EP1579524A2

EP1579524A2 - Gas diffuser substrate containing catalysts for fuel cells, in addition to a method for the production thereof

Info

Publication number: EP1579524A2
Application number: EP03789404A
Authority: EP
Inventors: Karsten Ruth; Andreas Schleunung; Karl-Anton Starz; Marco Lopez
Original assignee: Umicore AG and Co KG
Current assignee: Umicore AG and Co KG
Priority date: 2002-12-30
Filing date: 2003-12-23
Publication date: 2005-09-28
Also published as: CA2511920A1; JP2006512724A; WO2004059770A2; US20060177727A1; KR20050084512A; JP5134763B2; AU2003293990A8; AU2003293990A1; CA2511920C; WO2004059770A3; EP1435672A1

Abstract

The invention relates to a gas diffuser substrate containing catalysts for fuel cells, especially low temperature fuel cells, such as PEMFC and DMFC. The gas diffuser substrate is used on the anode side of the fuel cell and contains catalyst components which result in the removal of carbon monoxide (in the PEMFC) and respectively the oxidation of methanol (in the DMFC). Said catalyst components are produced directly in porous substrate material by thermal treatment of suitable precursor compounds and are homogeneously distributed over the total volume of the gas diffuser substrate. As a result, the catalyst components have particularly high activity. The invention also relates to a method for the production of a gas diffuser substrate containing catalysts. The gas diffuser substrates used in membrane electrode units (MEEs) for low temperature fuel cells, especially for PEM-fuel cells, are operated with reformate gas containing CO. Said substrates are also used in direct-methanol-fuel cells (DMFC).

Description

Catalyst-containing gas distributor substrate for fuel cells and process for its production

The invention relates to a catalyst-containing gas distributor substrate for ^" fuel cells, in particular low-temperature fuel cells (such as PEMFC or DMFC), which have an ion-conducting polymer as the electrolyte. The gas distributor substrate is used on the anode side of the fuel cell and contains catalyst components which remove or remove carbon monoxide (CO), for example A product can be used in membrane electrode assemblies (MEEs) for low-temperature fuel cells, for example PEM fuel cells, which are operated with CO-containing reformate gas but can also be used for direct methanol fuel cells (DMFC).

Fuel cells convert a fuel and an oxidizing agent locally separated from each other on two electrodes into electricity, heat and water. Hydrogen, methanol or a hydrogen-rich gas can be used as fuel, oxygen or air as oxidizing agent. The process of energy conversion in the fuel cell is characterized by a high level of pollution-free and particularly high efficiency. For this reason, fuel cells are becoming increasingly important for alternative drive concepts, home energy supply systems and portable applications.

The membrane fuel cells, for example the polymer electrolyte fuel cell (English: PEMFC) and the Direlrt methanol fuel cell (English: DMFC), are suitable for many mobile and stationary applications due to their low operating temperatures, their compact design and their power density. The technology of fuel cells is described in detail in the literature, for example in K. Kordesch and G. Simader, "Fuel Cells and its Applications", VCH Verlag Chemie, Weinheim (Germany) 1996.

PEM fuel cells are constructed in a stacked arrangement ("stack") from many fuel cell units. These are electrically connected in series to increase the operating voltage. Each fuel cell unit contains a 5-layer membrane electrode unit ("MEE") which is between bipolar plates, also called separator plates, is arranged for gas supply and power conduction. Such a 5- Layered membrane electrode unit is in turn constructed from a polymer electrolyte membrane, which is provided with an electrode layer on each side (3-layer, catalyst-coated membrane, CCM). One of the electrode layers is designed as an anode for the oxidation of hydrogen and the second electrode layer as a cathode for the reduction of oxygen. The polymer electrolyte membrane consists of proton-conducting polymers. These materials are also referred to as ionomers in the following. The anode and cathode of the CCM contain electrocatalysts that catalytically support the respective reaction (oxidation of hydrogen or reduction of oxygen). The metals of the platinum group of the periodic table of the elements are preferably used as catalytically active components. So-called supported catalysts are used in the majority.

