JP2010015908A - Substrate for gas diffusion electrode and method for manufacturing the same, and membrane-electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate for a gas diffusion electrode, which can be manufactured at low temperature and has both high electroconductivity and high permeability to gases; to provide a method for forming the substrate; and to provide an MEA including the substrate. <P>SOLUTION: The substrate for the gas diffusion electrode is configured to mutually assemble a lot of carbon fibers 22 with a thermosetting resin 26 in a state in which a lot of carbon fine particles 24 exist between them. Since the carbon fibers 22 having sizes of fiber length/film thicknesses which are in the range of 0.1 to 1 and the carbon fine particles 24 having particle diameters which are smaller than the fiber diameters are used, both high electroconductivity and high permeability to gases are obtained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas diffusion electrode substrate for constituting a polymer electrolyte fuel cell, a method for producing the same, and a membrane-electrode assembly provided with the same.

A fuel cell uses a reducing agent such as hydrogen, methanol, or reformed hydrogen from fossil fuels as a fuel, and electrochemically oxidizes the fuel in the cell using air or oxygen as an oxidant, thereby chemical energy of the fuel. Is directly converted into electrical energy and extracted. As a result, it has higher efficiency and quietness compared to internal combustion engines, and has low emissions of NO _x , SO _x , particulate matter (PM), etc. that cause air pollution. It is attracting attention as an energy supply source. For example, it is expected to be used as a distributed power source or a thermoelectric supply system for automobile engines, residential use, etc.

  Such fuel cells are classified into alkali type, phosphoric acid type, molten carbonate type, solid oxide type, solid polymer type, and the like depending on the type of electrolyte used. Among these, the phosphoric acid form and the solid polymer form using a proton-conducting electrolyte can be operated with high efficiency without being restricted by the Carnot cycle in thermodynamics, and the theoretical efficiency is 25 (° C). It reaches 83 (%). In particular, solid polymer fuel cells have been remarkably improved in performance in recent years due to the development of electrolyte membranes and catalyst technology, and are attracting attention as a low-pollution automobile power source and high-efficiency power generation method.

  By the way, a solid polymer fuel cell has a structure in which a gas diffusion electrode is provided on both sides of a thin polymer electrolyte layer, for example, via a pair of catalyst layers. Usually, such a membrane-electrode is used. The assembly (Membrane Electrode Assembly: hereinafter referred to as MEA) is used in a stack structure in which fuel gas or oxidizing gas is supplied and stacked through a separator that forms a gas flow path for discharging generated gas and excess gas. The gas diffusion electrode is required to have both high gas diffusion performance and high conductivity in order to introduce fuel gas and air to the catalyst layer and electrolyte layer surfaces and to take out the generated current. Conventionally, as such a gas diffusion electrode, a carbon fiber or the like bonded with a resin carbide has been generally used (see, for example, Patent Documents 1 to 6).

JP 2007-080742 A JP 2007-012440 A JP 2006-222025 A JP 2006-233692 A JP 2004-311431 A JP 2002-327355 A JP 2003-323897 A JP 2006-012569 A JP 2004-079406 A JP 2005-149745 A JP 2005-190701 A JP 2005-310660 A Japanese Patent No. 3778506 JP 2007-157736 A

  However, in the structure in which carbon fibers and the like are bound with resin carbide as described above, after binding the carbon fibers and the like with a thermosetting resin, the resin is heated to a high temperature of 1700 (° C.) or higher in an inert atmosphere or a reducing atmosphere. Carbonize with. For this reason, there are problems in that the manufacturing cost is high and the method cannot be applied to the coating laminated MEA.

