JP2009289573A - Composite type electrolyte film, and fuel cell equipped with the same - Google Patents

Abstract

[PROBLEMS] To provide a composite electrolyte membrane having sufficient water retention performance, particularly at low humidification, without increasing the film thickness, and further excellent in reverse diffusibility of moisture from the cathode side to the anode side. A fuel cell is provided.
SOLUTION: An outer electrolyte resin layer 1B, 1A in contact with an anode side catalyst layer 30 and a cathode side catalyst layer 20, and at least two or more porous layers interposed between the two outer electrolyte resin layers 1A, 1B. These reinforcing layers 2 and 3 and at least one or more inner electrolyte resin layers 1C have an alternating layer structure, and the cathode-side reinforcing layer 2 as compared with the ratio of the anode-side reinforcing layer 3 This is the composite electrolyte membrane 10 in which the ratio of is small. As one example, the cathode-side reinforcing layer has a relatively thin layer thickness, and as another example, the cathode-side reinforcing layer has a relatively high porosity. Is.
[Selection] Figure 1

Description

  The present invention relates to a composite electrolyte membrane having an alternating layer structure of a reinforcing layer and an electrolyte resin layer, and a fuel cell including the same.

  A polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) comprising an ion-permeable electrolyte membrane, an anode-side catalyst layer and a cathode-side catalyst layer sandwiching the electrolyte membrane, and a membrane electrode assembly (MEA). A separator is arranged on the outer side to form a single cell. A gas diffusion layer (GDL) for promoting gas flow and enhancing current collection efficiency is provided outside each catalyst layer to form a membrane electrode assembly (MEGA: MEA and GDL assembly). There is also a form in which a separator is disposed outside the diffusion layer. In actuality, these single cells are stacked in stages corresponding to the power generation performance, thereby forming a fuel cell stack.

  In the fuel cell described above, hydrogen gas or the like is provided as a fuel gas to the anode electrode, oxygen or air is provided as the oxidant gas to the cathode electrode, and each electrode has a gas flow layer in its in-plane direction. Then, the gas diffused in the gas diffusion layer is led to the electrode catalyst to cause an electrochemical reaction. In this electrochemical reaction, protons (hydrogen ions) and water generated at the anode electrode pass through the electrolyte membrane in a hydrated state to reach the cathode electrode, and generated water is generated at the cathode electrode.

  By the way, since the movement of protons necessary for power generation of the fuel cell uses water as a medium, when the water content of the electrolyte membrane decreases, the proton conductivity decreases, resulting in a decrease in power generation performance. In particular, in power generation in a low humidified atmosphere, it has been found that the water content of the electrolyte membrane is greatly reduced and the proton conductivity is more significantly reduced.

  Therefore, as characteristics required for the electrolyte membrane described above, water content, water retention, and permeability such as hydrogen ions and water are extremely important. As a measure for controlling the characteristics of the electrolyte membrane, it is generally known to study and improve the ion exchange capacity, the primary structure and the higher order structure of the electrolyte resin constituting the electrolyte membrane having proton conductivity. However, it is easy to understand that it is not easy to improve the ion exchange capacity of the electrolyte resin, the primary structure of the molecule, and the higher order structure. Therefore, the development of simpler measures to improve the above characteristics of the electrolyte membrane is not possible in this field. One of the important issues.

  In addition, by reducing the thickness of the electrolyte membrane, for example, by promoting the reverse diffusion of water (for example, generated water) from the cathode side, which tends to be wet, to the anode side, which is easy to dry, the water content and water retention of the electrolyte membrane can be ensured. As a result, the electrical resistance of the electrolyte membrane can be reduced. However, the mechanical strength of the electrolyte membrane decreases as the electrolyte membrane becomes thinner, reducing the durability of the electrolyte membrane (and hence the durability of the fuel cell), and the work when joining the electrolyte membrane and catalyst layer that have been reduced in thickness. New problems arise, such as a decrease in production efficiency due to poor performance.