So-called gas diffusion layers (GDLs or "backings") are then attached to the two sides of the CCM, so that the five-layer membrane electrode assembly is thereby obtained. The gas distributor substrates usually consist of carbon fiber paper or carbon fiber fabric and enable one good access of the reaction gases to the reaction layers and good drainage of the cell flow and the water that forms.

For the wide commercial use of. PEM fuel cells in motor vehicles and domestic energy supply systems require a further improvement in the electrochemical cell performance and service life, in particular when using CO-containing reformate gases.

Typical hydrogen-containing fuel gases, which are generated by reforming hydrocarbons such as natural gas, methane, petroleum, gasoline or alcohols, contain up to 2-3 vol.% Carbon monoxide (CO) depending on the cleaning process. The carbon monoxide components in turn poison the Pt or PtRu anode catalyst and thus lead to one

Performance loss of the entire PEM fuel cell.

There has been no lack of attempts in the past to remedy the poisoning of the anode catalysts by CO or to reduce their effect. There is extensive work on the development of CO-tolerant electrocatalysts, primarily based on platinum / ruthenium alloys, which have an improved tolerance when operating with CO-containing fuel gases (see, for example, US 6,007,934 and US 6,066,410). The so-called "air-bleed" process is also known from the literature. In addition, approximately 1 to 3% by volume of air is passed into the anode compartment of the cell in order to convert the CO adsorbed on the Pt or PtRu electrocatalyst to CO ₂ to oxidize and thus to remove (see, for example, S. Gottesfeld and J. Pafford, J. Electrochem. Soc. 135, (1988), 139-146). The reaction takes place in the gas phase and can be represented as follows:

^" CO + ^> / ₂ O ₂ (air) => CO ₂ _ (1)

Another option for removing carbon monoxide from hydrogen-containing 5 fuel gases is the so-called methanation reaction. The existing CO is reacted with hydrogen to inert methane on a catalyst and thus removed from the mixture:

CO + 3 H ₂ => CH ₄ + H ₂ 0 _ (2)

In contrast to the selective oxidation according to Eq. (1) The methanation of carbon monoxide is inherently linked to the consumption of hydrogen, but 10 does not require "air bleed" and therefore no external air supply. This means less

) Standard effort. While the method of CO removal by methanation is still described relatively sparsely in the literature, there are numerous proposals in the patent literature which deal with the incorporation or integration of a gas-phase-active catalyst for CO oxidation in a gas distributor substrate.

15 For example, EP 0 736 921 B1 describes an electrode which contains two different catalytic components. The first catalytic component is active for gas phase reaction sites, while the second catalytic component is active at electrochemical reaction sites. Both catalytic components are applied to the gas distributor substrate as a double layer (“bi-layer”) and are in mutual relationship

20 physical contact.

WO 00/36679 describes a gas distribution substrate (“backing”) for a PEM anode

), which only has a gas-phase-active catalyst for the oxidation of CO on the side facing away from the ionomer membrane. Gas phase active catalyst and electrocatalyst are both formed as thin layers and as such are not

25 in direct contact with each other.

EP 0 985 241 describes an integral PEM fuel cell stack which has an anode which is designed as a three-layer anode. This has a CO oxidation-selective catalyst layer on the side facing away from the membrane and an electrochemically active layer on the side facing the membrane.

30 JP 9-129243 proposes a low-temperature (PEM) fuel cell, which likewise contains a gas diffusion layer with a CO oxidation catalyst. The CO oxidation catalyst is in a mixture of conductive material (eg carbon black) and water-repellent material (eg PTFE) processed into a porous film and applied to the gas diffusion layer.

All of the approaches proposed here have the disadvantage that the gas-phase-active catalyst is formed only in a thin layer on the gas distributor substrate.

