Wet spray coating of SOEC and SOFC interconnects

Abstract

To provide a coating method of an interconnect for avoiding deterioration of a SOFC stack generated in relation to chromia formation of components of a metal interconnect.SOLUTION: There are provided systems, devices, and methods that utilize a method of coating an interconnect for a SOEC or SOFC. The method includes wet spraying a coating precursor powder onto an interconnect, and sintering the interconnect in an oxidizing ambient to form the coating.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 139,907, filed on 21 January 2021, which is incorporated herein by reference in its entirety.

[0002] Embodiments of the present invention generally relate to components of electrolytic cell stacks and fuel cell stacks, and more specifically to interconnects used in electrolytic cell stacks and fuel cell stacks, and methods for manufacturing interconnects. [Background technology]

[0003] Generally, solid oxide electrolytic (SOE) systems include an SOE stack consisting of solid oxide electrolytic cells (SOECs) and metal interconnects (ICs) that require functional coatings. Similarly, solid oxide fuel cells (SOFCs) also include metal interconnects that require functional coatings.

[0004] For example, a typical solid oxide fuel cell stack includes multiple fuel cells separated by metal interconnects that electrically connect both adjacent cells within the stack and channels for delivering and removing fuel and oxidizer. These metal interconnects are typically made of Cr-based alloys, such as CrF with a composition of 95 wt% Cr-5 wt% Fe, or an alloy known as Cr-Fe-Y with a composition of 94 wt% Cr-5 wt% Fe-1 wt% Y. CrF and CrFeY alloys maintain their strength and dimensional stability under typical SOFC operating conditions, e.g., 700-900°C, in both air and humid fuel atmospheres. However, during SOFC operation, chromium in the CrF or CrFeY alloy reacts with oxygen to form chromia, degrading the SOFC stack.

[0005] Two major degradation mechanisms affecting SOFC stacks are directly related to the formation of chromia in the metal interconnect components: i) increased stack ohmic resistance due to the formation of native chromium oxides (chromia, Cr2O3) on the interconnect, and ii) chromium poisoning of the SOFC cathode.

[0006] Although Cr2O3 is an electronic conductor, its conductivity at the operating temperature of SOFCs (e.g., 700-900°C) is very low, on the order of 0.01 S / cm at 850°C (compared to 7.9 × 10⁻⁶ for metallic Cr). 4 (This is S / cm). The chromium oxide layer thickens over time on the surface of the interconnect, and thus the ohmic resistance of the interconnect, i.e., the ohmic resistance of the SOFC stack, increases over time due to this oxide layer.

[0007] A second degradation mechanism associated with chromia formation in metal interconnects is known as cathode chromium poisoning. At SOFC operating temperatures, chromium vapor can diffuse through cracks or pores in the coating, and chromium ions can diffuse into the SOFC cathode by solid-phase diffusion through the lattice structure of the interconnect coating material. Furthermore, during fuel cell operation, ambient air (moist air) flows on the air (cathode) side of the interconnect, and moist fuel flows on the fuel (anode) side of the interconnect. At SOFC operating temperatures, if moist air is present (on the cathode side), chromium on the surface of the Cr2O3 layer on the interconnect reacts with water and evaporates in the form of a gaseous chemical species, chromium hydroxide (CrO2(OH)2). The chromium hydroxide chemical species is transported in vapor form from the interconnect surface to the fuel cell cathode electrode, where Cr2O3 may deposit in solid form. Cr2O3 deposits on and within SOFC cathodes (e.g., by grain boundary diffusion) and / or reacts with the cathode (e.g., to form Cr-Mn spinels), significantly degrading the performance of the cathode electrode. Common SOFC cathode materials such as perovskite materials (e.g., LSM, LSC, LSCF, LSF) are particularly vulnerable to various causes of chromium oxide degradation.

Summary of the Invention

[0008] Therefore, embodiments of the present invention propose a wet spray coating for interconnects of SOECs and SOFCs that substantially avoid one or more problems resulting from the limitations and drawbacks of related technologies.

[0009] Additional features and advantages of the present invention will be set forth in the following description, become more apparent from the description, or may be learned by the practice of the present invention. The objectives and other advantages of the present invention will be realized and achieved by the structure particularly pointed out in the written description, claims, and appended drawings.

