DE102010042932A1 - New electrocatalyst (comprising a carrier that is organic compound with polycyclic aromatic structure functionalized with e.g. dicarboxylic anhydride group and active material) useful as catalyst for cathodic oxygen reduction in fuel cell - Google Patents

Abstract

Electrocatalyst (I) (comprising a carrier and at least one catalytically active material) is new, where: the carrier is at least one optionally substituted organic compound with polycyclic aromatic structure, which is functionalized with at least one dicarboxylic acid imide group, dicarboxylic anhydride group and/or a carbonyl group; the catalytic active material is applied on the carrier; and (I) is present as powder with an average particle size of 5 nm to 100 mu m. An independent claim is included for the preparation of (I).

Description

The present invention relates to an electrocatalyst comprising a carrier and at least one catalytically active material, wherein the carrier used are graphite-like polycyclic aromatic compounds on which the catalytically active material is applied. The invention further relates to a process for the preparation of such a catalyst and its use.

Fuel cells are electrochemical cells designed for both mobile and stationary electric power generation. In a fuel cell, the principle of electrolysis is reversed. Today, various types of fuel cells are known, which generally differ in operating temperature from each other. The structure of the cells is basically the same for all types. They are generally composed of two electrode layers, an anode and a cathode, where the reactions take place, and an electrolyte between the two electrodes in the form of a membrane. This membrane has three functions: it establishes the ionic contact, prevents the electrochemical contact, and ensures the separation of the media fed to the electrode layers. The electrode layers are usually supplied with gases or liquid, which are reacted in the context of a redox reaction. For example, the anode is supplied with hydrogen or methanol and the cathode with oxygen. To ensure this, the electrode layers are usually contacted with electrically conductive gas distribution layers. These are, for example, plates with a grid-like surface structure from a system of fine channels.

To operate the fuel cell, gaseous and liquid fuels capable of providing protons are used. Examples are hydrogen and methanol, with hydrogen being preferred. The hydrogen is delivered to the anode of the fuel cell. Oxygen (in the form of atmospheric oxygen) is the cell oxidant and is supplied to the cathode of the cell. Typically, the electrodes are formed of porous conductive materials, such as graphite cloth, graphitized sheets, or carbon paper, to allow the fuel to be distributed over the surface of the membrane facing the fuel supply electrode. Each electrode comprises finely divided catalyst particles (for example platinum particles on a support), which are usually applied to carbon particles in order to promote ionization of hydrogen at the anode and reduction of oxygen at the cathode. Protons flow from the anode through an ion-conducting polymer membrane to the cathode, where they combine with oxygen to form water that is discharged from the cell. Printed circuit boards lead away the electrons formed at the anode.

A problem with the fuel cells of the prior art, for example, the loss of performance during the continuous operation of the fuel cell or the cyclic load in normal motor vehicle operation. A significant proportion of this power loss of the fuel cells is associated with the damage to the oxygen reduction electrode catalyst. This damage is likely to be caused by a combination of mechanisms that alter the properties of the originally prepared catalyst and its carrier.

One document dealing with the durability or stability of catalysts for fuel cells is the US 2006/0257719 , In this document, it is proposed to use titanium dioxide particles and carbon as a carrier for the catalyst material, thereby reducing the corrosion rate of carbon in the carrier material.

In the DE 69327799 For example, elaborately manufactured electrodes made of nanostructured carrier material (so-called whiskers) embedded in an encapsulation layer are disclosed. To make these whiskers, organic compounds containing planar molecules, chains or rings, via which the pi electron density is highly delocalized, are used.

An object of the present invention is to provide a catalyst which is particularly suitable for the cathodic reduction of oxygen in fuel cells and has an improved corrosion stability compared with the prior art. In particular, it is an object of the present invention to provide a method by which such a catalyst can be prepared.

