JP2007149461A - Ink for electrode of polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst ink for an electrode having high handling capability. <P>SOLUTION: The catalyst ink for a fuel cell contains a mixed solvent of water and alcohol, a non-fluorine solid polymer electrolyte, and a catalyst. The catalyst ink contains the mixed solvent of water and alcohol, at least one electrolyte selected from a group comprising the non-fluorine solid polymer electrolyte and a hydrocarbon solid polymer electrolyte, and a catalyst, and the electrolyte is a solution or a dispersion liquid obtained by being dissolved into a favorable solvent, and then substituted with the mixed solvent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polymer electrolyte fuel cell electrode ink.

  The MEA (electrolyte membrane-electrode assembly) for polymer electrolyte fuel cells is well known (for example, see Non-Patent Document 1).

As a solvent for catalyst ink for catalyst layer preparation using a hydrocarbon electrolyte as a binder when manufacturing MEA, a highly polar solvent such as N-methylpyrrolidone or dimethyl hydride having high solubility of hydrocarbon electrolyte Is used (for example, refer to Patent Document 1).
“Research and development of highly durable hydrocarbon electrolyte membranes for polymer electrolyte fuel cells”, New Energy and Industrial Technology Development Organization, March 2004 JP 2002-298855 A

  High polar solvents such as N-methylpyrrolidone and dimethyl sulfoxide have a high boiling point, so it is difficult to completely remove them when adsorbed on the platinum surface as an electrode catalyst, and the power generation performance of the battery may be reduced by poisoning the catalyst. was there.

  In addition, since a highly polar solvent has high solubility in a solid polymer electrolyte, forming a catalyst layer using this solvent increases the uniformity of the polymer electrolyte used as a binder, resulting in permeation of the reaction gas. There is a risk that the performance will be reduced. The platinum-supported carbon fine particles used as the electrode catalyst are present in the catalyst layer in a state of being encapsulated in a polymer electrolyte. Therefore, if a binder with low gas permeability is used, the reaction gas does not reach the catalyst, and the battery There was a possibility that the power generation performance would decrease.

  Accordingly, an object of the present invention is to provide an ink for a polymer electrolyte fuel cell electrode in which such problems are eliminated.

  Another object of the present invention is to provide a method for producing an ink for a polymer electrolyte fuel cell electrode, which has solved such problems.

  The present invention relates to a fuel cell catalyst ink comprising a mixed solvent of water and alcohol, a non-fluorine-based solid polymer electrolyte, and a catalyst.

  The present invention also includes a mixed solvent of water and alcohol, at least one electrolyte selected from the group consisting of a non-fluorine-based solid polymer electrolyte and a hydrocarbon-based solid polymer electrolyte, and a catalyst, The present invention relates to a catalyst ink for fuel cells, wherein the electrolyte is a solution or dispersion obtained by dissolving the electrolyte in a good solvent and then substituting with the mixed solvent.

  According to the solid polymer fuel cell electrode ink of the present invention, catalyst poisoning can be reduced by using a mixed solvent of water and alcohol having a low boiling point as the solvent of the catalyst ink.

  Further, according to the solid polymer fuel cell electrode ink of the present invention, by using a mixed solvent of water and alcohol having low solubility in the solid polymer electrolyte, the uniformity of the polymer electrolyte used as the binder is increased. As a result, the permeability of the reaction gas is improved, and the power generation performance of the obtained battery can be improved.

  Perfluorosulfonic acid electrolytes typified by Nafion (registered trademark) are currently considered to be the materials closest to commercialization in PEFC (solid polymer fuel cells). Nafion is excellent in PEFC performance and can provide a dispersion solution with excellent handling properties as a catalyst ink for electrodes.

  Therefore, the present invention is directed to a catalyst ink for electrodes having excellent handling properties even when a Nafion substitute material is used.

(First embodiment of the present invention)
The fuel cell catalyst ink of the present invention contains a mixed solvent of water and alcohol, a non-fluorine solid polymer electrolyte, and a catalyst.

