JP4958133B2 - Electrode catalyst for hydrogen electrode of low temperature fuel cell - Google Patents

Description

  INDUSTRIAL APPLICABILITY The present invention is effective as an electrode catalyst for a hydrogen electrode of a low temperature fuel cell having an operating temperature of about 300 ° C. or less, such as a polymer fuel cell using reformed gas, an alkaline fuel cell, and a phosphoric acid fuel cell The present invention relates to a mixed metal / organometallic complex catalyst and a low-temperature fuel cell using the catalyst.

  In polymer fuel cells using reformed gas, and low temperature fuel cells having an operating temperature of about 300 ° C. or lower, such as alkaline fuel cells and phosphoric acid fuel cells, electrons are transferred between hydrogen gas and an electrolyte. The performance of the electrocatalyst that performs the battery greatly affects the battery performance. In particular, when an electrode is disturbed by a catalyst poisoning substance such as CO, the development of a catalyst having resistance to poisoning substances is an important research subject.

Conventionally, as a catalyst for a fuel electrode having low CO poisoning resistance in such a low-temperature fuel cell, a binary alloy such as platinum / ruthenium, platinum / tin, platinum / molybdenum, or a ternary system based on them. Alloy catalysts and catalysts based on metals and oxides such as platinum / titanium oxide and platinum tungstic acid have been developed.
However, these catalysts have the following problems.
1. It is inferior in CO-toxication resistance in a system with high CO concentration.
2. As a reaction mechanism that exhibits resistance to CO poisoning, a dual function mechanism, a d-electron deficiency mechanism, and the like have been proposed, all of which are designed with interatomic interactions in mind, and are new functions. The development of new catalysts based on this is no longer the limit.
3. Based on experience, the types of metals and oxides that can be selected as the second component and the third component are limited, and improvement in catalytic ability cannot be expected.

  Based on the above problems, the present inventors have two or more kinds of valence metals such as transition metal elements or alloys thereof and transition metal elements of Group V, VI, VII, and VIII of the Periodic Table. A mixed catalyst in which an organometallic complex in which an element is a central element and a ligand containing nitrogen, oxygen, sulfur or the like is coordinated in a plane is mixed is proposed (see Patent Document 1).

JP 2002-329500 A

However, in the fuel electrode of a low-temperature fuel cell that is susceptible to catalyst poisoning due to CO gas or the like, the catalyst containing the organometallic complex described in the above document has been developed as a methanol oxidation catalyst and has methanol oxidation characteristics. It is shown. In order not to be poisoned by CO generated as a by-product in the process of methanol oxidation, the CO coverage on the catalyst surface is set to 50% or less, which is the same as that of a platinum-ruthenium alloy catalyst that has been put into practical use. The purpose is to obtain a degree of CO poisoning resistance.
The present invention has been made in view of the actual situation of such a technology, and has a superior performance as a hydrogen oxidation catalyst, and is a well-known platinum-ruthenium alloy catalyst even when the CO poisoning resistance is a CO concentration of 10 ppm to 100 ppm. An object of the present invention is to provide an electrode catalyst for a hydrogen electrode of a low temperature fuel cell which is further superior and advantageous in terms of cost and production, and a low temperature fuel cell using the same.

