KR20230006471A - Manufacturing method of platinum cobalt chrome alloy supported carbon catalyst for fuel cell - Google Patents

Abstract

(Problem) In particular, to provide a platinum-cobalt-chromium alloy-supported carbon catalyst having high performance stability and durability during use.
(Solution) By adding an aqueous solution of chloroplatinic acid to an aqueous suspension of carbon powder containing L-ascorbic acid heated to 80 to 100° C. at a charge rate of 0.001 g/min to 0.03 g/min in terms of platinum per 1 g of carbon powder , As a first reduction step of supporting platinum particles grown to a size of the order of nanometers on the surface of the carbon powder in a spiral shape, ascorbic acid is used in a molar ratio of 2.33 to 3.17 times that of the chloroplatinic acid used above. By adding L-ascorbic acid in an amount capable of reducing all of the chloroplatinic acid remaining after the first reduction step and the suspension heated to 80 to 100° C. after the first reduction step to reduce the chloroplatinic acid, , a second reduction step of depositing platinum on the surface of the platinum particle, depositing platinum particles on the surface of the carbon powder obtained in this way, and further, cobalt hydroxide and chromium hydroxide on the platinum particle A method for producing a platinum-cobalt-chromium alloy-supported carbon catalyst for a fuel cell, characterized by obtaining a powder supporting precipitated platinum particles in a form, and heat-treating the powder in an inert gas or nitrogen atmosphere.

Description

Manufacturing method of platinum cobalt chrome alloy supported carbon catalyst for fuel cell

The present invention relates to a method for producing a platinum-cobalt-chromium alloy-supported carbon catalyst for a fuel cell.

Conventionally, catalysts in which platinum or a platinum alloy is supported on the surface of a carbon support as an electrode catalyst for fuel cells or on an inorganic oxide support such as silica as an exhaust gas treatment catalyst have been used.

In the production of a platinum alloy-supported catalyst, a method of first supporting platinum on a carbon support or the like, then adding a metal to be alloyed in the form of a compound, and finally alloying these metals may be used.

Regarding the method for producing platinum-supported carbon, Patent Document 1 discloses that a catalyst carrier made of carbon black or the like is brought into contact with an aqueous acid solution to undergo a hydrophilic treatment, and an aqueous solution of chloroplatinic acid is brought into sufficient contact, then the pH of the system is made alkaline. , by raising the temperature of the system to the temperature at which the reducing agent acts, adding hydrogen peroxide as a colloidal aggregation inhibitor, gradually adding a reducing agent having an aldehyde group, and reducing and supporting chloroplatinic acid, the supported amount is about 10.5% and the platinum particle size is about It is described that catalysts that are 30 angstroms are obtained.

Further, in Patent Literature 2, carbon powder as a carrier is added to a solution in which dinitrodiammine platinum is dissolved in nitric acid, stirring is continued for 60 minutes to sufficiently disperse, an aqueous solution of L-ascorbic acid is added, and the mixture is stirred and mixed. It is described that carbon powder carrying 9% by weight of platinum can be obtained by heating and holding overnight (16 hours) in a 65°C hot water bath, and then filtering, washing, and drying after standing to cool.

Japanese Unexamined Patent Publication No. 63-49253 Japanese Laid-open Patent Publication Hei 04-298238

Patent Literatures 1 and 2 are methods in which a platinum compound is first brought into contact with a carbon support, then the platinum compound is reduced with a reducing agent, and fine platinum particles having a size of several nanometers are supported on the surface of the carbon powder. There was a problem that the aggregation of the catalyst particles progressed during the process, and the performance changed (decreased).

Catalysts for fuel cells, for example, cathode catalysts for phosphoric acid type fuel cells, for which it is strongly desired to improve performance stability and durability from the initial stage to the end of use, catalyst particles having a larger size and smaller size variation are used. It has become a subject to make it supported by carbon powder.

