KR20080024706A - Pt/pd catalysts for use of direct methanol fuel cell - Google Patents

Abstract

A catalyst for an air electrode, an electrode containing the catalyst for a fuel cell, a membrane electrode assembly containing the electrode, a direct methanol fuel cell containing the membrane electrode assembly, and a method for preparing the catalyst are provided to lower the reactivity to the crossover methanol, to prevent the deterioration of oxygen reduction and to decrease the adsorption to carbon monoxide. A catalyst for an air electrode comprises 0.5-99.5 mol% of platinum (Pt); and 0.5-99.5 mol% of palladium (Pd). Preferably the platinum and the palladium are supported by a catalyst carrier material. Preferably the catalyst carrier material is at least one porous carbon selected from the group consisting of activated carbon, carbon fiber, graphite fiber and carbon nanotube; at lest one conductive polymer selected from the group consisting of poly(vinyl carbazole) and its derivative, polyaniline and its derivative, and polypyrrole and its derivative; or at least one metal oxide selected from the group consisting of tungsten oxide, titanium dioxide, nickel oxide, ruthenium oxide, tantalum oxide and cobalt oxide.

Description

Platinum / Palladium Catalysts for Direct Methanol Fuel Cells {Pt / Pd CATALYSTS FOR USE OF DIRECT METHANOL FUEL CELL}

1 is a schematic diagram showing a direct methanol fuel cell.

FIG. 2 shows the results of X-ray diffraction (XRD) analysis of the platinum / palladium binary catalyst prepared by Example 1 and Comparative Example 1 of the present invention and the platinum catalyst.

FIG. 3 shows the results of X-ray spectroscopy composition analysis (EDX) for the composition analysis of the platinum / palladium binary catalyst prepared by Example 1 and Comparative Example 1 of the present invention and the platinum catalyst. The mole% composition of platinum / palladium catalysts is 5:95.

Figure 4 is a comparison of the oxygen reduction current by the platinum / palladium binary catalyst and the platinum catalyst prepared in Example 1 and Comparative Example 1 of the present invention, the result in a 0.05 mol sulfuric acid aqueous solution.

FIG. 5 is a graph comparing oxygen reduction currents of platinum / palladium binary catalysts prepared by Example 1 and Comparative Example 1 of the present invention with platinum catalysts, and in a 0.05 mol sulfuric acid solution containing 0.5 mol methanol. The result is.

FIG. 6 shows a comparison of fuel cell performance curves of a platinum / palladium binary catalyst and a pure platinum catalyst under 2 molar concentration (2 M) methanol conditions.

FIG. 7 shows the result of comparing the fuel cell performance curves of the platinum / palladium binary catalyst and the pure platinum catalyst under 4 molar concentration (4 M) methanol conditions.

FIG. 8 shows a comparison of fuel cell performance curves of a platinum / palladium binary catalyst and a pure platinum catalyst under 6 molar concentration (6 M) methanol conditions.

FIG. 9 shows a comparison of long-term fuel cell performance curves at 30 mA / cm ² of platinum / palladium binary catalysts and pure platinum catalysts under 2 mol and 4 mol methanol conditions. Results are from 2 moles of methanol from 0 to 100 hours and from 4 moles of methanol from 100 to 200 hours.

10 is carbon monoxide adsorbed on a platinum / palladium binary catalyst prepared by Example 1 and Comparative Example 1 of the present invention and a platinum catalyst at different times using a constant potential method (chroropotentiometry) on a 0.05 mol sulfuric acid solution. Is the result of the oxidation reaction test.

The present invention relates to a synthesis catalyst for a direct methanol fuel cell based on platinum and other precious metals, and more particularly, to a cathode catalyst of a direct methanol fuel cell (DMFC), which includes platinum (Pt) and palladium (Pd). It relates to an air cathode catalyst.

Recently, due to the rapid spread of portable electronic devices and wireless communication devices, much attention and research is being conducted on the development of fuel cells as a battery as a portable power supply device, a fuel cell for a pollution-free automobile, and a fuel cell for power generation as a clean energy source.