The object is achieved by a catalyst comprising a support (A) and at least one catalytically active material (B), wherein as support optionally substituted organic compounds having a polycyclic aromatic structure, with at least one dicarboxylic acid imide group, dicarboxylic acid anhydride group and / or carbonyl group are functionalized, are used, on which the catalytically active material is applied and the catalyst is present as a powder having an average particle size in the range of 5 nm to 100 microns.

In order to achieve a sufficiently good catalytic activity, it is advantageous if the catalyst according to the invention has the largest possible surface area. This is achieved by: the catalyst contains a carrier as defined above, on which the at least one catalytically active metal or the corresponding alloy is deposited. An advantage of using an optionally substituted organic material having a polycyclic aromatic structure as a carrier, which is functionalized as described above, is that the corrosion stability of the catalyst according to the invention is markedly improved over the catalysts known from the prior art.

A further advantage of the electrocatalyst according to the invention is that, in contrast to the catalysts known from the prior art, it is not black, but usually has a yellow, orange or red color. This enables color coding of the catalyst alone by using different carriers. For example, as the anode catalyst, a catalyst supported by a carbon carrier known in the art may be used, as it may be less corrosion resistant than a cathode catalyst. As Katodenkatalysator then the catalyst according to the invention is used, which has no black color. Due to the different color, a clear assignment of anode catalyst and cathode catalyst is possible, whereby a likelihood of confusion of the catalysts can be reduced or even ruled out.

In the organic, preferably semiconducting organic compound having a polycyclic aromatic structure, which serves as a carrier for the electrocatalysts according to the invention, are in particular compounds having as a backbone a perylene, naphthalene, coronene and / or Quaternary skeleton, preferably one Perylenimide or naphthalimide backbone.

allgemeine Formel (I) in der

– X unabhängig voneinander die Bedeutung O oder NR¹ mit R¹ gleich H, Aryl, Aralkyl, Heteroaryl, Cycloalkyl, C₁-C₂₂-Alkyl haben, wobei die Gruppen Aryl, Aralkyl, Heteroaryl, Cycloalkyl und C₁-C₂₂-Alkyl, gegebenenfalls mit einem oder mehreren Substituenten substituiert, sind, bevorzugt R¹ gleich Alkyl, Aryl, Alkyl-aryl oder Aralkyl ist,
– n gleich 0,1 oder 2 ist und
– R¹, R², R³, R⁴, R⁵, R⁶, R⁷ und R⁸ unabhängig voneinander gleiche oder verschiedene der folgenden Reste sind:
H, Alkyl, Cycloalkyl, Aralkyl, Aryl, Alkoxyaryl und Heterocyclyl, wobei die Gruppen Alkyl, Cycloalkyl, Aralkyl, Aryl, Alkoxyaryl und Heterocyclyl gegebenenfalls mit einem oder mehreren Substituenten substituiert, und die Gruppen Alkyl, Cycloalkyl, Aralkyl, Aryl und Alkoxyaryl gegebenenfalls durch 1 bis 3 Heteroatome oder funktionelle Gruppen unterbrochen sind.According to a general embodiment of the invention, the carrier comprises at least one compound according to general formula I shown below:

general formula (I) in the

X independently of one another have the meaning O or NR ¹ where R ¹ is H, aryl, aralkyl, heteroaryl, cycloalkyl, C ₁ -C ₂₂ -alkyl, the groups being aryl, aralkyl, heteroaryl, cycloalkyl and C ₁ -C ₂₂ - Alkyl, optionally substituted by one or more substituents, preferably R ¹ is alkyl, aryl, alkylaryl or aralkyl,
- n is equal to 0.1 or 2 and
R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ^{8 are} independently the same or different of the following radicals:
H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl, wherein the groups alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl optionally substituted with one or more substituents, and the groups alkyl, cycloalkyl, aralkyl, aryl and alkoxyaryl optionally by 1 to 3 heteroatoms or functional groups are interrupted.

