EP3853935A1

EP3853935A1 - Component having a two-layered, oxidic protective layer

Info

Publication number: EP3853935A1
Application number: EP19790421.2A
Authority: EP
Inventors: Martin Andritschky; Klaus PREINFALK
Original assignee: High Tech Coatings GmbH
Current assignee: High Tech Coatings GmbH
Priority date: 2018-09-21
Filing date: 2019-09-18
Publication date: 2021-07-28
Also published as: AT521011A4; AT521011B1; WO2020056440A1

Abstract

The invention relates to a component (6) having a metal main body (7) and protective layer (8) arranged thereon, the protective layer (8) being formed in a number of layers, at least comprising a first oxidic layer (9) and a second layer (10) forming oxides having a spinel structure, the first oxidic layer (9) being arranged closer to the metal main body (7) than the second layer (10) forming oxides having a spinel structure. The first, oxidic layer (9) contains a metal oxide of a metal of the group of the rare earths and/or a metal alloy oxide which contains at least one element from the group of rare earths.

Description

Component with a two-layer, oxidic protective layer

The invention relates to a component with a metallic base body and a protective layer arranged thereon, the protective layer being embodied in multiple layers, at least comprising a first, oxide layer and a second layer, forming oxides with a spinel structure, the first oxide layer being arranged closer to the metallic base body is, as the second layer, forming oxides with spinel structure.

The invention further relates to a high-temperature fuel cell comprising at least one connector.

In addition, the invention relates to a method for producing a protective layer on a component with a metallic base body, according to which the protective layer is formed from multiple layers, at least comprising a first, oxidic layer and a second, oxide with layer structure forming Spi, the first oxide layer closer to the metallic base body is arranged as the second layer forming oxides with spinel structure.

Metallic components of the type described above are used in high-temperature fuel cells (abbreviated as SOLC Solid Oxygen Luel Cell), in particular for interconnectors (also called bipolar plates). The operating temperatures are usually in the range of approx. 600 ° C to approx. 1,000 ° C and allow the use of numerous fuels, the most important of which are H2, CH4 and CO together with air.

Several fuel cells are usually connected in series to generate electricity. The interconnector, which is usually plate-shaped, is used to connect the individual cells. These interconnectors are arranged as fuel gas and oxidizing agent separately connecting link between two fuel cells and can also function as a load-bearing component for the entire construction with appropriate design. A preferred design of the interconnectors consists of metal sheets which contain chromium as an essential alloy component, since chromium oxide-forming high-temperature materials have good oxidation resistance. These chromium-containing metallic materials form chromium oxide-containing surface layers even under normal conditions. Under the operating conditions of the fuel cells, the chromium oxides react with oxygen and water to form chromium trioxide (Cr203) and / or its hydrates (Cr02 (0H) 2 (chromic acid) and CrO (OH) 4). However, the chromium trioxide of the surface layer itself has only a low level of electrical conductivity. On the other hand, the chromium oxide hydrates are gaseous species at the operating temperatures of the high-temperature fuel cells, which can be transported through the gas space to the interface between the electrolyte and the cathode. The Cr (VI) compounds are deposited there. This will hinder oxygen reduction at this point. The result is a significant reduction in the performance and service life of the fuel cell. Mechanisms which lead to a reduction in the electrical power and ability to function and thus to a limitation of the life of a fuel cell stack are, inter alia, the growth of an electrically poorly conductive oxide layer on the metallic substrate and the evaporation of Cr compounds (with subsequent deposition and thus poisoning the cathode).

Both mechanisms can be controlled by a protective layer on the interconnector. There are a number of approaches in the patent literature for the formation of these protective layers. A rough distinction can be made between non-metallic, mostly oxidic, protective layers and metallic protective layers. For the first group, plasma spraying, PVD deposition, or wet chemical deposition are used as coating techniques. However, these oxidic protective layers often have layer thicknesses of more than 50 pm, which limits the electrical conductivity. Furthermore, these protective layers can form continuous cracks, which generally do not heal and therefore do not effectively prevent the chromium diffusion to the surface and the subsequent evaporation. A ceramic protective layer based on lanthanum strontium manganese perovskites is often used commercially, as described, for example, in WO

2008/003113 A1 or US 2010/0129693 A1. Ceramic protective layers consisting of two- or three-phase alloys such as CoM-nCr spinels, which are known from US 2017/0054159 Al, proved to be not very effective in reducing the chromium, especially at temperatures> 750 ° C. - evaporation.

