KR100728187B1 - Catalyst for fuel cell, method of preparing same, membrane-electrode assembly for fuel cell comprising same - Google Patents

Abstract

The present invention relates to a catalyst for a fuel cell, a method for manufacturing the same, and a membrane-electrode assembly for a fuel cell including the same, wherein the catalyst for a fuel cell includes a compound including at least one element selected from the group consisting of silicon, zirconium, aluminum, and titanium, And a catalyst metal having an average particle size of 1 to 8 nm, wherein the compound is included at 5 wt% or less based on the total weight of the catalyst.

The catalyst for a fuel cell according to the present invention has an optimum catalyst particle size according to the amount of catalyst supported, thereby exhibiting excellent catalyst activity and self-humidification effect, and thus can improve the performance of the fuel cell.

Fuel cell, catalyst, Pt, nanoparticle size, high purity, catalytic activity.

Description

Catalyst for fuel cell, method for manufacturing same, and membrane-electrode assembly for fuel cell comprising the same {CATALYST FOR FUEL CELL, METHOD OF PREPARING SAME, MEMBRANE-ELECTRODE ASSEMBLY FOR FUEL CELL COMPRISING SAME}

1 is a view schematically showing the structure of a fuel cell system according to an embodiment of the present invention.

Figure 2 is a graph showing the X-ray diffraction (XRD) pattern for the catalyst precursor obtained during the catalyst preparation process of Example 1 and Comparative Examples 1 to 4 of the present invention.

3 is a photograph taken with a high-resolution transmission electron microscope (HRTEM) of the catalyst for a fuel cell prepared in Example 2 of the present invention.

Figure 4 is a graph showing the results of measuring the cyclic voltammogram for the catalyst prepared according to Example 2 and Comparative Examples 5, 6 of the present invention.

5 is a graph showing the results of measuring the output characteristics of the unit cells prepared according to Example 3 and Comparative Example 7 of the present invention.

[Industrial use]

The present invention relates to a fuel cell catalyst, a method for manufacturing the same, and a membrane-electrode assembly for a fuel cell including the same. More particularly, a fuel cell catalyst, a method for manufacturing the same, and a fuel cell comprising the same, having excellent catalytic activity and self-humidifying effect A membrane-electrode assembly is provided.

[Private Technology]

The fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol, and natural gas into electrical energy. This fuel cell is a clean energy source that can replace fossil energy, and has the advantage of generating a wide range of outputs by stacking unit cells, and having an energy density of 4-10 times that of a small lithium battery. It is attracting attention as a compact and mobile portable power source.

Representative examples of the fuel cell include a polymer electrolyte fuel cell (PEMFC) and a direct oxidation fuel cell (Direct Oxidation Fuel Cell). The use of methanol as fuel in the direct oxidation fuel cell is called a direct methanol fuel cell (DMFC).

The polymer electrolyte fuel cell has the advantages of high energy density and high output, but requires attention to handling hydrogen gas and reforms fuel for reforming methane, methanol, natural gas, etc. to produce hydrogen, which is fuel gas. There is a problem that requires additional equipment such as a device.

On the other hand, the direct oxidation fuel cell has a lower energy density than the polymer electrolyte fuel cell, but it is easy to handle fuel and has a low operating temperature, so that it can be operated at room temperature, in particular, it does not require a fuel reformer.

In such fuel cell systems, the stack that substantially generates electricity comprises several unit cells consisting of a membrane-electrode assembly (MEA) and a separator (also called a bipolar plate). It has a structure laminated to several tens. The membrane-electrode assembly is called an anode electrode (also called "fuel electrode" or "oxidation electrode") and a cathode electrode (also called "air electrode" or "reduction electrode") with a polymer electrolyte membrane containing a hydrogen ion conductive polymer therebetween. ) Is located.

The principle of generating electricity in a fuel cell is that fuel is supplied to an anode electrode, which is a fuel electrode, adsorbed to a catalyst of the anode electrode, the fuel is ionized by an oxidation reaction, and electrons are generated, and the generated electrons are oxidized according to an external circuit. Reaching the cathode, which is the pole, hydrogen ions pass through the polymer electrolyte membrane and are delivered to the cathode. An oxidant is supplied to the cathode, and the oxidant, hydrogen ions, and electrons react on the catalyst of the cathode to generate electricity while producing water.

It is an object of the present invention to provide a catalyst for a fuel cell having excellent catalytic activity and self-humidifying effect.

Another object of the present invention is to provide a method for preparing the catalyst.

Yet another object of the present invention is to provide a membrane-electrode assembly for a fuel cell comprising the catalyst.

In order to achieve the above object, according to the first exemplary embodiment of the present invention, a compound comprising at least one element selected from the group consisting of silicon, zirconium, aluminum and titanium, and a catalyst having an average particle size of 1 to 8 nm It includes a metal, the compound provides a fuel cell catalyst that is contained in 5% by weight or less based on the total weight of the catalyst.

According to a second exemplary embodiment of the present invention, a compound of an element selected from the group consisting of silicon, zirconium, aluminum and titanium is added to a catalyst metal precursor solution to prepare a catalyst precursor, and the catalyst precursor is subjected to a first heat treatment And a second heat treatment of the first heat-treated catalyst precursor in a reducing atmosphere, and an acid or alkali treatment of the second heat-treated catalyst precursor.