  Therefore, recently, a composite electrolyte membrane that has an alternating layer structure of an electrolyte resin layer and a porous reinforcing layer has been developed as a technique for suppressing the decrease in mechanical strength while reducing the thickness of the electrolyte membrane. As the disclosed technique, an electrolyte membrane disclosed in Patent Document 1 can be cited.

  The electrolyte membrane disclosed in Patent Document 1 is composed of a porous reinforcing layer, a cathode side electrolyte layer and an anode side electrolyte layer located on both sides thereof, and the volume of the electrolyte layer existing on the electrode side having a high water content is determined by the water content. It is intended to make the water content in each electrolyte layer uniform by making it larger than that of the electrolyte membrane on the electrode side with less.

  In the electrolyte membrane disclosed in Patent Document 1, the volume of the electrolyte layer on the anode side and the cathode side is changed depending on the water content, but the water content of both electrodes generally changes during the power generation process. Therefore, there may be a case where the water content changes somewhat with respect to the initially set volume of the electrolyte layer of both electrodes. In particular, when the moisture content is low, the moisture content in the electrolyte membrane is likely to be reduced, and the amount of protons that can be transferred is reduced, resulting in a decrease in power generation performance. This three-layer structure (two electrolyte layers, In the interlaminar structure of the central reinforcing layer sandwiched between them, it is difficult to maintain a sufficient water retention state at the time of this low humidification, and it is considered that the reduction of the moisture content cannot be effectively suppressed.

  Another disclosed technique is an electrolyte membrane having a composite structure disclosed in Patent Document 2. This electrolyte membrane has two or more reinforcing layers. Therefore, for example, moisture is secured in the electrolyte layer located in the center between the two reinforcing layers, and water retention (water content) of the electrolyte membrane is ensured. It can be secured. However, simply increasing the number of reinforcing layers does not promote the reverse diffusion of water described above, and therefore effective water management in the electrolyte membrane cannot be achieved.

JP 2007-265898 A JP 2006-155924 A

  The present invention has been made in view of the above problems, and relates to a composite electrolyte membrane having an alternate structure of an electrolyte resin layer and a porous reinforcing layer, and improves the layer configuration and layer characteristics of the constituent members. Therefore, the composite electrolyte membrane has sufficient water retention performance, particularly at low humidification, without increasing the film thickness, and also has excellent reverse diffusibility of moisture from the cathode side to the anode side. An object of the present invention is to provide a fuel cell.

  In order to achieve the above object, a composite electrolyte membrane according to the present invention includes an outer electrolyte resin layer in contact with the anode side catalyst layer and the cathode side catalyst layer, and at least two layers interposed between the two outer electrolyte resin layers. Proportion of the anode side reinforcing layer having the porous reinforcing layer described above and at least one inner electrolyte resin layer, and having an alternate structure of the outer electrolyte resin layer, the reinforcing layer, and the inner electrolyte resin layer. The proportion of the reinforcing layer on the cathode side is smaller than that in FIG.

  The electrolyte membrane of the present invention comprises a total of 5 or more layers, including an outer electrolyte resin layer adjacent to both the anode and cathode catalyst layers, two or more porous reinforcing layers and one or more inner electrolyte resin layers positioned therebetween. And a ratio of the cathode-side reinforcing layer is smaller than that of the anode-side reinforcing layer. Examples of this alternate layer structure include, for example, a five-layer alternate structure of an outer electrolyte resin layer on the anode side, a reinforcing layer, an inner electrolyte resin layer, a reinforcing layer, and an outer electrolyte resin layer on the cathode side, and an outer electrolyte resin layer on the anode side. And a seven-layered structure of a reinforcing layer, an inner electrolyte resin layer, a reinforcing layer, an inner electrolyte resin layer, a reinforcing layer, and an outer electrolyte resin layer on the cathode side.