"Alkyl" means a saturated aliphatic hydrocarbon group which may be straight chain or branched and may have from 1 to 20 carbon atoms in the chain. Preferred alkyl groups may be straight-chain or branched and have from 1 to 12 carbon atoms in the chain. Branched means that a lower alkyl group, such as methyl, ethyl or propyl, is attached to a linear alkyl chain. Alkyl is, for example, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl,

2-butyl, 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-1-butyl, 3 Methyl 1-butyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-1 -Pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl , 3-methyl-3-pentyl, 2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3 Dimethyl 2-butyl, 3,3-dimethyl-2-butyl, 1-heptyl, 1-octyl, 1-nonyl, 1-decyl, 1-undecyl, 1-dodecyl, 1-tetradecyl, 1-hexadecyl and 1 octadecyl.

"Substituted alkyl" means that the alkyl group is substituted with one or more substituents selected from alkyl, optionally substituted aryl, optionally substituted aralkyl, alkoxy, nitro, carboalkoxy, cyano, halo, alkylmercaptyl, trihaloalkyl or carboxyalkyl.

"Cycloalkyl" means an aliphatic ring having from 3 to about 10 carbon atoms in the ring. Preferred cycloalkyl groups have from 4 to about 7 carbon atoms in the ring.

"Aryl" means phenyl or naphthyl. "Aralkyl" means an alkyl group substituted with an aryl group. "Substituted aralkyl" and "substituted aryl" mean that the aryl group or aryl group of the aralkyl group is substituted with one or more substituents selected from alkyl, alkoxy, nitro, carboalkoxy, cyano, halo, alkylmercaptyl, trihaloalkyl or carboxyalkyl.

"Alkoxy" means an alkyl-O-group in which "alkyl" has the meaning described above. Lower alkoxy groups are preferred. Exemplary groups include methoxy, ethoxy, n-propoxy, i -propoxy and n-butoxy.

"Lower alkyl" means an alkyl group having from 1 to about 7 carbon atoms.

"Alkoxyalkyl" means an alkyl group as described above which is substituted with an alkoxy group as described above.

"Halogen" (or "halo") means chloro, fluoro, bromo or iodo.

"Heterocyclyl" means an approximately 4 to about 10 membered ring structure in which one or more of the ring atoms is other than carbon, for example N, O or S. Heterocyclyl may be aromatic or non-aromatic, i. H. it can be saturated, partially or completely unsaturated.

"Substituted heterocyclyl" means that the heterocyclyl group is substituted with one or more substituents, which include as substituents: alkoxy, aryl, carbalkoxy, cyano, halo, heterocyclyl, trihalomethyl, alkylmercaptyl or nitro.

"Alkoxycarbonyl" means an alkoxy C = O group.

"Aralkoxycarbonyl" means an aralkyl-O-C = O group.

"Aryloxycarbonyl" means an aryl-O-C = O group.

"Carbalkoxy" means a carboxyl substituent esterified with an alcohol of the formula C _n H _{2n + 1} OH, where n is from 1 to about 6.

"Alkoxyalkyl" means an alkyl group as described above which is substituted with an alkoxy group as described above.

As hetero atoms In the definition of R ^1, R ^2, R ^3, R ^4, R ^5, R ^6, R ^7, R ^8, R ⁹ and R ¹⁰ are in principle all heteroatoms in question, which are able to formally to replace a -CH ₂ -, a -CH =, a -C≡ or a = C = -group. If the rest contains heteroatoms, oxygen, nitrogen, sulfur and phosphorus are preferred. Particularly preferred groups which may be mentioned are -O-, -S-, -SO-, -SO ₂ -, -NR'-, -N =, -PR'- and -PR ' ₂ , where the radicals R' is about the remaining part of the rest.

Suitable functional groups are in principle all functional groups which may be bonded to a carbon atom or a heteroatom. As suitable examples may be mentioned = O (in particular as carbonyl group), -OH (hydroxy) and -CN (cyano). Functional groups and heteroatoms may also be directly adjacent, so that combinations of several adjacent atoms, such as -O- (ether), -S- (thioether), -COO- (ester) or -CONR '- (tertiary amide) , are included, for example di (C ₁ -C ₄ alkyl) amino, C ₁ -C ₄ alkyloxycarbonyl or C ₁ -C ₄ alkoxy.

