JP2002042825A - Electrode catalyst for fuel cell, method for producing the same, and fuel cell - Google Patents

Abstract

(57) [Problem] To provide an electrode catalyst for a fuel cell, which exhibits excellent characteristics with a small amount of support. SOLUTION: An electrode catalyst for a fuel cell comprising platinum particles, of which 5% by weight or more are cubic or tetrahedral platinum particles. The production method of the electrode catalyst is platinum (II) chloride
A step of bubbling hydrogen into an aqueous solution in which potassium acid and sodium polyacrylate are dissolved to form a platinum colloid solution, and adding a conductive carbon material to the platinum colloid solution, and then adjusting the pH of the solution to 3 or less or 12 or more The step of preparing, the step of separating the colloid particles from the liquid together with the carbon material, and the step of
A step of heat-treating at a temperature of 0 to 350 ° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly active electrode catalyst for use in polymer electrolyte fuel cells, phosphoric acid fuel cells, direct methanol fuel cells, etc., a method for producing the same, and a fuel using the catalyst. It relates to batteries.

[0002]

2. Description of the Related Art As an electrode catalyst of a polymer electrolyte fuel cell, a phosphoric acid fuel cell, and a direct methanol fuel cell, a catalyst in which platinum black or a noble metal containing platinum is supported on carbon black has been used. Platinum black is prepared by a method of neutralizing a heated aqueous solution of chloroplatinic acid with sodium carbonate and pouring it into boiled sodium formate, or a method of adding formalin to an aqueous solution of chloroplatinic acid and adding sodium hydroxide. Platinum-supported carbon black is prepared by adding sodium hydrogen sulfite to an aqueous solution of chloroplatinic acid, then adding aqueous hydrogen peroxide, supporting the resulting platinum colloid on the carbon black, washing, and heat-treating as necessary. It is generally done. In direct methanol type fuel cells, platinum black is mainly used. In a polymer electrolyte fuel cell, platinum-supported carbon black is dispersed in a polymer electrolyte solution to form an ink. The ink is applied to a gas diffusion electrode such as carbon paper, dried, and then dried with two gas diffusion electrodes. The electrolyte membrane and the electrode assembly are manufactured by hot pressing the electrolyte membrane.

[0003]

Since platinum is expensive, it is desired that a small amount of platinum be used to exhibit sufficient performance. However, the platinum particles used in the conventional method have a tetrahedral shape (cu
booctahedra), icosahedra, and amorphous particles were mostly mixed, and less than 1% of all particles had a cubic or tetrahedral shape. . The activity of the platinum catalyst varies depending on the crystal plane of platinum, and the (111) plane or the (100) plane is considered to have the highest activity (PN Ross; Ultramicroscop).
y, Vol. 20, p. 21 (1986) and K. Kinoshita; J. Electr
ochem. Soc., Vol. 137, No. 3, p. 845 (1990)). But,
In the conventional method, there are various surfaces, of which only a few are active surfaces.

[0004]

SUMMARY OF THE INVENTION The present invention provides a fuel cell electrode catalyst comprising platinum particles selectively having a highly active surface. That is, the fuel cell electrode catalyst of the present invention comprises platinum particles, of which at least 5% by weight are cubic and / or tetrahedral platinum particles. According to another aspect, the electrode catalyst for a fuel cell of the present invention is composed of platinum particles, of which 5% by weight or more are platinum particles having a (100) plane or a (111) plane.

According to the present invention, there is provided a step of introducing a hydrogen into an aqueous solution in which a platinum salt and at least one of a carboxylic acid and a carboxylic acid salt are dissolved to form a platinum colloid solution, and adding a conductive carbon material to the platinum colloid solution. Adjusting the pH of the colloid solution to 3 or less or 12 or more after the addition,
An electrode catalyst for a fuel cell, comprising: a step of separating colloid particles from the colloid solution together with the carbon material; and a step of removing carboxylic acid and / or carboxylate contained from the separated carbon material with colloid particles. A manufacturing method is provided. The present invention provides a step of introducing a hydrogen into an aqueous solution in which a platinum salt and at least one of a carboxylic acid and a carboxylate is dissolved to form a platinum colloid solution, and adding a conductive carbon material to the platinum colloid solution. A step of adding a cation having a valence of 2 or more, a step of separating colloid particles from the colloid solution together with the carbon material, and a step of separating carboxylic acid and / or carboxylic acid contained in the separated carbon material with colloid particles.
Alternatively, the present invention relates to a method for producing a fuel cell electrode catalyst having a step of removing a carboxylate.

Further, the present invention provides a step of introducing hydrogen into an aqueous solution in which a platinum salt and at least one of a carboxylic acid and a carboxylate are dissolved to form a colloidal platinum solution, and forming colloidal particles from the colloidal platinum solution. The present invention relates to a method for producing an electrode catalyst for a fuel cell, comprising a step of electrodepositing a conductive carbon material and a step of removing a carboxylic acid and / or carboxylate contained in the carbon material on which colloid particles are electrodeposited.

According to the present invention, there is provided a step of introducing a hydrogen into an aqueous solution in which a platinum salt and at least one of a carboxylic acid and a carboxylate are dissolved to form a platinum colloid solution, and adding a conductive carbon material to the platinum colloid solution. After the addition, the step of adsorbing the colloid particles to the carbon material at a pH of the colloid solution equal to or higher than the isoelectric point and lower than 12, separating the carbon material having adsorbed the colloid particles from the colloid solution, and Provided is a method for producing an electrode catalyst for a fuel cell, comprising a step of removing a carboxylic acid and / or a carboxylate contained in the separated carbon material with colloidal particles.