[0010] To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and generally described, a wet spray coating for interconnects of SOECs and SOFCs includes wet spraying a powdered precursor of the coating onto the interconnect and sintering the interconnect in an oxidizing atmosphere to form the coating, and includes systems, devices, and methods for coating interconnects for use in SOECs or SOFCs.

[0011] In another aspect, a wet spray coating for interconnects of SOECs and SOFCs includes adding metal powder to manganese cobalt oxide to form a coating material, wet spraying the coating material onto the interconnect, and sintering the interconnect in an oxidizing atmosphere to form the coating, and includes systems, devices, and methods for coating interconnects for use in SOECs or SOFCs.

[0012] It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the claimed invention.

[0013] Included to deepen the understanding of the present invention, incorporated herein and constituting a part thereof, the accompanying drawings show embodiments of the present invention and are provided to explain the principles of the present invention together with the description of the specification.

Brief Description of the Drawings

[0014] [Figure 1A] FIG. 1A is a perspective view of a SOFC stack according to various embodiments of the present invention. [Figure 1B] FIG. 1B is a partial cross-sectional view of the stack of FIG. 1A according to various embodiments of the present invention. [Figure 2] FIG. 2 shows a cross-sectional view of an interconnect according to various embodiments of the present invention. [Figure 3] FIG. 3 shows a method of coating an interconnect according to various embodiments of the present invention. [Figure 4A] FIG. 4A shows a microscopic photograph of a cross-section of a sintered interconnect coating according to various embodiments of the present invention. [Figure 4B] FIG. 4B shows a microscopic photograph of a cross-section of a sintered interconnect coating according to various embodiments of the present invention. [Figure 4C] FIG. 4C shows a microscopic photograph of a cross-section of a sintered interconnect coating according to various embodiments of the present invention. [Figure 4D] FIG. 4D shows a microscopic photograph of a cross-section of a sintered interconnect coating according to various embodiments of the present invention. [Figure 5A] FIG. 5A shows a microscopic photograph of a cross-section of a sintered interconnect coating according to various embodiments of the present invention. [Figure 5B] FIG. 5B shows a microscopic photograph of a cross-section of a sintered interconnect coating according to various embodiments of the present invention.

Modes for Carrying Out the Invention

[0015] Embodiments of the present invention are described below in detail, with examples shown in the accompanying drawings. Wherever possible, the same reference numerals are used for the same elements.

[0016] In general, air plasma spray (APS) coating provides good results for reducing interconnect degradation. For example, the coating material can be applied using a spray method such as air plasma spray (APS), or using a coating method such as a wet coating method using a coating material ink. The APS process is a thermal spraying process in which powdered coating material is supplied to a coating apparatus. The coating particles are introduced into a plasma jet, where they are melted and then accelerated toward the substrate. Upon reaching the substrate, the molten droplets are flattened and cooled to form a coating. The plasma can be generated by either direct current (DC plasma) or induction (RF plasma). Furthermore, unlike atmosphere-controlled plasma spray (CAPS), which requires an inert gas or vacuum, air plasma spray is performed in an air atmosphere. Despite several advantages, the APS method is not very preferred due to its high cost.

[0017] Figure 1A is a perspective view of a solid oxide fuel cell (SOFC) stack 100 according to various embodiments of the present invention, and Figure 1B is a partial cross-sectional view of the same stack 100. While an SOFC stack is used as an example, embodiments of the present invention are further applicable to any other components, including an SOE / SOEC system and an interconnect 10.

[0018] As shown in Figures 1A and 1B, the stack 100 includes fuel cells 1 separated by an interconnect 10. As shown in Figure 1B, each fuel cell 1 includes a cathode electrode 3, a solid oxide electrolyte 5, and an anode electrode 7.

[0019] Various materials can be used for the cathode electrode 3, electrolyte 5, and anode electrode 7. For example, the anode electrode 3 may include a cermet containing a nickel-containing phase and a ceramic phase. The nickel-containing phase may consist only of nickel in a reduced state. This phase may form nickel oxide when in an oxidized state. Therefore, it is preferable that the anode electrode 7 be annealed in a reducing atmosphere prior to operation in order to reduce nickel oxide to nickel. The nickel-containing phase may include other metals in addition to nickel and / or nickel alloys. The ceramic phase may include stabilized zirconia such as yttria-stabilized zirconia and / or scandia-stabilized zirconia, and / or doped ceria such as gadolinia-doped ceria, yttria-doped ceria and / or samaria-doped ceria.

