JP2010205655A - Method for manufacturing fuel cell, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain performance reduction of a fuel cell caused by a thermal cycle. <P>SOLUTION: In a method for manufacturing the fuel cell where an electrolyte film is sandwiched by two catalyst layers, one of the catalyst layers is the first catalyst layer including an electrolyte in which glass transition temperature becomes first glass transition temperature, the other of the catalyst layers is the second catalyst layer including an electrolyte in which the glass transition temperature becomes second glass transition temperature. The method for manufacturing the fuel cell has a step of heat-treating the first and second catalyst layers so as to make strength of the first catalyst layer higher than strength of the second catalyst layer by making use of the relationship between the first and second glass transition temperature of the first and second catalyst layers. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell.

  As a fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidizing gas, a membrane electrode assembly (hereinafter referred to as MEA (Membrane Electrode Assembly)) in which a catalyst layer is bonded to both surfaces of an electrolyte membrane having proton conductivity. What you have is known. Conventionally, various techniques have been proposed for the structure of such an MEA (for example, Patent Document 1 below).

JP 2006-236631 A

  In the above technique, the cathode-side catalyst layer has a two-layer structure, and the ratio of the electrolyte to the carbon support is increased by the catalyst layer, thereby suppressing the deterioration of the carbon support at the interface between the electrolyte membrane and the catalyst layer. The catalyst is prevented from eluting to the membrane.

  By the way, in the fuel cell, when the electrolyte membrane expands and contracts due to the thermal cycle, a large stress is generated in the catalyst layer, and there is a possibility that the vicinity of the interface with the electrolyte membrane is destroyed in the catalyst layer. As a result, the activity of the electrochemical reaction in the catalyst layer is lowered, and the fuel cell performance may be lowered.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A method of manufacturing a fuel cell in which an electrolyte membrane is sandwiched between two catalyst layers, wherein one of the catalyst layers is a first catalyst layer containing an electrolyte whose glass transition temperature is a first glass transition temperature, and the catalyst layer The other is a second catalyst layer containing an electrolyte having a glass transition temperature of the second glass transition temperature, and using the relationship between the first and second glass transition temperatures of the first and second catalyst layers, A method of manufacturing a fuel cell, comprising a step of heat-treating the first and second catalyst layers so that the strength of the first catalyst layer is higher than the strength of the second catalyst layer.

  According to this method of manufacturing a fuel cell, the first catalyst layer is stronger than the second catalyst layer. Therefore, when the fuel cell is placed in a cold cycle environment, the electrolyte membrane expands and contracts, When stress is applied to the second catalyst layer, the second catalyst layer can be more easily broken than the first catalyst layer. Since the second catalyst layer can be more likely to break than the first catalyst layer, there is an advantage that the fuel cell can be designed in anticipation of this.

[Application Example 2]
The method of manufacturing a fuel cell according to Application Example 1, wherein the heat treatment is performed on the first catalyst layer at a temperature higher than the first glass transition temperature, and the second catalyst layer is heated at a temperature higher than the second glass transition temperature. A method for producing a fuel cell, comprising a heat application step of performing a heat treatment at a low temperature.

  According to this fuel cell manufacturing method, the first catalyst layer is heat-treated at a temperature higher than the first glass transition temperature, and the second catalyst layer is heat-treated at a temperature lower than the second glass transition temperature. The crystallinity of the catalyst layer becomes higher than the crystallinity of the second catalyst layer. Therefore, the strength of the first catalyst layer can be made higher than the strength of the second catalyst layer.

[Application Example 3]
The method of manufacturing a fuel cell according to Application Example 2, wherein the heat application step performs heat treatment at a temperature higher than the first glass transition temperature in a state where the first catalyst layer and the electrolyte membrane are in contact with each other. 1 heat provision process, and after the said 1st heat provision process, after making the said 2nd catalyst layer and said electrolyte membrane contact | abut, the 2nd heat provision process which heat-processes at a temperature lower than the said 2nd glass transition temperature is included. Manufacturing method of fuel cell.

  According to this method of manufacturing a fuel cell, heat is applied after the first catalyst layer and the second catalyst layer are brought into contact with the electrolyte membrane, respectively, so that the peel strength between the first catalyst layer and the electrolyte membrane is set to the second catalyst layer. The peel strength between the layer and the electrolyte membrane can be made larger.

[Application Example 4]
The fuel cell manufacturing method according to Application Example 2, wherein the second glass transition temperature is higher than the first glass transition temperature, and the heat application step is higher than the first glass transition temperature and the second glass transition temperature. A method of manufacturing a fuel cell in which heat treatment is performed at a lower temperature.

  According to this fuel cell manufacturing method, the first catalyst layer and the second catalyst layer are heat-treated at a temperature higher than the first glass transition temperature and lower than the second glass transition temperature. The number of heat treatment steps for increasing the strength of the two catalyst layers can be reduced.