In order to solve the above-mentioned problems, the inventors of the present invention further carefully arranged platinum or an alloy thereof and an organometallic complex in which a ligand containing nitrogen, oxygen, sulfur, etc. is coordinated in a planar manner and a central metal atom thereof in a mixed catalyst. As a result of examining heat treatment adjustment conditions, etc., when a combination of a specific organometallic complex and a specific central metal atom is used as a hydrogen oxidation catalyst, particularly excellent CO poisoning resistance that has not been obtained so far is obtained. The present inventors have found an electrode catalyst for a hydrogen electrode having the present invention, and have reached the present invention.
That is, the present invention
(1) platinum or its alloys, N, a mixed catalyst of N'- bis (Sarishiriden) ethylene diamino metal complex, a metal complex the central metal is selected oxovanadium, manganese, iron, cobalt, nickel or al An electrode catalyst for a hydrogen electrode of a low-temperature fuel cell using a reformed gas containing hydrogen, which is an atom, supported on a support, and heat-treated at 200 ° C. to 550 ° C.,
(2) platinum or its alloys, N, a mixed catalyst of N'- mono-8-quinolyl -o- phenylene diamine metal complexes, complexes central metal, oxo vanadium, manganese, iron, cobalt, or nickel An electrode catalyst for a hydrogen electrode of a low-temperature fuel cell using a reformed gas containing hydrogen, which is a metal atom selected from the above, supported on a support and heat-treated at 200 ° C. to 550 ° C.,
(3) The platinum or an alloy thereof is derived from a compound selected from an ammine complex, a carbonyl complex, an acetylacetonate complex, a nitroso complex, acetate, chloride, bromide, and iodide, (1) or (2) characterized in that it is supported in the form of fine particles on the surface of the support, which is produced by mixing with the metal complex described in the solution in advance and supporting the support on a support and then heat-treating at 200 ° C. to 550 ° C. (1) or (2) a hydrogen electrode electrode catalyst,
(4) The electrode catalyst for a hydrogen electrode according to any one of (1) to (3), wherein the heat treatment is performed in an inert gas or an inert gas partially including a reducing gas. ,
(5) The electrode catalyst for a hydrogen electrode according to any one of (1) to (4), wherein the support is a carbonaceous material,
(6) The electrode catalyst for a hydrogen electrode according to (5), wherein the carbonaceous material is at least one selected from graphite, carbon black, ketjen black, activated carbon and glassy carbon,
(7) The hydrogen electrode of the low-temperature fuel cell using the hydrogen electrode catalyst according to any one of (1) to (6),
(8) The low-temperature fuel cell having the hydrogen electrode according to (7), and (9) the low-temperature fuel cell is a solid polymer fuel cell or a phosphoric acid fuel cell using a reformed gas. The low-temperature fuel cell according to (8) is provided.

The electrode catalyst for a hydrogen electrode of a low-temperature fuel cell according to the present invention has the following advantages.
(1) Even in a system having a higher CO concentration than conventional alloy-based catalysts and oxide-based catalysts, it exhibits better CO poisoning resistance and has the same durability as these conventional catalysts.
(2) Complex ligands of simple structure such as N, N′-bis (salicylidene) ethylenediamine, N, N′-mono-8-quinolyl-o-phenylenediamine, nickel, iron, cobalt, vanadium, etc. By using a low-cost organometallic complex selected from the above as raw materials, the cost of the catalyst material is reduced, and its preparation method is easy.

A preferred embodiment of the electrode catalyst for hydrogen electrode of the present invention will be described in detail.
The electrode catalyst in the present invention includes (a) platinum or an alloy thereof, (b) N, N′-bis (salicylidene) ethylenediamino metal complex, or N, N′-mono-8-quinolyl-o-phenylenediamine metal. It contains a complex.
The second component of the platinum-based alloy (a) is preferably a transition metal element centered on Group VIII of the periodic table, which has been used in the fuel electrode of a fuel cell, but will be described later. As a result of the concerted effect with the organometallic complex, the catalyst function is 10 times or more superior to that of the metal catalyst alone or the catalyst of the organometallic complex alone when the mixed catalyst is configured. But you can choose.
Examples of such transition metal elements include titanium, rhenium, tin, molybdenum, silver, gold, and the like in addition to group VIII metal elements such as cobalt, nickel, palladium, and ruthenium.

Wherein the center metal in the organometallic complexes of (b) is oxo vanadium, manganese, iron, cobalt, selected nickel or al. Among these, metal elements preferably used in the present invention are oxovanadium, manganese, and nickel. When the central metal is other than these, good CO poisoning resistance is not exhibited, and the object of the present invention cannot be achieved.

