JP2019102345A - Catalyst ink for fuel cell, and manufacturing method thereof - Google Patents

Abstract

To provide a catalyst ink for a fuel cell, which is arranged so that the worsening of the catalyst activity attributed to the change in the composition of metal catalyst particles can be suppressed.SOLUTION: In a catalyst ink 900 for a fuel cell, the ion-exchange group concentration of an ionomer 601 which is located in a region in close proximity to an exposed surface of a metal catalyst particle 400 exposed from a carrier particle 300, which is in contact with the exposed surface of the metal catalyst particle 400 and which covers the exposed surface of the metal catalyst particle 400 is lower than the ion-exchange group concentration of an ionomer 701 which is located in a region more distant from the exposed surface of the metal catalyst particle 400 than the ionomer 601, and which covers the exposed surface of the metal catalyst particle 400 and a region in close proximity to the metal catalyst particle 400 in the surface of the carrier particle 300 with the ionomer 601 interposed between itself and the exposed surface of the metal catalyst particle 400 without touching the exposed surface of the metal catalyst particle 400.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell used for portable power sources, power sources for portable devices, power sources for electric vehicles, household cogeneration systems, and the like.

  A conventional common fuel cell includes an electrolyte membrane-electrode assembly in which an anode and a cathode are formed on both sides of an electrolyte membrane, and a fuel gas containing hydrogen is electrochemically reacted with an oxidant containing oxygen. Generate electricity.

  The electrochemical reaction of the fuel cell is an oxidation reaction of the fuel gas supplied to the anode to form electrons and protons, the electrons are transferred to the cathode via an external circuit, and the protons are passed via the electrolyte membrane Move to the cathode. Then, the oxidant gas supplied to the cathode is generated by reduction reaction with protons and electrons formed at the anode.

  The anode and the cathode have an electrocatalyst and an electrocatalyst layer consisting of an ionomer. The electrode catalyst has metal catalyst particles in which two or more types of transition metals supported in a highly dispersed manner on the surface of carrier particles are alloyed. The ionomer has a proton-conductive acidic ion exchange group.

  In order to supply the reaction gas and protons to the electrode catalyst that is to be an electrochemical reaction site, the electrode catalyst layer is formed of aggregates of an ionomer thinly coated with an ionomer, so that aggregates and aggregates are formed. There is a continuous hole between them.

  As one example of such an electrode catalyst layer, there is proposed an electrolyte membrane-electrode assembly as shown in Patent Document 1, which uses an ionomer having a large number of acidic ion exchange groups for the electrode catalyst layer.

  In this electrolyte membrane-electrode assembly, the ion channels for transporting protons in the ionomer can be increased without increasing the thickness of the ionomer coating on the electrode catalyst, so that the reaction gas for the electrode catalyst of the electrode catalyst layer can be increased. The proton conductivity in the electrode catalyst layer is improved while maintaining the diffusibility of

WO 2009/119017

  However, in the conventional configuration, the metal catalyst particles of the electrode catalyst contained in the fuel cell catalyst ink for forming the electrode catalyst layer are in direct contact with the acidic ion exchange groups of the ionomer.

  Thereby, the composition of the metal catalyst particles is changed, in particular, by ionizing part of the metal catalyst particles and eluting into the ionomer. The compositional change of the metal catalyst particles has a problem that the catalytic activity of the metal catalyst particles is reduced.

  The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a catalyst ink for a fuel cell in which a decrease in catalytic activity due to a change in composition of metal catalyst particles is suppressed and a method for producing the same.

  In order to solve the above-mentioned conventional problems, a fuel cell catalyst ink according to the present invention comprises a fuel cell comprising an electrode catalyst having metal catalyst particles supported on carrier particles, and an ionomer having an acidic ion exchange group. Catalyst ink, wherein the surfaces of the metal catalyst particles and the carrier particles are coated with an ionomer, and the concentration of ion exchange groups of the ionomer in the region close to the surface of the metal catalyst particles covers the surface of the carrier particles The catalyst ink for a fuel cell is characterized in that the concentration is lower than the ion exchange group concentration of the ionomer.

  As a result, the amount of acidic ion exchange groups directly contacting the metal catalyst particles constituting the electrode catalyst in the fuel cell catalyst ink is small, so that the catalyst for fuel cells is inhibited from the decrease in the catalytic activity due to the composition change of the metal catalyst particles. Ink can be provided.

  In the method for producing a catalyst ink for a fuel cell according to the present invention, an electrode catalyst in which metal catalyst particles are supported on carrier particles, an ionomer having an acidic ion exchange group, a base, and a solvent are mixed. A first step of coating the ionomer on the electrode catalyst, and a second step of removing ion exchange groups from the ionomer in a region close to the surface of the metal catalyst particles; It is a manufacturing method.

  As a result, since the base is coordinated to the acidic ion exchange group of the ionomer in the fuel cell catalyst ink, the acidity of the ion exchange group of the ionomer can be reduced.

  For this reason, the concentration of the acidic ion exchange groups of the ionomer coated on the surface of the metal catalyst particles is lowered. As a result, the acidic ion exchange group in direct contact with the metal catalyst particles constituting the electrode catalyst in the fuel cell catalyst ink is reduced, and the catalyst for the fuel cell is suppressed in the reduction of the catalyst activity due to the composition change of the metal catalyst particles The ink can be manufactured.

  The catalyst ink for a fuel cell of the present invention has a small amount of acidic ion exchange groups in direct contact with the metal catalyst particles, so that the decrease in the catalytic activity due to the composition change of the metal catalyst particles is suppressed.

  Therefore, by forming a fuel cell using the catalyst ink for a fuel cell of the present invention, it is possible to suppress a decrease in the power generation efficiency of the fuel cell.

FIG. 2 is a cross-sectional view showing a schematic configuration of a fuel cell catalyst ink according to Embodiment 1 of the present invention. FIG. 5 is a cross-sectional view showing a schematic configuration of a fuel cell catalyst ink according to Embodiment 2 of the present invention. Flow chart showing manufacturing process of fuel cell catalyst ink according to Embodiment 2 of the present invention FIG. 2 is a cross-sectional view showing a schematic configuration of a fuel cell according to Embodiment 2 of the present invention. FIG. 6 is a cross-sectional view showing a schematic configuration of a fuel cell catalyst ink according to Embodiment 3 of the present invention. Flowchart showing manufacturing process of fuel cell catalyst ink according to Embodiment 3 of the present invention Sectional view showing a schematic configuration of a fuel cell according to Embodiment 3 of the present invention FIG. 6 is a cross-sectional view showing a schematic configuration of a fuel cell catalyst ink according to Embodiment 4 of the present invention. Flowchart showing manufacturing process of fuel cell catalyst ink according to Embodiment 4 of the present invention FIG. 6 is a cross-sectional view showing a schematic configuration of a fuel cell according to Embodiment 4 of the present invention. FIG. 6 is a cross-sectional view showing a schematic configuration of a fuel cell catalyst ink according to Embodiment 5 of the present invention. Flowchart showing manufacturing steps of fuel cell catalyst ink according to Embodiment 5 of the present invention FIG. 6 is a cross-sectional view showing a schematic configuration of a fuel cell according to Embodiment 5 of the present invention.

  The first invention is a fuel cell catalyst ink comprising an electrode catalyst in which metal catalyst particles are supported on carrier particles, and an ionomer having an acidic ion exchange group, which comprises metal catalyst particles and carrier particles. The surface is coated with an ionomer, and the ion exchange group concentration of the ionomer in the area close to the surface of the metal catalyst particle is characterized by being lower than the ion exchange group concentration of the ionomer in the area covering the surface of the carrier particle. Fuel cell catalyst ink.

  Since there are few acidic ion exchange groups directly contacted to metal catalyst particles by this, the fall of the catalyst activity by composition change of metal catalyst particles can be controlled.

  In the second invention, the electrocatalyst is coated with an ionomer by mixing an electrocatalyst in which metal catalyst particles are supported on a carrier particle, an ionomer having an acidic ion exchange group, a base, and a solvent. A method for producing a fuel cell catalyst ink, comprising: one step; and a second step of removing ion exchange groups from an ionomer in a region close to the surface of the metal catalyst particles.

  Thereby, since the base is coordinated to the acidic ion exchange group of the ionomer, the acidity of the ion exchange group of the ionomer can be reduced. For this reason, the concentration of the acidic ion exchange groups of the ionomer coated on the surface of the metal catalyst particles is lowered. As a result, direct contact of the acidic ion exchange group with the metal catalyst particles can be reduced, and therefore, a fuel cell catalyst ink can be manufactured in which the decrease in catalyst activity due to the composition change of the metal catalyst particles is suppressed.