The present invention comprises a polymer electrolyte membrane, an anode and a cathode sandwiching the polymer electrolyte membrane, wherein the anode-side catalyst layer comprises a layer containing a platinum catalyst in contact with the polymer electrolyte membrane, and ruthenium and platinum. The present invention relates to a fuel cell comprising a layer in contact with the above-mentioned layer, wherein at least 5% of all the platinum particles in the layer containing the platinum catalyst have a cubic or tetrahedral shape. The present invention also provides a polymer electrolyte membrane and an anode and a cathode sandwiching the polymer electrolyte membrane, wherein the anode-side catalyst layer contains ruthenium and platinum and is located in the vicinity of the fuel gas inlet, and The present invention relates to a fuel cell comprising a platinum catalyst layer located at a downstream portion of the fuel cell, wherein 5% or more of the platinum particles in the platinum catalyst layer have a cubic or tetrahedral shape.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An aqueous solution of potassium chloroplatinate (II) and an aqueous solution of sodium polyacrylate are mixed, and an argon gas is bubbled through the mixed solution, and then a hydrogen gas is bubbled and kept in a sealed state for about half a day. , A platinum colloid is formed. This platinum colloid is a regular tetrahedron → a tetrahedron → a cube →
It grows into an irregular shape. The crystal growth process varies depending on the amount of sodium polyacrylate added, the reduction time with hydrogen, and the pH of the solution. Therefore, by changing these factors, platinum particles of a certain shape can be the main product of the product particles (MA El-Sayed et al .;
Science, Vol.272, No.28, p.1924 (1996)). Specifically, when the addition amount of sodium polyacrylate is small, cubic platinum particles are easily generated, and when the addition amount of sodium polyacrylate is large, particles having many tetrahedrons can be obtained. In the platinum particles having these unique shapes, tetrahedral particles are rich in the (111) plane, and tetradecahedrons in which the vertices of the octahedron are cut off are rich in the (111) plane and the (100) plane, Cubic particles are rich in (100) plane.

[0010] The platinum particles of the present invention can be used in place of platinum black. This is particularly effective in a direct methanol type fuel cell. The platinum particles are preferably supported on a conductive carbon material, particularly carbon black, in order to reduce the amount of the platinum particles themselves. Next, a method for producing an electrode catalyst in which platinum particles are supported on a conductive carbon material will be described. First Electrode Catalyst for Fuel Cell of the Present Invention
Comprises the following steps. (1) a step of introducing hydrogen into an aqueous solution in which a platinum salt and at least one of a carboxylic acid and a carboxylate are dissolved to form a platinum colloid solution; and (2) adding a conductive carbon material to the platinum colloid solution. After the p
Adjusting H to 3 or less or 12 or more, (3) separating colloidal particles from the colloid solution together with the carbon material, and (4) carboxylic acid contained in the carbon material with separated colloidal particles And / or removing the carboxylate. The above step (2)
Is a step of easily separating colloid particles from the colloid solution. Step (3) separates the colloid particles and the carbon material from the liquid by, for example, applying the liquid to a centrifuge. By the steps (2) and (3), most of the colloid particles in the liquid are adsorbed or deposited on the carbon material. The isoelectric point of the above colloid is pH 2-3. Therefore, by setting the pH of the colloid solution to 3 or less, protons are attached to the dissociated carboxylic acid ions of the carboxylic acid, and the carboxylic acid ions are destabilized. Further, the carboxylic acid or a salt thereof protecting the colloid is destabilized because the carboxylate ion is surrounded by cations at an alkaline pH of 12 or more. In the present invention, this is used to facilitate separation of colloid particles.

In the second production method, in the step (2), a cation having a valence of two or more is added to the colloid solution instead of adjusting the pH of the colloid solution.
This facilitates separation of the colloid particles from the colloid solution. The carboxylic acid or salt thereof that protects the colloid is stabilized by dissociating into carboxylic acid ions, but is destabilized by the presence of a polyvalent cation such as aluminum sulfate. In the present invention, this is used to facilitate separation of colloid particles. In the third production method, colloid particles are electrodeposited on a carbon material from a colloid solution instead of the steps (2) and (3). That is, the colloid particles are applied to the carbon material by electrophoretic electrodeposition. A carboxylic acid or a salt thereof that protects the colloid has a negative charge because it is dissociated into carboxylic acid ions. Therefore, a DC voltage can be applied to the pair of electrodes immersed in the solution to immobilize the colloid particles on the carbon material on the positive electrode side. For example, a carbon material may be coated on an electrode in advance using a binder such as polytetrafluoroethylene, and the colloidal platinum particles may be supported on the carbon material by electrophoretic electrodeposition.

In a fourth manufacturing method, after the conductive carbon material is added to the platinum colloid solution, the colloid particles are mixed with the carbon particles at a pH equal to or higher than the isoelectric point (pH 2 to 3) and lower than 12. Adsorb to the material. When the colloid particles are supported on the carbon material in this manner,
Since the aggregation of the colloid particles is suppressed, the platinum particles can be more highly dispersed than in the first production method. In this case, the pH is desirably 3 to 5.5. In order to increase the amount of platinum supported on the carbon material, the pH is lowered once to about 5, and the mixture is left with stirring for a while.
It is more desirable to further reduce

The last step in the first to fourth methods is a step of removing impurities. The easiest way is
Heat treatment. Polyacrylic acid or a salt thereof, which is preferable as a carboxylic acid or a salt thereof, decomposes at 180 to 260 ° C. and is removed. When the heating temperature exceeds 350 ° C., the shape of the platinum particles changes and gradually approaches a spherical shape. Therefore, it is desirable that the heat treatment temperature does not exceed 350 ° C. The atmosphere of the heat treatment desirably does not contain oxygen in order to suppress oxidation of the carbon material. When the carboxylic acid or a salt thereof is a polymer such as polyacrylic acid, a preferable heat treatment temperature is 180 to 350 ° C. After this heat treatment, it is preferable to wash with water in order to remove residual sodium and the like.

