阅读说明：本技术 导电的碳材料的应用 (Use of electrically conductive carbon materials ) 是由 A·奥法尼迪 于 2018-05-07 设计创作，主要内容包括：本发明涉及一种导电的碳材料(1)在用于燃料电池的催化剂层(7)中用于改善离聚物(6)在催化剂层(7)中的分布的应用。碳材料(1)在此具有包含碳原子(3)和氮原子(4)的碳晶格(2)。(The invention relates to the use of an electrically conductive carbon material (1) in a catalyst layer (7) for a fuel cell for improving the distribution of an ionomer (6) in the catalyst layer (7). The carbon material (1) has a carbon lattice (2) comprising carbon atoms (3) and nitrogen atoms (4).)

1. Use of an electrically conductive carbon material (1) in a catalyst layer (7) for a fuel cell for improving the distribution of an ionomer (6) in the catalyst layer (7), which catalyst layer comprises the carbon material (1), at least one catalytically active material (8) and at least one ionomer (6), wherein the carbon material (1) has a carbon lattice (2) comprising carbon atoms (3) and nitrogen atoms (4), and wherein the carbon material (1) has a carbon lattice (2)

i) The content of the carbon material (1) in the catalyst layer (7) is 25 to 65 mass% with respect to the total mass of the catalyst layer (7), and/or

ii) the weight ratio of ionomer (6) to carbon material (1) is 0.2 to 1.0.

2. Use according to claim 1, wherein the carbon lattice (2) of the carbon material (1) is composed of carbon atoms (3) and nitrogen atoms (4) and optionally additionally of hydrogen atoms and/or oxygen atoms.

3. Use according to claim 1 or 2, wherein the nitrogen (4) content in the carbon material (1) is 0.2 to 1.2 mass%, in particular 0.3 to 1.0 mass%, relative to the total mass of the carbon material (1).

4. Use according to any one of the preceding claims, wherein the carbon lattice (2) has pyridine units (6) and/or pyrrole units.

5. Use according to any one of the preceding claims, wherein the carbon material (1) is graphitized.

6. Use according to any one of the preceding claims, wherein the content of carbon material (1) in the catalyst layer (7) is between 35% and 55% by mass relative to the total mass of the catalyst layer (7).

7. Use according to any one of the preceding claims, wherein the catalytically active material (8) has at least one noble metal and in particular platinum.

8. Use according to any one of the preceding claims, wherein the content of the catalytically active material (8) is 0.02 to 0.4mg/cm relative to the total mass of the catalyst layer (1)²In particular from 0.06 to 0.1mg/cm²。

9. Use according to any one of the preceding claims, wherein the ionomer (6) is selected from sulphonic thermoplastics.

10. Use according to any one of the preceding claims, wherein the weight ratio of ionomer (6) to carbon material (1) is from 0.25 to 0.70.

Technical Field

The invention relates to the use of an electrically conductive carbon material in a catalyst layer for a fuel cell.

Background

Fuel cells are energy generating systems that produce electrical energy, for example, by electrochemical conversion of hydrogen and oxygen. Fuel cells in this case usually comprise a plurality of single cells stacked one on top of the other, each of which usually comprises a cathode, an anode and a membrane between these electrodes. The cathode and the anode are here the catalytically active layers of the single cell and are also referred to as catalyst layers. Each located on one side of the membrane and comprising a carbon-supported catalytically active material. As a binder and also to improve proton conductivity, the carbon supported catalytically active material is usually embedded in an ionomer. Good interaction between the ionomer and the carbon support material is obtained when the carbon support material is modified by nitrogen atoms and thus contains amide, imide or lactam groups as functional side groups. However, the disadvantage here is that such modified carbon support materials are susceptible to corrosion and lack stability, especially when used in dynamically operating fuel cells.

Disclosure of Invention

The object of the present invention is therefore to provide an application of an electrically conductive carbon material which can be used particularly well in fuel cell applications and which overcomes the disadvantages of the prior art.

The object is achieved by the use of specific nitrogen-modified, electrically conductive carbon materials. The carbon material used according to the invention has a carbon lattice comprising carbon atoms and nitrogen atoms. In conventional nitrogen-modified carbon materials comprising nitrogen atoms in the form of amide groups, imide groups or lactam groups, the nitrogen atoms are present only as side groups of the carbon lattice, whereas in the carbon materials used according to the invention, nitrogen, to be precise one or more nitrogen atoms, is incorporated directly into the carbon lattice. In other words, nitrogen is a constituent of the carbon lattice, which preferably consists essentially of sp²-hybridized carbon atoms and especially graphite-based.