[Application Example 5]
It is a manufacturing method of the fuel cell of application example 4, Comprising: It has the lamination process which laminates | stacks the said 1st catalyst layer and the said 2nd catalyst layer on both sides of the said electrolyte membrane, The said heat provision process is after the said lamination process. A method for producing a fuel cell, comprising a step of simultaneously heat-treating the first catalyst layer and the second catalyst layer at a temperature higher than the first glass transition temperature and lower than the second glass transition temperature.

  According to this fuel cell manufacturing method, after laminating the first catalyst layer and the second catalyst layer on both sides of the electrolyte membrane, at a temperature higher than the first glass transition temperature and lower than the second glass transition temperature, Since the first catalyst layer and the second catalyst layer are heat-treated at the same time, the number of heat treatment steps for making the peel strength between the first catalyst layer and the electrolyte membrane larger than the peel strength between the second catalyst layer and the electrolyte membrane is increased. Can be reduced.

[Application Example 6]
The method of manufacturing a fuel cell according to any one of Application Example 2 to Application Example 5, wherein the heat application step includes performing heat treatment on the second catalyst layer at a temperature lower than the second glass transition temperature. A method of manufacturing a fuel cell, wherein a heat treatment is performed so that a temperature of a contact surface of the second catalyst layer contacting the electrolyte membrane is higher than a temperature of a surface opposite to the contact surface.

  According to this method of manufacturing a fuel cell, the heat treatment is performed so that the temperature of the contact surface that contacts the electrolyte membrane of the second catalyst layer is higher than the temperature of the surface opposite to the contact surface. The strength of the contact surface that contacts the electrolyte membrane of the catalyst layer can be made higher than the strength of the surface opposite to the contact surface.

[Application Example 7]
The fuel cell manufacturing method according to any one of application examples 1 to 6, wherein the first catalyst layer is a cathode catalyst layer, and the second catalyst layer is an anode catalyst layer.

  According to this fuel cell manufacturing method, it is possible to manufacture a fuel cell in which the strength of the cathode catalyst layer is higher than the strength of the anode catalyst layer.

[Application Example 8]
A fuel cell having an electrolyte membrane sandwiched between a first catalyst layer and a second catalyst layer, wherein a first peel strength that is a peel strength between the first catalyst layer and the electrolyte membrane is the second catalyst layer. And a second peel strength which is a peel strength between the electrolyte membrane and the electrolyte membrane.

  According to this fuel cell, the first peel strength is greater than the second peel strength. Therefore, when the fuel cell expands and contracts due to the thermal cycle, the first catalyst layer breaks near the interface between the second catalyst layer and the electrolyte. Can occur before the breakage near the interface between the electrolyte membrane and the electrolyte membrane. Accordingly, the first catalyst is compared with the fuel cell having the same first peel strength and the second peel strength by relaxing the large stress on the catalyst layer due to the thermal cycle by breaking near the interface between the second catalyst layer and the electrolyte. Breakage in the vicinity of the interface between the layer and the electrolyte membrane can be suppressed.

[Application Example 9]
The fuel cell according to Application Example 8, wherein the first catalyst layer includes a first electrolyte, and is heat-treated at a temperature higher than a first glass transition temperature of the first electrolyte, and the second catalyst layer includes: A fuel cell comprising a second electrolyte and heat-treated at a temperature lower than a second glass transition temperature of the second electrolyte.

  According to this fuel cell, the first catalyst layer includes the first electrolyte and is heat-treated at a temperature higher than the first glass transition temperature of the first electrolyte, the second catalyst layer includes the second electrolyte, Since the heat treatment is performed at a temperature lower than the second glass transition temperature of the two electrolytes, the strength of the first catalyst layer can be made higher than the strength of the second catalyst layer.

[Application Example 10]
10. The fuel cell according to Application Example 8 or Application Example 9, wherein the first catalyst layer is a cathode catalyst layer and the second catalyst layer is an anode catalyst layer.

  According to this fuel cell, since the first catalyst layer is a cathode catalyst layer and the second catalyst layer is an anode catalyst layer, the interface between the anode catalyst layer and the electrolyte when the fuel cell expands and contracts by a thermal cycle. The nearby breakage can occur before the breakage near the interface between the cathode medium layer and the electrolyte membrane. Accordingly, the relaxation near the interface between the cathode catalyst layer and the electrolyte membrane can be suppressed by relieving the large stress on the catalyst layer due to the thermal cycle by the breakdown near the interface between the anode catalyst layer and the electrolyte.