  On the other hand, it has been proposed to form a film at a low temperature of 400 (° C.) or less for the purpose of solving the problem of manufacturing cost and structural limitations (see, for example, Patent Documents 7 to 10). ), Each has the following problems. What is described in Patent Document 7 uses polyaniline, which is a conductive polymer, instead of a thermosetting resin. However, since polyaniline is water-soluble, there is a risk of elution during use of the fuel cell and the conductivity may be significantly reduced. Polyaniline decomposes at around 300 (° C), which is the film-forming temperature of a general water-repellent layer. Furthermore, since polyaniline is expensive, there is a problem that the manufacturing cost is relatively high.

  In addition, what is described in Patent Document 8 is a substrate made from phenol resin, pulp, and carbon fiber, impregnated by applying a paste in which carbon fine particles are dispersed in a fluororesin dispersion by roll coating. It is to be burned out. However, since the conductivity differs between the impregnated surface and the back surface, there is a problem that uneven conductivity occurs in the thickness direction and the impregnated component does not function uniformly in the thickness direction.

  Moreover, what was described in patent document 9 makes papermaking the slurry containing electroconductive powders, such as expanded graphite, carbon fiber, organic fiber, and resin, and performs a drying process. However, since the conductive powder mixed to impart conductivity between the carbon fibers is relatively coarse, there is a problem that gas permeation is hindered and conductivity is low.

  Moreover, what was described in patent document 10 papermaking the slurry containing carbon nanofiber or carbon nanohorn, and performs a drying process. However, since there is no conductive component at the contact point of carbon nanofiber or the like, there is a problem that the conductivity is low and the mechanical strength of the molded body is also low. In addition, since carbon nanofibers and carbon nanohorns are expensive, there is a problem that the manufacturing cost is relatively high.

  The present invention has been made in the background of the above circumstances, and its object is to produce a base material for a gas diffusion electrode that can be manufactured at a low temperature and has both high conductivity and high gas permeability, a method for forming the same, and the same. It is providing the MEA provided with.

  In order to achieve such an object, the gist of the first invention is that a porous gas provided in a state in which a gas can be guided on a solid polymer electrolyte in order to constitute a gas diffusion electrode of a solid polymer fuel cell. A gas diffusion electrode base material, wherein (a) the ratio of the fiber length to the film thickness of the gas diffusion electrode base material (= fiber length / film thickness) is in the range of 0.1 to 1 The present invention includes a large number of carbon fine particles having a diameter smaller than the fiber diameter of the carbon fibers and a resin that joins the large number of carbon fibers to each other with the many carbon fine particles interposed therebetween.

  Further, the gist of the second invention is a method for producing a porous substrate for a gas diffusion electrode provided in a state in which gas can be guided onto a solid polymer electrolyte in order to constitute a solid polymer fuel cell. And (a) the ratio of the fiber length to the film thickness of the base material for gas diffusion electrode to be manufactured (= fiber length / film thickness) within a range of 0.1 to 1, and the particle diameter A slurry preparation step of preparing a slurry for an electrode base material containing a large number of carbon fine particles smaller than the fiber diameter of the carbon fiber, a resin, and a solvent; and (b) a sheet-like molded body using the slurry for an electrode base material And a molding process for manufacturing.

  Further, the gist of the membrane-electrode assembly of the third invention is that (a) a solid polymer electrolyte layer, a catalyst layer provided on one side and the other side thereof, and (b) each of the catalyst layers. And the base material for a gas diffusion electrode according to the first aspect of the present invention provided on the surface.

  According to the first aspect of the present invention, the base material for the gas diffusion electrode is configured by joining a large number of carbon fibers to each other with a resin in a state where a large number of carbon fine particles are interposed therebetween. At this time, carbon fibers having a fiber length / film thickness in the range of 0.1 to 1 are used, and carbon fine particles having a particle diameter smaller than the fiber diameter are used, so that high conductivity is obtained. And high gas permeability are both obtained. In addition, according to the above configuration, sufficiently high conductivity can be obtained without carbonizing the resin, so that it is not necessary to fire at high temperature in an inert atmosphere or the like in order to carbonize the resin. Therefore, it is possible to obtain a gas diffusion electrode substrate that can be manufactured at a low temperature and has both high conductivity and high gas permeability.