A fuel cell is a power generation system that converts chemical energy of fuel gas (hydrogen, methanol, or other organic substance) and oxidant (oxygen or air) directly into electrical energy through an electrochemical reaction. Battery, molten carbonate electrolyte fuel cell, phosphate electrolyte fuel cell and polymer electrolyte fuel cell.

The polymer electrolyte fuel cell (Polymer Electrolyte Membrane Fuel Cell) is subdivided directly into a fuel supply using hydrogen gas as a fuel (Proton Exchange Membrane Fuel Cell: PEMFC) and liquid methanol directly Methanol Fuel Cell (DMFC). Polymer electrolyte fuel cell is a clean energy source that can replace fossil energy. It has high power density and energy conversion efficiency, can operate at room temperature, and can be miniaturized and encapsulated. It can be widely used in fields such as portable power supply and military equipment.

In general, gaseous fuel cells using hydrogen as a fuel have an advantage of high energy density, but require attention to handling hydrogen gas, and fuel for reforming methane, methanol, and natural gas to produce hydrogen, fuel gas. There is a problem that requires additional equipment such as a reformer.

Direct methanol fuel cells using methanol as a direct fuel simplifies the overall fuel cell system due to the ease of handling of liquid fuels, low operating temperatures, and particularly no need for a fuel reformer. However, platinum / ruthenium (Pt / Ru) binary catalysts have been developed and commercialized to improve the slow reaction rate of methanol oxidation and to improve the catalyst poisoning resistance of carbon monoxide. Nevertheless, research on the ternary or quaternary catalysts based on platinum / ruthenium is still underway due to the low activity for methanol oxidation.

In addition, due to methanol cross-over phenomenon, in which the methanol to be oxidized at the anode passes through the polymer electrolyte to the cathode (cathode) and causes oxidation at the cathode, cathode poisoning as well as formation of a mixed voltage is generated. This results in lower overall fuel cell performance and reduced fuel utilization. For this reason, there are restrictions on the methanol concentration available.

In order to prevent the methanol crossover phenomenon, the researches that have been conducted so far can be classified into two categories. One is to develop a new polymer electrolyte that essentially prevents methanol from passing through the cathode, while the other reacts selectively with oxygen, even though methanol flows into the cathode, instead of the electrochemical reaction. It is to develop a new cathode catalyst that is resistant to methanol.

Polymer electrolytes that have been reported to reduce methanol crossover include conventional membranes such as hybrid membranes containing NafionTM (Dupont) and inorganic materials such as SiO ₂ , TiO ₂ , BaTiO ₃ , and ZrO (HPO ₄ ) _2. Polybenzimidazole (PBI) and polyacrylamide (PAA). However, these electrolytes also reduce methanol permeability, but show a corresponding decrease in ion conductivity, degradation in durability, and selective ion conductivity at high temperatures.

Cathode catalysts reported to be resistant to methanol (Ru _{1 - x} Mo _x ) _y SeO _z (TJ Schmidt, UA Paulus, HA Gasteiger, N. Alonso-Vante, RH Behm, J. Electrochem. Soc. 147) 7), 2000, 2026), Mo _x Ru _y S _z (RW Reeve, PA Christensen, A. Hamnett, SA Hatdock, SC Haydock, SC Roy, J. Electrochem.Soc. 145, 1998, 3463), Mo _x RhS _z (RW Reeve, PA Christensen, AJ Dickinson, A. Hamnett, K. Scott, Electrochimica Acta, 45, 2000, 4237), and porphyrin systems containing metals (SL Gojkovic, S. Gupta, RF Savinell, J.). Electroanal. Chem. 462, 1999, 63). Some metal compounds that do not contain platinum show selective oxygen reduction. However, since the oxygen reduction reaction rate is very slow compared to pure platinum, it is practically limited in application to fuel cell cathodes. These catalysts are at a level of approximately 50 mW / cm ² at 90 ° C.