  In the third invention, in particular, in the first step in the second invention, the ionomer, the base and the solvent are first mixed, and then the electrode catalyst is mixed.

  As a result, the ratio of coordination of the base to the ion exchange group of the ionomer is increased, and direct contact of the acidic ion exchange group of the ionomer with the metal catalyst particle is further reduced, and catalytic activity due to composition change of the metal catalyst particle The drop can be further suppressed.

  In the fourth invention, in particular, the concentration of the base in the second or third invention is higher than the concentration of ion exchange groups possessed by the ionomer.

  As a result, the ratio of coordination of the base to the ion exchange group of the ionomer is further increased, and the direct contact of the acidic ion exchange group of the ionomer with the metal catalyst particle is further reduced. Can be further suppressed.

  In the fifth invention, in particular, in the first step in the second invention, the electrocatalyst, the base and the solvent are first mixed, and then the ionomer is mixed.

  As a result, the base is coordinated to the surface of the metal catalyst particles, whereby the direct contact of the acidic ion exchange groups of the ionomer with the metal catalyst particles is reduced, and the catalyst activity is reduced due to the composition change of the metal catalyst particles. Can be suppressed.

  According to a sixth aspect of the present invention, in the second step according to any one of the second to fifth aspects, ion exchange groups are removed from the ionomer in a region close to the surface of the metal catalyst particles by electrophilic substitution reaction. It is.

  This enables selective cleavage of an ion exchange group having a molecular chain with high electron density and low binding energy, thereby improving the selectivity and reaction rate of the reaction site of the ion exchange group removal reaction. As a result, the fuel cell catalyst ink can be produced efficiently.

  According to a seventh invention, in addition to any one of the second to sixth inventions, a third step of removing a base contained in a fuel cell catalyst ink is provided.

  As a result, the base contained in the ionomer is removed, so the acidity of the ion exchange group of the ionomer can be increased, and the reduction in proton conductivity of the ionomer due to the base can be suppressed.

Embodiment 1
FIG. 1 is a cross-sectional view showing a schematic configuration of a fuel cell catalyst ink according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the fuel cell catalyst ink 900 of the present embodiment comprises an electrode catalyst 500 having metal catalyst particles 400 supported on the surface of carrier particles 300, an ionomer 800, and a solvent 30. ing.

  The ionomer 800 is located in a region close to the exposed surface of the metal catalyst particle 400 exposed from the carrier particle 300, and an ionomer 600 in contact with the exposed surface of the metal catalyst particle 400 to cover the exposed surface of the metal catalyst particle 400; Located outside of 600 (area farther from the exposed surface of the metal catalyst particle 400 than the ionomer 600) and between the exposed surface of the metal catalyst particle 400 and the exposed surface of the metal catalyst particle 400 without contacting the exposed surface of the metal catalyst particle 400 It consists of an ionomer 700 which is interposed to cover the exposed surface of the metal catalyst particles 400 and the area of the surface of the carrier particles 300 adjacent to the metal catalyst particles 400.

  The concentration of ion exchange groups of ionomer 600 is lower than the concentration of ion exchange groups of ionomer 700. In other words, the concentration of ion exchange groups of ionomer 700 is higher than the concentration of ion exchange groups of ionomer 600.

  Here, the fuel cell catalyst ink 900 according to the present embodiment and the fuel cell using the fuel cell catalyst ink 900 will be described in more detail.

  The solvent 30 is a solvent in which water and ethanol are mixed in a mass ratio of 1: 1. The carrier particles 300 are carbon particles, and the metal catalyst particles 400 are platinum Colt alloy catalyst particles. The platinum-cobalt alloy catalyst particles are platinum-cobalt alloy catalyst-supporting carbon carried 52 wt% on carbon particles.

  The ionomer 700 is a perfluorosulfonic acid, and the ion exchange group is an acidic sulfonic acid group. The ionomer 600 is a perfluorosulfonic acid of the ionomer 700 with some of the ion exchange groups removed.

The molar concentration of ion exchange groups of the ionomer 700 is 200 mol / m ³ . The molar concentration of the amount of ion exchange groups of the ionomer 600 is 0.2 mol / m ³ . The amount of ionomer 800 is the same as that of carrier particles 300.

  As described above, the fuel cell catalyst ink 900 according to Embodiment 1 includes the electrode catalyst 500 in which the metal catalyst particles 400 are supported on the carrier particles 300, and the ionomer 800 having an acidic ion exchange group. A catalyst ink 900 for a fuel cell, wherein the surfaces of the metal catalyst particles 400 and the carrier particles 300 are coated with an ionomer 800 (ionomer 600 and ionomer 700) and located in a region close to the exposed surface of the metal catalyst particles 400 The concentration of ion exchange groups of the ionomer 600 in contact with the exposed surface of the catalyst particle 400 and covering the exposed surface of the metal catalyst particle 400 is outside the ionomer 600 (area farther from the exposed surface of the metal catalyst particle 400 than the ionomer 600) Exposure of the metal catalyst particles 400 without contacting the exposed surface of the metal catalyst particles 400 Characterized in that the concentration of ion exchange groups of the ionomer 700 covering an area adjacent to the metal catalyst particles 400 on the exposed surface of the metal catalyst particles 400 and the surface of the carrier particles 300 with the ionomer 600 interposed between the surfaces. Do.

  As a result, since there are few acidic ion exchange groups directly in contact with the metal catalyst particles 400, it is possible to suppress a decrease in catalyst activity due to a change in composition of the metal catalyst particles 400.

  In the present embodiment, the metal catalyst particle 400 is a platinum-cobalt alloy catalyst particle, but in addition to this, metals such as platinum, ruthenium, palladium, iron, copper, chromium, cobalt, nickel, manganese and the like and These alloys can be used.

  In this embodiment, although the ionomer 700 is a perfluorosulfonic acid, in addition to this, an ionomer containing an ion exchange group other than a sulfonic acid group in a fluorine compound, a sulfonic acid group in a hydrocarbon or It is also possible to use an ionomer in which an ion exchange group other than a sulfonic acid group is introduced.

Second Embodiment
FIG. 2 is a cross-sectional view showing a schematic configuration of a fuel cell catalyst ink according to a second embodiment of the present invention. FIG. 3 is a flow chart showing steps of producing a catalyst ink for a fuel cell according to a second embodiment of the present invention. FIG. 4 is a cross-sectional view showing a schematic configuration of a fuel cell according to Embodiment 2 of the present invention.

  As shown in FIG. 2, the fuel cell catalyst ink 901 according to the present embodiment comprises an electrode catalyst 500 having metal catalyst particles 400 supported on the surface of carrier particles 300, an ionomer 801, and a solvent 30. ing.

  The ionomer 801 is located in a region close to the exposed surface of the metal catalyst particle 400 exposed from the carrier particle 300 and is in contact with the exposed surface of the metal catalyst particle 400 to cover the exposed surface of the metal catalyst particle 400; Located outside 601 (region farther from the exposed surface of the metal catalyst particle 400 than the ionomer 601), the ionomer 601 is interposed between the exposed surface of the metal catalyst particle 400 without contacting with the exposed surface of the metal catalyst particle 400 It is composed of an ionomer 701 which covers the exposed surface of the metal catalyst particle 400 and the region of the surface of the carrier particle 300 adjacent to the metal catalyst particle 400.

  The concentration of ion exchange groups of the ionomer 601 is lower than the concentration of ion exchange groups of the ionomer 701. In other words, the concentration of ion exchange groups of the ionomer 701 is higher than the concentration of ion exchange groups of the ionomer 601.

Here, the fuel cell catalyst ink 901, the method for producing the fuel cell catalyst ink 901, and the fuel cell 101 using the fuel cell catalyst ink 901 in the present embodiment will be described in more detail.

  The solvent 30 is a solvent in which water and ethanol are mixed in a mass ratio of 1: 1. The carrier particles 300 are carbon particles, and the metal catalyst particles 400 are platinum Colt alloy catalyst particles. The platinum-cobalt alloy catalyst particles are platinum-cobalt alloy catalyst-supporting carbon carried 52 wt% on carbon particles.

  The ionomer 701 is a perfluorosulfonic acid, and the ion exchange group is an acidic sulfonic acid group. In addition, the ionomer 601 is obtained by removing a part of ion exchange groups from the perfluorosulfonic acid of the ionomer 701.

The molar concentration of ion exchange groups of the ionomer 701 is 200 mol / m ³ . The molar concentration of the amount of ion exchange groups of the ionomer 601 is 40 mol / m ³ . The amount of ionomer 801 is the same as that of carrier particles 300.

  Next, a method of manufacturing the fuel cell catalyst ink 901 according to the present embodiment will be described.

