JP2008034134A - Manufacturing method of solid polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a solid polymer fuel cell capable of improving durability while maintaining power generation performance. <P>SOLUTION: The manufacturing method of a solid polymer fuel cell is provide with a rare earth salt solution contact process in which a catalyst layer formed by coating and drying an ink containing a catalyst component and a cation exchange resin on a support body is contacted to a solution dissolving salt of a rare earth element in pressure reduced environment, a drying process in which the catalyst layer is dried after the rare earth salt solution contact process, and a thermo-compression bonding process in which the catalyst layer is thermocompression bonded on at least one side of the polymer electrolyte membrane. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a polymer electrolyte fuel cell.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle and thus exhibit high energy conversion efficiency. A fuel cell is usually formed by laminating a plurality of single cells having a basic structure of a membrane / electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes. Among them, a solid polymer fuel cell using a solid polymer electrolyte membrane as an electrolyte membrane has advantages such as easy miniaturization and operation at a low temperature. It is attracting attention as a power source.

In the polymer electrolyte fuel cell, the reaction of the formula (1) proceeds at the anode (fuel electrode).
H ₂ → 2H ⁺ + 2e ⁻ (1)
The electrons generated by the equation (1) reach the cathode (oxidant electrode) after working with an external load via an external circuit. Then, the proton generated in the formula (1) moves in the solid polymer electrolyte membrane from the anode side to the cathode side by electroosmosis while being hydrated with water.
On the other hand, the reaction of the formula (2) proceeds at the cathode.
4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O (2)

  In the electrode of the fuel cell, a side reaction proceeds in addition to the main reaction, and a representative example thereof is a reaction for generating a peroxide such as hydrogen peroxide. It is known that hydrogen peroxide undergoes radical decomposition under the operating environment of a fuel cell and generates radicals with strong oxidizing power such as hydroxy radicals (.OH) and peroxide radicals (.OOH). When these radicals move to the solid polymer electrolyte membrane, hydrogen, fluorine, or the like is extracted from the solid polymer electrolyte, or the polymer chain is cut to cause deterioration of the solid polymer electrolyte membrane. As a result of such deterioration, the solid polymer electrolyte membrane is deteriorated in proton conductivity, perforated or broken, which causes cross leak. A cross leak causes fuel loss and a decrease in potential, and is one of the causes of reducing the power generation performance and durability of a fuel cell.

In order to prevent the solid polymer electrolyte membrane from being deteriorated by the radical species generated by radical decomposition of the peroxide as described above, and to reduce the durability and power generation performance of the fuel cell, various technologies have been proposed in the past. ing.
For example, in Patent Document 1, a phosphate containing at least one metal element selected from rare earth elements and Ti, Fe, Al, and Bi is fixed to any one or more of the solid polymer electrolyte membrane and the electrode. A polymer electrolyte fuel cell is described. As a specific example, Patent Document 1 discloses that the solid polymer electrolyte membrane includes the solid polymer electrolyte membrane or a precursor thereof, a first solution containing a water-soluble salt of the metal element or an organometallic complex, and phosphorus. A polymer electrolyte fuel cell obtained by contacting one of the second solutions containing an acid and then contacting the other is described.

  In Patent Document 2, a transition metal oxide having catalytic ability to catalytically decompose a peroxide generated by a battery reaction is dispersed and blended in a polymer electrolyte material, or a peroxide that suppresses the decomposition of the peroxide. It is characterized in that at least one of the following is taken: a compound stabilizer is dispersed and compounded, a compound having a phenolic hydroxyl group is dispersed and compounded, or a phenolic hydroxyl group is introduced by an electrolytic polymer chemical bond A highly durable solid polymer electrolyte is described.

