DE102006056251A1 - High temperature fuel cell with ferritic component - Google Patents

Abstract

The invention relates to a high-temperature fuel cell together with a method for operation.
It is an object of the invention to provide an efficient and long-term stable high-temperature fuel cell using ferritic material.
In order to minimize interaction between ferritic components and nickel components of an SOFC, a barrier layer is provided between the problematic components, for example between interconnector and nickel mesh or between metal substrate and anode. A barrier layer according to the invention is present when a layer is present which reduces or eliminates the interdiffusion of critical elements, especially iron, chromium and nickel. So if there is no such layer, then there is an increased interdiffusion.

Description

The The invention relates to a high-temperature fuel cell together with a Procedure for the company.

A Fuel cell is an electrochemical energy converter consisting from anode, electrolyte and cathode, the chemical energy of a fuel can convert into electrical energy without combustion process. in the Case of High Temperature Fuel Cell (SOFC) is the electrolyte material a gas-tight oxygen ion conductor. A sufficient ionic conductivity is dependent of the material and the thickness of the electrolyte between 500 ° C and 1000 ° C given. According to the current state of the art, yttrium oxide is usually stabilized Zirconia (YSZ) used. The cathode of a SOFC exists regularly out a ceramic with perovskite crystal structure. For the anode becomes usually a cermet (ceramic / metal composite) of YSZ and nickel used.

A planar design of the cells with a thin electrolyte layer of a few micrometers is advantageous in order to be able to realize high power densities with a simultaneously low operating temperature, preferably below 800 ° C. Mostly, the mechanical stability of such cells is ensured by a cermet anode substrate having a thickness of 0.3 to 2 mm. In order to achieve the required overall performance for a system, fuel cells are known by means of so-called interconnectors, for example DE102005014077A1 or the DE102005005116A1 , electrically connected in series and built into stacks (English Stocks).

A Operating temperature below 800 ° C allows the use of ferritic steels for components the SOFC. Interconnectors made of ferritic chrome steels already extensively studied and have proved suitable. Furthermore, it tries to be porous ferritic support structures in place of the established cermet anode substrates use the stability across from mechanically or thermally induced stresses. As a rule, this support structure is used on the anode side. The functional cell layers can be over thermal Coating method, physical coating method or be applied sintering technology.

If ferritic steels used in an SOFC, they are based on current concepts in direct, cohesive Contact with components containing nickel. So is known, the electrical contacting between ceramic cells and interconnectors via nickel networks to realize. Become on the anode side porous, ferritic metal substrates used, these are usually in contact with a nickel-containing Anode.

At interfaces between steel and nickel occurs disadvantageous interdiffusion in particular the elements iron, chromium and nickel are involved. However, you can also trace elements of the alloys used such as Manganese at CroFer22APU (Thyssen Krupp VDM) or impurities to be involved in the reaction.

The Interactions run both during production processes as well as during operation. Of the Contact area between an interconnector and a nickel network is subject to current concepts a high temperature cycle during the coincidence of a stick and the continuous load in operation. For the contact area between a metallic substrate and an anode is still coming a temperature load in the context of cell production added. Become the functional layers anode, electrolyte and cathode through applied thermal spraying process is this manufacturing step at high temperature only for a short time. Be the functional Layers applied by physical coating methods or by sintering, find the reactions over several hours instead.

The Interdiffusion of the elements iron, chromium and nickel has both for the ferritic Component (interconnector or metallic substrate) as well for the Nickel component (nickel mesh or nickel-containing anode) negative Consequences.

Of the Entry of nickel into the ferritic steel may increase the Oxidation rate and thus to a shortening of the oxidation-related lifetime to lead. About that In addition, from a nickel content of about 10 wt.% Austenitization of To expect steel. The associated increase in the thermal expansion coefficient leads to a Mismatch and tensions between the ceramic cell layers and the steel component. Loss of performance or complete cell failure due to cracking and consequent loss of electrical contact can to be the result.