  As shown in FIG. 3, in the method of producing the catalyst ink 901 for fuel cell, the first step of coating the ionomer 701 on the metal catalyst particles 400 exposed from the carrier particles 300 of S11 to S21, and the metal catalyst particles of S31 to S41. By removing the ion exchange groups from the ionomer 701 in the area adjacent to the exposed surface of 400, the ionomer 601 having a lower ion exchange group concentration than the ionomer 701 in the area away from the exposed surface of the metal catalyst particle 400 can be metalized. It has a second step of forming in a region close to the exposed surface of the catalyst particle 400 and a third step of removing a base from the fuel cell catalyst ink 901 from S51 to S61.

  First, in S11, 15 g of the electrode catalyst 500 in platinum amount, 13 g of the ionomer 701, 30 mg of the base, and 200 ml of the solvent 30 are weighed. Ammonia is used as the base. The amount of ammonia added is set such that the molar concentration of ammonium ions formed by ammonia is 1.5 times the molar concentration of ion exchange groups contained in the ionomer 701.

  Next, the electrode catalyst 500, the ionomer 701, and the solvent 30 are dispersed and mixed in S21 to prepare a catalyst dispersion liquid having a low hydrogen ion concentration, in which ammonia is coordinated to the acidic ion exchange group of the ionomer 700. .

Next, in step S31, hydrogen gas containing 4% of oxygen gas is supplied to the catalyst dispersion at a gas flow rate of 8 L / min for 10 minutes, and the ionomer 701 in the region close to the exposed surface of the metal catalyst particles 400 By removing a portion, an ionomer 601 having an ion exchange group concentration of 40 mol / m ³ is produced.

  Next, in step S41, nitrogen gas is supplied to the catalyst dispersion at a gas flow rate of 1 L / min for 1 minute to degas the hydrogen from the catalyst dispersion. Next, the catalyst dispersion liquid filled with nitrogen is subjected to a high temperature and high pressure treatment at 150 ° C. for 3 hours using an autoclave in S51 to oxidize and decompose ammonia contained in the catalyst dispersion liquid.

  Next, the catalyst dispersion liquid is cooled in S61, and the production of the fuel cell catalyst ink 901 is completed.

  Next, the details of the reaction in which ammonia, which is a base contained in the catalyst dispersion liquid of S21, is coordinated to the sulfonic acid group of the ionomer 701 and the hydrogen ion concentration decreases will be described.

  By mixing ammonia into the solvent 30, the water contained in the solvent 30 and the ammonia react with each other to form ammonium ions and hydroxide ions. The formed ammonium ion is coordinated to the outer periphery of the sulfonic acid group by forming an ionic bond with the sulfonic acid group contained in the adjacent ionomer 701.

  As a result, the concentration of hydroxide ions contained in the catalyst dispersion increases, whereby the hydrogen ion concentration of the catalyst dispersion can be reduced.

  Next, details of the reaction for removing ion exchange groups from the ionomer 701 of S31 will be described.

  First, hydrogen and oxygen are reacted on the surface of the metal catalyst particles 400 to form hydrogen peroxide. Next, the formed hydrogen peroxide reacts with cobalt ions present in a region close to the surface of the metal catalyst particles 400 to form hydroxyl radicals which become reactive species of the electrophilic substitution reaction.

  The hydroxyl radical is very reactive, has a feature of reacting with a molecular chain with high electron density and low binding energy.

  The perfluorosulfonic acid used as the ionomer 701 has a low bond energy between carbon and sulfur and a low bond energy between oxygen and hydrogen of the ion exchange group sulfonic acid group, so hydroxyl radicals attack these reaction sites. By doing this, it becomes possible to cleave the sulfonic acid group of the ionomer 701 coated in the region close to the surface of the metal catalyst particle 400.

  Next, a fuel cell 101 using the fuel cell catalyst ink 901 of the present embodiment will be described.

  As shown in FIG. 4, in the fuel cell 101 of the present embodiment, an electrolyte membrane-electrode assembly 91, an anode separator 70a, and a cathode separator 70b are stacked.

  A fuel gas channel 71 a is provided on the surface of the anode separator 70 a facing the electrolyte membrane-electrode assembly 91. Similarly, an oxidant gas channel 71 b is provided on the surface of the cathode separator 70 b facing the electrolyte membrane-electrode assembly 91. The anode separator 70a and the cathode separator 70b use a carbon separator.

  An electrolyte membrane 10 and an anode 61 a and a cathode 61 b sandwiching the electrolyte membrane 10 are provided. For the electrolyte membrane 10, a perfluorosulfonic acid membrane is used. The anode 61 a includes an electrode catalyst layer 81 and a gas diffusion layer 40. The cathode 61 b is composed of an electrode catalyst layer 81 and a gas diffusion layer 40.

The electrode catalyst layer 81 is prepared by applying the catalyst ink 901 for a fuel cell on both sides of the electrolyte membrane 10 so that the amount of platinum is 0.1 mg / cm ² and drying at 60 ° C.

The electrolyte membrane-electrode assembly 91 is thermocompression-bonded at 120 ° C. and 10 kgf / cm ² in a state where the gas diffusion layers 40 are laminated on both sides of the electrolyte membrane 10 having the electrode catalyst layers 81 formed on both sides. The one in which the anode 61 a and the cathode 61 b are bonded to the electrolyte membrane 10 is used.

  The fuel cell 101 generates electric power by the reaction of the fuel gas supplied to the anode 61a and the oxidant gas supplied to the cathode 61b. Hydrogen gas is used as the fuel gas, and air is used as the oxidant gas.

  As described above, the fuel cell catalyst ink 901 according to the second embodiment includes the electrode catalyst 500 in which the metal catalyst particles 400 are supported on the carrier particles 300, and the ionomer 801 having an acidic ion exchange group. A catalyst ink 901 for a fuel cell, wherein the surfaces of the metal catalyst particles 400 and the carrier particles 300 are coated with an ionomer 801 (ionomer 601 and ionomer 701) and located in a region close to the exposed surface of the metal catalyst particles 400 The ion exchange group concentration of the ionomer 601 in contact with the exposed surface of the catalyst particle 400 and covering the exposed surface of the metal catalyst particle 400 is outside the ionomer 601 (region farther from the exposed surface of the metal catalyst particle 400 than the ionomer 601) Exposure of the metal catalyst particles 400 without contacting the exposed surface of the metal catalyst particles 400 Characterized in that the concentration of ion exchange groups of the ionomer 701 covering an area adjacent to the metal catalyst particles 400 on the exposed surface of the metal catalyst particles 400 and the surface of the carrier particles 300 with the ionomer 601 interposed between the surfaces. Do.

  As a result, since there are few acidic ion exchange groups directly in contact with the metal catalyst particles 400 of the fuel cell catalyst ink 901, it is possible to suppress a decrease in catalyst activity due to a change in the composition of the metal catalyst particles 400. Further, by forming the fuel cell 101 using the fuel cell catalyst ink 901 of the present embodiment, it is possible to suppress a decrease in the power generation efficiency of the fuel cell 101.

  Furthermore, in the method for producing the catalyst ink 901 for fuel cell, the electrode catalyst 500 in which the metal catalyst particles 400 are supported on the carrier particles 300, the ionomer 701 having an acidic ion exchange group, a base and the solvent 30 are mixed. , And the second step of removing ion exchange groups from the ionomer 701 in a region close to the surface of the metal catalyst particle 400. .

  Thereby, the acidity of the ion exchange group of the ionomer 701 can be reduced by the base being coordinated to the ion exchange group of the ionomer 701. In addition, the concentration of ion exchange groups of the ionomer 701 coated on the surface of the metal catalyst particles 400 can be lowered. As a result, it is possible to manufacture a fuel cell catalyst ink 901 in which the acidic ion exchange group is not in direct contact with the metal catalyst particles 400, and the decrease in the catalytic activity due to the composition change of the metal catalyst particles 400 is suppressed. .

  Further, by setting the concentration of the base to be higher than the concentration of the ion exchange group possessed by the ionomer 701, the ratio of coordination of the base to the ion exchange group of the ionomer 701 is further increased. The direct contact of the acidic ion exchange groups of the above can be further reduced, and the reduction in catalyst activity due to the composition change of the metal catalyst particles 400 can be further suppressed.

  Further, since the second step of the method for producing the fuel cell catalyst ink 901 is configured to remove ion exchange groups from the ionomer 701 in a region close to the surface of the metal catalyst particles 400 by electrophilic substitution reaction, Since it is possible to selectively cleave an ion exchange group having a molecular chain with high electron density and low binding energy, it is possible to improve the selectivity and reaction rate of the reaction site of the ion exchange group removal reaction. As a result, the fuel cell catalyst ink 901 can be manufactured efficiently.

