HK1142720A - A method of producing a multilayer barrier structure for a solid oxide fuel cell - Google Patents

Abstract

The present invention provides a method of producing a multilayer barrier structure in a solid oxide cell stack, comprising the steps of: - providing a metal interconnect; - applying a first metal oxide layer on said metal interconnect; - applying a second metal oxide layer on top of said first metal oxide layer; - applying a third metal oxide layer on top of said second metal oxide layer; - forming a solid oxide cell stack comprising said metal interconnect having said metal oxide layers thereon; and - reacting the metal oxide in said first metal oxide layer with the metal of said metal interconnect during the SOC-stack initialisation, and a solid oxide stack comprising an anode contact layer and support structure, an anode layer, an electrolyte layer, a cathode layer, a cathode contact layer, a metallic interconnect, and a multilayer barrier structure which is obtainable by the above method and through an initialisation step, which is carried out under controlled conditions for atmosphere composition and current load, which depends on the layer composition facilitating the formation of the desired reaction products as a dense barrier layer without chromium species migrating to the air-electrode.

Description

Method for manufacturing multilayer barrier component for solid oxide fuel cell

Technical Field

The present invention relates to a method of manufacturing a multilayer barrier member in a solid oxide cell stack, such as a Solid Oxide Fuel Cell (SOFC) stack or a Solid Oxide Electrolysis Cell (SOEC) stack, and to a multilayer member made by said method, which is particularly suitable for use on the oxygen side of an interconnect separating adjacent cells of said stack.

Background

Solid Oxide Cells (SOC) generally include cells designed for different applications, such as Solid Oxide Fuel Cells (SOFC), or Solid Oxide Electrolysis Cells (SOEC). These types of batteries are well known in the art. In general, a solid oxide fuel cell includes an electrolyte layer sandwiched between two electrode layers. In operation, typically at a temperature of about 500 c to about 1100 c, one electrode is exposed to oxygen or air and the other electrode is exposed to fuel gas.

Under typical operating conditions, a single solid oxide fuel cell produces less than 1V. In order to obtain high voltage and power from an SOFC, it is therefore necessary to stack multiple cells together. The manufacturing process for SOFC flat cell stacks includes the manufacture of a single cell, followed by stacking the resulting cell together with additional layers such as interconnects, current collectors, contact layers and seals to produce a fuel cell stack suitable for the desired application.

One of the problems that currently limits the mass production of fuel cells on an industrial level is the high cost of the finished cells. Therefore, for fuel cells and electrolysis cells operating in the mid-temperature range (about 500 ℃ C. to 900 ℃ C.), it is advisable to use relatively inexpensive metal interconnects to separate the individual cells.

Suitable materials for the metal interconnect layer need to be resistant to oxidation by the anode and cathode gases at higher operating temperatures and must also have a Thermal Expansion Coefficient (TEC) that matches that of the ceramic components of the cell. In view of these requirements, alloys that form chromium oxide, particularly during fabrication, have been investigated as support materials that will form the subsequent interconnect layers. The alloy has a high chromium content, i.e. about 15 to 22 wt%, and under oxidising conditions the chromium migrates towards the surface and forms a chromia barrier or chromia scale on the surface to prevent further oxidation of the component. At the same time, the chromia oxide layer has a sufficiently high conductivity so as not to interfere with the overall performance of the device.

However, during operation of the cell, chromium ions may diffuse from the chromium-containing metal interconnect material into the adjacent air electrode layer and adversely affect catalytic performance, thereby limiting cell performance over time. This phenomenon is commonly referred to as "chromium poisoning". Chromium poisoning is due to chromium in the metal interconnect being transported from the metal in the form of gaseous chromium-containing oxides and hydroxides by surface diffusion across the metal oxide assembly to electrochemically active sites near or on the air side of the electrode where they rapidly reduce the electrochemical activity by a large amount.

In order to obtain low electrical resistance and to reduce chromium poisoning due to the chromium oxide layer forming alloys used as interconnect materials, it has been proposed to coat a layer of manganese chromium spinel on a layer of chromium oxide. For example, US-a1-2003/0059335 proposes a chromium oxide forming iron based alloy containing 12 to 28 wt% chromium and small amounts of La, Mn, Ti, Si and Al. The material can form MnCr on the surface thereof at the temperature of 700-950 DEG C₂O₄A spinel phase. The manganese chromium spinel so formed is expected to have a specific chromium oxide per se for chromium-containing speciesA slightly lower vapor pressure.

However, it was found to be disadvantageous that in fact MnCr₂O₄The diffusion of Cr in spinel proceeds faster than in chromium oxide layers. Thus, Cr₂O₃-(Mn，Cr)₃O₄The double oxide layer does not have any significant effect on preventing chromium poisoning compared to a pure chromium oxide layer.