The Diffusion of iron and chromium into nickel results in the operation of a SOFC for the formation of iron oxides and chromium oxides on free nickel surfaces or also along grain boundaries. Because the oxidation with an increase in volume goes along significant stresses are induced in a structure that too a destruction of integrity. The Formation of oxides, especially chromium oxide, on the nickel surface also leads to a passivation of the catalytically active material.

For a composite of a porous, ferri In the case of a substrate and a nickel-containing anode, interdiffusion should be regarded as particularly critical. On the one hand, the extent of the interactions is greater than in the contact area of a nickel mesh with the interconnector, because cell production already leads to a reaction. Second, the passivation of the nickel surface leads to a reduction of the catalytically active three-phase interface of an anode, which leads to high power losses during cell operation.

It Object of the invention, a powerful and long-term stable high-temperature fuel cell using ferritic steel.

Around an interaction between ferritic components and nickel components Minimizing a SOFC will create a barrier layer between the problematic components provided, so for example between Interconnector and nickel network or between metal substrate and Anode. A barrier layer according to the invention is present when a layer is present, which is the interdiffusion of critical elements, especially iron, chromium and nickel, reduces or eliminates. If there is no such layer, then there is an increased interdiffusion in front.

The barrier layer may consist of Ce _1-xy (Y, Ln) _x (Ti, Nb) _y O ₂ , (Ca, Sr, Ba) _{1-3x / 2} (Y, Ln) _x TiO ₃ , Cr ₂ O ₃ , ( Cr, Mn) ₃ O ₄ , FeO, Fe ₃ O ₄ or Ln _1-x (Sr, Ca) _x (Mg, Al, Cr) O ₃ (where: Ln = lanthanides). Typical ferritic components or steels are CroFer22APU (Thyssen Krupp VDM), IT-11 and IT-14 (Plansee) or ZMG232 (Hitachi Metals).

In an advantageous embodiment, the barrier layer is chosen so that it makes only a small contribution to the electrical resistance of the cell. The barrier layer thus consists of a material with high electronic conductivity. The area-specific, electronic conductivity of the barrier layer is therefore preferably above 200 S / cm ² .

In According to an advantageous embodiment, the barrier layer is designed so that at least on one side of the surface of the metal substrate through a thin (<10 μm), dense Film protected However, the pore network of the metal substrate is not closed becomes. Alternatively covered the barrier layer covers the pores of the metal substrate when the barrier layer itself is open-pored, so the gas passage to the anode is not is hampered.

A thin coating the particle surfaces is especially preferable to a small contribution to resistance to ensure the cell.

In particular, CeO _{2 has} proven to be suitable as the material for the barrier layer, because it effectively prevents the interdiffusion of iron, chromium and nickel, and has a higher electronic conductivity than other materials tested. Furthermore, it is thermodynamically stable throughout the temperature and oxygen partial pressure range during production and operation of the SOFC.

In one embodiment of the invention, the material of the barrier layer dopants to increase the electronic conductivity and / or adjustment of the thermal expansion coefficient of the steel component. Thus, an increase in the electronic conductivity is achieved with a doping of CeO ₂ with niobium, yttrium or samarium. A doping of CeO ₂ with gadolinium reduces the swelling behavior known under anode-side operating conditions of an SOFC, which could lead to stresses in the cell network.

In general, Ce _1-xy (Y, Ln) _x (Ti, Nb) _y O ₂ with 0 ≦ x ≦ 0.5 and 0 ≦ y ≦ 0.2 is particularly well suited as a barrier layer material, since this material is usually a particularly good Conductivity is achieved.

If the barrier layer consists of Ln _1-x (Sr, Ca) _x (Mg, Al, Cr) O ₃ with 0.1 ≤ x ≤ 0.5 (where: Ln = lanthanides) or from (Ca, Sr, Ba) _{1-3x / 2} (Y, Ln) _x TiO ₃ with 0 ≤ x _y ≤ 0.1 or 0 ≤ x _Ln ≤ 0.67 (where Ln = lanthanides), a particularly good barrier effect is achieved. By doping, the electrical conductivity can be increased and thus provide a suitable material.