JP-A-2005-71760 JP 2001-118591 A

However, although the polymer electrolyte fuel cell of Patent Document 1 can prevent the electrolyte membrane from being deteriorated by peroxide radicals, the solid polymer fuel cell can be obtained by depositing phosphate that is not directly involved in power generation. Therefore, the power generation performance may be reduced. Moreover, in the process of adding a phosphate to the electrolyte membrane after film formation and the catalyst layer after layer formation in Patent Document 1, there is a problem that complicated processing is required and productivity is low.
Also in Patent Document 2, the electrolyte contains a transition metal oxide or the like as fine particles, and there is a risk that the power generation performance may be reduced as in Patent Document 1.
Furthermore, in the techniques described in Patent Document 1 and Patent Document 2, the dispersibility of rare earth elements is poor, and there is a possibility that a sufficient effect of preventing deterioration of the polymer electrolyte membrane may not be obtained.

  The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to provide a method for producing a polymer electrolyte fuel cell capable of improving durability while maintaining power generation performance.

  The method for producing a polymer electrolyte fuel cell according to the present invention is a solution in which a catalyst layer formed by applying a catalyst ink containing a catalyst component and a cation exchange resin on a support and drying the solution is dissolved in a salt of a rare earth element And a rare earth salt solution contact step for contacting in a reduced pressure environment, a drying step for drying the catalyst layer after the rare earth salt solution contact step, a thermocompression bonding step for thermocompression bonding the catalyst layer to at least one surface of the polymer electrolyte membrane, It is characterized by providing.

The method for producing a polymer electrolyte fuel cell according to the present invention comprises contacting a catalyst layer formed on a support with a solution in which a salt of a rare earth element is dissolved (hereinafter sometimes referred to as a rare earth salt solution). A part of the ion exchange groups of the cation exchange resin contained in the layer is ion-exchanged with rare earth ions, and the rare earth is contained in the catalyst layer in an ionic state. In the present invention, in the contact step between the catalyst layer and the rare earth salt solution, by reducing the pressure, the permeability of the rare earth salt solution to the catalyst layer having water repellency and a porous structure is improved. The cation exchange resin in the entire catalyst layer leading to the inside can be ion-exchanged with rare earth ions.
Thus, by containing rare earth elements in an ionic state throughout the catalyst layer, it is possible to obtain an effect of suppressing radical decomposition of peroxide by the rare earth elements while maintaining power generation performance. Therefore, the polymer electrolyte fuel cell provided by the production method of the present invention has high durability as well as excellent power generation performance.

  As a specific embodiment of the present invention, for example, a catalyst layer formed by applying a catalyst ink containing a catalyst component and a cation exchange resin on a transfer support and drying, a solution in which a salt of a rare earth element is dissolved, A rare earth salt solution contact step for contacting in a reduced pressure environment, a drying step for drying the catalyst layer after the rare earth salt solution contact step, a thermocompression bonding step for thermocompression bonding the catalyst layer to at least one surface of a polymer electrolyte membrane, And a step of peeling the transfer support from the catalyst layer after the thermocompression bonding step.

From the viewpoint of improving durability, both catalyst layers provided on both surfaces of the electrolyte membrane are preferably produced by the production method of the present invention. That is, in the thermocompression bonding step, the catalyst layer is preferably thermocompression bonded to both surfaces of the polymer electrolyte membrane.
As the rare earth element, cerium is particularly preferable from the viewpoints of cost and the effect of suppressing radical decomposition of peroxide.
The reduced pressure environment in the rare earth salt solution contact step is such that the specific conditions are particularly as long as the permeability of the rare earth salt solution to the catalyst layer is increased and the cation exchange resin and the rare earth salt solution can be brought into contact with each other over the entire catalyst layer. Although not limited, it is preferably 50 mmHg or less.

  According to the present invention, it is possible to provide a polymer electrolyte fuel cell with improved durability while maintaining power generation performance.

  The method for producing a polymer electrolyte fuel cell according to the present invention is a solution in which a catalyst layer formed by applying a catalyst ink containing a catalyst component and a cation exchange resin on a support and drying the solution is dissolved in a salt of a rare earth element And a rare earth salt solution contact step for contacting in a reduced pressure environment, a drying step for drying the catalyst layer after the rare earth salt solution contact step, a thermocompression bonding step for thermocompression bonding the catalyst layer to at least one surface of the polymer electrolyte membrane, It is characterized by providing.

