JP5217131B2 - Catalyst ink for fuel cell, membrane electrode assembly, and production method thereof - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a catalyst ink and membrane electrode assembly used in a fuel cell and a method for producing the same, and more particularly to a catalyst ink and membrane electrode assembly used in a polymer electrolyte fuel cell and a method for producing the same. It is about.

In a fuel cell, electric power is generated by electrochemically reacting a fuel gas with an oxidizing gas containing oxygen such as air, and the catalyst of the fuel cell determines the performance of the fuel cell. A fuel cell catalyst is formed by applying a catalyst ink to a polymer electrolyte membrane. As a conventional fuel cell catalyst ink, a polymer electrolyte colloid is generated, and the polymer electrolyte colloid is supported on a noble metal. A catalyst ink having a fluororesin adsorbed on carbon powder and having a fluororesin in a mass ratio of 25 to 70% of the total amount is known (Patent Document 1).

JP-A-8-264190

  The conventional catalyst ink has a problem that the polymer electrolyte is difficult to uniformly adsorb on the carbon powder supporting the noble metal, and solid-liquid separation is likely to occur. As a result, the stability of the dispersion of the catalyst ink over time decreases, and even when the catalyst ink is applied to the polymer electrolyte membrane to form a membrane electrode assembly, the voltage variation increases and the performance of the fuel cell is improved. I can't.

  An object of the present invention is to solve the above-mentioned problems and improve the performance of the fuel cell by improving the temporal stability of the dispersion of the catalyst ink.

  In order to solve the above problems, a fuel cell catalyst ink according to the present invention is a polymer electrolyte having hydrophobic catalyst particles obtained by supporting a noble metal on a support, a hydrophobic group and a hydrophilic group, A catalyst ink particle comprising: a polymer electrolyte having the hydrophobic group oriented toward the catalyst particle and substantially covering an outer periphery of the catalyst particle. According to the catalyst ink of the present invention, the outer periphery of the catalyst ink particles is substantially covered with the polymer electrolyte in which the hydrophobic groups are oriented toward the catalyst particles. Therefore, since the hydrophilic group of the polymer electrolyte is oriented outward, the dispersion with time of the dispersion of the catalyst ink can be improved, the variation in the voltage of the fuel cell can be reduced, and the performance of the fuel cell can be improved. .

In the fuel cell catalyst ink according to the present invention, the catalyst particles, relative to the weight of the catalyst particles, it is preferably covered by a 30% by mass or more polyelectrolytes. According to the catalyst ink according to the present invention, catalyst particles relative to the weight of the catalyst particles, because they are coated with a polymeric electrolyte above 30% by mass, almost the entire outer periphery of the catalyst particles coated with a polyelectrolyte Has been. As a result, it is possible to improve the temporal stability of the dispersion of the catalyst ink, reduce the variation in the voltage of the fuel cell, and improve the performance of the fuel cell.

  A fuel cell membrane electrode assembly according to the present invention is a membrane electrode assembly in which a fuel cell catalyst ink is applied to a polymer electrolyte membrane, on both sides of the polymer electrolyte membrane and the polymer electrolyte membrane. And a catalyst layer having catalyst particles in which the outer periphery of the catalyst particles is substantially covered with a polymer electrolyte. According to the membrane electrode assembly according to the present invention, since the catalyst particles are almost covered with the polymer electrolyte, the variation in the voltage of the fuel cell can be reduced and the performance of the fuel cell can be improved.

  A fuel cell according to the present invention comprises a polymer electrolyte membrane and a catalyst layer formed on both surfaces of the polymer electrolyte membrane, the catalyst particles having catalyst particles substantially covered with a polymer electrolyte. A membrane electrode assembly including the catalyst layer, and separators disposed on both sides of the membrane electrode assembly. According to the present invention, since the outer periphery of the catalyst particles of the membrane electrode assembly is substantially covered with the polymer electrolyte, if the membrane electrode assembly is used for a fuel cell, the electrochemical reaction of the fuel cell is promoted. The performance of the fuel cell can be improved.

