TWI566461B - Coatings for sofc metallic interconnects - Google Patents

Description

Coating for solid oxide fuel cell (SOFC) metal interconnects Related application

The present application claims US Provisional Application No. 13/409,629, filed on March 1, 2012, US Provisional Application No. 61/605,309, filed on March 1, 2012, and US Provisional Application, filed on September 18, 2012 The rights of Case No. 61/702,397, which are hereby incorporated by reference in their entirety.

The present invention relates to fuel cell stack assemblies, and more particularly to interconnects and methods of making interconnects for fuel cell stacks.

A typical solid oxide fuel cell stack includes a plurality of fuel cells separated by metal interconnects (ICs) that are adjacent to the cells in the stack and channels for transferring and removing fuel and oxidant. An electrical connection is provided. The metal interconnects are usually composed of a Cr-based alloy, such as CrF (95% by weight Cr-5 wt% Fe) or Cr-Fe-Y (composition 94 wt% Cr-5 wt% Fe-1 weight) % Y) alloy. CrF and CrFeY alloys maintain their strength and are dimensionally stable under typical solid oxide fuel cell (SOFC) operating conditions, such as 700-900 ° C in both air and wet fuel atmospheres. However, during operation of the SOFC, chromium in the CrF or CrFeY alloy reacts with oxygen and forms chromium oxide, resulting in degradation of the SOFC stack.

Two of the major degradation mechanisms affecting the SOFC stack are directly related to the formation of chromium oxide in the metal interconnect component: i) Stacked ohmic resistors due to the formation of natural chromium oxide (chromium oxide, Cr ₂ O ₃ ) on the interconnect Higher, and ii) SOFC cathode chromium poisoning.

Although Cr ₂ O ₃ is an electron conductor, the conductivity of this material at the SOFC operating temperature (700-900 ° C) is extremely low, and the value at 850 ° C is about 0.01 S/cm (7.9 × 10 relative to Cr metal). ⁴ Scm ^-1 ). The thickness of the chromium oxide layer on the surface of the interconnect increases with time, and thus the ohmic resistance of the interconnect and thus the oxide layer produced by the oxide layer on the SOFC stack increases over time.

The second degradation mechanism associated with the formation of metal interconnects with chromium oxide is known as cathode chromium poisoning. At the SOFC operating temperature, the chromium vapor diffuses through the cracks or pores in the coating, and the chromium ions can diffuse through the lattice of the interconnect coating material into the SOFC cathode via solid state diffusion. In addition, during operation of the fuel cell, ambient air (wet air) flows through the air (cathode) side of the interconnect and wet fuel flows through the fuel (anode) side of the interconnect. At the operating temperature of the SOFC and in the presence of humid air (cathode side), the chromium on the surface of the Cr ₂ O ₃ layer on the interconnect reacts with water and the chromium oxide hydroxide CrO ₂ (OH) ₂ forms of evaporation. The chromium oxide hydroxide material is transported in vapor form from the surface of the interconnect to the cathode electrode of the fuel cell where it can be deposited in solid form Cr ₂ O ₃ . The deposition of Cr ₂ O ₃ on the SOFC cathode or in the SOFC cathode (eg, via grain boundary diffusion) and/or reaction with the cathode (eg, formation of Cr-Mn spinel) results in a significant degradation in the performance of the cathode electrode. Typical SOFC cathode materials, such as perovskite materials such as LSM, LSC, LSCF, and LSF, are particularly susceptible to degradation by chromium oxide.

One embodiment relates to a coated interconnect for a solid oxide fuel cell comprising an interconnect substrate comprising iron and chromium and a manganese oxide cobalt spinel formed on the air side of the interconnect substrate Coating, as well as its manufacturing and processing methods. The manganese oxide cobalt spinel coating comprises a composition of the (Mn,Co) ₃ O ₄ family between the final composition of Co ₃ O ₄ and Mn ₃ O ₄ .

One embodiment relates to a method of coating an interconnect for a solid oxide fuel cell, comprising providing an interconnect substrate comprising Cr and Fe, and using a plasma jet process The air side of the interconnect substrate is coated with a manganese oxide cobalt spinel coating.

Another embodiment relates to a coated interconnect for a solid oxide fuel cell comprising an interconnect substrate comprising at least 70% by weight chromium and manganese oxide cobalt formed on the air side of the interconnect substrate A spinel coating wherein the spinel has a Co:Mn atomic ratio of at least 1:3.

Another embodiment relates to a coated interconnect for a solid oxide fuel cell comprising an interconnect substrate comprising iron and chromium, and a manganese oxide cobalt spinel formed on the air side of the interconnect substrate A stone coating, a manganese-cobalt-chromium intermediate spinel layer between the spinel coating and the air side of the interconnect substrate, and a perovskite layer on the spinel coating.

Another embodiment is directed to a coated interconnect for a solid oxide fuel cell. The interconnect includes an interconnect substrate comprising iron and chromium and a composite spinel and perovskite coating formed on the air side of the interconnect substrate. In one aspect, the spinel phase comprises manganese oxide cobalt spinel and the perovskite phase comprises barium manganate.

Another embodiment is directed to a method of fabricating an interconnect for a solid oxide fuel cell, comprising forming a manganese oxide cobalt spinel coating on the air side of the interconnect, but on the air side of the interconnect Except for at least one sealing zone.

Another embodiment is directed to a method of fabricating an interconnect for a solid oxide fuel cell, comprising coating a silicon side of a Cr-Fe interconnect with a ceramic layer to form a native oxidation on the fuel side of the interconnect The chromium layer deposits a material containing nickel on the natural chromium oxide layer and diffuses the nickel into the natural chromium oxide layer to form a nickel metal-chromium oxide composite layer.

Another embodiment is directed to a method of fabricating an interconnect for a solid oxide fuel cell, comprising coating a gas side of an interconnect with a ceramic layer to form natural chromium oxide on a fuel side of the interconnect, and The interconnect is annealed at a temperature of at least 900 ° C in an atmosphere having an oxygen partial pressure of 10 ^-16 to 10 ^-24 atm to reduce or remove the native chromium oxide layer.

Another embodiment is directed to a method of making an interconnect for a solid oxide fuel cell, comprising providing an interconnect comprising a compact mixture of Cr powder and Fe powder, The material layer comprising the ceramic powder coats the air side of the interconnect and the green mixture of the Cr powder and the Fe powder and the ceramic powder layer are sintered in the same sintering step.

Another embodiment is directed to a method of fabricating an interconnect for a solid oxide fuel cell, comprising providing an interconnect comprising Cr and Fe, comprising MnO, CoO, Mn metal, Co metal, and combinations thereof One or more of the manganese oxide cobalt precursors coat the interconnect and sinter the manganese oxide cobalt precursor to form a manganese oxide cobalt spinel coating.

Another embodiment relates to a coated interconnect for a solid oxide fuel cell comprising an interconnect substrate comprising iron and chromium, and a manganese oxide cobalt tip formed on the air side of the interconnect substrate Spar coating. The manganese oxide cobalt spinel coating comprises a composition of the (Mn,Co) ₃ O ₄ family between the final composition of Co ₃ O ₄ and Mn ₃ O ₄ , wherein Mn; atomic ratio of Co 5:1.

Another embodiment relates to a coated interconnect for a solid oxide fuel cell comprising an interconnect substrate comprising iron and chromium, and a manganese oxide cobalt tip formed on the air side of the interconnect substrate Spar coating. The manganese oxide cobalt spinel coating additionally comprises at least one of iron, titanium, vanadium, chromium, aluminum, manganese, calcium, strontium, and/or cerium.

Another embodiment relates to a coated interconnect for a solid oxide fuel cell comprising an interconnect substrate comprising iron and chromium, manganese oxide cobalt spinel formed on the air side of the interconnect substrate A stone coating, and a barrier layer between the interconnect substrate and the manganese oxide cobalt spinel coating.

Another embodiment is directed to a method of fabricating a coated interconnect for a solid oxide fuel cell, comprising forming a reactive layer and a cobalt manganese cobalt spinel layer on the interconnect, and allowing the dopant to self The reaction layer diffuses into the manganese oxide cobalt spinel layer.

Another embodiment is directed to a method of fabricating a coated interconnect for a solid oxide fuel cell, comprising forming an interconnect comprising Fe, Cr, and a dopant, coated with a layer of manganese oxide cobalt spinel The interconnect is covered and the dopant is diffused from the interconnect into the manganese oxide cobalt spinel layer.

Another embodiment is directed to a method of fabricating a coated interconnect for a solid oxide fuel cell, comprising providing an interconnect comprising a ferrochrome alloy, removing the air side rather than the fuel side of the interconnect a natural chromium oxide, coating the air side of the interconnect with a layer of manganese oxide cobalt spinel, and forming a second natural chromium oxide on the fuel side of the interconnect and removing the second from the fuel side of the interconnect Natural oxides.

Another embodiment is directed to a method of fabricating an interconnect for a solid oxide fuel cell, comprising providing an interconnect comprising Cr and Fe, and coating the interconnect with a ceramic layer using an air plasma spray process. The ceramic layer includes a sintering aid.

Another embodiment is directed to a method of fabricating an interconnect for a stack of solid oxide fuel cells, comprising providing a first metal powder particle comprising Cr and Fe in a cavity, and providing Sr, La in a cavity a second powder particle of one or more of Mn and Co oxides, and compacting the first powder particles and the second powder particles to form an interconnect.

Another embodiment relates to a coated interconnect for a solid oxide fuel cell comprising an interconnect substrate comprising iron and chromium; manganese oxide cobalt spinel formed on the air side of the interconnect substrate a stone coating, wherein the manganese oxide cobalt spinel coating further comprises at least one of nickel and copper; and manganese and chromium between the manganese oxide cobalt spinel coating and the air side of the interconnect substrate An oxide intermediate spinel layer; and a perovskite layer on the manganese oxide cobalt spinel coating.