It is explanatory drawing which shows the general view of the fuel cell 10 in 1st Example. 2 is an exploded perspective view showing a schematic configuration of a fuel cell CL in the fuel cell 10. FIG. It is the schematic diagram which showed typically the cross section of the fuel cell CL. It is process drawing which shows the manufacturing method of MEA5 in 1st Example. It is explanatory drawing which shows the mode of the performance change of the Example goods 1 and comparative example goods in a cooling-heat test. It is a graph which shows the mode of the performance change of the Example goods 1 and comparative example goods in a cold-heat test. It is a schematic diagram which shows the result of having observed the cross section of MEA of Example goods 1 and a comparative example goods with the scanning electron microscope. It is a graph which shows the transfer temperature dependence of the peeling strength of the test piece and electrolyte membrane in 1st Example. It is explanatory drawing which shows the peeling strength of the test piece and electrolyte membrane in 1st Example for every catalyst layer of Example goods 1 and a comparison goods. It is process drawing which shows the manufacturing method of MEA in 2nd Example. It is explanatory drawing which shows the mode of the performance change of the Example goods 2 and comparative example goods in a cold-heat test. It is a graph which shows the mode of the performance change of the Example goods 2 and comparative example goods in a cooling-heat test. It is a graph which shows the transfer temperature dependence of the peeling strength of the test piece and electrolyte membrane in 2nd Example. It is explanatory drawing which shows the peeling strength of the test piece and electrolyte membrane in 2nd Example for every catalyst layer of Example goods 2 and a comparison goods. FIG. 10 is an explanatory diagram showing the relationship between the MEA thickness direction and the transfer temperature in Modification 1;

Embodiments of the present invention will be described based on examples.
A. First embodiment:
(A1) Configuration of Fuel Cell FIG. 1 is an explanatory diagram showing an overview of a fuel cell 10 according to an embodiment of the present invention. The fuel cell 10 according to this embodiment includes a plurality of fuel cells CL, an end plate EP, a tension plate TS, an insulator IS, and a terminal TM. The plurality of fuel cells CL are sandwiched by two end plates EP with the insulator IS and the terminal TM interposed therebetween. That is, the fuel cell 10 has a stack structure in which a plurality of fuel cells CL are stacked. Further, in the fuel cell 10, the tension plate TS is coupled to each end plate EP by a bolt BT, and each fuel cell CL is connected to each member in the stacking direction (hereinafter also simply referred to as “stacking direction”), that is, FIG. The structure is fastened with a predetermined force in the X direction shown in FIG. In the fuel cell 10 of this embodiment, air is used as the oxidizing gas, and hydrogen is used as the fuel gas. A direction perpendicular to the stacking direction and along the fuel cell CL is referred to as a plane direction (Y direction in FIG. 1).

  FIG. 2 is an exploded perspective view showing a schematic configuration of one fuel cell CL in the fuel cell 10. FIG. 3 is a schematic diagram schematically showing the configuration of the fuel cell CL. Specifically, FIG. 3 is a schematic diagram schematically showing an AA cross section in the fuel cell CL of FIG. The fuel cell CL includes a MEA 5 that is a membrane electrode assembly, gas diffusion layers 14 and 15, and separators 6 and 7. The fuel cell CL is formed by sandwiching the MEA 5 between the gas diffusion layers 14 and 15 and sandwiching the sandwich structure between the separators 6 and 7. In FIG. 2, the gas diffusion layer 14 is not shown because it is formed on the back side of the MEA 5.

  The MEA 5 includes an electrolyte membrane 11, a catalyst layer (hereinafter also referred to as a cathode catalyst layer) 12 to which an oxidizing gas is supplied, and a catalyst layer (hereinafter also referred to as an anode catalyst layer) 13 to which a fuel gas is supplied. The electrolyte membrane 11 is sandwiched between the cathode catalyst layer 12 and the anode catalyst layer 13. In other words, the MEA 5 is configured such that the cathode catalyst layer 12 is disposed on one surface of the electrolyte membrane 11 and the anode catalyst layer 13 is disposed on the other surface.

  The electrolyte membrane 11 is a proton conductive ion exchange membrane formed of a fluorine-based electrolyte that is a solid polymer material, and exhibits good proton conductivity in a wet state. The electrolyte membrane 11 is not limited to a fluorine-based electrolyte membrane, and may be a hydrocarbon-based electrolyte membrane, for example. In this example, a Nafion film (Nafion is a registered trademark) was used.

  The anode catalyst layer 13 includes carbon (hereinafter also referred to as platinum-supported carbon) supporting platinum (Pt), which is a catalyst metal, and a fluorine-based electrolyte. The electrolyte contained in the anode catalyst layer 13 is not limited to a fluorine-based electrolyte, and may be a hydrocarbon-based electrolyte.

  The cathode catalyst layer 12 includes platinum-supported carbon and a fluorine-based electrolyte. Note that the electrolyte contained in the cathode catalyst layer 12 is not limited to a fluorine-based electrolyte, but may be a hydrocarbon-based electrolyte.

  The gas diffusion layers 14 and 15 are porous members having conductivity, and are formed of, for example, a carbon-based porous body such as carbon cloth or carbon paper, or a metal porous body such as a metal mesh or foam metal.

  The separators 6 and 7 can be formed of a gas-impermeable conductive member, for example, dense carbon that has been made to be gas-impermeable by compressing carbon, or a press-molded metal plate. As shown in FIGS. 2 and 3, the separator 6 has a concavo-convex shape in which convex portions 6 a and concave portions 6 b are alternately formed on one side. In the separator 6, the convex portion 6 a presses the gas diffusion layer 14 (the cathode catalyst layer 12 or the electrolyte membrane 11), and the concave portion 6 b is between the gas diffusion layer 14 and the gas diffusion layer 14 (cathode catalyst layer 12). ), An oxidizing gas supply / discharge passage 20 is formed to supply and discharge oxidizing gas. In the separator 7, the convex portion 7 a presses the gas diffusion layer 15 (the anode catalyst layer 13 or the electrolyte membrane 11), and the concave portion 7 b is between the gas diffusion layer 15 and the gas diffusion layer 15 (the anode catalyst layer 13). The fuel gas supply / discharge passage 30 is formed to supply and discharge the fuel gas.