To apply the platinum-supported carbon material thus prepared to a polymer electrolyte fuel cell, the platinum-supported carbon material is mixed with an alcohol solution containing a polymer solid electrolyte and an organic solvent to form an ink. Apply to a gas diffusion layer such as carbon paper. After drying, the polymer electrolyte membrane is sandwiched between the two gas diffusion layers with their catalyst layers inside, and hot pressed. Thereby, an electrolyte membrane / electrode assembly for a fuel cell is manufactured.

A polymer electrolyte membrane, an anode and a cathode sandwiching the polymer electrolyte membrane, wherein the anode-side catalyst layer contains a platinum catalyst in contact with the polymer electrolyte membrane, and the above-mentioned layer contains ruthenium and platinum In a fuel cell composed of a layer in contact with, the poisoning by carbon monoxide is suppressed by a platinum-ruthenium catalyst and the migration of platinum is suppressed. In the present invention, 5% or more of the platinum particles in the platinum layer in contact with the polymer electrolyte membrane have a cubic or tetrahedral shape.
Such an effect can be further improved. That is, it is considered that the migration of platinum is partly due to the movement of platinum together with the hydrogen atoms when the hydrogen atoms or protons spill over the platinum particles. It is considered that cubic or tetrahedral platinum particles have many (100) planes and (111) planes, respectively, so that spillover is suppressed and aggregation of particles is suppressed.

In a fuel cell in which the anode-side catalyst layer is composed of a layer containing ruthenium and platinum and located near the fuel gas introduction section, and a platinum layer located near the fuel gas discharge section, of the platinum particles of the platinum layer With a configuration in which 5% or more of the entire structure is cubic or tetrahedral, the platinum-ruthenium catalyst suppresses the deterioration of the characteristics due to carbon monoxide and also suppresses the migration of platinum. The oxidation of carbon monoxide usually occurs in the upstream part on the fuel electrode side. Therefore, by configuring the layer of the anode-side catalyst layer located in the vicinity of the fuel gas introduction portion with a layer containing ruthenium and platinum, it is possible to suppress the deterioration of characteristics due to carbon monoxide.

The water-soluble platinum salt used in the present invention includes chloroplatinic acid, dinitrodiamineplatinum, tetrachlorohexammineplatinum, dichlorotetraammineplatinum and the like. Of these, potassium chloroplatinate (II) is preferred.
Examples of carboxylic acids or salts thereof include acetic acid, propionic acid, sodium propionate, polyacrylic acid, sodium polyacrylate, ammonium polyacrylate, acrylic acid / maleic acid copolymer or salt thereof, and acrylic acid / sulfonic acid copolymer. And coalesced salts. The cubic and tetrahedral platinum particles of the present invention also include cubic and tetrahedral particles that appear to have slightly sharpened corners and sides when observed with a high-resolution transmission electron microscope. Including.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described. Example 1 A 1 × 10 ⁻⁴ mol / l aqueous solution of potassium chloroplatinate (II) was prepared and then left for 1 day. To this aqueous solution, a 0.1 mol / l aqueous solution of sodium polyacrylate (molecular weight: 2300) was added so that the molar ratio of potassium chloroplatinate (II) to sodium polyacrylate became 1: 5. This solution was bubbled with argon gas for 20 minutes, and then hydrogen gas for 5 minutes. Thereafter, the solution was sealed and left for 12 hours to obtain a golden transparent platinum colloid solution. Carbon black (acetylene black, manufactured by Denki Kagaku Kogyo KK) was added to the colloid solution, and after sufficiently dispersing the mixture, hydrochloric acid was added to adjust the pH of the solution to 2. When this solution was centrifuged, the supernatant was colorless and transparent. The separated solid was heat-treated at 300 ° C in a nitrogen stream, washed with water, and reduced with hydrogen at 250 ° C. Thus, an electrode catalyst in which platinum was supported on acetylene black at a weight ratio of 75:25 was prepared. The amount of platinum carried was determined by dissolving the catalyst with an acid and performing ICP analysis. When the platinum-supported catalyst thus prepared was observed with a high-resolution transmission electron microscope (TEM) at a magnification of 2,000,000, about 60% by weight of the platinum particles had a cubic shape, and the particle diameter was 10 to 20 nm.
However, a large number of aggregates in which several tens of particles were solidified were observed.

Next, a 9% by weight ethanol solution of perfluorosulfonic acid ionomer (Flemion manufactured by Asahi Glass) 4
75 g of ethanol and water were added to 2 g, and 6.5 g of the platinum-supported catalyst prepared above was further added to prepare an ink.
0.3mg of platinum on carbon paper
/ Cm ² by the doctor blade method,
Dried at 60 ° C. A polymer electrolyte membrane (Nafion 11 manufactured by DuPont) is used with the two gas diffusion electrodes thus manufactured.
2) was sandwiched and hot pressed at 130 ° C. to produce an electrolyte membrane / electrode assembly (hereinafter, referred to as MEA). This MEA
Was used to assemble the fuel cell. Oxygen humidified and heated to a dew point of 65 ° C is supplied to one gas diffusion electrode of this fuel cell, and hydrogen humidified and heated to a dew point of 70 ° C is supplied to the other gas diffusion electrode, respectively. Oxygen utilization rate 4
The battery characteristics were measured at 0%, a hydrogen utilization rate of 70%, and a cell temperature of 75 ° C. As a result, a voltage of 850 mV was shown at an output current density of 61 mA / cm ² .