Different coatings for preventing the formation of chromium-containing vapors on iron-chromium alloys used as interconnects in batteries have been discussed in the patent and scientific journals (e.g., Tietz, F. et al (2004) DE 10306649A 1, Tietz, & Zahid (2004) DE 10306647A 1, Hilliard D.B, (2003) US2003194592-A1, Orlovskaya N et al, (2004) J.Am.Cer, Soc 87, pp 1981-7, Chen, X. et al, (2004) Solid State Ionics 176, pp 425-33). A common coating concept involves the formation of a spinel or perovskite layer on the surface of the metal interconnect in a final microstructure prior to its insertion into the SOFC cell stack, wherein the coating acts as a barrier to prevent chromium migration from the metal interconnect to the air electrode assembly. In order for these coatings to be sufficiently tight, the bond between the coating and the substrate must be good both initially and over extended periods of time (i.e., after thermal cycling), which imposes severe limitations on the process and matching of the thermal expansion coefficients of these coatings to the steel.

In view of these problems, reactive coatings provide a better solution in that they can be transformed into barrier layers at high temperatures with a gradual change and typically can show a more gradual change in microstructure between the metal substrate and the applied oxide coating. Such reactive coatings are discussed, for example, in the following articles on spinel and perovskite barrier coatings: fujiata, k, et al, (2004) j.powersources 131, pp.261-9; and Larring & Norby (2000), j.of the electrochem. soc.147, pp.3251-6. These disclosed coatings are single phase or single substance coatings and are applied to metal surfaces to form a conductive corrosion protection coating. The coating comprises as little chromium as possible to reduce chromium migration from the metal surface for as long as possible and to reduce oxygen migration from the air into the metal.

For example, protective coatings as chromium traps are disclosed in the following articles: jiang S.P et al (2002) J.Eur cer.Soc.22, pp.361-73; and Matsuzaki & Yasuda (2001) J of the electrochem. Soc.148, pp.A126-31. Therein is discussed how chromium-containing phases precipitate on various air electrode materials and different electrolyte materials. Research has focused particularly on chromium deposited on non-cathodically polarized air electrode materials including LSM and LSCF.

The disclosure also relates to the ease with which chromium can combine with other elements (e.g., Mn) from the perovskite structure of LSM cathodes and produce a well-crystallized spinel phase. If the LSM air electrode is electrochemically polarized, the spinel phase can recover at the interface between the electrolyte and the air electrode material. Although LSCF air electrodes are less dependent on the electrochemical potential of the electrode, chromium-containing phases may still precipitate in the pore volume of the electrode.

In summary, the barrier layers proposed in the prior art to date serve to inhibit the formation of chromium-containing vapors from the outset during cell operation, but still require additional and often expensive processing of the metal interconnect prior to its use in the SOFC stack, thus preventing the stack from being mass produced. Also, the surface coating applied must match the metal interconnect material both chemically and thermo-mechanically over a wide temperature range, i.e., over the operating temperature range of the cell of about 500 to 900 ℃ (which severely limits the use of other suitable materials). Finally, while the initial chromium diffusion or evaporation may be reduced to some extent, most coatings do not prevent chromium diffusion throughout the life of the cell and thus do not avoid chromium poisoning of the electrode layers over time.

Thus, there remains a need to provide a cost effective method of eliminating evaporation of chromium from the interconnect surface in a solid oxide cell that allows for containment of chromium vapor species and minimizes contact resistance between the interconnect and the air electrode layer.

In view of the above considerations, the present invention advantageously provides a reactive coating that is applied by an inexpensive method, such as spraying a suspension of particles on the interconnect surface and/or air side of a solid oxide cell prior to stack assembly. Once a dense, preferably chromium-free, reaction layer is formed in sufficient thickness, the coating minimizes chromium evaporation from the metal surface. At the same time, the coating layer covering the above traps chromium-containing substances diffused from the metal surface at an initial stage before the chromium-containing substances reach the active sites of the air electrode layer.

The multifunctional coating of the present invention reduces the problem of chromium poisoning to a technically negligible level while avoiding the much more expensive coating approaches proposed hitherto in the prior art for coating coatings in a similar range and providing a cost-effective multilayer barrier member capable of extending the SOC lifetime.

Disclosure of Invention

In view of the above-mentioned drawbacks of the prior art, the present invention provides a method of manufacturing a multilayer barrier member in a solid oxide cell stack, the method comprising the steps of:

providing a metal interconnection;

coating a first metal oxide layer on the metal interconnect;

coating a second metal oxide layer on the first metal oxide layer;

coating a third metal oxide layer on the second metal oxide layer;

forming a solid oxide cell stack comprising the metal interconnect having the metal oxide layer thereon; and

reacting the metal oxide in the first metal oxide layer with the metal of the metal interconnect during SOC stack initialization.

The invention also provides a multilayer barrier member prepared by the above method.

The present invention also provides a solid oxide cell stack comprising an anode contact layer and a support member, an anode layer, an electrolyte layer, a cathode contact layer, a metal interconnect and the above multilayer barrier member.

The invention also provides a method for controlling the heating sequence and the gas phase composition, preferably the oxygen partial pressure, during the initialization of the solid oxide cell stack, to convert the barrier layer into an electrically conductive and dense reaction product.

Finally, the invention provides a method of reducing the affinity between the air electrode and the chromium during the initialisation process of the stack described above, the method comprising the step of applying a constant or alternating voltage between the air electrode and the interconnect.

