of the intersecting portion can be reduced, and carbon The step between the concave portion and the convex portion on the surface of the fiber woven fabric can be reduced. Thereby, the surface of the carbon fiber woven fabric becomes smoother, and a uniform water-repellent layer can be formed.

  In addition, by increasing the yarn density, a large number of gap portions of the carbon fiber woven fabric can be present, and the area of each gap portion can be reduced. This makes it possible to form many fine spaces suitable for smoothly discharging excess water to the outside of the MEA through the gas diffusion layer or for diffusing the reaction gas in the gas diffusion layer. With these effects, it is possible to provide an MEA in which surplus water can be smoothly discharged in the high humidification operation, and the occurrence of the flooding phenomenon can be more effectively prevented.

  The higher the warp yarn density and the higher weft yarn density of the carbon fiber woven fabric, the more remarkable the above-mentioned effect is obtained.However, if the density exceeds the preferred density, the yarn becomes too thin. Difficulty handling woven fabric. On the other hand, when the yarn density is lower than the above preferable density, the yarn becomes too thick, so that the step between the concave portion and the convex portion on the surface of the carbon fiber woven fabric increases. When an MEA is manufactured using this carbon fiber woven fabric, a gap where water stays tends to be generated at a joint between the catalyst layer and the gas diffusion layer.

  As a water-repellent material contained in the water-repellent layer, a fluorine-based resin such as polytetrafluoroethylene (PTFE) is generally used because of its excellent heat resistance, acid resistance, and chemical resistance. It is also possible to use a system or other water-repellent material that can ensure long-term water repellency. Since the water-repellent layer is a layer formed on one side of the gas diffusion layer functioning as a current collector, the water-repellent layer needs to have conductivity. Therefore, the water-repellent layer needs to contain a conductive material.

  As the conductive material, carbon is generally used because of its excellent acid resistance, and among them, acetylene black having strong water repellency is mainly used. However, since carbon having high water repellency is difficult to make into a paint, conversely, depending on the combination with a water repellent material, Ketjen black, which is hydrophilic carbon, may be preferable. A metal material can be used as another conductive material. A general method of forming a water-repellent layer is to apply a water-repellent layer-forming paint prepared by dispersing the above-described water-repellent material and a conductive material in a dispersion medium such as water directly to one side of a carbon fiber woven fabric. Is the way. The coating method may be any of spraying, spin coating, doctor blade, screen printing, coater coating, and gravure printing.

  As a gas passage formed in the separator plate, a straight type in which a plurality of straight paths are provided in parallel in one direction from an inlet to an outlet, and a serpentine type in which one or more paths are provided in a bellows shape, etc. There is. The form of the gas flow path is further classified into an orthogonal type, a facing type, and a parallel type according to the difference in the gas flow direction between the anode side and the cathode side. The present invention can be effectively applied to a PEFC having any of the above gas flow paths.

  The method for operating a fuel cell according to the present invention is a method for operating a PEFC including the MEA according to the present invention and a pair of separator plates having a gas flow path in contact with the outside of the MEA. , And the temperature of the MEA during operation is controlled within a predetermined temperature range.

  Since the MEA according to the present invention includes the gas diffusion layer in which the uniform water-repellent layer is formed on the carbon fiber woven fabric having a smooth surface as described above without the non-uniform penetration of the coating material for forming the water-repellent layer, PEFC has sufficient discharge capacity and gas diffusion capacity required for high humidification operation of PEFC. Therefore, the PEFC equipped with the MEA is operated under the most typical high humidification conditions, that is, the dew point temperature of the fuel gas supplied to the anode, the dew point temperature of the oxidizing gas supplied to the cathode, and the temperature during the operation of the MEA. In particular, excellent performance can be exhibited when the vehicle is operated while being controlled to be equal to each other. In this case, by controlling the dew point of the fuel gas and the dew point of the oxidizing gas to a lower temperature within 5 ° C. with respect to the temperature at the time of operation of the electrolyte membrane-electrode assembly, the operation is substantially performed. Can obtain excellent performance according to the case where the temperatures of the three are equal.

  Next, the present invention will be specifically described with reference to examples. In each of the examples and comparative examples, a unit cell was produced by the following method. FIG. 2 shows a representative diagram of these cells. A coating material for forming a water-repellent layer was applied to one surface of a plain-woven carbon fiber woven fabric determined for each example and each comparative example using a doctor blade. The coating material for forming a water-repellent layer was prepared by mixing acetylene black (AB) and water at a weight ratio of 1: 4, adding a small amount of a surfactant thereto and kneading the mixture, and then adjusting the weight ratio of PTFE solids to AB to 1: 7. The dispersion was prepared by adding a dispersion of PTFE (D1 manufactured by Daikin Industries, Ltd.). The carbon fiber woven fabric coated with this paint on one side was dried at about 100 ° C. for 1 hour, and further baked at about 270 ° C. for 1 hour to produce a gas diffusion layer 13 having a water repellent layer formed on the carbon fiber woven fabric. .