Next, the following experiment was conducted in order to examine the effect of the proportion of cubic particles among the platinum particles on the battery characteristics. First, when preparing the above-mentioned platinum-supported acetylene black, by increasing the amount of acetylene black added to the colloid solution, Pt /
Acetylene black was prepared. On the other hand, after adding sodium hydrogen sulfite to the aqueous chloroplatinic acid solution, the pH of the solution was adjusted to 5 by adding an aqueous sodium hydroxide solution, and an aqueous hydrogen peroxide solution was added. To the platinum colloid solution thus obtained, an aqueous solution of sodium hydroxide was added to adjust the pH of the solution to 5, while the above-mentioned Pt / acetylene black was added, sufficiently dispersed, filtered, washed with water and dried. . As described above, platinum was additionally supported on the above-mentioned Pt / acetylene black by a general method, and an electrode catalyst having a weight ratio of acetylene black to the total supported amount of platinum of 75:25 was prepared. Thus, electrode catalysts having different cubic platinum particle ratios were prepared. For these electrode catalysts, the proportion of cubic platinum particles was confirmed by TEM. Electrodes were produced using these catalysts, and the characteristics were evaluated under the same conditions as above. Table 1 shows the results.

[0021]

[Table 1]

As shown in Table 1, when the proportion of cubic particles in all the platinum particles is 5% by weight or more, a remarkably high activity can be obtained. For comparison, the amount of platinum was 0.3 m
When the characteristics of a fuel cell manufactured using a commercially available gas diffusion electrode (manufactured by E-TEK) having a g / cm ² were measured, the voltage at an output current density of 40 mA / cm ² was 85.
It was 0 mV. When this catalyst was partially scraped and observed with a TEM at a magnification of 2,000,000, the proportion of cubic platinum was less than 1% by weight. The proportion of tetrahedral platinum was also less than 1% by weight. Next, the following experiment was performed in order to examine the pH dependence of the stability of the platinum colloid solution. Acetylene black was added to the golden transparent platinum colloid solution prepared in the same manner as above. At this point, the pH of the solution was 7-8. Hydrochloric acid was added to the colloid solution to change the pH one by one to the acidic side, and each time the mixture was centrifuged, and the supernatant was checked. p
Until H4, the color of the supernatant remains golden transparent and does not change.
It was confirmed that the supernatant was slightly colorless in H3 and almost colorless at pH2.

Example 2 The same platinum chloride (I
I) A 0.1 mol / l aqueous solution of sodium polyacrylate was added to the aqueous solution of potassium acid so that the molar ratio of potassium chloroplatinate (II) to sodium polyacrylate was 1: 1. This solution was bubbled with argon gas for 20 minutes, hydrogen gas was bubbled for 5 minutes, then sealed and left for 12 hours to prepare a platinum colloid. Using this colloid solution, an electrode catalyst in which platinum was supported on acetylene black at a weight ratio of 75:25 was prepared in the same manner as in Example 1. Observation of the platinum-supported catalyst thus prepared by TEM revealed that about 5% of the platinum particles were present.
0% by weight has a regular tetrahedral shape, and the particle size is 5 to 10%.
nm. Using the above electrode catalyst, a polymer electrolyte fuel cell was assembled in the same manner as in Example 1, and its characteristics were measured. As a result, the voltage at an output current density of 53 mA / cm ² was 850 mV.

Next, the following experiment was conducted in order to examine the effect of the ratio of the tetrahedral-shaped platinum particles on the battery characteristics. First, when preparing the above-mentioned platinum-supported acetylene black, the amount of acetylene black added to the colloid solution was increased to prepare Pt / acetylene black having a small platinum-supported amount. Pt was additionally supported on the Pt / acetylene black by the general method described in Example 1 to prepare an electrode catalyst having a weight ratio of acetylene black to the total amount of supported platinum of 75:25. Thus, electrode catalysts having different percentages of tetrahedral platinum particles were prepared.
With respect to these electrode catalysts, the proportion of platinum particles having a tetrahedral shape was confirmed by TEM. Electrodes were produced using these catalysts, and the characteristics were evaluated. Table 2 shows the results.

[0025]

[Table 2]

As shown in Table 2, when the proportion of tetrahedral particles in all the platinum particles was 5% by weight or more, remarkably high activity was obtained.

Example 3 In order to examine the pH dependence of the stability of a platinum colloid solution, the following experiment was performed. Acetylene black was added to the golden transparent platinum colloid solution prepared in Example 1. At this point, the pH of the solution was 7-8. To this colloid solution, an aqueous solution of sodium hydroxide is added to change the pH one by one to the alkaline side,
The supernatant was checked after each centrifugation. As a result, it was confirmed that up to pH 11, the color of the supernatant remained golden and transparent and did not change. At pH 12, the supernatant was slightly colorless, and at pH 13, it was almost colorless. The precipitate precipitated at pH 13 was heat-treated at 300 ° C in a nitrogen stream, washed with water, and then reduced at 250 ° C with hydrogen. Thus, an electrode catalyst in which platinum was supported on acetylene black at a weight ratio of 75:25 was prepared. A fuel cell was produced using this electrode catalyst, and the characteristics of the cell were measured under the same conditions as in Example 1. As a result, the output current density was 57 mA / cm ²
At 850 mV.

Example 4 Carbon black (acetylene black manufactured by Denki Kagaku Kogyo Co., Ltd.) was added to the platinum colloid solution prepared in Example 2, and then aluminum sulfate hydrate was converted to platinum. The mixture was added so as to be 5 times the volume, and stirred with a magnetic stirrer for 24 hours. Then, when the mixture was centrifuged, the supernatant became colorless and transparent, and precipitation of platinum colloid was confirmed.
The precipitate was heat-treated at 300 ° C. in a nitrogen stream, washed with water, and then reduced with hydrogen at 250 ° C. to obtain an electrode catalyst in which platinum was supported on acetylene black at a weight ratio of 75:25. Using this electrode catalyst, a fuel cell was fabricated in the same manner as in Example 1, and its characteristics were measured. As a result, the voltage at an output current density of 50 mA / cm ² was 850 mV.