  The electrolyte membrane of the present invention is the same as the reinforcing layer of a conventional composite electrolyte membrane (generally, a three-layer structure comprising one reinforcing layer located in the center and an anode-side and cathode-side electrolyte resin layer sandwiching it). The reinforcing layer having a certain thickness is divided into two or more, and therefore, a plurality of reinforcing layers having a small thickness per layer are used to form a multi-layered alternating structure. By adopting such a multilayer structure, at least the inner electrolyte resin layer located in the center is sandwiched between two reinforcing layers, and this inner electrolyte resin layer can ensure good water retention and low An electrolyte membrane having water content (water retention) necessary for proton conduction even during humidification can be obtained.

  Here, the material of the porous reinforcing layer is not particularly limited, and examples thereof include polytetrafluoroethylene, polyethylene, polypropylene, polyimide, polyamide, and polyetheretherketone. The electrolyte resin layer is not particularly limited as long as it is a material having proton conductivity. For example, perfluorocarbon sulfonic acid resins represented by Nafion (trade name, manufactured by DuPont), sulfonic acid groups, Examples thereof include hydrocarbon resins such as polyethersulfone, polyetheretherketone, polyimide, polyphenylene, polyethylene, and polycycloolefin having an ion conductive group such as carboxylic acid group and boronic acid group in the side chain.

  In addition, a melt impregnation method or the like can be applied as a bonding method (compositing method) between the reinforcing layer and the electrolyte resin layer. This melt impregnation method is easier to control the film thickness than the cast film-forming method using a solution, and surface cracks due to solvent evaporation cannot occur, so that an electrolyte membrane of good quality can be produced. Furthermore, high molecular weight of the electrolyte molecules and entanglement of the molecules can be promoted, and a highly durable electrolyte membrane can be manufactured.

  In the composite electrolyte membrane of the present invention, on the premise of the above-described alternate layer structure, the ratio of the reinforcing layer on the cathode side is further reduced as compared with that on the anode side.

  The reinforcing layer does not contribute to proton conduction performance, that is, power generation performance, and has a function of reinforcing the electrolyte membrane to the last, so that the proportion of the reinforcing layer is small, the proportion of the electrolyte resin layer is large. It means that. A large proportion of the electrolyte resin layer means that the ion exchange capacity per unit weight is large (the number of sulfonic acid groups is large), and the ion exchange group equivalent weight (EW value: Equivalent Weight) is small. Also means.

  The proportion of the cathode side reinforcing layer is relatively small, and therefore the ion exchange capacity on the cathode side is relatively large, so that the water retention or water content can be inclined between the cathode side and the anode side. (A water concentration distribution is formed in the thickness direction of the electrolyte membrane), and the reverse diffusion of moisture from the cathode side to the anode side is promoted.

  In the composite electrolyte membrane of the present invention, for example, the water retention performance of the electrolyte membrane is adopted by adopting an alternate layer structure of an outer electrolyte resin layer on the anode side, a reinforcing layer, an inner electrolyte resin layer, a reinforcing layer, and an outer electrolyte resin layer on the cathode side. In addition to this, by reducing the proportion of the cathode-side reinforcing layer, the water reverse diffusion performance is improved, and the water management performance of the electrolyte membrane itself is improved.

  Here, regarding the above-described configuration of “decreasing the ratio of the cathode-side reinforcing layer”, there are mainly two embodiments.

  One embodiment is to reduce the thickness of the cathode-side reinforcing layer compared to the anode-side reinforcing layer.

  Reducing the thickness of the cathode-side reinforcing layer leads to relatively increasing the thickness of the cathode-side electrolyte resin layer, and as a result, increases the cathode-side ion exchange capacity. .

  Another embodiment is to increase the porosity of the cathode side reinforcing layer compared to the anode side reinforcing layer.

  Of course, the cathode-side reinforcing layer may be made relatively thin, and the cathode-side reinforcing layer may have a relatively high porosity, which can further increase the moisture back-diffusion. It leads to further enhancement.