The present inventors, in the case of forming platinum particles of a shear layer to obtain platinum cobalt chromium alloy particles, 70% to 95% of a predetermined amount of chloroplatinic acid in a reducible amount to a suspension obtained by suspending carbon powder in water, , L-ascorbic acid in a molar ratio of 2.33 to 3.17 times that of chloroplatinic acid is added to the suspension heated to 80 to 100°C, and then an aqueous solution of chloroplatinic acid is added at a rate of 0.001 g/min to 0.03 in terms of platinum per 1 g of carbon powder. Platinum particles grown to a size on the order of nanometers are supported on the surface of the carbon powder in a form by adding to the suspension at a feed rate of g/min (first reduction step), and then In the suspension heated to 80 to 100 ° C. after the first reduction step, chloroplatinic acid that can still remain without being reduced (corresponding to 5% to 30% of the initial amount in the first reduction step, although not limited thereto), Furthermore, if the second reduction step of reducing all of the remaining chloroplatinic acid is performed using L-ascorbic acid, all of the initial amount of chloroplatinic acid can be efficiently supported on the surface of the carbon powder, and furthermore , through subsequent cobalt hydroxide and chromium hydroxide precipitation steps, it was found that platinum-cobalt-chromium alloy particles having a relatively large and non-variable particle size can be supported on the surface of the carbon powder.

Therefore, the above object has the following characteristics or is solved by the present invention of the aspect.

Aspect 1: Step of preparing an aqueous suspension of carbon powder;

A step of preparing an aqueous solution of chloroplatinic acid;

Adding L-ascorbic acid to an aqueous suspension of the carbon powder heated to 80 to 100°C, and then, while maintaining this heating temperature, to the obtained aqueous suspension of the carbon powder containing ascorbic acid, in terms of platinum per 1 g of the carbon powder As a first reduction step of supporting platinum particles grown to a size of nanometer order on the surface of the carbon powder, A first reduction step in which ascorbic acid is used in a molar ratio of 2.33 to 3.17 times that of chloroplatinic acid used in;

The surface of the platinum particles is reduced by adding L-ascorbic acid in an amount capable of reducing all of the chloroplatinic acid remaining after the reduction step to the suspension heated to 80 to 100° C. after the first reduction step, and reducing the chloroplatinic acid. A second reduction step of depositing platinum on the phase;

A resuspension solution after filtering the suspension containing the carbon particles carrying platinum particles obtained in the second reduction step to obtain a filter cake containing the carbon particles carrying platinum particles, washing the filter cake and resuspending it in water. a precipitation step of precipitating cobalt hydroxide and chromium hydroxide on the surface of the platinum particle by adding an aqueous solution of a chromium compound and an aqueous solution of a cobalt compound to the solution, and then adjusting the pH to 9 to 11 with aqueous ammonia;

The suspension obtained in the precipitation step is filtered, the particles in which cobalt hydroxide and chromium hydroxide are precipitated on the surfaces of the platinum particles are washed and dried, and the platinum particles in which cobalt hydroxide and chromium hydroxide are precipitated on the surface of the carbon powder are obtained. A step of obtaining powder to be supported in a form;

Preparation of a platinum-cobalt-chromium alloy-supported carbon catalyst for a fuel cell, comprising a heat treatment step of heat-treating the carbon powder carrying the platinum particles on which cobalt hydroxide and chromium hydroxide are precipitated in the form obtained in the above step in an inert gas or nitrogen atmosphere. Way.

Aspect 2: A method for producing a platinum cobalt chromium alloy supported carbon catalyst for a fuel cell according to Aspect 1, wherein the amount of platinum in the platinum cobalt chromium alloy supported carbon catalyst is adjusted to 11 wt% to 15 wt% on a weight basis.

Embodiment 3: In the first and second reduction steps of chloroplatinic acid, the temperature of the suspension is set to 92 ° C. to 95 ° C., and the average particle size of the platinum cobalt chrome alloy particles is adjusted to 10 to 20 nm. A method for producing a platinum-cobalt-chromium alloy-supported carbon catalyst for a fuel cell of aspect 1 or 2.