Next, instead of the above aluminum sulfate hydrate, calcium nitrate tetrahydrate and potassium sulfate were added so that the mole numbers of calcium ions and potassium ions became 15 times those of platinum. The precipitation of the colloid was observed. As a result, the supernatant liquid after centrifugation was colorless and transparent when calcium nitrate tetrahydrate was added, but remained golden and transparent when potassium sulfate was added. From the above results, it was found that divalent or higher metal ions are effective for easily separating colloid particles.

Example 5 To 14 g of a 9 wt% ethanol solution of perfluorosulfonic acid ionomer (Flemion manufactured by Asahi Glass), 75 g of ethanol and water were added, and 6.5 g of acetylene black was further added to obtain an ink. This ink was applied to one side of a gold-plated brass plate with a bar coater and dried at 130 ° C. A platinum colloid solution prepared in the same manner as in Example 1 was placed in a beaker, and electrolysis was performed at 140 V and 0.18 A using the above gold-plated plate as a positive electrode. Immediately after the start of the electrolysis, the colloid particles were electrodeposited on acetylene black of the positive electrode, and the colloid solution became colorless and transparent. Thereafter, the gold-plated plate on which the colloidal particles are electrodeposited is heat-treated at 180 ° C. in a nitrogen stream, washed with water, and further cooled to 18
Hydrogen reduction at 0 ° C. Next, a 9% by weight ethanol solution of a perfluorosulfonic acid ionomer was uniformly dropped onto the acetylene black film so that the weight ratio (perfluorosulfonic acid ionomer) / (acetylene black) became 0.78, followed by drying. did. A polymer electrolyte membrane (Napion 112 manufactured by DuPont) is sandwiched between the two gold-plated plates with a catalyst layer thus prepared, with the catalyst layer inside.
By hot pressing at 130 ° C., the catalyst layer was transferred onto the polymer electrolyte membrane. The amount of platinum carried on the catalyst layer prepared here was I
As a result of CP analysis, the weight ratio of acetylene black to platinum was 77:23.

On the other hand, a water-repellent carbon paper having a water-repellent layer made of polytetrafluoroethylene and acetylene black provided on one side of the carbon paper was produced. Then, the carbon paper is overlaid with the water repellent layer facing the polymer electrolyte membrane with the catalyst layer prepared earlier,
The MEA was manufactured by hot pressing at 130 ° C. Using this, a fuel cell was manufactured, and the cell characteristics were measured under the same conditions as in Example 1. As a result, the output current density was 55 mA / cm
The voltage at ² was 850 mV.

Example 6 A 2 × 10 ⁻⁴ mol / l aqueous solution of potassium chloroplatinate (II) was left standing for one day after preparation.
0.1 of sodium polyacrylate (molecular weight 2300)
The mol / l aqueous solution was mixed such that the molar ratio of potassium chloroplatinate (II) to sodium polyacrylate was 1: 5. After argon gas was bubbled through the solution for 20 minutes, hydrogen gas was bubbled for 5 minutes. Thereafter, the solution was sealed and left for 12 hours. Thus, a golden transparent platinum colloid solution was obtained. When a part of this colloid solution was collected and the zeta potential was measured by changing the pH, it was found that the isoelectric point was around pH 2.5.

On the other hand, carbon black (Ketjen EC manufactured by Ketjen Black International) was dispersed in 300 ml of water. This dispersion was added to the above colloid solution, adjusted to pH 5 by adding hydrochloric acid, stirred with a magnetic stirrer for half a day, and then further adjusted to pH 3.5 and stirred for half a day. Thus, the colloid particles were adsorbed on the carbon black. This was filtered to collect carbon black adsorbing platinum colloid. This was heat-treated at 300 ° C. in a nitrogen stream, washed with water, and then reduced with hydrogen at 250 ° C. to prepare an electrode catalyst A in which platinum was supported on carbon black at a weight ratio of 3: 1. Observation of the platinum-supported catalyst thus prepared by TEM at a magnification of 2,000,000 revealed that about 60% of the platinum particles had a cubic shape and a particle diameter of 10 to 20 nm. Although some of the platinum particles formed an aggregate of several particles, they were generally uniformly dispersed. Subsequently, water and a perfluorosulfonic acid ionomer ethanol solution (Asahi Glass Co., Ltd., Flemion, perfluorosulfonic acid ionomer concentration 9 wt.%) Were added to 6.5 g of the electrode catalyst A.
%) Was added to obtain an ink. This ink was applied to carbon paper by a doctor blade method so that the Pt amount was 0.3 mg / cm ^2, and dried at 60 ° C. A polymer electrolyte membrane (Nafion 112 membrane manufactured by DuPont) is sandwiched between the two gas diffusion electrode layers thus produced,
MEA-a was produced by hot pressing at 130 ° C.

The cell using the MEA-a was maintained at 75 ° C., and the cathode was supplied with humidified air at a dew point of 65 ° C., and the anode was supplied with hydrogen humidified at a dew point of 70 ° C. Then, the battery characteristics were measured at an oxygen utilization of 40% and a hydrogen utilization of 70%. As a result, 75 mA /
It showed 850 mV at a current density of cm ² . Next, the following experiment was conducted in order to investigate the state of platinum particles supported on carbon black at a pH below the isoelectric point. First, in the above experiment, the pH was adjusted to 2 by adding carbon black dispersion water to the colloid solution, and then adding hydrochloric acid. After the solution was filtered, heat treatment and hydrogen reduction were performed in the same manner as above to obtain an electrode catalyst B. When the platinum-supported catalyst thus prepared was observed by TEM, the shape distribution of platinum was almost the same as that of catalyst A. However, agglomeration was progressing, and many agglomerates in which several tens of particles were solidified were found. Using this electrode catalyst B in the same manner as the catalyst A,
EA-b was fabricated and fuel cell characteristics were examined. As a result, 6
It showed 850 mV at a current density of 1 mA / cm ² .