  As shown in FIG. 2, the separators 6 and 7 are provided with openings 53 to 56 at positions corresponding to each other near the outer periphery thereof. When the fuel cell 10 is assembled by laminating the separators 6 and 7 together with the MEA 5 and the gas diffusion layers 14 and 15, the openings provided at the corresponding positions of the laminated separators 6 and 7 overlap each other. A flow path penetrating the inside of the fuel cell 10 is formed in the direction. Specifically, the opening 53 forms an oxidizing gas supply manifold, the opening 54 forms an oxidizing gas discharge manifold, the opening 55 forms a fuel gas supply manifold, and the opening 56 forms a fuel. A gas exhaust manifold is formed. The oxidizing gas supply manifold is a flow path for introducing oxidizing gas into the oxidizing gas supply / discharge flow path 20, and the oxidizing gas discharge manifold is a flow path for discharging oxidizing gas from the oxidizing gas supply / discharge flow path 20. is there. The fuel gas supply manifold is a flow path for introducing fuel gas into the fuel gas supply / discharge flow path 30, and the fuel gas discharge manifold is a flow path for discharging fuel gas from the fuel gas supply / discharge flow path 30. is there.

  In the fuel cell CL, in order to ensure gas sealing performance in each of the manifold, the oxidant gas supply / discharge channel 20 and the fuel gas supply / discharge channel 30, the outer peripheral portion of the fuel cell CL and the openings 53 to A sealing member (not shown) is disposed on the peripheral portion of 56. In the fuel cell 10, a cooling water channel (not shown) for cooling the fuel cell CL is provided between the fuel cells CL.

(A2) Fuel cell manufacturing method:
Below, the manufacturing method of the fuel cell 10 of a present Example is demonstrated. In this method of manufacturing the fuel cell 10, the MEA 5 is manufactured, the fuel cell CL is manufactured using the MEA 5, and the fuel cell 10 is manufactured by stacking a large number of fuel cells CL. This will be specifically described below.

  FIG. 4 is a process diagram showing a method for manufacturing the MEA 5 in this embodiment. In this MEA 5 manufacturing method, an electrolyte membrane 11 and two Teflon substrates (Teflon is a registered trademark) are prepared (step S100).

  Next, platinum-supporting carbon, a fluorine-based electrolyte, and a solvent (water or ethanol) are prepared, and a catalyst ink for the cathode catalyst layer is prepared (S110). Specifically, platinum-supported carbon and a fluorine-based electrolyte are dissolved in a solution and mixed using an ultrasonic vibration device to prepare a cathode catalyst ink. When the platinum-supporting carbon and the fluorine-based electrolyte are mixed, the weight ratio of the fluorine-based electrolyte to the carbon (hereinafter referred to as “I / C”) is adjusted to I / C = 0.75. As the fluorine-based electrolyte, one having a glass transition temperature (Tg) of around Tg = 115 ° C. is used.

  Subsequently, a cathode catalyst ink is applied to a Teflon substrate and dried for a predetermined time to form a cathode catalyst layer. (Step S120). Next, the cathode catalyst layer is transferred to the electrolyte membrane 11. Specifically, the formed cathode catalyst layer is laminated on one surface of the electrolyte membrane 11, and the cathode catalyst layer outer surface and the electrolyte membrane 11 outer surface are sandwiched by using a hot press apparatus (not shown). Then, the transfer temperature is set to 130 ° C. and hot pressing is performed at a predetermined pressure for a predetermined time (step S130). After hot pressing, the Teflon substrate is removed from the cathode catalyst layer.

  Next, a catalyst ink for the anode catalyst layer is prepared using the same material and method as in step S110. That is, I / C = 0.75, and a fluorine-based electrolyte having a Tg of around 115 ° C. is used (step S140). Subsequently, similarly to step S120, the anode catalyst ink is applied to the Teflon substrate and dried for a predetermined time to form an anode catalyst layer (step S150). Thereafter, the formed anode catalyst layer is laminated on the surface of the electrolyte membrane 11 opposite to the surface on which the cathode catalyst layer 12 is formed, and the outer surface of the anode catalyst layer 13 is formed using a hot press apparatus (not shown). The transfer temperature is set to 110 ° C. with the outer surface of the cathode catalyst layer 12 and hot pressing is performed at a predetermined pressure for a predetermined time (step S160), and the method for manufacturing the MEA 5 is completed. In addition, step S130 and step S160 of the manufacturing method of the MEA 5 described above correspond to the heat treatment process described in the claims, and individually, step S130 corresponds to the first heat application process described in the claims. Correspondingly, step S160 corresponds to the second heat application step described in the claims.