On the other hand, the catalyst layer 12 was bonded to both surfaces of the polymer electrolyte membrane 11 (made by DuPont, USA: Nafion 112) by a transfer method, except for the peripheral portion. Next, the gas diffusion layer 13 was joined to each of the catalyst layers 12 so that the water-repellent layer side was in contact with the outside of each of the catalyst layers 12, thereby producing the MEA 15. The catalyst layer 12 transferred to the polymer electrolyte membrane 11 was formed by applying a catalyst paste to a resin sheet and drying. The area of the MEA catalyst layer 12 was 25 cm ² . The catalyst paste is composed of 100 parts by weight of a catalyst in which a platinum catalyst is supported on carbon fine powder (Lion Corporation: Ketjen Black EC) at a weight ratio of 1: 1 and a perfluorosulfonic acid resin dispersed in ethanol. 80 parts by weight were mixed, and this mixture was poured into a mixed dispersion medium of water and ethanol, followed by stirring to prepare.

Next, gaskets 18 were arranged on both sides of the polymer electrolyte membrane 11 at the periphery of the MEA 15 and were joined by hot pressing at 100 ° C. for 5 minutes. The joined body is sandwiched between carbon separator plates 17 on the cathode and anode sides from both sides thereof, and is fastened to a rib 19 formed on the separator plate 17 so that a surface pressure of about 7 kgf / cm ² is applied. Was prepared. The cathode-side and anode-side separator plates 17 are each provided with a serpentine-type gas flow path 16 composed of three grooves having a sectional area of 1.0 cm ² .

  The thickness of the warp and the weft of the carbon fiber woven fabric used in each Example and each Comparative Example was measured from a SEM photograph at a magnification of 100 times taken at an acceleration voltage of 15 kV. The number of yarns per 1 cm (warp yarn density and weft yarn density) was obtained by measuring the number of yarns per 5 cm from a 25-fold micrograph and calculating the average value per 1 cm from the measured value. The basis weight was obtained by punching a carbon fiber woven fabric into a size of 12 cm × 12 cm, and was calculated from the measured value of the weight. The density was determined from the calculated basis weight and the thickness of the carbon fiber woven fabric.

<< Example 1 >>
A single cell was produced using a carbon fiber woven fabric woven with a warp yarn having a thickness of 0.480 mm made of twin yarn and a weft yarn having a thickness of 0.480 mm made of twin yarn as a base material of the gas diffusion layer. The warp yarn density of this carbon fiber woven fabric was 20.1 yarns / cm, the weft yarn density was 18.1 yarns / cm, the basis weight was 110 g / m ² , the thickness was 0.28 mm, and the density was 0.393 g / cc. .

<< Example 2 >>
A single cell was produced using a carbon fiber woven fabric woven with a warp yarn having a thickness of 0.450 mm made of a twin yarn and a weft yarn having a thickness of 0.450 mm made of a single yarn as a base material of a gas diffusion layer. The warp yarn density of this carbon fiber woven fabric was 17.7 yarns / cm, the weft yarn density was 15.4 yarns / cm, the basis weight was 105 g / m ² , the thickness was 0.29 mm, and the density was 0.362 g / cc. .

<< Example 3 >>
A single cell was manufactured using a carbon fiber woven fabric woven with a warp yarn having a thickness of 0.445 mm made of twin yarn and a weft yarn having a thickness of 0.445 mm formed of twin yarn as a base material of the gas diffusion layer. The warp yarn density of this carbon fiber woven fabric was 15.7 yarns / cm, the weft yarn density was 15.4 yarns / cm, the basis weight was 80 g / m ² , the thickness was 0.20 mm, and the density was 0.400 g / cc. .

<< Example 4 >>
A single cell was produced using a carbon fiber woven fabric woven with a 0.360 mm thick warp made of twin yarns and a 0.360 mm thick weft made of twin yarns as the base material of the gas diffusion layer. The warp yarn density of this carbon fiber woven fabric was 23.6 yarns / cm, the weft yarn density was 22.0 yarns / cm, the basis weight was 115 g / m ² , the thickness was 0.29 mm, and the density was 0.397 g / cc. .

<< Example 5 >>
A single cell was produced using a carbon fiber woven fabric woven with a warp yarn having a thickness of 0.465 mm made of twin yarn and a weft yarn having a thickness of 0.470 mm made of twin yarn as a base material of the gas diffusion layer. The warp yarn density of this carbon fiber woven fabric was 21.3 yarns / cm, the weft yarn density was 20.1 yarns / cm, the basis weight was 125 g / m ² , the thickness was 0.30 mm, and the density was 0.417 g / cc. .