  As described above, peroxides typified by hydrogen peroxide generated at the electrodes of the fuel cell are decomposed into radicals having strong oxidizing properties such as hydroxy radicals and peroxide radicals in the operating environment of the fuel cell. . These radicals cause deterioration of the polymer electrolyte membrane by extracting hydrogen, fluorine, or the like from the polymer electrolyte membrane, or by cutting the polymer chain. As a result, a decrease in proton conductivity, perforations, cracks, and the like occur in the polymer electrolyte membrane, and as a result, the power generation performance and durability of the fuel cell decrease.

The rare earth element has a catalytic activity to decompose the peroxide, which causes the deterioration of the performance and durability of the fuel cell as described above, into water (H ₂ O) and hydrogen (H ₂ ). By containing a rare earth element in the layer, radical decomposition of the peroxide can be suppressed. However, when the rare earth element is contained in the electrolyte membrane or the catalyst layer in the solid state such as phosphorus oxide or oxide as in the past, the deterioration of the polymer electrolyte membrane is prevented and the durability of the fuel cell is improved. However, there is a problem that the power generation performance of the fuel cell is lowered.

  Therefore, in the present invention, in the catalyst layer, a part of the ion exchange group of the cation exchange resin functioning as a proton conductive component and a binder component is replaced with rare earth ions, and the rare earth element is contained in the catalyst layer in an ionic state. Let By containing the rare earth element in the ionic state in the catalyst layer, unlike the conventional case where the rare earth element is contained in a solid state, it is possible to highly disperse the rare earth in the catalyst layer at the molecular level, and It is possible to prevent a decrease in power generation performance.

  And in the manufacturing method of this invention, in order to substitute the ion exchange group of the cation exchange resin contained in a catalyst layer with rare earth ions, when contacting the catalyst layer and rare earth salt solution formed on the support body, The catalyst layer is placed in a reduced pressure environment. In many cases, the catalyst layer contained in the catalyst layer and the support have water repellency, and due to its porous structure, the rare earth salt solution is simply brought into contact with the rare earth salt solution simply by contacting with the rare earth salt solution. Can not penetrate. That is, simply contacting the catalyst layer with the rare earth salt solution cannot replace the ion exchange groups present in the catalyst layer with the rare earth ions, and rare earth ions in the entire catalyst layer from the surface to the inside. Cannot be included.

On the other hand, in the present invention, the penetration of the rare earth salt solution into the catalyst layer is promoted by placing the catalyst layer formed on the support in a reduced pressure environment and extracting air from the pores of the catalyst layer. The contact property between the cation exchange resin and the rare earth salt solution was improved, and the cation exchange groups present in the catalyst layer could be replaced with rare earth ions.
In the present invention, the radical decomposition of the peroxide can be sufficiently suppressed, and the proton conductivity of the electrolyte membrane can be maintained, so that the catalyst layer (electrode) that is the main generation source of the peroxide is used. Only rare earth was included.

Hereinafter, the method for producing the polymer electrolyte fuel cell of the present invention will be described in detail.
The catalyst layer on the support can be formed by applying and drying a catalyst ink containing at least a catalyst component and a cation exchange resin on the support.
Here, the support means a conductive porous body (gas diffusion layer base material) constituting the gas diffusion layer, a gas diffusion layer sheet provided with a functional layer on the conductive porous body, and a transfer support. Etc.
As the transfer support, those generally used as a base material when the catalyst layer formed on the transfer support is thermally transferred to a gas diffusion layer or an electrolyte membrane can be used. Examples thereof include tetrafluoroethylene (PTFE), polypropylene and the like.

  The conductive porous body has a gas diffusibility that can efficiently supply a gas to the catalyst layer, a conductivity, and a strength required as a material constituting the gas diffusion layer, such as carbon paper. Carbon porous bodies such as carbon cloth, carbon felt, titanium, aluminum, copper, nickel, nickel-chromium alloy, copper and its alloys, aluminum alloy, zinc alloy, lead alloy, titanium, niobium, tantalum, iron, Examples thereof include a metal mesh composed of a metal such as stainless steel or a metal porous body.