In the mixed catalyst of the present invention, the mixing ratio of the platinum (or alloy thereof) catalyst (a) and the organometallic complex (b) is not particularly limited, and is optimally determined empirically for each selected catalyst raw material. What is necessary is just to find a ratio and it sets suitably as needed.
Usually, the mixing ratio of the platinum (or alloy) catalyst of (a) and the organometallic complex of (b) is selected in the range of 20:80 to 90:10 to maximize the concerted effect. Is preferably in the ratio of 40:60 to 60:40.

As a method for preparing the catalyst, any conventionally known method such as a physical mixing method, a thermal decomposition method, a liquid phase method, and a plasma co-evaporation method can be used.
As a specific method for preparing the catalyst by the thermal decomposition method, for example, a platinum (or alloy thereof) catalyst of (a) is used as a complex compound precursor of the same metal, such as an ammine complex, a carbonyl complex, an acetylacetonate complex, a carboxylic acid. Complexes, nitroso complexes, acetates, chlorides, bromides, iodides, etc. are easily decomposed, and this and the organometallic complex (b) are simultaneously dissolved in a soluble organic solvent and evaporated to dryness. Or a method of mixing a water-soluble complex compound of the transition metal catalyst of (a) such as an ammine complex and an aqueous solution of the organometallic complex of (b) and evaporating to dryness.

  The catalyst according to the present invention is preferably used while being supported on the surface of a catalyst carrier. Examples of the carrier include conventionally known materials such as graphite, carbon black, ketjen black, activated carbon, glassy carbon such as glassy carbon, porous metal such as Raney nickel, Raney silver, etc. used. If it is a carbonaceous material, carrying | supporting will be performed satisfactorily when a thing with a particle size of 0.01-100 micrometers, preferably 0.02-10 micrometers is used.

As a method for supporting the catalyst on the carrier, any conventionally known method such as a dissolution drying method, a plasma vapor deposition method, a heat vapor deposition method, or a CVD method can be used.
In the case of the dissolution drying method, for example, the transition metal catalyst of (a) is easily decomposed thermally, such as a complex compound of the same metal such as an ammine complex or a carbonyl complex, and this is combined with an organometallic complex of (b) Are dissolved in a soluble organic solvent, a carrier, for example, carbon particles is stirred and mixed in the organic solvent, and then the solvent is dried.

The mixed catalyst thus obtained can be used as an electrode catalyst for a hydrogen electrode in the form of being directly supported on an electrode carrier (carbon particles, etc.). However, in the present invention, the organometallic complex is eluted on the electrolyte side. In order to prevent this and achieve excellent CO poisoning resistance, the mixed catalyst is supported on a carrier and then heat-treated in a gas such as an inert gas.
The heat treatment temperature is preferably low from the viewpoint of preventing the particle size of the metal catalyst component (a) from increasing, but a temperature of about 200 ° C. or higher is required to stabilize the organometallic complex. 200 ° C to 550 ° C, preferably 300 ° C to 500 ° C. In the heat treatment at 300 ° C. or higher, a mixture of the precursor of the metal catalyst component (a) and the metal complex (b) is considered to form a complex, and is particularly preferable, and has excellent CO poisoning resistance. Is 550 ° C. or lower, preferably 500 ° C. or lower.
This heat treatment is preferably performed in an atmosphere such as an inert gas such as argon or nitrogen or an inert gas partially containing a reducing gas such as hydrogen.

In the present invention, such an electrode catalyst is in the form of a mixture comprising a carbon-supported paste, a Teflon (registered trademark) emulsion, a polymer electrolyte solution and a binder, if necessary, and is known per se on the hydrogen electrode or electrolyte side. For example, a desired hydrogen electrode of a low-temperature fuel cell can be obtained by a method such as spraying, screen printing, or brushing.