1‧‧‧Battery

3‧‧‧Anode electrode/anode/fuel electrode

5‧‧‧Solid oxide electrolyte

7‧‧‧Cathode/Cathode/Air Electrode

8‧‧‧Air passage or passage/fuel passage/air passage

9‧‧‧Interconnects

10‧‧‧ ribs

11‧‧‧LSM Coating/Metal Oxide Layer/Layer

13‧‧‧One side of the interconnect

14‧‧‧ opposite sides of the interconnect

15‧‧‧ Sealing part / ring seal part / glass seal part

16A‧‧‧Fuel inlet opening/hole/lift tube opening/opening

16B‧‧‧Fuel outlet opening/hole/lift tube opening/opening

17‧‧‧ Flat Zone/Fuel Dispensing Inflator/District

18‧‧‧Window seal

19‧‧‧Strip seal/seal/glass seal

25‧‧‧Green Cr ₂ O ₃ oxide thin layer / Cr ₂ O ₃ oxide layer / oxide layer / layer

36‧‧‧Fuel inlet riser

100‧‧‧Interconnects

101‧‧‧Intermediate oxide layer/intermediate layer/layer/intermediate spinel layer/interface spinel layer

102‧‧‧MCO spinel layer/MCO spinel coating/MCO coating/coating

103‧‧‧ crack / micro crack

104‧‧‧LSM Interconnect Coating/LSM IC Coating/LSM Coating/Perovskite Layer/Second Perovskite Barrier Layer/Layer/Composite Coating

105‧‧‧ Spinel phase/chromium crystal

110‧‧‧Composite LSM/MCO coating/composite coating

112‧‧‧Debut/LSM phase matrix/perovskite phase

114‧‧‧Dark phase/spinel phase/plate or flat structure

200‧‧‧ cavity

202‧‧‧Cr/Fe powder/powder

204‧‧‧Coating material powder/powder/coated powder/coating material

206‧‧‧Second column foot

208‧‧‧ punch

Figure 1A is a photomicrograph showing the Mn-Cr spinel phase inside the pores of a LSM based cathode.

Figure 1B is a photomicrograph showing the phase of Cr in the crack of the LSM interconnect coating deposited by air plasma spray. The SOFC stack was operated at 850 ° C for 2000 hours.

2A is a side view illustration of an embodiment of an interconnect having a spinel MCO coating and a lower interfacial oxide. 2B illustrates a photomicrograph of a as-deposited APSMn _1.5 Co _1.5 O ₄ coating, in accordance with one embodiment.

Figure 2C illustrates the voltage vs. time curve of a SOFC stack tested in dry air comparing the rate of degradation of repeating elements with LSM and repeating elements with Mn _1.5 Co _1.5 O ₄ spinel interconnect coating.

Figure 2D illustrates the voltage versus time curve for a SOFC stack tested in wet air comparing duplicates of LSM, Mn _1.5 Co _1.5 O ₄ spinel and double layer LSM-Mn _1.5 Co _1.5 O ₄ interconnect coatings The rate of degradation of the component.

2E and 2F respectively show photomicrographs of Mn _1.5 Co _1.5 O ₄ spinel coating and LSM perovskite coating after 1000 hours of SOFC stacking operation.

3A-3C are illustrations of steps in a method of fabricating an interconnect in accordance with one embodiment.

4 is another illustration of a method of fabricating an interconnect in accordance with one embodiment.

Figure 5 is a graph showing the increase in surface specific resistance (ASR) over time for doped and undoped interconnects.

Figure 6A is a side elevational illustration of one embodiment of an interconnect having a two-layer composite coating. 6B is a side view illustration of one embodiment of a solid oxide fuel cell stack including interconnects having a double layer coating on the ribs.

Figures 7A-7C are diagrams illustrating the following: (A) an air side of an interconnect according to one embodiment, (B) a close-up view of the air-side sealing portion of the interconnect, and (C) an interconnect Fuel side.

Figure 8 is a photomicrograph illustrating chromium oxide on the fuel side (uncoated side) of the interconnect after the reduction sintering step.

Figure 9 is a photomicrograph of a portion of a SOFC stack illustrating the reduction of the MCO coating (in the strip seal region) at the coating/IC interface due to diffusion of fuel through the porous IC.

Figure 10 is a phase diagram illustrating the Mn ₃ O ₄ -Co ₃ O ₄ system.

Figure 11 is a graphical illustration of a fuel inlet riser tube in a conventional fuel cell stack.

Figure 12 is a graphical illustration of a SOFC illustrating the theory of electrolyte corrosion.

Figure 13 is a photomicrograph illustrating one embodiment of an interconnect having a composite LSM-MCO coating.

To limit the diffusion of chromium ions (e.g., Cr3 ⁺ ) through the interconnect coating material to the SOFC cathode, materials having very few cationic vacancies and therefore low chromium diffusivity can be selected. A series of materials with low cation diffusivity in the perovskite family, such as cerium oxide, such as La _1-x Sr _x MnO ₃ (LSM), of which 0.1 x 0.3, such as 0.1 x 0.2. These materials have been used as interconnect coating materials. In the case of LSM, the material has high electron conductivity with low anion and cation diffusion.

The second function of the interconnect coating is to inhibit the formation of natural oxides on the surface of the interconnect. A natural oxide is formed when oxygen reacts with chromium in the interconnect alloy to form a relatively high resistance Cr ₂ O ₃ layer. Oxide growth kinetics can be reduced if the interconnect coating inhibits the transport of oxygen and water vapor from the air to the interconnect surface.

Similar to chromium, oxygen (e.g., O2 ^- ion) can be transported through the coating via solid state diffusion or by gas transport through pores and cracks in the coating. This mechanism can also be used to transport water vapor by air, which is an accelerator for the evaporation of Cr and the possible growth of oxides. As discussed above, in a humid air environment, chromium evaporates from the surface of Cr ₂ O _{3 in the} form of gas molecules CrO ₂ (OH) ₂ and can subsequently diffuse through defects (such as pores and cracks) in the coating. In the case of oxygen and water vapor, depending on the size of the defect or pore, the molecule diffuses through the defect by bulk diffusion or by a Knudsen diffusion process.

If the CrO ₂ (OH) ₂ molecule contacts the surface of the coating, it can react to form crystals, which are then evaporated to continue to diffuse into the gas stream (in cracks or pores). Experiments have shown that CrO ₂ (OH) ₂ reacts with the LSM interconnect coating 104 to form a spinel phase 105, such as manganese oxide chromium (Mn, Cr) ₃ O ₄ , as shown in Figure 1A. Although CrO ₂ (OH) ₂ reacts with LSM to form a spinel phase, it does not prevent the chromium species from re-evaporating and further spreading along cracks or defects. It has been observed that chromium is transported along the length of the crack in the LSM IC coating, which has been operating in the fuel cell for a longer period of time. 1B shows the chromium crystals 105 in the cracks 103 in the LSM IC coating 104 operating at 800-850 ° C in the SOFC stack at 2000-850 ° C under normal conditions for ambient air on the cathode side. The crystal containing chromium is formed as a feature formed by vapor phase-solid phase conversion. SEM and EDS analysis of the LSM coating away from the crack did not show the presence of chromium. Thus, it can be inferred that most of the chromium transport from the CrF interconnect passes through the LSM IC coating, which is transported through the vapor phase and along the microcracks and large cracks in the LSM coating, intraparticle spacing, and pore transport.

In the case of solid state transport, materials having very few oxide ion vacancies and therefore low oxide ionic conductivity are selected. For example, perovskite LSM is unique in that it exhibits low cation and anion conductivity with high electron conductivity, making it an excellent coating material. Other perovskites such as La _1-x Sr _x FeO _3-d , La _1-x Sr _x CoO _3-d and La _1-x Sr _x Co _1-y Fe _y O _3-d exhibit high electron conductivity And low cation conductivity (low chromium diffusion rate). However, such specific materials also exhibit high oxide ionic conductivity and are therefore less effective in protecting the interconnect from oxidation (oxide growth).

A second family of materials that can be used for interconnect coatings are manganese oxide cobalt (MCO) spinel materials. 2A illustrates a MCO spinel layer 102 on the air side of a chromium containing interconnect 100. The MCO spinel layer 102 can have the formula: (M1, M2) ₃ O _{4 ± 0.1} , wherein M1 accounts for at least 70 atom%, such as 70-100 atom% manganese, and M2 accounts for at least 70 atom%, such as 70-100. Atomic % cobalt. M1 and/or M2 may contain other elements as described below with respect to subsequent embodiments. The MCO spinel covers the composition range of M1 ₂ M2 ₁ O _4±0.1 to M2 ₂ M1 ₁ O _4±0.1 .

In one embodiment, M1 consists of Mn (and unavoidable impurities (if present) and M2 consists of Co (and unavoidable impurities (if present)) and the spinel is stoichiometric (ie metal) The atomic ratio to oxygen is 3:4).

In one embodiment, the MCO spinel encompasses a compositional range of Mn ₂ CoO ₄ to Co ₂ MnO ₄ . That is, a composition having Mn _2-x Co _1+x O ₄ (0) can be used. x 1) or write z(Mn ₃ O ₄ )+(1-z)(Co ₃ O ₄ ) (of which (1/3 z 2/3)) or write any spinel of (Mn, Co) ₃ O ₄ , such as Mn _1.5 Co _1.5 O ₄ , MnCo ₂ O ₄ or Mn ₂ CoO ₄ . Many transition metal-containing spinels exhibit good electronic conductivity and relatively low anion and cation diffusivity, and are therefore suitable coating materials.

The spinel composition preferably contains at least 25 atomic percent cobalt oxide, such as 25 atomic percent to 60 atomic percent cobalt oxide. Another way of expression is that the atoms of Co and Mn in the spinel are preferably at least 1:3, such as 1:3 to 6:4, preferably 1:1. Thus, a preferred, but non-limiting, spinel composition is Mn _1.5 Co _1.5 O ₄ which comprises 50 atomic percent manganese oxide and 50 atomic percent cobalt oxide. The MCO coating 102 can have any suitable thickness, such as from 20 to 100 microns, preferably greater than 20 microns, such as from 25 to 40 microns.

Any suitable chromium-containing interconnect substrate 100 can be used. The substrate 100 is preferably a chromium-based alloy such as an alloy containing at least 70% by weight chromium, such as 92% to 97% by weight chromium, 3% to 7% by weight iron, and optionally 0 to 1 weight. %钇, yttria, other alloying elements and/or unavoidable impurities. The substrate 100 preferably contains a so-called CrF alloy (for example, 95% by weight of Cr and 5% by weight of Fe). The surface of the alloy and/or its entire volume may be oxidized such that the substrate contains a layer of chromium oxide and/or iron oxide on its surface or contains an oxide region in its volume. However, other suitable substrate 100 materials may alternatively be used, such as nicrofer, Inconel 600 or X750, Crofer 22 APU or other chromium-containing stainless steel.

As shown in FIG. 2A, the interconnect may contain an intermediate (ie, interfacial) oxide layer 101 between the substrate 100 and the MCO spinel coating 102. The intermediate oxide layer 101 may comprise a native chromium oxide layer on the CrF interconnect substrate 100 and/or the intermediate oxide layer 101 may comprise an intermediate spinel layer comprising Cr, Mn, O and optionally Co. For example, the intermediate oxide layer 101 can include the MCO coating 102 and the chromium-containing layer during high temperature operation or stack annealing of the SOFC stack to melt the sealing portion or reduce the nickel oxide in the cermet SOFC anode electrode to nickel. The substrate 100 reacts to form a (Mn, Cr, Co) ₃ O ₄ spinel layer, as described below. The intermediate layer 101, if present, can have a thickness of 5 microns or less, such as from 1 to 5 microns.

