JP2010140699A - Paste for catalyst layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a paste for a catalyst layer which can maintain high power generation efficiency and durability performance by securely preventing generation of fine cracks in coating and drying, can prevent degradation of a catalyst layer coating composition by maintaining a drying temperature after coating the paste for a catalyst layer low so as to reduce a load in a drying process. <P>SOLUTION: The paste for a catalyst layer is for a fuel cell electrode to form a catalyst layer of a polymer electrolyte fuel cell formed mainly of a polymer electrolyte film. The paste for a catalyst layer is made by mixing an organic solvent, which is mixed with water at an optional ratio within a boiling point range of 120-150 °C, with mixture paste containing catalyst support carbon, ion exchange resin, and solvent containing 40 wt.% or more of water, at a ratio of 50-200 pts.wt. to 100 pts.wt. of the catalyst-supporting carbon. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a catalyst layer paste for a fuel cell electrode for forming a catalyst layer of an electrode used in a polymer electrolyte fuel cell, and in particular, generates fine cracks when the coating film is dried to generate power generation efficiency and durability performance. The present invention relates to a paste for a catalyst layer that does not lower the temperature.

  In a polymer electrolyte fuel cell, a cathode side electrode and an anode side electrode are formed on both sides of a polymer electrolyte membrane. Usually, the cathode side electrode and the anode side electrode are carbon carrying a catalyst such as platinum. Electrocatalyst layer composed of black and ion exchange resin, carbon black powder for imparting conductivity to carbon substrate such as carbon cloth and carbon paper, and polytetrafluoroethylene dispersion for imparting water repellency The gas diffusion layer is formed by applying a kneaded water repellent paste.

  Here, in order to put the polymer electrolyte fuel cell to practical use, it is necessary to mass-produce the electrode catalyst layer, but in order to continuously produce the electrode catalyst layer, the catalyst layer paste is continuously applied automatically and dried. In the case of the conventional catalyst layer paste, fine cracks are generated in the dried coating film, and this cracked portion is not in contact with the polymer electrolyte membrane or the gas diffusion layer. It was causing.

Therefore, in the invention disclosed in Patent Document 1, ethylene glycol is added to the catalyst layer paste in order to prevent the occurrence of cracks. Accordingly, it is possible to surely prevent fine cracks from occurring in the dry coating film of the catalyst layer paste, and to prevent a decrease in power generation efficiency and durability performance.
JP 2002-280003 A

  However, in the technique described in Patent Document 1, since ethylene glycol having a high boiling point of 198 ° C. is added, the drying temperature of the coating film formed by applying the catalyst layer paste is set to a high temperature of 150 ° C. or higher. The catalyst layer coating film component deteriorates due to such high temperature drying, and the load of the drying process after application of the catalyst layer paste increases.

  Therefore, the present invention has been made to solve such problems, and can reliably prevent generation of fine cracks during drying of the coating film and maintain high power generation efficiency and durability performance, An object of the present invention is to provide a catalyst layer paste that can prevent deterioration of the catalyst layer coating film component and reduce the load of the drying step by keeping the drying temperature after coating the layer paste at a low temperature.

  The paste for a catalyst layer according to the invention of claim 1 is a paste for a catalyst layer for a fuel cell electrode for forming a catalyst layer of a solid polymer type fuel cell constituted mainly by a polymer electrolyte membrane, An organic solvent that has a boiling point in the range of 120 ° C. to 150 ° C. and is mixed with water at a free ratio to a mixed paste containing catalyst-supporting carbon, an ion exchange resin, and a solvent containing 40% by weight or more of water. , And 50 parts by weight to 200 parts by weight with respect to 100 parts by weight of the catalyst-supporting carbon.

  Here, examples of the “organic solvent having a boiling point within the range of 120 ° C. to 150 ° C. and mixed with water at a free ratio” include propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono n-propyl. And propylene glycol monoalkyl ethers such as ether.

  The catalyst layer paste according to the invention of claim 2 is the structure of claim 1, wherein the mixing ratio of the catalyst-carrying carbon, the ion-exchange resin, and the solvent is 5% by weight of the catalyst-carrying carbon. % To 15% by weight, the ion exchange resin in the range of 2% to 10% by weight, and the solvent in the range of 75% to 93% by weight.

  Here, when the catalyst-supporting carbon and the ion exchange resin are mixed in a state including a solution, the “solvent” includes those solutions.

  The catalyst layer paste according to the invention of claim 3 is the structure of claim 1 or claim 2, wherein 80% by weight or more of the solvent of the mixed paste is a mixture of water and ethanol, and 40% by weight. % To 60% by weight is water.