[0020] Electrolyte 5 may include stabilized zirconia such as scandia-stabilized zirconia (SSZ) or yttria-stabilized zirconia (YSZ). Alternatively, the electrolyte may include another ion-conducting material such as doped ceria.

[0021] The cathode electrode 3 may include a conductive material such as a conductive perovskite material such as lanthanum strontium manganite (LSM). Other conductive perovskites, such as LSCo, or metals, such as Pt, may also be used. The cathode electrode 3 may also include a ceramic phase similar to that of the anode electrode 7. The electrode and electrolyte may each include one or more sublayers made of one or more of the above materials.

[0022] Fuel cell stacks, such as stack 100, are often constructed from multiple SOFCs 1 in the form of planar components, tubes, or other shapes. While the fuel cell stack shown in Figure 1 is stacked vertically, fuel cell stacks can be stacked horizontally or in any other orientation. Fuel and air can be supplied to electrochemically active surfaces. For example, fuel can be supplied through fuel conduits 22 (e.g., fuel riser openings) formed in each interconnect 10.

[0023] Each interconnect 10 electrically connects adjacent fuel cells 1 within the stack 100. In particular, an interconnect 10 can electrically connect the anode electrode 7 of one fuel cell 1 to the cathode electrode 3 of an adjacent fuel cell 1. In Figure 1B, the lower fuel cell 1 is positioned between two interconnects 10. Ni mesh can be used to electrically connect the interconnects 10 to the anode electrodes 7 of adjacent fuel cells 1.

[0024] Each interconnect 10 includes a fuel-side rib 12A that at least partially defines a fuel channel 8A and an air-side rib 12B that at least partially defines an oxidant (e.g., air) channel 8B. The interconnect 10 can act as a gas-fuel separator, separating the fuel, e.g., hydrocarbon fuel, flowing to the fuel electrode (i.e., anode 7) of one cell in the stack from the oxidant, e.g., air, flowing to the air electrode (i.e., cathode 3) of an adjacent cell in the stack. The ends of the stack 100 may have air end plates or fuel end plates (not shown) for supplying air or fuel to the end electrodes, respectively.

[0025] Each interconnect 10 is made of, or may include, a conductive material such as a metal or metal alloy (e.g., chromium-iron alloy) having a coefficient of thermal expansion similar to that of the solid oxide electrolyte in the cell (e.g., a difference of 0-10%). For example, the interconnect 10 may include a metal or metal alloy (e.g., a chromium-iron alloy such as an alloy of 4-6 wt% iron, optionally 1 wt% or less yttrium, and the remainder being chromium), and can electrically connect the anode side or fuel side of one fuel cell 1 to the cathode side or air side of an adjacent fuel cell 1. A conductive contact layer, such as a nickel contact layer, can be provided between the anode electrode 7 and each interconnect 10. Another optional conductive contact layer can be provided between the cathode electrode 3 and each interconnect 10.

[0026] Figure 2 shows a cross-sectional view of an interconnect 10 according to various embodiments of the present invention. As shown in Figure 2, the interconnect 10 includes a plurality of ribs 12A and an optional contact layer 14 disposed on the tops of the ribs 12A of the interconnect 10.

[0027] As further shown in Figure 2, the coating material can be applied to the air side of the interconnect 10 prior to sintering to form a protective coating layer 40. As discussed below, the method for forming the coating layer 40 may include sintering the interconnect 10. In some cases, sintering may cause partial interdiffusion between the interconnect material and the iron of any contact layer 14. The coating layer 40 and any contact layer 14 may be sintered simultaneously.