  Incidentally, a gas diffusion electrode base material using both carbon fibers and carbon particles has been proposed in, for example, Patent Document 9, but as described above, both the conductivity and gas permeability are insufficient. Stayed in. However, in order to reduce the manufacturing cost of the base material for the gas diffusion electrode and relax the structural limitation, it is possible to realize high characteristics by using low-temperature film formation as described in Patent Document 9 and the like. It is essential.

  As a result of intensive studies under the above-mentioned problems, the present inventor has found that the relationship between the fiber length of the carbon fiber and the film thickness of the base material for the gas diffusion electrode, and the fiber diameter of the carbon fiber and the particles of the carbon fine particles. It has been found that by defining the relationship with the diameter within the above range, both the conductivity (particularly the conductivity in the film thickness direction) and the gas permeability can be enhanced while the film is formed at a low temperature. The first invention has been made based on such knowledge.

  In the first invention, it is ideal that the carbon fine particles intervene between the carbon fibers, but there may be a portion where the carbon fibers are in direct contact with each other. Further, there may be a portion where the resin is interposed between the carbon fibers.

  In the first invention, “on the electrolyte” means that the gas diffusion electrode is provided via another layer such as a catalyst layer in addition to the case where the gas diffusion electrode is directly provided on the solid polymer electrolyte. Is included.

  According to the second aspect of the invention, the electrode substrate slurry containing carbon fibers, carbon fine particles, resin, and solvent is prepared in the slurry preparation step, and a sheet-like molded body is formed from this slurry in the molding step. Thus, a sheet-like base material for gas diffusion electrode is obtained. That is, the base material for a gas diffusion electrode can be obtained without performing a baking treatment for carbonizing the resin. At this time, carbon fibers having a fiber length / film thickness in the range of 0.1 to 1 are used, and carbon fine particles having a particle diameter smaller than the fiber diameter are used, so that high conductivity is obtained. And high gas permeability are both obtained. Therefore, it is possible to manufacture a gas diffusion electrode base material that is both low in conductivity and high in gas permeability. That is, the gas diffusion electrode of the first invention can be easily obtained.

  Further, according to the third invention, the MEA is configured by providing the gas diffusion electrode base material of the first invention via the catalyst layer on one surface and the other surface of the solid polymer electrolyte layer, An MEA having a gas diffusion electrode having high conductivity, high mechanical strength, and high gas permeability is obtained.

  Here, preferably, in the first invention, the second invention, and the third invention, the aspect ratio (= fiber length / fiber diameter) of the carbon fiber is in the range of 4.5 to 25. In this way, since the carbon fibers are relatively thick and short, it is easy to contact the carbon fibers with each other via carbon fine particles or directly, and the gap between the carbon fibers becomes an appropriate size. Conductivity and high gas permeability are obtained. If the aspect ratio is less than 4.5, the carbon fiber is short, so the density increases and the gas permeability decreases. In addition, when the aspect ratio exceeds 25, the carbon fibers are long, so that the carbon fibers are oriented sideways along the surface of the gas diffusion electrode base material, so that the conductivity in the thickness direction is reduced and the structure has many voids between the carbon fibers. The water repellent becomes soaked too much.

  Preferably, the carbon fine particles have a cluster structure. In this way, the plurality of carbon fibers can be brought into contact with each other through an infinite number of contacts with the cluster-structured carbon fine particles, so that high conductivity and gas permeability can be obtained.

  Preferably, the carbon fine particles have a primary particle size of 100 (nm) or less. In this way, since a conductive path is sufficiently secured at the contact points between the carbon fibers, higher conductivity can be obtained.

  Preferably, the resin is a thermosetting resin. In this way, since the carbon fibers and the carbon fine particles are bound by the thermosetting resin, even when the water-repellent film is provided, the binding state hardly changes even when exposed to the film forming temperature. As a result, there is an advantage that the conductivity is hardly lowered.