In addition, platinum-based catalysts include Pt / Ni (M. Neergat, AK Shukla, KS Gandhi, J. Appl. Electrochem. 31, 2001, 373), Pt / Fe (Wenzhen Li, Weijiang Zhou, Hyanqiao Li, Zhemhua Zhou, Bing Zhou, Gongquan Sun, Qin Xin, Electrochimica Acta, 2004, 1045), Pt / Co (M. Neergat, AK Shulkla, KS Gandhi, J Appl. Electrochem. 31, 2001, 373). These catalysts have been reported to perform well when used as DMFC cathode catalysts because they are known to be faster than pure platinum. However, the platinum-based multicomponent catalysts (Pt-Ni, Pt-Fe, Pt-Co) reported in the above documents show higher performance than pure platinum catalysts in the absence of methanol, but methanol oxidation in the presence of methanol It is difficult to solve the methanol crossover due to its activity.

In particular, the catalysts showed good performance at low concentrations of methanol (0.5 mol to 2 mol), but no performance results were reported at high concentrations (more than 2 mol).

As a result of experimenting with various transition metals to develop a cathode catalyst having better performance than the cathode catalyst of the prior art, the platinum / palladium cathode catalysts of the present invention make it difficult to coalesce carbon monoxide acting as a catalyst poison and high oxygen reduction reaction rate While maintaining, it was confirmed that the crossover was very low reactivity to methanol flowing into the cathode.

In addition, the activity was maintained not only in the low concentration of methanol, but also in the high concentration of methanol, and it was confirmed that an excellent performance fuel cell was obtained.

Accordingly, the present invention is a synthetic catalyst for a direct methanol fuel cell based on platinum / palladium which is resistant to carbon monoxide and has a low reactivity with respect to methanol flowing into the air electrode and can rapidly cause an oxygen reduction reaction. An object of the present invention is to provide an electrode for a fuel cell, a membrane electrode assembly, and a direct methanol fuel cell including a catalyst.

The present invention provides a catalyst comprising platinum (Pt) and palladium (Pd) in a cathode catalyst of a direct methanol fuel cell (DMFC).

The present invention also provides a fuel cell electrode, a membrane electrode assembly, and a direct methanol fuel cell including the catalyst.

And, the present invention a) a first step of preparing an aqueous solution of a salt of platinum and palladium; b) a second step of obtaining a precipitate of alloy catalyst particles of platinum / palladium by adding a reducing agent to the aqueous solution; And c) a third step of separating the precipitate from the solution and lyophilizing it; It provides a method for producing the catalyst described above.

Hereinafter, the present invention will be described in detail.

<Platinum / Palladium Catalyst>

Metal salts of platinum and palladium used in the production of the platinum / palladium catalyst of the present invention are not particularly limited, but chlorides, nitrides, sulfates and the like containing the metals can be used. Non-limiting examples of the metal salt include _{H 2 PtCl 6 · xH 2 O} , K 2 PtCl 6, PdCl 2, PdBr 2, Pd (NO 3) 3 · xH 2 O.

An appropriate amount of the metal salt is added to the desired molar ratio, and the mixture is added to distilled water and stirred at room temperature, followed by mixing and mixing the respective metal salt solutions. After adjusting the pH of the mixed metal salt solution to 7 to 8, preferably pH 8, a reducing agent is added thereto to reduce the metal salts to obtain a precipitate.

The reducing agent is not particularly limited, but sodium borohydride (NaBH ₄ ), hydrazine (N ₂ H ₄ ), sodium formate (HCOONa), or the like may be used.

The obtained precipitate may be washed with distilled water and then lyophilized to finally obtain a synthetic catalyst.

In the catalyst of the present invention, the content of platinum may range from 0.5 mol% to 99.5 mol%, the content of palladium may range from 0.5 mol% to 99.5 mol%, preferably the content of platinum is 0.5 mol It may range from% to 50 mol%, and the content of palladium may range from 50 mol% to 99.5 mol%.

In the platinum / palladium catalyst of the present invention, the content of platinum is not limited to the above range, but in the case of a fuel cell using a high concentration of methanol as a fuel, it is more preferable that the amount of platinum is limited as described above. This is even more so in that the cost of manufacturing fuel cells can be lowered by reducing the amount of high platinum. However, the platinum / palladium catalyst of the present invention can be applied not only to a high concentration of methanol but also to a low concentration of methanol as a fuel. In this case, the electrode performance is increased by increasing the content of platinum having a high oxygen reduction activity higher than the above range. You can also improve.