The MCO coating 102 is deposited on the interconnect substrate 100 using any suitable deposition method. The coating 102 is preferably deposited by a plasma jet process, such as an air plasma jet (APS) process. In the plasma jet process, the raw material powder is introduced into a plasma jet or spray from a plasma source such as a plasma torch. The raw material powder is melted in the plasma jet (where the temperature exceeds 8,000 K) and is advanced to the interconnect substrate 100. Here, the molten droplets flatten, rapidly solidify and form the MCO spinel coating 102. The raw material powder preferably comprises the same MCO powder as the coating 102. However, a metal (eg, Mn, Co or Mn-Co alloy) powder may alternatively be used and subsequently oxidized to form the MCO spinel coating 102.

The plasma may be generated by direct current (e.g., arc DC plasma) or by induction (e.g., by providing a plasma jet through the center of the induction coil while RF alternating current is passed through the coil). The plasma may comprise a gas stable plasma (e.g., argon, helium, etc.). The plasma jet is preferably an air plasma jet (APS) performed in ambient air. Alternatively, a controlled atmosphere plasma jet (CAPS) process performed in a closed chamber filled with an inert gas or evacuated may be used.

The native oxide layer is preferably removed from the interconnect substrate 100 prior to deposition of the coating. For example, the native chromium oxide layer can be removed from the CrF substrate 100 by grinding, polishing, sandblasting, etching, or other suitable method prior to deposition of the MCO coating 102 such that the native chromium oxide is substantially absent prior to deposition of the MCO coating. Will be re-formed. 2B is a photomicrograph illustrating a deposited state Mn _1.5 Co _1.5 O ₄ coating 102 on interconnect 100 after removal of the native chromium oxide layer. The Mn _1.5 Co _1.5 O ₄ coating 102 exhibits good density as well as some porosity and micro-cracks.

A flat SOFC stack containing some interconnects coated with a Mn _1.5 Co _1.5 O ₄ coating and some interconnects with LSM coatings was tested to obtain a head-to-head comparison of the coating. The results of these tests are illustrated in Figures 2C and 2D. 2C and 2D are voltage versus time curves for two different SOFC stacks comprising interconnects 100 coated with Mn _1.5 Co _1.5 O ₄ and LSM coated interconnects 100. The results shown in Figure 2C are the stacks tested in dry air, while the results shown in Figure 2D are the stacks tested in wet air. In both cases, the rate of degradation of the repeating layer with the Mn _1.5 Co _1.5 O ₄ coating was significantly lower than that of the repeating layer with the LSM coating.

In the case of a dry air test (Fig. 2C), the Mn _1.5 Co _1.5 O ₄ coating exhibited a lower ASR degradation relative to the LSM coating. The lower resistivity of the Cr spinel layer 101 doped with Mn and Co such that the interconnect coated with Mn _1.5 Co _1.5 O ₄ is relative to the LSM coated interconnect (and its adjacent SOFC cathode electrode) With lower interconnects and adjacent SOFC cathode electrodes degraded. The electrical resistance of the intermediate chromium-containing oxide layer depends on both the thickness of the intermediate oxide layer and the electrical conductivity of the oxide layer. The coating affects the resistance of the oxide layer in two ways: i) reducing the growth rate of the oxide layer and thus reducing its thickness at a given time, and ii) reacting with the oxide layer to produce a second composition having a different composition and conductivity. Oxide phase.

The MCO coating 102 acts as a barrier layer that inhibits the diffusion of oxygen from the gas stream to the intermediate oxide layer 101 on the interconnect substrate 100. This in turn reduces the growth rate of the native chromium oxide layer and/or the intermediate spinel layer 101. Coatings that effectively reduce the transport of oxygen from the gas stream to the natural oxide include materials that exhibit low oxygen diffusivity (solid diffusion of oxide ions), such as the spinel phase. The physical characteristics of a good protective coating include high density, low connectivity porosity, no micro cracks, and complete coverage of the interconnect.

The coating 102 also affects the electrical resistance of the natural oxide by interdiffusion and formation of a secondary phase. The oxide layer formed on the uncoated CrF interconnect is a natural oxide Cr ₂ O ₃ . This oxide exhibited a conductivity of about 0.01 S/cm at 850 °C. However, for the coating on the interconnect, a reaction occurs between the natural Cr ₂ O ₃ oxide and the coating material. This reaction forms a reaction zone oxide layer with a conductivity different from that of the Cr ₂ O ₃ natural oxide or coating material.

In the case of a CrF interconnect coated with LSM, the resulting reaction zone oxide layer is in the spinel family (Mn, Cr) ₃ O ₄ . The conductivity of (Mn,Cr) ₃ O ₄ spinel depends on the composition, and the examples provided are as follows: at 800 ° C, MnCr ₂ O ₄ 0.003 S/cm, Mn _1.2 Cr _1.8 O ₄ 0.02 S/cm and Mn _1.5 Cr _1.5 O ₄ 0.07 S/cm.

In general, the conductivity of (Mn,Cr) ₃ O ₄ spinel is slightly better than that of natural Cr ₂ O ₃ . However, the thickness of the oxide in the reaction zone can be thicker than the native oxide. Therefore, the total ohmic resistance can be large. For the Mn _1.5 Co _1.5 O ₄ spinel coating on the CrF material, the reaction zone intermediate oxide layer 101 comprises a (Mn, Cr, Co) ₃ O ₄ spinel phase. Layer 101 may comprise from 60 to 100 volume percent (Mn, Cr, Co) ₃ O ₄ spinel phase, with the remainder, if present, being chromium oxide or other phase. The conductivity of the cobalt-containing (Mn, Cr, Co) ₃ O ₄ family of spinel is significantly higher than that of the (Mn,Cr) ₃ O ₄ spinel provided by the following examples: MnCo ₂ O ₄ : 36 S /cm, CoCr ₂ O ₄ : 7 S/cm, and CoMn ₂ O ₄ : 6 S/cm. The higher conductivity of the oxide of the reaction zone formed by the Mn _1.5 Co _1.5 O ₄ spinel coating on CrF, which preferably has an electrical conductivity of at least 20 S/cm, such as at least 38 S/cm, thereby The ohmic resistance loss caused by the interface is low and thus the SOFC performance is degraded over time.

The rate of evaporation of chromium from the interconnect surface is relatively high in a humid air atmosphere and at SOFC operating temperatures. Therefore, the containment resistance caused by the coating is preferred. The results of the SOFC stack tested in wet air are illustrated in Figure 2D. These results also show that the repeating layer with the Mn _1.5 Co _1.5 O ₄ spinel coating exhibits a lower degradation compared to the repeating layer with the LSM coating.

The lower degradation of the Mn _1.5 Co _1.5 O ₄ spinel coating can be attributed to the following two: i) lower ohmic resistance of the oxide layer of the reaction zone, and ii) reduced evaporation rate of chromium. 2E shows a photomicrograph of a Mn _1.5 Co _1.5 O ₄ coating 102 on a CrF substrate 100 after 1000 hours of operation in a SOFC stack (described below) at high operating temperatures. 2F shows a photomicrograph of the LSM coating 104 on the CrF substrate 100 in a SOFC stack operating at high operating temperatures for 1000 hours. As is apparent from the photomicrograph, the Mn _1.5 Co _1.5 O ₄ coating 102 is dense, has no open pores and does not have microcracks 103. This is in contrast to the LSM coating 104 with micro-cracks after SOFC operation.

The LSM coating 104 tends to sinter during operation of the SOFC, resulting in the formation of microcracks 103 that allow chromium vapor to pass through the coating. A comparison of FIG. 2B with FIG. 2E indicates that although the as-deposited APS coating of Mn _1.5 Co _1.5 O ₄ shown in FIG. 2B may contain some micro-cracks and cracks, a section at the SOFC operating temperature (eg, 700 to 900 ° C) After the time, the MCO coating appeared to densify in the manner shown in Figure 2F, thereby repairing and eliminating the connected microcracks. Likewise, the intermediate chrome-containing spinel layer 101 is formed by a reaction between the MCO coating 102 and the CrF interconnect substrate 100 during operation during stack fabrication annealing and/or during stacking at elevated temperatures.

In one embodiment, a spinel powder such as (Mn,Co) ₃ O ₄ is doped with Cu to reduce the melting temperature of the spinel. The lower melting temperature improves (improves) the coating density after deposition using a coating process such as air plasma jet (APS) and increases the conductivity of the oxide in the reaction zone. Improvements in coating density due to lower melting temperatures can occur during APS deposition and during long-term operation at SOFC temperatures.

Adding Cu to the spinel layer has another advantage. The Cu doping of a spinel such as (Mn,Co) ₃ O ₄ can make the basic spinel phase and the conductivity of any reaction zone oxide formed between the spinel and the natural Cr ₂ O ₃ oxide. high. Examples of the electrical conductivity of the oxide of the (Mn, Co, Cu, Cr) ₃ O ₄ family include: CuCr ₂ O ₄ : 0.4 S/cm at 800 ° C, Cu _1.3 Mn _1.7 O ₄ : 225 S at 750 ° C / Cm, and CuMn ₂ O ₄ : 40 S/cm at 800 °C.

The material of the spinel family has the general formula AB ₂ O ₄ . Depending on the elements occupying the A and B sites, these materials can form octahedral or cubic crystal structures. In addition, depending on the doping conditions, the copper atom may occupy the A site, the B site, or a combination of the A site and the B site. In general, Cu preferentially enters the B site. When the A element is Mn, the B element is Co and the spinel is doped with Cu, the spinel family can be described by the general formula (Mn, Co, Cu) ₃ O ₄ . More specifically, depending on the location of the Cu alloying elements, the spinel family can be described by the following formula:

(1) If Cu enters the A site, it is Mn _2-xy Co _1+x Cu _y O ₄ (0) x 1), (0 y 0.3)

(2) If Cu enters the B site, it is Mn _2-x Co _1+xy Cu _y O ₄ (0 x 1), (0 y 0.3)

(3) If Cu enters the A site and the B site equally, it is Mn _2-xy/2 Co _1+xy/2 Cu _y O ₄ (0) x 1), (0 y 0.3).

The specific (Mn, Co, Cu) ₃ O ₄ composition includes, but is not limited to, Mn _1.5 Co _1.2 Cu _0.3 O ₄ , Mn _1.5 Co _1.4 Cu _0.1 O ₄ , Mn ₂ Co _0.8 Cu _0.2 O ₄ and Co ₂ Mn _0.8 Cu _0.2 O ₄ . If Cu enters the B site, the other composition includes Mn ₂ Co _1-y Cu _y O ₄ , where (0 y 0.3). These compositions can also be written as (Mn ₂ O ₃ )+(1-z)(CoO)+z(CuO), where (0 z 0.3). If Cu enters the B site, the other composition includes Co ₂ Mn _1-y Cu _y O ₄ , where (0 y 0.3). These compositions can also be written as (Co ₂ O ₃ )+(1-z)(MnO)+z(CuO), where (0 z 0.3). In a preferred Mn, Co spinel composition, the Mn/Co ratio is 1.5/1.5, such as Mn _1.5 Co _1.5 O ₄ . When the B site is doped with Cu, the preferred composition includes Mn _1.5 Co _1.5-y Cu _y O ₄ , where (0 y 0.3).