5 Because of these thin layers, the residence time of the CO-containing fuel gas on the catalyst material is reduced. This leads to only a partial conversion and thus to incomplete CO oxidation. Furthermore, the gas-phase-active catalysts are used in the form of prefabricated supported catalysts (for example Ru on carbon black, Pt on aluminum oxide) and then processed further in a mixture with carbon black, Teflon and possibly other components. In many cases, the active catalyst surface is blocked by these additional components. This means that the active catalyst surface is not used optimally, which in turn means that the last residues of CO (e.g. fractions below 100 ppm) are not removed. This means that CO poisoning of the electrocatalysts continues to take place on the anode of the fuel cell stack.

5 The proposed solutions described above further complicate the fuel cell, in particular the gas distribution and electrode system. Additional layers have to be applied to the gas distribution substrates, which ultimately increase the production costs of the products because they lead to a more complex manufacturing process.

It is therefore an object of the present invention to provide an improved catalyst-containing gas distributor substrate for low-temperature fuel cells and to find a suitable production process for such a product.

Accordingly, the invention relates to a catalyst-containing gas diffusion layer for

Low-temperature fuel cells containing a porous support material and 5 catalyst particles, the catalyst particles being distributed uniformly over the entire volume of the gas distributor substrate. Advantageous embodiments of this substrate and suitable manufacturing processes therefor are described in the following claims.

Advantageously, in the catalyst-containing gas distributor substrate according to the invention, a good utilization of the catalyst or the catalyst surface 0 and thus a high activity and selectivity in the removal of carbon monoxide (either by CO oxidation or by methanization) and in the oxidation of methanol (in the DMFC). Furthermore, the method according to the invention for producing such gas distributor substrates is characterized by a low level of complexity. It is practical and can be easily integrated into a continuous manufacturing process, which 5 reduces manufacturing costs. The catalyst-containing gas diffusion layer according to the invention contains a catalytically active component; which is evenly distributed over the entire volume of the gas distributor substrate. It can be generated in a process in which precursors are soluble like water

5 and / or easily decomposable metal compounds which have previously been introduced into the gas distribution substrate in question are decomposed or pyrolyzed. Precious metal compounds are preferably used. In a preferred embodiment, a gas diffusion layer is impregnated or impregnated with an aqueous solution of a precursor (e.g. with an easily decomposable metal compound). This potion process can

10 by simply diving, by spraying. Brushing or by impregnation. In the simplest case, the gas diffusion layer is placed in a tub that contains a solution of the metal compound, then removed and dried. The process is

^J - for so long. repeated until the necessary loading of the substrate with the catalytically active metal compound is reached. Typically, occupancy quantities are in

15 surface concentrations of 0.05 to 5 mg metal / cm ² achieved by one to ten repetitions. However, higher surface concentrations up to about 100 mg / cm ² can also be achieved. In addition, it is also possible to spray the precursor solution onto both sides of the gas distributor substrate and then to dry it. If you work in the screen printing process, the impregnation or impregnation of the gas distributor substrate can be carried out

20 screen prints of a thin ink, the viscosity of which is adjusted so that it wets and penetrates the entire substrate. In the gas distributor substrate according to the invention, the catalyst component is uniformly distributed over the entire volume of the substrate and preferably the catalytically active particles are fixed on the support material. This ensures optimal distribution of the particles in the substrate as well as very good accessibility of the reactants

25 ensures the catalytically active sites of the particles.

The impregnation or impregnation process can be carried out continuously in suitable devices, for example from roll to roll. The gas distribution substrate can be used as an endless, flexible belt and can be guided through various stations, consisting, for example, of hydrophobization, impregnation / impregnation with precursor solution, drying, coating with a compensating layer and tempering. The impregnation or impregnation with the precursor compound can thus be easily incorporated into a continuous manufacturing process for gas distributor substrates. It causes low additional costs, but at the same time leads to a higher quality product.