According to the present invention, it is possible to manufacture a platinum-cobalt-chromium alloy-supported carbon catalyst for a fuel cell in which platinum-cobalt-chromium alloy particles having a relatively large particle size and small size variation are supported.

BRIEF DESCRIPTION OF THE DRAWINGS It is an example of the TEM image of platinum carrying carbon after passing through the 2nd reduction process in the manufacturing method of this invention.
Fig. 2 is an example of a TEM image of a platinum-cobalt-chromium alloy-supported carbon catalyst obtained by the production method of the present invention.

Terms used in this specification are understood to have meanings commonly used in the art unless otherwise specified.

By chloroplatinic acid is meant hexachloride platinum (IV) acid (H ₂ PtCl ₆ ). In addition, L-ascorbic acid is also simply referred to as "ascorbic acid".

Embodiment 1 is characterized in that the first reduction step and the second reduction step are employed. In addition to adopting such a characteristic configuration, the first reduction step and the second reduction step include the following characteristic configuration. Specifically, in the first reduction step, L-ascorbic acid is added to a heated solution at 80 to 100°C of an aqueous suspension of carbon powder prepared in advance, and then, while maintaining this heating temperature, the resulting ascorbic acid-containing carbon powder Platinum particles grown to a size on the order of nanometers on the surface of the carbon powder by adding the aqueous chloroplatinic acid solution to the aqueous suspension at an input rate of 0.001 g/min to 0.03 g/min in terms of platinum per 1 g of the carbon powder. In addition, it is characterized in that the ascorbic acid is used in a molar ratio of 2.33 to 3.17 times the chloroplatinic acid used in the treatment. As used herein, the molar ratio of ascorbic acid to chloroplatinic acid is greater than the stoichiometric molar ratio required for reducing electrons. This is based on the fact that it has been confirmed that ascorbic acid used according to the stoichiometry does not act under the reaction conditions of the first reduction step in Embodiment 1. Although not limited, in Embodiment 1, about 70% to about 95% of the chloroplatinic acid used is reduced by the above-mentioned “2.33 to 3.17 times the ascorbic acid is used”. In this way, the second reduction step is adopted, and in this step, L-ascorb in an amount capable of reducing all of the chloroplatinic acid remaining after the reduction step is added to the suspension heated to 80 to 100 ° C. after the first reduction step acid is added. However, it has been confirmed that in order to reduce the entire amount of chloroplatinic acid used in the first reduction step, it is necessary to use ascorbic acid in a molar ratio of approximately 3.33 times. Therefore, the amount of ascorbic acid capable of reducing all (calculated 5% to 30%) of the chloroplatinic acid remaining after the first reduction step is X times that of chloroplatinic acid in the amount of ascorbic acid added in the first reduction step. In the case of a molar ratio of moles, ascorbic acid at a molar ratio of (3.33-X) times or more to chloroplatinic acid may be added to the heated suspension after the first reduction step.

Although the scope of the present invention is not limited by theory, this is understood as follows.

When an aqueous solution of chloroplatinic acid is added to a heated suspension containing ascorbic acid, a reduction reaction of platinum proceeds immediately at the initial stage of addition, and nanometer-sized platinum particles are formed. On the other hand, from the latter half of the addition of the aqueous chloroplatinic acid solution to the end of the addition, the amount of L-ascorbic acid is limited to an amount capable of reducing 70% to 95% of the chloroplatinic acid. Platinic acid is reduced slowly. When this slowly reduced chloroplatinic acid becomes larger particles and is about to reach a stable state, it acts like an adhesive connecting the platinum particles to each other, and on the platinum particles supported on the carbon, the platinum particles initially formed have a linking effect. Thus, in this production method, the platinum particles grow in a linear fashion and are supported on the carbon carrier. In this way, in the invention of aspect 1, the first reduction step and the second reduction step are employed.