The organic, preferably organic semiconducting compounds having a polycyclic aromatic structure generally contain in their unsubstituted skeleton at least 12 and at most 75 carbon atoms, preferably at most 50 carbon atoms, more preferably 24 carbon atoms.

The proportion of the at least one carrier, component (A), can be varied over wide ranges and is generally in the range of 50 to 90 wt .-%, preferably in the range of 70 to 85 wt .-%, based on the sum of the wt .-% of components (A) and (B).

The at least one catalytically active material, component (B), which is used according to the invention is, for example, a metal of the platinum group, a transition metal, a ternary system or an alloy containing one or more of the platinum group metals. According to the invention, the platinum group metal is rhodium, iridium, nickel, palladium, platinum, copper, cobalt, silver and gold. According to a preferred embodiment of the invention, the platinum group metal is platinum or palladium.

According to a further embodiment of the invention, the catalyst according to the invention comprises a catalytically active alloy which contains at least one platinum group metal and optionally a transition metal. The transition metal is selected according to a preferred embodiment of the invention from the group nickel, vanadium, chromium and cobalt.

According to a preferred embodiment of the invention, the alloy containing the catalyst as component (B) is selected from the group consisting of PtNi, PtFe, PtV, PtCr, PtTi, PtCu, PtPd, PtRu, PdNi, PdFe, PdCr, PdTi, PdCu, PtCo and PdRu.

An alloy in the sense of the invention is a homogeneous, solid solution of at least two different metals, one element being referred to as base element and the other as alloying element (s). The basic element is the element that has the largest mass fraction within the alloy. For alloys containing the same basic elements and the same alloying elements, different phases result due to a different composition. Thus, in the individual phases, the proportions of the alloying elements in the basic element differ. Optionally, it is even possible that in one phase the proportion of the base element is smaller than the proportion of at least one alloying element.

The proportion of the catalytically active material, component (A), based on the total weight of the electrocatalyst according to the invention can be varied over wide ranges and is generally 10 to 50 wt .-%, preferably 15 to 30 wt .-%.

The details of the percentages by weight of components (A) and (B) relate to the sum of the wt .-% of components (A) and (B) without consideration of residual moisture, if the catalyst is not completely, especially under vacuum, dried, or impurities.

According to the invention, the electrocatalyst is present as a powder and has an average particle size in the range from 5 nm to 100 μm, preferably in the range from 50 nm to 5 μm, particularly preferably in the range from 200 nm to 2 μm.

In the preparation of the catalyst according to the invention, the at least one catalytically active metal (B) or the at least one catalytically active alloy is deposited on the support (A). This is preferably done in solutions. For this purpose, for example, metal compounds may be dissolved in a solvent. The corresponding metal or the metals of the alloy can be bound covalently, ionically or complexed. Furthermore, it is also possible that the metal is deposited reductively as a precursor or alkaline by precipitation of the corresponding hydroxide. Further possibilities for the deposition of the catalytically active metal are also impregnations with a solution containing the metal, chemical vapor deposition (CVD) or physical vapor deposition (PVD) processes as well as all other processes known to a person skilled in the art with which a metal can be deposited , Preferably, a salt of the at least one catalytically active metal is first precipitated. This is followed by drying and optionally a temperature treatment for the preparation of the catalyst, which contains the at least one catalytically active metal or the at least one catalytically active alloy.

• (a) Abscheidung des mindestens einen katalytisch aktiven Materials (B) auf dem wie vorstehend definierten Träger (A), und
• (b) Gegebenenfalls Durchführung einer Temperaturbehandlung.

Thus, within the scope of the invention, a method for producing a catalyst as defined above is provided, comprising the steps

• (A) deposition of the at least one catalytically active material (B) on the support (A) as defined above, and
• (b) If necessary, carrying out a temperature treatment.