  The MEA 5 thus manufactured is sandwiched between the gas diffusion layers 14 and 15, and the sandwich structure is sandwiched between the separators 6 and 7 to manufacture the fuel cell CL. In this way, a plurality of fuel cells CL are manufactured, the plurality of fuel cells CL are sandwiched between the insulator IS and the terminal TM, and the sandwich structure is sandwiched between the two end plates EP. The fuel cell 10 can be manufactured by connecting the tension plate TS to the end plate EP with the bolt BT.

  In the MEA 5 of the fuel cell 10 obtained by such a manufacturing method, the cathode catalyst layer 12 is given heat at a temperature (130 ° C.) higher than the glass transition temperature (Tg = 115 ° C.) of the electrolyte contained therein and transferred to the electrolyte membrane 11. As a result, the anode catalyst layer 13 was transferred to the electrolyte membrane 11 by applying heat (110 ° C.) lower than the glass transition temperature (Tg = 115 ° C.) of the electrolyte contained therein. Therefore, in the MEA 5, the anode catalyst layer 13 to which heat at a temperature lower than the glass transition temperature is applied has lower crystallinity than the cathode catalyst layer 12 to which heat at a temperature higher than the glass transition temperature is applied. As a result, the peel strength at the interface between the anode catalyst layer 13 and the electrolyte membrane 11 is smaller than the peel strength at the interface between the cathode catalyst layer 12 and the electrolyte membrane 11.

(A3) MEA performance evaluation:
The performance evaluation of the MEA 5 of the fuel cell 10 obtained as described above will be described. The performance of the MEA 5 (hereinafter also referred to as “Example Product 1”) is evaluated by comparing with the MEA of the Comparative Product. First, the comparative example product will be described. The comparative example product has a structure in which the electrolyte membrane is sandwiched between the cathode catalyst layer and the anode catalyst layer, and has the same structure as the MEA 5 which is the example product 1. The material of both catalyst layers of the comparative example product and the material mixing ratio are the same as both catalyst layers of Example product 1. That is, I / C = 0.75, and a fluorine-based electrolyte having a Tg of around 115 ° C. is used. The same electrolyte membrane as that of Example Product 1 is used. In the manufacturing method for the comparative product, the catalyst ink is applied to two Teflon substrates for the cathode catalyst layer and the anode catalyst layer, and dried for a predetermined time to form the cathode catalyst layer and the anode catalyst layer. The formed catalyst layers are laminated so as to sandwich the electrolyte membrane, and using a hot press device, the transfer temperature between the outer surface of the cathode catalyst layer and the outer surface of the anode catalyst layer is set to 130 ° C. at a predetermined pressure for a predetermined time. Hot press to manufacture. The difference between the example product 1 and the comparative example product is that the anode catalyst layer 13 of the example product has lower crystallinity than the cathode catalyst layer 12, whereas the comparative example product has both catalyst layers as the example product. It has the same crystallinity as the cathode catalyst layer 12.

  Using the above comparative example product, the performance evaluation of the example product 1 in the cooling cycle was performed. The example product 1 and the comparative example product are each sandwiched by a separator or the like to form the fuel cell CL shown in FIG. 2, and then each fuel cell CL is placed in an environment of 80 ° C. and −20 ° C. It used for the cold test. This cooling test includes <1> a humidification cycle in which nitrogen (humidified nitrogen) humidified at 80 ° C. is supplied to the cathode catalyst layer and the anode catalyst layer of the fuel cell CL at a flow rate of 0.5 L / min for 10 minutes, and <2 The fuel cell CL was repeatedly subjected to a cooling cycle in which the fuel cell CL was cooled to −20 ° C. over 1 hour after the gas supply was stopped, and this cooling / heating cycle was repeated 100 times. FIG. 5 is an explanatory diagram showing changes in performance of the example product 1 and the comparative example product before and after the cooling test, and FIG. 6 is a graph of the numerical values shown in FIG. The battery performance is determined by current / voltage characteristics. Before and after the above cooling test, the cell voltage per unit area is measured at 0.8 A / cm2, and the measured voltage is measured. Used for battery performance evaluation.

  As shown in the figure, in both the example product 1 and the comparative product, after the cooling test, the output energy of the battery decreases, and is observed as a decrease in output voltage (hereinafter also referred to as “performance decrease”). . In Example Product 1, the degree of performance degradation was low, and only about 10% performance degradation was observed. In contrast, the performance of the comparative example product was reduced by about 30%. From such a cooling test result, it can be said that the MEA 5 of the fuel cell 10 of this example exhibits high durability against the cooling cycle.

  When the cooling cycle in the above-described cooling test is repeated, a stress accompanying a temperature change acts on the example product 1 and the comparative example product, and this stress causes deterioration of the catalyst layer. The battery performance is expected to deteriorate. The presence or absence of deterioration of the catalyst layer was examined for the example product and the comparative example product 1. FIG. 7 is an explanatory view schematically showing the results of observation of the cross sections of the MEAs of Example Product 1 and Comparative Product with a scanning electron microscope. As shown in FIG. 7, in the example product 1, the anode catalyst layer was confirmed to be broken. In the comparative product, almost no destruction was observed at the anode, and the destruction was confirmed at the cathode catalyst layer.