  In addition, the hydrogen electrode obtained above is suitably used as a CO-toxic electrode for low-temperature fuel cells under conditions containing, for example, 10 ppm to 100 ppm of CO even when the operating temperature is below 80 ° C. In particular, it is preferable as a hydrogen electrode of a fuel cell using a reformed gas having a high CO concentration and an operating temperature of about 300 ° C. or less, such as a polymer fuel cell using a reformed gas and a phosphoric acid fuel cell.

Next, the electrode catalyst for a hydrogen electrode of the present invention will be described in more detail with reference to examples, and the effect will be clarified.
Example 1
Platinum tetraammine complex and nickel N, N′-mono-8-quinolyl-o-phenylenediamine [nickel monoquinolylphenylenediamine] were prepared as raw materials. The former was synthesized by commercially available reagent [Pt (NH ₃ ) ₄ ] Cl ₂ .nH ₂ O, and the latter was synthesized by the following method.
In a flask equipped with a reflux condenser, 2.9 g of 8-hydroxyquinoline, 1.1 g of o-phenylenediamine, 3.8 g of sodium disulfite, and 20 ml of pure water were added and heated to reflux at about 110 ° C. for 1 week. Thereafter, 50% sodium hydroxide solution was added to the reaction solution to make it alkaline. After cooling, the mixture was extracted with benzene, separated and purified by alumina column chromatography, and recrystallized from hexane to obtain yellow crystals of monoquinolylphenylenediamine (yield: about 14%). Nickel monoquinolylphenylenediamine crystals were obtained by mixing equimolar monoquinolylphenylenediamine and nickel (II) acetate tetrahydrate in acetonitrile degassed with nitrogen gas at room temperature.

Next, the platinum tetraammine complex and the nickel monoquinolylphenylenediamine complex were mixed at a weight ratio of 50:50. The obtained mixed catalyst was weighed to a ratio of 1: 4 with carbon black particles (Vulcan XC-72R), dissolved in a small amount of ethanol, thoroughly mixed using an agate mortar, and then 80 ° C. in air. And dried.
The catalyst-supported carbon black particles thus prepared were divided into three parts, each was put in an annular atmosphere furnace, and each was heat treated at 400 ° C., 500 ° C., and 600 ° C. for 2 hours in an argon gas atmosphere. Catalyst-supported carbon particles were obtained [abbreviated as Pt-Ni (mqph) / C].

Carbon paper with a diameter of 8 mm (trade name: TGP-H-090) manufactured by Toray International Co., Ltd., together with 20% by weight Nafion (registered trademark) polymer 5% solution (manufactured by Aldrich Chemicals Co.). A catalyst surface was prepared by dripping and drying, and then half-cell MEA was prepared by hot pressing one side so that the catalyst surface was in contact with the Nafion (registered trademark) 115 membrane.

The MEA for half-cell was mounted on a Teflon holder for hydrogen gas flows in contact pure hydrogen gas and carbon paper over side, Nafion (registered trademark) film side to 1M perchloric acid solution, perchloric acid solution Was kept at 70 ° C. while degassing with nitrogen gas. In such a half-cell, the MEA for half-cell was placed as a test electrode, a counter electrode of a platinum plate and a reversible hydrogen electrode (RHE) in a perchloric acid aqueous solution, and the hydrogen oxidation current was measured. For the measurement, a potentiostat was used, a current-potential curve was recorded, and the hydrogen oxidation current at 100 mV vs RHE was evaluated.

  Similarly, the gas containing 10, 50, and 100 ppm carbon monoxide (CO) in hydrogen gas was introduced into the half cell, and the hydrogen oxidation current at 100 mV vs RHE was evaluated to compare the CO poisoning resistance of the catalysts. The result is shown in FIG. 1 as a ratio (%) of the current value in the hydrogen gas containing CO when the current value at 100 mV when using pure hydrogen is 100%.

Also, for catalyst-carrying carbon particles heat-treated at 500 ° C. or 600 ° C., half-cell MEAs were similarly prepared, and the hydrogen oxidation current was similarly measured and evaluated by introducing pure hydrogen and CO-containing hydrogen, The results are shown in FIG.
Excellent CO resistance was exhibited at Pt—Ni (mqph) / C at a heat treatment temperature of 400 ° C. or 500 ° C.