The deposition of the at least one catalytically active material, component (B), which, as defined above, is at least one metal of the platinum group, a transition metal or an alloy containing one or more of the platinum group metals, in process step (a) can thereby for example, by means of the methods described above. The carrier is one or more carriers, component (A), as defined above.

According to an advantageous embodiment of the invention, the support is thermally pretreated prior to the application of the catalytically active material. The thermal pretreatment is generally carried out at a temperature in the range of 150 ° C to 250 ° C, preferably in the range of 170 ° C to 220 ° C, usually over a period of 1 to 4 hours, preferably over a period of about 2 Hours, carried out at a pressure of less than 1000 mbar.

According to a further embodiment of the invention, after carrying out process step (a), the carrier on which the at least one catalytically active metal is deposited is mixed with at least one transition metal and / or another catalytically active metal and, in a subsequent process step, a temperature treatment in Step (b) subjected to the formation of an alloy.

According to another preferred embodiment of the invention, in process step (a), a hydrolyzable precursor compound and / or a compound of the catalytically active material are deposited on the carrier after intensive mixing of the material and the carrier and then a temperature treatment is carried out in process step (b).

The compounds containing the at least one catalytically active metal or the transition metal are preferably complex compounds, in particular organometallic complex compounds in which the metal of the platinum group or of the transition metals is complexed. The metal is preferably selected from the group consisting of platinum, titanium, iron, chromium, ruthenium, cobalt, nickel and palladium.

Preferred ligands for forming the organometallic complex compound are olefins, preferably dimethyloctadiene, aromatics, preferably pyridine, or 2,4-pentanedione. Furthermore, it is also preferred that the at least one metal is in the form of a mixed cyclopentadienyl-carbonyl complex or as a pure or mixed carbonyl, phosphine, cyano or isocyano complex.

It is particularly preferred if the transition metal is present as organometallic complex compound with acetylacetonate or 2,4-pentanedione as ligand. The transition metal is preferably ionic.

According to a further embodiment of the invention, the at least one compound which contains the at least one catalytically active metal of the platinum group and / or the at least one compound which contains the at least one transition metal is present as a thermally decomposable compound in the dry state. Alternatively, however, it is also possible for the thermally decomposable compound (s) to be dissolved in a solvent. The solvent here is preferably selected from the group consisting of water, ethanol, hexane, cyclohexane, toluene and ether compounds. Preferred ether compounds are open-chain ethers, for example diethyl ether, di-n-propyl ether or 2-methoxypropane, and also cyclic ethers, such as tetrahydrofuran or 1,4-dioxane.

Mixing of the carrier with the at least one compound containing the at least one platinum group catalytically active metal, and optionally with the at least one compound containing the at least one transition metal, as part of the deposition in step (a) is effected by any one A method of mixing solids known to those skilled in the art. Suitable solids mixers usually include a container in which the material to be mixed is agitated. Suitable solids mixers are z. B. paddle mixer, screw mixer, Silomischer and pneumatic mixer.

When the compound (s) are in a solvent, blending is done by a conventional dispersing method. For this purpose, z. B. a container used in the fast rotating blades or blades are included. Such a device is z. As an Ultra-Turrax ^® . The carrier or carriers, in particular the perylene compounds, can also be in the form of a dispersion or dispersed in the presence of the salts. Mechanical crushing can be achieved for example, by an agitator bead mill or a kneading by a RedDevil ^® or Scandex ^®. According to a further embodiment of the invention, the preparation is carried out in the presence of one or more surfactants.

In order to produce an alloy of the metal of the platinum group and optionally the second metal selected from the metals of the platinum group or the transition metals, the mixture obtained by the blending in process step (a) is heated. For this purpose, the mixture obtained in process steps (a) and (b) is heated in an oven to a temperature in the range of 90 to 500 ° C, preferably in the range of 250 to 500 ° C, more preferably in the range of 350 to 500 ° C. , brought. Upon heating, the at least one complex compound is decomposed and the metal bound in it is liberated. The metal combines in the case of alloy formation with the other metal of the platinum group or the transition metal. The result is an alloy in which each metal crystallites are juxtaposed. The individual metal crystallites generally have an average particle size in the range of 2 to 7 nm.