The tempering that can be used to decompose the precursors and at which the

35 catalyst particles are formed, one usually leads at temperatures from 200 to

900 ° C, preferably 200 to 600 ° C through. It can be in an air atmosphere, but also under Shielding gas (for example nitrogen, argon or mixtures thereof) or reducing gases (for example nitrogen / hydrogen mixtures or forming gas). Continuous belt furnaces, muffle furnaces, chamber furnaces and combinations thereof can be used.

As catalysts for the CO oxidation according to Eq. (1) Ru, PfRu or Pt alloys with base metals are preferred. Gold-containing catalysts such as Au, Au / titanium oxide or .Au / iron oxide can also be used. Supported silver-containing catalysts (for example Ag / titanium oxide) can also be used.

For the methanation of CO according to Eq. (2) are suitable, for example, catalysts based on nickel and / or ruthenium. The operating temperatures of the cell should preferably be slightly above the normal temperatures of the PEM fuel cell when using gas distribution substrates with a methanation catalyst. At operating temperatures of over 90 ° C, an increase in the methanation activity of the catalyst is achieved and, at the same time, the CO poisoning of the Pt-containing anode catalyst is suppressed.

The precursors for the catalytically active components are water-soluble, easily decomposable metal compounds, preferably compounds from the group of amine nitrates, nitrates, carbonates, carboxylates, hydrooxycarboxylates, acetates, lactates, butanoates, oxalates, formates, octanoates, or ethylhexanoates, which are used in the Decompose the desired catalyst particles. Preferred catalytic articles include metals, in particular noble metals such as Pt, Pd, Ru. Rh, Au, Ag, Ir, Os. and / or their oxides, and / or their mixtures or alloys with base metals, but also base metals such as Ti, Fe. Co, Mn, Cr or Ni. Corrosion greens are used to avoid halogen- or chlorine-containing precursors if possible. However, organometallic complexes of the metals, so-called resinates, can also be used, for example.

Examples of suitable noble metal compounds are the Pt precursors platinum (II) nitrate, platinum (II) lactate, platinum (II) amine nitrate, ethylammonium platinum hexahydrate, platinum acetate etc. Examples of suitable Ru precursors are ruthenium (III) nitrosyl nitrate or ruthenium (III) acetate. Examples of Au-containing precursors are gold resinates such as Au polymer esters (from FERRO GmbH, Frankfurt) or gold-containing complex salts. Analog complexes of the other noble metals can of course also be used.

Precursors for base metals that can be used alone or in combination with the noble metal precursors are, for example, cobalt (II) nitrate, manganese (II) oxalate, chromium (III) nitrate, nickel (II) nitrate, iron (II) -carbonate and comparable compounds other elements such as the base metals listed above. Here too, halogen-containing precursors are avoided for reasons of corrosion.

Furthermore, additional components can be added to the noble metal and base metal precursors described, which act as cocatalysts, as support materials or as precursors thereof. Examples of this are high-surface precious metal tubes, fine metal powders, carbon blacks, pyrogenic oxides such as, for example, silica (“Aerosil” from Degussa), pyrogenic titanium oxides and comparable materials. Also other inorganic components that can be converted into oxidic materials during pyrolysis or temperature treatment Examples of these are organic silicon esters, organosilanes, organotitanates, organostannates, aluminates, borates and similar compounds.

The precursor compounds are processed into a preparation that is suitable for the respective application process on the gas distributor substrate. A correspondingly low-viscosity solution is produced for the application in the immersion or impregnation process. This can contain auxiliaries such as surfactants, wetting agents, binders, thickeners, anti-settling agents or organic solvents to improve the processing properties. For the application by brushing or by screen printing, the viscosity of the solutions is modified accordingly. Means and ways of doing this are known to the skilled worker.