  The mixed solvent of water and alcohol that can be used in the present invention is not particularly limited as long as it is a mixed solvent of water such as ion-exchanged water or distilled water and alcohol such as a lower alcohol having 1 to 4 carbon atoms. Used without. The mixing ratio of water and alcohol is not particularly limited as long as the non-fluorinated solid polymer electrolyte can be dissolved. For example, the alcohol is mixed in an amount of 0.9 to 0. A ratio of 4 (parts by mass) can be mentioned. Here, regarding the solubility of the non-fluorinated solid polymer electrolyte, it is desirable to completely dissolve it in a mixed solvent, but the obtained catalyst ink is obtained by a known method such as a screen printing method, a transfer pressure bonding method, or a spray method. As long as a sheet can be formed and the sheet can be transferred to a solid polymer film, a slurry in which a part of the electrolyte is dispersed may be used. Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, i-butanol, and t-butanol. Alcohols may be used alone or in combination. By using such an alcohol, the solvent evaporation during the application of the catalyst ink is appropriate, so that the evaporation rate is not too high and the ink application is not difficult, and the evaporation rate is too low and the drying time is too long. Therefore, there is an advantage that workability is not lowered.

  The non-fluorine solid polymer electrolyte that can be used in the present invention is not particularly limited as long as it is a solid polymer electrolyte excluding fluorine-containing polymer such as perfluorosulfonic acid electrolyte, Polyarylene hydrocarbon-based solid polymer electrolytes having a polyarylene main chain skeleton such as sulfonated poly (4-phenoxybenzoyl-1,4-phenylene) (S-PPBP) or polyarylene ether sulfone (SPES); polyimide, poly Examples include adducts obtained by adding a sulfonic acid group to benzimidazole (PBI), polybenzoxazole (PBO), polyether ether ketone (PEEK), and the like. Polyarylene refers to a compound in which aromatic compounds are continuously bonded. Here, the non-fluorine-based solid polymer electrolyte is required to function as a bonding material.

  The catalyst that can be used in the present invention is not particularly limited as long as it can be used as a catalyst for a fuel cell. For example, a catalyst in which a predetermined amount of noble metal such as platinum or platinum / ruthenium is supported on carbon. Particles.

  The catalyst ink for a fuel cell of the present invention can be prepared by using a pulverizer such as a homogenizer with the above-mentioned mixed solvent, non-fluorinated solid polymer electrolyte, and catalyst in a predetermined ratio. The catalyst ink may contain a thickener such as ethylene glycol or glycerin. Here, the predetermined ratio is not particularly limited as long as the catalyst ink can be applied to the solid polymer film. For example, the mass ratio of the carbon constituting the catalyst and the non-fluorine solid polymer electrolyte is 1: 0.8, and a mixed solvent solution containing 3% by mass of a non-fluorinated solid polymer electrolyte may be used.

  In addition, the ratio of the mixed solvent, the electrolyte, and the catalyst is usually in the range of 4 to 99: 1: 1.5 to 5 (mass ratio). By setting within this range, the power generation performance can be exhibited more effectively.

(Second embodiment of the present invention)
The catalyst ink for fuel cells of the present invention comprises a mixed solvent of water and alcohol, at least one electrolyte selected from the group consisting of a non-fluorine solid polymer electrolyte and a hydrocarbon solid polymer electrolyte, a catalyst, Here, the electrolyte is a solution or dispersion obtained by dissolving in a good solvent and then substituting with the mixed solvent.

  The mixed solvent of water and alcohol that can be used in the present invention is not particularly limited as long as it is a mixed solvent of water such as ion-exchanged water or distilled water and alcohol such as a lower alcohol having 1 to 4 carbon atoms. Used without. The mixing ratio of water and alcohol is not particularly limited as long as the non-fluorinated solid polymer electrolyte can be dissolved. For example, the alcohol is mixed in an amount of 0.9 to 0. A ratio of 4 parts by mass is mentioned. Here, regarding the solubility of the non-fluorinated solid polymer electrolyte, it is desirable to completely dissolve it in a mixed solvent, but the obtained catalyst ink is obtained by a known method such as a screen printing method, a transfer pressure bonding method, or a spray method. As long as a sheet can be formed and the sheet can be transferred to a solid polymer film, a slurry in which a part of the electrolyte is dispersed may be used. Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, i-butanol, and t-butanol. Alcohols may be used alone or in combination. By using such an alcohol, the solvent evaporation during the application of the catalyst ink is appropriate, so that the evaporation rate is not too high and the ink application is not difficult, and the evaporation rate is too low and the drying time is too long. Therefore, there is an advantage that workability is not lowered.

  The non-fluorine-based solid polymer electrolyte and the hydrocarbon-based solid polymer electrolyte may be used alone or in combination. The polymer electrolyte is required to function as a bonding material.