  The method for producing a catalyst ink according to the present invention includes a step of mixing and stirring catalyst particles obtained by supporting a noble metal on a support, a polymer electrolyte solution, and water, and stirring and mixing ethanol to the stirred solution. And a step of dispersing the mixed solution. According to the method for producing a catalyst ink according to the present invention, since no ethanol is added in the step of stirring the catalyst particles, the polymer electrolyte solution and the water in which the noble metal is supported on the support, the catalyst particles are polymer electrolyte. It is almost covered by the membrane. Therefore, it is possible to improve the temporal stability of the dispersion of the catalyst ink, reduce the variation in the voltage of the fuel cell, and improve the performance of the fuel cell.

  In the method for producing a catalyst ink according to the present invention, the step of adding and stirring the catalyst particles obtained by supporting the noble metal on the support, the polymer electrolyte solution, and water is performed under reduced pressure. According to the present invention, by carrying out the process under reduced pressure, it is possible to remove bubbles adhering to the surfaces of the catalyst particles or the pores thereof, and to increase the amount of adsorption of the polymer electrolyte. . As a result, the performance of the fuel cell can be improved.

  The method for producing a membrane electrode assembly for a fuel cell according to the present invention comprises a step of applying a catalyst ink for a fuel cell produced by the production method to a polymer electrolyte membrane, and the fuel applied to the polymer electrolyte membrane. And drying the battery catalyst ink. According to the method for producing a membrane electrode assembly for a fuel cell according to the present invention, it is possible to easily produce a membrane electrode assembly for a fuel cell having good performance with little voltage variation when used in a fuel cell.

A. Structure of catalyst ink 100 The catalyst ink 100 according to the present embodiment will be described with reference to FIGS. 1, 2, and 3. FIG. 1 is an explanatory view schematically showing the structure of the catalyst ink 100 according to the first embodiment. FIG. 2 is a chemical formula showing the structure of the polymer electrolyte 108. FIG. 3 is an explanatory view schematically showing the structure of a conventional catalyst ink 400.

  The catalyst ink 100 is a mixed liquid obtained by dispersing catalyst ink particles 101 in a solvent. The catalyst ink particle 101 has a substantially spherical shape, and is formed of a catalyst particle 102 at the center and a polymer electrolyte 108 covering the periphery of the catalyst particle 102. The catalyst particles 102 are obtained by supporting a noble metal 106 on a carrier 104. In this embodiment, for example, hydrophobic carbon black (particle diameter of about 0.1 to 20 μm) is used as the carrier 104. Moreover, as the noble metal 106 to be supported, for example, platinum or a platinum alloy is used.

  The polymer electrolyte 108 in this embodiment has a hydrophobic group 112 and a hydrophilic group 113. Since the catalyst particles 102 are hydrophobic, the polymer electrolyte 108 is adsorbed by the catalyst particles 102 with the hydrophobic groups 112 facing the catalyst particles 102, and catalyst ink particles 101 are formed. The catalyst ink particle 101 exposes the hydrophilic group 113 of the polymer electrolyte 108 toward the spherical surface. As a result, the catalyst ink particles 101 form a hydrocolloid and are difficult to settle, and the dispersion stability over time is improved.

  As the polymer electrolyte 108, for example, a perfluorocarbon sulfonic acid polymer 110 shown in FIG. 2 can be used. The perfluorocarbon sulfonic acid polymer 110 has a hydrophobic main chain 114 and side chains 115 having sulfonic acid groups 116 as hydrophilic groups 113.

  On the other hand, in the conventional catalyst ink 400, as shown in FIG. 3, for example, ethanol is adsorbed on the catalyst particles 102, so that the catalyst particles 102 cannot be sufficiently covered with the polymer electrolyte 108. On the other hand, carbon black is used for the carrier 104 of the catalyst particles 102, and the carbon blacks are easily adsorbed to each other. As a result, portions of the catalyst particles 102 that are not covered with the polymer electrolyte 108 are adsorbed, and large catalyst ink particles 401 are easily formed. The large catalyst ink particle 401 has a higher specific gravity because the catalyst particle 102 occupies a larger proportion than the catalyst ink particle 101. Therefore, the catalyst ink particles 401 are likely to settle, and the stability of the dispersion of the catalyst ink 400 over time is poor.

B. Method for Producing Catalyst Ink 100 Next, a method for producing the catalyst ink 100 will be described with reference to FIG. FIG. 4 is a process diagram illustrating a method for manufacturing the catalyst ink 100.