  Preferably, in the second invention, the resin is a thermosetting resin, and includes a drying step of drying the sheet-like molded body to cure the thermosetting resin. If it does in this way, the base material for gas diffusion electrodes can be obtained only by performing a drying process to a sheet-like molded object. In addition, when the water repellent film is provided, there is an advantage that even if it is exposed to the film forming temperature, the binding state hardly changes and the conductivity is not easily lowered.

  In addition, when the resin is a thermosetting resin as described above, the kind thereof is not particularly limited, and an appropriate one such as a phenol resin, an epoxy resin, a melamine resin, a silicone resin, a polyester resin, or the like. Can be used. These resins are selected according to the intended use in consideration of desired properties and the like, and for example, a phenol resin is particularly preferable in terms of mechanical strength and heat resistance.

  The polymer electrolyte fuel cell preferably has a catalyst at the three-phase interface where the reaction occurs. For example, the catalyst is provided in a layer form between the solid polymer electrolyte layer and the gas diffusion electrode. Further, the catalyst may be provided in a state supported on carbon fibers or carbon particles in the gas diffusion electrode. The mode provided in the gas diffusion electrode is, for example, a method of impregnating a slurry containing a catalyst after the gas diffusion electrode is formed, or a catalyst is loaded simultaneously with the formation of the gas diffusion electrode by mixing the catalyst in the electrode slurry. Or the like.

  Further, the carbon fiber is not particularly limited, and appropriate ones such as polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, and rayon-based carbon fiber can be used. When polyacrylonitrile-based carbon fiber is used, a gas diffusion electrode with particularly high mechanical strength can be obtained because the strength of the carbon fiber is high. In addition, when pitch-based carbon fibers are used, a gas diffusion electrode having particularly high electrical conductivity can be obtained.

  The carbon fibers preferably have an average diameter in the range of 1 to 30 (μm). If the average diameter is 5 (μm) or more, sufficiently high mechanical strength can be obtained because the fibers are sufficiently thick and difficult to break. Further, when the average diameter is 20 (μm) or less, mixing with carbon fine particles, a thermosetting resin or a solvent is easy.

  The carbon fibers preferably have an average fiber length in the range of 50 to 250 (μm). When the average fiber length is 50 (μm) or more, the entanglement between the carbon fibers is sufficiently increased and the mechanical strength is sufficiently increased. Further, when the average fiber length is 250 (μm) or less, the dispersibility of the carbon fibers is sufficiently enhanced, and the homogeneity of the structure of the gas diffusion electrode is sufficiently increased.

  Further, the polymer electrolyte fuel cell is provided with gas diffusion electrodes on the fuel electrode side and the air electrode side, respectively, but the present invention can be applied to any electrode on the fuel electrode side and the air electrode side. . However, it is not essential that electrodes having the same configuration are provided in both electrodes, and an appropriate electrode configuration can be adopted according to desired characteristics and manufacturing convenience, and the present invention is applied to both electrodes. Only one of them may be used.

Further, the present invention is applied to a solid polymer fuel cell using various solid polymer electrolytes, and the material of the solid polymer electrolyte is not particularly limited. For example, a homopolymer or copolymer of a monomer having an ion exchange group (such as —SO ₃ H group), a copolymer of a monomer having an ion exchange group and another monomer copolymerizable with the monomer, hydrolysis Similar to the homopolymer or copolymer (proton conductive polymer precursor) of a monomer having a functional group (that is, a precursor functional group of an ion exchange group) that can be converted into an ion exchange group by a post-treatment such as The thing etc. which processed are mentioned.