If the barrier layer consists of Cr ₂ O ₃ and / or (Cr, Mn) ₃ O ₄ or of FeO and / or Fe ₃ O ₄ , the material costs are low. If very thin layers are provided, the material costs, however, play a subordinate role. In particular, more powerful materials such as CeO ₂ (doped or undoped) are to be preferred.

embodiments

• 1.) Herstellung eines pulvermetallurgischen, ferritischen Metallsubstrats
• 2.) Vorsinterung des Metallsubstrats bei 1000 °C, 3 h in Argon Atmosphäre
• 3.) CeO₂ Beschichtung mittels PVD, Magnetronsputtern (alternativ: CVD, Sol Gel Spincoating oder Infiltration, Sintern, thermisches Spritzen)
• 4.) Beschichtung mit einer NiO/YSZ oder Ni/YSZ Siebdruckschicht
• 5.) Sintern des Verbundes bei 1250 °C, 3 h in Argon Atmosphäre
• 6.) Auftrag eines thermisch gespritzten Elektrolyten (alternativ: PVD, Sol Gel, Sintern)
• 7.) Auftrag einer siebgedruckten Kathode

In a first example, a CeO ₂ diffusion barrier is formed between a ferritic metal substrate and a sintered Ni / YSZ anode as follows.

• 1.) Production of a powder metallurgical, ferritic metal substrate
• 2.) Presintering of the metal substrate at 1000 ° C, 3 h in argon atmosphere
• 3.) CeO ₂ coating by means of PVD, magnetron sputtering (alternatively: CVD, sol gel spin coating or infiltration, sintering, thermal spraying)
• 4.) Coating with a NiO / YSZ or Ni / YSZ screen printing layer
• 5.) sintering of the composite at 1250 ° C, 3 h in argon atmosphere
• 6.) Application of a thermally sprayed electrolyte (alternatively: PVD, sol gel, sintering)
• 7.) Application of a screen printed cathode

This resulted in a fuel cell with a 1 mm thick metal substrate 1 of ferritic Cr steel, a 5 μm thick CeO ₂ barrier layer 2 , a 20 μm thick Ni / YSZ anode 3 , a 60 μm thick YSZ electrolyte 4 and a 60 μm thick (LaSr) (CoFe) O ₃ cathode 5 ,

By means of the CeO ₂ diffusion barrier layer between metal substrate and Ni / YSZ anode, it was possible to produce SOFCs that achieved power densities of 430 mW / cm ² at 800 ° C and 0.7 V in a single cell test. 2 shows the measured current and voltage characteristics at the start of operation and after 165 h of continuous operation at 800 ° C and a current density of 0.3 A / cm ² . An interdiffusion of the elements iron, chromium and nickel could not be determined in a follow-up examination by scanning electron microscopy (SEM) and X-ray microanalysis (EDX).

By using the CeO ₂ diffusion barrier layer at a current density of 0.3 A / cm ² at 800 ° C operation over 165 h was possible, without there being a significant deterioration in cell performance, such as 3 clarified.

One Abandonment of the diffusion barrier layer resulted in a comparative experiment with otherwise the same structure to a complete cell failure, since it by the volume increase during the formation of iron oxides and chromium oxides in the anode to cracking came in the electrolyte.