  The support 104 (catalyst particles 102) supporting the noble metal 106, the polymer electrolyte solution, and water are mixed and stirred (first step). By stirring, the polymer electrolyte 108 in the polymer electrolyte solution is adsorbed on the surface of the catalyst particles 102 to form a colloid.

  Next, ethanol is added to the stirring solution and further stirred (second step). By adding ethanol, after applying the catalyst ink to the electrolyte membrane, the excess solvent can be easily evaporated to dry the catalyst ink.

  Next, the stirred solution to which ethanol has been added is dispersed by means of ultrasonic waves or the like to obtain the catalyst ink 100 (third step). In general, the colloid of the stirring solution is agglomerated in a considerably large mass because the hydrophilic groups of the catalyst ink particles 101 are adsorbed when ethanol is added and stirred. Here, the adsorption of the hydrophilic groups of the catalyst ink particles 101 is cut by vibration by ultrasonic waves, the aggregated mass is decomposed, and the aggregate size is reduced. The catalyst ink particles 101 have a low specific gravity and are likely to float in the solvent. As a result, the catalyst ink particles 101 are less likely to settle and the dispersion stability over time increases. Further, when the catalyst ink 100 is applied to the polymer electrolyte membrane by spraying, the catalyst ink can be applied so as to be uniformly distributed, and the performance of the fuel cell can be improved.

  The step of mixing and stirring the catalyst particles 102, the polymer electrolyte solution, and water (first step) may be performed under reduced pressure. Bubbles are attached to the surface of the carrier 104 of the catalyst particles 102 or pores formed on the surface. Although the polymer electrolyte 108 is difficult to adsorb to the bubble portion, the adhering bubbles can be removed by reducing the pressure, and more polymer electrolyte 108 can be adsorbed to the catalyst particles 102. As a result, the specific gravity of the catalyst ink particles 101 is reduced, the stability of the catalyst ink dispersion over time is increased, and the performance of the fuel cell can be improved.

  The catalyst ink obtained by the catalyst ink production method is compared with the catalyst ink of the conventional production method.

Example 1
20 g of Nafion (registered trademark: NAFION) solution (DuPont DE-2020 20% solution) and 60 g of water with respect to 10 g of catalyst particles having platinum alloy particles supported on carbon black (Ketjen EC made by Ketjen Black International) And stirred for 12 hours. Next, 50 g of ethanol was added to the stirring solution, and the mixture was thoroughly stirred and mixed. The mixed solution was subjected to a dispersion treatment using an ultrasonic homogenizer to prepare a catalyst ink.

(Example 2)
12. 20 g of Nafion solution (DE-2020 20% solution manufactured by DuPont) and 60 g of water are added to 10 g of catalyst particles in which platinum alloy particles are supported on carbon black (Ketjen EC manufactured by Ketjen Black International). The pressure was reduced to 3 kPa, and the mixture was stirred for 12 hours. Next, the pressure was returned to normal pressure, 50 g of ethanol was added to the stirred solution, and the mixture was stirred well and mixed. The mixed solution was subjected to a dispersion treatment using an ultrasonic homogenizer to prepare a catalyst ink.
(Example 3)
A catalyst ink was prepared in the same manner as in Example 2 except that the catalyst particles carrying platinum alloy particles, the Nafion solution, and water were mixed and stirred for 24 hours.

(Comparative Example 1)
20 g of Nafion solution (DE-2020 20% solution manufactured by DuPont), 60 g of water, and 50 g of ethanol are added to 10 g of catalyst particles on which platinum alloy particles are supported on carbon black (Ketjen EC manufactured by Ketjen Black International). Stir well and mix. The mixed solution was subjected to a dispersion treatment using an ultrasonic homogenizer to prepare a catalyst ink.

  In Example 1, the catalyst particles supporting the platinum alloy particles, the Nafion solution, and water were mixed and stirred, and then ethanol was added to the stirring solution and stirred. In Comparative Example 1, the platinum alloy particles were initially mixed. The difference is that the supported catalyst particles, Nafion solution, water and ethanol are mixed and stirred.

  In Example 1, the step of mixing and stirring the catalyst particles, the Nafion solution, and water is performed at normal pressure, but Example 2 is different in that it is performed at reduced pressure. Moreover, in Example 2 and Example 3, the stirring time in the process which mixes and stirs a catalyst particle, a Nafion solution, and water differs.