Next, the suspension after the second reduction step is filtered to obtain a filter cake containing carbon particles carrying platinum particles. This filter cake is washed with water and resuspended in water to prepare a resuspended liquid. used Further, this suspension is subjected to a precipitation step in which cobalt hydroxide and chromium hydroxide are precipitated on the surface of the platinum particles by adding an aqueous solution of a chromium compound and an aqueous solution of a cobalt compound, and then adjusting the pH to 9 to 11 with aqueous ammonia. The suspension obtained in this precipitation step is filtered, washed, and dried in the same way as obtaining the above-mentioned filter cake containing carbon particles supporting platinum particles, and cobalt hydroxide and chromium hydroxide are precipitated on the surface of the carbon powder. It is provided in the process of obtaining a powder in which platinum particles are supported in a spiral shape. The powder can provide a desired platinum-cobalt-chromium alloy-supported carbon catalyst for a fuel cell, which is further subjected to a heat treatment step of heat-treating the powder in an inert gas or nitrogen atmosphere.

Although the description may be overlapped below, the present invention will be described more concretely.

The carbon powder used in Embodiment 1 is not particularly limited, but may be used to support platinum in the production of the electrode catalyst, and examples include carbon black such as furnace black, channel black, and acetylene black; The graphitized carbon etc. which carried out the graphitization process of these are mentioned. For example, a suspension is obtained by suspending conductive graphitized carbon having a specific surface area of 50 m 2 /g to 300 m 2 /g in water. The carbon concentration in the suspension can be 10 g/L to 18 g/L.

The water used here can be ion-exchanged pure water.

A step of preparing an aqueous solution of chloroplatinic acid is included. The concentration can be 130 g/L to 660 g/L in terms of platinum.

In the first reduction step and the second reduction step, L-ascorbic acid is used as a reducing agent for platinum, but ascorbic acid is a reducing agent that is safe and easy to handle compared to aldehydes, hydrazine, and ethanol, which are frequently used in various reduction systems. In addition, chloroplatinic acid is the most common and relatively inexpensive among platinum compounds.

Further, in the first reduction step, the aqueous chloroplatinic acid solution is added to an aqueous suspension of the ascorbic acid-containing carbon powder at 80 to 100°C at a feeding rate of 0.001 g/min to 0.03 g/min in terms of platinum per 1 g of the carbon powder. . Here, when the temperature of the suspension is lower than 80 ° C., the reduction reaction of chloroplatinic acid hardly proceeds, and at 100 ° C. or higher, the evaporation amount of water as the solvent increases, making it difficult to titrate the solvent amount. Therefore, the heating temperature is 80 to 100 ° C. It is common to have a range. In addition, since the heating temperature in the first reduction step affects the rate of the reduction reaction and the degree of growth of the linear platinum particles, in order to control the linear platinum particles with good precision, the heating temperature is of a predetermined ±1.5°C. It is desirable to control within the range.

Next, an aqueous solution of chloroplatinic acid is added in an amount of 0.001 g/min to 0.03 g/min, preferably 0.002 g/min to 0.01 g/min, more preferably 0.003 g/min in terms of platinum per 1 g of carbon powder in the suspension. min to 0.006 g/min, and added to the suspension.

1 shows an example of a TEM image of platinum-carrying carbon after the second reduction step produced by this production method.

According to FIG. 1, most of the platinum is reduced in the first reduction step, and it is considered that after the first reduction step, the platinum particles are supported on the carbon carrier in a linear shape as shown in the TEM image. The degree of growth of these asymmetric platinum particles may be the largest factor in determining the alloy particle size.

By adding an aqueous solution of chloroplatinic acid at a predetermined feed rate for 0.001 g/min to 0.03 g/min in terms of platinum per 1 g of carbon powder, the degree of particle growth can be stably and uniformly controlled to an industrially feasible level. there is.

This reason is considered to be because the reduction reaction rate can be controlled under sufficient mixing and diffusion conditions by controlling the rate at which chloroplatinic acid is added in the step.