  The relationship between the destruction of the catalyst layer and the decrease in battery performance will be considered. From the above results, it can be seen that the influence of deterioration due to destruction of the anode catalyst layer on the battery performance is smaller than the influence of deterioration due to destruction of the cathode catalyst layer on the battery performance. This is because the hydrogen oxidation reaction at the anode catalyst layer is more reactive than the oxygen reduction reaction at the cathode catalyst layer, so that even if breakdown occurs in the anode catalyst layer, it has less effect on battery performance degradation. Because.

  Next, performance evaluation will be described from the viewpoint of peel strength at the interface between the catalyst layer and the electrolyte membrane of each of Example Product 1 and Comparative Product. FIG. 8 shows the transfer temperature dependence of the peel strength between the test piece formed of the catalyst ink (I / C = 0.75, Tg = 115 ° C.) of Example Product 1 and Comparative Product and the electrolyte membrane. It is a graph. The graph plots the peel strength at three transfer temperatures of 110 ° C., 130 ° C., and 150 ° C. The peel strength was measured in accordance with JISK 6854-2 (adhesive peel strength test). FIG. 8 shows that the peel strength increases as the transfer temperature increases. That is, the higher the transfer temperature, the higher the crystallinity of the fluorine-based electrolyte contained in the catalyst layer and the higher the peel strength.

  FIG. 9 is an explanatory diagram showing the peel strength of FIG. 8 for each catalyst layer of Example Product 1 and Comparative Product. From FIG. 9, it can be understood that when the difference in peel strength of Example Product 1 is 0.02 N or more, the anode catalyst layer is easily broken.

  As described above, the cathode catalyst layer is transferred to the electrolyte membrane at a temperature higher than the glass transition temperature of the fluorine electrolyte contained in the cathode catalyst layer, and the anode catalyst layer is transferred to the fluorine electrolyte glass contained in the anode catalyst layer. By transferring to the electrolyte membrane at a temperature lower than the transition temperature, the crystallinity of the anode catalyst layer can be made lower than that of the cathode catalyst layer. Therefore, by making the crystallinity of the anode catalyst layer lower than that of the cathode catalyst layer, the peel strength of the anode catalyst layer becomes smaller than the peel strength of the cathode catalyst layer, and when the stress is applied to the catalyst layer by the thermal cycle, the peel strength is low. The anode catalyst layer can be destroyed before the cathode catalyst layer. As a result, it is possible to suppress a decrease in performance as a fuel cell, as compared with MEA in which both catalyst layers have the same peel strength.

B. Second embodiment:
(B1) Manufacturing method of fuel cell:
Since the configuration of the fuel cell in the second embodiment is the same as that of the fuel cell 10 in the first embodiment, the description thereof is omitted. The difference between the second embodiment and the first embodiment is a method for manufacturing an MEA for a fuel cell. Hereinafter, a method for manufacturing the MEA in the second embodiment will be described.

  FIG. 10 is a flowchart of the MEA manufacturing method of the second embodiment. In this MEA manufacturing method, an electrolyte membrane and two Teflon substrates are prepared as in the first embodiment (step S200).

  Next, similarly to step S110 of the first embodiment, a catalyst ink is prepared for the cathode catalyst layer (step S210). The material and material ratio of the catalyst ink are also the same as in step S110 (I / C = 0.75, Tg = 115 ° C.). The cathode catalyst layer catalyst ink prepared in step S210 is applied to a Teflon substrate and dried for a predetermined time to form a cathode catalyst layer. (Step S220).

  Next, a catalyst ink for the anode catalyst layer is created (step S230). As the electrolyte used for the anode catalyst layer, a fluorine-based electrolyte having a glass transition temperature of 150 ° C. is used. Other materials and material ratios used are the same as those of the cathode catalyst electrode. The anode catalyst ink is applied to a Teflon substrate and dried for a predetermined time to form an anode catalyst layer. (Step S240).

  The cathode catalyst layer and the anode catalyst layer formed by the above steps are laminated with the electrolyte membrane interposed therebetween, and the transfer temperature is set to 130 ° C. between the outer surface of the cathode catalyst layer and the outer surface of the anode catalyst layer using a hot press apparatus. And hot pressing at a predetermined pressure for a predetermined time (step S250). This is the end of the MEA manufacturing method in the fuel cell of the second embodiment. Using the MEA thus created, a fuel cell is manufactured using the same method as in the first embodiment.

  The MEA in the second embodiment uses a fluorine-based electrolyte used for the anode catalyst layer having a glass transition temperature of 150 ° C., and transfers the cathode catalyst layer and the anode catalyst layer to the electrolyte membrane at a transfer temperature of 130 ° C. at a time. is doing. This point is different from the manufacturing method of the MEA 5 in the first embodiment. When a glass transition temperature of 150 ° C. is used for the anode catalyst layer and transferred at 130 ° C., the cathode catalyst layer is higher than the glass transition temperature (Tg = 115 ° C.) of the fluorinated electrolyte contained in the cathode catalyst layer. On the other hand, the anode catalyst layer is transferred at a temperature lower than the glass transition temperature (Tg = 150 ° C.) of the fluorinated electrolyte contained in the anode catalyst layer.