C. Evaluation of catalyst ink The adsorption ratio of the polymer electrolyte 108 of the produced catalyst ink and the sedimentation rate of the catalyst ink were evaluated. The temporal stability of the dispersion of the catalyst ink can be seen from the sedimentation rate of the catalyst ink. In other words, the lower the sedimentation speed of the catalyst ink 100, the more the catalyst ink 100 can float in the ink solution, and the longer the sustaining stability. Polyelectrolyte adsorption ratio is one in which the amount of the polymer electrolyte 108 adsorbed on the catalyst particles 102 shown in weight percentage of the weight of the catalyst particles 102.

  In this embodiment, since the Nafion solution is used as the polymer electrolyte solution, the component of the polymer electrolyte 108 is the perfluorocarbon sulfonic acid polymer 110 contained in the Nafion solution. The amount of the polymer electrolyte 108 adsorbed on the catalyst particles 102 can be determined as follows.

  The produced catalyst ink 100 is filtered to separate the residue 118 and the filtrate 120. The residue 118 includes the catalyst particles 102 and the polymer electrolyte 108 adsorbed on the catalyst particles 102, and the filtrate 120 includes the polymer electrolyte 108 that is not adsorbed on the catalyst particles 102. Since the polymer electrolyte 108 has the sulfonic acid group 116, the amount of the sulfonic acid group 116 of the polymer electrolyte 108 in the filtrate can be measured by acid-base titration. If the amount of the sulfonic acid group 116 in the filtrate 120 is known, the amount of the polymer electrolyte 108 in the filtrate 120 can be known. Therefore, the amount of the polymer electrolyte 108 adsorbed on the catalyst particles 102 is obtained by subtracting the amount of the polymer electrolyte 108 in the filtrate 120 from the amount of the polymer electrolyte 108 contained in the charged Nafion solution. be able to.

The amount of the polymer electrolyte 108 can also be obtained by drying the filtrate 120 and subtracting the amount of the remaining polymer electrolyte 108 from the amount of the polymer electrolyte 108 that has been added. Although the residue 118 is dried and the mass of the residue 118 is measured, the amount of adsorbed polymer electrolyte 108 can be determined by subtracting the mass of the charged catalyst particles 102 from the mass of the residue 118. Since the noble metal 106 (platinum alloy) is supported on the particles 102, there are cases where ignition occurs when the residue 118 is dried.

  The sedimentation speed of the catalyst ink 100 was measured by a centrifugal sedimentation method. 2 ml of the catalyst ink was put in a glass syringe, and light was applied to the syringe while rotating at 3000 rpm. The amount of light transmitted through the catalyst ink portion of the syringe was measured, and the sedimentation rate of the catalyst ink was estimated from the rate of change in the amount of transmitted light.

  The relationship between the electrolyte adsorption ratio and the sedimentation rate will be described with reference to Table 1 and FIG. FIG. 5 is a graph showing the relationship between the electrolyte adsorption ratio and the sedimentation rate.

  When the electrolyte adsorption ratios of Example 1 and Comparative Example 1 are compared, Example 1 is higher. When the catalyst particles 102, water and the Nafion solution are mixed and stirred, the amount of adsorption of the polymer electrolyte when ethanol is simultaneously added is smaller than when ethanol is not simultaneously added. Since ethanol has a hydrophobic ethyl group and a hydrophilic alcohol group, when ethanol is added at the same time when the catalyst particles 102 and water are mixed and stirred, ethanol also tends to be adsorbed on the catalyst particles 102. . That is, the amount of adsorption of the polymer electrolyte 108 on the catalyst particles 102 is reduced by the amount of ethanol adsorbed on the catalyst particles 102.

  Therefore, in order to increase the adsorption amount of the polymer electrolyte 108 on the catalyst particles 102, the catalyst particles 102, water and Nafion solution are mixed and stirred without adding ethanol, and the polymer electrolyte 108 is added to the catalyst particles 102. After adsorbing, ethanol may be added and stirred. It is possible to suppress the adsorption of ethanol to the catalyst particles 102 and to adsorb more polymer electrolyte 108 to the catalyst particles 102.