Preferred embodiments are set forth in the dependent claims.

Drawings

Figure 1 shows a preferred embodiment of the multilayer structure of the invention.

Fig. 2a and 2b are photomicrographs of the cross-section of a barrier member according to the invention as a function of the thickness of the layer.

Figure 3 is a photomicrograph of a cross-section of a barrier member according to the present invention.

Figure 4 shows the difference in the rate of decay of electrical performance of elements in a similar assembly of a stack with and without a protective coating on the air electrode surface of the interconnect.

Detailed Description

The invention provides a method of manufacturing a multilayer barrier member in a solid oxide cell stack, the method comprising the steps of:

providing a metal interconnection;

coating a first metal oxide layer on the metal interconnect;

coating a second metal oxide layer on the first metal oxide layer;

coating a third metal oxide layer on the second metal oxide layer;

forming a solid oxide cell stack comprising the metal interconnect having the metal oxide layer thereon; and

reacting the metal oxide in the first metal oxide layer with the metal of the metal interconnect during SOC stack initialization.

With the method of the present invention, a multilayer barrier member is applied between the metal interconnect and the air electrode layer of the SOC cell stack. When the stack is initialized, the formation of a thermally generated barrier is facilitated, which in turn minimizes chromium evaporation from the interconnect surface, contains chromium vapor species and simultaneously minimizes contact resistance between the two components of the interconnect and air electrode.

Preferably, the metal interconnect is a layer of ferritic stainless steel. Ferritic stainless steels are relatively inexpensive and can cost effectively be mass produced for cell stacks. According to the present invention, the metal interconnect contains chromium, such as a chromium layer or a chromium alloy, and may preferably comprise a FeCrMx alloy, wherein Mx is selected from Ni, Ti, Ce, Mn, Mo, W, Co, La, Y, Al, Nb or mixtures thereof. The concentration of Mx in the alloy is preferably an amount that avoids austenite formation. Preferably, the concentration of Mx is from 0 to 15 wt%, more preferably from about 0.1 to 10 wt%, based on the total weight of the alloy. Most preferably, the concentration of Mx is from 0.25 wt% to 0.55 wt%.

Ferritic stainless steels, such as the commercial products of Crofer 22APU (from krupptyhyssen), either form well-defined double oxide layers of chromium oxide and Cr-Mn-spinel, or form mixed chromium oxide-spinel oxide layers with less pronounced phase separation, such as in the case of 0YC44 (available from Sandvik) and Hitachi ZGM232 (available from Hitachi).

Preferably, the first metal oxide layer coated onto the metal interconnect comprises a mixture of metal oxides having at least two different metal cations, or a mixture of a transition metal oxide and a metal oxide having at least two different metal cations. More preferably, the metal oxide mixture comprises lanthanum oxide and transition metal oxides, preferably cobalt oxide, manganese oxide or copper oxide, and mixtures thereof. One of the most preferred metal oxides is cobalt oxide.

The metal oxide having at least two different metal cations preferably has a perovskite structure. Suitable perovskite materials include doped lanthanum manganite, doped lanthanum cobaltite (lanthanum cobalt), doped lanthanum ferrite and mixtures thereof.

The first metal oxide layer may be applied by any suitable method known to those skilled in the art. The layer is preferably sprayed on or laminated with a casting film (tape cast film).

The first metal oxide layer in the final multilayer barrier is at least partially reacted with oxygen and metal elements that out-diffuse from the interconnect during the initialization step to form a seamless transition layer between the second layer and the protective chromium oxide layer formed under high temperature oxidation conditions. As shown in FIG. 1, the first metal oxide layer 2 forms a dense mixed oxide layer with as low a chromium oxide content as possible, for example MnCo₂O₄A layer in which Mn from the metal interconnect 1 reacts with the applied cobalt oxide. The layer thus forms an effective barrier layer,the barrier layer is effective to minimize migration of chromium from the metal through the layer.

Fig. 1 is a schematic diagram of a preferred embodiment of a multilayer component comprising a metal interconnect 1, a first metal oxide layer 2, a second mixed metal oxide layer 3 in which one oxide has a perovskite structure, a third mixed metal oxide 4 having a perovskite structure, and additionally, a spacer 5 for admitting air into an air electrode 6 deposited on an electrolyte, and an optional solid oxide cell support 7.

The thickness of the first metal oxide layer is preferably from about 1 to about 20 μm, more preferably from about 3 to about 15 μm.

In order to form a microstructure with the lowest electrical resistance, i.e. where the dense, low chromium oxide content first layer has a good contact with the second layer, the material content in the first layer must be reduced to a minimum. On the other hand, in order to form a layer with a low chromium content, it must be possible to provide a sufficient amount of metal oxide, as summarized in table 1. It was found that the chromium content decreased by a factor of two, from 0.7 to 0.3, when the thickness of the first layer was increased from 7 μm to 15 μm. This is also illustrated by FIGS. 2a and 2b, which show the microstructure of the resulting coating as a function of the thickness of the first coating, 7 μm Co, after 1000 hours at 900 deg.C₃O₄(FIG. 2a) and 15 μm Co₃O₄(FIG. 2 b). 15 μm thick Co₃O₄The coating does not react completely with the steel.