• 1.) Herstellung eines pulvermetallurgischen, ferritischen Metallsubstrats
• 2.) Sinterung des metallischen Substrats bei zum Beispiel 1250 °C
• 3.) CeO₂ Beschichtung mittels PVD, Magnetronsputtern (alternativ: CVD, Sol Gel, Sintern, thermisch Spritzen)
• 4.) Thermisches Spritzen einer NiO/YSZ oder Ni/YSZ Anode
• 5.) Thermisches Spritzen eines Elektrolyten
• 6.) Thermisches Spritzen einer Kathode

In another embodiment, a CeO ₂ diffusion barrier is formed between a ferritic metal substrate and a thermally sprayed Ni / YSZ anode as follows:

• 1.) Production of a powder metallurgical, ferritic metal substrate
• 2.) sintering of the metallic substrate at, for example, 1250 ° C
• 3.) CeO ₂ coating by means of PVD, magnetron sputtering (alternatively: CVD, sol gel, sintering, thermal spraying)
• 4.) Thermal spraying of a NiO / YSZ or Ni / YSZ anode
• 5.) Thermal spraying of an electrolyte
• 6.) Thermal spraying of a cathode

• 1.) Fertigung einer SOFC
• 2.) Fertigung eines ferritischen Interkonnektors
• 3.) CeO₂ Beschichtung des Interkonnektors mittels PVD, Magnetronsputtern (alternativ: CVD, SolGel, Sintern, thermisch Spritzen)
• 4.) Kontaktierung zwischen der SOFC und dem Interkonnektor mit einem Nickel Kontaktelement (Netz, Gewebe, Gestrick, Pulver)

In a further embodiment, a CeO ₂ diffusion barrier between a ferritic interconnector and a nickel contact element to the ceramic cell is produced as follows:

• 1.) Production of a SOFC
• 2.) Production of a ferritic interconnector
• 3.) CeO ₂ coating of the interconnector by means of PVD, magnetron sputtering (alternatively: CVD, SolGel, sintering, thermal spraying)
• 4.) contacting between the SOFC and the interconnector with a nickel contact element (mesh, fabric, knitted fabric, powder)

The features of a high temperature fuel cell (SOFC) mentioned in the introduction to the description can in principle also be features of the present invention.

Claims (13)

High-temperature fuel cell with a ferritic component ( 1 ) and a nickel component ( 3 ) and an intermediate barrier layer ( 2 ). High temperature fuel cell according to claim 1, wherein the barrier layer consists of CeO ₂ . High-temperature fuel cell according to claim 1 or 2, wherein the barrier layer with yttrium, gadolinium niobium or samarium is doped. High-temperature fuel cell according to claim 1, 2 or 3, the barrier layer being thinner, preferably denser Film covered on at least one side of the ferritic component. High-temperature fuel cell according to one of the preceding Claims, wherein the barrier layer is not thicker than 10 microns, preferably thinner than 2 μm. High temperature fuel cell according to one of the preceding claims, wherein the ferritic component is a porous metallic substrate ( 1 ) and the nickel component is an anode ( 3 ). High-temperature fuel cell according to one of the preceding Claims, wherein the ferritic component is an interconnector and the Nickel component is a nickel network. A high-temperature _{fuel cell} according to any one of the preceding claims, wherein the barrier _layer of (Ca, Sr, Ba) _{1-3x / 2} (Y, Ln) _x TiO ₃ with 0 ≤ x _y ≤ 0.1 and 0 ≤ x _Ln ≤ 0.67 (where Ln = lanthanides). High-temperature fuel cell according to one of the preceding claims, wherein the barrier layer consists of Cr ₂ O ₃ and / or (Cr, Mn) ₃ O ₄ . High-temperature fuel cell according to one of the preceding claims, wherein the barrier layer consists of FeO and / or Fe ₃ O ₄ . High-temperature fuel cell according to one of the preceding claims, wherein the barrier layer of Ce _1-xy (Y, Ln) _x (Ti, Nb) _y O ₂ with 0 ≤ x ≤ 0.5 and 0 ≤ y ≤ 0.2 (where: Ln = Lanthanides). The high-temperature fuel cell according to claim 1, wherein the barrier layer consists of Ln _1-x (Sr, Ca) _x (Mg, Al, Cr) O ₃ with 0.1 ≤ x ≤ 0.5 (where Ln = lanthanides). Method for operating a high-temperature fuel cell according to one of the preceding claims, characterized that the high-temperature fuel cell does not open during operation Temperatures of more than 800 ° C is heated.