<< Comparative Example 1 >>
A unit cell was produced using a carbon fiber woven fabric woven with a warp yarn having a thickness of 0.420 mm made of twin yarn and a weft yarn having a thickness of 0.420 mm made of twin yarn as a base material of the gas diffusion layer. The warp yarn density of this carbon fiber woven fabric was 15.7 yarns / cm, the weft yarn density was 15.7 yarns / cm, the basis weight was 114 g / m ² , the thickness was 0.30 mm, and the density was 0.380 g / cc. .

<< Comparative Example 2 >>
A single cell was produced using a carbon fiber woven fabric woven with a warp yarn having a thickness of 0.470 mm made of twin yarn and a weft yarn having a thickness of 0.470 mm made of twin yarn as a base material of the gas diffusion layer. The warp yarn density of this carbon fiber woven fabric was 21.3 yarns / cm, the weft yarn density was 17.3 yarns / cm, the basis weight was 100 g / m ² , the thickness was 0.27 mm, and the density was 0.370 g / cc. .

  Various battery tests were performed by the following procedure using each unit cell of Examples 1 to 5 and Comparative Examples 1 and 2 using various carbon fiber woven fabrics produced by changing the weaving method as described above. Was. First, a fuel gas (hydrogen gas) heated and humidified so that the dew point becomes 70 ° C. is supplied to the anode, and an oxidant gas (air) heated and humidified so that the dew point becomes 70 ° C. is supplied to the cathode. The battery test 1 was performed under the conditions of a temperature of 70 ° C., a hydrogen gas utilization rate of 70%, and an air utilization rate of 40% during the operation of the MEA. Next, the battery test 2 was performed by changing the air utilization rate from 40% to 80%.

  Then, under the conditions that the dew point of hydrogen gas supplied to the anode is 67 ° C., the dew point of air supplied to the cathode is 70 ° C., the temperature during MEA operation is 70 ° C., the fuel gas utilization rate is 70%, and the air utilization rate is 40%. Test 3 was performed. Further, the battery test 4 was performed by changing the air utilization rate from 40% to 80%.

  Then, under the conditions that the dew point of the hydrogen gas supplied to the anode is 67 ° C., the dew point of the air supplied to the cathode is 65 ° C., the temperature during the operation of the MEA is 70 ° C., the fuel gas utilization rate is 70%, and the air utilization rate is 40%. Test 5 was performed. Further, the battery test 6 was performed with the air utilization rate changed from 40% to 80%.

  Next, under conditions of a hydrogen gas dew point of 65 ° C. supplied to the anode, an air dew point of 65 ° C. supplied to the cathode, a temperature of 70 ° C. during operation of the MEA, a fuel gas utilization rate of 70%, and an air utilization rate of 40%. Test 7 was performed. Further, the battery test 8 was performed while changing the air utilization rate from 40% to 80%.

Next, under conditions of a dew point of hydrogen gas supplied to the anode of 65 ° C., a dew point of air supplied to the cathode of 55 ° C., a temperature during operation of the MEA of 70 ° C., a fuel gas utilization rate of 70%, and an air utilization rate of 40%. Test 9 was performed. Further, the battery test 10 was performed with the air utilization rate changed from 40% to 80%. The current density during operation was 0.3 A / cm ^{2 in} any of the above battery tests 1 to 10.

  Table 1 shows the area ratio (10 / WY) (10 / ZX) / XY of the intersecting portion and the gap portion of the carbon fiber woven fabric used in Examples 1 to 5, Comparative Example 1 and Comparative Example 2, and the battery. The respective operating voltage values in Tests 1 to 10 are shown. In Table 1, the above-mentioned area ratio is simply represented by the area ratio for convenience.

  The operating voltage differences (AB, CD, EF, G) when the humidifying condition of the reaction gas and the temperature during the operation of the MEA are the same and the air utilization rate is changed from 40% to 80%. -H and IJ) are positive values when the operating voltage at a utilization of 40% is higher than the operating voltage at a utilization of 80%, and when the values are small, it means that the supply voltage to the cathode is low. This indicates that the voltage fluctuation due to the utilization rate (flow velocity) of the generated air is small, and that a stable output can be obtained during operation. Conversely, a large difference in the operating voltage indicates that the operating voltage is likely to fluctuate depending on the flow rate of the air, and at the same time indicates that the operating state tends to be slightly flooding if the flow rate of the air is reduced. Further, the fact that the difference between the operating voltages is a negative value indicates that when the flow rate is decreased, the voltage value is increased, so that when the flow rate is increased, the operation becomes slightly dry.