  In addition, since the base included in the ionomer 801 is removed by the configuration including the third step of removing the base included in the fuel cell catalyst ink 901, the acidity of the ion exchange group of the ionomer 801 is increased. It is possible to suppress the decrease in proton conductivity of the ionomer 801 due to the base.

  In the present embodiment, the metal catalyst particle 400 is a platinum-cobalt alloy catalyst particle, but in addition to this, metals such as platinum, ruthenium, palladium, iron, copper, chromium, cobalt, nickel, manganese and the like and These alloys can be used.

  In this embodiment, although the ionomer 701 is a perfluorosulfonic acid, in addition to this, an ionomer containing an ion exchange group other than a sulfonic acid group in a fluorine compound, a sulfonic acid group in a hydrocarbon or It is also possible to use an ionomer in which an ion exchange group other than a sulfonic acid group is introduced.

  Although ammonia is used as the base in the present embodiment, hydroxides such as alkali metals and alkaline earth metals can also be used besides this.

  Although hydrogen gas and oxygen gas are used in the manufacturing process for removing ion exchange groups in the present embodiment, it is also possible to use an oxide substance and a reduction substance which can form hydrogen peroxide besides this. it can.

  In the present embodiment, a hydroxyl radical is used in the manufacturing process for removing the ion exchange group, but other electrophilic species may be used.

  In the present embodiment, the oxidative decomposition reaction of the base is used in the production process for removing the base, but zirconium phosphate or the like may be added to remove the base by ion exchange.

Third Embodiment
FIG. 5 is a cross-sectional view showing a schematic configuration of a fuel cell catalyst ink according to a third embodiment of the present invention. FIG. 6 is a flowchart showing steps of manufacturing a fuel cell catalyst ink according to a third embodiment of the present invention. FIG. 7 is a cross-sectional view showing a schematic configuration of a fuel cell according to Embodiment 3 of the present invention.

  As shown in FIG. 5, the fuel cell catalyst ink 902 according to the present embodiment includes an electrode catalyst 500 having metal catalyst particles 400 supported on the surface of carrier particles 300, an ionomer 802, a base 22, and a solvent 30. , Is composed of.

  The ionomer 802 is located in a region close to the exposed surface of the metal catalyst particle 400 exposed from the carrier particle 300 and is in contact with the exposed surface of the metal catalyst particle 400 to cover the exposed surface of the metal catalyst particle 400; The ionomer 602 is located between the exposed surface of the metal catalyst particle 400 and is located on the outside of the 602 (region farther from the exposed surface of the metal catalyst particle 400 than the ionomer 602) and without contacting the exposed surface of the metal catalyst particle 400. It is comprised from the ionomer 702 which intervenes and covers the area | region close to the metal catalyst particle 400 in the exposed surface of the metal catalyst particle 400, and the surface of the support | carrier particle 300. FIG.

  The concentration of ion exchange groups of ionomer 602 is lower than the concentration of ion exchange groups of ionomer 702. In other words, the concentration of ion exchange groups of ionomer 702 is higher than the concentration of ion exchange groups of ionomer 602.

  Here, the fuel cell catalyst ink 902, the method for producing the fuel cell catalyst ink 902, and the fuel cell 102 using the fuel cell catalyst ink 902 in the present embodiment will be described in more detail.

The solvent 30 is a solvent in which water and ethanol are mixed in a mass ratio of 1: 1. The base 22 is
It is ammonium carbonate. The carrier particles 300 are carbon particles, and the metal catalyst particles 400 are platinum Colt alloy catalyst particles. The platinum-cobalt alloy catalyst particles are platinum-cobalt alloy catalyst-supporting carbon carried 52 wt% on carbon particles.

  The ionomer 702 is a perfluorosulfonic acid, and the ion exchange group is an acidic sulfonic acid group. Further, the ionomer 602 is obtained by removing some of the ion exchange groups from the perfluorosulfonic acid of the ionomer 702. Further, a base 22 is coordinated to a part of the ion exchange group of the ionomer 802.

The molar concentration of ion exchange groups of the ionomer 702 is 200 mol / m ³ . The molar concentration of the amount of ion exchange groups of the ionomer 602 is 2 mol / m ³ . The amount of ionomer 802 is the same as that of carrier particles 300.

  Next, a method of manufacturing the fuel cell catalyst ink 902 according to the present embodiment will be described.

  As shown in FIG. 6, in the method of producing the fuel cell catalyst ink 902, a first step of coating the ionomer 702 on the exposed surface of the metal catalyst particles 400 exposed from the carrier particles 300 of S12 to S42; By removing ion exchange groups from the ionomer 702 in the area close to the exposed surface of the metal catalyst particle 400, an ionomer having a lower ion exchange group concentration as compared to the ionomer 702 in the area away from the exposed surface of the metal catalyst particle 400 It has the 2nd process of forming 602.

  First, in S12, 13 g of the ionomer 702, 115 mg of the base 22, and 200 ml of the solvent 30 are weighed. Next, by dispersing and mixing the ionomer 702, the base 22, and the solvent 30 in S22, an ionomer mixed solution having a low hydrogen ion concentration, in which the base 22 is coordinated to the acidic ion exchange group of the ionomer 702, is prepared. Do.

  Further, the addition amount of ammonia carbonate which is the base 22 is set such that the molar concentration of the ammonium ion formed by the ammonia ammonia is twice the molar concentration of the ion exchange group contained in the ionomer 702.

  Next, in S32, 15 g of the electrode catalyst 500 in the amount of platinum is weighed. Next, in step S42, the electrode catalyst 500 and an ionomer mixed solution having the ionomer 702 in which the base 22 is coordinated to the ion exchange group of the ionomer 702 are dispersed and mixed to prepare a catalyst dispersion.

Next, in step S52, hydrogen gas containing 4% of oxygen gas is supplied to the catalyst dispersion at a gas flow rate of 10 L / min for 10 minutes, and the ionomer 702 is coated in a region close to the surface of the metal catalyst particles 400. By removing a part of the exchange groups, an ionomer 602 having a concentration of ion exchange groups of 2 mol / m ³ is produced.

  Next, in S61, nitrogen gas is supplied to the catalyst dispersion at a gas flow rate of 1 L / min for 1 minute to degas the hydrogen from the catalyst dispersion, thereby completing the manufacture of the fuel cell catalyst ink 902.

  Next, details of the reaction in which the base 22 contained in the ionomer mixed solution of S22 is coordinated to the sulfonic acid group of the ionomer 702 and the hydrogen ion concentration decreases will be described.

By mixing ammonium carbonate which is the base 22 with the solvent 30, water contained in the solvent 30 and ammonium carbonate react to form ammonium ions, carbon dioxide and hydroxide ions. . The formed ammonium ion is coordinated to the outer periphery of the sulfonic acid group by forming an ionic bond with the sulfonic acid group contained in the adjacent ionomer 702.

  As a result, by increasing the concentration of hydroxide ions contained in the ionomer mixed solution, the hydrogen ion concentration of the ionomer mixed solution can be reduced.

  Next, the details of the reaction for removing ion exchange groups from the ionomer S702 of S52 will be described.

  First, hydrogen and oxygen are reacted on the exposed surface of the metal catalyst particles 400 to form hydrogen peroxide. Next, the formed hydrogen peroxide reacts with cobalt ions present in a region close to the exposed surface of the metal catalyst particles 400 to form hydroxyl radicals which become reactive species of the electrophilic substitution reaction.

  The hydroxyl radical is very reactive, has a feature of reacting with a molecular chain with high electron density and low binding energy. The perfluorosulfonic acid used as the ionomer 702 has a low bond energy between carbon and sulfur and a low bond energy between oxygen and hydrogen of the ion exchange group sulfonic acid group, so hydroxyl radicals attack these reaction sites. By doing this, it becomes possible to cleave the sulfonic acid group of the ionomer 702 coated in the area close to the surface of the metal catalyst particle 400.

  Next, a fuel cell 102 using the fuel cell catalyst ink 902 of the present embodiment will be described.

  As shown in FIG. 7, in the fuel cell 102 of the present embodiment, an electrolyte membrane-electrode assembly 92, an anode separator 70a, and a cathode separator 70b are stacked.

  A fuel gas channel 71 a is provided on the surface of the anode separator 70 a facing the electrolyte membrane-electrode assembly 92. Similarly, an oxidant gas channel 71 b is provided on the surface of the cathode separator 70 b facing the electrolyte membrane-electrode assembly 91. The anode separator 70a and the cathode separator 70b use a carbon separator.