  Specific examples of the polymer electrolyte include, for example, perfluoro proton conductive polymer such as perfluorocarbon sulfonic acid resin, perfluorocarbon carboxylic acid resin film, sulfonic acid type polystyrene-graft-ethylenetetrafluoroethylene (ETFE). Copolymer membrane, sulfonic acid type poly (trifluorostyrene) -graft-ETFE copolymer membrane, polyetheretherketone (PEEK) sulfonic acid membrane, 2-acrylamido-2-methylpropanesulfonic acid (ATBS) membrane, carbonized Examples include hydrogen-based films.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following embodiments, the drawings are appropriately simplified or modified, and the dimensional ratios, shapes, and the like of the respective parts are not necessarily drawn accurately.

  FIG. 1 is a diagram showing a cross-sectional structure of a flat plate MEA 10 according to an embodiment of the present invention. In FIG. 1, an MEA 10 includes a thin flat layer electrolyte membrane 12, catalyst layers 14 and 16 provided on both surfaces thereof, and gas diffusion electrodes 18 and 20 provided on the surfaces of the catalyst layers 14 and 16, respectively. It is configured.

  The electrolyte membrane 12 is made of a proton conductive electrolyte such as Nafion (registered trademark of DuPont) DE520, and has a thickness of about 50 (μm), for example.

  The catalyst layers 14 and 16 are made of, for example, Pt-supported carbon black in which a catalyst such as platinum is supported on spherical carbon powder. For example, those commercially available from Tanaka Kikinzoku Kogyo Co., Ltd. (for example, TEC10E70TPM) can be used. The thickness dimension of the catalyst layers 14 and 16 is, for example, about 50 (μm).

  Further, each of the gas diffusion electrodes 18 and 20 has a thickness dimension of about 300 (μm), for example, and gas easily flows between the front surface and the back surface (that is, one surface on the catalyst layers 14 and 16 side). It is a porous layer comprised so that it can do.

  The gas diffusion electrodes 18 and 20 are made of, for example, carbon fibers, carbon fine particles, and a thermosetting resin. The carbon fiber is, for example, a so-called PAN-based fiber obtained by carbonizing polyacrylonitrile fiber, and has a diameter of about 10 (μm) and a fiber length of about 50 to 250 (μm), for example, about 250 (μm). is there. That is, the carbon fibers constituting the gas diffusion electrodes 18 and 20 have a fiber length of 1/6 to 5/6 of the film thickness. The thermosetting resin is made of, for example, a resole resin.

Further, since the carbon fibers of the gas diffusion electrodes 18 and 20 have a fiber length smaller than the film thickness as described above, the carbon fibers 22 are gas diffusion as schematically shown in FIG. The electrodes 18 and 20 exist in the gas diffusion electrodes 18 and 20 in the direction extending in the thickness direction or the direction inclined thereto. Further, the carbon fibers 22 are entangled with each other, and are bound by a thermosetting resin 26 with carbon fine particles 24 interposed at their contact points as schematically shown in FIG. The carbon fine particles 24 have a very small primary particle diameter of, for example, about 30 (nm), and a large number of them are aggregated to form a cluster structure. The carbon fibers 22 are brought into contact with each other through an infinite number of contacts. Yes. Because of such a structure, the gas diffusion electrodes 18 and 20 have a sufficiently high conductivity with a cross-sectional pressure resistance of 300 (mΩ · cm) or less and 10000 (ml · mm / cm ² / min). ) High gas permeability as described above.

  3 schematically shows a typical structural example of the gas diffusion electrodes 18 and 20 of the present embodiment, and the structure as shown in FIG. Not formed with dots. That is, there are also portions where the carbon fibers 22 are in direct contact with each other or are joined only by the thermosetting resin 26 without the carbon fine particles 24 interposed.

  The flat gas diffusion electrodes 18 and 20 are manufactured, for example, as follows. Hereinafter, the manufacturing method will be described with reference to FIG. First, the carbon fiber, the carbon fine particles, the thermosetting resin such as a resol resin, and a solvent such as 1-propanol are prepared. These mixing ratios are determined as appropriate. For example, carbon fiber is 3 (g), thermosetting resin is 1.5 (g), solvent is 20 (g), and carbon fine particles are 0.5 (g). is there.