  As can be seen from Table 1, the area ratios (10 / WY) (10 / ZX) / XY of Examples 1 to 5 using carbon fiber woven fabrics having a range of 1/1500 to 1/5 were used. Regarding the battery, since the surplus water was discharged smoothly in the high humidification operation, the operating voltage was higher than that of the unit cells of Comparative Examples 1 and 2 in all of Battery Tests 1 to 8.

  On the other hand, the cells of Comparative Examples 1 and 2 using the carbon fiber woven fabric in which the area ratio of the carbon fiber woven fabric was out of the above range were lower in the operating voltage than in the Examples in any of the battery tests 1 to 6. In addition, the differences in the operating voltages (AB, CD, and EF) due to the differences in the air utilization rate (flow rate) are large. This is considered to be because the water generated at the cathode was not discharged smoothly and caused flooding.

  That is, in Comparative Example 1, a uniform water-repellent layer was not formed because the gap portion of the carbon fiber woven fabric was too large, and excess water was not discharged smoothly due to a large step of the uneven portion on the surface. It is considered. Conversely, in Comparative Example 2, it is considered that the surplus water was not discharged smoothly because the surplus water did not easily permeate the gas diffusion layer due to the small gap portion of the carbon fiber woven fabric.

  In Battery Tests 9 and 10, in each of Examples 1 to 5 and Comparative Example 1, an operating voltage lower than the operating voltage in Battery Tests 1 to 8 was shown. Furthermore, since the difference (IJ) between the operating voltages of these cells is a negative value or zero, when air having a relatively low dew point of 55 ° C. is supplied to the cathode, the air becomes slightly dry. It turns out that it becomes driving. On the other hand, in Comparative Example 2, since it is difficult for water to permeate through the gas diffusion layer, even in Battery Tests 9 and 10, the operation was not slightly dry, and the operating voltage difference (I-J) had a positive value. Is shown.

  The electrolyte membrane-electrode assembly according to the present invention can be suitably used for a polymer electrolyte fuel cell.

It is a top view of the carbon fiber woven fabric in the present invention. 1 is a longitudinal sectional view of a unit cell provided with an electrolyte membrane-electrode assembly according to an embodiment of the present invention.

Explanation of reference numerals

1 Warp 2 Weft 3 Intersection of warp and weft (intersection)
4 Gap part where neither warp nor weft exists (gap part)
Reference Signs List 11 polymer electrolyte membrane 12 catalyst layer 13 gas diffusion layer 15 MEA
16 Gas flow path 17 Separator plate 18 Gasket 19 Rib

Claims (6)

An electrolyte membrane-electrode comprising a polymer electrolyte membrane and a pair of electrodes sandwiching the polymer electrolyte membrane, wherein the electrode comprises a catalyst layer in contact with the polymer electrolyte membrane and a gas diffusion layer having a water-repellent layer in contact with the catalyst layer. A conjugate,
A fuel cell, wherein the base material of the gas diffusion layer is a carbon fiber woven fabric woven with warp yarns and weft yarns made of electron conductive carbon fiber, and an opening is formed between intersections of the warp yarns and the weft yarns. Electrolyte membrane-electrode assembly for use. When the warp density of the carbon fiber woven fabric is Z yarns / cm, the weft yarn density is W yarns / cm, the warp yarn thickness is X mm, and the weft yarn thickness is Y mm,
1/1500 ≦ (10 / W−Y) (10 / Z−X) / XY ≦ 1/5
The fuel cell electrolyte membrane-electrode assembly according to claim 1, which satisfies the following relationship:   The electrolyte membrane-electrode assembly for a fuel cell according to claim 1 or 2, wherein the carbon fiber woven fabric has a thickness in a range of 0.05 to 0.30 mm.   The electrolyte membrane-electrode assembly for a fuel cell according to any one of claims 1 to 3, wherein the carbon fiber woven fabric has a density in a range of 0.32 to 0.42 g / cc.   5. The carbon fiber woven fabric according to claim 1, wherein one of the warp yarn density and the weft yarn density is in a range of 16 to 45 yarns / cm, and the other is in a range of 12 to 40 yarns / cm. Fuel cell electrolyte membrane-electrode assembly. A fuel cell comprising the electrolyte membrane-electrode assembly for a fuel cell according to any one of claims 1 to 5, supplying a humidified fuel gas to an anode, and supplying a humidified oxidant gas to a cathode to generate power. Driving method,
The fuel cell and the oxidizing gas are controlled such that the dew point of the fuel gas and the dew point of the oxidizing gas are controlled to the same temperature or a lower temperature within a range of 5 ° C. with respect to the temperature at the time of operation of the electrolyte membrane-electrode assembly. Operating method of the fuel cell.

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