TABLE 1

First coating layer, thickness	Second coating layer of thickness	500h	1000h	2000h	4000h
						LSM，15μm		Cr1.4Mn1.6O4	Cr1.5Mn1.5O4	Cr1.6Mn1.4O4	Cr1.6Mn1.4O4
Co3O4，7μm	LSM，15μm	Cr0.7Mn1.4Co0.8Fe0.1O4	Cr0.7Mn1.6Co0.6Fe0.1O4	Cr0.9Mn1.5Co0.5Fe0.1O4	Cr1.3Mn1.2Co0.5O4
						Co3O4，15μm	LSM，15μm	Cr0.3Mn0.9Co1.7Fe0.1O4	Cr0.4Mn0.9Co1.6Fe0.1O4	Cr0.5Mn1.1Co1.4O4	Cr0.7Mn0.8Co1.5O4

The compromise between the chromium resistance of the barrier layer and the microstructure required for reducing the electrical resistance is preferably achieved by adding more metal oxide in the second layer of the multilayer structure while keeping the layer thickness of the first layer to a minimum.

Preferably, the metal oxide of the second metal oxide layer of the multilayer barrier member is the same as the metal oxide of the first metal oxide layer. More preferably, the second metal oxide layer comprises a mixture of a transition metal oxide and a metal oxide having at least two different metal cations. Suitable metal oxides for the second oxide layer include oxides selected from the group consisting of: alkaline earth metal oxides, preferably magnesium oxide, barium oxide, strontium oxide, calcium oxide; and transition metal oxides, preferably cobalt oxide, manganese oxide, copper oxide, lanthanum oxide; and mixtures thereof.

Also, the metal oxide of the second oxide layer having at least two different metal cations preferably has a perovskite structure and is selected from the group consisting of doped lanthanum manganite, doped lanthanum cobaltite, doped lanthanum ferrite and mixtures thereof.

The second metal oxide coating may be applied by any suitable method known to those skilled in the art. Preferably the layer is sprayed on or laminated by a cast film.

The thickness of the second metal oxide layer is preferably from about 10 to about 30 μm, more preferably from about 15 to about 25 μm.

The second layer of the multilayer barrier member facilitates formation of the barrier layer, and the chromium trapping material is capable of trapping chromium-rich vapor species that evaporate and migrate from the metal oxide layer during the first stage of initialization and subsequently if small amounts of chromium vapor continue to migrate out of the metal oxide layer before the first barrier layer is fully formed. As mentioned above, the monolayer is not able to minimize chromium poisoning to a technically acceptable level.

In another preferred embodiment, the method further comprises the step of forming a third metal oxide layer on said second metal oxide layer. In the case of applying the third metal oxide layer, the metal oxide of the third layer is selected from the group consisting of doped lanthanum nickelate, doped lanthanum manganite, doped lanthanum cobaltite, doped lanthanum ferrite, doped ceria, and mixtures thereof.

The third metal oxide coating may be applied by any suitable method known to those skilled in the art. Preferably the layer is sprayed on or laminated by a cast film.

The thickness of the third metal oxide layer is preferably from about 10 to about 35 μm, more preferably from about 20 to about 30 μm.

The third layer may also serve as a current collector layer in direct contact with the air electrode. In this case, a maximum in-plane conductivity can be achieved by the third layer, which distributes the conductivity as uniformly as possible.

After each metal oxide layer is coated onto the metal interconnect, the cell stack fabrication is complete. More specifically, contact layers are applied to both sides of the solid oxide cell, and the cell and the interconnect are assembled together in an alternating sequence with a sealing assembly interposed therebetween.

Figure 3 shows an example of a final multilayer barrier. In addition, so-called line scan results are shown, in which the EDS response of a selected range of chemical elements is recorded along a predetermined path of an incident electron beam, which is shown as a white solid line on a photomicrograph. Referring to the line-scanned Cr-profile, the light gray metallic phase on the left is covered by a 4-6 μm thick dark gray chromium oxide layer and a 6-10 μm thick Mn-Co-spinel layer of low chromium oxide content is formed. After applying a first 10 μm thick layer of cobalt oxide and reacting said layer with manganese diffused from the steel forming the interconnect, these layers were formed in air at 950 ℃. The resulting microstructure is dense and adheres well to the protective oxide layer between the resulting steel surface and the Mn-Co-spinel layer. The second porous, 24 μm thick coating layer consisted of LSM.

The initialization step of the resulting stack is carried out at elevated temperatures, preferably at a temperature of at least about 500 c, and more preferably at a temperature of from about 700 c to about 1100 c. Also, this initialization step is performed under controlled conditions of atmospheric composition and current load, the actual range of which depends on both temperature and coating material. For example, if the initialization temperature is about 950 ℃ and the first coating layer is preferably composed mainly of cobalt oxide, the atmospheric air can be directly used while using 0.02 to 0.1A/cm in combination with the reversal of direction in the fuel cell²Current loading of the fuel cell area. When the initiation temperature is about 850 ℃ and the first coating material preferably consists essentially of cobalt oxide, then the oxygen partial pressure is maintained below about 0.06 bar and is used in conjunction with the current load.