  Regarding the change of the layer thickness of the reinforcing layer on the anode side and the cathode side, according to the verification by the present inventors, the ratio of the layer thickness of the cathode side reinforcing layer to the layer thickness of the entire reinforcing layer is 0.3. By making the following, it has been found that the power generation performance of the fuel cell can be improved by about 10% as compared with the case where the thicknesses of the reinforcing layers on both the anode side and the cathode side are about the same.

  Further, regarding the change of the porosity of the reinforcing layer on the anode side and the cathode side, according to the verification by the present inventors, the ratio of the porosity of the cathode-side reinforcing layer to the porosity of the anode-side reinforcing layer is 1 Knowledge that the power generation performance of the fuel cell can be improved by about 2 to 5% by setting the range of .06 to 1.11 as compared with the case where the porosity of the reinforcing layer on both the anode side and the cathode side is about the same. Is obtained.

  According to the composite electrolyte membrane of the present invention described above, the water retention performance of the electrolyte membrane can be improved without increasing the thickness of the reinforcing layer as compared with the conventional composite electrolyte membrane, particularly at low humidification. It is possible to effectively suppress the decrease in power generation performance. In addition, the back diffusion performance of moisture from the cathode side to the anode side can be improved, the water management of the electrolyte membrane itself is improved, and flattening that tends to occur on the cathode side without performing precise gas humidification control The problem of dry-up that tends to occur on the anode side can be effectively solved by the structure of the electrolyte membrane.

  The above-described fuel cell having the composite electrolyte membrane of the present invention is applied to the other side, such as a stationary fuel cell for home use and a fuel cell for vehicle use, but its production has recently been expanded. It is suitable for electric vehicles and hybrid vehicles that require higher performance for in-vehicle devices.

  As can be understood from the above description, according to the composite electrolyte membrane of the present invention, it is possible to improve both the water retention performance particularly at the time of low humidification and the moisture reverse diffusion performance.

  Embodiments of the present invention will be described below with reference to the drawings. The composite electrolyte membrane shown in the figure has a five-layered alternating structure of an electrolyte resin layer and a reinforcing layer, but has a multilayered structure such as a seven-layered alternating layer structure and a nine-layered alternating layer structure. Of course, it is also good. Note that, in principle, the thickness of one reinforcing layer is reduced as the thickness of the reinforcing layer increases, so that the thickness of the entire reinforcing layer is not changed.

  FIG. 1 is a longitudinal sectional view showing a membrane electrode assembly including an embodiment of a composite electrolyte membrane of the present invention. The composite electrolyte membrane 10 is sandwiched between the anode-side catalyst layer 30 and the cathode-side catalyst layer 20, and the outer electrolyte resin layers 1A and 1B that are in contact with the cathode-side catalyst layer 20 and the anode-side catalyst layer 30, respectively. The porous cathode-side reinforcing layer 2, the anode-side reinforcing layer 3, and the inner electrolyte resin layer 1C sandwiched between these reinforcing layers 2 and 3 are formed in a composite structure. The MEA 40 (membrane electrode assembly) is formed from the type electrolyte membrane 10, the cathode side catalyst layer 20, and the anode side catalyst layer 30.

  Here, the above-described reinforcing layers 2 and 3 are formed of polytetrafluoroethylene, polyethylene, polypropylene, polyimide, polyamide, polyether ether ketone, or the like. Further, the electrolyte resin layers 1A, 1B, and 1C described above have ion conductivity such as perfluorocarbon sulfonic acid resin represented by Nafion (trade name, manufactured by DuPont), sulfonic acid group, carboxylic acid group, and boronic acid group. It is formed from polyethersulfone having a group in the side chain, polyetheretherketone, polyimide, polyphenylene, polyethylene, polycycloolefin and the like. The cathode-side and anode-side catalyst layers 20 and 30 are formed of a porous material in which a catalyst made of platinum or an alloy thereof is supported on carbon or the like.

  The reinforcing layers 2 and 3 and the electrolyte resin layers 1A, 1B, and 1C can be bonded to each other by a melt impregnation method in which the layers are bonded to each other and melted and hot pressed.