  Comparing Example 1 and Example 2, and looking at the adsorption ratio of the polymer electrolyte 108, the adsorption ratio of the polymer electrolyte 108 is higher in Example 2. When the catalyst particles 102, water, and Nafion solution are mixed and stirred, the amount of adsorption of the polymer electrolyte 108 increases when the pressure is reduced. Carbon black is used for the carrier 104 of the catalyst particles 102. There are a large number of pores on the surface, and bubbles are attached to the pores or the surface of the carbon black, and the polymer electrolyte is difficult to adsorb on the bubble portions. However, by reducing the pressure, adhering bubbles can be removed, and adsorption of the polymer electrolyte 16 to the surface of the catalyst particles 102 can be promoted.

Comparing the results of Example 2 and Example 3, the sedimentation rate is almost unchanged. The settling velocity depends on the size of the surface of the catalyst particle 102 that is not covered with the polymer electrolyte 108, and the lower the surface that is not covered with the polymer electrolyte 108, the smaller the settling rate. Since the amount of adsorption of the polymer electrolyte 108 is constant and sedimentation rate substantially greater than 30 weight percent of the weight of the catalyst particles 102, the mass of the polymer electrolyte 108 adsorbed on the catalyst particles 102 is the mass of the catalyst particles 102 If it is 30 mass percent or more, it is considered that the catalyst particles 102 are almost covered with the polymer electrolyte.

  Comparing the polymer electrolyte adsorption ratios of Example 2 and Example 3, Example 3 is higher. It can be said that the polymer electrolyte adsorption ratio can be increased by increasing the stirring time for stirring the catalyst particles 102, water, and Nafion solution together. In Example 1 where there is no influence of ethanol on the adsorption of the polyelectrolyte 108, the electrolyte adsorption ratio was slightly less than 30%, but an electric field adsorption ratio of 26.8% was achieved. Therefore, in Example 1, it is expected that if the stirring is continued for a longer time, an electrolyte adsorption ratio of 30% is achieved and the catalyst particles 102 are almost covered with the polymer electrolyte 108.

  According to the present example, the carrier 104 carrying the platinum alloy particles, the Nafion solution, and water are stirred without adding ethanol, and after sufficient stirring, ethanol is added. Therefore, the surface of the catalyst particle 102 is almost covered with the polymer electrolyte 108. As a result, the adsorption of the catalyst particles 102 is less likely to occur after the adsorption of the hydrophilic groups of the catalyst ink particles 101 is cut off by ultrasonic vibration to reduce the aggregation. The catalyst ink particles 101 are less likely to settle, and the temporal stability of the dispersion of the catalyst ink 100 can be increased.

Further, according to the present example, when the carrier 104 carrying the platinum alloy particles, the Nafion solution, and water are mixed and stirred, the polymer is applied to the catalyst particles 102 in a short time by stirring under reduced pressure. The adsorption amount of the electrolyte 108 can be 30 mass percent or more of the mass of the catalyst particles 102. If the adsorption amount of the polymer electrolyte 108 on the catalyst particles 102 is 30 mass percent or more of the mass of the catalyst particles 102, the surface of the catalyst particles 102 is almost covered with the polymer electrolyte 108 from the result of the sedimentation rate of the catalyst ink. Can be judged.

D. Configuration of Membrane / Electrode Assembly A membrane / electrode assembly catalyst layer 200 will be described with reference to FIG. FIG. 6 is an explanatory view schematically showing the configuration of the membrane electrode assembly.

  The membrane electrode assembly 200 includes a polymer electrolyte membrane 202 and a catalyst layer 204. The catalyst layer 204 includes catalyst particles 102 and a polymer electrolyte 108 that substantially covers the catalyst particles 102. The catalyst layer 204 is formed on both surfaces of the polymer electrolyte membrane 202, and becomes a catalyst layer 204a on the anode side and a catalyst layer 204b on the cathode side, respectively. A space 206 is formed in the gap between the catalyst layers 204. Fuel gas (hydrogen gas) is supplied to the anode-side space 206a, and oxidizing gas (air) is supplied to the cathode-side space 206b.

  According to the membrane electrode assembly 200 according to this example, the catalyst particles 102 of the catalyst layer 204 are almost covered with the polymer electrolyte 108, so that the area of the interface between the catalyst particles 102 and the polymer electrolyte 108 is wide. Since the electrochemical reaction of the fuel cell occurs at the interface between the catalyst particle 102 and the polymer electrolyte 108, the electrochemical reaction is promoted when the area of the interface between the catalyst particle 102 and the polymer electrolyte 108 is large. Therefore, when the membrane electrode assembly 200 is used for a fuel cell, voltage variation is reduced, and the performance of the fuel cell can be improved.