During initialization, a reaction occurs between the metal interconnect and the applied first metal oxide layer. Preferably, the reaction product of the reaction between the metal oxide of the first metal oxide layer and the metal of the metal interconnect is electrically conductive and dense, more preferably having a spinel structure.

During operation of the stack, a chromium oxide rich layer may form directly on the metal surface due to the reaction of the metal and oxygen. However, in the multilayer barrier member of the present invention, the reaction product of the metal oxide in the first metal oxide layer and the metal component of the interconnect forms a chromium oxide-free or chromium oxide-depleted layer, preferably a chromium oxide-free spinel layer, at its uppermost layer. The layer formed by the reaction of the metal oxide of the first metal oxide layer and the interconnect thus forms a barrier layer that effectively inhibits the transmission of chromium in the metal through the layer.

The second metal oxide layer acts as a barrier material for chromium-containing species that evaporate and migrate out during cell initialization before the layer formed by the metal oxide of the first metal oxide layer reacting with the interconnect is fully formed. Therefore, chromium poisoning of the electrode is effectively prevented even in the initialization stage of the battery. Also, at any point in the entire life of the battery, in the case where chromium-containing substances are diffused through the first layer during the operation of the battery, the second metal oxide layer serves as an additional chromium scavenger, thereby effectively preventing chromium poisoning of the electrode layer.

In a preferred embodiment, a third metal oxide layer is coated on the second metal oxide. The third metal oxide layer maximizes in-plane electrical contact of the barrier layer and contact with the electrode layer and minimizes surface diffusion of chromium from the second metal oxide layer to the active air electrode. Therefore, in-plane conductivity is improved, chromium poisoning is suppressed, and the life of the battery can be improved.

The invention also provides a multilayer barrier member prepared by the above method. The multilayer barrier is suitable for use in the production of a multilayer barrier in a Solid Oxide Fuel Cell (SOFC) or Solid Oxide Electrolysis Cell (SOEC) stack.

Advantageously, by the barrier layer of the present invention, chromium poisoning of the electrode layer is effectively inhibited, thereby increasing the life of the battery. At the same time, the barrier layer of the present invention has a low inter-layer resistance so that the overall efficiency of the cell is not affected.

The method of the invention is a simple method of preparing the barrier layer and is therefore more cost effective than the suggested methods in the prior art using complicated and expensive production steps, such as plasma spraying and the like.

Also, the barrier layer can be efficiently formed during initialization of the cell stack, so that it is not necessary to separately pre-treat the interconnect before it is assembled into the cell stack, thereby simplifying the production of the cell.

Finally, the composition of the barrier layer does not significantly increase the overall cost of the cell since inexpensive materials can be used, thereby enabling mass production of cells having barrier layers that prevent chromium poisoning.

The present invention is illustrated below by means of detailed examples, which, however, do not limit the scope of the invention.

Examples

-preparing a metal interconnection

The ferritic chromium-containing steel interconnect material is cut to shape prior to treatment with the surface coating. Removing the surface oxides of the interconnect metal that are originally present as a result of the steel production by: the samples were uniformly sanded with 1000SiC sandpaper, after which the surface was dusted with high pressure air and then rinsed first in acetone and then in ethanol using an ultrasonic bath.

Application of a Metal oxide coating

The coating is applied by spraying a slurry mixture at room temperature, which is about 6 to 14 vol% of granular powder dispersed in an organic medium including a solvent, a dispersant and a binder, and then drying at about 50 to 60 ℃ in an air stream.

Lanthanum strontium manganite (La)_0.85Sr_0.15MnO₃) Hereinafter LSM, lanthanum strontium cobaltite (La)_0.84Sr_0.16CoO₃) Hereinafter referred to as LSC, and (La)_0.3Sr_0.7CoO₃) Hereinafter referred to as LSC', strontium cobaltite (SrCoO)_2.5) Hereinafter referred to as SC, iron lanthanum nickelate (LaNi)_0.59Fe_0.41O_3-d) Hereinafter referred to as LNF and iron lanthanum strontium cobaltite (La)_0.6Sr_0.4Fe_0.8Co_0.2O₃) Hereinafter referred to as SLFC; these perovskite powders were prepared from nitrate solutions by the glycine-nitrate method [ L.A. Chick, L.R. Pederson, G.D. Maupin, J.L.Bates, L.E.Thomas and G.J.Exarhos, Materials Letters, 10, (1990), p.6-12]Fired and milled to the desired particle size distribution by ball milling (0.8 μm < d)₅₀＜5μm)。

Commercially available single oxide powder (Co)₃O₄，Mn₃O₄CuO) as analytical grade material and milled to the desired particle size distribution (0.6 μm < d) by ball milling₅₀< 2.5 μm). The particle size distribution was measured by a Beckman coulter I/S particle size analyzer.