According to the invention, the carbon material is a constituent of a catalyst layer for a fuel cell. The catalyst layer can be configured as an anode or as a cathode and in particular as a cathode. The catalyst layer comprises, in addition to the carbon material, at least one catalytically active material and at least one ionomer, wherein the catalytically active material catalyzes a fuel cell reaction. Ionomers are used as binders and can also be used to improve proton conductivity.

The distribution of the ionomer in the catalyst layer is improved by using a specific nitrogen-modified carbon material. This is because of the good electrostatic interaction between the ionic groups of the ionomer and the carbon material. Carbon materials are more polar by nitrogen modification of the carbon material in the carbon lattice. The nitrogen may also be positively charged, for example by protonation when the carbon material is processed into a catalyst ink or catalyst paste. Whereby strong coulomb interactions occur between nitrogen and ionic groups of the ionomer, especially with anionic groups or at least polar groups of the ionomer, such as sulfonic acid groups. This active interaction enables the ionomer to be evenly distributed around the carbon material. The carbon material is surrounded by a uniform layer of ionomer.

Since nitrogen is a constituent of the carbon lattice of the carbon material, degradation of the carbon material does not occur either. Nitrogen is permanently and stably embedded in the carbon mesh so that no performance loss due to ionomer migration, ionomer non-uniformity, or degradation of the catalyst layer (e.g., due to corrosion) occurs either during manufacture of the catalyst layer or during operation of the fuel cell in which the catalyst layer is used. The catalyst layer can be produced in a simple manner.

Thus, by using a specific nitrogen-modified carbon material according to the invention, a catalyst layer with a permanently stable and uniform ionomer distribution can be obtained, which catalyst layer is also characterized by a high corrosion resistance and good oxygen transport properties, even during dynamic operation of the fuel cell using the catalyst layer. Fuel cells comprising a catalyst layer with an ionomer, a catalytically active material and especially a nitrogen-modified carbon material are also characterized by high power density and service life, even if the fuel cell is continuously operated in dynamic mode.

The dependent claims have advantageous embodiments and embodiments of the invention.

According to one advantageous embodiment, the carbon lattice of the carbon material is formed by carbon atoms and nitrogen atoms and optionally additionally by hydrogen atoms and/or oxygen atoms. This effectively improves the stability of the carbon material, in particular its corrosion stability. If present, hydrogen and/or oxygen atoms may be used to saturate the carbon and/or nitrogen atoms in the carbon lattice. Alternatively or additionally, for example, hydrogen atoms can also be bonded to one or more nitrogen atoms in such a way that the nitrogen atoms are positively charged. The positive charge on the nitrogen atoms improves the interaction with the ionomer in the catalyst layer and achieves a particularly homogeneous distribution of the ionomer in the catalyst layer.

In order to improve the homogeneous distribution of the ionomer in the catalyst layer and in particular to promote the formation of a homogeneous ionomer layer around the carbon material, it is advantageous if the nitrogen content in the carbon material is 0.2 to 1.2 mass%, in particular 0.3 to 1.0 mass%, relative to the total mass of the carbon material.

A carbon material which is particularly stable with respect to degradation reactions is obtained by an advantageous embodiment of the carbon lattice with pyridine units and/or pyrrole units. This may be due to the aromatic character of the pyridine and pyrrole units, thereby allowing good incorporation of pyridine and pyrrole into the carbon lattice and especially into the graphite-based carbon lattice.

In order to improve the electrical conductivity and the stability of the carbon material, it is provided according to a further advantageous embodiment that the carbon material is graphitized.

Particularly good electrical conductivity in the catalyst layer can be advantageously achieved by making the content of the carbon material in the catalyst layer 25 to 65% by mass, in particular 35 to 55% by mass, relative to the total mass of the catalyst layer.

On account of the high catalytic activity, the catalytically active material preferably comprises at least one noble metal, platinum being particularly preferred here. The noble metal can be used as a single metal or in the form of an alloy or a core-shell catalyst. Exemplary alloy-based noble metal catalysts include PtPd, PtCo, and PtNi. The same metals may also form core-shell catalysts.