According to a third exemplary embodiment of the present invention, an anode electrode and a cathode electrode positioned opposite to each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, any one of the anode electrode and the cathode electrode or Both provide a membrane-electrode assembly for a fuel cell comprising the catalyst.

Hereinafter, the present invention will be described in more detail.

In general, there are various commercially available methods for supporting platinum on a carrier. Among the methods that can be used to prepare easy and low loading catalysts is the Incipient wetness process. This method first calculates the pores of the carrier, then prepares a catalyst metal precursor solution suitable for the amount of the pores, drops the carrier and dries, and fills the catalyst metal precursor solution between the carrier pores. A method of supporting a catalyst metal on a carrier. This process is simple but requires increasing the amount of catalyst metal in the catalyst metal precursor solution in order to produce high supported catalysts. However, since the pores of the carrier are too small relative to the amount of the catalyst metal precursor solution that can be used, the concentration of the catalyst metal precursor solution becomes high, which makes it difficult to prepare the solution due to solubility problems. As a result, it is impossible to produce a high-damage catalyst in this way. In addition, even if partially prepared, the catalyst metal aggregates to exist as large particles, which causes a problem of lowering catalytic activity.

In addition, although surfactants are used to prevent agglomeration of the catalyst metal and to easily control the particle size of the catalyst, it is not easy to remove the surfactant after preparing the catalyst, and the surfactant remaining in the catalyst causes catalyst poisoning. There was a problem.

In contrast, the present invention was able to prepare a catalyst for a fuel cell having a high purity nanoparticle size by using a novel additive compound and controlling the heat treatment conditions. In addition, by controlling the optimum catalyst particle size in accordance with the catalyst loading amount, it shows excellent catalytic activity and self-humidification effect, thereby improving the performance of the fuel cell.

That is, the fuel cell catalyst according to the embodiment of the present invention,

Compounds comprising at least one element selected from the group consisting of silicon, zirconium, aluminum and titanium; And

Includes a catalytic metal having an average particle size of 1 to 8 nm

The compound is included at 5% by weight or less based on the total weight of the catalyst.

More preferably, the compound may be included in 0.1 to 3% by weight or less based on the total weight of the catalyst. When the compound is included in less than 5% by weight may act as a material to assist the humidification and methanol oxidation, but when it exceeds 5% by weight is not preferred to lower the conductivity of the catalyst layer.

The compound is preferably an oxide containing at least one element selected from the group consisting of silicon, zirconium, aluminum and titanium, more preferably selected from the group consisting of silica, fumed silica, zeolite, zirconia, alumina and titania. It is one or more.

The catalyst metal may be produced to have various particle sizes depending on the control conditions in the production method. Preferably, the catalyst metal preferably has an average particle size of 1 to 8 nm, even more preferably may have an average particle size of 2 to 8 nm. If the average particle size of the catalyst metal is less than 1 nm, the characteristics of the catalyst are lost, which is not preferable. The catalytic metal also has a particle size uniformity of at least 80%.

The catalyst metal may be a two- or more member alloy of platinum and platinum-transition metal (V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Ir, W, Mo, and Rh). One or more selected from the group consisting of can be used.

The catalyst metal may be used as a metal catalyst black or may be supported on a carrier. When supported, the carrier may be acetylene black, denka black, activated carbon, ketjen black, graphite, vapor grown carbon fiber (VGCF), carbon nanotube, carbon nanohorn, carbon nano ring, carbon nanowire or Carbon-based materials such as carbon nanorods may also be used.

When supported on the carrier, the catalyst metal having a nanoparticle size may be supported by 5 to 95 wt%, more preferably 10 to 80 wt%, based on the total weight of the catalyst. When the content of the catalyst metal is less than 5% by weight, the catalyst use efficiency is lower than that of the carrier, and when the content of the catalyst metal is more than 95% by weight, the use efficiency of the catalyst metal is lowered. However, when the content of the catalyst metal is low, it is suitable for a polymer electrolyte fuel cell, and when it is highly supported at 50% by weight or more, it may exhibit good performance in a direct methanol type fuel cell.

More preferably, when the catalyst metal has an average particle size of 2 to 5nm, it may be supported on the carrier at 85 to 95% by weight based on the total weight of the catalyst, and also 90 to 90 when the catalyst metal has an average particle size of 5 to 8nm. It can be supported by the carrier at 95% by weight.

The catalyst for a fuel cell as described above can be produced by the following method.

Hereinafter, the method for preparing a catalyst according to the present invention will be described separately according to a type of catalyst, that is, a black type catalyst not supported on a carrier or a catalyst of a type supported on a carrier. As used herein, the term "black" refers to a state in which a catalyst metal is not supported on a carrier.

First, a black type catalyst preparation method will be described.

Method for producing a fuel cell catalyst according to a second embodiment of the present invention,

A catalyst precursor is prepared by adding a compound of an element selected from the group consisting of silicon, zirconium, aluminum and titanium (hereinafter referred to as "additive compound") to a catalyst metal precursor solution,

Primary heat treatment of the catalyst precursor,

Second heat treatment of the first heat-treated catalyst precursor in a reducing atmosphere,

Acid or alkali treatment of the secondary heat treated catalyst precursor.

Specifically, an additive compound is added to the catalyst metal precursor solution to prepare a catalyst precursor.

The additive compound serves to increase the amount and dispersion of the catalyst metal, and typically, a compound of an element selected from the group consisting of silicon, zirconium, aluminum, and titanium may be used. Preferably, at least one selected from the group consisting of silica, fumed silica, zeolite, zirconia, alumina and titania may be used, and more preferably fumed silica may be used.