-cell stack assembly

Based on the planar cell design, coated metal interconnects are stacked alternately with fuel cells, with glass-based seal assemblies disposed between the layers of the SOFC cell stack.

In the initialization process, the anode and the cathode chambers are both 5-6 ml/min²Air is supplied at a flow rate of surface area until the binder burnout step at 500 to 650 ℃ is completed, and then the gas composition in the two chambers is made different, as exemplified by a combined anode reduction and cathode coating reaction step, for example, at 950 ℃ for 2.5 hours, in which dry hydrogen is supplied to the anode chamber and air is supplied to the cathode chamber, while reversing 0.02 to 0.1A/cm depending on the direction in the operating fuel cell²A current load of the fuel cell area passes through the stack.

Evaluation of the batteries

After initialization, the stack is heated to an operating temperature of about 650 ℃ to about 850 ℃, where the degradation is determined under constant conditions of specific current load and temperature over a period of between 200 hours and 1500 hours.

When the air electrode is poisoned with chromium, the maximum power density is significantly reduced within several hundred hours after initialization, as measured by using an uncoated metal interconnect as a comparison. Degradation is assessed by changes in impedance spectra, normalized voltage, or region specific resistance over time. In comparison to an uncoated metal part and a metal part coated with a dense, gas-tight oxide coating prepared by plasma spraying a metal oxide powder on steel, the degradation of the uncoated stack of the metal part, for example at 750 ℃, reaches the range of 10-30% per 1000 hours, while the degradation of the stack of the coated metal part, detected every 1000 hours, is approximately in the range of 0.2-0.5%, which is almost close to the detection limit established by testing individual cells in the same way in a chromium-free environment. The degradation of the stack measured in the same way for the multilayer coated metal part according to the invention is in the range of 0.2 to 3% per 1000 hours, see fig. 4.

FIG. 4: experimental confirmation of the interconnect coating of example 1 was performed by testing the stack at 750 c for 1000 hours.

Example 1

Crofer 22APU was cleaned and coated with a 7 μm thick cobalt oxide layer by means of slurry coating (d)₅₀2.5 μm), dried and further coated with 90 wt% LSM and 10 wt% cobalt oxide in a 20 μm thickness by means of slurry coating. With the coated part facing the cathode of a Solid Oxide Fuel Cell (SOFC) and assembled into a SOFC stack, the metal parts are in an air stream (5.4 ml/min/cm)²Surface area) was heated to 650 c at a rate of 3 c per minute and held at that temperature for 2 hours to burn off all residual organic binder and subsequently heated to 950 c under the same conditions for 3 hours to form a spinel barrier on the metal surface of the cathode compartment. The SOFC stack is then cooled to an operating temperature (750 ℃) and connected to an electrical load with a degradation rate of 0.25A/cm²The evaluation was carried out under a current load of a cell area, and was 0.2% per 1000 hours.

Example 2

Sandvik 0YC44 was cleaned and coated with 7 μm thick layers of cobalt oxide and copper oxide (2: 1wt/wt) by means of slurry coating, dried and further coated with 60 wt% LSM, 30 wt% LSFC and 10 wt% cobalt oxide 20 μm thick by means of slurry coating. With the coated part facing the cathode of a Solid Oxide Fuel Cell (SOFC) and assembled into a SOFC stack, the metal parts are in an air stream (5.4 ml/min/cm)²Surface area) was heated to 550 c at a rate of 3 c per minute and held at that temperature for 2 hours to burn off all residual organic binder, and subsequently heated to 950 c at a rate of 3 c per minute in a mixed gas stream of air and nitrogen (1: 50 vol: vol), where it was held for 4.5 hours to form a spinel barrier on the metal surface of the cathode compartment. The SOFC stack is then cooled to operating temperature (750 ℃) and connected to an electrical load while air is supplied to the cathode compartment.

Example 3

The ZMG232 was cleaned and coated with a 5 μm thick layer of copper oxide and manganese oxide (4: 1mol/mol) by slurry coating, dried and further coated with 50 wt% LSM, 30 wt% LSC and 20 wt% cobalt oxide 25 μm thick by slurry coating. The coated part was brought to face the cathode of a Solid Oxide Fuel Cell (SOFC) and assembled into a SOFC stack, the metal part was heated to 550 ℃ at a rate of 3 ℃ per minute in an air stream and held at that temperature for 2 hours to burn off all residual organic binder, and subsequently heated to 950 ℃ at a rate of 5 ℃ per minute in a mixed gas stream of air and nitrogen (1: 9 vol: vol), where it was held for 4 hours to form a spinel barrier on the metal surface of the cathode compartment. The SOFC cell stack is then cooled to an operating temperature (850 ℃) and connected to an electrical load.