  An electrolyte membrane 10 and an anode 62 a and a cathode 62 b sandwiching the electrolyte membrane 10 are provided. For the electrolyte membrane 10, a perfluorosulfonic acid membrane is used. The anode 62 a includes an electrode catalyst layer 82 and a gas diffusion layer 40. The cathode 62 b is composed of an electrode catalyst layer 82 and a gas diffusion layer 40.

The electrode catalyst layer 82 is prepared by applying the fuel cell catalyst ink 902 to the gas diffusion layer 40 so that the amount of platinum is 0.1 mg / cm ² and drying at 60 ° C.

The anode 62 a and the cathode 62 b are attached to the electrolyte membrane 10 by thermocompression bonding at 120 ° C. and 10 kgf / cm ² with the anode 62 a and the cathode 62 b laminated on the electrolyte membrane 10 in the electrolyte membrane-electrode assembly 92. Use the bonded one.

  The fuel cell 102 generates electric power by the reaction of the fuel gas supplied to the anode 62a and the oxidant gas supplied to the cathode 62b. Hydrogen gas is used as the fuel gas, and air is used as the oxidant gas.

As described above, the fuel cell catalyst ink 902 according to Embodiment 3 includes the electrode catalyst 500 in which the metal catalyst particles 400 are supported on the carrier particles 300, and the ionomer 802 having an acidic ion exchange group. A fuel cell catalyst ink 902, wherein the surfaces of the metal catalyst particles 400 and the carrier particles 300 are coated with an ionomer 802 (ionomers 602 and ionomers 702) and close to the exposed surfaces of the metal catalyst particles 400 exposed from the carrier particles 300. The ion exchange group concentration of the ionomer 602 located in the area and in contact with the exposed surface of the metal catalyst particle 400 covers the exposed surface of the metal catalyst particle 400 is higher than that of the ionomer 602 (the metal catalyst particle 400 is exposed than the ionomer 602). Located in an area away from the surface, without contacting the exposed surface of the metal catalyst particles 400 Based on the concentration of ion exchange groups of ionomer 702 covering an area adjacent to metal catalyst particle 400 on the exposed surface of metal catalyst particle 400 and the surface of support particle 300 with ionomer 602 interposed between the exposed surface of metal catalyst particle 400 Is also characterized by low.

  As a result, since there are few acidic ion exchange groups in direct contact with the metal catalyst particles 400 of the fuel cell catalyst ink 902, it is possible to suppress a decrease in catalyst activity due to a change in composition of the metal catalyst particles 400. Further, by forming the fuel cell 102 using the fuel cell catalyst ink 902 of the present embodiment, it is possible to suppress a decrease in the power generation efficiency of the fuel cell 102.

  Furthermore, in the method of producing catalyst ink for fuel cell 902 of the present embodiment, an electrode catalyst 500 having metal catalyst particles 400 supported on carrier particles 300, an ionomer 702 having an acidic ion exchange group, a base 22, and A first step of coating the ionomer 702 on the electrode catalyst 500 by mixing the solvent 30; and a second step of removing ion exchange groups from the ionomer 702 in a region close to the exposed surface of the metal catalyst particle 400; It is characterized by having.

  Thereby, the acidity of the ion exchange group of the ionomer 702 can be reduced by the coordination of the base 22 to the ion exchange group of the ionomer 702. In addition, removal of ion exchange groups can lower the concentration of ion exchange groups of the ionomer 702 in a region close to the exposed surface of the metal catalyst particle 400.

  As a result, direct contact of the acidic ion exchange group with the metal catalyst particles 400 can be reduced, and a fuel cell catalyst ink 902 can be manufactured in which the decrease in catalyst activity due to the composition change of the metal catalyst particles 400 is suppressed. .

  Further, the first step of the method for producing the fuel cell catalyst ink 902 is configured such that the ionomer 702, the base 22, and the solvent 30 are first mixed, and then the electrode catalyst 500 is mixed. The ratio in which the base 22 is coordinated to the ion exchange group of the metal catalyst particle 400 is increased, and the direct contact of the acidic ion exchange group of the ionomer 702 with the metal catalyst particle 400 is further reduced. Can be further suppressed.

  In addition, by setting the concentration of the base 22 to be higher than the concentration of the ion exchange group possessed by the ionomer 702, the ratio of coordination of the base 22 to the ion exchange group of the ionomer 702 is further increased. The direct contact of the acidic ion exchange groups of the ionomer 702 is further reduced, and the reduction in catalytic activity due to the change in the composition of the metal catalyst particles 400 can be further suppressed.

  Further, the second step of the method for producing the fuel cell catalyst ink 902 is configured to remove the ion exchange group from the ionomer 702 in a region close to the exposed surface of the metal catalyst particles 400 by an electrophilic substitution reaction. Since the ion exchange group having a molecular chain with high electron density and low binding energy can be selectively cleaved, the selectivity and reaction rate of the reaction site of the removal reaction of ion exchange group can be improved As a result, the fuel cell catalyst ink 902 can be manufactured efficiently.

In the present embodiment, the metal catalyst particle 400 is a platinum-cobalt alloy catalyst particle, but in addition to this, metals such as platinum, ruthenium, palladium, iron, copper, chromium, cobalt, nickel, manganese and the like and These alloys can be used.

  In this embodiment, the ionomer 702 is a perfluorosulfonic acid, but in addition to this, an ionomer containing an ion exchange group other than a sulfonic acid group in a fluorine compound, a sulfonic acid group in a hydrocarbon or It is also possible to use an ionomer in which an ion exchange group other than a sulfonic acid group is introduced.

  In the present embodiment, the base 22 is ammonium carbonate, but in addition to this, ammonium salts such as ammonium hydrogen carbonate and ammonium carbamate can also be used.

  Although hydrogen gas and oxygen gas are used in the manufacturing process for removing ion exchange groups in the present embodiment, it is also possible to use an oxide substance and a reduction substance which can form hydrogen peroxide besides this. it can.

  In the present embodiment, a hydroxyl radical is used in the manufacturing process for removing the ion exchange group, but other electrophilic species may be used.

Embodiment 4
FIG. 8 is a cross-sectional view showing a schematic configuration of a fuel cell catalyst ink according to a fourth embodiment of the present invention. FIG. 9 is a flow chart showing a manufacturing process of a fuel cell catalyst ink according to a fourth embodiment of the present invention. FIG. 10 is a cross-sectional view showing a schematic configuration of a fuel cell according to Embodiment 4 of the present invention.

  As shown in FIG. 8, the fuel cell catalyst ink 903 of the present embodiment has an electrode catalyst 500 in which metal catalyst particles 400 are supported on the surface of carrier particles 300, an ionomer 803, a base 23, and a solvent 30. , Is composed of.

  The ionomer 803 is located in a region close to the exposed surface of the metal catalyst particle 400 exposed from the carrier particle 300, and an ionomer 603 which contacts the exposed surface of the metal catalyst particle 400 and covers the exposed surface of the metal catalyst particle 400; Located outside of 603 (area farther from the exposed surface of the metal catalyst particle 400 than the ionomer 603), and between the exposed surface of the metal catalyst particle 400 and the exposed surface of the metal catalyst particle 400 without contacting the exposed surface of the metal catalyst particle 400 It consists of an ionomer 703 which covers the exposed surface of the metal catalyst particles 400 and the region of the surface of the carrier particles 300 adjacent to the metal catalyst particles 400.

  The concentration of ion exchange groups of the ionomer 603 is lower than the concentration of ion exchange groups of the ionomer 703. In other words, the concentration of ion exchange groups of ionomer 703 is higher than the concentration of ion exchange groups of ionomer 603.

  Here, the fuel cell catalyst ink 903 in the present embodiment, the method for producing the fuel cell catalyst ink 903, and the fuel cell 103 using the fuel cell catalyst ink 903 will be described in more detail.

  The solvent 30 is a solvent in which water and ethanol are mixed in a mass ratio of 1: 1. The base 23 is imidazole. The carrier particles 300 are carbon particles, and the metal catalyst particles 400 are platinum Colt alloy catalyst particles. The platinum-cobalt alloy catalyst particles are platinum-cobalt alloy catalyst-supporting carbon carried 52 wt% on carbon particles.

The ionomer 703 is a perfluorosulfonic acid, and the ion exchange group is an acidic sulfonic acid group. Further, the ionomer 603 is obtained by removing a part of ion exchange groups from the perfluorosulfonic acid of the ionomer 703. The base 23 is coordinated to a part of the ion exchange group of the ionomer 803. Further, the base 22 is also adsorbed to a part of the surface of the metal catalyst particle 400.

The molar concentration of ion exchange groups of the ionomer 703 is 200 mol / m ³ . The molar concentration of the amount of ion exchange groups of the ionomer 603 is 0.2 mol / m ³ . The amount of ionomer 803 is the same as that of carrier particles 300.