  In the invention according to claim 1, an organic solvent having a boiling point in the range of 120 ° C. to 150 ° C. is mixed with a mixed paste containing catalyst-supporting carbon, an ion exchange resin, and a solvent containing 40% by weight or more of water. Thus, when drying the coating film formed by applying the catalyst layer paste, it is possible to reliably prevent the occurrence of cracks, and the organic solvent is also mixed with water in a free ratio. In addition, the uniformity, stability, and coatability of the catalyst layer paste are not impaired, and it does not cause cracks during drying.

  And since the said organic solvent has a boiling point in the range of 120 degreeC-150 degreeC, since it can be dried on the heating conditions of about 100 degreeC, in the case of the invention which concerns on the said patent document 1 which added ethylene glycol Thus, there is no possibility that the high temperature drying is required and the catalyst layer coating film component is deteriorated by the high temperature, and the load of the drying process after the application of the catalyst layer paste is not increased.

  Furthermore, as a result of accumulating earnest experimental research on the addition amount for obtaining an effect specific to such an organic solvent, the present inventor has found that when adding to a mixed paste containing a catalyst-supporting carbon, an ion exchange resin, and a solvent, By mixing 50 parts by weight to 200 parts by weight of the organic solvent with respect to 100 parts by weight of the supported carbon, it is possible to reliably prevent cracks during drying and to completely dry at a low temperature of about 100 ° C. The present invention has been completed based on the finding and this finding.

  That is, if the addition amount of the organic solvent is less than 50 parts by weight with respect to 100 parts by weight of the catalyst-supporting carbon, it is not possible to sufficiently obtain the cracking prevention effect during drying due to the addition of the organic solvent having a boiling point higher than that of the solvent. On the other hand, when the addition amount of the organic solvent exceeds 200 parts by weight with respect to 100 parts by weight of the catalyst-supporting carbon, it is not preferable because it takes time to dry the organic solvent having a higher boiling point than the solvent of the mixed paste. Therefore, the amount of the organic solvent added to 100 parts by weight of the catalyst-carrying carbon is preferably 50 to 200 parts by weight.

  In this way, it is possible to reliably prevent generation of fine cracks during drying of the coating film and maintain high power generation efficiency and durability performance, and by keeping the drying temperature after applying the catalyst layer paste at a low temperature. Thus, the catalyst layer paste can be prevented from deterioration of the coating component of the catalyst layer and the load of the drying process can be reduced.

  In the invention according to claim 2, in the mixed paste, the mixing ratio of the catalyst-carrying carbon, the ion exchange resin and the solvent is within the range of 5 to 15% by weight of the catalyst-carrying carbon and 2% by weight of the ion exchange resin. The solvent is in the range of 10% by weight and the solvent is in the range of 75% by weight to 93% by weight.

  The present inventor has conducted extensive experimental research on the mixing ratio of the catalyst-carrying carbon, the ion-exchange resin, and the solvent in the mixed paste. As a result, the catalyst-carrying carbon is in the range of 5 to 15% by weight, and the ion-exchange resin is When the solvent is in the range of 2 wt% to 10 wt% and the solvent is in the range of 75 wt% to 93 wt%, it is possible to reliably prevent the occurrence of cracks during drying and to have excellent coating properties, and further, In addition to the effect of the invention according to No. 1, it has been found that a more efficient polymer electrolyte fuel cell can be obtained, and the present invention has been completed based on this finding.

  In the invention according to claim 3, in the catalyst layer paste, 80% by weight or more of the solvent of the mixed paste is a mixture of water and ethanol, and the range of 40% by weight to 60% by weight is water. is there.

  As a result of accumulating extensive experimental research on the composition of the solvent in the mixed paste, the present inventor found that 80% by weight or more of the solvent in the mixed paste is a mixture of water and ethanol, and 40% to 60% by weight of the mixture. In the case where the water content is water, it is possible to reliably prevent the occurrence of cracks during drying and to be excellent in coating properties, and in addition to the effect of the invention according to claim 1 or claim 2, The present inventors have found that a polymer electrolyte fuel cell can be obtained, and have completed the present invention based on this finding.

  Hereinafter, a paste for a catalyst layer used for a polymer electrolyte fuel cell electrode according to an embodiment of the present invention and a method for producing the same will be described.

  First, blending of the mixed paste, which is the basis of the catalyst layer paste according to the embodiment of the present invention, will be described. The mixed paste used as the base of the catalyst layer paste according to the present embodiment is made of 50% Pt (platinum) -supported carbon black as catalyst-supported carbon, manufactured by Wako Pure Chemical Industries, Ltd. as a component 20% ion-exchange resin solution. It is a paste-like mixture containing 20% Nafion dispersion, distilled water as a solvent and ethanol. Table 1 shows the composition of the mixed paste that is the basis of the catalyst layer paste according to the present embodiment.