[0028] The coating material may include the following spinel compositions, for example, one comprising at least two (e.g., two or three) metal oxides selected from Cu, Mn, Co, Fe, and / or Ni. 1.3 Mn 1.7 O4, MnCu 0.5 Co 1.5 O4, MnCo 1.7 Fe 0.3O4, CoFe2O4, MnCo 1.7 Cu 0.3 O4, Mn 1.4 Co 1.4 Cu 0.2 O4, Cu 0.77 ]>Ni 0.45 Mn 1.78 [[ID=]16]]O4, NiCo 2-x Fe x O4 and so on. The selection of the material is determined by balancing the electron conductivity of the spinel, the vapor pressure of the starting oxide, and the sinterability of the material. An air-oxidized coating is considered not to need to be fully densified in order to effectively suppress the evaporation of chromium in the coating and the formation of the natural oxide of chromium. This is particularly considered to be the case for SOECs where the anodic reaction occurs in an air stream and is less affected by chromium poisoning due to the oxidation reaction at the three-phase interface.

[0029] Interconnects such as interconnect 10 are fabricated by powder metallurgy. Even after compressing and sintering the metal powder in high temperature and hydrogen, the conventional interconnects are not fully densified. Appropriately, the interconnects are oxidized to fill the remaining pores. In the conventional method, the interconnects are grit-blasted to remove part of the oxide layer. Both oxidation and grit-blasting add additional costs. By applying the embodiments of the present invention, the interconnect 10 does not require an initial oxidation step and grit-blasting. Instead, a wet spray coating powder precursor is applied to the interconnect 10. Then, the interconnect 10 coated with the wet spray is oxidized. In some embodiments, the interconnect 10 coated with the wet spray is oxidized within a stack (e.g., stack 100). In some embodiments, the interconnect 10 is sintered and then subsequently oxidized after the wet spray is applied.

[0030] According to various embodiments of the present invention, the coating process for SOE or SOFC interconnects utilizes wet spraying and in-situ stack sintering. This process reduces the cost of interconnect coating and enables mass production. The wet spray coating method is more efficient than APS, eliminates the need for grid blasting surface treatment of interconnects, and allows the oxidation step of interconnects to be performed in-situ for SOFC stacks and / or SOEC stacks.

[0031] Figure 3 shows a method 300 for coating an interconnect according to various embodiments of the present invention.

[0032] In 310, the wet spray step includes applying a powdery precursor in a fluid carrier (e.g., a suspension or mixture of powders in a fluid solvent containing any binder) to the interconnect. For example, metal powders suspended in ink can be used, and the metal powders include, for example, Mn, Co, Cu, Fe, Ni, combinations thereof, and alloys thereof. Next, in 320, following the wet spray coating step to the interconnect, an oxidation / sintering step in an oxidizing atmosphere (e.g., air) is performed to provide a functional interconnect, eliminating the need for a costly reduction annealing step in a reducing atmosphere (e.g., a hydrogen atmosphere). When any of the various metal powders, alloy powders, or combinations of metal powders are applied and exposed to an air atmosphere (ambient air), oxidation and sintering occur simultaneously, creating a dense coating layer (e.g., coating layer 40) brought about by the volume expansion of the applied metal.

[0033] In various embodiments, for example, a wet-sprayed coating material is reacted with the surface of a chromium-based interconnect (e.g., a chromium-iron alloy containing 4-6 volume% iron with the remainder being chromium) through an oxidation step. The interconnect may include, as described above, an alloy plate having ribs separated by flow channels on the cathode and anode-facing sides. The interconnect may optionally include a fluid riser opening and / or a fluid flow plenum.

[0034] The coating material may include the following spinel compositions, for example, one comprising at least two (e.g., two or three) metal oxides selected from Cu, Mn, Co, Fe, and / or Ni. 1.3 Mn 1.7 O4, MnCu 0.5 Co 1.5 O4, MnCo 1.7 Fe 0.3 O4, CoFe2O4, MnCo 1.7 Cu 0.3 O4, Mn 1.4 Co 1.4 Cu 0.2 O4, Cu 0.77 Ni 0.45 Mn 1.78 O4, NiCo 2-x Fe x O4, etc. The material selection is determined by balancing the electronic conductivity of spinel, the vapor pressure of the starting oxide, and the sinterability of the material. In some cases, air-oxidized coatings do not need to be fuldensified to effectively suppress chromium evaporation and the formation of native chromium oxides in the coating. This is especially true in the case of SOEC, where the anodic reaction occurs in an airflow and is less susceptible to chromium poisoning caused by oxidation reactions at the three-phase interface.