Example 2
It was obtained in the same manner as in Example 1 except that N, N′-bis (salicylidene) ethylenediamine oxovanadium [oxovanadium salen] was used in place of nickel monoquinolylphenylenediamine as the organometallic complex raw material ( A similar CO poisoning resistance test was conducted using catalyst-supported carbon particles (abbreviated as Pt-VO (salen) / C) having heat treatment temperatures of 400 ° C., 500 ° C., and 600 ° C.
FIG. 2 shows a graph in which the current value at 100 mV measured with pure hydrogen and hydrogen gas containing 10, 25, and 50 ppm of CO is converted per mg of platinum contained in the mixed catalyst prepared at each heat treatment temperature. It can be seen that 400 ° C. is suitable as the heat treatment temperature.
Next, the mixed catalyst prepared at a heat treatment temperature of 400 ° C. is a standard catalyst material, 20% platinum-supported carbon (abbreviated as Pt / C) and 20% platinum, 10% ruthenium alloy-supported carbon [Pt-Ru]. / Abbreviated as / C], and evaluated as a ratio (%) of the current value in hydrogen gas containing 10, 25, 50, and 100 ppm of CO when the current value at 100 mV in pure hydrogen is 100%. did. The result is shown in FIG.
Standard electrocatalysts such as Pt / C and Pt-Ru / C show a significant decrease in performance when the CO concentration exceeds 25 ppm, whereas Pt-VO (salen) / C catalysts are hydrogen even when they contain 100 ppm CO. Oxidation current flows and it was shown that it is a very excellent hydrogen electrode catalyst for reformed gas.

Example 3
Using pure hydrogen gas as a fuel, the current value on a Pt-VO (salen) / C catalyst at a potential of 100 mV was continuously measured to investigate durability. FIG. 4 shows the change with time of the current on the Pt—VO (salen) / C catalyst in the continuous operation for 100 hours in comparison with the result of the aforementioned Pt—Ru / C catalyst.
FIG. 4 shows that the catalyst of the present invention using an organometallic complex as a raw material has the same durability as a normal fuel cell catalyst.

Example 4
A catalyst prepared in the same manner as in Example 1 except that manganese monoquinolylphenylenediamine or ruthenium monoquinolylphenylenediamine in which the central metal is manganese or ruthenium is used instead of Pt—Ni (mqph) / C. Supported carbon particles were obtained [abbreviated as Pt-Mn (mqph) / C or Pt-Ru (mqph) / C].
FIG. 5 shows the results of a CO poisoning resistance test and evaluation using pure hydrogen, hydrogen gas containing 10, 50, and 100 ppm of CO as in Example 1 and Example 2.
From FIG. 5, even in the case of a metal complex using monoquinolylphenylenediamine, the performance of ruthenium is inferior to that of nickel or manganese corresponding to the present invention. It can be seen that it does not show CO toxicity.

Comparative Example 1
An oxovanadium antenene (abbreviated as Pt-VO (anthen) / C) and a complex in which the complex ligand is N, N′-bis (anthranylidene) ethylenediamine instead of the oxovanadium salen of Example 2. Catalyst-supported carbon particles were prepared in the same manner except that the ligand was N, N′-diquinolylpropylenediamine and a diquinolylpropylenediamine oxovanadium complex was used [Pt-VO (dqpr) / C and Abbreviated].
FIG. 6 shows the results of evaluation by performing a CO poisoning resistance test in the same manner as in Example 1 and Example 2, together with Pt—VO (salen) / C in Example 2. FIG. 6 shows that even a metal complex using oxovanadium as a central metal does not show good CO poisoning resistance depending on the choice of complex ligand.