  The non-fluorinated solid polymer electrolyte that can be used in the present invention is not particularly limited as long as it is a solid polymer electrolyte excluding a solid polymer containing fluorine such as perfluorosulfonic acid electrolyte, A polyarylene hydrocarbon-based solid polymer electrolyte having a polyarylene main chain skeleton such as sulfonated poly (4-phenoxybenzoyl-1,4-phenylene) (S-PPBP) or polyarylene ether sulfone (SPES); Examples include adducts obtained by adding a sulfonic acid group to polybenzimidazole (PBI), polybenzoxazole (PBO), polyether ether ketone (PEEK), and the like. Polyarylene refers to a compound in which aromatic compounds are continuously bonded.

  Examples of the hydrocarbon solid polymer electrolyte that can be used in the present invention include other solid polymer electrolytes excluding fluorinated solid polymer electrolytes and non-fluorinated solid polymer electrolytes. Or a sulfonated olefin / styrene-based solid polymer electrolyte.

  The catalyst that can be used in the present invention is not particularly limited as long as it can be used as a catalyst for a fuel cell. For example, a catalyst in which a predetermined amount of noble metal such as platinum or platinum / ruthenium is supported on carbon. Particles.

  When the solid polymer electrolyte cannot be easily dissolved directly in a mixed solvent of water and alcohol, or when it is difficult, the polymer electrolyte is previously dissolved in a good solvent with respect to the polymer electrolyte. Then, it is desirable to replace with a mixed solvent of water and alcohol to obtain a solution or dispersion. By passing through such means, it becomes possible to substantially dissolve the solid polymer electrolyte having poor solubility in the mixed solvent. Of course, even if this method is applied to a soluble solid polymer electrolyte, it can be said that it does not adversely affect the performance of the resulting catalyst ink.

  Here, the good solvent is a boiling point equal to or lower than the boiling point of the alcohol constituting the mixed solvent, preferably lower by 10 ° C., more preferably lower by 20 ° C., or a volatility equal to or higher than the volatility of the alcohol. A compound having is preferred.

  The good solvent is preferably an organic solvent having an affinity for water and alcohol. This is because if the good solvent does not have an affinity for water and alcohol, solvent replacement becomes difficult. Examples of good solvents include tetrahydrofuran (THF), oxetane (boiling point 47 ° C), ethyloxirane (boiling point 63 ° C), 2,2-dimethyloxirane (boiling point 55 ° C), 2,3-dimethyloxirane (boiling point 66 ° C). And cyclic ethers.

  Here, for the solvent substitution, a known method can be adopted. For example, the following method can be mentioned. After the electrolyte is dissolved in a good solvent, a mixed solvent containing a predetermined amount of water and alcohol is added thereto. The amount of the good solvent added is not particularly limited as long as the electrolyte can be dissolved, but it is usually set to the same level as the concentration of the catalyst ink to be obtained. When the solubility is poor, there is no limitation on adding more good solvent. The predetermined amount of the mixed solvent is not particularly limited as long as the desired catalyst ink can be obtained, but it is usually preferably about the same as the amount of the good solvent added. Next, bubbling is performed using an inert gas such as nitrogen gas to volatilize the good solvent from the solution. Further, in bubbling, the bubbling efficiency may be improved by using a vacuum pump, an aspirator, or the like to reduce the atmosphere. Furthermore, volatility may be increased by heating. In addition, it is preferable to perform the temperature in that case normally in the range which does not exceed the boiling point of a good solvent from normal temperature. This is because, at a temperature exceeding the boiling point, the reaction is too intense and it is difficult to determine the end of bubbling. Note that the bubbling is completed with reference to a state where the solution is liquid but the mass of the solution hardly changes. By bubbling, not only the good solvent but also the alcohol volatilizes at the same time, so the mixed solvent is added and the concentration of the charged electrolyte is set to a predetermined concentration.

  In addition, it is preferable that the ratio of a mixed solvent, electrolyte, and a catalyst exists in the range of 4-99: 1: 1.5-5 (mass ratio). By setting within this range, the power generation performance can be exhibited more effectively.

  As described above, the fuel cell catalyst ink of the present invention can be prepared by a solvent replacement method. The catalyst ink may contain a thickener such as ethylene glycol or glycerin.

  Thus, even a solid polymer electrolyte having extremely low solubility in a mixed solvent containing water and alcohol can be easily dissolved. Therefore, a wide range of solid polymer electrolytes can be used.

Example 1
(Preparation of electrolyte solution)
In a 1-propanol / H ₂ O mixed solution of 1-propanol: H ₂ O = 1: 1 (mass ratio), powder of S-PES (sulfonated polyethersulfone) is 3.0% by mass as a whole. The powder was completely dissolved while stirring under reflux at 70 ° C.