[0035] In some embodiments, a blend of elemental metal powders (i.e., non-alloys) is deposited onto a substrate of the interconnect. Here, the interconnect containing the blend of elemental metal powders undergoes a thermal process to oxidize the metals to metal oxides. Starting metal powders include Ni, Fe, Mn, Co, and Cu, with nominal particle diameters in the range of 0.3–10 μm, e.g., d50 on the order of 2–3 μm. An ink containing one or more powders may be formulated with a solids content of 10–40% and applied to the substrate using an ultrasonic spray nozzle. This process may include one or more coating applications (e.g., 1–10 coating applications), along with drying steps between (or after) each coating application. Drying may be performed in situ using an internal heating plate, or the coated interconnect may be dried in an external oven / furnace. In mass production embodiments, the interconnects move along a conveyor belt through a series of spray stations and an in-line drying oven / furnace. After drying, the interconnects are heat-treated in an air atmosphere at approximately 940°C to 950°C for a processing time of 1 to 5 hours, or at approximately 800°C to 1000°C for a different processing time of 5 to 6 hours.

[0036] While other known wet coating processes require an N2, H2, or N2 / H2 atmosphere to densify the coating, embodiments of the present invention utilize an air atmosphere. In embodiments of the present invention, an air atmosphere is sufficient and offers the advantage of its low cost.

[0037] During heat treatment, metal powders are oxidized to metal oxides, forming an oxide coating on the interconnects. The volume expansion from metal to metal oxide fills pores (e.g., voids, gaps, and open spaces), forming a connected, semi-dense coating without open pores. For example, in the case of a 50% Fe-50% Mn powder blend, during oxidation, firstly, Fe, which has a considerably large specific volume, is oxidized to FeO2. x It is oxidized to (FeO, Fe2O3, Fe3O4), and similarly, Mn is MnO xIt is oxidized to (MnO, Mn2O3, Mn3O4), which also has a large specific volume. Over time and with temperature, the Fe oxide and Mn oxide interdiffuse to form other oxides such as Fe-Mn-O spinel, e.g., MnFe2O4 or (Mn,Fe)3O4. The final coating does not need to be single-phase, but an oxide Fe containing Fe or Mn-rich regions. x Mn y O z It consists of a mixture of several spinel phases.

[0038] To form a conductive spinel phase, several transition metal powder blends have been studied, including binary, ternary, or quaternary combinations of metal powders Ni, Fe, Mn, Co, and Cu. Some examples include, but are not limited to, Mn-Fe, Mn-Co, Ni-Fe, Ni-Co, Cu-Mn, Mn-Co-Fe, Mn-Co-Cu, Ni-Mn-Co, Ni-Mn-Fe, and Mn-Co-Fe-Cu. The proportion of each metal can range from 2 to 95%, and the d50 particle size is preferably 0.3 to 10 μm, more preferably 0.3 to 3 μm. The shape of the metal powder may be spherical, rod-shaped, or irregular.

[0039] Figures 4A to 4D show micrographs of cross-sections of interconnect coatings after sintering according to various embodiments of the present invention. Figure 4A shows a Mn-Fe; 50-50 wt% coating 440A on interconnect 410A. Figure 4B shows a Mn-Co; 50-50 wt% coating 440B on interconnect 410B. Figure 4C shows a Mn-Fe-Co; 50-25-25 wt% coating 440C on interconnect 410C. Figure 4D shows a Mn-Fe-Cu; 50-40-10 wt% coating 440D on interconnect 410D. As shown in Figures 4A to 4D, each of the coatings 440A to 440D achieves at least a semi-dense coating without connected open pores, or a dense coating with closed pores.

[0040] To produce various coatings, a slurry is prepared by thoroughly mixing metal powder, an organic solvent, a dispersant, and an optional organic binder. The solids content is 10-40%, preferably 20-30%, the dispersant is about 0.1-5%, and the optional binder is about 2-10%. Mixing is performed by stirring, shaking, or ball milling. The slurry is then sprayed onto the surface of the interconnect at a substrate temperature between 20°C and 200°C. One or more coating steps can be used, along with drying during (or after), to form the desired coating thickness. The interconnect, along with the applied coating, is then sintered, for example, in air at 950°C for 5 hours.