As can be seen from Table 1 shown later, since the average particle diameter of the alloy changes with the rate of introduction of the aqueous chloroplatinic acid solution, using this relationship, the average particle diameter of the alloy is particularly targeted among 8 to 20 nm. It is possible to adjust to the average particle diameter of The average particle diameter of the alloy can be preferably 8 to 16 nm, more preferably 10 to 14 nm.

In the second reduction step, as described above, ascorbic acid in an amount capable of reducing all of the chloroplatinic acid remaining unreduced in the first reduction step is added to the suspension heated to 80 to 100°C after the first reduction step. In this way, additional platinum can be deposited on the platinum particles precipitated on the carbon powder in the first reduction step.

The amount of L-ascorbic acid added to the suspension in the second reduction step is equal to or greater than the amount capable of reducing all of the remaining chloroplatinic acid in the first reduction step. For example, when L-ascorbic acid is added in a molar ratio of 2.33 times that of chloroplatinic acid in the first reduction step, (3.33 - 2.33) = 1.00 times more L-ascorbic acid in the second reduction step. with the amount of acid.

Further, for example, when 3.17 times mole of L-ascorbic acid is added to chloroplatinic acid in the first reduction step, (3.33 - 3.17) = 0.16 times mole or more of L- in the second reduction step. the amount of ascorbic acid.

By adjusting the amount of L-ascorbic acid added to the suspension in the second reduction step as described above, the remaining 5 to 30% of unreduced chloroplatinic acid after the first reduction step plays an adhesive role in the second reduction step. Including the chloroplatinic acid formed, all of the chloroplatinic acid can be reduced and supported on the platinum carbon. Needless to say, it is industrially important to carry almost completely on carbon in this way and not to generate unreduced platinum leading to platinum loss, and for that reason, a large excess (the amount of reducing all of chloroplatinic acid) It is preferable to reduce by adding L-ascorbic acid in an amount of about 3 times). That is, in the second reduction step, a large excess (about 3 times the amount capable of reducing all of the chloroplatinic acid) of L-ascorbic acid can be added in order to completely reduce the remaining unreduced chloroplatinic acid. - You may divide and add ascorbic acid in multiple times.

As described above, the suspension after the second reduction step is filtered to obtain a filter cake containing carbon particles carrying platinum particles. This filter cake is washed with water and resuspended in water. used in preparation Further, this suspension is subjected to a precipitation step in which cobalt hydroxide and chromium hydroxide are precipitated on the surface of the platinum particles by adding an aqueous solution of a chromium compound and an aqueous solution of a cobalt compound, and then adjusting the pH to 9 to 11 with aqueous ammonia. The suspension obtained in this precipitation step is filtered, washed, and dried in the same way as obtaining the above-mentioned filter cake containing carbon particles supporting platinum particles, and cobalt hydroxide and chromium hydroxide are precipitated on the surface of the carbon powder. It is provided in the process of obtaining a powder in which platinum particles are supported in a spiral shape. The powder can provide a desired platinum-cobalt-chromium alloy-supported carbon catalyst for a fuel cell, which is further subjected to a heat treatment step of heat-treating the powder in an inert gas or nitrogen atmosphere. The above-described precipitation step of depositing cobalt hydroxide and chromium hydroxide on the surface of the platinum particles can generally be performed at a temperature of 5°C to 50°C for 0.1 hour to 3 hours.

The cleaning method described above is not particularly limited and can be performed by various means. Filtration can be performed using a belt filter, a drum filter, a centrifugal separator, a vacuum filter, a pressure filter, a filter press, or the like.