  Next, the manufacturing method of the paste for catalyst layers concerning this Embodiment is demonstrated. First, 50% Pt-supported carbon black, 20% Nafion dispersion, distilled water and ethanol were weighed and blended according to the blending in Table 1, stirred with a disperser, and then subjected to a split acid treatment with an ultrasonic homogenizer. Three kinds of catalysts according to the present embodiment are prepared by mixing the organic solvent A as Example 1, the organic solvent B as Example 2, and the organic solvent C as Example 3 into the mixed paste thus manufactured. A layer paste was produced.

  Further, for comparison, by mixing organic solvents D to K as Comparative Examples 1 to 8, respectively, and adding no organic solvent as Comparative Example 9 to the mixed pastes produced in the same manner. The catalyst layer pastes according to Comparative Examples 1 to 9 were manufactured. The contents of the catalyst layer pastes according to Examples 1 to 3 and Comparative Examples 1 to 9 are summarized in the upper part of Table 2.

Here, in the solubility of the organic solvent in water (H ₂ O), “complete dissolution” means that the organic solvent and water are mixed at an arbitrary ratio. The contents of the organic solvents A to K are shown below Table 2. The catalyst layer pastes according to Examples 1 to 3 and Comparative Examples 1 to 9 were subjected to evaluation tests for drying properties and crack prevention properties.

Specifically, the drying property was evaluated by applying a catalyst layer paste with an applicator so that the amount of Pt supported was 1 mg / cm ² on the water-repellent diffusion layer, and the internal temperature was 80 Drying was carried out for 30 minutes in a dryer set at ℃ and 100 ℃ to form a catalyst coating film. The catalyst coating film was additionally dried for 8 hours using a vacuum dryer at 100 ° C. and 3 KPa, and a film showing no weight loss (that is, a film completely dried before vacuum drying) was marked with ○. Evaluation was made, and a weight loss was evaluated as x.

Further, as an evaluation method for crack prevention, specifically, a catalyst layer paste was applied with an applicator so that the amount of Pt supported was 1 mg / cm ² on the diffusion layer subjected to the water repellent treatment. Drying was performed for 30 minutes in a dryer set at a temperature of 100 ° C. to form a catalyst coating film. The surface of the catalyst coating film was observed with a metal microscope of 10 times objective lens × 10 times eye lens, and the case where no crack was observed was evaluated as “good”, and the case where crack was observed was evaluated as “poor”. The evaluation results on the drying property and cracking prevention property are shown in the lower part of Table 2.

  Here, “addition of catalyst * 0.2” means that 0.2 weight of organic solvent is added to 1 weight of Pt 50% supported carbon black as a catalyst, that is, Table 1 shows in this embodiment. Thus, 10 g of Pt 50% supported carbon black is used, meaning that 2 g of an organic solvent is added. Hereinafter, similarly, “addition of catalyst * 0.5” means that 5 g of an organic solvent is added to 10 g of Pt 50% supported carbon black, and “addition of catalyst * 1” means organic for 10 g of Pt 50% supported carbon black. “Addition of 10 g of solvent”, “addition of catalyst * 2” means addition of 20 g of organic solvent to 10 g of Pt 50% supported carbon black.

  As shown in the lower part of Table 2, in Example 1 according to the present embodiment, the dryness is evaluated as ◯ for those dried at 80 ° C. for 30 minutes and those dried at 100 ° C. for 30 minutes. As for crack prevention, cracks were observed for those added with 2 g of the organic solvent A, and the evaluation was x, but for those added with 5 g, 10 g, and 20 g of the organic solvent A, all were evaluated as ◯. Met.

  Moreover, in Example 2 which concerns on this Embodiment, about dryability, what was dried for 30 minutes at 80 degreeC and what was dried for 30 minutes at 100 degreeC are evaluation of (circle), and about crack prevention property, it is organic. Cracks were observed for those added with 2 g of solvent B, and the evaluation was x. However, those with addition of 5 g, 10 g, and 20 g of organic solvent B were all evaluated as o.

  Furthermore, in Example 3 which concerns on this Embodiment, about the drying property, about what was dried for 30 minutes at 80 degreeC, the weight loss was seen by vacuum drying of 100 degreeC and 3 KPa, but it was evaluation of x. What was dried for 30 minutes at 100 degreeC was evaluation of (circle). This is thought to be because the boiling point of the organic solvent C is 150 ° C., so that it is difficult to dry compared to the organic solvents A and B. For crack prevention, cracks were observed for those added with 2 g of the organic solvent C, and the evaluation was x, but for those added with 5 g, 10 g, and 20 g of the organic solvent C, all were evaluated as ○. there were.

  From the evaluation results of Examples 1 to 3 according to the present embodiment, the organic solvent needs to be “addition of catalyst * 0.5” or more, that is, with respect to 100 parts by weight of Pt 50% supported carbon black. It has been clarified that the effect of preventing cracks cannot be reliably obtained unless 50 parts by weight or more of the organic solvent is added.