(Catalyst ink preparation)
<Catalyst ink for cathode> Fine particles of Pt-supported carbon (platinum supported amount: 50 mass%) in the previously prepared S-PES solution, and the mass ratio of carbon to PES is carbon: S-PES = 1: 0.8. After mixing as described above, a cathode catalyst ink was produced in a homogenizer (pulverizer) for about 3 hours.

  <Anode Catalyst Ink> A commercially available Nafion solution (5% by mass solution manufactured by Aldrich) was used to prepare an anode catalyst ink in the same procedure as the cathode catalyst ink.

(Catalyst layer transfer sheet production)
The ink prepared as described above was applied onto a Teflon sheet used as a mount using a screen printer to prepare a catalyst layer transfer sheet for cathode and anode. As the mount, a PET (polyethylene terephthalate) sheet or the like is excellent in addition to the Teflon sheet. Coating and drying were repeated until the Pt carrying amount reached 0.4 mg / cm ² to prepare a catalyst layer transfer sheet having a predetermined platinum amount.

(Catalyst layer transfer)
When the catalyst layer surface of the cathode and anode catalyst layer transfer sheets prepared as described above is sprayed and infiltrated with ethanol, and the catalyst layer surface has dried, the S-PES electrolyte membrane is sandwiched between these transfer sheets, Hot pressing was performed at 130 ° C., 7 MPa, and a holding time of 10 minutes. The reason for infiltrating with ethanol is to make the catalyst layer and membrane electrolyte flexible and to facilitate the transfer of the catalyst layer.

  After cooling, the mount of the transfer sheet was peeled off to produce a membrane-catalyst layer assembly.

  In this example, a non-fluorine solid polymer electrolyte was used only for the cathode binder, and ordinary Nafion was used for the anode binder. This is because it is more convenient to use Nafion as the anode binder for CV (cyclic voltammetry) measurement. Both binders are made of a non-fluorinated solid polymer electrolyte. Needless to say, there is essentially no change.

(Comparative Example 1)
A membrane-catalyst layer assembly was produced in the same manner as in Example 1 except that N-methylpyrrolidone (NMP) was used as the solvent for S-PES.

(Comparative Example 2)
Membrane-catalyst layer assembly in the same manner as in Example 1 except that NMP was used as a solvent for S-PES and the prepared cathode catalyst layer transfer sheet was soaked in 1 mol / L dilute hydrochloric acid for 24 hours. Was made.

(Example 2)
(Preparation of electrolyte solution)
The powder of the sulfonated styrene-butadiene copolymer was dissolved in THF (tetrahydrofuran) so as to be 5% by mass. After dissolution, 1-propanol (boiling point: 97 ° C.) / Water mixed solvent (mixing mass ratio 1: 1) of the same mass as THF was added to this solution and stirred, then the solution was heated to 40 ° C., and the mass of the solution changed substantially. Heating continued until no longer. By this heating, highly volatile (boiling point: 66 ° C.) THF was selectively evaporated to prepare a 5 mass% 1-propanol / water mixed solvent solution of a sulfonated styrene-butadiene copolymer.

  A membrane-catalyst layer assembly was produced in the same manner as in Example 1.

(Evaluation of membrane-catalyst layer assembly)
The membrane-catalyst layer assembly produced as described above was sandwiched between carbon papers and then incorporated into a power generation evaluation cell to conduct a power generation test.

(Power generation conditions)
Power generation is performed by supplying pure hydrogen to the anode and air (both atmospheric pressure) to the cathode. The power generation conditions are a cell temperature of 90 ° C., an anode gas relative humidity of 90%, a cathode gas relative humidity of 50%, a hydrogen utilization rate of 67%, and an air utilization rate of 40%.

  FIG. 1 is a graph showing the results of a power generation test. In FIG. 1, since Comparative Example 1 could not generate power, the results are not shown.

  In FIG. 1, the cell produced using the membrane-catalyst layer assembly obtained in Comparative Example 1 could not generate power. This is probably because the catalyst poisoning was enormous.

  In the cell using the catalyst layer transfer sheet (Comparative Example 2) soaked in dilute hydrochloric acid for 24 hours, power generation was possible, but sufficient power generation was not obtained. Compared to Comparative Example 1, it is considered that NMP remaining in the catalyst layer was eluted into the diluted hydrochloric acid by the amount immersed in diluted hydrochloric acid, and the catalyst poisoning was reduced. In the experiment described in Non-Patent Document 1 given as a conventional example, it is presumed that power generation is possible because the catalyst layer produced using the NMP solvent is immersed in dilute sulfuric acid for 17 hours.