Meanwhile, the catalyst of the present invention may be used as an alloy metal particle itself including platinum and palladium or may be supported by a catalyst carrier material in order to reduce the amount of catalyst used. Since the carrier material has a very large specific surface area relative to the weight, the carrier material may increase the active area of the catalyst and may support the catalyst metal to prevent loss of the catalyst.

The catalyst carrier material is known to those skilled in the art, and is not particularly limited as long as it is a porous material, and non-limiting examples thereof include at least one porous carbon or polyvinyl selected from the group consisting of activated carbon, carbon fiber, graphite fiber and carbon nanotubes. One or more conductive polymers selected from the group consisting of polyvinylcarbazole and its derivatives, polyaniline and its derivatives, and polypyrrole and its derivatives, and tungsten oxide, titanium oxide, nickel oxide, ruthenium oxide, tantalum At least one metal oxide selected from the group consisting of oxides and cobalt oxides.

In this case, the weight ratio of the catalyst carrier material to the catalyst metal may be 5 wt% to 99 wt%.

The catalyst of the present invention is based on a binary catalyst of platinum and palladium, but in some cases selected from the group consisting of iron, cobalt, nickel, ruthenium, rhodium, gold, silver, osmium, and iridium in addition to platinum and palladium. It may further comprise at least a metal element.

In addition to platinum and palladium, the above-mentioned elements (Fe, Co, Ni, etc.), which are further included, form an alloy with platinum and are pure in the absence of methanol when produced with Pt-Fe, Pt-Co, and Pt-Ni catalysts. These elements can exhibit the characteristics of oxygen reduction reaction larger than Pt. Therefore, it is expected that the catalyst containing the above elements together with palladium having low activity for methanol oxidation can suppress the methanol oxidation as much as possible and can improve the oxygen reduction reaction more selectively.

On the other hand, when the catalyst of the present invention is used as a cathode catalyst of a fuel cell, since it has low reactivity with respect to the crossover methanol, even when using a high concentration of methanol as a fuel it can exhibit excellent output performance.

The very low activity of the platinum-palladium in the methanol oxidation reaction of the present invention is considered to be related to the change of the electronic structure according to the alloy formation of platinum and palladium. When platinum and palladium form an alloy, electrons move from platinum to palladium, and palladium is in a reduced state, with more outer electrons, and platinum is in an oxidized state, with the outer electrons lost. do. Therefore, platinum with increased oxidation number becomes stronger to fill the outermost electrons through adsorption with molecules such as hydroxyl (-OH, hydroxy), and the hydroxyl adsorbed on the surface of platinum adsorbs methanol or oxygen molecules on the surface of platinum. It acts as a barrier to doing so, reducing the active site of platinum, where methanol can be oxidized. Thus, the generation of the oxidation current at the cathode is reduced, and as a result, the reduction of the oxidation current at the cathode can improve the electrode performance of the fuel cell.

Since the catalyst of the present invention is characterized by low methanol oxidation reactivity, it may have a better effect when methanol is present in the cathode of the fuel cell, which may be more severe when the concentration of methanol as fuel is high. It is a problem. Therefore, the anode fuel concentration of the fuel cell in which the catalyst of the present invention is used is preferably a high concentration of 2 mol or more, more preferably in the range of 2 mol to 6 mol. (See 3 in Experimental Example 1)

<Electrode, membrane electrode assembly, and fuel cell>

The electrode for a fuel cell including the cathode catalyst including platinum and palladium according to the present invention may be formed of, for example, a gas diffusion layer and a catalyst layer, and may be manufactured according to conventional methods known to those skilled in the art. For example, a slurry may be prepared by mixing the catalyst with a catalyst ink including a polymer material having high hydrogen ion conductivity and a mixed solvent for enhancing catalyst dispersion, and then printing, spraying, and rolling. Or by brushing, or the like, and can be produced by coating and drying the carbon paper.

The present invention also provides a membrane electrode assembly (MEA) for a fuel cell comprising the above electrode, wherein one of the first electrode and the second electrode is an anode, and the other is a cathode. .

The electrode membrane assembly (MEA) refers to a conjugate of an electrode in which an electrochemical catalytic reaction between fuel and air occurs and a polymer membrane in which hydrogen ions are transferred, and is a single unitary unit to which a catalyst electrode and an electrolyte membrane are bonded.