  Next, in the mixing step 1, the carbon fiber, the resol resin, the solvent, and the carbon fine particles are mixed while being sequentially put in a suitable mixing container. This mixing process is performed for about one day at a rotational speed of about 300 (rpm), for example. Thereby, the slurry for electrode base materials is obtained.

  Next, in the forming step 2, the prepared electrode substrate slurry is formed by using a well-known appropriate sheet forming method such as slip casting, or by applying it on an appropriate plate.

  Next, in the drying step 3, for example, a drying treatment is performed at room temperature for about 4 hours, and in the heat treatment step 4, for example, a heat treatment is performed at 150 (° C.) for about 3 hours. Thereby, the solvent is removed from the slurry, and a sheet-like material in which the carbon fibers are entangled with each other and bonded with the thermosetting resin through the carbon fine particles having the cluster structure is obtained. That is, the base material for gas diffusion electrodes for constituting the gas diffusion electrodes 18 and 20 of the MEA 10 is obtained. The thickness dimension after drying and heat treatment is, for example, about 320 (μm).

  The MEA 10 is prepared by applying a catalyst slurry to the gas diffusion electrode base material manufactured as described above to produce an electrode sheet, and the sheet-like electrolyte is formed of two sheets so that the catalyst layers 14 and 16 are inside. It is obtained by sandwiching between electrode sheets and applying hot pressing. The details of the catalyst slurry and the electrolyte are omitted because they are not necessary for understanding this example.

  Here, the cross-sectional pressure resistance and gas permeability of the gas diffusion electrodes 18 and 20 are evaluated by using various kinds of carbon fibers having different fiber lengths and various addition amounts of resole resin, solvent, and carbon fine particles. The results will be described. The cross-sectional pressure resistance is a resistance value between the front surface and the back surface measured in a state of being pressurized in the thickness direction, and was measured using, for example, a small hot press machine AH-2003 manufactured by AS ONE Corporation. The gas permeability was measured using, for example, a capillary flow porometer 1200AEL manufactured by PMI. The specifications and results of each evaluated specimen are shown in Table 1 below. The evaluation results are summarized in FIG. The bar graph represents the cross-sectional pressure resistance, and the line graph represents the gas permeability.

  As shown in Table 1 above, the fiber length is 12 (mm), 9 (mm), 6 (mm), 3 (mm), 250 (μm), 150 (μm), 50 (μm) for evaluation. The carbon fiber was used. Among these carbon fibers, those having a fiber length of 50 (μm) (used for Nos. 14 and 15) are manufactured by Mitsubishi Chemical Corporation, and others are manufactured by Nippon Graphite Fiber. Both are pitch-based carbon fibers. The fiber diameter is 10 (μm) manufactured by Nippon Graphite Fiber and 11 (μm) manufactured by Mitsubishi Chemical Corporation. The respective aspect ratio and fiber length / film thickness ratio are shown directly below each sample number. Further, in the column of carbon fiber, the fiber length is shown in the upper part and the preparation amount is shown in the lower part, respectively, and the preparation amount is all 3 (g).

  Moreover, the thermosetting resin is, for example, a resol resin made by Sumitomo Bakelite, and the preparation amount is in the range of 0.5 (g) to 3.1 (g). In addition, the solvent was 1-propanol manufactured by Wako Pure Chemical Industries, and the preparation amount was 15 (g) or 20 (g). The carbon fine particles are, for example, Cabot ketjen black having a primary particle size of 30 (nm), and the blending amount is 0.3 (g) to 0.6 (g).

  In Table 1 above, Comparative Example 1 is carbon paper TGP-H-090 manufactured by Toray that has been conventionally used as a base material for gas diffusion electrodes.