In another embodiment, the (Mn,Co) ₃ O ₄ or (Mn,Co,Cu) ₃ O ₄ spinel family is doped with one or more monovalent species. That is, one or more substances having only one valence state. Doping with a monovalent species reduces cation transport at elevated temperatures and thus reduces the thickness of the intermediate oxide layer 101. The primary ion transport mechanism in spinels is the diffusion of cations through cation vacancies in the crystal lattice structure. In spinels with multivalent species M ^2+/3+ (such as Mn ^3+/4+ and Co ^2+/3+ ), when substance M is oxidized from a lower valence state to a higher valence state to maintain local charge At neutral, cation vacancies are produced. The introduction of a monovalent species generally reduces the amount of cationic vacancies and reduces the amount of interdiffusion between the spinel coating 102 and the natural Cr ₂ O ₃ oxide or CrF substrate 100. In this way, the amount of the intermediate oxide layer 101 formed is reduced. Examples of monovalent materials that can be introduced into the spinel coating include Y ³⁺ , Al ³⁺ , Mg ^{2+ ,} and/or Zn ²⁺ metals. In one aspect, the spinel coating has a (Mn, Co, M) ₃ O ₄ composition, where M = Y, Al, Mg or Zn. For example, if M = A is doped in the A position, the spinel composition may include Mn _2-y Al _y CoO ₄ (0 y 0.3) or (1-z)(Mn ₂ O ₃ )+z(Al ₂ O ₃ )+CoO, where (0 z 0.15).

In one embodiment, an interconnect plasma coating is deposited on a Cr-based alloy interconnect using an air plasma jet (APS) process, such as an IC containing 93-97 wt% Cr and 3-7 wt% Fe. A Cr-Fe-Y or CrF interconnect such as described above. The air plasma jet process is a thermal spray process that feeds the powdered coating material into the coating apparatus. The coating particles are introduced into a plasma jet where the particles melt and then accelerate toward the substrate. Melt when reaching the substrate The droplets flatten and cool to form a coating. The plasma can be produced by direct current (DC plasma) or by induction (RF plasma). In addition, unlike controlled atmosphere plasma jet (CAPS), which requires an inert gas or vacuum, air plasma jets are carried out in ambient air.

Cracks in the coating can occur at two different times: a) during deposition, and b) during operation under SOFC conditions. Cracks formed during deposition are affected by both the parameters of the spray gun and the material properties of the coating material. Cracks formed during operation vary primarily with material properties and, more specifically, with the density and sinterability of the material. Without being bound by a particular theory, the cracks that occur during the work of the letter are the result of continuous sintering of the coating and thus increase the densification of the coating over time. As the coating densifies, it shrinks laterally. However, the coating is constrained by the substrate and thus forms a crack to relieve stress. Coatings applied at low density are likely to be further densified during operation, resulting in crack formation. In contrast, coatings applied at higher densities are less likely to form cracks.

In one embodiment, a sintering aid is added to the IC coating to reduce crack formation and thus reduce chromium evaporation. The sintering aid is a material that increases the density of the deposited coating and/or reduces the densification after deposition of the coating. Since the sintering aid increases the deposition state density of the coating material, it thereby reduces crack formation due to subsequent densification and/or work stress on the porous material after formation of the coating. Suitable sintering aids include materials that a) reduce the melting temperature of the bulk phase of the coating material, b) melt to cause liquid phase sintering at a lower temperature than the bulk phase, or c) form a lower melting temperature The second phase. For the perovskite family including LSM, the sintering aids include Fe, Co, Ni, and Cu. These transition metals are soluble in LSM and are easily doped at the B site in the ABO ₃ perovskite phase. The melting temperature of the oxide in the 3d transition metal tends to decrease in the order of Fe>Co>Ni>Cu. Adding these elements to the B site of the LSM reduces the melting temperature and improves the spray state density. In one embodiment, one or more of Fe, Co, Ni, and Cu are added to the coating such that the coating comprises from 0.5% to 5% by weight, such as from 1% to 4% by weight, such as 2% by weight. Up to 3% by weight of such metals. In an alternate embodiment, the coating composition is expressed in atomic percent and comprises La _1-x Sr _x Mn _1-y M _y O _3-d , where (M = Fe, Co, Ni and/or Cu), 0.1 x 0.3, 0.005 y 0.05, and 0 d 0.3. It should be noted that the atomic percentage ranges of Fe, Co, Ni, and Cu do not necessarily match the weight percentage ranges of such elements in the previous examples.

Other elements may also be added in combination with the above transition metals to optimize conductivity, stability, and sinterability. Such elements include, but are not limited to, Ba, Bi, B, Cu, or any combination thereof (eg, Cu+Ba combination), such as in the range of 5% by weight or less, such as from 0.5% by weight to 5% by weight. . In addition, a sintering aid (such as Y) specifically doping the A site of the LSM may be added to achieve a similar effect. An example according to this embodiment is La _y Y _x Sr _1-xy MnO ₃ , where x = 0.05 - 0.5, y = 0.2 - 0.5, such as La _0.4 Y _0.1 Sr _0.5 MnO ₃ . For coating materials other than LSM, copper can be used as a sintering aid in the MCO spinel materials described above.

In another embodiment, instead of introducing the transition metal powder into the air plasma spray during deposition, a metal oxide powder that is easily reduced to a metallic state in the APS atmosphere is added to the plasma. The metal of the metal oxide preferably exhibits a lower melting temperature than the coating phase (perovskite or spinel phase). For example, a binary oxide cobalt oxide (eg, CoO, Co ₃ O ₄ or Co ₂ O ₃ ), NiO may be added to the coating powder (ie, LSM powder or La+Sr+Mn powder or an oxide thereof). In ₂ O ₃ , SnO, B ₂ O ₃ , copper oxide (for example CuO or Cu ₂ O), BaO, Bi ₂ O ₃ , ZnO or any combination thereof (for example, (Cu, Ba)O) as the second phase. This addition produces a two phase powder mixture that is fed into the gun. The amount of the second phase may be less than or equal to 5% by weight, such as in the range of from 0.1% by weight to 5% by weight based on the total powder weight.

In an APS gun, the metal oxide is reduced to its metal phase, melted, and promotes sintering of the molten LSM particles as the LSM particles solidify on the surface of the IC. The lower melting temperatures of metals and binary oxides promote densification during deposition and solidification.

In another embodiment, a material that reacts with a coating material (such as LSM) and forms a secondary phase having a lower melting temperature is added to the coating feed during the APS process. The secondary phase of lower melting temperature promotes densification. For example, citrate and/or calcium aluminate powder can be combined with The coating material powder in the hot plasma portion of the APS gun reacts to form a glass phase. In one embodiment, La from the LSM material reacts with Si-Ca-Al oxide (which may also include K or Na) to form a glass phase, such as La-Ca-Si-Al oxide formed between LSM particles. . The coating may include less than or equal to 5% by weight, such as 0.5 to 5% of silicate, Ca-Al oxide or Si-CaAl oxide.

In one embodiment, the coating is post treated in a manner that causes stress free densification. Thereafter the treatment can be carried out in combination with or without the addition of the sintering aid of the previous examples. In one case of the process according to this embodiment example, for N ₂ and O ₂ atmosphere in the "redox" cycle. In this cycle, the coating is alternately exposed to a neutral and oxidizing atmosphere. For example, the coating can be treated in a neutral atmosphere containing nitrogen or a rare gas such as argon, followed by treatment in an oxidizing atmosphere containing oxygen, water vapor, air, and the like. If necessary, one or more cycles may be performed, such as 2, 3, 4 or more times. If necessary, a reducing (e.g., hydrogen) atmosphere may be used instead of a neutral atmosphere, or a reducing (e.g., hydrogen) atmosphere may be used in addition to the neutral atmosphere. The redox cycle in the N ₂ and O ₂ atmospheres produces a cation vacancy concentration gradient that increases the diffusion of cation vacancies and thereby effectively increases the sintering rate. By using a lower Sr content LSM coating La _1-x Sr _x MnO _3-d (where x 0.1, for example 0.01 x 0.1,d 0.3) to further enhance this effect, maximizing oxygen non-stoichiometry. Any or all of the above sintering aid techniques can be enhanced using this sintering procedure.

In another embodiment, the surface area of the electrical interaction between the coating and the underlying Cr-Fe IC surface is enlarged. As the thickness of the chromium oxide layer increases, the chromium oxide layer formed between the coating and the IC causes the millivolts to decrease over time. The total voltage drop depends on the area and thickness of the voltage drop. Increasing the area of oxide growth between the IC and the coating reduces the effect on voltage loss, thereby increasing stack life. This embodiment effectively increases the contact surface area and thereby reduces the effect of the growing chromium oxide layer by adding a substance that will penetrate the coating deeply.

The method according to this embodiment includes embedding a small amount of coating material into the IC. There are two alternative aspects of this embodiment. One aspect includes the IC powder before compaction to form the IC The coating material (such as LSM or MCO) is sufficiently and uniformly distributed within (e.g., Cr-Fe powder). When the lubricant is mixed with the Fe, Cr (or Cr-Fe alloy) powder prior to compaction, the coating powder (eg, LSM and/or MCO powder) may be included. The powder mixture is preferably capable of withstanding sintering temperatures and reducing environments. The second aspect includes incorporating (e.g., embedding) a predetermined amount of coating powder only in the top surface of the Cr alloy IC. The oxide region embedded in the surface of the CrF or CrFeY IC increases the surface roughness of the IC after the IC sintering step. After the extrusion and sintering steps, the entire coating is deposited on the Cr alloy interconnect.

A method of embedding a coating material in the top surface of an interconnect is illustrated in Figures 3A-3C. As shown in FIG. 3A, a lubricant and a Cr/Fe powder 202 for forming an IC body are added to the cavity 200 using a first leg (not shown) or by another suitable method. As shown in FIG. 3B, prior to the compacting step, a second column 206 is used to provide a coating material powder 204 (eg, LSM or MCO) or coating material powder 204 over the powder 202 located in the cavity in the cavity. A mixture of lubricant/Cr/Fe powder 202. As shown in Figure 3C, the powders 204, 202 are then compacted using a punch 208 to form an interconnect of the coating material in the air-side embedded surface (i.e., if the air side of the IC is formed face up in the mold).