  Examples of the gas diffusion layer sheet in which the functional layer is provided on the conductive porous body include those in which a water repellent layer is provided on the side of the conductive porous body facing the catalyst layer. The water-repellent layer usually has a porous structure containing conductive particles such as carbon particles and carbon fibers, a water-repellent resin such as polytetrafluoroethylene, and the like. The method for forming the water repellent layer on the conductive porous body is not particularly limited. For example, water repellent obtained by mixing conductive particles such as carbon particles, water repellent resin, and other components as necessary with an organic solvent such as ethanol, propanol, propylene glycol, water or a mixture thereof. The layer paste may be applied to at least the side of the conductive porous body facing the catalyst layer, and then dried and / or fired.

  At this time, the water repellent layer paste may be impregnated inside the conductive porous body. The shape of the water repellent layer is not particularly limited, and may be, for example, a shape that covers the entire surface of the conductive porous body on the catalyst layer side or a shape having a predetermined pattern such as a lattice shape. Examples of the method for applying the water repellent layer paste to the conductive porous body include a screen printing method, a spray method, a doctor blade method, a gravure printing method, and a die coating method.

  In addition, the conductive porous body is formed by impregnating and applying a water-repellent resin such as polytetrafluoroethylene to the side facing the catalyst layer with a bar coater or the like, so that the moisture in the catalyst layer is efficiently removed from the gas diffusion layer. You may process so that it may be discharged well.

The catalyst component is not particularly limited as long as it has catalytic activity for the oxidation reaction of the fuel at the fuel electrode or the reduction reaction of the oxidant at the oxidant electrode, and is generally used for solid polymer fuel cells. Can be used. For example, platinum or an alloy of platinum and a metal such as ruthenium, iron, nickel, and manganese can be used.
The catalyst component is usually used in a state where it is supported on conductive particles. As the conductive particles as the catalyst carrier, carbon particles such as carbon black, conductive carbon materials such as carbon fibers, and metal materials such as metal particles and metal fibers can also be used.

  The cation exchange resin is not particularly limited, and those commonly used in solid polymer fuel cells can be used. For example, fluorine electrolyte resin such as perfluorocarbon sulfonic acid resin represented by Nafion, polyether ether ketone (PEEK), polyether ketone, polyether sulfone (PES), polyphenylene sulfide (PPS), polysulfone (PSU), Hydrocarbon polymers such as polyparaphenylene (PPP), polyetherimide (PEI), polybenzimidazole (PBI), cation exchange groups such as sulfonic acid groups, hydroxy groups, phosphoric acid groups, carboxylic acid groups, etc. Is introduced.

  The catalyst ink is obtained by dissolving or dispersing the above catalyst component and cation exchange resin in a solvent. The solvent of the catalyst ink may be appropriately selected according to the cation exchange resin to be used. For example, in addition to alcohols such as methanol, ethanol and propanol, dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), Dimethylacetamide (DMAC), dichloromethane, chloroform, 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane, tetrahydrofuran, diethyl ether, acetone, methyl ethyl ketone, dimethylformamide, or a mixture of these organic solvents or these A mixture of an organic solvent and water can be used.

A catalyst layer sheet in which a catalyst layer is formed on the support is obtained by applying the catalyst ink to the surface of the sheet-like support and drying. At this time, the catalyst layer sheet is a catalyst layer transfer sheet when a transfer support is used as a support, and a gas diffusion layer sheet or a conductive porous material (gas diffusion layer) is used as the support. When the substrate is used, a catalyst layer-gas diffusion layer assembly is obtained.
A method for applying the catalyst ink to the support, a drying method, and the like can be appropriately selected. For example, examples of the coating method include a spray method, a screen printing method, a doctor blade method, a gravure printing method, a die coating method, and the like. Examples of the drying method include reduced pressure drying, heat drying, and reduced pressure heat drying. There is no restriction | limiting in the specific conditions in reduced pressure drying and heat drying, What is necessary is just to set suitably.