E. Method for Producing Membrane / Electrode Assembly 200 A method for producing the membrane / electrode assembly 200 will be described with reference to FIG. FIG. 7 is a schematic view showing a method for producing the membrane electrode assembly 200. The catalyst ink 100 produced by the manufacturing method described above is put into the sprayer 208, pressure is applied, and the catalyst ink 100 is sprayed from the nozzle 210 onto the polymer electrolyte membrane 202 in a mist form. As a result, the catalyst ink 100 can be sprayed on the polymer electrolyte membrane 202 so as to be evenly distributed. Then, the excess solvent is dried and the membrane electrode assembly 200 is produced. The catalyst ink is sprayed on both sides of the polymer electrolyte membrane.

F. Evaluation of Membrane / Electrode Assembly 200 Hereinafter, the voltage stability and cell voltage of the membrane / electrode assembly 200 formed using the catalyst inks produced in Examples 1 to 3 and Comparative Example 1 will be compared.

  The voltage stability and cell voltage of the membrane electrode assembly 200 were measured using a fuel cell performance evaluation and measurement apparatus 300 shown in FIG. FIG. 8 is an explanatory diagram schematically showing the fuel cell performance evaluation measuring apparatus 300. The membrane electrode assembly 200 includes a hydrogen gas channel 310 that supplies hydrogen gas, a hydrogen cylinder 314 that is sandwiched between an oxidizing gas channel 312 that supplies air and discharges water that is generated, and a gas channel 310. In between, the pipe 320 insulated with the humidifier 316 and the heat insulating material 318 is provided. A pipe 326 thermally insulated by a humidifier 322 and a heat insulating material 324 is provided on the air and water flow path 312 side. A load 328 is connected between the anode side catalyst layer 204a and the cathode side catalyst layer 204b of the membrane electrode assembly.

  After leaving the cylinder 314, the hydrogen gas is heated to a temperature of 70 ° C. by the humidifier 316 and supplied to the hydrogen gas flow path 310 through the pipe 320 insulated by the heat insulating material 318. The hydrogen gas diffuses from the hydrogen gas flow path 310 to the anode side catalyst layer 204a. The membrane electrode assembly 200 is heated to 80 ° C. The hydrogen gas causes the following reaction on the anode catalyst layer 204a.

Anode electrode: H ₂ → 2H ⁺ + 2e ⁻ (1)

  The generated hydrogen ions pass through the polymer electrolyte membrane 202 and move to the cathode catalyst layer 204b. On the other hand, the generated electrons move from the anode side catalyst layer 204a through the load 328 to the cathode side catalyst layer 204b. That is, the membrane electrode assembly 200 becomes a part of a battery that allows current to flow through the load 328.

  The air is heated to 70 ° C. by the humidifier 322 and supplied to the oxidizing gas flow path 312 through the pipe 326 insulated by the heat insulating material 324. Air diffuses into the catalyst layer 204b on the cathode electrode plate side. Air causes the following reaction with hydrogen ions that have passed through the electrolyte membrane and electrons that have passed through the load 328 on the catalyst layer 204b.

Cathode electrode: (1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ 0 (2)

  The voltage stability of the catalyst layer and the cell voltage are measured by measuring the voltage across the load 328 of the fuel cell performance evaluation measuring device 300. Table 2 shows the measurement results.

  For the membrane / electrode assembly coated with the catalyst ink produced using Example 1, Example 2, Example 3 and Comparative Example 1, the voltage across the load 328 was measured and the voltage stability was compared. The variation is 5 to 6 mV for the membrane electrode assembly using the catalyst ink produced in Example 2 or Example 3, 10 mV for the membrane electrode assembly using the catalyst ink produced in Example 1, and produced in Comparative Example 1. The membrane electrode assembly using the catalyst ink was 13 mV, and the higher the electrolyte adsorption ratio (the lower the sedimentation rate), the lower the voltage variation and the higher the voltage stability. The cell voltage was 0.63 to 0.65 V for the membrane electrode assembly using the catalyst ink prepared in Examples 2 and 3, and 0 for the membrane electrode assembly using the catalyst ink prepared in Example 1. The membrane electrode assembly using the catalyst ink produced in the comparative example of .60 V was 0.55 V, and the cell voltage was higher when the adsorption ratio of the polymer electrolyte 108 was higher.