The fuel cell electrode membrane assembly is a type in which the catalyst layer of the cathode and the catalyst layer of the anode are in contact with the electrolyte membrane, and may be manufactured according to conventional methods known to those skilled in the art. For example, it may be prepared by placing an electrolyte membrane between the cathode and the anode, and then placing the electrolyte membrane between two hot plates that are hydraulically operated while maintaining a temperature of about 140 ° C., and then applying pressure under pressure.

As the electrolyte membrane, any material having hydrogen ion conductivity, mechanical strength enough to form a film, and high electrochemical stability can be used without particular limitation, and non-limiting examples thereof include tetrafluoroethylene and fluorine. There is a copolymer of rhovinyl ether, and the fluorovinyl ether moiety has a function of conducting hydrogen ions.

The fuel cell provided in the present invention may be a polymer electrolyte fuel cell and a direct liquid fuel cell employing an oxygen reduction reaction as a cathode reaction, but are not limited thereto. In particular, a direct methanol fuel cell, a direct formic acid fuel cell, a direct ethanol fuel cell or a direct dimethyl ether fuel cell is preferable. It can also be used in phosphate electrolyte fuel cells.

At this time, all the materials constituting the fuel cell can be used any material used in the conventional fuel cell known in the art, except for the electrode catalyst prepared in the present invention. In addition, the manufacturing method of the fuel cell is not particularly limited, and a membrane electrode assembly (MEA) and a bipolar including an electrolyte coated with a cathode, an anode, and an active layer including the catalyst material according to conventional methods known in the art. It can be manufactured by constructing a bipolar plate.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited thereto.

Example 1 Platinum / Palladium Binary System Preparation of Cathode Catalyst

The metal salts of platinum (H ₂ PtCl ₆ .xH ₂ O) and the metal salts of palladium (PdCl ₂ ) were each taken so that the molar ratio of platinum: palladium was 0.5: 0.95. Each of the metal salts was put in distilled water and stirred at room temperature (25 ° C.) for 3 hours, and then mixed with each of the metal salt solutions, and stirred for another 3 hours. In this experiment, AlDRICH metal salt was used, but metal salts such as SIGMA or Samwha Co., Ltd. of the above composition can be used, and K ₂ PtCl ₆ , PdBr ₂ , and Pd (NO ₃ ) ₃ · xH Other forms of metal salts, such as ₂ O, can also be used.

After adjusting the pH of the mixed metal salt solution to 8, an excess of 2 mol of sodium borohydride (NaBH ₄ ) aqueous solution with a reducing agent (approximately three times the stoichiometric requirement) was added to the mixed metal salt solution at a time to obtain the metal salts. Reduction gave a precipitate. The obtained precipitate was washed three times with distilled water and then lyophilized for 12 hours to obtain a synthetic catalyst, and performance measurement experiments were performed on the catalyst thus prepared.

Comparative Example 1 Preparation of Platinum Catalyst

In order to prepare a single metal catalyst composed of platinum, a catalyst was prepared in the same manner as in Example 1, except that only a metal salt of platinum (H ₂ PtCl ₆ .xH ₂ O) was used, without using a palladium raw material. Platinum synthesis catalysts were obtained, and physical properties analysis and performance measurement experiments were conducted on the catalysts thus prepared.

Experimental Example 1 Physical Property Analysis and Performance Measurement Experiment of Catalyst

1) Analysis of physical properties of catalyst

X-ray diffraction analysis and X-ray spectroscopy composition analysis (EDX) were performed on the metal catalysts prepared in Example 1 and Comparative Example 1 to confirm the synthesis and composition ratio of the metal catalysts. Indicated. As a result of the analysis, it was confirmed that a relatively small crystalline nano-synthesis catalyst was synthesized in the synthesis catalyst, and the synthesized composition ratio was in good agreement with the intended composition ratio.

2) catalyst activity measurement

Catalyst slurry using the catalyst powder prepared in Example 1 and Comparative Example 1 (Nafion perfluorinated ion-exchange resin, 5 wt.% Solution in a mixture of lower aliphatic alcohols and water, Aldrich. Co.) Was prepared, and the prepared slurry was applied to a rotating disc electrode to prepare an electrode for measuring catalytic activity.