  In the composite electrolyte membrane 10 shown in FIG. 1, the electrolyte resin layers 1A, 1B, and 1C have the same layer thickness, and the cathode-side reinforcing layer 2 and the anode-side reinforcing layer 3 have the same layer thickness. The porosity of the reinforcing layer 2 on the side is relatively larger than that of the reinforcing layer 3 on the anode side.

  Increasing the porosity of the cathode-side reinforcing layer 2 means that the proportion of the reinforcing layer is reduced on the cathode side, in other words, the cathode-side ion exchange capacity is relatively increased. In addition, the water content can be inclined between the anode side and the anode side, which leads to the promotion of moisture reverse diffusion from the cathode side to the anode side.

  On the other hand, FIG. 2 is a longitudinal sectional view showing a membrane electrode assembly 40A having another embodiment of the membrane electrode assembly. This composite electrolyte membrane 10A also has a five-layered alternating layer structure like the composite electrolyte membrane 10, but the outer electrolyte resin layers 1A ′ and 1B ′ are thinner than the inner electrolyte resin layer 1C ′. Further, the cathode-side reinforcing layer 2A is thinner than the anode-side reinforcing layer 3A.

  By making the inner electrolyte resin layer 1C ′ sandwiched between the two reinforcing layers 2A and 3A thicker than the other electrolyte resin layers 1A ′ and 1B ′, water is retained by the thick inner electrolyte resin layer 1C ′. Since the water content increases, it is possible to ensure good proton conductivity especially at low humidification. The total thickness of the outer electrolyte resin layers 1A 'and 1B' and the inner electrolyte resin layer 1C 'is approximately the same as the total thickness of the electrolyte resin layers in the composite electrolyte membrane 10 shown in FIG.

  Further, since the thickness of the cathode-side reinforcing layer 2A is relatively smaller than that of the anode-side reinforcing layer 3A, the cathode-side reinforcing layer has a thickness similar to that when the porosity is changed. The ratio can be reduced, and the back diffusion property of moisture from the cathode side to the anode side is promoted.

  In addition to changing the layer thickness, the porosity of the cathode-side reinforcing layer 2A may be made larger than that of the anode-side reinforcing layer 3A. In this case, the cathode-side and anode-side porosity may be increased. The water concentration gradient in the meantime can be given a larger slope, and the back diffusion of moisture is further promoted.

  FIG. 3 is a longitudinal sectional view showing an embodiment of a fuel cell (single cell) including the MEA 40 shown in FIG. 1, and shows a so-called flat type module cell in which a gas flow path layer is separated from the separator. It is a thing.

  In this fuel cell 100, an MEGA 60 (membrane electrode assembly) is formed from the MEA 40 and gas diffusion layers 50 and 50 on the anode side and cathode side that sandwich the MEA 40. The membrane electrode assembly 60 is formed on the cathode side, The gas flow path layers 70, 70 on the anode side are sandwiched, and the gas flow path layers 70, 70 are further sandwiched by separators 80, 80.

  Here, the gas diffusion layer 50 is formed from a gas permeable material such as carbon paper or carbon cloth, and the gas flow path layer 70 is formed from a porous expanded metal.

  The separator 80 having a three-layer structure is sandwiched between a face material 83 that defines a cell between adjacent single cells, a face material 81 on the MEGA side facing the face material 81, and the face materials 81 and 83. The spacer 82 is made of a resin material formed in a frame shape (endless shape) along the outer peripheral contour of the face materials 81 and 83. The face materials 81 and 83 are formed of a dense carbon material or dense graphite material that is impermeable to gas. The side surface of the face material 81 facing the face material 83 is provided with a large number of projections (dimples) (not shown), and the projections have a height corresponding to the thickness of the spacer 82, thereby providing a three-layer structure. At this time, the tip of the protrusion comes into contact with the side surface of the face material 83, and a flow path of cooling water flowing between the protrusions is formed in a turbulent manner.