The rare earth salt solution contact step is a step in which the catalyst layer formed on the surface of the support as described above is brought into contact with a rare earth salt solution in which a rare earth element salt is dissolved in a reduced pressure environment.
The rare earth elements are scandium (Sc), yttrium (Y), and 15 lanthanoid elements (atomic numbers 57 to 71). Among these, cerium and yttrium are inexpensive and can be reduced in cost. In particular, cerium is suitable because it has a strong peroxide decomposition action.
The salt of the rare earth element is not particularly limited as long as it has solubility, and examples thereof include nitrates and phosphates. In particular, nitrate is preferable from the viewpoint of solubility.

  The solvent of the rare earth salt solution may be any solvent that dissolves the rare earth salt but does not dissolve the cation exchange resin of the catalyst layer. Examples thereof include water, alcohol, and a mixture thereof. Among these, water is preferable from the viewpoints of solubility and resin insolubility.

Depending on the concentration of the rare earth salt contained in the rare earth salt solution, the ion exchange rate by the rare earth ions of the cation exchange resin in the catalyst layer can be controlled. Accordingly, the concentration of the rare earth salt in the rare earth salt solution may be set as appropriate according to the amount of rare earth ions introduced into the cation exchange resin, and usually the concentration of the cation exchange resin in the catalyst layer to be substituted with rare earth ions. The ion exchange amount is preferably 1 to 95% equivalent to the cation exchange group.
The method of bringing the catalyst layer of the catalyst layer sheet into contact with the rare earth salt solution is not particularly limited as long as the cation exchange resin in the catalyst layer can ion exchange with the rare earth ions in the rare earth salt solution. For example, a method of immersing the catalyst layer sheet in the rare earth salt solution, a method of applying the rare earth salt solution to the catalyst layer of the catalyst layer sheet, and the like are exemplified, and among these, the immersing method is preferable.

The pressure reduction environment in the rare earth salt solution contact step is not limited as long as the rare earth salt solution has a porous structure and can promote the penetration of the rare earth salt solution into the water-repellent catalyst layer. Etc. are not particularly limited. In order to reliably promote the penetration of the rare earth salt solution into the catalyst layer, the degree of vacuum is preferably 50 mmHg or less, for example, about 20 to 50 mmHg, and particularly preferably 20 mmHg or less.
Moreover, the timing of pressure reduction may be that the catalyst layer sheet is brought into contact with the rare earth salt solution after being in a reduced pressure environment (see FIG. 1), or the catalyst layer of the catalyst layer sheet is in contact with the rare earth salt solution. Although pressure reduction may be started, it is usually preferable that the catalyst layer sheet is brought into contact with the rare earth salt solution in a reduced pressure environment.
As a decompression method, a general method can be used, and a decompression pump or the like can be used.

The contact time between the catalyst layer and the rare earth salt solution may be appropriately determined according to the amount of rare earth ions introduced into the cation exchange resin (ion exchange rate) and the like. It depends on the degree of vacuum and the timing of pressure reduction. Usually, it may be about 0.5 to 24 hours.
Although the temperature in a rare earth salt solution contact process is not specifically limited, Usually, it is preferable to set it as about 25-80 degreeC.

  In the present invention, the cation exchange resin contained in the catalyst layer replaces only a part of the cation exchange groups with rare earth ions in order to ensure proton conductivity of the catalyst layer. The ion exchange rate by the rare earth ions of the cation exchange resin may be appropriately determined from the balance between the proton conductivity due to the cation exchange groups and the durability improving effect due to the rare earth ions, and is not particularly limited. Specifically, it is preferably about 5 to 80%, particularly preferably about 5 to 63%.