In a preferred embodiment, the temperature treatment takes place in two temperature stages, wherein the temperature of the first temperature stage is lower than the temperature of the second temperature stage. It is also possible that the heating takes place in more than two temperature stages. Usually, in each case the temperature of the subsequent temperature stage is higher than the temperature of the preceding temperature stage. However, it is preferred that the heating takes place in two temperature stages.

The temperature treatment in step (b) can be carried out either batchwise or continuously, for example in a rotary tube.

In a preferred embodiment, the temperature treatment in step (b) is discontinuous, wherein the mixture produced in step (a) initially under an inert gas atmosphere, for example under a nitrogen or argon atmosphere, to a temperature in the range from 100 to 350 ° C., preferably from 200 to 300 ° C. over a period of from 1 to 10 h, preferably from 2 to 5 h, usually from 3 to 4 h is heated. Thereafter, the gas mixture is switched to a reducing atmosphere and set the second temperature level. The temperature of this second temperature stage is generally 350 to 500 ° C, and preferably 400 to 500 ° C; the residence time is generally in the range of 1 to 10 hours, usually in the range of 2 to 6 hours, preferably about 3 hours. Thereafter, the furnace is slowly cooled to room temperature under an inert gas atmosphere, and the catalyst is passivated.

In a further preferred embodiment, the temperature treatment in step (b) is carried out continuously, wherein the mixture produced in step (a) is first installed in a storage container in front of the furnace and purged under inert gas, for example under nitrogen or argon. The continuous furnace may have different heating zones, it being preferred that it contains at least two heating zones.

If the heating in step (b) takes place in two temperature stages in continuous operation, it is preferred if the temperature of the first temperature stage (heating zone) in the range of 300 to 500 ° C, preferably in the range of 350 to 450 ° C and in particular in the range of 400 to 450 ° C, and the temperature of the second temperature stage (heating zone) in the range of 400 to 500 ° C, more preferably in the range of 450 to 500 ° C. The temperature of the second temperature stage is preferably at least 100 ° C., preferably at least 150 ° C., higher than the temperature of the first temperature stage.

The residence time in the continuous furnace in step (b) is preferably in the range of 30 minutes to 10 hours, more preferably in the range of 45 minutes to 5 hours and especially in the range of 1 to 2 hours.

The heating of the alloy precursor in step (b) is preferably carried out under a reducing atmosphere. The reducing atmosphere preferably contains hydrogen. The proportion of hydrogen is dependent on the composition of the catalyst to be prepared. The proportion of hydrogen in the reducing atmosphere can be 2 to 100% by volume. Preferably, a Formiergasatmosphäre is used, wherein the concentration of hydrogen is usually less than 30 vol .-%, generally less than 20 vol .-%. More preferably, the amount of hydrogen in the reducing atmosphere is in the range of 2 to 15% by volume, more preferably about 5% by volume. In particular, in the production of a Pt-Ni catalyst, or a ternary catalyst containing PtNi or PtCo, the content of hydrogen in the reducing atmosphere is preferably in the range of 4 to 10% by volume, more preferably about 5% by volume. %.

In addition to hydrogen, the reducing atmosphere preferably contains at least one inert gas. Preferably, the reducing atmosphere contains nitrogen. Alternatively, however, it is also possible that argon is used instead of the nitrogen, for example. It is also possible to use a mixture of nitrogen and argon. However, nitrogen is preferred.

In particular, it is preferred if the reducing atmosphere contains no further constituents in addition to the hydrogen and the inert gas. However, it should not be ruled out that, for example due to gas production, traces of other gases are still present.

After heating to form the alloy in step (b), passivation is preferably performed. For this purpose, the produced alloy is cooled, for example, to ambient temperature under an inert atmosphere. The inert atmosphere is preferably a nitrogen atmosphere or an argon atmosphere. It is also possible to use a mixture of nitrogen and argon. Also, the passivation alloy prepared in step (b) may be incorporated into a water blanket, for example, in continuous operation.