Commercial carbon fiber substrates can be used as starting materials for the production of the catalyst-containing gas diffusion layer according to the invention. Porous carbon fiber substrates (carbon fiber paper or carbon fiber fabric) with a layer thickness of 100 to 400 μm are often used. These materials usually have a porosity of 60 to 90% and an average pore diameter of 20 to 50 μm. There are various substrate materials that differ in structure, manufacturing process and properties. Examples of such porous materials are Toray paper,

Carbon fiber fleeces from SGL (type Sigracet) or woven carbon fiber structures from Textron

(Type AvCarb). Many of these materials are available as sheets or rolls.

Furthermore, metal mesh, fine, is also used as the starting material for gas distributor substrates

Metal nets, conductive coated plastic fabrics, conductive coated textile fabrics, coated glass fibers and similar materials can be used. Basically, they can

Gas distribution substrates previously hydrophobicized, hydrophilized, pressed, rolled or otherwise

Kind be treated before they are treated with the precursor solution.

The catalyst-containing gas diffusion layer according to the invention can be with or without

Equalization layer must be equipped. In the context of this invention, a layer on that side of the gas distributor substrate is used as a compensating layer (so-called “microlayer”) understood, which is in contact with the electrode layer in the fuel cell. The leveling layer usually contains a mixture of a hydrophobic polymer such as PTFE and finely divided carbon blacks. The compensation layer is usually applied by screen printing, its thickness is, for example, from 5 to 100 μm.

A complete membrane electrode assembly ("MEE") of a PEM or DMFC fuel cell contains a catalyst-coated polymer electrolyte membrane ("CCM") with gas distributor substrates attached on both sides. The gas distributor substrate according to the invention is preferably used on the anode side of the membrane electrode unit. The membrane electrode assemblies thus produced can be used as fuel gas due to the improved tolerance to carbon monoxide for the use of CO-containing hydrogen mixtures. Such fuel gases are often produced by reforming hydrocarbons such as natural gas, methane or gasoline and are used in the stationary use of the fuel cell.

However, the catalyst-containing gas diffusion layer according to the invention can also be used in MEEs for direct methanol fuel cells (DMFC). For example, it causes better oxidation of the methanol on the anode side and improves the performance of the DMFC cell.

The following figures show embodiments of the invention.

Figure 1: Schematic representation of the inventive kata ^{'lysatorhaltigen} gas diffusion layer with compensation layer

Figure 1 shows a schematic cross section through an inventive catalyst-containing gas diffusion layer. Here, (11) denotes the porous substrate material. The catalyst particles (12) are fixed to the surface of the substrate and are evenly distributed over the entire volume of the substrate. They are therefore optimally accessible, for example for a fuel gas contaminated with CO. An optional compensation layer (13), which consists for example of PTFE and carbon black, is applied in order to improve the contact with the electrode layer on the ionomer membrane.

Figure 2: Complete 5-layer membrane electrode assembly with a catalyst-containing gas distribution substrate according to the invention on the anode side.

FIG. 2 shows a schematic cross section through a complete 5-layer MEU with a gas distributor substrate (21) according to the invention containing catalyst particles (22) on the anode side. The gas distributor substrate (21) is in contact with a three-layer catalyst-coated ionomer membrane, consisting of an anode catalyst layer (23a), Ionomer membrane (23) and cathode catalyst layer (23b). An uncatalyzed gas diffusion layer (24) is attached to the cathode side. In this embodiment, the two gas distributor substrates do not have a compensation layer.

The following examples are intended to explain the invention in more detail. However, the invention is not limited to the embodiments described therein.