The target value of the cross-sectional pressure resistance is 300 (mΩ · cm) or less, and the target value of the gas permeability is 10000 (ml · mm / cm ² / min) or more. As shown in the result column of Table 1 above, All sample Nos. 1 to 15 satisfy the target values of the cross-sectional pressure resistance and gas permeability. A typical evaluation result is shown in FIGS. According to these results, it is understood that the cross-sectional pressure resistance is lower than that of carbon paper (Comparative Example 1) when the fiber length / film thickness ratio is in the range of 0.1-20. Further, the gas permeability tends to increase as the fiber length / film thickness ratio increases.

  When the fiber length / film thickness ratio is small, that is, when the fiber length is short and the number of contact points between fibers increases, more contacts pass through when electrons move. As a result, the cross-sectional pressure resistance increases. Incidentally, when a substrate in which the same amount of a thermosetting resin and carbon fine particles was mixed without adding carbon fiber was evaluated, the cross-sectional pressure resistance was an extremely high value of 1 to 2 (Ω · cm). Since the resistance value of the carbon fiber is, for example, about 0.15 (mΩ · cm), it can be seen that a material not including the carbon fiber as described above has a resistance as high as 10,000 times. According to this evaluation result, the contact point significantly reduces conduction, and it is desirable that the number of contacts on the conduction path be as small as possible.

  On the other hand, when the fiber length / thickness ratio is larger than 1, the carbon fiber does not go in the film thickness direction as shown in the schematic diagram shown in FIG. 2, but lies in the direction along the surface. Become. As a result, at least in the film thickness direction, the number of contacts that pass though the fiber length is long increases, so that the resistance value is considered to increase.

  From these facts, the cross-sectional pressure resistance is lowered only in an appropriate fiber length range. As described above, the resistance value has a fiber length / film thickness ratio in the range of 0.1 to 20. Would be preferable. On the other hand, the gas permeability tends to increase because the voids increase as the fiber length increases.

  8 and 9 are diagrams showing the relationship between the fiber length / film thickness ratio and the surface roughness Ra and Rmax. The target values of the surface roughness are less than 3 for Ra and less than 50 for Rmax. 8 and 9, it can be seen that the target value is satisfied when the fiber length / film thickness ratio is 1 or less. Among these target values, the average roughness Ra takes into consideration the ease of application when a water repellent layer or a catalyst layer is provided on the surface of the gas diffusion electrode substrate. Further, the maximum roughness Rmax is determined so that the membrane is not completely damaged even if the electrolyte membrane is pierced because the electrolyte membrane is usually provided with a thickness of about 50 (μm).

  In Comparative Examples 2 to 5 in Table 1, both the cross-sectional pressure resistance and the gas permeability satisfied the target values, but the surface condition was poor, and when the MEA was produced, the electrolyte membrane was damaged. These are due to the fiber length being too long. Therefore, according to FIGS. 6 to 9, the fiber length / film thickness ratio should be within the range of 0.1 to 1 in order to satisfy the cross-sectional pressure resistance, gas permeability, and surface roughness. I understand that.

  Although no particular data is shown, when the MEA 10 was manufactured, heating was performed in air (300 ° C.) for 1 hour for the purpose of providing a water repellent film on the surface. No particular changes were observed in the resistance values and gas permeability of the gas diffusion electrodes 18 and 20. This is considered to be due to the use of resole resin as a binder. And since sufficient mechanical strength is provided by containing resole resin, the base material for gas diffusion electrodes has the advantage that it is excellent also in handling property.