  Next, a method of manufacturing the fuel cell catalyst ink 903 of the present embodiment will be described.

  As shown in FIG. 9, in the method of producing the catalyst ink 903 for fuel cell, the first step of coating the ionomer 703 on the exposed surface of the metal catalyst particles 400 exposed from the carrier particles 300 of S13 to S43; An ionomer having an ion exchange group concentration lower than that of the ionomer 703 in a region close to the exposed surface of the metal catalyst particle 400 by removing ion exchange groups from the ionomer 703 in the region close to the exposed surface of the metal catalyst particle 400 And the second step of forming 603.

  First, in S13, 15 g of the electrode catalyst 500, 40 mg of the base 23, and 200 ml of the solvent 30 are weighed.

  Next, in step S23, the base 23 is adsorbed on the surface of the metal catalyst particles 400 of the electrode catalyst 500 by dispersing and mixing the electrode catalyst 500, the base 23, and the solvent 30, and the catalyst mixture with a low concentration of hydrogen ions Make a solution.

  Next, 13 g of the ionomer 703 is weighed in S33. Next, a catalyst dispersion is prepared by dispersing and mixing the ionomer 703 and the catalyst mixed solution in which the base 23 is adsorbed on the surface of the metal catalyst particles 400 in S43.

Next, in S53, hydrogen gas containing 4% of oxygen gas is supplied to the catalyst dispersion at a gas flow rate of 10 L / min for 10 minutes, and ion exchange is performed from the ionomer 703 coated in a region close to the surface of the metal catalyst particles 400. By removing a part of the groups, an ionomer 603 with a concentration of ion exchange groups of 0.2 mol / m ³ is produced.

  Next, in S63, nitrogen gas is supplied to the catalyst dispersion at a gas flow rate of 1 L / min for 1 minute to degas the hydrogen from the catalyst dispersion, thereby completing the production of the fuel cell catalyst ink 903.

  Next, the details of the reaction in which the base 23 contained in the catalyst mixed solution of S23 is adsorbed on the surface of the metal catalyst particles 400 to reduce the hydrogen ion concentration will be described.

  By mixing the imidazole which is the base 23, the solvent 30, and the electrode catalyst 500, the lone electron pair of nitrogen whose electron density of imidazole is high is unique to the surface of the metal catalyst particle 400 in which the unsaturated bond exists. Adsorb.

  In addition, imidazole reacts with water of the solvent 30 to form hydroxide ions, so that the concentration of hydroxide ions in the catalyst mixed solution can be increased to reduce the hydrogen ion concentration.

  Next, details of the reaction for removing ion exchange groups from the ionomer S703 of S53 will be described.

  First, hydrogen and oxygen are reacted on the surface of the metal catalyst particles 400 to form hydrogen peroxide. Next, the formed hydrogen peroxide reacts with cobalt ions present in a region close to the surface of the metal catalyst particles 400 to form hydroxyl radicals which become reactive species of the electrophilic substitution reaction.

  The hydroxyl radical is very reactive, has a feature of reacting with a molecular chain with high electron density and low binding energy.

  The perfluorosulfonic acid used as the ionomer 703 has a low bond energy between the carbon and sulfur of the sulfonic acid group which is an ion exchange group and a low bond energy between oxygen and hydrogen, so hydroxyl radicals attack these reaction sites. By doing so, it becomes possible to cleave the sulfonic acid group of the ionomer 703 coated in the area close to the surface of the metal catalyst particle 400.

  Next, a fuel cell 103 using the fuel cell catalyst ink 903 of the present embodiment will be described.

  As shown in FIG. 10, in the fuel cell 103 of the present embodiment, an electrolyte membrane-electrode assembly 93, an anode separator 70a, and a cathode separator 70b are stacked.

  A fuel gas channel 71 a is provided on the surface of the anode separator 70 a facing the electrolyte membrane-electrode assembly 93. Similarly, an oxidant gas channel 71 b is provided on the surface of the cathode separator 70 b facing the electrolyte membrane-electrode assembly 91. The anode separator 70a and the cathode separator 70b use a carbon separator.

  An electrolyte membrane 10 and an anode 63 a and a cathode 63 b sandwiching the electrolyte membrane 10 are provided. For the electrolyte membrane 10, a perfluorosulfonic acid membrane is used. The anode 63 a includes an electrode catalyst layer 83 and a gas diffusion layer 40. The cathode 63 b is composed of an electrode catalyst layer 83 and a gas diffusion layer 40.

The electrode catalyst layer 83 is prepared by applying the fuel cell catalyst ink 903 to the gas diffusion layer 40 so that the amount of platinum is 0.1 mg / cm ² and drying at 60 ° C.

The anode 63 a and the cathode 63 ^b are attached to the electrolyte membrane 10 by thermocompression bonding at 120 ° C. and 10 kgf / cm ² with the anode 63 a and the cathode 63 ^b laminated on the electrolyte membrane 10 in the electrolyte membrane-electrode assembly 93. Use the bonded one.

  The fuel cell 103 generates electric power by the reaction between the fuel gas supplied to the anode 63a and the oxidant gas supplied to the cathode 63b. Hydrogen gas is used as the fuel gas, and air is used as the oxidant gas.

As described above, the fuel cell catalyst ink 903 of the fourth embodiment is composed of the electrode catalyst 500 in which the metal catalyst particles 400 are supported on the carrier particles 300, and the ionomer 803 having an acidic ion exchange group. A catalyst ink 903 for a fuel cell, in which the surfaces of the metal catalyst particles 400 and the carrier particles 300 are coated with an ionomer 803 (ionomer 603 and ionomer 703) and close to the exposed surface of the metal catalyst particles 400 exposed from the carrier particles 300. The ion exchange group concentration of the ionomer 603 located in the area and in contact with the exposed surface of the metal catalyst particle 400 covers the exposed surface of the metal catalyst particle 400 is higher than that of the ionomer 603 (the metal catalyst particle 400 is exposed than the ionomer 603). Located in an area away from the surface, without contacting the exposed surface of the metal catalyst particles 400 From the concentration of ion exchange groups of ionomer 703 covering an area adjacent to metal catalyst particle 400 on the exposed surface of metal catalyst particle 400 and the surface of support particle 300 with ionomer 603 interposed between the exposed surface of metal catalyst particle 400 Is also characterized by low.

  As a result, since there are few acidic ion exchange groups directly in contact with the metal catalyst particles 400 of the fuel cell catalyst ink 903, it is possible to suppress a decrease in catalyst activity due to a change in the composition of the metal catalyst particles 400. Further, by forming the fuel cell 103 using the fuel cell catalyst ink 903 of the present embodiment, it is possible to suppress a decrease in the power generation efficiency of the fuel cell 103.

  Further, the method for producing the fuel cell catalyst ink 903 comprises: an electrode catalyst 500 in which the metal catalyst particles 400 are supported on the carrier particles 300; an ionomer 703 having an acidic ion exchange group; a base 23; It has a first step of coating the ionomer 703 on the electrode catalyst 500 by mixing, and a second step of removing ion exchange groups from the ionomer 703 in a region close to the exposed surface of the metal catalyst particles 400. I assume.

  Thereby, the acidity of the ion exchange group of the ionomer 703 can be reduced by the base 23 being coordinated to the ion exchange group of the ionomer 703. In addition, the concentration of ion exchange groups of the ionomer 703 coated on the surface of the metal catalyst particles 400 can be lowered.

  As a result, direct contact of the acidic ion exchange group with the metal catalyst particles 400 can be reduced, and a fuel cell catalyst ink 903 can be manufactured in which the decrease in the catalytic activity due to the composition change of the metal catalyst particles 400 is suppressed. .

  In addition, the solvent 30 is adsorbed on the surface of the metal catalyst particles 400 by first mixing the electrode catalyst 500, the base 23, and the solvent 30 in the first step of the method for producing the fuel cell catalyst ink 903. Thus, the direct contact of the acidic ion exchange group of the ionomer 703 with the metal catalyst particles 400 can be reduced, and a decrease in catalyst activity due to a change in the composition of the metal catalyst particles 400 can be reliably suppressed.

  Further, the second step of the method for producing the fuel cell catalyst ink 903 is configured to remove the ion exchange group from the ionomer 703 in a region close to the surface of the metal catalyst particles 400 by an electrophilic substitution reaction. Since the ion exchange group having a molecular chain with high electron density and low binding energy can be selectively cleaved, the selectivity and reaction rate of the reaction site of the removal reaction of the ion exchange group can be improved. As a result, the fuel cell catalyst ink 903 can be manufactured efficiently.