On the other hand, in the cell using the membrane-catalyst layer assembly of Example 1 using an alcohol / water mixed solvent, a sufficient power generation amount of 0.461 V could be obtained at a current density of 1 A / cm ² . This is because the catalyst poisoning did not occur because a highly polar solvent such as NMP was not used, and the uniformity of S-PES used as the binder was lowered and the permeability of the reaction gas was increased. The performance is thought to have improved.

That is, the voltage value with a current density of 0.1 A / cm ² or less reflects the electrode reaction, and the faster the electrode reaction, the higher the voltage. The voltage at 0.08 A / cm ² is 0.649 V in Comparative Example 1, whereas it is as high as 0.690 V in Comparative Example 1, and the electrode reaction is improved. The effective catalyst surface area of the platinum electrode catalyst obtained from the CV, whereas Comparative Example 1 is 32.6m ² / g, has been greatly increased and 69.6m ² / g in Example 1, catalyst poisoning of Has been improved.

Furthermore, the voltage value with a current density of 0.1 A / cm ² or more reflects the gas diffusibility of the electrode catalyst layer, and the voltage becomes higher as the gas diffusibility is better. The voltage at 0.4 A / cm ² is 0.317 V in Comparative Example 1, whereas it is as high as 0.553 V in Example 1, suggesting that the gas diffusibility of the electrode catalyst layer is improved. The gas diffusivity of the electrode catalyst layer depends on the pore structure of the electrode catalyst layer and the gas permeability of the polymer used as the binder, but the change in the pore structure of the catalyst layers of Comparative Example 1 and Example 1 is SEM. Since it is not recognized as long as observation is performed, it is presumed that the gas permeability of the polymer has changed.

  The result of Example 2 was almost the same as that of Example 1.

  In general, when a polymer is dissolved in a solvent with good solubility, the polymer chain has good dispersibility. Therefore, the polymer produced by removing the solvent from the solution has a dense structure, whereas the polymer has a soluble structure. When dissolved in a bad solvent, the dispersibility of the polymer chain is poor, and therefore the polymer produced by removing the solvent from the solution is considered to have a rough structure. Since the non-fluorinated solid polymer electrolyte used this time is not very soluble in water / alcohol mixed solvent, the binder in the catalyst layer is considered to have a rough structure, resulting in improved gas permeability, It is estimated that the voltage on the high current side has improved.

It is a graph which shows the result of the electric power generation test regarding the membrane-catalyst layer assembly produced by the example and the comparative example.

Claims (9)

  A fuel cell catalyst ink comprising a mixed solvent of water and alcohol, a non-fluorine solid polymer electrolyte, and a catalyst.   The catalyst ink according to claim 1, wherein the non-fluorine-based solid polymer electrolyte is a polyarylene hydrocarbon-based solid polymer electrolyte having a polyarylene main chain skeleton.   The catalyst ink according to claim 2, wherein the polyarylene hydrocarbon solid polymer electrolyte is sulfonated poly (4-phenoxybenzoyl-1,4-phenylene) or polyarylene ether sulfone.   The mixed solvent is at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, i-butanol, and t-butanol. The catalyst ink according to any one of the above.   A mixed solvent of water and alcohol, at least one electrolyte selected from the group consisting of a non-fluorine-based solid polymer electrolyte and a hydrocarbon-based solid polymer electrolyte, and a catalyst, wherein the electrolyte is good A catalyst ink for a fuel cell, which is a solution or dispersion obtained by dissolving in a solvent and then substituting with the mixed solvent.   The catalyst ink according to claim 5, wherein the good solvent has a boiling point equal to or lower than a boiling point of the alcohol, or a volatility equal to or lower than a volatility of the alcohol.   The catalyst ink according to claim 5 or 6, wherein the good solvent is an organic solvent having an affinity for water and alcohol.   The electrolyte is dissolved in the good solvent, the mixed solvent is added, the good solvent is volatilized by bubbling with an inert gas, and the mixed solvent is added so that the charged electrolyte has a predetermined concentration. The catalyst ink according to any one of claims 5 to 7.   The catalyst ink according to any one of claims 5 to 8, wherein the hydrocarbon solid polymer electrolyte is an olefin / styrene copolymer.

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