  On the cathode side, in order to provide the oxidant gas to the cathode-side catalyst layer 20 via the gas flow path layer 70, the supply manifold M1 that penetrates the separator 80 and the frame material 71 surrounding the gas flow path layer 70 is provided. At the same time, a discharge manifold M2 for discharging the gas and generated water flowing through the gas flow path layer 20 is formed. Similarly, on the anode side, a supply manifold M1 and a discharge manifold M2 for providing fuel gas to the catalyst layer 30 on the anode side via the gas flow path layer 70 are formed.

  Further, a rubber gasket 90 for ensuring the sealing performance of the gas provided to both the cathode-side catalyst layer 20 and the anode-side catalyst layer 30 is integrally formed on the periphery of the MEGA 60 by injection molding. .

  In an actual fuel cell, a fuel cell stack is formed by stacking predetermined fuel cell units 100 according to a desired power generation amount. Further, the fuel cell stack includes an end plate, a tension plate, and the like on the outermost side, and a compressive force is applied between the tension plates at both ends to form a fuel cell.

  A fuel cell system mounted on an electric vehicle or the like includes this fuel cell, various tanks for storing hydrogen gas and air, a blower for supplying these gases to the fuel cell, a radiator for cooling the fuel cell, a fuel The battery is generally composed of a battery that stores electric power generated by the battery, a drive motor that is driven by the electric power, and the like.

[Experiment comparing the cell voltage in a low humidified atmosphere of a fuel cell (Examples 1 and 2) comprising a composite electrolyte membrane of the present invention and a fuel cell (Comparative Example) comprising a conventional composite electrolyte membrane as a result]
The inventors have made a prototype of a fuel cell having a composite electrolyte membrane having a conventional structure and a fuel cell having the composite electrolyte membrane of the present invention shown in FIGS. 1 and 2, and actually measured the cell voltage in a low humidified atmosphere. The experiment which compares is done. 4 schematically shows the models of the example and the comparative example, FIG. 4a shows the model of the comparative example, FIG. 4b shows the model of the example 1, and FIG. 4c shows the model of the example 2. Show.

  A comparative example model M1 shown in FIG. 4a is a composite electrolyte membrane model having a three-layer structure in which a reinforcing layer model Mh having a layer thickness: L1 is sandwiched between electrolyte resin layer models Md and Md having both layer thicknesses L2. The cathode side catalyst layer model Mk and the anode side catalyst layer model Ma sandwich the MEA. Further, in Example 1 model M2 shown in FIG. 4b, the inner electrolyte resin layer model Md1 having a layer thickness of 2 / 3L2 is sandwiched between the reinforcing layer models Mh1 and Mh2 having both layer thicknesses of 1 / 2L1, and this has the layer thickness. Both are 2 / 3L2 cathode-side and anode-side outer electrolyte resin layer models Md2 and Md3 sandwiched by a composite electrolyte membrane model having a five-layer structure. This is a cathode-side catalyst layer model Mk and anode-side catalyst layer model Ma. The MEA is formed by clamping. Further, in Example 2 model M3 shown in FIG. 4c, the inner electrolyte resin layer model Md1 ′ having a layer thickness of 4 / 3L2 is compared with the reinforcing layer model Mh1 ′ on the cathode side having a layer thickness of 1 / 3L1, and the layer thickness is 2 / 3L1. The anode-side reinforcing layer model Mh2 ′ is sandwiched between the cathode-side and anode-side outer electrolyte resin layer models Md2 ′ and Md3 ′ each having a layer thickness of 1/3 L2, and is a composite electrolyte membrane having a five-layer structure. This is a model, and this is sandwiched between the cathode side catalyst layer model Mk and the anode side catalyst layer model Ma to form the MEA.