  In the present embodiment, the metal catalyst particle 400 is a platinum-cobalt alloy catalyst particle, but in addition to this, metals such as platinum, ruthenium, palladium, iron, copper, chromium, cobalt, nickel, manganese and the like and These alloys can be used.

  In this embodiment, although the ionomer 703 is a perfluorosulfonic acid, in addition to this, an ionomer containing an ion exchange group other than a sulfonic acid group in a fluorine compound, a sulfonic acid group in a hydrocarbon or It is also possible to use an ionomer in which an ion exchange group other than a sulfonic acid group is introduced.

  In the present embodiment, the base 23 is imidazole, but in addition to this, an aromatic having a basic nitrogen such as pyridine or aniline can also be used.

  Although hydrogen gas and oxygen gas are used in the manufacturing process for removing ion exchange groups in the present embodiment, it is also possible to use an oxide substance and a reduction substance which can form hydrogen peroxide besides this. it can.

  In the present embodiment, a hydroxyl radical is used in the manufacturing process for removing the ion exchange group, but other electrophilic species may be used.

Fifth Embodiment
FIG. 11 is a cross-sectional view showing a schematic configuration of a fuel cell catalyst ink according to a fifth embodiment of the present invention. FIG. 12 is a flowchart showing steps of producing a catalyst ink for a fuel cell according to a fifth embodiment of the present invention. FIG. 13 is a cross-sectional view showing a schematic configuration of a fuel cell according to Embodiment 5 of the present invention.

  As shown in FIG. 11, the fuel cell catalyst ink 904 is composed of an electrode catalyst 500 having metal catalyst particles 400 supported on the surface of carrier particles 300, an ionomer 804, a base 24, and a solvent 30. There is.

  The ionomer 804 is located in a region close to the exposed surface of the metal catalyst particle 400 exposed from the carrier particle 300 and is in contact with the exposed surface of the metal catalyst particle 400 to cover the exposed surface of the metal catalyst particle 400; Located on the outside of 604 (area farther from the exposed surface of the metal catalyst particle 400 than the ionomer 604), the ionomer 604 is placed between the exposed surface of the metal catalyst particle 400 and not in contact with the exposed surface of the metal catalyst particle 400 It is comprised from the ionomer 704 which intervenes and covers the area | region close to the metal catalyst particle 400 in the exposed surface of the metal catalyst particle 400, and the surface of the support | carrier particle 300. FIG.

  The concentration of ion exchange groups of ionomer 604 is lower than the concentration of ion exchange groups of ionomer 704. In other words, the concentration of ion exchange groups of ionomer 704 is higher than the concentration of ion exchange groups of ionomer 604.

  Here, the fuel cell catalyst ink 904, the method for producing the fuel cell catalyst ink 904, and the fuel cell 104 using the fuel cell catalyst ink 904 according to the present embodiment will be described in more detail.

  The solvent 30 is a solvent in which water and ethanol are mixed in a mass ratio of 1: 1. Base 24 is imidazole. The carrier particles 300 are carbon particles, and the metal catalyst particles 400 are platinum Colt alloy catalyst particles. The platinum-cobalt alloy catalyst particles are platinum-cobalt alloy catalyst-supporting carbon carried 52 wt% on carbon particles.

  The ionomer 704 is a perfluorosulfonic acid, and the ion exchange group is an acidic sulfonic acid group. In addition, the ionomer 604 is obtained by removing a part of ion exchange groups from the perfluorosulfonic acid of the ionomer 704. The base 22 is coordinated to a part of the ion exchange group of the ionomer 804. Further, the base 24 is also adsorbed to a part of the surface of the metal catalyst particle 400.

The molar concentration of ion exchange groups of the ionomer 704 is 200 mol / m ³ . The molar concentration of the ion exchange group weight of the ionomer 604 is 0.2 mol / m ³ . The amount of ionomer 804 is the same as that of carrier particles 300.

  Next, a method of manufacturing the fuel cell catalyst ink 904 of the present embodiment will be described.

As shown in FIG. 12, the method for producing the fuel cell catalyst ink 904 of the present embodiment is S1.
Ion exchange groups from the ionomer 704 in a region close to the exposed surface of the metal catalyst particles 400 from the first step of coating the ionomer 704 on the exposed surfaces of the metal catalyst particles 400 exposed from the carrier particles 300 from 4 to S54. The second step is to form an ionomer 604 having a low ion exchange group concentration in a region close to the exposed surface of the metal catalyst particles 400 as compared to the ionomer 704.

  First, in S14, 15 g of the electrode catalyst 500 in platinum amount, 58 mg of the base 24, and 100 ml of the solvent 30 are weighed.

  Next, in step S24, the base 24 is adsorbed on the surface of the metal catalyst particles 400 of the electrode catalyst 500 by dispersing and mixing the electrode catalyst 500, the base 24, and the solvent 30, and the catalyst mixture has a low hydrogen ion concentration. Make a solution.

  Next, 13 g of the ionomer 704 and 58 g of the base 24 are weighed in S34. Next, by dispersing and mixing the ionomer 704 and the base 24 in S44, an ionomer dispersion having a low hydrogen ion concentration in which the base 24 is coordinated to the acidic ion exchange group of the ionomer 704 is prepared.

  Further, the addition amount of ammonia carbonate which is the base 24 is set such that the molar concentration of the ammonium ion formed by the ammonia ammonia is equal to the molar concentration of the ion exchange group contained in the ionomer 704.

  Next, in step S54, the ionomer dispersion and the catalyst mixture solution are dispersed and mixed to prepare a catalyst dispersion.

Next, in S64, hydrogen gas containing 4% of oxygen gas is supplied to the catalyst dispersion at a gas flow rate of 10 L / min for 10 minutes, and ion exchange is performed from the ionomer 704 coated in the area close to the surface of the metal catalyst particles 400. By removing a part of the groups, an ionomer 604 with a concentration of ion exchange groups of 0.2 mol / m ³ is produced.

  Next, in S64, nitrogen gas is supplied to the catalyst dispersion at a gas flow rate of 1 L / min for 1 minute to degas hydrogen from the catalyst dispersion, thereby completing the manufacture of the fuel cell catalyst ink 904.

  Next, details of the reaction in which the base 24 contained in the catalyst mixed solution of S24 is adsorbed on the exposed surface of the metal catalyst particles 400 and the hydrogen ion concentration decreases will be described.

  By mixing ammonium carbonate which is the base 24, the solvent 30, and the electrode catalyst 500, the electron density of ammonium carbonate is high, and the lone electron pair of nitrogen has a unsaturated bond on the surface of the metal catalyst particle 400. Adsorb specifically to

  In addition, ammonium carbonate reacts with water of the solvent 30 to form hydroxide ions, so that the concentration of hydroxide ions in the catalyst mixed solution can be increased to reduce the hydrogen ion concentration. .

  Next, details of the reaction for removing ion exchange groups from the ionomer S704 of S64 will be described.

First, hydrogen and oxygen are reacted on the surface of the metal catalyst particles 400 to form hydrogen peroxide. Next, the formed hydrogen peroxide reacts with cobalt ions present in a region close to the surface of the metal catalyst particles 400 to form hydroxyl radicals which become reactive species of the electrophilic substitution reaction. The hydroxyl radical is very reactive, has a feature of reacting with a molecular chain with high electron density and low binding energy.

  The perfluorosulfonic acid used as the ionomer 704 has a low bond energy between carbon and sulfur and a low bond energy between oxygen and hydrogen of the ion exchange group sulfonic acid group, so hydroxyl radicals attack these reaction sites. By doing so, it becomes possible to cleave the sulfonic acid group of the ionomer 704 coated in the area close to the surface of the metal catalyst particle 400.

  Next, a fuel cell 104 using the fuel cell catalyst ink 904 of the present embodiment will be described.

  As shown in FIG. 13, in the fuel cell 104 of the present embodiment, an electrolyte membrane-electrode assembly 94, an anode separator 70a, and a cathode separator 70b are stacked.

  A fuel gas channel 71 a is provided on the surface of the anode separator 70 a facing the electrolyte membrane-electrode assembly 94. Similarly, an oxidant gas channel 71 b is provided on the surface of the cathode separator 70 b facing the electrolyte membrane-electrode assembly 94. The anode separator 70a and the cathode separator 70b use a carbon separator.

  An electrolyte membrane 10 and an anode 64 a and a cathode 64 b sandwiching the electrolyte membrane 10 are provided. For the electrolyte membrane 10, a perfluorosulfonic acid membrane is used. The anode 64 a is composed of an electrode catalyst layer 84 and a gas diffusion layer 40. The cathode 64 b is composed of an electrode catalyst layer 84 and a gas diffusion layer 40.