According to a preferred embodiment, the catalyst according to the invention is still free-flowing after preparation. It is not essential that the catalyst is completely dried. A catalyst is generally still flowable if it has a residual moisture of up to 50 wt .-% water. The residual moisture content of the catalyst according to the invention is particularly preferably in the range from 10 to 30% by weight of water. A residual wet catalyst is obtained, for example, by air drying in the production.

The catalyst prepared according to the invention is suitable, for example, for use as electrode material in a fuel cell. Suitable fields of application are the electrooxidation of oxygen. The catalyst according to the invention can also be used for other electrochemical processes, such as chloralkali electrolysis. In a particularly preferred embodiment, the catalyst according to the invention is used for an electrode in a polymer electrolyte fuel cell (PEFC), also called proton exchange membrane fuel cell. The electrode for which the catalyst is used is, in particular, a cathode of the polymer electrolyte fuel cell. at When used as a cathode of a polymer electrolyte fuel cell, the catalyst of the present invention exhibits a surprisingly high activity with respect to the oxygen reduction reaction.

In a further preferred embodiment, the catalyst according to the invention is used as a cathode catalyst in a high-temperature phosphoric acid fuel cell.

The invention will be further characterized by the following examples.

Example 1: Preparation of a platinum catalyst (30 wt% platinum) on PR179

5 g Paliogen ^® Red L 4120, N, N'-3,4,9,10-tetracarboxylic dimethylperylene-having an average particle size of 100 to 750 nm as determined by TEM, available from BASF SE, were thermally treated at 200 ° C pretreated in vacuo over a period of 2 hours and then dispersed in 500 ml of water. 1.25 g of Pt (NO ₃ ) ₂ were dissolved in 100 ml of water and added to the carrier dispersion. Then, 200 ml of water and 900 ml of ethanol were added, and the mixture was refluxed for 6 hours under a nitrogen atmosphere. The catalyst was filtered off and washed with 2 liters of hot water nitrate-free and dried in vacuo at 80 ° C over a period of 8 hours. The platinum loading of the catalyst was 30% by weight and the average crystallite size of the platinum crystallites, measured in the XRD, was about 3.3 nm.

Example 2: Determination of the catalytic activity with respect to the oxygen reduction reaction

The oxygen reduction reaction (ORR) is determined by measurement on a rotating disk electrode (RDE) in the oxygen-saturated electrolyte (1 M HClO ₄ ) (potential range: 50 to 950 mV, scan speed: 20 mV / s).

In this case, the rotating electrode for the oxygen reduction reaction measurement was coated with a quantity of catalyst of about 40 μg / cm ² . According to the Pt content of the respective samples, the Pt loading varies between 8 and 20 μg Pt / cm ² . As a direct comparison of the power one can compare, for example, the potential at a constant current density (-1 mA / cm ² ), wherein the higher the voltage, the more active the catalyst, since the overvoltage for the oxygen reduction reaction is correspondingly lower.

Alternatively, one can compare the current density at a given voltage. Since, in particular, the kinetic current in the potential range between about 800 and 1000 mV allows a statement about the catalytic activity (the steeper the current-voltage curve, the lower the kinetic inhibition of the reaction, the better the catalyst), ORR activities are usually at 0, _9V, evaluated according to the following formula, where i _{d is} the _{limiting diffusion} current and i _{0.9V is} the current at _0.9V . In order to compensate for different loads, normalization is carried out either on the existing Pt amount mm, or on the existing Pt surface.

The catalyst prepared according to Example 1 achieved 60 to 80% of the ORR activity (at 0.9V) compared to C-supported catalysts known in the art. This is surprising due to the lower conductivity of the carrier and its significantly lower BET surface area.