CO 50 of 10, 50, 100 ppm obtained with the Pt—Ni (mqph) / C mixed catalyst of each heat treatment of Example 1 when the current value at 100 mV when using pure hydrogen is 100% It is the figure which showed the ratio (%) of the electric current value in hydrogen gas containing. The values obtained by converting the current value at 100 mV with pure hydrogen and hydrogen gas containing 10, 25, and 50 ppm of CO obtained with the Pt—VO (salen) / C mixed catalyst of Example 2 to each mg of supported platinum It is the graph compared with the heat processing temperature. 10 and 25 when the current value at 100 mV when using pure hydrogen obtained by the Pt-VO (salen) / C mixed catalyst prepared by heat treatment at 400 ° C. in Example 2 is 100%. It is the figure which showed the ratio (%) of the electric current value in hydrogen gas containing 50 and 100 ppm CO, and also compares with the performance in a Pt / C and a Pt-Ru / C catalyst simultaneously. It is the graph which compared with the performance in a Pt-Ru / C catalyst the time-current change in 100 mV when using pure hydrogen obtained with the Pt-VO (salen) / C mixed catalyst of Example 3. When the current value at 100 mV when using pure hydrogen obtained with the Pt-Mn (mqph) / C mixed catalyst and the Pt-Ru (mqph) / C mixed catalyst of Example 4 is 100%, It is the figure which showed the ratio (%) of the electric current value in the hydrogen gas containing 10, 50, and 100 ppm CO, and also shows about the Pt-Ni (mqph) / C catalyst of Example 1 simultaneously. When the current value at 100 mV when using pure hydrogen obtained with the Pt-VO (anthen) / C mixed catalyst and the Pt-VO (dqpr) / C mixed catalyst of Comparative Example 1 is 100%, It is the figure which showed the ratio (%) of the electric current value in hydrogen gas containing 10, 50, and 100 ppm CO, and also shows about the Pt-VO (salen) / C mixed catalyst of Example 2 simultaneously.

Claims (9)

Platinum or its alloys, N, a mixed catalyst of N'- bis (Sarishiriden) ethylene diamino metal complex, complex central metal, oxo vanadium, manganese, iron, cobalt, be nickel or we chosen metal atom An electrode catalyst for a hydrogen electrode of a low-temperature fuel cell using a reformed gas containing hydrogen, which is supported on a carrier and heat-treated at 200 ° C. to 550 ° C. Platinum or its alloys, N, a mixed catalyst of N'- mono-8-quinolyl -o- phenylene diamine metal complexes, complexes central metal, oxo vanadium, manganese, iron, cobalt, selected nickel or al An electrode catalyst for a hydrogen electrode of a low-temperature fuel cell using a reformed gas containing hydrogen, which is a metal atom, supported on a support, and heat-treated at 200 ° C to 550 ° C.   The platinum or an alloy thereof is derived from a compound selected from an ammine complex, a carbonyl complex, an acetylacetonate complex, a nitroso complex, an acetate, a chloride, a bromide, and an iodide. The metal complex is mixed in advance in a solution state, and is supported on the support surface in the form of fine particles produced by heat-treating the metal complex on the support and then heat-treating at 200 ° C to 550 ° C. 2. Electrode catalyst for hydrogen electrode according to 2.   The electrode catalyst for a hydrogen electrode according to any one of claims 1 to 3, wherein the heat treatment is performed in an inert gas or an inert gas partially containing a reducing gas.   The electrode catalyst for a hydrogen electrode according to any one of claims 1 to 4, wherein the support is a carbonaceous material.   6. The electrode catalyst for a hydrogen electrode according to claim 5, wherein the carbonaceous material is at least one selected from graphite, carbon black, ketjen black, activated carbon and glassy carbon.   A hydrogen electrode of a low-temperature fuel cell using the catalyst for a hydrogen electrode according to any one of claims 1 to 6.   A low-temperature fuel cell comprising the hydrogen electrode according to claim 7. 9. The low-temperature fuel cell according to claim 8, wherein the low-temperature fuel cell is a solid polymer fuel cell or a phosphoric acid fuel cell using a reformed gas.

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