Further, the pH of the stability of the colloidal platinum solution
The following experiment was performed to examine the dependency. First, carbon black was added to the platinum colloid solution prepared by the above method. At this point, the pH of the solution became 7 to 8. Next, an aqueous sodium hydroxide solution was added to change the pH of the solution to the alkaline side one by one, and each time, an experiment was performed in which centrifugation was performed and the supernatant was checked. As a result, p
Until H11, the color of the supernatant remains golden transparent and does not change,
At pH 12, the supernatant becomes slightly more colorless and at pH 1
It was confirmed that the sample was almost colorless at 3. Therefore, a colloidal platinum solution was prepared in the same manner as for the electrode catalyst A, carbon black was added thereto, the pH was adjusted to 13 with an aqueous sodium hydroxide solution, and the solution was filtered. Electrode catalyst C was obtained by heat-treating and hydrogen-reducing carbon black carrying platinum particles in the same manner as described above. When the platinum-supported catalyst thus prepared was observed by TEM, the shape distribution of platinum was almost the same as that of catalyst A. However, agglomeration was progressing, and many agglomerates in which several tens of particles were solidified were found. When the characteristics of the battery prepared using this electrode catalyst C were examined by the same method as that for the catalyst A, it was 57 mA / c.
It showed 850 mV at a current density of m ² .

Example 7 The ink prepared in Example 6, comprising the electrode catalyst A, water and the ethanol solution of perfluorosulfonic acid ionomer, was applied to a polypropylene sheet so that the Pt amount was 0.1 mg / cm ² . The resultant was coated with a bar coater and dried to form an anode-side catalyst layer. Similarly, a Pt content of 0.3 mg /
A cathode-side catalyst layer of cm ² was formed. These catalyst layers are formed on a polymer electrolyte membrane (Nafion 112 manufactured by DuPont).
Membrane). On the other hand, acetylene black was mixed with an aqueous dispersion of polytetrafluoroethylene (PTFE) powder, and this was applied to carbon paper by a spray method, and heat-treated to form a water-repellent layer. This was used as a cathode-side gas diffusion layer. An ink solution was prepared by adding an ethanol solution of a perfluorosulfonic acid ionomer to the carbon paper on which the water-repellent layer was formed, and to carbon black carrying platinum and ruthenium. Here, the weight ratio of carbon black to Pt and Ru is 56:30:24. This ink was applied on the water-repellent layer of the water-repellent treated carbon paper so as to have a Pt amount of 0.15 mg / cm ² by a doctor blade method, and dried to form an anode-side gas diffusion layer. . The polymer electrolyte membrane with the catalyst layer is sandwiched between the two gas diffusion layers thus produced,
MEA-d was produced by hot pressing at ℃.

Next, in order to prepare an electrode catalyst rich in tetrahedral particles, a 0.1 mol / l aqueous solution of sodium polyacrylate was added to an aqueous solution of potassium chloroplatinate (II) in the step of preparing a colloid of the catalyst. Has a molar ratio of potassium chloroplatinate (II) to sodium polyacrylate of 1:
1 was added. Otherwise in the same manner as the catalyst A, an electrode catalyst E in which platinum was supported on carbon black at a weight ratio of 75:25 was prepared. Observation of the platinum-supported catalyst thus prepared by TEM showed that about 50% of the platinum particles had a tetrahedral shape, and the particle diameter was 5%.
〜１０10 nm. Catalyst E in the same manner as MEA-d
Was used to produce MEA-e. On the other hand, a commercially available platinum-carrying acetylene black catalyst (weight ratio of acetylene black and platinum of 75:25) containing mostly spherical platinum particles was used as an anode catalyst on the polymer electrolyte membrane side, and MEA-d was used as catalyst A as a cathode catalyst. MEA-f was produced in the same manner as in the above.

Next, Pt-Ru catalyst was used as the anode side catalyst.
A catalyst supporting t and Ru at a weight ratio of 46:30:24, water and an ethanol solution of perfluorosulfonic acid ionomer (manufactured by Asahi Glass Co., Ltd.) were added to obtain an ink. This ink was applied to a polypropylene sheet with a bar coater such that the Pt amount was 0.25 mg / cm ² and dried. Electrode catalyst A was used as a cathode catalyst, and each catalyst layer was transferred to a polymer electrolyte membrane (Napion 112 membrane manufactured by DuPont) so that the Pt amount was 0.3 mg / cm ² . On the other hand, a water-repellent layer composed of PTFE and acetylene black was applied to carbon paper by a spray method and heat-treated to form a gas diffusion electrode. The above-mentioned polymer electrolyte membrane with a catalyst layer (Nafion 112 membrane manufactured by DuPont) was sandwiched between the two gas diffusion electrode layers thus produced, and hot pressed at 130 ° C. to produce MEA-g.
The fuel cell using MEA-d, e, f, and g was operated under the same conditions as in Example 6, and the current density was 200 mA.
/ Cm ² and then 75% H ₂ -25% CO ₂
The voltage was switched to -50 ppm CO reforming simulation gas and the voltage drop was measured. Subsequently, operation was performed for 500 hours under the reformed gas conditions. The voltage at a current density of 200 mA / cm ² under the flow of hydrogen after 500 hours, and the voltage drop at the same current density under the flow of reformed gas were measured again. Table 3 shows the results.