Example 4

22APU was cleaned and a 7 μm thick layer of cobalt oxide (d) was applied by means of a slurry coating₅₀0.6 μm), dried and further coated by means of slurry coating with a 20 μm thick layer of 90 wt% LSM and 10 wt% cobalt oxide. Make itThe coated part was taken facing the cathode of a Solid Oxide Fuel Cell (SOFC) and assembled into a SOFC stack, the metal part was heated to 550 ℃ at a rate of 3 ℃ per minute in an air stream and held at that temperature for 2 hours to burn off all residual organic binder, and subsequently heated to 750 ℃ at a rate of 3 ℃ per minute in a mixed gas stream of air and nitrogen (1: 30 vol: vol), where it was held for 15 hours to form a spinel barrier layer on the metal surface of the cathode compartment. In the subsequent step, the current was allowed to flow (0.05A/cm)²) From the anode to the cathode end through the SOFC cell stack. The SOFC stack is then cooled to operating temperature (650 ℃) and connected to an electrical load while supplying air to the cathode compartment.

Example 5

Sandviken 0YC44 was cleaned and coated with a 10 μm thick layer of cobalt oxide by means of slurry coating (d)₅₀2.5 μm), dried and further coated by means of slurry coating with a 30 μm thick layer of 85 wt% LSM and 15 wt% cobalt oxide. With the coated part facing the cathode of a Solid Oxide Fuel Cell (SOFC) and assembled into a SOFC stack, the metal part was heated to 550 ℃ at a rate of 3 ℃ per minute in an air stream and held at that temperature for 2 hours to burn off all residual organic binder, and subsequently heated to 1050 ℃ under the same conditions, where it was held for 2.5 hours to form a spinel barrier on the metal surface of the cathode compartment. The SOFC cell stack is then cooled to an operating temperature (850 ℃) and connected to an electrical load.

Example 6

The metal part (ZMG232) was cleaned and coated with a 10 μm thick layer of cobalt oxide and manganese oxide (4: 1mol/mol) by means of slurry coating, dried and further coated with a 25 μm thick layer of 55 wt% LSC, 25 wt% LSC' and 20 wt% SC by means of slurry coating. With the coated part facing the cathode of a Solid Oxide Fuel Cell (SOFC) and assembled into a SOFC stack, the metal part is heated in an air stream to 550 ℃ at a rate of 3 ℃ per minute and held at this temperatureAfter 2 hours to burn off all the residual organic binder, it was heated to 850 ℃ at the same rate in a mixed gas stream of air and nitrogen (1: 100 vol: vol), where it was kept for 5 hours to form a barrier layer of spinel on the metal surface of the cathode compartment. In the following step, an alternating current (1kHz, 0.05A/cm) was applied²) Between the anode and cathode, through the SOFC cell stack. The SOFC cell stack is then cooled to an operating temperature (750 ℃) and connected to an electrical load.

Example 7

Crofer 22APU was cleaned and coated with a 5 μm thick cobalt oxide layer (d) by means of slurry coating₅₀0.6 μm), dried and further coated by means of slurry coating with a 25 μm thick layer of 75 wt% LSM, 10 wt% barium oxide, 10 wt% calcium carbonate and 5 wt% magnesium oxide. With the coated part facing the cathode of a Solid Oxide Fuel Cell (SOFC) and assembled into a SOFC stack, the metal parts are in an air stream (5.4 ml/min/cm)²Surface area) was heated to 550 c at a rate of 3 c per minute and held at that temperature for 2 hours to burn off all residual organic binder and subsequently heated to 900 c under the same conditions for 3.5 hours to form a spinel barrier on the metal surface of the cathode compartment. The SOFC cell stack is then cooled to an operating temperature (750 ℃) and connected to an electrical load.

Example 8

Sandvik 1C44Mo20 was cleaned and coated with 10 μm thick cobalt oxide and copper oxide layers (2: 1wt/wt) by means of slurry coating, dried and further coated with a 35 μm thick layer of 90 wt% LSM and 10 wt% cobalt oxide by means of slurry coating. The coated part was brought to face the cathode of the solid oxide fuel cell and assembled into a SOFC stack, the metal part was heated to 550 ℃ in an air stream at a rate of 3 ℃ per minute and held at that temperature for 2 hours to burn off all residual organic binder, and subsequently heated to 950 ℃ in an air stream at a rate of 3 ℃ per minute, where it was held for 4.5 hours to form a spinel barrier on the metal surface of the cathode compartment. The SOFC stack is then cooled to operating temperature (750 ℃) and connected to an electrical load while air is supplied to the cathode compartment.

Example 9

The ZMG232 was cleaned and coated with a 10 μm thick layer of copper oxide, manganese oxide and LSM by slurry coating (16: 4: 1mol/mol), dried and further coated with a 25 μm thick layer of copper oxide, manganese oxide and LSM by slurry coating (4: 1: 8 mol/mol). The coated part was brought to face the cathode of the solid oxide fuel cell and assembled into a SOFC stack, the metal part was heated to 550 ℃ at a rate of 3 ℃ per minute in an air stream and held at that temperature for 2 hours to burn off all residual organic binder, and subsequently heated to 950 ℃ at a rate of 5 ℃ per minute in a mixed gas stream of air and nitrogen (1: 9 vol: vol), where it was held for 4 hours to form a spinel barrier layer on the metal surface of the cathode compartment. The SOFC cell stack is then cooled to an operating temperature (850 ℃) and connected to an electrical load.