The application of opaque, thin protective layers (thin layers are generally deposited using PVD processes) is often technically impossible due to the surface roughness of the metallic substrates.

Metallic protective layers are produced using PVD (physical vapor deposition), CVD (chemical vapor deposition), or application from the ionized state by electrolytic or chemical deposition (e.g. electroplating, anodizing, electrophoretic painting). The metallic coating is oxidized during operation and oxidic spinels are formed, which have a relatively high (relative to chromium oxides) electrical conductivity.

Multi-layer protective layers are also known, for example from EP 1 819 507 B1, US 2015/0079498 A1, US 2009/0029187 A1 and US 7,875,360 B2.

The present invention is based on the object of improving the service life of a high-temperature fuel station.

This object is achieved with the component mentioned at the beginning, in which the first, oxide layer contains a metal oxide of a metal from the group of rare earths and / or a metal alloy oxide which contains at least one element from the group of rare earths. Furthermore, the object of the invention is achieved with the high-temperature fuel station, which contains a component according to the invention.

The object of the invention is also achieved with the method mentioned at the outset, according to which it is provided that the first, oxidic layer is formed from a metal or a metal alloy which contains at least one element from the group of rare earths.

The applied first, oxidic layer is able to form largely gas-tight ceramic layers at high temperatures and in an oxidizing atmosphere. this in turn has the advantage that even metallic base bodies with a very rough surface can be used directly for the coating. A residual porosity in the oxide layer after the coating process therefore has no negative influence on the layer properties. Due to the metals or metal alloys used for the production of the oxide layer, the oxides have electrical resistances of less than 5 mQ / cm2.

Another advantage is that occurring micro-cracks during long-term operation, which can be induced by temperature fluctuations, for example, are curable.

According to an embodiment variant of the component, it can be provided that the second layer, which forms oxides with a spinel structure, contains at least one element from the group of rare earths. According to an embodiment variant of the method, in addition to the metals from a group consisting of Mn, Co, Fe, Nb, Cr, V, at least one element from the group of rare earths can also be deposited to form the second layer forming oxides with a spinel structure , in particular that element which was also deposited for the formation of the first, metallic layer. The advantage here is that, due to the protective effect of the second layer, the first, oxidic layer can be made very thin and thus also very stable. This is important, for example, when manufacturing fuel cell stacks.

According to another embodiment variant of the component, it can be provided that the proportion of the at least one element from the group of rare earths in the second,

Oxides with a spinel structure-forming layer is selected from a range of 0.01 atom% to 10 atom%. It is thereby achieved that cracks, which occur due to temperature changes in the first metallic layer, can be better healed via diffusion processes. If the proportion of the element from the group of rare earths is too high, own rare earth oxides can form which do not have the advantageous properties of the spinel structures (high electrical conductivity).

According to a further embodiment variant of the invention, it can preferably be provided that the metallic base body is formed from an alloy with chromium as the alloying element, in particular from a ferritic chromium alloy with a minimum chromium content of 15% by weight. The use of such basic bodies per se is known from the prior art, as was explained above. But it has been shown that the protective layer has advantages, in particular with alloy with chromium as the main constituent, since chromium can be effectively prevented from being removed from the component or converted into a form which is disadvantageous for a high-temperature fuel cell. According to a further embodiment variant of the component, it is thus also possible to use chromium alloys which have a chromium content in the chromium alloy of at least 70% by weight without the cell's performance as a result of a relatively rapid decrease as a result of chromium loss. This in turn is advantageous with regard to the electrical conductivity of the component.

Because of the thin first layer, the protective layer can be made relatively thin overall. According to a preferred embodiment variant, the protective layer can have a layer thickness which is selected from a range from 1 pm to 20 pm. The effects mentioned above regarding the reduction in conductivity due to thick oxide layers can thus be significantly reduced.

For reasons of better self-healing effect, according to a further embodiment variant of the component, the first, oxidic layer can have a smaller layer thickness than the second, oxide-forming layer with spinel structure.

The metallic base body is preferably plate-shaped or sheet-shaped or structured, since its coating makes it easier to achieve a constant layer thickness with high quality.