The electrode catalyst layer 84 is prepared by applying the fuel cell catalyst ink 904 to the gas diffusion layer 40 so that the amount of platinum is 0.1 mg / cm ² and drying at 60 ° C.

The anode 64 a and the cathode 64 b are bonded to the electrolyte membrane 10 by thermocompression bonding at 120 ° C. and 10 kgf / cm ² with the anode 64 a and the cathode 64 b laminated on the electrolyte membrane 10 in the electrolyte membrane-electrode assembly 94. Use the bonded one.

  The fuel cell 104 generates electric power by the reaction of the fuel gas supplied to the anode 64a and the oxidant gas supplied to the cathode 64b. Hydrogen gas is used as the fuel gas, and air is used as the oxidant gas.

  As described above, the fuel cell catalyst ink 904 according to Embodiment 5 includes the electrode catalyst 500 in which the metal catalyst particles 400 are supported on the carrier particles 300, and the ionomer 804 having an acidic ion exchange group. A catalyst ink 904 for a fuel cell, in which the surfaces of the metal catalyst particles 400 and the carrier particles 300 are coated with an ionomer 804 (ionomer 604 and ionomer 704) and close to the exposed surface of the metal catalyst particles 400 exposed from the carrier particles 300. The concentration of ion exchange groups of the ionomer 604 located in the area and in contact with the exposed surface of the metal catalyst particle 400 covering the exposed surface of the metal catalyst particle 400 is higher than that of the ionomer 604 (the metal catalyst particle 400 is exposed than the ionomer 604). Located in an area away from the surface, without contacting the exposed surface of the metal catalyst particles 400 Based on the concentration of ion exchange groups of ionomer 704 covering an area adjacent to metal catalyst particle 400 on the exposed surface of metal catalyst particle 400 and the surface of support particle 300 with ionomer 604 interposed between the exposed surface of metal catalyst particle 400 Is also characterized by low.

As a result, since there are few acidic ion exchange groups directly in contact with the metal catalyst particles 400 of the fuel cell catalyst ink 904, it is possible to suppress a decrease in catalyst activity due to a change in the composition of the metal catalyst particles 400. Further, by forming the fuel cell 104 using the fuel cell catalyst ink 904 according to the present embodiment, it is possible to suppress a decrease in the power generation efficiency of the fuel cell 104.

  Furthermore, the method for producing the catalyst ink 904 for fuel cell comprises: an electrode catalyst 500 in which the metal catalyst particles 400 are supported on the carrier particles 300; an ionomer 704 having an acidic ion exchange group; a base 24; It is characterized by having a first step of coating the ionomer 704 on the electrode catalyst 500 by mixing, and a second step of removing ion exchange groups from the ionomer 704 in a region close to the exposed surface of the metal catalyst particle 400. I assume.

  Thereby, the acidity of the ion exchange group of the ionomer 704 can be reduced by the base 24 being coordinated to the ion exchange group of the ionomer 704. Also, the concentration of ion exchange groups of the ionomer 704 coated on the surface of the metal catalyst particles 400 can be lowered.

  As a result, direct contact of the acidic ion exchange group with the metal catalyst particles 400 can be reduced, and a fuel cell catalyst ink 904 can be manufactured in which the decrease in catalyst activity due to the composition change of the metal catalyst particles 400 is suppressed. .

  Further, by mixing the ionomer 704, the base 24 and the solvent 30 in advance in the first step of the method for producing the fuel cell catalyst ink 904, the base 24 is coordinated to the ion exchange group of the ionomer 704. The ratio is increased, and the direct contact of the acidic ion exchange groups of the ionomer 704 with the metal catalyst particles 400 is further reduced, and the reduction of the catalyst activity due to the composition change of the metal catalyst particles 400 can be further suppressed.

  In addition, by setting the concentration of the base 24 to be higher than the concentration of the ion exchange group possessed by the ionomer 704, the ratio of coordination of the base 24 to the ion exchange group of the ionomer 704 is further increased. The direct contact of the acidic ion exchange groups of the ionomer 704 is further reduced, and the reduction in catalyst activity due to the change in the composition of the metal catalyst particles 400 can be further suppressed.

  In addition, the first step of the method for producing the catalyst ink 904 for fuel cell is performed by first mixing the electrode catalyst 500, the base 24 and the solvent 30 to make the metal catalyst particles 400 acidic ion exchange of the ionomer 704. Direct contact of the groups is reduced, and a decrease in catalyst activity due to a change in the composition of the metal catalyst particles 400 can be reliably suppressed.

  Further, the second step of the method for producing the fuel cell catalyst ink 904 is configured to remove the ion exchange group from the ionomer 704 in a region close to the surface of the metal catalyst particles 400 by an electrophilic substitution reaction. Since the ion exchange group having a molecular chain with high electron density and low binding energy can be selectively cleaved, the selectivity and reaction rate of the reaction site of the removal reaction of the ion exchange group can be improved. As a result, the fuel cell catalyst ink 904 can be manufactured efficiently.

  In the present embodiment, the metal catalyst particle 400 is a platinum-cobalt alloy catalyst particle, but in addition to this, metals such as platinum, ruthenium, palladium, iron, copper, chromium, cobalt, nickel, manganese and the like and These alloys can be used.

In this embodiment, although the ionomer 704 is a perfluorosulfonic acid, in addition to this, an ionomer containing an ion exchange group other than a sulfonic acid group in a fluorine compound, a sulfonic acid group in a hydrocarbon or It is also possible to use an ionomer in which an ion exchange group other than a sulfonic acid group is introduced.

  In the present embodiment, the base 24 is imidazole, but in addition to this, an aromatic having a basic nitrogen such as pyridine or aniline can also be used.

  Although hydrogen gas and oxygen gas are used in the manufacturing process for removing ion exchange groups in the present embodiment, it is also possible to use an oxide substance and a reduction substance which can form hydrogen peroxide besides this. it can.

  In the present embodiment, a hydroxyl radical is used in the manufacturing process for removing the ion exchange group, but other electrophilic species may be used.

  As described above, the fuel cell catalyst ink of the present invention has a small amount of acidic ion exchange groups in direct contact with the metal catalyst particles, and the decrease in the catalyst activity due to the composition change of the metal catalyst particles is suppressed. It is most suitable for solid polymer fuel cells such as cell systems.

10 electrolyte membrane 22, 23, 24 base 30 solvent 40 gas diffusion layer 61a, 62a, 63a, 64a anode 61b, 62b, 63b, 64b cathode 70a anode separator 70b cathode separator 71a fuel gas flow path 71b oxidant gas flow path 81, 82, 83, 84 Electrode catalyst layer 91, 92, 93, 94 Electrolyte membrane-electrode assembly 101, 102, 103, 104 Fuel cell 300 Carrier particle 400 Metal catalyst particle 500 Electrode catalyst 600, 601, 602, 603, 604 Ionomer 700, 701, 702, 703, 704 Ionomer 800, 801, 802, 803, 804 Ionomer 900, 901, 902, 903, 904 Fuel cell catalyst ink

Claims (7)

A catalyst ink for a fuel cell, comprising: an electrode catalyst in which metal catalyst particles are supported on carrier particles; and an ionomer having an acidic ion exchange group, wherein the surfaces of the metal catalyst particles and the carrier particles are the ionomers. The concentration of ion exchange groups of the ionomer in the area adjacent to the surface of the metal catalyst particles is lower than the concentration of the ion exchange groups of the ionomer in the area covering the surface of the carrier particles. Catalyst ink for fuel cells characterized by A first step of coating the electrocatalyst with the ionomer by mixing the electrocatalyst in which the metal catalyst particles are supported on the carrier particles, an ionomer having an acidic ion exchange group, a base, and a solvent; A second step of removing the ion exchange group from the ionomer in a region close to the surface of the metal catalyst particles, and a method of producing a fuel cell catalyst ink. The fuel cell catalyst ink according to claim 2, wherein in the first step, the ionomer, the base, and the solvent are first mixed, and then the electrode catalyst is mixed. Method. The method for producing a fuel cell catalyst ink according to claim 2 or 3, wherein the concentration of the base is higher than the concentration of ion exchange groups possessed by the ionomer. The fuel cell catalyst ink according to claim 2, wherein in the first step, the electrocatalyst, the base, and the solvent are first mixed, and then the ionomer is mixed. Method. 6. The ion exchange group is removed from the ionomer in a region close to the surface of the metal catalyst particles by an electrophilic substitution reaction in the second step. The manufacturing method of the catalyst ink for fuel cells as described in-. The method for producing a fuel cell catalyst ink according to any one of claims 2 to 6, further comprising a third step of removing a base contained in the fuel cell catalyst ink.

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