  Since the chemical reactions (1) and (2) occur at the interface between the catalyst particles 102 and the polymer electrolyte 108, the surface of the catalyst particles 102 is more adsorbed to the catalyst particles 102. However, it is considered that since the area not covered with the polymer electrolyte 108 is small and the area of the interface between the catalyst particles 102 and the polymer electrolyte is large, the voltage stability is high and the cell voltage is also high.

G. Fuel Cell A fuel cell 400 using the membrane electrode assembly 200 will be described with reference to FIG. FIG. 9 is an explanatory diagram schematically showing the fuel cell 400. The fuel cell 400 has a stack structure in which separators 402 and membrane electrode assemblies 200 are alternately overlapped. As described above, the membrane / electrode assembly 200 is obtained by applying the catalyst ink 100 to the polymer electrolyte membrane 202. The separator 402 is a plate that separates the fuel gas (hydrogen gas) and the oxidizing gas (air) so that they do not come into direct contact with each other. The fuel cell is also provided with communication holes 404 to 414. The communication hole 404 is a fuel gas supply port, and the communication hole 406 is a fuel gas discharge port. The communication hole 408 is a supply port for oxidizing gas (air), and the communication hole 410 is a discharge port for oxidizing gas and water generated by the reaction. The communication hole 412 is a cooling water supply port, and the communication hole 414 is a cooling water discharge port.

  The fuel cell 400 according to the present embodiment is a membrane electrode assembly 200 that includes a polymer electrolyte membrane 202, catalyst particles 102 adsorbed on the polymer electrolyte membrane, and a high height that substantially covers the outer periphery of the catalyst particles. A membrane electrode assembly 200 having a molecular electrolyte 108. Therefore, the voltage stability of the membrane electrode assembly 200 is high and the cell voltage is also large. Therefore, the fuel cell 400 can have high performance.

  As described above, the catalyst particles 102, water and the Nafion solution are mixed and stirred without adding ethanol to adsorb the polymer electrolyte 108 to the catalyst particles 102, and then ethanol is added to the mixed stirred solution and stirred. In the catalyst ink 100 obtained by dispersing the stirring solution with ultrasonic waves, the catalyst particles 102 are almost covered with the polymer electrolyte 108, so that the catalyst particles 102 are adsorbed to form large catalyst ink particles. This can be suppressed and the temporal stability of the dispersion of the catalyst ink 100 can be improved.

  When the catalyst ink 100 is manufactured, it is more preferable to reduce the pressure in the step of stirring the catalyst particles 102, water, and Nafion solution together. There are a large number of pores on the surface of the support 104 constituting the catalyst particles 102, and air bubbles are attached to the surface of the support 104 or the pores. Since it can be removed and the amount of adsorption of the polymer electrolyte 108 can be increased, the stability over time of dispersion of the catalyst ink 100 can be improved.

  In addition, by applying such a catalyst ink to the polymer electrolyte membrane 202, a membrane electrode assembly 200 having a catalyst layer 204 having a structure in which the catalyst particles 102 are substantially covered with the polymer electrolyte 108 can be produced. The membrane / electrode assembly according to this example has a large area at the interface between the catalyst particles 102 and the polymer electrolyte 108, so that the voltage stability of the membrane / electrode assembly 200 is high and the cell voltage is also large. Therefore, if such a membrane electrode assembly 200 is used, the performance of the fuel cell 400 can be improved.

  The embodiments of the present invention have been described above based on some examples. However, the above-described embodiments of the present invention are for facilitating the understanding of the present invention and limit the present invention. It is not a thing. The present invention can be changed and improved without departing from the spirit and scope of the claims, and it is needless to say that the present invention includes equivalents thereof.