As a method for calculating the ion exchange rate of the cation exchange resin in the catalyst layer, for example, when ion exchange is performed between the cation exchange group (H ⁺ ) and the rare earth ion (r ^{t +} ) of the cation exchange resin, first, { [(Charge amount of rare earth ions in the rare earth salt solution brought into contact with the catalyst layer (mole)) − (remaining amount of rare earth salt ions in the rare earth salt solution after contact with the catalyst layer (mole))] × t} / ( From the area of the catalyst layer brought into contact with the rare earth salt solution), the amount (equivalent / cm ² ) of cation exchange groups (H ⁺ ) exchanged for rare earth ions per unit area of the catalyst layer can be converted.
On the other hand, from the amount (mole) of the cation exchange resin used in forming the catalyst layer, the valence (1) of the cation exchange group H ⁺ and the area of the catalyst layer, the catalyst layer before contacting with the rare earth salt solution The amount of cation exchange groups (equivalent / cm ² ) can be converted.
And {[amount of cation exchange groups (H ⁺ ) exchanged for rare earth ions (equivalent / cm ² )] / [amount of cation exchange groups in the catalyst layer before contacting with the rare earth salt solution (equivalent / cm ²⁾ )]} × 100 to obtain the ion exchange rate.

  The rare earth salt solution contact step may be performed for each catalyst layer or a plurality of catalyst layers may be collectively performed. Moreover, the catalyst layer sheet | seat which provided the catalyst layer in the support surface is not restricted to the state of FIG. 1, You may roll in roll shape and may contact with a rare earth salt solution.

  After the rare earth salt solution contacting step, if necessary, a washing step of washing the catalyst layer with deionized water may be provided in order to remove the residue of the rare earth salt solution. By removing excess rare earth ions, rare earth ion counter ions, solvent of the rare earth salt solution, etc., process reliability is improved. The washing method is not particularly limited, and examples thereof include a method of impregnating a catalyst layer sheet in deionized water and a method of spraying deionized water onto the catalyst layer on the catalyst layer sheet.

  After the rare earth salt solution contact step or the washing step, the catalyst layer is dried in order to remove the solvent of the rare earth salt solution or deionized water from the catalyst layer on the support (drying step). The drying method in the drying step is not particularly limited, and examples thereof include reduced pressure drying, heat drying, and reduced pressure heat drying. There is no restriction | limiting in the specific conditions in each drying method, What is necessary is just to set suitably.

  Next, the catalyst layer of the catalyst layer sheet is thermocompression bonded to the polymer electrolyte membrane, and the catalyst layer and the electrolyte membrane are joined (thermocompression bonding step). Here, the thermocompression bonding means that the catalyst layer and the polymer electrolyte membrane are joined by pressurizing simultaneously with heating, and the catalyst layer provided on the transfer support is thermally transferred to the polymer electrolyte membrane. It is also included.

  The polymer electrolyte membrane is not particularly limited, and those used in solid polymer fuel cells can be widely used. Specific examples include those obtained by molding the above cation exchange resin into a membrane. It is done. Perfluorocarbon sulfonic acid resin membranes (trade name Nafion, etc.) are preferably used.

The catalyst layer on the support is superposed on the surface of the electrolyte membrane by overlapping the catalyst layer and the electrolyte membrane on the support so that the catalyst layer and the polymer electrolyte membrane face each other and pressurizing simultaneously with heating. be able to. What is necessary is just to set suitably the heating temperature and applied pressure in a thermocompression bonding process according to the glass transition temperature of a polymer electrolyte membrane, or the glass transition temperature of a cation exchange resin.
At this time, when a conductive porous body constituting the gas diffusion layer or a gas diffusion layer sheet provided with a functional layer on the conductive porous body is used as the support, the electrolyte membrane and the catalyst are formed by a thermocompression bonding process. A membrane / electrode assembly in which a layer and a gas diffusion layer are laminated in this order can be obtained.

On the other hand, when a transfer support is used as the support, the catalyst layer on the transfer sheet is transferred to the surface of the polymer electrolyte membrane by a thermocompression bonding process, and then the transfer support is transferred to the catalyst layer. The electrolyte membrane-catalyst layer assembly in which the catalyst layer on the electrolyte membrane is formed can be obtained.
The electrolyte membrane-catalyst layer assembly, in which the catalyst layer is thermally transferred onto the surface of the electrolyte membrane as described above, is usually thermocompression bonded in a state of being sandwiched between the conductive porous body and the gas diffusion layer sheet as described above. Then, it is bonded to the conductive porous body or the gas diffusion layer sheet to form a membrane / electrode assembly.