  As described above, according to the present embodiment, the gas diffusion electrode base material is bonded to each other by the thermosetting resin 26 in a state where a large number of carbon fibers 22 are interposed between the carbon fibers 22. The carbon fiber 22 having a fiber length / film thickness in the range of 0.1 to 1 is used, and the carbon fine particle 24 has a particle diameter smaller than the fiber diameter. Since it is used, both high conductivity and high gas permeability can be obtained. In addition, since sufficiently high conductivity can be obtained without carbonizing the thermosetting resin 26, it is not necessary to fire at a high temperature in an inert atmosphere or the like in order to carbonize it. In addition, since the thermosetting resin 26 is used as the resin for binding the carbon fibers 22 and the carbon fine particles 24, when the water repellent film is provided, the conductive property due to exposure to the film forming temperature is also provided. There is no decline. Therefore, it is possible to obtain a gas diffusion electrode substrate that can be manufactured at a low temperature and has both high conductivity and high gas permeability.

  As mentioned above, although this invention was demonstrated in detail with reference to drawings, this invention can be implemented also in another aspect, A various change can be added in the range which does not deviate from the main point.

It is a figure which shows the flat plate type MEA which is one Example of this invention. It is a figure which shows typically the structure of the gas diffusion electrode with which MEA of FIG. 1 was equipped. It is a schematic diagram for demonstrating the binding state of the carbon fiber in the gas diffusion electrode of FIG. It is process drawing for demonstrating the manufacturing method of the gas diffusion electrode of FIG. It is the figure which put together the characteristic evaluation result of the Example and the comparative example. It is a figure which shows the relationship between fiber length / film thickness ratio and cross-sectional pressing resistance. It is a figure which shows the relationship between fiber length / film thickness ratio and gas permeability. It is a figure which shows the relationship between fiber length / film thickness ratio and surface roughness Ra. It is a figure which shows the relationship between fiber length / film thickness ratio and surface roughness Rmax.

Explanation of symbols

10: MEA, 12: electrolyte membrane, 14, 16: catalyst layer, 18, 20: gas diffusion electrode, 22: carbon fiber, 24: carbon fine particle, 26: thermosetting resin

Claims (7)

A porous base material for a gas diffusion electrode provided in a state in which a gas can be guided onto a solid polymer electrolyte in order to constitute a gas diffusion electrode of a polymer electrolyte fuel cell,
The ratio of the fiber length to the film thickness of the base material for gas diffusion electrode (= fiber length / film thickness) is a large number of carbon fibers in the range of 0.1 to 1, and a large number of particle diameters smaller than the fiber diameter of the carbon fibers. A base material for a gas diffusion electrode, comprising: carbon fine particles; and a resin that joins the multiple carbon fibers to each other in a state where the multiple carbon fine particles are interposed therebetween.   The base material for a gas diffusion electrode according to claim 1, wherein an aspect ratio (= fiber length / fiber diameter) of the carbon fiber is within a range of 4.5 to 25.   The gas diffusion electrode substrate according to claim 1 or 2, wherein the carbon fine particles have a cluster structure.   The base material for a gas diffusion electrode according to any one of claims 1 to 3, wherein the carbon fine particles have a primary particle size of 100 (nm) or less.   The base material for a gas diffusion electrode according to any one of claims 1 to 4, wherein the resin is a thermosetting resin. A method for producing a porous base material for a gas diffusion electrode provided in a state in which a gas can be guided on a solid polymer electrolyte to constitute a solid polymer fuel cell,
The ratio of the fiber length to the film thickness of the base material for gas diffusion electrode to be manufactured (= fiber length / film thickness) is within a range of 0.1 to 1, and the particle diameter is larger than the fiber diameter of the carbon fibers. A slurry preparation step of preparing a slurry for an electrode substrate including a large number of carbon fine particles, a resin, and a solvent,
And a molding step of producing a sheet-like molded body using the electrode substrate slurry. A method for producing a gas diffusion electrode substrate.   The gas diffusion electrode according to any one of claims 1 to 5, wherein the solid polymer electrolyte layer, a catalyst layer provided on one surface and the other surface thereof, and a gas diffusion electrode provided on each surface of the catalyst layer are provided. A membrane-electrode assembly comprising a substrate for use.

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