As the catalyst metal precursor, H ₂ PtCl ₆ , PtCl ₂ , PtBr ₂ , (NH ₃ ) ₂ Pt (NO ₂ ) ₂ , K ₂ PtCl ₆ , K ₂ PtCl ₄ , K ₂ [Pt (CN) ₄ ] 3H ₂ O, K ₂ Pt (NO ₂ ) ₄ , Na ₂ PtCl ₆ , Na ₂ [Pt (OH) ₆ ] platinum acetylacetonate and ammonium tetrachloroplatinate One or more may be used, and more preferably H ₂ PtCl ₆ may be used.

It is also possible to further add a transition metal precursor to produce an alloy catalyst of two or more, preferably two to four, members of the platinum-transition metal. The transition metal may be V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Ir, W, Mo or Rh, although it is common to use the same catalyst for the cathode and anode electrodes in a fuel cell. When the catalyst of the present invention is used for the cathode, V, Cr, Mn, Fe, Co, Ni or Cu is used as the transition metal used with platinum, and Ru, Ir, W, Mo or Rh is used for the anode. It is more preferable to do. As the kind of the precursor, compounds of any type such as halides, nitrates, hydrochlorides, sulfates, and amines can be used, and halides are preferred among them.

In the catalyst metal precursor solution, an alcohol such as water, methanol, ethanol, isopropanol, or a mixture thereof may be used as a solvent.

The catalyst metal precursor solution is prepared by calculating the amount of catalyst to be supported on a supporting aid. In consideration of the loading of the catalyst, the support and the catalyst metal precursor are preferably mixed in a weight ratio of 70:30 to 90:10, and more preferably in a weight ratio of 80:20 to 85:15. Within the mixing ratio, it is preferable to control the particle size or shape of the catalyst metal. If the mixing ratio is out of the mixing ratio, the particles of the catalyst become large or the carrier is inefficiently used.

The addition process may be carried out by a drop so that the catalyst metal precursor solution may be evenly applied to the additive compound.

The drying step may be further performed on the catalyst precursor obtained before the heat treatment step, which is a subsequent step. When performing a drying process further, a more uniform dispersion state is obtained and it is preferable. The drying process may be a method such as ultrasonic drying (ultra-sonication), and after performing the drying process, a pulverization process may be carried out to prepare a fine powder catalyst precursor.

Subsequently, the catalyst precursor is subjected to a first heat treatment.

The primary heat treatment is preferably performed under vacuum. The heat treatment under vacuum can easily produce particles having a nano size.

The heat treatment temperature during the first heat treatment is preferably 100 to 500 ° C, more preferably 150 to 250 ° C. If the heat treatment temperature exceeds 500 ° C, the particles become large, which is not preferable. If the heat treatment temperature is less than 100 ° C, the crystallinity is not good, which is not preferable.

The first heat treatment process may be carried out for 10 minutes to 5 hours, more preferably 1 to 5 hours. If the heat treatment time is less than 10 minutes, the crystallinity of the catalyst metal is not good, and it is not preferable. If the heat treatment time is more than 5 hours, the particle size of the catalyst metal becomes large, which is not preferable.

Thereafter, the first heat treated catalyst precursor is subjected to a second heat treatment under a reducing atmosphere.

More preferably, the secondary heat treatment step is preferably performed under hydrogen or CO atmosphere, and most preferably under CO atmosphere. CO is good as a reducing atmosphere because it can poison the catalyst metal and prevent the aggregation of particles.

It is preferable that the heat processing temperature at the time of the said secondary heat processing is 250 degrees C or less, More preferably, it carries out at 150-200 degreeC. If the heat treatment temperature exceeds 250 ° C., the particles become large, which is undesirable.

The secondary heat treatment process may be performed for 10 minutes to 10 hours, more preferably 1 to 3 hours. If the heat treatment time is less than 10 minutes, the crystallinity of Pt is not good, which is not preferable. If the heat treatment time is more than 10 hours, the particle size of Pt becomes large, which is not preferable.

In the second heat treatment step, the temperature increase rate is preferably performed at 10 ° C / min or less, and more preferably at 0.5 to 2 ° C / min. If the temperature increase rate exceeds 10 ° C / min, the size of the catalyst particles becomes large, which is not preferable.

According to the heat treatment process as described above, the catalyst metal precursor is reduced and converted to the catalyst metal according to this heat treatment process.

Thereafter, the product obtained by performing the heat treatment is treated with an acid or a base to prepare a catalyst for a fuel cell.

The acid or base treatment step is performed by mixing the product with an acid or a base, and the additive mixture can be removed according to this step. At this time, the elution process for the additive mixture may be adjusted to completely remove the additive mixture, or may remove only a part of the additive mixture.

The acid treatment process may be performed by adjusting for 24 to 48 hours using 40% hydrofluoric acid. In addition, the base treatment step may be carried out by adjusting the pH to 10 to 12 using NaOH, KOH, NH ₃ OH, NH ₃ CO ₃ , Na ₂ CO ₃ or the like, or adjusting the mixing time to 30 minutes to 24 hours. . More specifically, in the case of using fluoric acid, 40% HF solution is added about 3 times to the quantitative formula and is performed with stirring for 24 hours. In addition, when using NaOH, 1M NaOH solution or more can be stirred for 24 hours and then filtered to remove.