Regarding the method of depositing and supporting cobalt hydroxide and chromium hydroxide, the filter cake containing carbon particles supporting platinum obtained in the second reduction step is resuspended in water, for example, with an aqueous solution of chromium acetate and an aqueous solution of cobalt acetate. By mixing and adjusting the pH of the mixture obtained in this way to 9 to 11 with aqueous ammonia, cobalt hydroxide and chromium hydroxide can be deposited on the surface of the platinum particles. As the cobalt compound and the chromium compound, chromium acetate and cobalt acetate can be used. Moreover, compounds, such as chromium nitrate and cobalt nitrate, can be used instead of acetate.

In this way, it is possible to obtain a powder in which cobalt hydroxide and chromium hydroxide are precipitated on the surface of the carbon powder and platinum particles of nanometer order are supported in a linear shape. This powder is heat-treated in an inert gas or nitrogen atmosphere.

The filtration and washing of the suspension of the platinum-cobalt hydroxide-chromium hydroxide-carrying carbon powder can be performed by the same means as the filtration and washing of the platinum-carrying carbon suspension.

The drying method used in these steps is not particularly limited, but can be dried using various dryers, specifically, using a hot air dryer, vacuum dryer, inert oven, etc. A method of performing several hours to several tens of hours at a temperature may be mentioned.

The dried platinum-cobalt hydroxide-chromium hydroxide-supported carbon powder is subjected to heat treatment in an inert gas or nitrogen atmosphere at, for example, 800°C to 1100°C. As a result, alloy particles of platinum cobalt chromium are produced. At this time, the inert gas used is not particularly limited, but helium gas or argon gas can be used. Preferably, gas can be carried out under circulation.

Fig. 2 shows an example of a TEM image of the platinum-cobalt-chromium alloy-supported carbon catalyst obtained as described above.

Example

Examples of the present invention will be described below, but the present invention is not limited thereto.

(Example 1)

First, 1877 g of conductive graphitized carbon having a specific surface area of about 80 m 2 /g was suspended in 150 L of pure water, and the suspension was heated at 97 to 100° C. while stirring, and then 594 g of L-ascorbic acid was added, , 5 minutes after that, the addition of the aqueous chloroplatinic acid solution was started. At this time, what was dissolved in 1100 g of pure water of chloroplatinic acid corresponding to 264 g in terms of platinum content was added at a constant rate over 40 minutes using a liquid feed pump. Therefore, the feed rate of the aqueous chloroplatinic acid solution is 0.0035 g/min in terms of platinum per 1 g of carbon powder. Five minutes after completion of the addition of the aqueous chloroplatinic acid solution, 1306 g of L-ascorbic acid was added, and heating was stopped 10 minutes after that. In this way, a suspension containing a powder in which platinum particles were supported on a carbon carrier in a form was obtained. Hereinafter, this suspension is called "SPtC1".

<Precipitation of cobalt hydroxide and chromium hydroxide>

The suspension SPtC1 was filtered to obtain a filter cake. After washing this, it was suspended in 120 L of pure water, heated at 25 to 30 ° C. while stirring, and then a solution obtained by dissolving 174 g of cobalt (II) acetate tetrahydrate and 118 g of chromium (III) acetate in 3 L of water was added. and mixed for 30 minutes or longer. Thereafter, 762 g of 25% aqueous ammonia was added to the suspension at a constant rate over 10 minutes to precipitate cobalt hydroxide and chromium hydroxide using a liquid feed pump. In this way, a suspension containing the carbon powder on which the square-shaped platinum particles in which cobalt hydroxide and chromium hydroxide were precipitated on the surfaces of the platinum particles was supported was obtained. Hereinafter, this suspension is called "SPtCoCrC1".

The suspension SPtCoCrC1 was filtered to obtain a filter cake. After washing this, it used for vacuum drying at 100 degreeC over 48 hours. In this way, a carbon powder having cobalt hydroxide and chromium hydroxide precipitated on the surfaces of the platinum particles supported with linear platinum particles was obtained. Hereinafter, this powder is referred to as &quot;powder P1&quot;.

Subsequently, after pulverizing the powder P1 into a fine powder, it was subjected to heat treatment in a nitrogen atmosphere at 980°C for 1.5 hours.