Based on the use of the specific nitrogen-modified carbon material according to the invention and the homogeneous formation of the catalyst layer associated therewith, in particular with regard to the distribution of the ionomer, the proportion of catalytically active material can advantageously be reduced, while still providing excellent catalytic performance. This is achieved byNot only is the cost saved, but also the manufacturing of the catalyst layer is simplified. An advantageous embodiment is therefore characterized in that the content of catalytically active material is 0.02 to 0.4mg/cm, relative to the total mass of the catalyst layer²In particular from 0.06 to 0.1mg/cm²。

It is also advantageous that the ionomer is selected from sulfonic thermoplastics. Exemplary types of suitable sulfonic acid-based thermoplastics, such as PFSA, are available from DuPont under the trade designation "Nafion" or from Solvay or Asahi Kasei under the trade designation "Aquivion". The proportion of sulfonic acid groups improves the interaction with the specific nitrogen-modified carbon material, so that the ionomer can be particularly uniformly and stably distributed in the catalyst layer.

A highly stable and good proton-conducting catalyst layer with high catalytic activity can be achieved by a further advantageous embodiment with a weight ratio of ionomer to carbon material of 0.2 to 1.0 and in particular 0.25 to 0.70. If the weight ratio is within this range, uniform distribution of the ionomer around the carbon material is promoted. A particularly uniform ionomer layer is formed around the carbon material. In other words, the carbon material is therefore also homogeneously distributed in the ionomer.

Drawings

Other details, features and advantages of the invention are set forth in the following description and the accompanying drawings. Wherein:

FIG. 1 shows a partial schematic view of a carbon material according to one embodiment of the invention;

fig. 2 shows a schematic view of a catalyst layer according to an embodiment of the invention.

Detailed Description

The invention is explained in detail with reference to an embodiment. Fig. 1 and 2 show only important details of the invention. All other details are omitted for clarity. Further, like reference numerals denote like elements.

Fig. 1 shows a detail of an electrically conductive carbon material 1 which, according to the invention, is used in a catalyst layer of a fuel cell, which catalyst layer comprises, in addition to the carbon material 1, at least one ionomer and at least one catalytically active material.

Fig. 1 in particular shows a part of the carbon lattice 2 of the carbon material 1, in which the carbon material 1 is graphitized. The carbon lattice 2 here has predominantly sp²-a hybridized carbon atom 3 and for example a nitrogen atom 4. The nitrogen atoms 4 are directly embedded in the carbon lattice 2, i.e. are constituents of the carbon lattice and are therefore permanently stable and incorporated in the carbon lattice 2 in a degradation-protected manner, not merely as constituents of side groups on the carbon lattice 2. The nitrogen atoms 4 are incorporated in the carbon lattice 2 in the form of pyridine units 5, here for example in the form of pyridine rings. The pyridine ring acts here as an aromatic compound and is therefore very suitable for incorporation into the carbon lattice 2 on the basis of its planarity.

A certain polarity is introduced into the carbon material 1 via the nitrogen atoms 4, so that the distribution of the ionomer in the catalyst layer is improved and the stability of the carbon material 1 is also increased, in particular with regard to degradation reactions, such as corrosion reactions.

An exemplary manufacturing description of the carbon material 1 is given below:

5g of graphitized conductive carbon material (e.g. graphitized Ketjen black) was refluxed at 65 ℃ in 100ml of concentrated HNO₃(70% by mass) for 30 minutes. The resulting oxidized carbon material was then washed in hot water to remove residual HNO₃Trace amounts. The carbon material is then dried in an oven. In the case of a tube furnace, 5g of the carbon oxide material was heat-treated in an ammonia stream (1L/min) at a temperature ranging between 600 ℃ and 1000 ℃ for 2.5 hours. The ammonia-treated carbon material was then washed with hot water to remove reaction residues. Subsequently, the carbon material was again dried in the oven. Nitrogen is incorporated into the carbon lattice by high temperatures in the temperature range between 600 ℃ and 1000 ℃. Lower temperatures do not allow nitrogen to be incorporated into the carbon lattice as desired.

Fig. 2 shows a uniform distribution of ionomer 6 in catalyst layer 7. The catalyst layer 7 comprises a carbon material 1 on which a catalytically active material 8 is provided. In other words, the catalytically active material 8 is carbon supported. The carbon material 1 is also surrounded by a homogeneous layer of ionomer 6 and is uniformly surrounded by ionomer 6, in particular on all sides, on account of the good interaction (especially coulomb interaction) between carbon material 1 and ionomer 6. Therefore, in addition to stability and proton conductivity, oxygen conductivity or oxygen transport performance in the catalyst layer 7 is also permanently improved.

The foregoing description of the invention is for the purpose of illustration only and is not intended to be limiting of the invention. Within the scope of the present invention, various improvements and modifications may be made without departing from the scope of the present invention and its technical equivalents.

List of reference numerals

1 carbon Material

2 carbon lattice

3 carbon atom

4 nitrogen atom

5 pyridine unit

6 ionomer

7 catalyst layer

8 catalytically active Material