[0039]

[Table 3]

From the above results, in the polymer electrolyte fuel cell including the platinum catalyst layer in which the anode-side catalyst layer is in contact with the polymer electrolyte membrane and the layer containing ruthenium and platinum in contact with the platinum layer, the platinum layer in the platinum layer It can be seen that, due to the configuration having a cubic shape or a tetrahedral shape, there is little deterioration in characteristics due to carbon monoxide and good durability. After 500 hours of durability test, the anode side catalyst was
As a result, Pt-Ru was found to be about 2 in each MEA.
Particle growth occurred from nm to about 4 nm. Also, M
In EA-f, it was confirmed that the platinum particles grew from about 2.5 nm to about 4 nm. On the other hand, in the case of the anode-side Pt catalysts of MEA-d and MEA-e, no change in the particle diameter was observed. As described above, in the cubic and tetrahedral platinum particles, the (100) plane and the (111) plane
It is considered that aggregation of particles is suppressed because of having many surfaces.

Next, the following experiment was conducted to examine the effect of the ratio of the cubic particles on the characteristics. When supporting colloidal platinum particles by the same preparation method as the electrode catalyst A,
Pt / carbon black having a low Pt carrying amount was prepared by increasing the amount of carbon black. Pt / carbon black was additionally loaded with platinum to prepare an electrode catalyst having a weight ratio of carbon black to total platinum of 75:25.
The additional platinum was prepared by adding sodium hydrogen sulfite to chloroplatinic acid and then reacting with aqueous hydrogen peroxide to carry the resulting platinum colloid on carbon black. By this method, the ratio of the cubic platinum particles in the electrode catalyst was changed, and the ratio was confirmed by TEM. Using these catalysts, MEA-MEA was performed in the same manner as MEA-d.
-H was prepared, and the durability of CO poisoning resistance was evaluated in the same manner as in MEA-d. Table 4 shows the results.

[0042]

[Table 4]

As shown in Table 4, when the proportion of cubic particles in all the platinum particles was 5% or more, remarkable durability of CO poisoning resistance was recognized.

Next, the following experiment was conducted in order to examine the effect of the ratio of tetrahedral particles on battery characteristics. In the same preparation method as that for the electrode catalyst E, when supporting colloidal particles of platinum, the amount of carbon black was increased to increase the amount of Pt supported.
t / carbon black was prepared. Pt / carbon black was additionally loaded with platinum in the same manner as described above to prepare an electrode catalyst having a weight ratio of carbon black to the total amount of platinum of 75:25. Thus, the ratio of the tetrahedral-shaped platinum particles in the electrode catalyst was changed, and the ratio was confirmed by TEM. Using these catalysts, MEA-i was prepared in the same manner as MEA-d, and the durability of CO poisoning resistance was evaluated in the same manner. Table 5 shows the results.

[0045]

[Table 5]

As shown in Table 5, when the proportion of cubic particles in all the platinum particles was 5% or more, remarkable durability of CO poisoning resistance was recognized.

Example 8 The ink prepared in Example 6 and comprising the electrode catalyst A, water and an ethanol solution of perfluorosulfonic acid ionomer was applied to a polypropylene sheet so that the Pt amount was 0.3 mg / cm ^2. The mixture was applied with a bar coater and dried to form a catalyst layer. This sheet was cut into a rectangle of 4 cm × 6 cm to form an anode catalyst layer. Similarly, a catalyst layer having a Pt amount of 0.3 mg / cm ² was formed on a polypropylene sheet. This is 6cm
It was cut into a size of × 6 cm to form a cathode-side catalyst layer. These catalyst layers were transferred to both sides of a polymer electrolyte membrane (Nafion 112 membrane manufactured by DuPont).

The two catalyst layers were transferred to a polymer electrolyte membrane (Nafion 112 membrane manufactured by DuPont) such that one end thereof was fitted. The smaller catalyst layer was on the anode side, and the larger catalyst layer was on the cathode side. This is shown in FIG. 1 and FIG. A cathode-side catalyst layer 2 is joined to one surface of the polymer electrolyte membrane 1, and a catalyst layer 3a is joined to the anode side so as to correspond to a lower 2/3 portion of the cathode-side catalyst layer. On the other hand, a water-repellent layer composed of PTFE and acetylene black was applied to carbon paper by a spray method, and this was heat-treated. In addition, Pt and Ru are added to carbon black.
Was mixed at a weight ratio of 46:30:24 with an ethanol solution of a perfluorosulfonic acid ionomer to prepare an ink. The ink was applied onto the water-repellent layer of the carbon paper treated with the water-repellent treatment by a doctor blade method so that the Pt amount was 0.3 mg / cm ^2.
A t-Ru layer was provided and used as a gas diffusion electrode for an anode. This Pt-Ru catalyst layer 3b was formed in the upper half region of the anode channel. The electrode area was 6 cm × 6 cm, and the reaction gas was a fuel gas and an air flow using a carbon separator plate having serpentine-shaped grooves cut. As shown in FIG. 3, the separator plate 4 has inlet and outlet manifold holes 5a and 5b for fuel and inlet and outlet manifold holes 6a and 6b for air. On the surface of the separator plate 4 facing the anode, there is provided a fuel gas flow path 7 extending from the inlet-side manifold hole 5a to the outlet-side manifold hole 5b.
a and a turn portion 7b. On the surface of the separator plate 4 facing the cathode, similarly, there is an air flow path 8 that leads from the inlet-side manifold 6a to the outlet-side manifold hole 6b.