(B2) MEA Performance Evaluation The fuel cell MEA performance evaluation obtained as described above will be described. As a method for evaluating the performance of the MEA (hereinafter also referred to as “Example Product 2”), it is compared with the MEA of the Comparative Product. The comparative product is the same as that used in the performance evaluation of the first embodiment.

Using the example product 2 and the comparative example product, performance evaluation in a cooling cycle was performed. As the evaluation method, the same cooling test as in the first example was used. FIG. 11 is an explanatory view showing the state of performance change of the example product 2 and the comparative example product before and after the cooling test, and FIG. 12 is a graph showing the state of performance change. The battery performance is determined by the current / voltage characteristics. The cell voltage when the cell current per unit area is 0.8 A / cm ² is measured before and after the above cooling test, and the measured voltage is measured. Was used for battery performance evaluation.

  As shown in the figure, both the example product 2 and the comparative example product show a decrease in the battery performance after the cooling test, but the example product 2 has a low degree of performance decrease and a 22% performance decrease. Stays on. On the other hand, the performance of the comparative product was 28%. From these results of the cold test, it can be said that the MEA of the fuel cell of this example exhibits high durability against the cold cycle.

  As a result of observing the cross sections of the MEAs of Example Product 2 and Comparative Example Product after the cooling test with a scanning electron microscope, in Example Product 2, the anode catalyst layer was confirmed to be broken as in the first example. In the comparative product, almost no destruction was observed at the anode, and the destruction was confirmed at the cathode catalyst layer (not shown).

  Next, performance evaluation will be described from the viewpoint of peel strength at the interface between the catalyst layer and the electrolyte membrane of each of Example Product 2 and Comparative Example Product. FIG. 13 shows a test piece formed with the catalyst ink for the anode catalyst layer of the example product (I / C = 0.75, Tg = 150 ° C.), and the cathode catalyst layer of the example product 2 and the comparative example product. It is the graph which showed the transfer temperature dependence of the peeling strength with an electrolyte membrane of the test piece formed with the catalyst ink (I / C = 0.75, Tg = 115 degreeC) used for both electrode layers. The peel strength measurement method is the same as in the first embodiment. FIG. 14 is an explanatory diagram showing the peel strength of FIG. 13 for each catalyst layer of Example Product 2 and Comparative Product. It can be understood from FIG. 14 that when the difference in peel strength of Example Product 2 is 0.02 N or more, the anode catalyst layer is easily broken.

  As described above, in the fuel cell manufacturing method of the second embodiment, the peel strength of the anode catalyst layer can be made smaller than the peel strength of the cathode catalyst layer as in the first embodiment. The anode catalyst layer having a small peel strength can be selectively broken against the stress on the layer.

C. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

(C1) Modification 1:
In the first embodiment, in the MEA 5, the transfer temperature of the cathode catalyst layer is made higher than the glass transition temperature, and the transfer temperature of the anode catalyst layer is made lower than the glass transition temperature. The anode catalyst layer was selectively destroyed with respect to the thermal cycle, but the cathode catalyst layer and the anode catalyst layer were both made of a fluorine-based electrolyte having a glass transition temperature of Tg1, as shown in FIG. Alternatively, hot pressing may be performed on the outer surface of the anode catalyst layer at a temperature Tx (Tx <Tg1) and on the outer surface of the cathode catalyst layer at a temperature Ty (Ty> Tg1). In this way, in the thickness direction of the anode catalyst layer, the crystallinity on the outer surface side away from the interface between the anode catalyst layer and the electrolyte membrane becomes lower than the crystallinity on the interface side, and the anode catalyst layer becomes the cathode catalyst layer. The peel strength is smaller than that of the layer, and the strength on the outer surface side of the anode catalyst layer can be made smaller than that on the interface side. As a result, it is possible to suppress destruction near the interface where the activity of the electrochemical reaction is relatively high, preferentially destroy the outer surface side, and suppress deterioration in performance of the fuel cell.

  Further, even when the glass transition temperature of the anode catalyst layer (referred to as “Tga”) and the glass transition temperature of the cathode catalyst layer (referred to as “Tgc”) are different as in the second embodiment, the temperature correlation is Tx <Tga. What is necessary is just to hot-press so that it may become <Tgc <Ty or Tx <Tgc <Tga <Ty. In this way, in the thickness direction of the anode catalyst layer, the crystallinity on the outer surface side away from the interface between the anode catalyst layer and the electrolyte membrane becomes lower than the crystallinity on the interface side, and the anode catalyst layer becomes the cathode catalyst layer. The peel strength is smaller than that of the layer, and the strength on the outer surface side of the anode catalyst layer can be made smaller than that on the interface side. As a result, it is possible to suppress destruction near the interface where the activity of the electrochemical reaction is relatively high, preferentially destroy the outer surface side, and suppress deterioration in performance of the fuel cell.