Alternatively, a coating material powder 204 (e.g., LSM or MCO) (or a mixture of coating material powder 204 and lubricant/Cr/Fe powder 202) is first provided to cavity 200. Next, if the air side of the IC is formed face down in the mold, the lubricant/Cr/Fe powder 202 is provided over the powder 204 in the cavity 200 prior to the compacting step. In this way, the coating material is primarily incorporated into the IC on top of the air side surface of the IC.

Alternatively, as shown in FIG. 4, the coating powder 204 can be electrostatically attracted to the punch 208 above the press. Next, the upper punch 208 extrudes the coating powder 204 and the lubricant/interconnect powder material 202 in the cavity 200 to form an IC in which the coating material 204 is embedded in the top of the air side.

Using the above method, after the compacting step, the coating powder can be uniformly incorporated into the surface of the IC air side. Next, the compacting step is followed by a sintering and coating step, such as an MCO and/or LSM coating step by APS or another method described herein.

The ratio of coating powder to iron in the Cr-Fe alloy is preferably selected such that the top coating material has a coefficient of thermal expansion (CTE) similar to that of the sintered and oxidized interconnect. The coefficient of thermal expansion of the Cr-Fe alloy varies with the alloy composition and can be selected by selecting the ratio of Cr to Fe. The sintering process can be adjusted to keep the powder oxidized and stable. For example, sintering can be carried out using wet hydrogen or in an inert atmosphere such as nitrogen, argon or another noble gas. The wet hydrogen or inert gas atmosphere is oxidized or neutral, respectively, and thereby prevents the oxide powder from being reduced.

In another embodiment, the coating is a multilayer composite. Figure 6A illustrates an example of an embodiment of such an IC having a composite coating. The composite coating consists of a spinel layer 102 and a perovskite layer 104. A spinel layer 102 is first deposited on a Cr alloy (e.g., CrF) interconnect 100. A layer of perovskite layer 104 as described above is then deposited on top of the spinel layer 102. A natural chromium-containing interface spinel layer 101 may be formed between the interconnect 100 and the layer 102 during deposition of the layer 102 and/or during high temperature operation of the fuel cell stack containing the interconnect.

Perovskite layer 104 can comprise any suitable perovskite layer as described above, such as LSM. The LSM can have the formula: La _1-x Sr _x MnO ₃ (LSM), where 0.1 x 0.3, such as 0.1 x 0.2. The spinel coating 102 is first deposited and is in direct contact with the interconnect substrate 100 (if the native layer 101 is removed from the substrate 100) or in direct contact with the native layer 101 on the substrate 100.

The lower spinel layer 102 preferably comprises the above-described MCO spinel containing Cu and/or Ni. Layer 102 serves as a doped layer that increases the conductivity of the underlying layer of manganese oxide chromium (Mn,Cr) ₃ O ₄ or manganese oxide cobalt chromium (Mn,Co,Cr) ₃ O ₄ interface spinel layer 101. In other words, Cu and/or Ni from the spinel layer 102 diffuses into the interfacial spinel layer 101 during and/or after formation of layer 101. This produces a layer 101 doped with Cu and/or Ni (eg, (Mn and Cr) _3-xy Co _x (Cu and/or Ni) _y O ₄ , where (0 x 1), (0<y 0.3)), which lowers the resistivity of layer 101.

The layer 102 may include the above-described Cu-containing MCO layer and/or Ni-containing MCO layer and/or MCO layer containing Ni and Cu. In the MCO layer, when the A element is Mn, the B element is Co, and the spinel is doped with Cu and/or Ni, the spinel family can be of the general formula (Mn, Co) _3-y (Cu, Ni). _y O ₄ description, where (0<y 0.3). More specifically, depending on the location of the Cu and/or Ni alloying elements, the spinel family can be described by the following formula:

(1) If Cu and/or Ni enters the A site, it is Mn _2-xy Co _1+x (Cu, Ni) _y O ₄ (0) x 1), (0<y 0.3)

(2) If Cu and/or Ni enters the B site, it is Mn _2-x Co _1+xy (Cu, Ni) _y O ₄ (0) x 1), (0<y 0.3)

(3) If Cu and/or Ni enter the A site and the B site equally, then Mn _2-xy/2 Co _1+xy/2 (Cu, Ni) _y O ₄ (0) x 1), (0<y 0.3).

Figure 5 illustrates the surface specific resistance (ASR) degradation over time of a CrF interconnect coated with a manganese oxide doped layer containing Cu and Ni (e.g., (Cu, Ni, Mn) ₃ O ₄ spinel) The interconnects coated with the LSM layer are reduced. The interconnect with the doped layer initially begins with a higher ASR than the interconnect with the LSM layer coating. However, the rate of increase of the ASR of the IC coated with the LSM layer is much higher than that of the IC coated with the doped layer. The ASR of the IC coated with the LSM layer is higher than the IC with the doped layer coating in 1000-2000 hours. In addition, after about 2,500 hours of operation, the ASR of the interconnect with the doped layer remains constant, while the ASR of the interconnect coated with the LSM layer remains elevated over time.

Although the spinel doped layer 102 containing Cu and/or Ni reduces the ASR of the interconnect, it is permeable to oxygen and chromium. Thus, in an embodiment of the invention, a second perovskite barrier layer 104 is formed on the doped layer 102. Layer 104 is preferably a dense LSM layer that reduces or prevents the diffusion of Cr and oxygen. Layer 104 can be formed using the sintering aids described above to increase its density. The dense layer 104 reduces or prevents the growth of the interfacial spinel layer 101 by blocking the diffusion of air and oxygen from the cathode side of the fuel cell toward the surface of the CrF IC during stacking operations. Layer 104 also reduces or prevents chromium poisoning of the fuel cell cathode in the stack by reducing or preventing the diffusion of chromium from the IC to the cathode.

Thus, the composite coating 102/104 reduces or eliminates the effects of surface specific resistance (ASR) degradation of the interconnect on the stack and reduces overall degradation of the fuel cell stack by reducing or eliminating Cr poisoning of the fuel cell cathode. First, the spinel layer 102 is sputtered with a reduced chromium-containing interface. The element of the electrical resistance of the stone layer 101 (e.g., Co and/or Mn, and optionally one of Ni and/or Cu (if present)) is doped with the spinel layer 101. Second, the spinel layer 102 prevents direct interaction between the perovskite layer 104 and the Cr-containing interface spinel layer 101, which can result in an undesirable and resistive secondary phase formation. Third, the layer 102 of spinel (e.g., Mn-containing spinel having Co, Cu, and/or Ni) has a smaller tendency to crack than the LSM layer 104, which enhances the integrity of the coating. Fourth, the top perovskite layer 104 is a second barrier layer that reduces the transport of oxygen to the interfacial oxide 101 on the surface of the interconnect. The top perovskite layer 104 thus reduces the growth rate of the native oxide layer 101 and reduces the transport of chromium from the layer 101 through the spinel layer 102 to the fuel cell cathode.

An example of a solid oxide fuel cell (SOFC) stack is illustrated in Figure 6B. Each SOFC 1 includes a cathode electrode 7, a solid oxide electrolyte 5, and an anode electrode 3. Fuel cell stacks are often constructed from multiple SOFCs 1 in the form of planar elements or other geometric configurations. Fuel and air are supplied to the electrochemically active surfaces of the anode 3 and cathode 7 electrodes, respectively. Interconnects 9 containing airflow passages or channels 8 between the ribs 10 separate individual cells in the stack. The interconnect 9 electrically connects the anode or fuel electrode 3 of one battery 1 to the cathode or air electrode 7 of an adjacent battery 1. The interconnect 9 is separated from the fuel (such as a hydrocarbon fuel) of the fuel electrode (e.g., anode 3) of one of the cells 1 in the fuel passage 8 between the ribs 10 on the interconnect fuel side and interconnected. An oxidant (such as air) flows to the air electrode (i.e., the cathode 7) of the adjacent battery 1 in the stack in the air passage 8 between the ribs 10 on the body air side. At either end of the stack, there may be an air end plate or fuel end plate (not shown) for providing air or fuel to the end electrodes, respectively. FIG. 6B shows the lower SOFC 1 between two interconnects 9.

As shown in FIG. 6B, the MCO spinel coating 102 is located on the air rib 10 and air channel 8 on the air side of the interconnect 9 and faces the adjacent SOFC 1 cathode 7 in the stack. The perovskite layer 104 (e.g., LSM) is located on the MCO coating 102 only in the region of the rib 10 and not in the region of the air passage 8. This allows the perovskite (e.g., LSM) layer 104 to contact the same or similar perovskite (e.g., LSM) cathode 7 without the perovskite layer 104 coating the entire air of the interconnect 9 side. The intermediate oxide layer (not shown in FIG. 6B) may be formed between the CrF interconnect 9 substrate 100 and the MCO spinel coating 102 after stack annealing and/or operation.

In another embodiment, a second phase is added to the (Mn,Co) ₃ O ₄ spinel for use as an impurity (such as sulfur and ruthenium) collector. In this way, the adhesion of the coating to the CrF interconnect substrate 100 can be improved. For example, a metal oxide phase (such as a non-spinel metal oxide such as Al ₂ O ₃ , Y ₂ O ₃ or TiO ₂ ) may be added to the spinel phase of the coating 102 as the second phase. In one aspect, when the metal oxide phase is alumina, the coating composition can be (1-x) (Mn, Co) ₃ O ₄ and x (Al ₂ O ₃ ), wherein (0 x 0.02). In this case, Al ₂ O _{3 is} mainly present in the form of a second phase rather than a dopant in the spinel structure. However, some interdiffusion may occur during deposition and at SOFC operating temperatures. In this case, the spinel phase will be doped with aluminum, tantalum or titanium.

FIG. 7A shows the air side of the exemplary interconnect 100. The interconnect can be used in a stack where the fuel branches internally and the air branches in the outside. The interconnects contain airflow passages or channels 8 between the ribs 10 to allow air to flow from one side 13 of the interconnect to the opposite side 14. A ring (e.g., annular) seal portion 15 is located around the fuel inlet opening 16A and the fuel outlet opening 16B (i.e., through the holes 16A, 16B in the interconnect 100). The strip seal portion 19 is located on the side of the interconnect 100.

FIG. 7B shows a close up view of the exemplary sealing portion 15, passage 8 and rib 10. Sealing portion 15 can comprise any suitable sealing glass or glass ceramic material, such as borosilicate glass. Alternatively, the sealing portion 15 may comprise a glass-ceramic material as described in U.S. Application Serial No. 12/292,078, filed on Nov. 12, 2008, which is incorporated herein by reference.

The interconnect 100 may contain raised or raised regions below the sealing portion 15 as necessary. Further, as illustrated in FIG. 7B, the sealing portion 15 is preferably located in the flat region 17 of the interconnect 100. That is, the sealing portion 15 is located in the interconnect portion that does not include the rib 10. If necessary, the interconnect 100 can be configured for a stack of internal branches of air and fuel. In this case Next, interconnect 100 and corresponding fuel cell electrolyte will also contain other air inlet openings and outlet openings (not shown).