At this time, the acid or base treatment process is carried out so that some of the additive compound remains, that is, preferably less than 5% by weight, the additive compound has a property of absorbing water well, so that self-humidification It is possible to prepare a catalyst that can operate under a non-humidified condition because it can act as a catalyst). In addition, since the residual additive compound absorbs water, it is preferable because it can act more effectively on methanol oxidation or CO oxidation reaction. If the content of the additive compound is present in excess of 5% by weight, the conductivity of the catalyst layer may be lowered, which may lower battery performance.

More preferably, the acid or base treatment step is carried out so that the additive compound remains at 0.1 to 3% by weight.

The catalyst for a fuel cell of the present invention prepared by the above process includes the additive compound and the catalyst metal, and the additive compound is uniformly present in the catalyst. In the prepared catalyst, the additive compound is present at 5 wt% or less, preferably 0.1 to 3 wt% or less.

Secondly, a method for preparing a catalyst including a carrier will be described. In the following description, the same materials and the same processes used in the black type catalyst preparation method will be omitted.

First, a carrier is prepared by mixing a carbonaceous material and a supported adjuvant. At this time, the supported adjuvant as the above-described additive compound, when used on a carrier, the additive compound acts as a supporting adjuvant, so that the catalyst metal can be supported on the carrier with a high supported amount and high dispersion.

The carbonaceous materials include acetylene black, denka black, activated carbon, ketjen black, graphite, vapor grown carbon fiber (VGCF), carbon nanotubes, carbon nanohorns, carbon nano rings, carbon nanowires, and carbon. One or more selected from the group consisting of nanorods may be used. Although the carbon-based material may be used as it is, it is preferable to use the desulfurization treatment because the sulfur contained in the trace amount as an impurity may be adversely affected in the fuel cell properties.

The desulfurization treatment is first performed by heat treating the carbon-based compound at 400 to 500 ° C. for 5 to 12 hours in an air atmosphere, treating the heat-treated carbon-based compound with an acid, and washing it. The acid treatment process is performed at room temperature for 10 to 12 hours, and the acid treatment process increases functional groups (-OH, -COOH, etc.) in the carbonaceous material, thereby making it more stable to support the catalyst and increasing dispersion. Can be. In addition, this effect can change the hydrophobic carbon-based material to hydrophilic. The acid may be nitric acid, sulfuric acid, phosphoric acid or hydrofluoric acid.

Thereafter, the washing process is a process of removing the used acid, and may be washed with sufficient distilled water, and a small amount of acid may be removed through heat treatment. In addition, the heat treatment condition is to perform a second heat treatment again in the air atmosphere for 5 to 24 hours at 400 to 500 ℃ the carbon-based compound subjected to one or two washing process to completely remove the acid that may remain a trace It can be good.

The pretreated carbonaceous material and the supported auxiliaries are mixed as described above. At this time, the supported auxiliary agent is preferably added 2 to 6 times, more 4 times to 5 times the weight of the catalyst metal. If the content of the supported adjuvant is less than the above range, the amount of the supported adjuvant may not be good because it may not play a role as an auxiliary support, and the catalyst metal may be formed into large particles, which is not preferable. Too much of it is not economical.

The mixing step of the supported assistant and the carbonaceous substance is also preferably carried out in an organic solvent, water, or a mixed solvent thereof because the carbonaceous substance and the supported assistant are more uniformly mixed. As the organic solvent, n-propyl alcohol, isopropyl alcohol, methyl alcohol, ethyl alcohol or ethylene glycol may be used.

In the case of preparing a mixing step of the carbon-based material and the supporting aid using a solvent, the drying step is further performed, followed by grinding to prepare a powder carrier. However, when not using a solvent, you may pass only a grinding | pulverization process, without performing a drying process.

Next, a catalyst precursor is prepared by uniformly adding a catalyst metal precursor solution to the support, the catalyst precursor is first heat treated under vacuum, and the first heat treated catalyst precursor is second heat treated under a reducing atmosphere such as hydrogen or carbon monoxide. In addition, an acid or alkali treatment of the secondary heat treated catalyst precursor may produce a fuel cell catalyst having a form supported on a carrier.

Since the process after the preparation of the carrier is the same as described above, a detailed description thereof will be omitted.

By the preparation method as described above, the black catalyst without a carrier can be synthesized in a particle size of nano size, preferably 1 to 8 nm, more preferably 2 to 5 nm, without using a surfactant. In addition, when supported by the carbon-based material, the particle size of the catalyst metal can be appropriately adjusted according to the amount of the carbon-based material in consideration of the performance and stability of the fuel cell. Preferably, when the supported amount of the catalyst metal is 85 to 90% by weight, the catalyst metal may have an average particle size of 2 to 5 nm, and when the supported amount is 90 to 95%, the catalyst metal may have an average particle size of 5 to 8 nm. . Thus, the particle size of the catalyst metal can be uniformly controlled by the production method according to the present invention.

In addition, the catalyst prepared by the above production method has a high purity (carbon free) free of organic impurities, except for oxides produced by oxygen or water vapor in the air. Purity generally refers to organic impurities that adhere to the surface of hydrocarbons or platinum from surfactants, except for carriers such as carbonaceous materials, and according to the method of the present invention, metal blacks are not used because they do not use surfactants. There is no organic impurity in the catalyst. However, the case where the additive compound or auxiliary carrier used in the preparation of the catalyst is partially left without eluting by acid or base treatment and the case where the carrier of the carbonaceous material is included in the impurities are preferable. It has a purity of at least 90%, more preferably a high purity of 90 to 95%. If the purity of the catalyst metal is less than 90%, the catalyst poisoning may occur due to impurities contained in the catalyst metal, which is not preferable.