[0041] In another embodiment, a different coating process was developed in which metal powder is added to oxide powder to promote a dense coating. While MCO (manganese cobalt oxide) phase is a coating material for SOEC and SOFC interconnects, densifying the applied MCO coating by wet spraying followed by heat treatment in an air atmosphere alone is difficult. Here, metal powders such as Fe, Mn, Ni, Co, and Cu are added to the MCO powder to function as sintering aids. During heat treatment in air, the volume expansion from metal to metal oxide helps to fill pores (e.g., voids, gaps, and open spaces) between the partially sintered MCO powders. Furthermore, the oxidation of the metal powder promotes interdiffusion, thus accelerating the sintering of the coating. Composition Mn 1.5 Co 1.5 MCO powders such as O4 can be used, but Mn2CoO4, Mn 1.5 Co 1.5 Any (Mn O4, Co2MnO4, etc.) x Co 1-x )3O4 (for example, 0≦X≦1) is preferred. The blend of metal and MCO may be in the range of 5% to 95% metal, for example, 50%Fe-50%MCO.

[0042] MCOs mixed with two or more metals were also considered. For example, 50% Ni0.9 Fe 2.1 ~50% MCO, which is effectively 50% (30% Ni-70% Fe)-50% MCO, or 15% Ni-35% Fe-50% MCO. The starting powder size of the MCO ranges from 1 to 30 μm, but in some cases it was ground to 0.5 to 3 μm. In some coatings, the MCO was ground before being blended with the metal powder and then incorporated into the ink, while in other cases the MCO and metal powder were ground together to prepare the ink. As described above, the MCO-Fe ink was deposited on the interconnect by a spray process including one or more coatings and subsequent drying steps, and then treated, for example, in an air atmosphere at 940°C to 950°C for 1 to 5 hours. For example, MCO with added metal powder can be used. For example, other oxides containing perovskites such as LSM, LSC, and LSCF can be used. For example, NiFe2O4, Cu2MnO4, and Cu 1.5 Mn 1.5 Spinel containing O4 may also be used.

[0043] Figure 5 shows micrographs of cross-sections of interconnect coatings after sintering according to various embodiments of the present invention. Figure 5A shows MCO-Ni on interconnect 510A. 0.9 Fe 2.1 Figure 5B shows coating 540A. Figure 5B shows the MCO-Fe coating 540B on interconnect 510B. As shown in Figures 5A-5B, each of the coatings 540A-540B achieves at least a semi-dense coating without connected open pores, or a dense coating with closed pores.

[0044] In various embodiments described herein, wet spray coating processes, such as Method 300, are advantageous compared to APS coating processes. Compared to APS, wet spraying has a powder usage or powder efficiency that can exceed approximately 80%, compared to less than approximately 20% for APS, resulting in less wasted material and reduced costs. Furthermore, while APS coatings rely on mechanical bonding and therefore require surface treatment and roughening, wet spray coatings can be applied to smooth surfaces because the material interdiffuses with the interconnect alloy and naturally formed oxides to form chemical bonds, thus eliminating the need for grit blasting. This difference—that wet spray coatings do not require grit blasting in addition to the oxidation step that reacts them—leads to embodiments where the coating process is integrated into the stack / interconnect manufacturing process. For example, a glossy, unoxidized, sintered interconnect compact can then be coated by the wet spraying process and assembled into a stack. The coating and interconnect oxidation steps can then be performed in situ in the stack during the stack sintering step, during which the seals need to be set. This is described, for example, in U.S. Patent No. 9,065,127B2, issued on June 23, 2015, which is incorporated herein by reference in its entirety. The process of the embodiment eliminates oxidation of individual interconnects in the furnace, eliminates grit blasting, and eliminates the need for a separate coating oxidation step after wet spraying.