Examples

Example 1:

The production of a Ru-containing gas distributor substrate with a compensation layer is described. A hy ^{'drophobiertes} Kohlefaseφapier serves the area as a starting material 50 cm ² (dimensions of about 7x7 cm) with a thickness of 200 microns (Sigracet 10, Fa. SGL Carbon). The Teflon content is approx. 8% by weight. After the weight has been determined using a laboratory balance, the substrate is immersed in a large dish with ruthenium (III) acetate solution (5% by weight Ru in water, OMG, Hanau). After complete wetting, the substrate is removed from the immersion bath using tweezers. It is allowed to drain for a short time and then dried in a drying cabinet at 100 ° C. for 15 minutes. The mixture is then allowed to cool and the amount of Ru acetate absorbed is determined gravimetrically. The dipping process is repeated three times until a loading of 0.85 mg -Ru acetate / cm ^{2 is} obtained. The gas distributor substrate is then tempered for 30 minutes in an oven at 200 ° C. under forming gas (95% by volume nitrogen, 5% by volume hydrogen). After the substrate has cooled, the Ru content of the substrate is 0.48 mg Ru / cm ² . The Ru particles are evenly distributed in the substrate and fixed on the substrate surface. They have an average particle size of 5 nm, measured by means of transmission electron spectroscopy (TEM).

Then, a leveling layer made of carbon black / PFTE is applied by screen printing, dried and annealed at 390 ° C. for 10 minutes. The layer thickness of the compensation layer is approx. 20 μm.

The substrate is combined as a pre-anode with a catalyst-coated membrane (CCM) and combined to form a membrane electrode assembly (MEE). A CC-coated membrane of type 6 C is used as CCM (loading anode 0.2 mg Pt / cm ² ; loading cathode 0.4 mg Pt / cm ² , membrane EW 1100 with 50 micron thickness, from OMG, Hanau). A hydrophobized carbon fiber paper with a compensating layer (standard, from SGL, type Sigracet 10) is used on the cathode side. > The MEE is tested in a PEM fuel cell in hydrogen / air and reformate / air operation and shows very good results, especially in reformate / air operation with a content of 100 ppm CO (see Table 1). Compared to the catalyst-free gas distributor substrate (comparative example VB1), the tolerance towards CO is significantly improved. This shows that the catalyst-containing gas diffusion layer according to the invention has a very good effectiveness.

Example 2:

The production of an Ru-containing gas diffusion layer without a compensation layer is described. A hydrophobicized carbon fiber paper with an area of 50 cm ² (dimensions approx. 7x7 cm) and a thickness of 200 μm (Sigracet 10, SGL Carbon) is used as the starting material. The Teflon content is approx. 8% by weight. The impregnation with precursor solution is carried out as described in Example 1. The dipping process is repeated twice until a loading of 0.5 mg Ru acetate / cm ^{2 is} obtained. The gas distributor substrate is then tempered for 30 minutes in an oven at 250 ° C. under forming gas (95% by volume nitrogen, 5% by volume hydrogen). After the substrate has cooled, the Ru content of the substrate is 0.28 mg Ru / cm ² . The Ru particles are evenly distributed in the substrate and fixed on the substrate surface. They have an average particle size of 4 nm (measured with TEM). The substrate is combined as a pre-anode with a catalyst-coated membrane (CCM) and, as described in Example 1, combined to form a membrane electrode unit (MEE). When operating the MEE with a CO-containing reformate (100 ppm CO), very good results are obtained and, compared to comparative example VB1 (see below), a significantly improved CO tolerance.

Example 3:

This example describes the production of an Au / Ti0 ₂ -containing gas distribution substrate without a compensation layer. A hydrophobized carbon fiber paper with an area of 50 cm ² (dimensions approx. 7x7 cm) and a thickness of 200 μm (Sigracet 10, SGL Carbon) is again used as the starting material. The Teflon content is approx. 8% by weight. A water-containing precursor solution is produced containing Au polymer ester HF 3401 (from FERRO, Frankfurt) and titanium oxide (type P25, from Degussa, Frankfurt). The Au content of the solution is 5% by weight of Au, the proportion of titanium oxide is 0.1% by weight. The impregnation is carried out as described in Example 1. The diving process is repeated three times. Then the gas distributor substrate is annealed for 30 min in an oven at 250 ° C. under forming gas. To after cooling the substrate, the Au content of the substrate is approximately 0.1 mg Au / cm ² . The Au particles are evenly distributed in the substrate in combination with the titanium oxide. As described in Example 1, the substrate is combined as a pre-anode with a catalyst-coated membrane (CCM) and joined to form a membrane electrode assembly (MEE) 5.