  Even when only the catalyst layer provided on one surface of the polymer electrolyte membrane is produced by the production method of the present invention as described above, the effect of the present invention of securing the power generation performance and improving the durability is sufficiently obtained, In order to obtain a higher effect, it is preferable that both catalyst layers provided on both surfaces of the polymer electrolyte membrane are produced by the production method of the present invention.

  The membrane / electrode assembly in which a pair of electrodes is provided on the electrolyte membrane as described above can be further sandwiched by a separator to form a single cell. As the separator, for example, a carbon separator containing a high concentration of carbon fiber and made of a composite material with a resin, a metal separator using a metal material, or the like can be used. Examples of the metal separator include those made of a metal material excellent in corrosion resistance, and those coated with a coating that enhances the corrosion resistance by coating the surface with carbon or a metal material excellent in corrosion resistance. .

As described above, according to the manufacturing method of the present invention, it is possible to improve the durability of the polymer electrolyte fuel cell. Examples of the durability index of the polymer electrolyte fuel cell include a decrease in the molecular weight of the polymer electrolyte membrane, and the elution degree of fluorine when a fluorine-based polymer electrolyte membrane is used. Degradation of the polymer electrolyte membrane causes holes or tears that cause cross leaks in the polymer electrolyte membrane, thereby significantly reducing power generation performance. Therefore, by performing these evaluations, it is possible to determine the degree of decrease in durability of the polymer electrolyte fuel cell.
Specifically, for example, the degree of fluorine elution can be obtained by collecting moisture discharged from the fuel cell during power generation and analyzing the F concentration in the collected moisture by ion chromatography or the like. Further, the decrease in the molecular weight of the electrolyte membrane can be examined by performing GPC measurement after dissolving the electrolyte membrane before and after power generation in an appropriate solvent.

[Production of membrane / electrode assembly]
(Example)
A Pt / C catalyst, a cation exchange resin, and a solvent were mixed with stirring to prepare a catalyst ink.
The catalyst ink was applied to the surface of the sheet-like transfer support and dried to form a catalyst layer having a sulfonic acid group amount of 0.33 μequivalent / cm ² .
The obtained catalyst layer thermal transfer sheet was put in a decompression vessel, and first, the decompression condition was set with a vacuum pump, and the valve of the vacuum line was closed. Next, a Ce (NO ₃ ) · 6H ₂ O aqueous solution (prepared with an ion exchange amount of 80%) was poured into the reduced pressure vessel, and the catalyst layer thermal transfer sheet was immersed in the Ce (NO ₃ ) · 6H ₂ O aqueous solution ( (See FIG. 1). Thereafter, the mixture was allowed to stand at 25 ° C. for 18 hours, and the sulfonic acid group of the cation exchange resin in the catalyst layer was replaced with Ce ions. Subsequently, the catalyst layer thermal transfer sheet was taken out from the Ce (NO ₃ ) · 6H ₂ O aqueous solution and dried at 60 ° C. for 1 hour.

The catalyst layer of the catalyst layer thermal transfer sheet prepared above was thermally transferred to both surfaces of the polymer electrolyte membrane (perfluorocarbon sulfonic acid resin membrane), and the polymer electrolyte membrane and the catalyst layer were joined.
Further, the obtained electrolyte membrane with catalyst layer was sandwiched between carbon cloths for gas diffusion layers and thermocompression bonded to obtain a membrane / electrode assembly.

(Comparative Example 1)
A membrane / electrode assembly was produced in the same manner as in the above example except that the catalyst layer thermal transfer sheet was not immersed in the Ce (NO ₃ ) · 6H ₂ O aqueous solution.