To further improve the effects mentioned above, it can be provided according to other embodiment variants of the component that the proportion of the at least one element from the group of rare earths in the second layer forming oxides with a spinel structure varies over the layer thickness of this layer. It is possible to increase the healing effects of cracks.

The first, oxidic layer is preferably produced in accordance with an embodiment variant of the method by a PVD method. The first, oxidic layer can thus be deposited several times faster and more economically than conventional ceramic layers using vacuum coating processes. For the same reasons, it can also be provided, according to a further embodiment variant of the method, that the second layer, which forms oxides with a spinel structure, at least two metals from a group consisting of Mn, Co, Fe, Nb, Cr, V are deposited with one another, in particular by co-sputtering, with the proviso that the sum of the oxidation numbers of the metal cations forming the spinel structure is +8.

On account of the above-mentioned (automatic) formation of a gas-tight first layer, it can be provided according to a further embodiment variant that oxides adhering to the metallic base body are mechanically removed before the first oxide layer is arranged. For example, these oxides are typical of sintered components. As expected, the properties of the components can be improved by removing the oxides. It is an advantage, however, that this can be done using effective, simple methods, such as Sandblasting can take place, since - as has already been stated above - it is possible within the scope of the invention to make the first, oxidic layer largely gas-tight.

For a better understanding of the invention, this will be explained in more detail with reference to the following figures.

Each shows in a simplified, schematic representation:

1 shows a section of a high-temperature fuel cell;

2 shows a detail from a component;

Fig. 3 shows the reduction in Cr evaporation in comparison with an uncoated

Substrate at a temperature of 850 ° C and 3 vol.% Water vapor in the laboratory atmosphere.

In the introduction, it should be noted that in the differently described embodiments, the same parts are provided with the same reference symbols or the same component designations, the disclosures contained in the entire description correspondingly che parts with the same reference numerals or the same component names who who can. Also, the position information selected in the description, such as above, below, laterally, etc., are based on the figure described and illustrated immediately, and these position information are to be transferred to the new position in the event of a change in position.

1 shows a detail from a high-temperature fuel cell 1. The high-temperature fuel cell 1 has several identical modules 2 (only one is shown in FIG. 1), each module 2 having a cathode 3, an electrolyte 4 and an anode 5. Furthermore, the modules 2 also have components 6 for separating the individual modules, the so-called interconnectors.

This basic structure of a high-temperature fuel cell 1 is known from the prior art, so that reference is made to further details of the high-temperature fuel cell 1.

The present invention is primarily concerned with the component 6.

As already mentioned, the component 6 is preferably an interconnector. In the context of the invention, however, the component can also be provided for another application, in particular also for a high-temperature fuel cell 1, such as, for example, a gas supply element (gas supply line) or a gas discharge element (gas discharge line). However, the component 6 can also be used in other devices, for example a heat exchanger in which it is subjected in particular to similar operating conditions as in a high-temperature fuel cell 1.

The component 6 has a metallic base body 7. This metallic base body 7 is preferably plate-shaped or sheet-shaped. However, it can also have a different shape, for example a cylindrical shape, etc. In addition, the surface of the base body 7 can be structured. The structuring can be designed, for example, in the form of a wave pattern or a waffle pattern or in the form of grooves, etc.

In principle, the metallic base body 7 can consist of a metal or a metal alloy which is selected from a group comprising or consisting of stainless steels a chromium content of at least 15% by weight, in particular between 15% by weight and 97% by weight.

For example, the material Crofer® 22 APU from Thyssen Krupp VDK GmbH can be used as stainless steel.

In the preferred embodiment of the component 6, the metallic base body 7 consists of an alloy with chromium as an essential alloy element (in addition to any further alloy elements that may be present), in particular as a main component. The chromium content according to an embodiment of the invention is particularly preferably at least 70% by weight, in particular at least 90% by weight, for example 95% by weight. The chromium alloy can have a chromium content between 70% by weight and 95% by weight.

A ferritic chromium alloy is particularly preferred. The iron content of these alloys can be between 2% by weight and 10% by weight. For example, a ferritic chromium alloy with an iron content of 5% by weight and a chromium content of 95% by weight can be used.

For example, CFY from Plansee SE can be used as stainless steel.