Operating the MEE with a reformate containing CO (100 ppm CO) gives very good results and a significantly improved CO tolerance compared to VB1.

Comparative example - (VB 1)

10 In this example not according to the invention, the production and testing of an MEE is included

⁾ - a catalyst-free gas distributor substrate without a compensation layer on the anode side. A hydrophobicized carbon fiber paper with an area of 50 cm ² (dimensions approx. 7x7 cm) and a thickness of 200 μm (Sigracet 10, SGL Carbon) is used as the starting material. The Teflon content is approx. 8 ^" % by weight. The catalyst-free substrate is added

15 a catalyst-coated membrane (CCM) combined and, as described in Examples 1 and 2, combined to form a membrane electrode assembly (MEE). Operating the MEE with a reformate containing CO (100 ppm CO) gives very poor results due to the CO poisoning of the Pt catalyst. This shows that the catalyst-containing gas distributor substrates according to the invention (with or without a compensating layer) ^"are very good

20 have effectiveness.

) Example 4:

The production of a PtRu-containing gas distribution substrate without a compensation layer and its use as a pre-anode in a Direlct-methanol fuel cell (DMFC)

25 described.

A hydrophobicized carbon fiber paper with an area of 50 cm ² (dimensions approx. 7x7 cm) and a thickness of 200 μm (Sigracet 10, SGL Carbon) is used as the starting material. The Teflon content is approx. 8% by weight. After the weight has been determined using a laboratory balance, the substrate is placed in a large bowl with 6 parts of ruthenium (III) acetate.

30 solution (5% by weight Ru in water, OMG, Hanau) and 1 part platinum (II) nitrate (16% by weight Pt, OMG. Hanau) immersed. After complete wetting, the substrate is removed from the immersion bath using tweezers. It is allowed to drain for a short time and then dried in a drying cabinet at 100 ° C. for 15 minutes. Then let it cool and determines the absorbed amount of Ru acetate and Pt nitrate gravimetrically. The gas distributor substrate is then tempered for 30 minutes in an oven at 250 ° C. under forming gas (95% by volume nitrogen, 5% by volume hydrogen). After the substrate has cooled, the Ru content of the substrate is approximately 0.65 mg Ru / cm ² and the platinum content is approximately 0.35 mg Pt / cm ² . The Pt and Ru particles are evenly distributed over the entire volume of the substrate. The substrate is combined as a pre-anode with a catalyst-coated membrane (CCM, type R22 anode loading 0.3 mg Pt / cm ² and 0.15 mg Ru / cm ² , cathode loading 0.4 mg Pt / cm ² ; OMG, Hanau) and, as described in Example 1, combined to form a membrane electrode assembly (MEE). This is installed in a ^" Direlct-methanol fuel cell (DMFC) with an active cell area of 50 cm ^2. A 2-molar methanol / water solution is used for the measurement, the cell temperature is 60 ° C. Air in the A very high power density (peak power density) of over 80 mW / cm ^{2 is obtained} .

Electrochemical tests

In the PEMFC performance tests, a fuel gas mixture of 60% by volume H ₂ , 15% by volume N ₂ and 25% by volume C0 _{2 is} used as the anode gas. 100 ppm CO with an "airbleed" of 1% by volume or 3% by volume of air is added to the fuel gas. This fuel gas mixture simulates a reformate gas which can be obtained by reforming methane or hydrocarbons by means of steam reforming and subsequent purification stages Air is used as the cathode gas. The cell temperature is 75 ° C. The pressure of the working gases is 3 bar (absolute). The stoichiometry of the gases is 1.5 (anode gas) and 2.0 (cathode gas). The MEEs are in a cell with 50 cm ^{2 of} active area according to OMG standard conditions The results for Examples 1, 2 and 3 and for Comparative Example VB 1 are summarized in Table 1.