FIG. 7C illustrates the fuel side of interconnect 100. The window seal portion 18 is located at the periphery of the interconnect 100. A fuel flow passage 8 between the fuel distribution plenum 17 and the rib 10 is also shown. It is important to note that the interconnect 100 shown in Figure 7C has two types of fuel flow paths; however, this does not limit the invention. The fuel side of interconnect 100 can have fuel flow paths that are all of the same depth and length, or short and long paths and/or combinations of deep and shallow paths.

In one embodiment, the interconnect 100 is coated with Mn _1.5 Co _1.5 O ₄ (MCO) spinel using an aerosol spray method at room temperature and further processed by one or more heat treatments. In general, the MCO coating is omitted in these zones by masking or removing the MCO deposited in the seal zone (annular 15, strip 19).

The MCO coating can be reduced by the fuel in the riser orifice and then reacted with the glass seal material in the annular seal portion 15. Thus, in one embodiment, for the interconnect 100 shown in FIG. 7B, the MCO coating is removed from the flat region 17 on the air side of the interconnect prior to stack assembly and testing (eg, by grit blasting) . Alternatively, the flat zone 17 may be shielded during aerosol deposition to prevent coating of the flat zone 17. Accordingly, the MCO coating is omitted in the region 17 below the annular seal portion 15 adjacent the fuel inlet opening 16A and/or the fuel outlet opening 16B.

In another embodiment, the interconnect 100 is fabricated by a powder metallurgy process. The powder metallurgy process can produce a portion having interconnected pores within the body of interconnect 100 that allows fuel to diffuse from the fuel side to the air side. This fuel transported through the pores can react with the MCO coating on the air side at the coating/interconnect interface. This reaction can result in seal failure and stack separation. In one embodiment, the MCO coating under the strip seal portion 19 can be omitted by masking the location of the seal portion 19 on the edge of the interconnect during MCO deposition, thereby removing the coating in such seal regions. And allows the glass sealing portion 19 to be directly bonded to the metal interconnection Body, thereby alleviating this failure.

In another embodiment, interconnect 100 forms a thin layer 25 of green Cr ₂ O ₃ oxide on the fuel side of interconnect 100. A cross-sectional photomicrograph of this fuel side oxide is illustrated in FIG. The Cr ₂ O ₃ oxide was found to have a thickness of 0.5 to 2 μm. The three methods described below can be used to convert or remove this undesirable chromium oxide layer.

In one embodiment of the method, the oxide layer is removed by any suitable method (blasting). This method is effective. However, this method is time consuming and increases processing costs.

Alternatively, the Cr ₂ O ₃ oxide layer 25 may be left in place and converted into a composite layer. In this embodiment, a nickel mesh anode contact is deposited on the Cr ₂ O ₃ oxide layer 25 and allowed to diffuse into the chromium oxide layer. Nickel reacts with the Cr ₂ O ₃ oxide layer 25 and forms a Ni metal/Cr ₂ O ₃ composite layer that reduces the ohmic resistance of the layer 25. If necessary, the web is heated after the contact layer 25 to accelerate the formation of the composite.

In another embodiment, the oxide layer 25 is reduced or completely removed by burning the MCO coated interconnect in an environment having a low oxygen partial pressure. For example, based on thermodynamics, Cr ₂ O ₃ can be reduced to Cr metal at 900 ° C at 10 ^-24 atm pO ₂ (partial pressure), while CoO is reduced at 900 ° C at 10 ^-16 atm pO ₂ Into Co metal. By reducing the partial pressure of oxygen (ie, reducing the dew point) of the combustion atmosphere to less than 10 ^-24 atm at 900 ° C, formation of Cr ₂ O ₃ oxide on the fuel side (uncoated side) can be prevented while allowing mutual The MCO coating on the side of the conjoined air is reduced to MnO (or Mn metal if pO ₂ <10 ^-27 atm) and Co metal beneficial for sintering. At pO ₂ <10 ^-27 atm, the MCO will be reduced to Mn metal and Co metal, which produces a better sintered and denser coating than the MnO/Co metal. In general, MCO coated interconnects can be at 10 to ²⁴ atm (eg, 10 to ²⁵ atm to 10 ^-30 atm, including 10 ^-27 atm) at T > 850 ° C (such as 900 ° C to 1200 ° C). to 10 ^-30 atm) the pO ₂ annealed at 30 to 40 minutes, such as 10 hours.

In another embodiment, to reduce the cost of the MCO coating process, the MCO coating can be annealed (eg, burned or burned during the sintering step of the powder metallurgy (PM) formed interconnect. Knot). Sintering of the powder metallurgy interconnect 100 and the MCO coating on the interconnect can be carried out in the same step, in a reducing environment (such as a hydrogen reduction furnace with a dew point of -20 ° C to -30 ° C), at 1300 ° C to 1400 ° C. The temperature is carried out for 0.5 to 6 hours. At these temperatures and partial pressures of oxygen, the MCO coating will be completely reduced to Co metal and Mn metal. However, the melting temperature of Mn is about 1245 ° C, the melting temperature of Co is about 1495 ° C, and the Co-Mn system has a reduced liquidus. Therefore, sintering at a temperature of 1300 ° C to 1400 ° C can result in undesirable liquid phase formation.

Possible solutions to avoid liquid formation include reducing the sintering temperature to below 1300 ° C, such as below 1245 ° C, such as 1100 ° C to 1245 ° C; increasing the partial pressure of oxygen to reduce Mn in the MCO to MnO (melting temperature 1650 ° C) (but not oxidizing Cr), as opposed to Mn metal; reducing the Mn:Co ratio in MCO to increase the melting temperature of the Mn-Co metal system; adding a dopant such as Cr to the MCO to increase Co-Mn-Cr The melting temperature of the metal system; and/or the addition of dopants (such as Fe, V, and/or Ti) to the MCO coating to stabilize the binary and ternary oxides (to prevent reduction to the metal phase). For example, at a sintering temperature of 1400 ° C, MnO is reduced to Mn metal at 10 ^-17 atm pO ₂ , and Cr ₂ O ₃ is reduced to Cr metal at 10 ^-15 atm pO ₂ , which produces Cr reduction. The metal is formed while MnO is still a small window in the form of an oxide having a high melting point (pO _{2 is} between 10 ^-17 atm and 10 ^-15 atm). Thus, the interconnect and MCO coating can be sintered at 1300-1400 ° C at pO ₂ = 10 ^-15 -10 ^-17 atm.

In another embodiment, the IC sintering step may be performed first, after which an MCO coating is applied to the sintered IC. The IC and coating are then subjected to the reduction steps described in the above examples, which are more suitable for MCO coating.

In another embodiment, the interconnect fabrication cost can be reduced by depositing the MCO layer as a mixture of reduced components such as MnO, CoO, Mn metal, Co metal, or any combination of such components. The mixture is then preferably sintered under low pO ₂ conditions. However, the sintering may be easier or the starting material may be denser, thereby reducing the sintering time. Moreover, such precursor particles are less expensive than MCO precursors, which require expensive synthetic methods to manufacture.

Additionally, a sandblasting step can be performed prior to coating the interconnect with the MCO layer to remove the native chromium oxide layer from the air side and fuel side of the interconnect. To reduce cost, the native oxide can be removed only from the air side of the interconnect before the MCO coating is formed on the air side of the interconnect. An MCO coating is then deposited on the air side and the interconnect is annealed as described above. After the annealing is completed, the oxide can then be removed from the fuel side, such as by grit blasting. In this manner, the number of blasting steps is reduced because no other blasting steps are required to remove oxide growth that occurs on the interconnect fuel side during the MCO coating anneal.

In other embodiments, the composition of the MCO coating is modified to increase stability at SOFC operating temperatures, such as 800-1000 °C. The MCO composition of some of the foregoing examples is Mn _1.5 Co _1.5 O ₄ . This material has a high electrical conductivity. However, the MCO material can be reduced to binary oxides MnO and CoO, or reduced to binary oxides MnO and Co metal.

In some fuel cell geometries, the MCO coating is only directly exposed to the fuel stream at the riser openings 16A, 16B. This fuel/coating interface can be eliminated by not coating the flat zone 17 around the opening (Fig. 7B). However, interconnects made by powder metallurgy produce portions with some interconnected (open) pores that allow fuel to diffuse through the portion to the air side. The fuel diffusing through the pores can react with the MCO at the MCO/interconnect interface (shown in Figure 9) and reduce it to produce a porous layer composed of MnO and Co metal. The coating/IC interface may be damaged, resulting in failure of adhesion during normal processing and separation of the cell from the interconnect, as shown in FIG.

There is a need for coating materials that are relatively stable and less likely to be reduced when exposed to a fuel environment. The examples described below optimize the composition and/or blend the MCO with other elements to stabilize the material in a reducing atmosphere.

Figures 11 and 12 illustrate the theory of electrolyte corrosion. In the prior art SOFC stack shown in Figures 11 and 12, the LSM coating 11 on the interconnect is in contact with the ring seal portion 15. The sealing portion 15 contacts the battery electrolyte 5. Without wishing to be bound by a particular theory, it is believed that manganese and/or cobalt from the layer 11 of a metal oxide containing manganese and/or cobalt (e.g., LSM of LSCo) is immersed in and/or reacted with the glass seal portion 15, followed by The glass is transported to the electrolyte. Manganese and/or cobalt may be transported from the glass to the electrolyte in the form of manganese and/or cobalt atoms or ions or in the form of compounds containing manganese and/or cobalt, such as ceric acid compounds rich in manganese and/or cobalt. For example, manganese and cobalt react with glass to form a (Si,Ba)(Mn,Co)O _6±δ mobile phase that is transported from the glass seal to the electrolyte. Manganese and/or cobalt at the electrolyte 5 or in the electrolyte 5 (for example as part of the mobile phase) tend to accumulate at the grain boundaries of the zirconia-based electrolyte. This results in weakening intergranular corrosion and pits of the electrolyte grain boundaries, eventually resulting in cracks in the electrolyte 5 (e.g., openings 16A to 16B cracks). Without being bound by a particular theory, as shown in FIG. 11, fuel (eg, natural gas, hydrogen, and/or carbon monoxide) passing through the fuel inlet riser 36 may also react with the metal oxide layer 11 and/or the glass seal portion 15 to form The mobile phase and enhanced manganese and/or cobalt are immersed from the layer 11 into the sealing portion 15.

As discussed above, in other embodiments, the composition of the MCO coating is improved to increase stability at SOFC operating temperatures, such as 800-1000 °C. Therefore, the MCO composition can be optimized based on stability and conductivity. Example compositions include, but are not limited to, Mn ₂ CoO ₄ , Mn _1.75 Co _0.25 O ₄ , Co _1.75 Mn _0.25 O ₄ , Co ₂ MnO _{4 ,} and Co _2.5 Mn _0.5 O ₄ .