As described above, a platinum cobalt chromium alloy supported carbon catalyst was prepared. Hereinafter, this is called "Example 1".

(Example 2)

A supported catalyst was prepared in the same manner as in Example 1, except that the temperature at the time of reduction and supporting of chloroplatinic acid was set to 92 to 95 ° C., and the addition time of chloroplatinic acid was set to 35 minutes. Hereinafter, this is called "Example 2". At this time, the feed rate of chloroplatinic acid is 0.0040 g/min per 1 g of carbon powder.

(Example 3)

A supported catalyst was prepared in the same manner as in Example 1, except that the temperature at the time of reduction and supporting of chloroplatinic acid was set to 92 to 95° C. and the addition time of chloroplatinic acid was set to 31 minutes. Hereinafter, this is called "Example 3". At this time, the feed rate of chloroplatinic acid is 0.0045 g/min per 1 g of carbon powder.

(Example 4)

A supported catalyst was prepared in the same manner as in Example 1, except that the temperature at the time of reduction and supporting of chloroplatinic acid was set to 92 to 95 ° C., and the addition time of chloroplatinic acid was set to 29 minutes. Hereinafter, this is called "Example 4". At this time, the feed rate of chloroplatinic acid is 0.0049 g/min per 1 g of carbon powder.

(Comparative Example 1)

Except that the amount of L-ascorbic acid introduced in the first reduction step was 1900 g, which is an amount capable of reducing all chloroplatinic acid, the addition time of chloroplatinic acid was set to 10 seconds, and the second reduction step was not performed. , In the same manner as described for Example 1, a supported catalyst was prepared. Hereinafter, this is called "Comparative Example 1". At this time, the feed rate of chloroplatinic acid is 0.8443 g/min per 1 g of carbon powder.

In Table 1 below, the average particle diameter and standard deviation σ of the platinum cobalt chromium alloy of the platinum cobalt chromium alloy supported carbon catalysts of Examples 1 to 4 and Comparative Example 1 are shown.

<Measurement of Average Particle Diameter of Catalyst Particles>

It was obtained from TEM observation of each sample.

In Comparative Example 1 of Table 1, the variation in alloy grain size was large, which was undesirable catalyst property.

On the other hand, in the catalysts related to Examples 1 to 4 in Table 1, the average particle diameter of the alloy particles was in the range of 8 to 20 nm, and was relatively uniform. In addition, by changing the temperature and the dripping time of chloroplatinic acid, it is possible to adjust the particle size of the alloy to be particularly targeted. That is, from these results, by producing a catalyst by this production method, in a platinum-cobalt-chromium alloy catalyst, the target catalyst particle size in the range of 8 to 20 nm is well reproduced and produced on an industrial scale What could be done was suggested.

<Electrochemical evaluation>

To evaluate performance as an electrode catalyst for fuel cells, the oxygen reduction reaction (ORR) activity of the catalyst of Example 2 was evaluated by a rotating electrode method using a potentiogalvanostat manufactured by B.A.S.

A catalyst ink was prepared by dispersing the catalyst of Example 2 and a perfluorosulfonic acid dispersion in a mixed solvent of 2-propanol and water. The prepared catalyst ink was applied to glassy carbon (6 mm in diameter) in such a way that the amount of platinum was 18 μg/cm 2 to prepare a measuring electrode.

The prepared measurement electrode was immersed in 0.1 mol/L perchloric acid at 25°C saturated with nitrogen gas, and a reversible hydrogen electrode (RHE) was used as the reference electrode and a platinum wire was used as the counter electrode, and the potential scanning range was 0.05 V to 1.2 V (vs RHE), CV (cyclic current potential curve) was measured at a potential scan rate of 50 mV/sec. ECSA (electrochemically active surface area) was calculated from the hydrogen delipah of the obtained CV. Thereafter, oxygen gas was introduced into the cell, and the electrode for measurement was rotated at 1600 rpm under an oxygen gas saturated atmosphere, and a polarization curve was measured at a potential scanning speed of 10 mV/sec at a potential of 0.05 V to 1.2 V (vs. RHE). was measured. From the obtained polarization curve, the oxygen reduction current value (I) of 0.9 V and the oxygen reduction current value (Id) of 0.4 V as the diffusion limit current value, the activation dominant current value (Ik) excluding the diffusion effect of oxygen was calculated by the following formula.