The fuel cell catalyst thus prepared has a higher activity in a direct oxidation fuel cell using a hydrocarbon fuel and a very high catalytic activity in a direct methanol fuel cell using methanol as a fuel. Most useful in methanol fuel cells.

In addition, the fuel cell catalyst may be used for both the cathode and the anode electrode.

Cathode and anode electrodes in fuel cells are not distinguished by materials, but by their role. Fuel cell electrodes are anodes for oxidizing fuels (hydrogen, methanol, ethanol, formic acid, etc.) and cathodes for reducing oxygen (air). Are distinguished. That is, a fuel cell supplies hydrogen or fuel to the anode and oxygen to the cathode to generate electricity by an electrochemical reaction between the anode and the cathode. An oxidation reaction of the organic fuel occurs at the anode and a reduction reaction of oxygen occurs at the cathode, thereby generating a voltage difference between the two electrodes.

Accordingly, according to a third exemplary embodiment of the present invention, an anode electrode and a cathode electrode are disposed to face each other, and a polymer electrolyte membrane is positioned between the anode electrode and the cathode electrode, and the anode electrode and the cathode electrode are located. Either or both provide a membrane-electrode assembly for a fuel cell comprising the catalyst.

The catalyst included in the anode electrode and the cathode electrode is the same as described above.

In addition, the catalysts of the cathode electrode and the anode electrode are all formed on the electrode substrate. The electrode substrate plays a role of supporting the electrode and diffuses the fuel and the oxidant to the catalyst layer, thereby serving to easily access the fuel and the oxidant to the catalyst layer. A conductive substrate is used as the electrode substrate, and representative examples thereof include carbon paper, carbon cloth, carbon felt, or metal cloth (porous film or polymer fiber composed of metal cloth in a fibrous state). The metal film is formed on the surface of the cloth formed of (referred to as a metalized polymer fiber) may be used, but is not limited thereto.

In addition, the electrode substrate is water-repellent treatment with a fluorine-based resin such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene, polychlorotrifluoroethylene, fluoroethylene polymer The gas diffusion efficiency can be prevented from being lowered by water generated when the fuel cell is driven, which is more preferable.

In addition, the membrane-electrode assembly may further include a microporous layer on the electrode substrate to enhance the gas diffusion effect. This microporous layer may generally comprise a conductive powder having a small particle diameter, such as carbon powder, carbon black, acetylene black, ketjen black, activated carbon, carbon fiber, fullerene or carbon nanotubes. The microporous layer is prepared by coating a composition comprising a conductive powder, a binder resin and a solvent on the electrode substrate. As the binder resin, a polymer having electrical conductivity may be used. Specifically, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, cellulose acetate, or the like may be preferably used. As the solvent, alcohols such as ethanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, water, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone and the like may be preferably used. The coating process may be screen printing, spray coating, or coating using a doctor blade according to the viscosity of the composition, but is not limited thereto.

In addition, the polymer electrolyte membrane has a function of ion exchange that transfers hydrogen ions generated in the catalyst layer of the electrode to the catalyst layer of the cathode electrode, and is generally used as a polymer electrolyte membrane in a fuel cell and has a polymer of hydrogen ion conductivity. Anything prepared with may be used. Representative examples thereof include a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups and derivatives thereof in the side chain.

Representative examples of the polymer resin include a fluorine polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer and a polyether ketone It may include at least one selected from a polymer, a polyether-etherketone-based polymer or a polyphenylquinoxaline-based polymer, more preferably poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), Copolymers of tetrafluoroethylene with fluorovinyl ethers containing sulfonic acid groups, defluorinated sulfided polyether ketones, aryl ketones, poly (2,2'-m-phenylene) -5,5'-bibenzimidazole or at least one selected from (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) or poly (2,5-benzimidazole).

In addition, the polymer electrolyte membrane preferably has a thickness of 10 to 200㎛.

Since the method for preparing the polymer electrolyte membrane, the method and the conditions of hot rolling are well known in the art, detailed description thereof will be omitted.

According to a fourth exemplary embodiment of the present invention, there is provided a fuel cell system including the membrane-electrode assembly having the above configuration.

The fuel cell system includes at least one electricity generating unit including the membrane-electrode assembly and the separator, and includes a fuel supply unit supplying fuel to the electricity generating unit and an oxidant supply unit supplying an oxidant to the electricity generating unit.

The electricity generating unit includes a membrane-electrode assembly, a separator (also called a bipolar plate), and serves to generate electricity through an oxidation reaction of a fuel and a reduction reaction of an oxidant.

The fuel supply unit serves to supply fuel to the electricity generation unit, and the oxidant supply unit serves to supply an oxidant such as oxygen or air to the electricity generation unit. Fuels in the present invention include hydrogen or hydrocarbon fuels in gas or liquid state. Representative examples of the hydrocarbon fuel include methanol, ethanol, propanol, butanol or natural gas.

A schematic structure of the fuel cell system of the present invention is shown in FIG. 1, which will be described in more detail with reference to the following. Although the structure shown in FIG. 1 shows a system for supplying fuel and oxidant to an electric generator by using a pump, the fuel cell system of the present invention is not limited to such a structure, and does not use a pump, but uses a fuel diffusion method. Of course, it can also be used in the battery system structure.