Based on the phase diagram (Fig. 10) and from the viewpoint of stability, it is preferred to have a multiphase composition rich in Mn such as Mn _2.5 Co _0.5 O ₄ and Mn _2.75 Co _0.25 O ₄ (for example, an atomic ratio of Mn:Co of 5:1) Or greater than 5:1, such as 5:1 10 11:1. Higher Mn content can also produce a more stable composition, because the composition is higher than the two-phase spinel + binary oxidation seen at high Co content. The oxidation state of the species. However, any composition between the final composition Co ₃ O ₄ and Mn ₃ O ₄ in the (Mn,Co) ₃ O ₄ family may be suitable.

In another embodiment, the MCO is stabilized by the addition of another dopant having a lower tendency to reduce. For example, it is known that MCO reacts with Cr in an IC alloy to form a (Cr, Co, Mn) ₃ O ₄ spinel. If a low content (such as 0.1 atomic % to 10 atomic %) of Cr is intentionally added to the MCO coating, this will result in a spinel (Cr, Co, Mn) ₃ O ₄ that is more stable than MCO because of Cr ^{3 +} Extremely stable. Other transition metal elements that are soluble in the spinel structure and that improve stability include Fe, V, and Ti. The example coating material includes spinel (Fe, Co, Mn) ₃ O ₄ having 1 atom% to 50 atom% Fe, and (Ti, Co, Mn) ₃ O ₄ having 1 atom% to 50 atom% Ti. Or a combination of (Fe, Ti, Co, Mn) ₃ O ₄ .

The addition of Ti produces a relatively stable secondary phase, including Co ₂ TiO ₄ , MnTi ₂ O ₄ or FeTi ₂ O ₄ . These phases are beneficial for overall coating stability. Spinels having any combination of the above dopants are possible, including (Fe, Cr, Co, Mn) ₃ O ₄ , (Cr, Ti, Co, Mn) ₃ O ₄ and the like.

Spinels based on Mg, Ca and Al are known to be extremely stable and resistant to reduction. However, such spinels have low electrical conductivity and are therefore not preferred for use as interconnect coatings. In contrast, doping a low level of Ca, Mg, and/or Al into a conductive spinel (such as MCO) increases material stability while only slightly lowering the conductivity. Examples of spinels include 1 atomic% to 10 atomic% Ca of _{(Ca, Co, Mn) 3} O 4, with 1 atomic% to 10 atomic% Mg of _{(Mg, Co, Mn) 3} O 4, having an atomic % to 10 atom% Al (Al, Co, Mn) ₃ O ₄ , or a combination such as (Ca, Al, Mn, Co) ₃ O ₄ wherein Ca, Al and/or Mg are added in an amount of 1 to 10 atom% . Si and Ce are other elements which can be used as a dopant (1-10 atom%) of the MCO spinel.

In addition to the above-described methods pertaining to general material classes - specific stabilizing results, alternative embodiments are depicted to design changes that may be made in combination with or in place of the above-described embodiments to improve coating stability. In a first alternative embodiment, a stabilizing barrier layer can be added to the interconnect prior to the addition of the MCO coating. The barrier layer will preferably be made of an oxide that is more stable than MCO and that is sufficiently conductive and thin enough to not adversely affect the conductivity of the interconnect components. In addition, the barrier layer is preferably dense and airtight. Example barrier layers include, but are not limited to, a doped Ti oxide (eg, TiO ₂ ) layer or lanthanum manganate (LSM).

A second alternative embodiment includes the addition of a reactive barrier layer between the interconnect and the MCO coating, including any of the elements discussed above (eg, Cr, V, Fe, Ti, Al, Mg, Si, Ce, and/or Or Ca) as a possible dopant. Heat the interconnect to standard operating temperature After (800-1000 ° C), this layer diffuses these elements into the MCO coating, thereby forming a graded doping profile with a higher dopant concentration at the interface of the reduced interconnect. In this way, most coatings contain relatively few dopants and thus may have less impact on conductivity than uniformly doped coating materials. The reaction layer is a metal layer (for example, Ti or a metal-containing compound which allows the metal to diffuse outward at 800 ° C or higher).

Another embodiment includes designing the interconnect material to contain reactive doping elements that diffuse into the MCO coating in the same manner as described (eg, Si for Cr-4-6% Fe interconnects) , Ce, Mg, Ca, Ti and/or Al). Therefore, the interconnect will contain 90% by weight of Cr, 4-6% Fe and 0.1-2% of Mg, Ti, Ca and/or Al.

In addition, in addition to standard oxidation processes, any deposition or processing of ICs that reduce or close a portion of the pores will help limit the reduction of the MCO coating. For example, the Cr layer can be electroplated onto the porous portion prior to the MCO annealing step to further reduce porosity. Alternatively, as described above, the addition of a reactive barrier layer (if dense and airtight) will also reduce or block the diffusion of hydrogen from the surface pores.

Embodiments of the present invention provide composite perovskite and spinel coatings rather than double layer spinel and perovskite coatings. Figure 13 is a photomicrograph illustrating an interconnect having a composite LSM-MCO coating. The composite LSM/MCO coating 110 in accordance with this embodiment is designed to take advantage of the best features of each of these individual coatings discussed above. The composite coating 110 illustrated in Figure 13 contained 40% by weight MCO and 60% by weight LSM and was conditioned in the SOFC stack (two day cycle at 850 °C). Debut 112 is the LSM and dark phase 114 is the MCO. Therefore, the LSM and MCO phases exist in a unique region in the composite coating. Without wishing to be bound by a particular theory, the salty MCO phase may form a plate-like or flat (e.g., long, thicker) structure 114 in the LSM phase matrix 112. However, the structure may vary for different compositions and/or deposition methods of the composite coating 110.

The flat MCO structure in the composite coating 110 where the crack is repaired inhibits the evaporation of Cr through the cracks generated in the LSM. The presence of LSM allows the composite LSM/MCO coating to be reduced Stable in the enclosure, so that spalling does not occur and the integrity of the coating is maintained. The MCO content of the composite coating 110 is preferably sufficiently high to form a Mn-Cr-Co oxide (e.g., spinel 101) scale on the IC that provides a lower ohmic resistance than the single phase LSM coating, the single phase The LSM coating can only form MnCr oxide spinel on the surface of the interconnect. As can be seen in Figure 13, the composite coating 110 did not exhibit any cracks or spalling after conditioning for two days at 850 °C in the SOFC stack.

The composition of the composite coating 110 can be any ratio of LSM:MCO as long as it is a mixture of two materials (rather than a two-layer coating). For example, the weight ratio of perovskite to spinel (eg, LSM:MCO) can range from 20:80 to 90:10, such as from 50:50 to 80:20. The composition of the individual LSM and MCO materials in the composite coating 110 can vary as described above, and can have any content or ratio of non-oxygen components, and can include phases other than perovskites and spinel phases. / or other elements than Mn, Co, La, Sr and O. For example, the spinel phase 114 of the coating 110 can comprise Mn _2-x Co _1+x O ₄ , where 0 x 1, and the perovskite phase 112 may comprise La _1-x Sr _x MnO ₃ (LSM), wherein 0.1 x 0.3, such as 0.1 x 0.

The composite coating 110 can be deposited on the interconnect using any deposition method such as, but not limited to, APS. The perovskite and spinel are preferably deposited together in one step. For example, the APS material powder provided to the plasma in the APS process can comprise a mixture of LSM and MCO powder in the same weight ratio as that required for the coating 110.

The microstructure, thickness or any other physical property of the coating can vary and can take any form. However, a dense coating is preferred. Composite coating 110 can be deposited anywhere on the interconnect. That is, the composite coating is not limited to any particular portion of the interconnect, but is preferably deposited on the cathode side of the interconnect.

While the above is directed to certain preferred embodiments, it should be understood that the invention is not limited thereto. Various modifications may be made to the disclosed embodiments, and such modifications are intended to be within the scope of the invention. All publications, patent applications, and patents cited herein are hereby incorporated by reference in their entirety.

100‧‧‧Interconnects

101‧‧‧Intermediate oxide layer/intermediate layer/layer/intermediate spinel layer/interface spinel layer

102‧‧‧MCO spinel layer/MCO spinel coating/MCO coating/coating

Claims (60)