Example 10

Crofer 22APU was cleaned and coated with a 7 μm thick cobalt oxide layer by means of slurry coating (d)₅₀2.5 μm), dried and further coated with a 20 μm thick mixed layer of LSM and LSC (1: 1 w: w) by means of slurry coating. After drying, a 25 μm thick third layer of LNF was applied by slurry casting and the coated assembly was further dried. With the coated part facing the cathode of a Solid Oxide Fuel Cell (SOFC) and assembled into a SOFC stack, the metal parts are in an air stream (5.4 ml/min/cm)²Surface area) was heated to 550 c at a rate of 3 c per minute and held at that temperature for 2 hours to burn off all residual organic binder and subsequently heated to 950 c under the same conditions for 3 hours to form a spinel barrier on the metal surface of the cathode compartment. The SOFC stack was then cooled to an operating temperature (750 ℃) and connected to an electrical load at 0.25A/cm²Current of battery areaThe degradation rate was evaluated under load.

Claims (20)

1. A method of manufacturing a multilayer barrier member in a solid oxide cell stack, comprising the steps of:

providing a metal interconnection;

coating a first metal oxide layer on the metal interconnect;

coating a second metal oxide layer on the first metal oxide layer;

coating a third metal oxide layer on the second metal oxide layer;

forming a solid oxide cell stack comprising the metal interconnect having the metal oxide layer thereon; and

reacting the metal oxide in the first metal oxide layer with the metal of the metal interconnect during solid oxide stack initialization.

2. The method of claim 1, wherein the initializing step is performed at an elevated temperature of at least about 500 ℃, preferably 700 ℃ to 1100 ℃.

3. The method of claim 1 or 2, wherein the initializing step is performed under conditions of controlled atmosphere composition and current load, which depend on the composition of the layer and facilitate the formation of the desired reaction product as a dense barrier layer without chromium containing species migrating to the air electrode.

4. A method according to any one of claims 1 to 3, wherein the reaction product of the reaction between the metal oxide of the first metal oxide layer and the metal of the metal interconnect is electrically conductive and dense, preferably of spinel structure.

5. The method of any of claims 1-4, wherein the metal oxide of the first metal oxide layer and the metal oxide of the second metal oxide layer are the same.

6. A method according to any one of claims 1 to 5, wherein the first metal oxide layer comprises a mixture of metal oxides or a mixture of metal oxides and transition metal oxides having at least two different metal cations.

7. The method of claim 6, wherein the metal oxide is selected from lanthanum oxide and transition metal oxides, preferably cobalt oxide, manganese oxide, copper oxide, and mixtures thereof.

8. The method of claim 6, wherein the metal oxide having at least two different metal cations has a perovskite structure and is selected from the group consisting of doped lanthanum manganite, doped lanthanum cobaltite, doped lanthanum ferrite, and mixtures thereof.

9. The method of any of claims 1-8, wherein the second metal oxide layer comprises a metal oxide having at least two different metal cations and a mixture of metal oxides.

10. The method of claim 9, wherein the metal oxide is selected from the group consisting of alkaline earth metal oxides, preferably magnesium oxide, barium oxide, strontium oxide, calcium oxide, and transition metal oxides, preferably cobalt oxide, manganese oxide, copper oxide, lanthanum oxide, and mixtures thereof.

11. The method of claim 9, wherein the metal oxide having at least two different metal cations has a perovskite structure and is selected from the group consisting of doped lanthanum manganite, doped lanthanum cobaltite, doped lanthanum ferrite, and mixtures thereof.

12. The method of any of claims 1-11, wherein the first metal oxide layer has a thickness of about 1 to about 20 μ ι η.

13. The method of any of claims 1-12, wherein the second metal oxide layer has a thickness of about 10 to about 30 μ ι η.

14. The method of any one of claims 1-13, further comprising the step of forming a third metal oxide layer on the second metal oxide layer, wherein the metal oxide of the third layer is selected from the group consisting of doped lanthanum nickelate, nickel oxide, lanthanum manganite, doped lanthanum cobaltite, doped lanthanum ferrite, doped ceria, and mixtures thereof.

15. A multilayer barrier member produced by the method of any one of claims 1 to 14.

16. A solid oxide cell stack comprising an anode contact layer and support member, an anode layer, an electrolyte layer, a cathode contact layer, a metal interconnect, and the multilayer barrier member of claim 15.

17. The solid oxide cell stack of claim 16, wherein the multilayer barrier member is located between the electrode layer and a metal interconnect.

18. Use of a multilayer barrier according to claim 15 as a barrier in a solid oxide fuel cell or a solid oxide electrolysis cell.

19. The method of any one of claims 1 to 13, using cobalt oxide as a barrier layer precursor, wherein the initialisation of the stack is carried out at a temperature above 950 ℃.

20. Method for controlling the heating sequence and the gas phase composition, preferably the oxygen partial pressure, during the initialization of a solid oxide cell stack as claimed in claim 16 or 17, to convert the barrier layer into an electrically conductive and dense reaction product, preferably of spinel structure.