Table 1: Electrochemical tests in the PEM fuel cell (cell voltage at a current density of 500 mA / cm ² )

Claims

claims

1. Catalyst-containing gas distributor substrate for a fuel cell, containing a porous support material and catalyst particles, the catalyst particles uniformly over

10 the entire volume of the gas distributor substrate are distributed.

2. Catalyst-containing gas diffusion layer according to claim 1, wherein the catalyst particles are fixed on the surface of the porous support material.

3. Catalyst-containing gas diffusion layer according to claim 1, or 2, wherein the catalyst particles have an average particle size of 1 to 100 nm.

15 4. Catalyst-containing gas distributor substrate according to one of the preceding claims, wherein the catalytic particles include noble metals from the group Pt, Pd, Ru, Rh, Au, Ag, Ir, Os, and / or their oxides, and / or their mixtures or alloys with non-noble metals.

5. Catalyst-containing gas distributor substrate according to one of the preceding claims, wherein 20 the catalyst particles are present in a surface concentration of 0.01 to 100 mg metal / cm ² on the gas distributor substrate.

6. Catalyst-containing gas distributor substrate according to one of the preceding claims, wherein _{j is} the porous carrier material made of carbon fiber fabric, carbon fiber fleece, carbon paper,

Carbon fiber nets, conductive coated plastic nets, conductive coated 25 polymer fabrics, conductive coated glass fibers, conductive coated foams or metal fiber fabrics or metal wire nets.

7. Catalyst-containing gas diffusion layer according to one of the preceding claims, wherein the catalyst particles are gas-phase active and are suitable for the oxidation of carbon monoxide.

30 8. Catalyst-containing gas distributor substrate according to one of the preceding claims, wherein the catalyst particles are gas-phase active and are suitable for converting carbon monoxide to methane.

9. Catalyst-containing gas distributor substrate according to one of the preceding claims, wherein the catalyst particles are suitable for the oxidation of methanol.

10. A method for producing a catalyst-containing gas diffusion layer according to claims 1 to 9, wherein the catalyst particles on the porous support material

5 are formed by thermal decomposition of at least one precursor compound.

11. The method for producing a catalyst-containing gas diffusion layer according to claim 10, wherein the porous support material is treated with at least one precursor compound, dried and tempered, one of which

10 decomposition of the precursor compound occurs and the catalyst particles are formed and fixed on the surface of the support material.

12. A method for producing a catalyst-containing gas diffusion layer according to claim 10 or 11, wherein thermally decomposable metal compounds are used as precursor compounds.

13. A process for the preparation of a catalyst-containing gas diffusion layer according to one of claims 10 to 12, wherein one or more metal compounds from the group of nitrates, carbonates, carboxylates, hydroxycarboxylates, acetates, lactates, butanoates, oxalates, formates, resinates or ethylhexanoates are used as the precursor compound become.

14. A method for producing a catalyst-containing gas diffusion layer according to one of claims 10 to 13, wherein the heat treatment is carried out at a temperature of 200 to 900 ° C.

)

15. A method for producing a catalyst-containing gas distributor substrate according to one of claims 10 to 14, wherein the heat treatment is carried out under a gaseous atmosphere, preferably under air, nitrogen, hydrogen or mixtures thereof.

16. A method for producing a catalyst-containing gas diffusion layer according to claim 10, wherein the production takes place in a continuous process.

17. Use of a catalyst-containing gas distributor substrate according to one of claims 30 1 to 9 in fuel cells for removing carbon monoxide from hydrogen-containing

Fuel gases.

18. Use of a catalyst-containing gas distributor substrate according to one of claims 1 to 9 in direct methanol fuel cells for the oxidation of methanol.

19. Membrane-electrode unit for a low-temperature fuel cell, containing a catalyst-containing gas distributor substrate according to one of claims 1 to 9.