To compare the activities for the oxygen reduction reaction, at room temperature, Pt wire as counter electrode, Ag / AgCl as reference electrode, and glassy carbon as rotating disc electrode ( Reduction current density was measured in 0.05 mole sulfuric acid solution saturated with oxygen and 0.05 mole sulfuric acid solution saturated with 0.5 mole methanol / oxygen using a three electrode cell serving as a rotating disk electrode. The activity of the catalyst was then measured.

4 and 5 are measured sequentially by applying a range of voltage in a 0.05 mol sulfuric acid solution saturated with oxygen (FIG. 4) and a 0.05 mol sulfuric acid solution saturated with 0.5 mol methanol / oxygen (FIG. 5). And, it is a graph comparing the current measured for the relative comparison divided by the area obtained through the desorption of hydrogen ions of the catalyst. Even if the same metal was used, the oxygen reduction reaction was different according to the synthesized composition ratio, and as shown in FIGS. 4 and 5, the reduction reaction of the oxygen reduction reaction occurring under the same voltage was higher than that of pure platinum in the binary catalyst of the present invention. Although the current density showed a smaller value, it showed improved catalytic activity in the presence of methanol than the conventional catalyst.

3) Unit battery performance test

The performance was measured by preparing a unit cell using the catalysts prepared in Example 1 and Comparative Example 1 as the cathode catalyst.

The amount of each cathode catalyst was 2.8 mg / cm ² based on the metal, and the anode catalysts were all 5 mg / cm ² of PtRu black (Johnson Matthey, UK) and Nafion 117 (Dupont, USA). What formed the conjugate (Membrane Electrode Assembly, MEA) was used. The unit cell tested was 2 cm ^{2 in} size and supplied with methanol solution and oxygen at a flow rate of 0.2 to 2 cc / min and 300 cc / min through a graphite channel.

In FIG. 6, a graph comparing unit cell performance test results of the platinum / palladium binary catalyst and the pure platinum catalyst of the present invention in a 2-mole methanol solution and an oxygen supply condition is shown. As a result, when the pure platinum catalyst was used at 0.3 V, the current density was 169 mA / cm ² , but when the platinum / palladium binary catalyst prepared in Example 1 was used, 200 mA / cm ² was about 18%. Performance improvement was seen.

FIG. 7 is a graph comparing unit cell performance tests when 4 mole methanol solution is used under the same experimental conditions as FIG. 6. The test result showed a current density of 172 mA / cm ² when the pure platinum catalyst was used at 0.3 V. However, when the platinum / palladium binary catalyst prepared in Example 1 was used, about 45% of 249 mA / cm ² was used. The performance was improved.

8 is a graph comparing unit cell performance tests when 6 mole methanol solution was used under the same test conditions. The test result showed a current density of 85 mA / cm ² when using pure platinum catalyst at 0.3 V, but about 140% of 206 mA / cm ² when using the platinum / palladium binary catalyst prepared in Example 1 The performance was improved.

FIG. 9 is a graph comparing long-term unit cell performance according to operation time when air, not pure oxygen, is injected at a flow rate of 500 cc / min as a cathode fuel, and 2 mol and 4 mol methanol solutions are used. Results are for 2 moles of methanol up to 100 hours and 4 moles of methanol for 100 to 200 hours.

At this time, the operating temperature is 30 ° C, and the load applied to both electrodes is 30 mA / cm ² . Even when air having a greater methanol crossover effect was used as the cathode fuel, the platinum / palladium binary catalyst prepared in Example 1 exhibited greater performance. As a result, the pure platinum catalyst showed 365 mV after 100 hours of operation at 2 moles, but the performance of the platinum / palladium binary catalyst was 416 mV, which was about 14%. The pure platinum catalyst showed 334 mV after 100 hours of operation at 4 moles of the same condition, but the performance of the platinum / palladium binary catalyst was 405 mV at 21%.

4) Oxidation test of adsorbed carbon monoxide (CO)

Carbon monoxide was adsorbed on the platinum / palladium binary catalyst prepared by Example 1 and Comparative Example 1 and the platinum catalyst by varying the time using a constant potential method (chroropotentiometry) in 0.05 mol sulfuric acid solution, and then the oxidation thereof. The reaction characteristics were analyzed and the results are shown in FIG. 10.