The fuel cell system 100 of the present invention includes a stack 105 having at least one electricity generator 150 for generating electrical energy through an electrochemical reaction between a fuel and an oxidant, and a fuel supply unit for supplying the fuel. 101 and an oxidant supply unit 103 for supplying an oxidant to the electricity generating unit 150.

In addition, the fuel supply unit 101 for supplying fuel includes a fuel tank 110 for storing fuel, and optionally, may further include a fuel pump 120 connected to the fuel tank 110. The fuel pump 120 serves to discharge fuel stored in the fuel tank 110 by a predetermined pumping force.

The oxidant supply unit 103 supplying the oxidant to the electricity generating unit 150 of the stack 105 may include at least one oxidant pump 130 that sucks the oxidant with a predetermined pumping force.

The electricity generator 150 includes a membrane electrode assembly 151 for oxidizing and reducing a fuel and an oxidant, and separators 152 and 153 for supplying fuel and an oxidant to both sides of the membrane electrode assembly.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

(Example 1)

A catalyst precursor was prepared by dropwise adding 20 parts by weight of a solution of H ₂ PtCl ₆ , a Pt precursor solution, to 80 parts by weight of fumed silica powder. The prepared catalyst precursor was ultrasonicated (ultrasonication) to give a yellow catalyst precursor. This was subjected to a first heat treatment at 200 ° C. for 5 hours under vacuum, and then to a second heat treatment at 200 ° C. for 2.5 hours under a hydrogen atmosphere. The temperature increase rate during the second heat treatment was 2 ° C / min.

Next, the heat treated catalyst was left in a 60 ° C. vacuum oven for one day, and then treated with 0.5 M NaOH for 2 hours to elute and remove the fumed silica. Thereafter, the resultant was filtered, washed and dried in a drying oven to prepare a catalyst for a fuel cell. The prepared fuel cell catalyst was Pt nanoparticles containing 2 wt% of fumed silica based on a particle size of 3.5 nm and the total weight of the catalyst.

(Example 2)

Ketjen black was heat-treated at 500 ° C. for 10 hours in an air atmosphere, and 5 g of heat treated Ketjen black and 500 ml of HNO ₃ were mixed at room temperature for 24 hours and filtered. Subsequently, the obtained Ketjen Black was washed with water, dried, and then heat treated again at 500 ° C. for 24 hours in an air atmosphere to carry out a desulfurization treatment to remove sulfur which may be present as trace impurities in Ketjen Black.

The desulfurized Ketjen Black was mixed in a ball mill with fumed silica in a mixed solvent (1: 1: 1 volume ratio) of n-propyl alcohol, isopropyl alcohol and water in a weight ratio of 1: 1.

The mixture was dried and then ground in a grinder to prepare a powder carrier.

A catalyst precursor was prepared by dropwise adding 20 parts by weight of a solution of H ₂ PtCl ₆ , a Pt precursor solution, to 80 parts by weight of the carrier. The prepared catalyst precursor was ultrasonicated (ultrasonication) to give a yellow catalyst precursor. This was subjected to a first heat treatment at 200 ° C. for 5 hours under vacuum, and then to a second heat treatment at 200 ° C. for 2.5 hours under a hydrogen atmosphere. The temperature increase rate during the second heat treatment was 2 ° C / min.

Next, the heat treated catalyst was left in a 60 ° C. vacuum oven for one day, and then treated with 0.5 M NaOH for 2 hours to elute and remove the fumed silica. Thereafter, the resultant was filtered, washed and dried in a drying oven to prepare a catalyst for a fuel cell. The prepared fuel cell catalyst was a Pt nanoparticle supported on Catchen Black containing a platinum catalyst having a particle size of 3 nm, and 3 wt% fumed silica based on the total weight of the catalyst.

(Comparative Example 1)

Ultrasonic Treatment A catalyst for a fuel cell was prepared in the same manner as in Example 1 except that the dried catalyst precursor was heat-treated at a temperature of 200 ° C. under an H ₂ atmosphere. The prepared fuel cell catalyst was Pt nanoparticles having a particle size of 9.5 nm.

(Comparative Example 2)

A catalyst for a fuel cell was prepared in the same manner as in Example 1, except that the dried catalyst precursor by ultrasonic treatment was heat-treated at a temperature of 200 ° C. in the air. The prepared fuel cell catalyst could not be completely reduced to platinum metal and became a PtCl ₂ form whose particle size was unknown by X-ray diffraction.

(Comparative Example 3)

A catalyst for fuel cell was prepared by the same method as Example 1 except that the catalyst precursor dried by sonication was subjected to a first heat treatment at a temperature of 200 ° C. under air, and then a second heat treatment at a temperature of 200 ° C. under a hydrogen atmosphere. It was. The prepared fuel cell catalyst was Pt nanoparticles having a particle size of 8.5 nm.

(Comparative Example 4)

A catalyst for a fuel cell was prepared in the same manner as in Example 1, except that the dried catalyst precursor by ultrasonic treatment was heat treated at a temperature of 200 ° C. under vacuum. The fuel cell catalyst prepared was amorphous Pt nanoparticles containing 3 wt% fumed silica based on a particle size of 2.9 nm and the total weight of the catalyst.