Ik = Id I (Id I)

The specific activity was calculated by dividing this activation dominant current value (Ik) by ECSA, and the mass activity was calculated by dividing by the weight of platinum on the glassy carbon electrode. The ECSA of the catalyst of Example 2 was 8.4 m 2 /g, and the specific activity and mass activity were 5692 μA/cm 2 and 478 A/g, respectively. By increasing the catalyst particle size, ECSA is relatively small, but specific activity and mass activity are high, and high output is obtained. Therefore, the catalyst produced by this production method can be used as an electrode catalyst for fuel cells.

The catalyst obtained by the method of the present invention has a relatively large particle diameter and a carbon catalyst supported with platinum cobalt chromium alloy particles having a small size variation. In particular, since the performance stability and durability during use are high, platinum cobalt for fuel cells It can be used as a chromium alloy supported carbon catalyst.

Claims (3)

A step of preparing an aqueous suspension of carbon powder;
A step of preparing an aqueous solution of chloroplatinic acid;
Adding L-ascorbic acid to an aqueous suspension of the carbon powder heated to 80 to 100°C, and then, while maintaining the heating temperature, to the obtained aqueous suspension of the carbon powder containing ascorbic acid, in terms of platinum per 1 g of the carbon powder As a first reduction step of supporting platinum particles grown to a size of nanometer order on the surface of the carbon powder, a first reduction step in which, in a molar ratio, 2.33 to 3.17 times ascorbic acid is used relative to chloroplatinic acid used in;
The surface of the platinum particles is reduced by adding L-ascorbic acid in an amount capable of reducing all of the chloroplatinic acid remaining after the reduction step to the suspension heated to 80 to 100° C. after the first reduction step, and reducing the chloroplatinic acid. A second reduction step of depositing platinum on the phase;
The suspension containing the carbon particles supporting the platinum particles obtained in the second reduction step is filtered to obtain the carbon particles supporting the platinum, washed, and resuspended in water, and then to the resuspended solution, an aqueous solution of a chromium compound and an aqueous solution of a cobalt compound. A precipitation step of precipitating cobalt hydroxide and chromium hydroxide on the surface of the platinum particle by adding and then adjusting the pH to 9 to 11 with aqueous ammonia;
The suspension obtained in the precipitation step is filtered, the particles in which cobalt hydroxide and chromium hydroxide are precipitated on the surfaces of the platinum particles are washed and dried, and the platinum particles in which cobalt hydroxide and chromium hydroxide are precipitated on the surface of the carbon powder are obtained. A step of obtaining powder to be supported in a form;
Preparation of a platinum-cobalt-chromium alloy-supported carbon catalyst for a fuel cell, comprising a heat treatment step of heat-treating the carbon powder carrying the platinum particles on which cobalt hydroxide and chromium hydroxide are precipitated in the form obtained in the above step in an inert gas or nitrogen atmosphere. Way. According to claim 1,
A method for producing a platinum cobalt chromium alloy supported carbon catalyst for a fuel cell, characterized in that the amount of platinum in the platinum cobalt chromium alloy supported carbon catalyst is adjusted to 11 wt% to 15 wt% on a weight basis. According to claim 1 or 2,
In the first and second reduction steps of chloroplatinic acid, the temperature of the suspension is set to 92 ° C. to 95 ° C., and the average particle diameter of the platinum-cobalt-chromium alloy particles is adjusted to 10 to 20 nm. Platinum for a fuel cell, characterized in that A method for producing a cobalt chromium alloy supported carbon catalyst.

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