10, when the coverage (coverage) according to the adsorption time of the CO, it was confirmed that the platinum-palladium catalyst of the present invention is lower than the pure platinum catalyst, the coverage of CO, which is a poisoning phenomenon by CO ( CO poisoning) can be judged to decrease in Pt-Pd binary catalyst.

The platinum / palladium synthesis catalyst according to the present invention is an anode catalyst of a direct methanol fuel cell, and has an advantage of maintaining high oxygen reduction reactivity while having low reactivity to methanol flowing into the cathode by crossover. In addition, carbon monoxide has the advantage of low adsorption properties fundamentally.

These advantages make it possible to use concentrated fuels in particular, as well as applications in direct methanol fuel cells using low concentrations of fuel. When using a high concentration of fuel, there is an advantage that can increase the fuel cell operating time under a limited fuel tank volume.

In addition, due to the characteristics of the platinum / palladium synthesis catalyst, the composition of palladium is increased to maintain the catalytic activity of the oxygen reduction reaction in a high concentration of fuel. This advantage has the effect of significantly reducing the cost of preparing the catalyst.

Therefore, when comparing the platinum catalyst commercialized for the direct methanol fuel cell and the activity of oxygen reduction reaction under the environment similar to the actual methanol fuel cell cathode, the binary catalyst composed of platinum / palladium can obtain high output from the direct methanol fuel cell. It is expected that the catalyst can be accelerated.

Claims (17)

A cathode catalyst of a direct methanol fuel cell, the catalyst comprising platinum (Pt) and palladium (Pd). The catalyst according to claim 1, which is used in a fuel cell using an anode fuel having a concentration of 2 mol or more. The catalyst according to claim 1, which is used in a fuel cell using an anode fuel in a concentration range of 2 mol to 6 mol. The catalyst of claim 1 wherein the platinum content is in the range of 0.5 mol% to 99.5 mol% and the palladium content is in the range of 0.5 mol% to 99.5 mol%. The catalyst of claim 1 wherein the platinum content is in the range of 0.5 mol% to 50 mol% and the palladium content is in the range of 50 mol% to 99.5 mol%. The catalyst of claim 1 wherein platinum and palladium are supported by a catalyst carrier material. The catalyst of claim 6, wherein the catalyst carrier material is at least one porous carbon selected from the group consisting of activated carbon, carbon fiber, graphite fiber and carbon nanotubes. The method of claim 6, wherein the catalyst carrier material is at least one conductive polymer selected from the group consisting of polyvinylcarbazole and its derivatives, polyaniline and its derivatives, and polypyrrole and its derivatives. Phosphorus catalyst. The catalyst according to claim 6, wherein the catalyst carrier material is at least one metal oxide selected from the group consisting of tungsten oxide, titanium oxide, nickel oxide, ruthenium oxide, tantalum oxide, and cobalt oxide. The catalyst of claim 6 wherein the weight ratio of catalyst carrier material is from 5 wt% to 99 wt% relative to the platinum / palladium catalyst metal. The catalyst of claim 1, further comprising at least one metal element selected from the group consisting of iron, cobalt, nickel, ruthenium, rhodium, gold, silver, osmium, and iridium in addition to the platinum and palladium. A fuel cell electrode comprising the catalyst according to any one of claims 1 to 11. A membrane electrode assembly comprising the fuel cell electrode according to claim 12. A fuel cell comprising the membrane electrode assembly according to claim 13. 15. The fuel cell according to claim 14, wherein the anode (anode) fuel is at least one selected from the group consisting of methanol, ethanol, and formic acid, and its concentration is at least 2 moles. 15. The fuel cell according to claim 14, wherein the anode fuel is at least one selected from the group consisting of methanol, ethanol, and formic acid, and its concentration is in the range of 2 mol to 6 mol. a) a first step of preparing an aqueous solution of a salt of platinum and palladium; b) a second step of obtaining a precipitate of alloy catalyst particles of platinum / palladium by adding a reducing agent to the aqueous solution; And c) a third step of separating the precipitate from the solution and lyophilizing it; Method for producing a catalyst according to claim 1, including.

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