In the comparative example model, a reinforcing layer is manufactured by a general stretching method as a method for forming a porous film of PTFE (fluororesin), and an electrolyte resin precursor (terminal group is —SO ₂ F) is used as a reinforcing layer model. It was made to make composite by sticking to both sides and melt-heat-pressing. This was hydrolyzed with a mixed solution of sodium hydroxide and dimethyl sulfoxide (DMSO), then acid-treated with an aqueous sulfuric acid solution to make the molecular side chain terminal -SO ₃ H, and then dried. The comparative model M1 was manufactured by thermocompression bonding of the anode side catalyst layer.

  In the model of Example 1, the basic manufacturing method is the same as that of the comparative example model, but the reinforcing layer models Mh1 and Mh2 having different porosities by the stretching method are used.

  In the model of Example 2, as described above, the layer thickness of the cathode-side reinforcing layer model Mh1 ′ is half the layer thickness of the anode-side reinforcing layer model Mh2 ′, and the electrolyte resin layer also has a layer thickness on the inside and outside. It is changing.

  In all of the comparative example model, the example 1 model, and the example 2 model, the total thickness of the reinforcing layer is the same, and the total thickness of the electrolyte resin layer is also the same.

  A fuel cell was manufactured for each of the above models, and the cell voltage in a low humid atmosphere having a relative humidity of 40% Rh was measured while changing the current. The measurement result is shown in FIG. In the figure, the result of the fuel cell having the MEA of the comparative example model is indicated by a dotted Y line, the result of the fuel cell having the MEA of the Example 1 model is indicated by a solid X1 line, and the result of the Example 2 model is shown. The results of the fuel cell equipped with the MEA are indicated by the alternate long and short dash line X2.

  As shown in FIG. 5, as the current value increases, the ratio of the cell voltages of Examples 1 and 2 to the comparative example increases. This indicates that the five-layer structure of Examples 1 and 2 is changed from the three-layer structure of Comparative Example. This is because the water retention of the electrolyte membrane is enhanced and the proton conductivity is good.

  In Examples 1 and 2, since the ratio of the reinforcing layer on the cathode side is small, a water concentration distribution is formed in the film thickness direction of the electrolyte membrane from the cathode side to the anode side. As a result of the increase in the driving force of the water movement of the water and the back diffusion of the generated water generated on the cathode side by power generation to the anode side is promoted, it is specified that the power generation performance is improved.

[Experiments and results on the ratio of power generation performance when the ratio of the porosity of the cathode-side reinforcing layer to the porosity of the anode-side reinforcing layer is changed]
In addition, the inventors measured the cell voltage for each model by changing the ratio of the porosity of the anode side reinforcing layer and the cathode side reinforcing layer in the model of Example 1 shown in FIG. 4b. Among them, a graph in which the ratio of the porosity of both reinforcing layers is 1 (both are the same porosity), and the cell voltage in other ratios is normalized by the ratio to this reference value. Is shown in FIG.

  In FIG. 6, Pk on the horizontal axis indicates the porosity of the cathode side reinforcing layer, and Pa indicates the porosity of the anode side reinforcing layer.

  From the figure, the porosity ratio is 1.06 and the power generation performance ratio is 2%, and the porosity ratio is 1.11 and the power generation performance ratio is 5% higher. This indicates that the porosity on the cathode side is increased. By making it relatively large, the reverse diffusion of the generated water to the anode side is promoted, and the power generation performance is improved.

[Experiments and results on the ratio of power generation performance when the ratio of the cathode reinforcement layer to the entire reinforcement layer is changed]
Further, the inventors measured the cell voltage for each model by changing the ratio of the reinforcing layer on the cathode side to the entire reinforcing layer in the model of Example 2 shown in FIG. 4c. Among them, a graph in which the cell voltage when the thickness of the cathode side reinforcing layer is the total reinforcing layer is used as a reference and the cell voltage at other ratios is normalized by the ratio to the reference value is shown in FIG. Yes.

  In FIG. 7, d2 on the horizontal axis indicates the layer thickness of the cathode side reinforcing layer, and d indicates the layer thickness of the entire reinforcing layer.