  In contrast, for the catalyst layer pastes of Comparative Examples 1 to 9, the boiling points of the organic solvents D, E, and F were 97 ° C. in the case of the catalyst layer pastes of Comparative Examples 1 to 3, respectively. , 108 ° C and 118 ° C are low, so the dryness is evaluated as ○ for both those dried at 80 ° C for 30 minutes and those dried at 100 ° C for 30 minutes, but the crack prevention property is cracked for all items. Was observed, and was evaluated as x.

  Similarly, in the case of the catalyst layer paste of Comparative Example 4, the drying property was evaluated as x when the weight was reduced by vacuum drying at 100 ° C. and 3 KPa for those dried at 80 ° C. for 30 minutes. However, what was dried for 30 minutes at 100 degreeC was evaluation of (circle). This is presumably because the boiling point of the organic solvent G is 146 ° C. However, with regard to crack prevention, cracks were observed for all items, and the evaluation was x.

  Further, in the case of the catalyst layer paste of Comparative Example 9, since it is a conventional example in which no organic solvent is added, as a matter of course, the dryness is 30 ° C. for 30 minutes at 100 ° C. Although the thing dried for minutes was also evaluated as (circle), about the crack prevention property, the crack was observed about all the items and it became evaluation of x.

  On the other hand, in the case of the catalyst layer pastes of Comparative Examples 5 to 8, the organic solvents H, I, J, and K have high boiling points of 169 ° C., 170 ° C., 187 ° C., and 198 ° C., respectively. For Comparative Example 6, except for Comparative Example 6, the addition of 5 g, 10 g, and 20 g of the organic solvent was evaluated as “Good”, and the effect of preventing cracking was observed. However, the dryness was evaluated as x for both those dried at 80 ° C. for 30 minutes and those dried at 100 ° C. for 30 minutes.

  From the above evaluation results, as shown in the bottom row of Table 2, in the catalyst layer pastes according to Examples 1 to 3 of the present embodiment, the overall judgment is evaluated as “good” and sufficient. It became clear that it has practicality. In contrast, the catalyst layer pastes of Comparative Examples 1 to 9 were evaluated as x in the overall judgment.

  In this way, in the catalyst layer paste according to Examples 1 to 3 of the present embodiment, generation of fine cracks during drying of the coating film is surely prevented, and power generation efficiency and durability performance are maintained high. In addition, by maintaining the drying temperature after applying the catalyst layer paste at a low temperature, deterioration of the catalyst layer coating film component can be prevented and the load of the drying process can be reduced.

  In this embodiment, Pt (platinum) 50% supported carbon black is used as the catalyst-supported carbon, 20% Nafion dispersion manufactured by Wako Pure Chemical Industries, Ltd. is used as the ion exchange resin, and distilled water and ethanol are used as the solvent. Although the case has been described, the catalyst-supporting carbon, the ion exchange resin, and the solvent are not limited to these.

  In the present embodiment, the case where propylene glycol monomethyl ether (A), propylene glycol monoethyl ether (B), propylene glycol mono n-propyl ether (C) is used as the organic solvent has been described. The organic solvent used in the above is not limited to these propylene glycol monoalkyl ethers, and the condition that “the organic solvent has a boiling point in the range of 120 ° C. to 150 ° C. and is mixed with water in a free ratio” is used. Various organic solvents can be used as long as they satisfy the requirements.

  In carrying out the present invention, other configurations, components, materials, blending, shapes, sizes, manufacturing methods, and the like of the catalyst layer paste are not limited to the present embodiment. Note that the numerical values given in the embodiments of the present invention are not all critical values, and certain numerical values indicate preferred values suitable for implementation, so even if the numerical values are slightly changed. The implementation is not denied.

Claims (3)

A catalyst layer paste for a fuel cell electrode for forming a catalyst layer of a polymer electrolyte fuel cell composed mainly of a polymer electrolyte membrane,
An organic solvent that has a boiling point in the range of 120 ° C. to 150 ° C. and is mixed with water at a free ratio to a mixed paste containing catalyst-supporting carbon, an ion exchange resin, and a solvent containing 40% by weight or more of water. The catalyst layer paste is a mixture of 50 parts by weight to 200 parts by weight with respect to 100 parts by weight of the catalyst-supporting carbon.   In the mixed paste, the catalyst-supporting carbon, the ion-exchange resin, and the solvent have a mixing ratio of 5 to 15% by weight for the catalyst-supported carbon and 2 to 10% by weight for the ion-exchange resin. The catalyst layer paste according to claim 1, wherein the solvent is in the range of 75 wt% to 93 wt%.   3. The solvent of the mixed paste is 80% by weight or more of a mixture of water and ethanol, and 40 to 60% by weight of the solvent is water. The catalyst layer paste according to 1.