(Comparative Example 5)

Ketjen black was heat-treated at 500 ° C. for 10 hours in an air atmosphere, and 5 g of heat treated Ketjen black and 500 ml of HNO ₃ were mixed at room temperature for 24 hours and filtered. Subsequently, the obtained Ketjen Black was washed with water, dried, and then heat treated again at 500 ° C. for 24 hours in an air atmosphere to carry out a desulfurization treatment to remove sulfur which may be present as trace impurities in Ketjen Black.

A catalyst precursor was prepared by dropwise addition of 20 parts by weight of a solution of H ₂ PtCl ₆ , a Pt precursor solution, to 80 parts by weight of desulfurized Ketjen black. The prepared catalyst precursor was ultrasonicated (ultrasonication) and then heat treated at a temperature of 200 ° C. under H ₂ atmosphere to prepare a catalyst for a fuel cell.

(Comparative Example 6)

Ketjen black was heat-treated at 500 ° C. for 10 hours in an air atmosphere, and 5 g of heat treated Ketjen black and 500 ml of HNO ₃ were mixed at room temperature for 24 hours and filtered. Subsequently, the obtained Ketjen Black was washed with water, dried, and then heat treated again at 500 ° C. for 24 hours in an air atmosphere to carry out a desulfurization treatment to remove sulfur which may be present as trace impurities in Ketjen Black.

The desulfurized Ketjen Black was mixed in a ball mill with fumed silica in a mixed solvent (1: 1: 1 volume ratio) of n-propyl alcohol, isopropyl alcohol and water in a weight ratio of 1: 1. The mixture was dried and then ground in a grinder to prepare a powder carrier.

A catalyst precursor was prepared by dropwise adding 20 parts by weight of a solution of H ₂ PtCl ₆ , a Pt precursor solution, to 80 parts by weight of the carrier. The prepared catalyst precursor was ultrasonicated (ultrasonication) and then heat treated at a temperature of 200 ° C. under H ₂ atmosphere to prepare a catalyst for a fuel cell.

The content of fumed silica contained in the prepared catalyst was 33% by weight based on the total catalyst weight, and the content of Pt, which is a catalyst metal, was 33% by weight.

X-ray diffraction (X-ray) using X-Pert MPD1 (manufactured by PHILIPS Co.) for the catalyst precursors obtained after the heat treatment process before the acid or base treatment in the catalyst preparation according to Example 1 and Comparative Examples 1 to 4 diffraction: XRD) pattern was measured. The results are shown in FIG.

As shown in FIG. 2, only the amorphous SiO ₂ peak and the peak of the H ₂ PtCl ₆ derivative were confirmed in the catalyst precursor of Pt / SiO ₂ supported by SiO ₂ , a supporting agent before reduction by heat treatment. In the case of the catalyst of Comparative Example 1 prepared by heat treatment under a conventional hydrogen atmosphere, platinum nanoparticles were prepared, but the particle size was very large as 9.5 nm. In addition, in the case of the catalyst of Comparative Example 2 heat-treated in the atmosphere, it was confirmed that platinum was not completely reduced and remained as PtCl ₂ . In addition, it was confirmed that the catalyst of Comparative Example 3 subjected to the second heat treatment under hydrogen atmosphere after the first heat treatment in the atmosphere had a particle size of 8.5 nm smaller than the catalyst of Comparative Example 2 by about 1.0 nm. It was also confirmed that the catalyst of Comparative Example 4 obtained by heat treatment under vacuum had a particle size of 2.9 nm. However, in the case of the catalyst of Comparative Example 4 it can be confirmed that the peak strength is low, the crystallinity is not good. In conclusion, the most preferred was that the platinum particles of Example 1 obtained by the first heat treatment under vacuum and the second heat treatment under hydrogen had a particle size of 2 to 5nm level and good crystallinity.

A high-resolution transmission electron microscope (HRTEM) photograph of the catalyst prepared in Example 2 is shown in FIG. 3.

As shown in FIG. 3, it can be seen that the platinum particles having a particle size of 2 to 4 nm are uniformly well dispersed on the CNT carrier.

The cyclic voltammogram was measured for the catalysts prepared in Example 2 and Comparative Examples 5 and 6. The measurement results are shown in FIG. 4.

As shown in FIG. 4, the catalyst of Example 2 containing 3% by weight of fumed silica had a reaction surface area almost the same as that of Comparative Example 5 containing no fumed silica, whereas fumed silica was used. It was confirmed that it has an increased surface area compared to the catalyst of Comparative Example 6 containing 33% by weight.

(Example 3)

10 parts by weight of the catalyst prepared in Example 2 was added to a solvent in which water and isopropyl alcohol were mixed at a weight ratio of 10:80, and then 40 parts by weight of Nafion solution (Nafion 1100 EW, manufactured by Dupont) was mixed and ultrasonic waves were mixed. It was applied and stirred uniformly to prepare a catalyst layer forming composition.

The cathode electrode was prepared by spray coating the composition for forming a catalyst layer on a Teflon-treated carbon paper substrate (cathode / anode = SGL 31BC / 10DA; manufactured by SGL carbon group). An anode electrode was prepared in the same manner as above using a PtRu black catalyst (HiSPEC 6000, manufactured by Johnson Matthey). In this case, a catalyst layer of 6 mg / cm ² was coated for the anode electrode, and a catalyst layer of 4 mg / cm ² was coated for the cathode electrode to prepare an electrode.

Next, a membrane / electrode assembly was manufactured by laminating the polymer electrolyte membrane (catalyst coated membrane-type Fuel Cell MEA, manufactured by DuPont; Nafion 115 Membrane) for commercial fuel cells. After inserting the prepared membrane / electrode assembly between the gasket (gasket), and inserted into the two separator gas channel channel and the cooling channel formed of a predetermined shape, and then compressed between the copper end (end) plate to manufacture a unit cell It was.