Explanatory drawing which shows typically the structure of the catalyst ink which concerns on a 1st Example. Chemical formula showing the structure of the polymer electrolyte. Explanatory drawing which shows the structure of the conventional catalyst ink typically. Process drawing which shows the manufacturing method of catalyst ink. The graph which shows the relationship between the adsorption ratio of the polymer electrolyte of catalyst ink, and a sedimentation rate. Explanatory drawing which shows typically the structure of the catalyst layer which concerns on a 2nd Example. Explanatory drawing which shows the preparation methods of a catalyst layer typically. Explanatory drawing which shows a fuel cell performance evaluation measuring device typically. Explanatory drawing which shows a fuel cell typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Catalyst ink 101 ... Catalyst ink particle 102 ... Catalyst particle 104 ... Carrier 106 ... Precious metal 108 ... Polymer electrolyte 110 ... Perfluorocarbon sulfonic acid polymer 112 ... Hydrophobic group 113 ... Hydrophilic group 114 ... Main chain 115 ... Side chain 116 ... Sulfonic acid group 118 ... Residue 120 ... Filtrate 200 ... Membrane electrode assembly 202 ... Polymer electrolyte layer 204 ... Catalyst layer 206 ... Space 300 ... Fuel cell performance evaluation and measurement device 310 ... Hydrogen gas channel 312 ... Oxidizing gas channel 314 ... Hydrogen cylinders 316, 322 ... Humidifiers 318, 324 ... Heat insulation materials 320,326 ... Pipe 328 ... Load 400 ... Conventional catalyst ink 401 ... Catalyst ink particles

Claims (6)

A catalyst ink for fuel cells containing catalyst ink particles,
The catalyst ink particles are
Hydrophobic catalyst particles having a noble metal supported on a support, and
A polymer electrolyte having a hydrophobic group and a hydrophilic group, wherein the hydrophobic group is oriented toward the catalyst particle, and the hydrophilic group is exposed on the surface of the catalyst ink particle to cover the catalyst particle; ,
Equipped with a,
The catalyst particles, relative to the weight of the catalyst particles, that are covered by 30 mass% or more polyelectrolytes,
Catalyst ink for fuel cells. A membrane electrode assembly in which a fuel cell catalyst ink is applied to a polymer electrolyte membrane,
A polymer electrolyte membrane;
A catalyst layer formed on both surfaces of the polymer electrolyte membrane, the catalyst layer having catalyst ink particles;
With
The catalyst ink particles are
Hydrophobic catalyst particles having a noble metal supported on a support, and
A polymer electrolyte having a hydrophobic group and a hydrophilic group, wherein the hydrophobic group is oriented toward the catalyst particle, and the hydrophilic group is exposed on the surface of the catalyst ink particle to cover the catalyst particle; , equipped with a,
The catalyst particles, relative to the weight of the catalyst particles, that are covered by 30 mass% or more polyelectrolytes,
Membrane electrode assembly . A fuel cell,
A membrane electrode assembly comprising a polymer electrolyte membrane and a catalyst layer formed on both surfaces of the polymer electrolyte membrane, the catalyst layer having catalyst ink particles;
Separators disposed on both sides of the membrane electrode assembly;
With
The catalyst ink particles are
Hydrophobic catalyst particles having a noble metal supported on a support, and
A polymer electrolyte having a hydrophobic group and a hydrophilic group, wherein the hydrophobic group is oriented toward the catalyst particle, and the hydrophilic group is exposed on the surface of the catalyst ink particle to cover the catalyst particle; , equipped with a,
The catalyst particles, relative to the weight of the catalyst particles, that are covered by 30 mass% or more polyelectrolytes,
Fuel cell. A method for producing a catalyst ink for a fuel cell, comprising:
Mixing and stirring catalyst particles obtained by supporting a noble metal on a support, a polymer electrolyte solution having a hydrophobic group and a hydrophilic group, and water, the hydrophobic groups are oriented toward the catalyst particles, Producing a solution containing catalyst ink particles having a polymer electrolyte covering the catalyst particles with the hydrophilic groups exposed on the surfaces of the catalyst ink particles;
Adding ethanol to the stirred solution and stirring and mixing;
A step of dispersing the mixed solution;
A method for producing a fuel cell catalyst ink comprising: In the manufacturing method of the catalyst ink for fuel cells of Claim 4 ,
The step of mixing and stirring the catalyst particles obtained by supporting the noble metal on the support, the polymer electrolyte solution, and water is a method for producing a catalyst ink for a fuel cell, which is performed under reduced pressure. A method for producing a fuel cell membrane electrode assembly comprising:
The fuel cell catalyst ink was prepared by the method of any of claims 4 or claim 5, a step of applying the polymer electrolyte membrane,
Drying the fuel cell catalyst ink applied to the polymer electrolyte membrane;
The manufacturing method of the membrane electrode assembly for fuel cells which has these.

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