It has been found that a thermal pretreatment of the support material (vacuum, 200 ° C, 2 h) before deposition of the catalyst metal (according to Example 1) leads to a higher catalytic activity of the catalyst, compared to no thermal pretreatment. Analogously, it was found that a thermal aftertreatment (vacuum, 200 ° C, 2 h) of the finished catalyst leads to an increase in activity.

Example 3: Characterization of the stabilities of the catalysts

The stability of the catalyst systems was estimated by comparing the ORR activities before and after potential cycles (200 times between 0.5 and 1.3 V). Rapid cyclization simulates both the stability of the platinum crystallites (low potential range) and that of the carrier (potentials> 1 V). The ORR activity decreases by about half after these potential cycles (-53 (± 2)%). This is somewhat inferior (-46 (± 2)%) to a catalyst prepared on corrosion resistant carbon black, for example DenkaBlack ^™ , but with the corrosion resistance of, for example, Vulcan XC72 based Catalysts at about 84% loss of activity and thus significantly below the catalysts of the invention.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• US 2006/0257719 [0005]
• DE 69327799 [0006]

Claims (15)

An electrocatalyst comprising a support and at least one catalytically active material, characterized in that the support is at least one optionally substituted organic compound having a polycyclic aromatic structure and having at least one dicarboxylic acid imide group, a dicarboxylic acid anhydride group and / or a Carbonyl group is functionalized, on which the catalytically active material is applied, and the electrode catalyst is present as a powder having an average grain size in the range of 5 nm to 100 microns. An electrocatalyst according to claim 1, characterized in that the organic semiconductive compound having a polycyclic aromatic structure is a compound represented by the following general formula

where: X independently of one another have the meaning O or NR ¹ , with R ¹ being H, aryl, aralkyl, heteroaryl, cycloalkyl, C ₁ -C ₂₂ -alkyl, where the groups aryl, aralkyl, heteroaryl, cycloalkyl and C ₁ - C ₂₂ alkyl are optionally substituted with one or more substituents, - n is equal to 0.1 or 2, and - R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ^{8 are} independently the same or different groups selected from H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl, wherein the groups alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl optionally substituted with one or more substituents, and the groups alkyl, cycloalkyl, aralkyl , Aryl and alkoxyaryl are optionally interrupted by 1 to 3 heteroatoms or functional groups. Electrocatalyst according to claim 1 or 2, characterized in that the organically semiconductive compound has as its backbone a perylene, naphthalene, coronene or quarternary backbone. Electrocatalyst according to one of claims 1 to 3, characterized in that the skeleton of the organic semiconducting compounds contains 12 to 75 carbon atoms. Electrocatalyst according to one of claims 1 to 4, characterized in that the organic semiconductive compound has as a backbone a Perylenimid- or Quarterrylenimid skeleton. Electrocatalyst according to one of claims 1 to 5, characterized in that the catalytically active material is selected from the group consisting of metals of the platinum group and the transition metals and mixtures and alloys thereof. Electrocatalyst according to one of claims 1 to 6, characterized in that the catalytically active material is platinum or a platinum-containing alloy. A process for producing an electrocatalyst according to any one of claims 1 to 7, comprising the steps (a) depositing the at least one catalytically active material on the support as defined in claim 1 and (b) optionally carrying out a temperature treatment. A method according to claim 8, characterized in that the deposition in process step (a) takes place in a solvent. A method according to claim 9, characterized in that the deposition in process step (a) takes place in the presence of a surfactant. Method according to one of claims 8 to 10, characterized in that the temperature treatment in process step (b) is carried out at a temperature in the range of 90 to 500 ° C over a period of 1 h to 10 h. Process according to any one of Claims 8 to 11, characterized in that, prior to depositing the catalytically active material, the support is maintained at a temperature in the range of 150 ° C to 250 ° C over a period of 1 hour to 4 hours at a pressure of < Thermally treated at 1000 mbar. Electrocatalyst preparable by a process according to one of Claims 8 to 12. Use of the electrocatalyst according to one of claims 1 to 7 or 13 as a catalyst in a fuel cell. Use according to claim 14, characterized in that the catalyst is a cathode catalyst.

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