Part of the chromium can also be replaced by at least one further alloy element, for example yttrium, manganese, copper or other rare earth metals. The one or more iron other alloying elements of the chromium alloy can be present in a proportion which is selected from a range of a total of 0.01% by weight and 3% by weight.

The component 6 has a protective layer 8 on at least one surface. Preferably, several surfaces of the component 6 are provided with a protective layer 8, in particular those surfaces which come into contact with oxidizing substances, in particular (hot) gases. As can be seen better from FIG. 2, which shows a section of the component 6, the protective layer 8 is designed in multiple layers. It comprises a first layer 9 and a second layer 10 or consists thereof. The first layer 9 is oxidic. The first layer has a proportion of perovskite crystal structures.

The second layer 10 has or has oxides with a spinel structure (= second oxide layer 10).

As can be seen from FIG. 2, the first oxide layer 9 is arranged closer to the metallic base body 7 than the second layer 10 forming oxides with a spinel structure. In particular, the first oxide layer 9 is arranged directly on the metallic base body 7, and in particular associated with it.

The first, oxidic layer consists of or comprises a metal from the rare earth group or a metal alloy which contains at least one element from the rare earth group. These are the elements scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. If the first, oxide layer 9 is formed from a metal alloy, this can contain at least one further element from the group of rare earths.

Furthermore, the first, oxidic layer 9 has a chromium content and (according to the chemical stoichiometry) oxygen. The first, oxidic layer 9 can therefore consist, for example, of at least one rare earth metal, chromium and oxygen. If necessary, at least one further element can also be contained, which originates from the metallic base body 7.

The proportion of the at least one metal from the group of rare earths in the metal alloy of the first, oxidic layer 9 can be selected from a range from 10% by weight to 50% by weight. If there are several rare earth metals, their total proportion in the metal alloy can be selected from a range from 10% by weight to 50% by weight. The rest to 100 wt .-% form chromium, and possibly another alloying element or several other alloying elements of the metallic base body 7, and oxygen.

According to a preferred embodiment variant of the component 6, the second layer 10, which forms oxides with a spinel structure, also has at least one element from the group of rare earths. The proportion of the at least one element from the group of rare earths in the second layer 10 which forms oxides with a spinel structure can, according to a further embodiment, be selected from a range of 0.01 atom% to 10 atom%, in particular from a range of 0.1 atomic% to 5 atomic%.

For example, the second layer 10 forming oxides with a spinel structure can have the following compositions:

- CoMnLa, the proportion of La being 5 atom% and the rest being 100 atom%, 50% each being divided into Co and Mn. The first layer can preferably be formed by La, Cr and oxygen.

- CoMnCe, the proportion of Ce being at least approximately 7 atomic% and the remainder being divided into 100 atomic% and 50% each of Co and Mn. The first layer can preferably be formed by Ce, Cr and oxygen.

As already stated, the first, oxidic layer 9 can be made very thin. A layer thickness 11 of the entire protective layer 8 can be selected from a range from 1 pm to 20 pm, in particular from a range from 1 pm to 11 pm. The first, oxidic layer 9 is preferably made thinner than the second, layer 10 forming oxides with spinel structure. The first, oxidic layer 9 can preferably have a layer thickness 12 which is selected from a range from 2 nm to 0.5 μm , in particular from a range from 50 nm to 200 nm. The rest of the entire layer thickness 11 of the protective layer is formed by the second layer 10 forming oxides with a spinel structure.

The concentration of the at least one element from the group of rare earths in the second layer 10, which forms oxides with a spinel structure, can be over the entire layer thickness this layer 10 must be constant (within the framework of the production-related fluctuations). According to one embodiment variant of component 6, there is also the possibility that the proportion of the at least one element from the group of rare earths in the second,

Oxides with a layer 10 forming a spinel structure vary over the layer thickness of this layer 10, that is to say has a concentration gradient. For example, this concentration gradient serves to drop from 50 atom% at the interface to the first, oxidic layer 9 to 0.1 atom% over the layer thickness of the layer 10.

In the case of more than one rare earth element in the second, oxides with a spinel structure form the layer 10, all or more or only one of these elements can be formed with a concentration gradient over the layer thickness of the layer 10.

The concentration gradient can be linear or a function of x ² or x ³ or logarithmic, etc.