  From the figure, the power generation performance is greatly improved when the thickness of the cathode-side reinforcing layer is in the range of 0.6 (half or more) to 0.3 (30% thickness) of the whole, especially when the thickness is 0.3 or less. The ratio increased by about 10%. Similar to the experimental result shown in FIG. 6, this experimental result is due to the fact that the reverse diffusion of the produced water to the anode side is promoted by relatively increasing the porosity on the cathode side, and the power generation performance is improved. .

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

It is the longitudinal cross-sectional view which showed the membrane electrode assembly which comprises one Embodiment of the composite type electrolyte membrane of this invention. It is the longitudinal cross-sectional view which showed the membrane electrode assembly which comprises other embodiment of the composite type electrolyte membrane of this invention. It is a longitudinal cross-sectional view of the fuel cell provided with the membrane electrode assembly of FIG. It is the schematic diagram explaining the experimental model of the fuel cell (Examples 1 and 2) provided with the composite type electrolyte membrane of the present invention and the fuel cell (comparative example) provided with the conventional composite type electrolyte membrane. ) Is a diagram showing a comparative example model, (b) is a diagram showing a model of Example 1, and (c) is a diagram showing a model of Example 2. FIG. The measurement result of the cell voltage in the low humid atmosphere of the fuel battery cell (Examples 1 and 2) having the composite electrolyte membrane of the present invention and the fuel battery cell (Comparative Example) having the conventional composite electrolyte membrane was shown. It is a graph. It is the graph which showed the experimental result regarding the power generation performance ratio at the time of changing the ratio of the porosity of the cathode side reinforcement layer with respect to the porosity of the anode side reinforcement layer. It is the graph which showed the experimental result regarding the power generation performance ratio at the time of changing the ratio of the reinforcement layer of the cathode side with respect to the whole reinforcement layer.

Explanation of symbols

  1A, 1A '... outer electrolyte resin layer, 1B, 1B' ... outer electrolyte resin layer, 1C, 1C '... inner electrolyte resin layer, 2, 2A ... cathode side reinforcing layer, 3, 3A ... anode side reinforcing layer, DESCRIPTION OF SYMBOLS 10,10A ... Composite-type electrolyte membrane, 20 ... Cathode side catalyst layer, 30 ... Anode side catalyst layer, 40, 40A ... MEA (membrane electrode assembly), 50 ... Gas diffusion layer (GDL), 60 ... MEGA (membrane electrode) 70) Gas flow path layer, 80 ... Separator, 81, 83 ... Face material, 82 ... Spacer, 90 ... Gasket, 100 ... Fuel cell

Claims (6)

A composite electrolyte membrane forming a fuel cell,
An outer electrolyte resin layer in contact with the anode side catalyst layer and the cathode side catalyst layer, at least two porous reinforcing layers interposed between the two outer electrolyte resin layers, and at least one inner electrolyte resin And has an alternating layer structure of an outer electrolyte resin layer, a reinforcing layer, and an inner electrolyte resin layer,
A composite electrolyte membrane in which the proportion of the cathode-side reinforcing layer is smaller than the proportion of the anode-side reinforcing layer.   2. The composite electrolyte membrane according to claim 1, wherein a thickness of the cathode-side reinforcing layer is thinner than that of the anode-side reinforcing layer.   The composite electrolyte membrane according to claim 1 or 2, wherein the porosity of the cathode-side reinforcing layer is larger than that of the anode-side reinforcing layer.   The composite electrolyte membrane according to claim 2 or 3, wherein a ratio of a layer thickness of the cathode-side reinforcing layer to a layer thickness of the entire reinforcing layer is 0.3 or less.   5. The composite electrolyte membrane according to claim 3, wherein a ratio of a porosity of the cathode side reinforcing layer to a porosity of the anode side reinforcing layer is in a range of 1.06 to 1.11.   A membrane electrode assembly comprising the composite electrolyte membrane according to any one of claims 1 to 5, an anode side and a cathode side catalyst layer sandwiching the composite electrolyte membrane, and a separator sandwiching the membrane electrode assembly. A fuel cell.

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