[0045] Wet spray coating processes, such as Method 300, not only significantly reduce the cost of the coating process itself, but also reduce the cost of interconnect components through the synergistic properties of stack sintering. Replacing the APS process with a more efficient wet spray process with a higher powder yield is expected to reduce coating material costs by 60%. Furthermore, eliminating the grit blasting process reduces the total coating cost by another 30%, and combined with the reduction in material usage, the total coating cost is reduced by 50%. Combining the oxidation step of the interconnect and the sintering step of the stack eliminates an entire process in the interconnect manufacturing sequence. Combining the reduction in powder usage, in-situ sintering of the stack, and the elimination of grit blasting reduces the final cost of coated interconnect components by more than 25%.

[0046] A wet spray process, such as Method 300, can be used to coat an interconnect of either an SOEC or SOFC stack, or any other component that utilizes an interconnect, such as interconnect 10. The interconnect can be coated on its cathode side or anode side (e.g., the air-side and / or fuel-side).

[0047] It will be apparent to those skilled in the art that various modifications and variations can be made to the wet spray coating of SOEC and SOFC interconnects of the present invention without departing from the intent or scope of the present invention. Accordingly, the present invention is intended to cover modifications and variations of the present invention, provided that they fall within the scope of the appended claims and their equivalents.

Claims

1. A method for coating the interconnects of solid oxide electrolytic cells (SOECs) or solid oxide fuel cells (SOFCs), To provide a powdered precursor comprising the element Mn and at least one elemental metal selected from the group consisting of Fe, Co, Ni, and Cu. The powdered precursor is wet-sprayed onto an interconnect containing a chromium-iron alloy, and A method comprising heating the interconnect in an oxidizing atmosphere to oxidize the powdered precursor, and forming a conductive spinel coating on the interconnect containing Mn and at least one metal selected from the group consisting of Fe, Co, Ni, and Cu.

2. The method according to claim 1, wherein the powdered precursor comprises at least two metals selected from the group consisting of Cu, Fe, and Ni.

3. The method according to claim 2, wherein the powdered precursor comprises 50% by weight of Mn, 25% by weight of Fe, and 25% by weight of Co, or comprises 50% by weight of Mn, 40% by weight of Fe, and 10% by weight of Cu.

4. The method according to claim 3, wherein the heating is performed in a stack of multiple SOECs or multiple SOFCs.

5. The interconnect comprises the chromium-iron alloy containing 4 to 6 volume percent of iron and the remainder being chromium. The method according to claim 1, wherein the conductive spinel coating comprises at least one oxide selected from the group consisting of Cu, Fe, and Ni.

6. The method according to claim 1, wherein the coating has closed pores.

7. The method according to claim 1, wherein the coating is a dense coating having closed pores.

8. The method according to claim 1, wherein the oxidizing atmosphere is air.

9. The method according to claim 1, wherein the heating is performed during sintering used to reflow seals in an SOFC or SOEC stack comprising a plurality of interconnects and a plurality of SOFCs or SOECs.

10. The method further includes sintering the interconnect before wet spraying the powdered precursor, The heating further includes oxidizing the interconnect after the step of sintering the interconnect. The method according to claim 1.

11. The method according to claim 10, wherein the heating is performed in an SOFC or SOEC stack comprising a plurality of interconnects and a plurality of SOFCs or SOECs.

12. The method according to claim 10, wherein the interconnect is not grit-blasted before the wet spray.

13. The method according to claim 1, further comprising simultaneously sintering the powdered precursor and the interconnect during the heating process.

14. A method for coating the interconnects of solid oxide electrolytic cells (SOECs) or solid oxide fuel cells (SOFCs), To provide a powdered precursor comprising manganese cobalt oxide (MCO) powder and elemental metal powder containing Fe, Ni, Mn, Co, or Cu, The powdered precursor is wet-sprayed onto an interconnect containing a chromium-iron alloy, and A method comprising heating the interconnect in an oxidizing atmosphere to oxidize the powdered precursor and forming a conductive spinel coating on the interconnect.

15. The method according to claim 14, wherein the powdered precursor comprises 50% by weight of Fe and 50% by weight of MCO, or comprises 15% by weight of Ni, 35% by weight of Fe, and 50% by weight of MCO.

16. The method according to claim 15, wherein the elemental metal powder includes a sintering aid.

17. The method according to claim 15, wherein the coating has closed pores.

18. The method according to claim 15, wherein the coating is a dense coating having closed pores.

19. The method according to claim 15, wherein the oxidizing atmosphere is air.

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