According to a further embodiment variant of the component 6, it can be provided that the first, oxidic layer 9 has at least two elements from the group of rare earths, and that their proportion varies over the layer thickness 12 of this layer 9. With regard to the possible course of the concentration gradients, reference is made to the above explanations. The proportion of rare earths at the interface to the metallic base body 7 of the component is preferably higher than the proportion of MnCo and decreases in the direction of the second layer 10 which forms oxides with a spinel structure.

The production of the metallic component 6 is the metallic base body 7 be provided. This can be made by a casting or sintering process. Subsequent (cutting) processing steps can of course be carried out in both process variants. The protective layer 8 described above is then arranged on at least one surface of this metallic base body 7.

In the preferred embodiment variant of the method, the first, oxidic layer 9 is deposited on the metallic base body 7 by means of a PVD method in order to produce the protective layer 8. The first, oxidic layer 9 is deposited in particular by means of magnetron sputtering, preferably an unbalanced configuration, from one or more purely metallic targets or metal alloys. The substrates are in continuous rotation motion. Typical coating rates are 0.1 nm / s to 10 nm / s at a gas pressure of 5 * 10-4 mbar to 1 * 10-2 mbar. During the deposition process, a negative voltage is applied to the metallic target, with a pulsed or constant DC voltage between - 300 V and - 500 V being selected.

The second layer 10, which forms oxides with a spinel structure, is then deposited on this first, oxide layer 9. This is preferably done by the deposition of at least two metals from a group consisting of Mn, Co, Fe, Nb, Cr, V with one another, in particular by cosputtering, with the proviso that the sum of the oxidation numbers of the metal cations forming the spin structure +8 results.

The second layer 10, which forms oxides with a spinel structure, is preferably deposited with the aid of magnetron sputtering, preferably an unbalanced configuration, from one or more pure metal targets or metal alloys. The substrates are in a continuous rotational movement. Typical coating rates are 0.1 nm / s to 10 nm / s at a gas pressure of 5 * 10-4 mbar to 1 * 10-2 mbar. During the deposition process, a negative voltage is applied to the metallic target, with a pulsed or constant DC voltage between -300 V and - 500 V being selected.

For example, the following combinations of metals can be produced: Co with Mn, Co with Mn and Fe, Co with Mn and Al.

As explained above, the second layer 10, which forms oxides with a spinel structure, can also have at least one element from the group of rare earths, in particular that element of the first, oxidic layer 9. The at least one element from the group of rare earths is in the preferred embodiment variant of the method does not diffuse out of the first, oxidic layer 9, but is also deposited with the elements mentioned above to form the second layer 10, which forms oxides with a spinel structure, in particular simultaneously with the elements mentioned. It is provided that the second layer 10, which forms oxides with a spinel structure, is at least partially oxidized after the deposition of the first and the second metal. This can be carried out before the component 6 is used, that is to say before it is used in particular in the high-temperature fuel cell 1. However, it is also possible for this oxidative aftertreatment to take place during the joining of the fuel cell 1 (the joining takes place at approximately 950 ° C.) or during “running in” while the end product is being used.

This oxidative aftertreatment of the protective layer 8 is preferably carried out at a temperature of 750 ° C. to 970 ° C. and an oxygen partial pressure between 10-12 bar and 0.2 bar. The duration depends on the selected temperature and varies between 0.1 hours and 10 hours. The higher the temperature is selected, the shorter the duration can be.

According to another embodiment variant of the method it can be provided that prior to the arrangement of the first, oxidic layer 9 on the metallic base body 7, oxides adhering to it are mechanically removed. This can be done, for example, by grinding, sandblasting, etc. Preferably, the base body 7 is sandblasted before the arrangement of the protective layer 8 and this sandblasted surface, optionally after cleaning of the abrasive particles, is used without further (smoothing) aftertreatment. The surface on which the protective layer 8 is arranged can therefore have a surface roughness (average roughness depth) Rz> 20 pm, in particular between Rz = 20 pm to 50 pm. Rz is determined in accordance with DIN EN ISO 25178 in the version valid on the filing date.

The protective layer 8 contains all the elements for the effective protection of the component 6 at high temperatures in oxidizing atmospheres. A subsequent diffusion of elements into the protective layer is therefore not necessary. The protective layer 8 is also able to heal thermal cracks. A crack-free protective layer 8 can therefore be provided.