[Power generation evaluation]
For the membrane / electrode assemblies of Examples and Comparative Examples obtained above, the output current density (A / cm ² ) at a constant voltage of 0.4 V was measured under the following conditions.
<Conditions>
-Cell temperature: 80 ° C
・ Humidity: 100RH%
・ Fuel (hydrogen gas): 500 mL / min
・ Oxidizing agent (air): 1000 mL / min

The results are shown in Table 1. Although the membrane / electrode assembly of the example was obtained by replacing part of the cation exchange groups (sulfonic acid groups) of the cation exchange resin contained in the catalyst layer with cerium ions, the membrane / electrode of the comparative example Excellent power generation performance was achieved compared to the joined body.
This is because the ion exchange group density of the catalyst layer is changed by replacing H ^{+ of} some sulfonic acid groups with cerium ions, and as a result, the water balance of the membrane / electrode assembly as a whole is changed. Guessed.

[Durability test (fluorine elution measurement)]
The water discharged from the fuel cell during power generation was collected, and the F concentration in the collected water was analyzed by ion chromatography to measure the F elution degree.
The results are shown in FIG. As shown in FIG. 2, the F elution rate was greatly different between the membrane / electrode assembly of the comparative example and the membrane / electrode assembly of the example. Specifically, if the fluorine elution degree of the membrane / electrode assembly of the comparative example is 100, the fluorine elution degree of the membrane / electrode assembly of the example is 4, which is higher than that of the membrane / electrode assembly of the comparative example. Thus, it was confirmed that the fluorine elution amount was significantly reduced by about 1/25.
This is because a sufficient amount of sulfonic acid groups in the catalyst layer can be replaced with rare earth ions by contact between the rare earth salt solution and the catalyst layer in a reduced pressure environment, and radical decomposition of peroxide is suppressed by the rare earth ions. This is because of that. As a result, attack of the polymer electrolyte membrane and the cation exchange resin in the catalyst layer by the peroxide radical was suppressed, and it is considered that the fluorine elution degree could be reduced. The degree of fluorine elution is one of the typical indexes indicating the degree of deterioration of the fluorine-based polymer electrolyte membrane and the cation exchange resin. The higher the degree of fluorine elution, the higher the degree of deterioration.

  From the results of the above power generation evaluation and fluorine elution measurement, it can be seen that the membrane / electrode assembly produced by the production method of the present invention has excellent power generation performance and high durability. Therefore, according to the manufacturing method of the present invention, it is possible to provide an excellent fuel cell having both power generation performance and durability.

It is a figure which shows the one aspect | mode of the rare earth salt solution contact process in the manufacturing method of the polymer electrolyte fuel cell which concerns on this invention. It is a graph which shows the result of the fluorine elution degree in an Example.

Claims (5)

  A rare earth salt solution contacting step in which a catalyst layer formed by applying a catalyst ink containing a catalyst component and a cation exchange resin on a support and drying is contacted with a solution in which a salt of a rare earth element is dissolved in a reduced pressure environment; and A solid polymer fuel cell comprising: a drying step of drying the catalyst layer after the rare earth salt solution contact step; and a thermocompression bonding step of thermocompression bonding the catalyst layer to at least one surface of the polymer electrolyte membrane. Production method.   A rare earth salt solution contact step in which a catalyst layer formed by applying a catalyst ink containing a catalyst component and a cation exchange resin on a transfer support and drying is contacted with a solution in which a salt of a rare earth element is dissolved in a reduced pressure environment; A drying step for drying the catalyst layer after the rare earth salt solution contacting step, a thermocompression bonding step for thermocompression bonding the catalyst layer to at least one surface of the polymer electrolyte membrane, and a support for transfer after the thermocompression bonding step. The method for producing a polymer electrolyte fuel cell according to claim 1, comprising a step of peeling from the catalyst layer.   The method for producing a polymer electrolyte fuel cell according to claim 1 or 2, wherein in the thermocompression bonding step, the catalyst layer is thermocompression bonded to both surfaces of the polymer electrolyte membrane.   The method for producing a polymer electrolyte fuel cell according to any one of claims 1 to 3, wherein the rare earth element is cerium.   5. The method for producing a polymer electrolyte fuel cell according to claim 1, wherein in the rare earth salt solution contact step, a reduced pressure environment of 50 mmHg or less is used.

Images