A method of coating an interconnect for a solid oxide fuel cell, comprising: providing an interconnect substrate comprising Cr and Fe; and coating the interconnect with a manganese cobalt spinel coating using a plasma jet process The air side of the bulk substrate; wherein the spinel comprises one or more monovalent elements. The method of claim 1, wherein the one or more monovalent elements are selected from the group consisting of Y ³⁺ , Al ³⁺ , Mg ^{2+ ,} and Zn ²⁺ , and the spinel comprises (Mn, Co, M) ₃ O ₄ , wherein M=Y, Al, Mg or Zn. A method of coating an interconnect for a solid oxide fuel cell, comprising: providing an interconnect substrate comprising Cr and Fe; and coating the interconnect with a manganese cobalt spinel coating using a plasma jet process The air side of the bulk substrate; wherein the coating additionally comprises a binder. The method of claim 3, wherein the collector comprises at least one of Al ₂ O ₃ , Y ₂ O ₃ or TiO ₂ . A method of coating an interconnect for a solid oxide fuel cell, comprising: providing an interconnect substrate comprising Cr and Fe; coating the interconnect with a manganese cobalt spinel coating using a plasma jet process An air side of the substrate; and a perovskite layer deposited on the spinel coating. The method of claim 5, wherein the spinel coating is on the air ribs on the air side of the interconnect substrate and the air channel, and the perovskite layer is on the wings of the interconnect substrate The ribs are on the spinel coating on the air channels. A method of coating an interconnect for a solid oxide fuel cell, comprising: providing an interconnect substrate comprising Cr and Fe; The air side of the interconnect substrate is coated with a manganese oxide cobalt spinel coating using a plasma spray process; wherein the manganese cobalt cobalt spinel coating comprises a perovskite component to form a composite coating. The method of claim 7, wherein the composite coating comprises a plate-like spinel phase region in a perovskite phase matrix; the perovskite phase comprises barium manganate; and the manganese-cobalt-chromium intermediate spinel layer Located between the composite coating and the air side of the interconnect substrate. A coated interconnect for a solid oxide fuel cell, comprising: an interconnect substrate comprising iron and chromium; and a composite spinel and perovskite formed on an air side of the interconnect substrate coating. The coated interconnect of claim 9, wherein the composite coating comprises a plate-like spinel phase region in a matrix of perovskite phases. The coated interconnect of claim 10, wherein: the spinel phase comprises manganese oxide cobalt spinel; the perovskite phase comprises lanthanum manganate; and the manganese-cobalt-chromium intermediate spinel layer is located The composite coating is formed between the air side of the interconnect substrate; and the composite coating is formed using an air plasma jet process. A coated interconnect for a solid oxide fuel cell, comprising: an interconnect substrate comprising iron and chromium; a manganese oxide cobalt spinel coating formed on an air side of the interconnect substrate; a manganese-cobalt-chromium intermediate spinel layer between the spinel coating and the air side of the interconnect substrate; a perovskite layer on the spinel coating. The coated interconnect of claim 12, wherein the spinel of the spinel coating comprises Mn _2-x Co _1+x O ₄ , wherein x 1 and wherein the spinel comprises a Co:Mn atomic ratio of at least 1:3. The coated interconnect of claim 13, wherein the spinel of the spinel coating comprises Mn _1.5 Co _1.5 O ₄ and the perovskite layer comprises lanthanum manganate. The coated interconnect of claim 12, wherein the spinel coating is on the air ribs on the air side of the interconnect substrate and the air channel, and the perovskite layer is located in the interconnect The ribs of the substrate are on the spinel coating on the air channels. The coated interconnect of claim 13, wherein: the spinel coating comprises a Co:Mn atomic ratio of 1:3 to 6:4; and the interconnect substrate comprises 92% to 97% by weight Chromium, 3% by weight to 7% by weight of iron and 0 to 1% by weight of bismuth or cerium oxide chromium-iron alloy. The coated interconnect of claim 16, wherein the interconnect system is in a solid oxide fuel cell stack. A coated interconnect for a solid oxide fuel cell, comprising: an interconnect substrate comprising at least 70% by weight chromium; and a manganese oxide cobalt spinel formed on an air side of the interconnect substrate a coating, wherein the spinel comprises a Co:Mn atomic ratio of at least 1:3; wherein the spinel comprises one or more monovalent elements. The coated interconnect of claim 18, wherein the one or more monovalent elements are selected from the group consisting of Y ³⁺ , Al ³⁺ , Mg ^{2+ ,} and Zn ²⁺ , and the spinel comprises (Mn, Co, M) ₃ O ₄ , wherein M=Y, Al, Mg or Zn. A coated interconnect for a solid oxide fuel cell comprising: an interconnect substrate comprising at least 70% by weight chromium; A manganese oxide cobalt spinel coating formed on the air side of the interconnect substrate, wherein the spinel comprises a Co:Mn atomic ratio of at least 1:3; wherein the coating comprises a binder. The coated interconnect of claim 20, wherein the collector comprises at least one of Al ₂ O ₃ , Y ₂ O ₃ or TiO ₂ . A coated interconnect for a solid oxide fuel cell, comprising: an interconnect substrate comprising at least 70% by weight chromium; and a manganese oxide cobalt spinel formed on an air side of the interconnect substrate a coating, wherein the spinel comprises a Co:Mn atomic ratio of at least 1:3; and wherein the coated interconnect comprises a perovskite layer on the spinel coating. The coated interconnect of claim 22, wherein the spinel coating is on the air ribs on the air side of the interconnect substrate and the air channel, and the perovskite layer is located in the interconnect The ribs of the substrate are on the spinel coating on the air channels. A method of fabricating an interconnect for a solid oxide fuel cell, comprising: providing an interconnect comprising Cr and Fe; and coating the interconnect with a ceramic layer using an air plasma spray process, wherein the ceramic layer Contains sintering aids. The method of claim 24, wherein the sintering aid exhibits at least one of: a) lowering a melting temperature of the bulk phase of the ceramic; b) melting at a temperature lower than the bulk phase; or c) forming a low melting temperature The secondary phase of the bulk phase ceramic. The method of claim 24, wherein the ceramic layer comprises an LSM and the sintering aid comprises a B site dopant selected from the group consisting of Fe, Co, Ni, Cu, and combinations thereof. The method of claim 24, wherein the ceramic layer comprises LSM and the sintering aid comprises A site dopant of Y. The method of claim 24, wherein the air plasma spraying process comprises spraying a powder mixture of the ceramic and a metal oxide reduced to a metallic state in an APS atmosphere, the reduced temperature of the reduced metal being lower than a melting temperature of the ceramic layer . The method of claim 28, wherein the metal oxide comprises cobalt oxide, nickel oxide, indium oxide, tin oxide, boron oxide, cerium oxide, cerium oxide, copper oxide or zinc oxide, or any combination thereof; 0.1% to 5% by weight based on the total weight of the ceramic and metal oxide powder; and the ceramic and the reduced metal are melted in a gun of an air plasma system and the molten metal promotes the surface of the molten ceramic powder on the interconnect Sintered when solidified. The method of claim 25, wherein the sintering aid comprises a compound selected from the group consisting of silicate, calcium aluminate or calcium aluminum citrate, the compound reacting with the ceramic and forming one or more glass phases. A coated interconnect for a solid oxide fuel cell, comprising: an interconnect substrate comprising iron and chromium; a manganese oxide cobalt spinel coating formed on an air side of the interconnect substrate, Wherein the manganese oxide cobalt spinel coating further comprises at least one of nickel and copper; and the oxidation of manganese and chromium between the manganese oxide cobalt spinel coating and the air side of the interconnect substrate a middle spinel layer; and a perovskite layer on the manganese oxide cobalt spinel coating. A coated interconnect for a solid oxide fuel cell, comprising: an interconnect substrate comprising iron and chromium; a manganese oxide cobalt spinel coating formed on an air side of the interconnect substrate; And a barrier layer between the interconnect substrate and the cobalt manganese cobalt spinel coating. The coated interconnect of claim 32, wherein the barrier layer comprises titanium dioxide or a package Perovskite containing permanganate. The coated interconnect of claim 32, wherein the barrier is a reactive barrier comprising a dopant and the coating comprises a gradient doped manganese oxide cobalt spinel layer. The coated interconnect of claim 34, wherein the barrier layer comprises a dopant selected from one or more of Cr, Fe, Ti, V, Mg, Ca, Al, Si, or Ce. A method of fabricating a coated interconnect for a solid oxide fuel cell, comprising: forming a reactive layer and a manganese oxide cobalt spinel layer on the interconnect; and diffusing a dopant from the reactive layer To the manganese oxide cobalt spinel layer. The method of claim 36, wherein the manganese oxide cobalt spinel layer has a gradient doping profile. The method of claim 36, wherein the dopant comprises Cr, Fe, Ti, V, Mg, Ca, Al, Si, Ce, or a combination thereof. A method of fabricating a coated interconnect for a solid oxide fuel cell, comprising: forming an interconnect comprising Fe, Cr, and a dopant; coating the interconnect with a layer of manganese oxide cobalt spinel And diffusing dopants from the interconnect into the manganese oxide cobalt spinel layer. The method of claim 39, wherein the manganese oxide cobalt spinel layer has a gradient doping profile. The method of claim 39, wherein the dopant comprises Ti, V, Mg, Ca, Al, Si, Ce, or a combination thereof. A coated interconnect for a solid oxide fuel cell, comprising: an interconnect substrate comprising iron and chromium; and a manganese oxide cobalt spinel coating formed on an air side of the interconnect substrate Wherein the manganese oxide cobalt spinel coating additionally comprises iron, titanium, vanadium, chromium, aluminum, manganese, At least one of calcium, strontium and/or strontium. The coated interconnect of claim 42, wherein the manganese oxide cobalt spinel comprises 1-50 atom% Fe, 1-50 atom% Ti, 1-50 atom% V, 0.1-10 atom% Cr, 1 -10 at% of at least one of Mg, Ca, Al, Si or Ce. A method of fabricating an interconnect for a solid oxide fuel cell, comprising: providing an interconnect comprising a compact mixture of Cr and Fe powder; coating an air side of the interconnect with a layer of material comprising ceramic powder; And sintering the green mixture of the Cr and Fe powder and the ceramic powder layer in the same sintering step. The method of claim 44, wherein the sintering is carried out in a hydrogen reduction furnace having a dew point of -20 ° C to -30 ° C at a temperature of 1300 ° C to 1400 ° C for 0.5 to 6 hours. The method of claim 45, wherein the sintering is carried out at an oxygen partial pressure of 10 ^-17 to 10 ^-15 atm. A method of fabricating an interconnect for a solid oxide fuel cell, comprising: providing an interconnect comprising Cr and Fe; using one or more of MnO, CoO, Mn metal, Co metal, and combinations thereof A manganese oxide cobalt precursor is applied to the interconnect; and the manganese manganese cobalt precursor is sintered to form a manganese oxide cobalt spinel coating. The method of claim 47, further comprising removing the native oxide from at least one of an air side or a fuel side of the interconnect. The method of claim 48, comprising removing the native oxide from the air side and the fuel side of the interconnect. The method of claim 49, wherein the removing comprises blasting. A method of fabricating an interconnect for a stack of solid oxide fuel cells, comprising: providing a first metal powder particle comprising Cr and Fe in a cavity; Providing a second powder particle comprising one or more of Sr, La, Mn, and Co oxides in the mold cavity; and compacting the first powder particles and the second powder particles to form the interconnect . The method of claim 51, wherein the first powder particles are mixed with the second powder particles to form a powder mixture, and then supplied to the cavity as the powder mixture. The method of claim 52, additionally comprising adding a lubricant to the powder mixture prior to the compacting step. The method of claim 53, wherein the interconnect has at least one of Sr, La, Mn, and Co oxide regions throughout its thickness. The method of claim 51, wherein the first powder particles are first provided in the cavity, and the second powder particles are provided on the first powder particles in the cavity, and wherein the compaction is A lanthanum manganate (LSM) or manganese manganese cobalt (MCO) region is produced on the top surface of the Cr-Fe alloy interconnect. The method of claim 51, wherein the second powder particles are first provided in the cavity, and the first powder particles are provided on the second powder particles in the cavity, and wherein the compaction is A lanthanum manganate (LSM) or manganese manganese cobalt (MCO) region is produced on the underside of the Cr-Fe alloy interconnect. The method of claim 51, wherein: the first powder particles are first supplied to the mold, and the second powder particles are electrostatically attracted to a bottom surface of a punch for compacting the powder particles; and the punch Pressing the second powder onto the first powder to compact the first powder particles and the second powder particles to form lanthanum manganate (LSM) or oxidation on the top surface of the interconnect Cr-Fe alloy interconnects in the manganese cobalt (MCO) region. The method of claim 51, wherein the surface area of the interconnect is relative to only by phase The interconnects made by compacting the first powder particles in the same cavity increase. The method of claim 51, wherein the first powder particles comprise a mixture of elemental Cr and elemental Fe particles or Cr-Fe alloy powder particles. The method of claim 51, wherein the second powder particles comprise lanthanum manganate (LSM) or manganese cobalt cobalt (MCO) powder particles.