Execution examples:

Example 1: In a first exemplary embodiment, an interconnector with a sintered, metallic base body 7 made of a chromium-iron-yttrium alloy mentioned above was coated. In a first step, the native oxidation layer (from the pre-processes in the manufacture of the base body) was removed by sandblasting. The basic body is then introduced into a vacuum system by 7 and, after reaching the desired starting pressure, via an Ar plasma treatment (argon pressure approx. 5 10-3 mbar, pulsed negative voltage on the substrate between - 300 V and - 1200 V, duration 5 minutes to 30 minutes). An approx. 0.1 pm thick first metallic layer 9 with lanthanum is sprayed over magnetron sputtering (argon pressure approx. 5 10-3 mbar, constant negative voltage at the target between -300 V and - 400 V, duration 0.1 minutes to 10 minutes) applied. In a second step, an approx. 4 pm thick second layer 10 of oxides with a spinel structure is made of CoMn using magnetron sputtering (argon pressure approx. 5 10 -3 mbar, constant negative voltage at the target or at the targets between -300 V and - 400 V , Duration 0.1 minutes to 10 minutes). This CoMn layer was doped with an average of 5 at% lanthanum, which was deposited together with the Co and the Mn.

If necessary, the areas not to be coated can be masked.

The coated base body 7 was then subjected to post-treatment at a temperature> 800 ° C. in an oxidizing atmosphere (air or argon-oxygen mixture).

In this step, the metallic coating was converted into a multilayer oxide layer with an inner Cr203 layer, which was formed from the metallic base body 7, a crystalline, oxidic intermediate layer and an oxidic CoMnCr spinel layer 10 μm.

The inner Cr203 layer, which was formed from the metallic base body 7, can generally also be formed in other design variants of the invention if the protective layer 8 is post-treated by oxidation.

As could be determined from investigations, the entire rough surface of the metallic base body 7 was covered with an opaque gas-tight layer. The interconnector can thus be installed. In general, the oxidative aftertreatment can also be carried out after installation in the already functional stack of the high-temperature fuel cell 1.

In Fig. 3, the reduction in Cr evaporation from the base body 7 in the component 6 according to the invention (lower curve) compared to an uncoated base body (upper curve) at a temperature of 850 ° C and 3 vol .-% Water vapor is shown in the laboratory atmosphere. The improvement which is achieved with the protective layer 8 according to the invention can be clearly seen. The time in hours is plotted on the x-axis and the Cr evaporation in kg / m2 on the y-axis

Example 2.

In a second exemplary embodiment, an interconnector was coated with a base body 7 made of a metal alloy Crofer22APU. In a first step, the native oxidation layer and any existing organic contamination (from the preprocesses in the manufacture of the base body) was removed by chemical cleaning processes. The base body 7 was then introduced into a vacuum system and, after reaching the desired starting pressure, via an ar - Plasma treatment (see example 1) activated. An approximately 100 nm thick first layer 9 with lanthanum was applied using magnetron sputtering (see Example 1). In a second step, an approximately 2 pm thick CoMn layer 10 was applied using magnetron sputtering (see Example 1). This CoMn layer 10 is doped with up to 1 at% lanthanum.

In this example too, the reduction in chromium evaporation was found in comparison to the prior art designs.

The component 6 preferably has a two-layer oxide layer. The first layer 9 preferably consists of an oxide with a high La content, Cr and oxygen. This first layer 9 can have a crystal structure with a high percentage of perovskite.

The second layer 10 preferably consists of Co, Mn, La, some (<5%) Cr and oxygen. This oxide has a high spinel content.

The two layers 9, 10 preferably merge into one another in a flowing manner. Although the protective layer 8 is preferably produced by depositing the two layers from the metals and their subsequent oxidation, there is in principle the possibility that the first, oxidic layer 9 and / or the second, oxidic layer 10 is produced by deposition of the corresponding metal oxides will be.

The exemplary embodiments show possible design variants, it being noted at this point that combinations of the individual design variants with one another are also possible.

The invention relates independently of the component 6 and a protective layer 8 and de ren use for a metallic component 6, which is used at high temperatures in oxidizing atmospheres, in particular in high-temperature fuel cells 1 and their periphery. This protective layer 8 is composed in accordance with the above embodiments.