(C2) Modification 2:
In the above embodiment, when transferring both catalyst layers to the electrolyte membrane, the cathode catalyst layer applied heat higher than the glass transition temperature, and the anode catalyst layer applied heat lower than the glass transition temperature. Before the step of transferring the catalyst to the electrolyte membrane, heat higher than the glass transition temperature is applied to the cathode catalyst layer, and heat lower than the glass transition temperature is applied to the anode catalyst layer, and then transferred to the electrolyte membrane. Also good. Further, when heat is applied to the anode catalyst layer, heat may be applied so that the temperature on the side opposite to the contact surface is lower than the contact surface side with the electrolyte membrane.

(C3) Modification 3:
In the above embodiment, the MEA was manufactured so as to selectively destroy the anode catalyst layer side during the cooling cycle, but the cathode catalyst layer was given heat lower than the glass transition temperature, and the anode catalyst layer was subjected to glass transition. By applying heat higher than the temperature, the cathode catalyst layer can be selectively destroyed.

5 ... MEA
6 ... Separator 6a ... Convex part 6b ... Concave part 7 ... Separator 7a ... Convex part 7b ... Concave part 10 ... Fuel cell 11 ... Electrolyte membrane 12 ... Cathode catalyst layer 13 ... Anode catalyst layer 14 ... Gas diffusion layer 15 ... Gas diffusion layer 20 ... Oxidizing gas supply / discharge flow path 30 ... Fuel gas supply / discharge flow path 53 to 56 ... Opening CL ... Fuel cell TM ... Terminal EP ... End plate TS ... Tension plate IS ... Insulator BT ... Bolt

Claims (10)

A method of manufacturing a fuel cell in which an electrolyte membrane is sandwiched between two catalyst layers,
One of the catalyst layers is a first catalyst layer including an electrolyte whose glass transition temperature is a first glass transition temperature, and the other of the catalyst layers is a first catalyst including an electrolyte whose glass transition temperature is a second glass transition temperature. Two catalyst layers,
Utilizing the relationship between the first and second glass transition temperatures of the first and second catalyst layers, the first and first catalyst layers have a strength higher than that of the second catalyst layer. The manufacturing method of a fuel cell provided with the process of heat-processing 2 catalyst layers. A method of manufacturing a fuel cell according to claim 1,
The heat treatment
A method for producing a fuel cell, comprising: a heat application step in which heat treatment is performed on the first catalyst layer at a temperature higher than the first glass transition temperature, and heat treatment is performed on the second catalyst layer at a temperature lower than the second glass transition temperature. A method of manufacturing a fuel cell according to claim 2,
The heat application step includes a first heat application step of performing a heat treatment at a temperature higher than the first glass transition temperature in a state where the first catalyst layer and the electrolyte membrane are in contact with each other, and after the first heat application step, A method for producing a fuel cell, comprising: a second heat application step in which heat treatment is performed at a temperature lower than the second glass transition temperature after contacting the second catalyst layer and the electrolyte membrane. A method of manufacturing a fuel cell according to claim 2,
The second glass transition temperature is higher than the first glass transition temperature;
The method of manufacturing a fuel cell, wherein the heat application step performs heat treatment at a temperature higher than the first glass transition temperature and lower than the second glass transition temperature. A method of manufacturing a fuel cell according to claim 4,
A lamination step of laminating the first catalyst layer and the second catalyst layer on both sides of the electrolyte membrane;
The heat application step includes a step of heat-treating the first catalyst layer and the second catalyst layer simultaneously at a temperature higher than the first glass transition temperature and lower than the second glass transition temperature after the lamination step. A method for manufacturing a fuel cell. A method of manufacturing a fuel cell according to any one of claims 2 to 5,
The heat application step includes
In the case where the second catalyst layer is heat-treated at a temperature lower than the second glass transition temperature,
A method for manufacturing a fuel cell, wherein heat treatment is performed such that a temperature of a contact surface of the second catalyst layer that contacts the electrolyte membrane is higher than a temperature of a surface opposite to the contact surface. The method for producing a fuel cell according to any one of claims 1 to 6, wherein the first catalyst layer is a cathode catalyst layer, and the second catalyst layer is an anode catalyst layer. A fuel cell in which an electrolyte membrane is sandwiched between a first catalyst layer and a second catalyst layer,
A first peel strength, which is a peel strength between the first catalyst layer and the electrolyte membrane,
A fuel cell, wherein the fuel cell is larger than a second peel strength that is a peel strength between the second catalyst layer and the electrolyte membrane. The fuel cell according to claim 8, wherein
The first catalyst layer includes
Including a first electrolyte, heat-treated at a temperature higher than the first glass transition temperature of the first electrolyte,
The second catalyst layer includes
A fuel cell comprising a second electrolyte and heat-treated at a temperature lower than a second glass transition temperature of the second electrolyte. The fuel cell according to claim 8 or 9, wherein the first catalyst layer is a cathode catalyst layer, and the second catalyst layer is an anode catalyst layer.

Images