(Comparative Example 7)

A single cell was manufactured by the same method as Example 3, except that the catalyst prepared in Comparative Example 5 was used.

Cell performance was measured by driving the cells prepared in Example 3 and Comparative Example 7 under 1M methanol / dry air. The results are shown in FIG.

As shown in FIG. 5, the unit cell of Example 3 including the catalyst including 3 wt% of fumed silica and the unit cell of Comparative Example 7 including the catalyst containing no fumed silica showed nearly equivalent output characteristics. However, at a current density of 400 ° C. or less, the unit cell of Example 3 exhibited higher voltage and output characteristics than the unit cell of Comparative Example 7, which affected the self-humidifying effect of fumed silica contained in the catalyst in the unit cell of Example 3. It seems to have been followed.

The catalyst for a fuel cell according to the present invention has an optimum catalyst particle size according to the amount of catalyst supported, thereby exhibiting excellent catalyst activity and self-humidification effect, and thus can improve the performance of the fuel cell.

Claims (21)

Compounds comprising at least one element selected from the group consisting of silicon, zirconium, aluminum and titanium; And Includes a catalytic metal having an average particle size of 1 to 8 nm The compound is a fuel cell catalyst that is contained in less than 5% by weight based on the total weight of the catalyst. The method of claim 1, The compound is a fuel cell catalyst that is contained in less than 0.1 to 3% by weight based on the total weight of the catalyst.  The method of claim 1, The compound is a fuel cell catalyst that is an oxide containing at least one element selected from the group consisting of silicon, zirconium, aluminum and titanium. The method of claim 1, Wherein said compound is at least one catalyst selected from the group consisting of silica, fumed silica, zeolite, zirconia, alumina and titania.  The method of claim 1, The catalytic metal is composed of two or more alloys of platinum and platinum-transition metals (V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Ir, W, Mo and Rh). Catalyst for fuel cell, which is at least one selected from the group. The method of claim 1, The catalyst metal is a fuel cell catalyst which is supported by at least one carrier selected from the group consisting of carbon-based materials. The method of claim 6, The catalytic metal has an average particle size of 2 to 5 nm, A catalyst for a fuel cell, which is supported on a carrier at 85 to 95% by weight based on the total weight of the catalyst. The method of claim 6, The catalytic metal has an average particle size of 5 to 8 nm, A catalyst for a fuel cell, which is supported on a carrier at 90 to 95% by weight based on the total weight of the catalyst. A catalyst precursor is prepared by adding a compound of an element selected from the group consisting of silicon, zirconium, aluminum and titanium to the catalyst metal precursor solution, Primary heat treatment of the catalyst precursor, Second heat treatment of the first heat-treated catalyst precursor in a reducing atmosphere, A method of producing a catalyst for a fuel cell comprising the step of acid or alkali treatment of the secondary heat treated catalyst precursor. The method of claim 9, The catalytic metal precursor is H ₂ PtCl ₆ , PtCl ₂ , PtBr ₂ , (NH ₃ ) ₂ Pt (NO ₂ ) ₂ , K ₂ PtCl ₆ , K ₂ PtCl ₄ , K ₂ [Pt (CN) ₄ ] 3H ₂ O , K ₂ Pt (NO ₂ ) ₄ , Na ₂ PtCl ₆ , Na ₂ [Pt (OH) ₆ ] platinum acetylacetonate and 1 selected from the group consisting of ammonium tetrachloroplatinate A method for producing a catalyst for fuel cell that is more than one species. The method of claim 9, The compound and the catalyst metal precursor is a method for producing a catalyst for a fuel cell is mixed in a weight ratio of 70:30 to 90:10. The method of claim 9, The first heat treatment process is a method for producing a catalyst for a fuel cell that is carried out under vacuum. The method of claim 9, The primary heat treatment process is a method for producing a catalyst for a fuel cell that is carried out at a temperature of 100 ℃ to 500 ℃. The method of claim 9, The first heat treatment process is a method for producing a catalyst for a fuel cell that is carried out for 10 minutes to 5 hours. The method of claim 9, The secondary heat treatment process is a method for producing a catalyst for a fuel cell that is carried out under hydrogen or CO atmosphere. The method of claim 9, The secondary heat treatment process is a method for producing a catalyst for a fuel cell that is carried out at a temperature of 150 to 250 ℃. The method of claim 9, The secondary heat treatment process is a method for producing a catalyst for a fuel cell that is carried out for 10 minutes to 10 hours. The method of claim 9, The secondary heat treatment process is a method of producing a catalyst for a fuel cell that is heat-treated at a temperature rising rate of 10 ℃ / min or less. The method of claim 9, And a process of preparing a carrier by mixing a carbon-based material with a compound of an element selected from the group consisting of silicon, zirconium, aluminum and titanium before the catalyst precursor manufacturing process. The method of claim 19, Wherein the carbon-based material is prepared by the process of heat-treating the carbon-based compound in an air atmosphere, the acid-treated and the heat treatment of the heat-treated carbon-based compound. An anode electrode and a cathode electrode positioned opposite each other; And A polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, 9. The membrane-electrode assembly of a fuel cell, wherein any one or both of the anode electrode and the cathode electrode comprise the catalyst according to any one of the preceding claims.

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