Furthermore, the invention also relates to a preliminary product for a component 6 with a metallic base body 7 and a protective layer 8 arranged thereon, the protective layer 8 being embodied in multiple layers, at least comprising a first metallic layer 9 and a second layer 10 forming oxides with a spinel structure , wherein the first metallic layer 9 is arranged closer to the metallic base body 7 than the second layer 10, which forms oxides with a spinel structure, and wherein the first, metallic layer 9 consists of a metal from the rare earth group or a metal alloy, at least contains an element from the group of rare earths. From this preliminary product, the component 6 or the protective layer 8 according to the invention is produced via the aforementioned oxidative aftertreatment.

For the sake of order, it should finally be pointed out that, for a better understanding of the structure of the high-temperature fuel cell 1 or the component 6, these have not necessarily been shown to scale. List of reference symbols

High temperature fuel cell

module

cathode

electrolyte

anode

Component

Basic body

Protective layer

location

Layer thickness

Claims

Patent claims

1. Component (6) with a metallic base body (7) and a protective layer (8) arranged thereon, the protective layer (8) being constructed in several layers, at least comprising a first, oxidic layer (9) and a second, oxide with spinel structure forming layer (10), the first oxidic layer (9) being arranged closer to the metallic base body (7) than the second layer (10) forming oxides with spinel structure, characterized in that the first, oxidic layer ( 9) contains a metal oxide of a metal from the group of rare earths and / or contains a metal alloy oxide which contains at least one element from the group of rare earths.

2. The component (6) according to claim 1, characterized in that the second layer (10) forming oxides with spinel structure contains at least one element from the group of rare earths.

3. The component (6) according to claim 2, characterized in that the proportion of the at least one element from the group of rare earths in the second layer (10) forming oxides with a spin structure is selected from a range of 0.01 atomic % to 10 atomic%.

4. Component (6) according to one of claims 1 to 3, characterized in that the metallic base body (7) is made of an alloy with chromium as an alloying element, in particular of a ferritic chromium alloy with a minimum chromium content of 15% by weight. %.

5. The component (6) according to claim 4, characterized in that the proportion of chromium in the chromium alloy is at least 70% by weight.

6. The component (6) according to one of claims 1 to 5, characterized in that the protective layer (8) has a layer thickness (11) which is selected from a range from 1 pm to 20 pm.

7. The component (6) according to one of claims 1 to 6, characterized in that the first, oxide layer (9) has a smaller layer thickness (12) than the second layer (10) forming oxides with a spinel structure.

8. The component (6) according to one of claims 1 to 7, characterized in that the metallic base body (7) is plate-shaped or sheet-shaped and / or is formed with a structured surface.

9. The component (6) according to one of claims 2 to 8, characterized in that the proportion of the at least one element from the group of rare earths in the second layer (10) forming oxides with spinel structure over the layer thickness of this layer (10) varies.

10. High-temperature fuel cell comprising at least one interconnector, characterized in that the interconnector is designed as a component (6) according to one of claims 1 to 9.

11. A method for producing a protective layer (8) on a component (6) with a metallic base body (7), according to which the protective layer (8) is formed in multiple layers, at least comprising a first, oxidic layer (9) and a second, oxide with spinel structure-forming layer (10), the first oxide layer (9) being arranged closer to the metallic base body (7) than the second layer (10) forming oxide with spinel structure, characterized in that the first oxide layer (9 ) is formed from a metal or a metal alloy which contains at least one element from the group of rare earths.

12. The method according to claim 11, characterized in that the first, metallic layer (9) is produced with a PVD method.

13. The method according to claim 11 or 12, characterized in that for the second layer (10) forming oxides with spinel structure, at least two metals from a group consisting of Mn, Co, Le, Nb, Cr, V are deposited with one another The measure is that the sum of the oxidation numbers of the metal cations forming the spinel structure is +8.

14. The method according to claim 13, characterized in that in order to form the second layer (10) forming oxides with spinel structure, in addition to the two metals from the group consisting of Mn, Co, Fe, Nb, Cr, V, at least one element from the Group of rare earths is also deposited, in particular that element which was also deposited for the formation of the first metallic layer (9).

15. The method according to any one of claims 11 to 14, characterized in that before the arrangement of the first metallic layer (9) on the metallic base body (7) adhering oxides are removed mechanically.