As shown in FIG. 2, the anode side catalyst has a Pt-Ru catalyst at the fuel inlet and a Pt-Ru catalyst + at the center.
The Pt catalyst and the downstream portion have a configuration in which the Pt catalyst is disposed.
As the cathode gas diffusion electrode, one provided with only a water-repellent layer was used. A polymer electrolyte membrane with a catalyst layer (manufactured by DuPont) is sandwiched between the two gas diffusion electrode layers thus prepared, and 13
MEA-j was prepared by hot pressing at 0 ° C. Also,
Using the electrode catalyst E prepared in Example 7 as the anode-side Pt catalyst, MEA-k was prepared in the same manner as MEA-j. Further, a method similar to MEA-j using a commercially available Pt / acetylene black catalyst (weight ratio of acetylene black to Pt: 75:25) having mostly spherical platinum particles as a Pt catalyst on the anode side of the polymer electrolyte membrane. MEA
-L was prepared. For fuel cells using MEA-j, k and l, a durability test was performed in the same manner as in Example 7, and before and after that, the CO poisoning characteristics were measured. Table 6 shows the results
Shown in

[0050]

[Table 6]

As is clear from the above results, the anode-side catalyst layer is composed of a catalyst layer containing ruthenium and platinum located near the fuel gas inlet and a platinum catalyst layer located near the fuel gas outlet. In the electrolyte fuel cell, the platinum particles of the platinum catalyst layer have a cubic or tetrahedral shape, so that a decrease in the CO poisoning resistance can be suppressed. As a result of observing the anode-side catalyst by a TEM after the 500-hour durability test, it was confirmed that Pt-Ru had particle growth in any MEA. In addition, it was confirmed that the Pt particle diameter of MEA-1 grew from about 2.5 nm to about 4 nm. On the other hand, M
In the anode side Pt catalyst of EA-j and MEA-k,
No change in particle size was observed. From this, it is considered that the cubic and tetrahedral platinum particles have many (100) planes and (111) planes, respectively, so that aggregation of the particles was suppressed.

[0052]

As described above, by using the electrode catalyst of the present invention, excellent initial characteristics and excellent durability can be exhibited with a low loading amount.

[Brief description of the drawings]

FIG. 1 is a front view showing an arrangement of a cathode-side catalyst layer bonded to an electrolyte membrane in an example of the present invention.

FIG. 2 is a front view showing an arrangement of an anode-side catalyst layer bonded to the electrolyte membrane.

FIG. 3 is a front view of the anode side of the conductive separator plate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrolyte membrane 2 Cathode side catalyst layer 3a, 3b Anode side catalyst layer 4 Separator plate 5a, 5b Fuel gas manifold hole 6a, 6b Air manifold hole 7, 7a, 7b Fuel gas flow path

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 8/02 H01M 8/02 E 8/10 8/10 (72) Inventor Yoshihiro Hori Kadoma, Osaka 1006, Kadoma Matsushita Electric Industrial Co., Ltd. In-house (72) Inventor Teruhisa Kamihara 1006 Kadoma, Kazuma, Osaka Pref. BB03 BB05 BB06 BB07 BB08 BB12 BB13 BB16 BB17 DD08 EE03 EE05 EE08 EE18 EE19 HH05 5H026 AA04 AA06 AA08 BB00 BB10 CX05 EE02 EE05 EE18 HH05

Claims (8)

[Claims] 1. An electrode catalyst for a fuel cell comprising platinum particles, of which 5% by weight or more are cubic or tetrahedral platinum particles. 2. An electrode catalyst for a fuel cell comprising platinum particles, of which 5% by weight or more are platinum particles having a (100) plane or a (111) plane. 3. A step of introducing a hydrogen into an aqueous solution in which a platinum salt and at least one of a carboxylic acid and a carboxylic acid salt are dissolved to form a platinum colloid solution, wherein a conductive carbon material is added to the platinum colloid solution. Thereafter, a step of adjusting the pH of the colloid solution to 3 or less or 12 or more, a step of separating colloid particles from the colloid solution together with the carbon material, and a carboxylic acid contained in the separated colloid particle-containing carbon material and A method for producing an electrode catalyst for a fuel cell, comprising a step of removing a carboxylate. 4. A step of introducing a hydrogen into an aqueous solution in which a platinum salt and at least one of a carboxylic acid and a carboxylate is dissolved to form a platinum colloid solution, wherein a conductive carbon material is added to the platinum colloid solution. Thereafter, a step of adding a cation having a valence of 2 or more, a step of separating colloid particles from the colloid solution together with the carbon material,
And a method for producing an electrode catalyst for a fuel cell, comprising a step of removing a carboxylic acid and / or a carboxylate salt contained in the separated carbon material with colloidal particles. 5. A step of introducing a hydrogen into an aqueous solution in which a platinum salt and at least one of a carboxylic acid and a carboxylate are dissolved to form a platinum colloid solution, and converting colloid particles from the platinum colloid solution to a conductive carbon material. A method for producing an electrode catalyst for a fuel cell, comprising: a step of electrodepositing the carbon material; 6. A step of introducing a hydrogen into an aqueous solution in which a platinum salt and at least one of a carboxylic acid and a carboxylate is dissolved to form a platinum colloid solution, wherein a conductive carbon material is added to the platinum colloid solution. Thereafter, a step of adsorbing the colloid particles to the carbon material at a pH of the colloid solution equal to or higher than the isoelectric point and lower than 12; a step of separating the carbon material having adsorbed the colloid particles from the colloid solution; and A method for producing an electrode catalyst for a fuel cell, comprising a step of removing a carboxylic acid and / or a carboxylate contained from the carbon material provided with the colloid particles. 7. A polymer electrolyte membrane, comprising an anode and a cathode sandwiching the polymer electrolyte membrane, wherein the anode-side catalyst layer contains a layer containing a platinum catalyst in contact with the polymer electrolyte membrane, and contains ruthenium and platinum. And wherein at least 5% of all platinum particles in the layer containing the platinum catalyst have a cubic or tetrahedral shape. 8. A polymer electrolyte membrane, comprising an anode and a cathode sandwiching the polymer electrolyte membrane, wherein the anode-side catalyst layer contains ruthenium and platinum and is located in the vicinity of the fuel gas inlet, and A fuel cell comprising a platinum catalyst layer located downstream, wherein at least 5% of all platinum particles in the platinum catalyst layer have a cubic or tetrahedral shape.