Protection arrangement of solid oxide cell stacks

Abstract

An object of the invention is a protection arrangement of solid oxide cell stacks, each solid oxide cell stack being used in at least one of a fuel cell system and an electrolysis system. The solid oxide cell stack comprises of at least one metallic component (103) in an oxygen rich gas side to arrange gas flow (105) for at least one solid oxide cell and to transfer current and heat to and from the solid oxide cell. The solid oxide cell comprises of a fuel gas electrode (100), an oxygen rich gas electrode (101), and an electrolyte (102) between the fuel gas electrode and the oxygen rich gas electrode. The protection arrangement comprises protective coating (104) applied on at least one metallic component (103) and the protective coating being comprised of oxygen and at least three cations comprising as principal elements at least three of an Al, Ce, Cu, Co, Cr, Fe, Gd, La, Mg, Mn, Mo, Nb, Ni, Sc, Si, Sm, Sn, Sr, Ta, Ti, Y, V, W, Zn, and Zr which has a same kind of atomic fraction.

Description

[0001] Protection arrangement of solid oxide cell stacks

[0002] The field of the invention

[0003] Most of the energy in the world is produced by means of oil, coal, natural gas, or nuclear power. All these production methods have their specific problems as far as, for example, availability and friendliness to the environment are concerned. As far as the environment is concerned, especially oil and coal cause pollution when they are combusted. The problem with nuclear power is, at least, the storage of used fuel.

[0004] Especially because of environmental problems, new energy sources that are more environmentally friendly and, for example, having a better efficiency than conventional energy sources have been developed.

[0005] Solid oxide cells operate via a chemical reaction in an environmentally friendly process and are very promising future energy conversion devices. The intermittency of renewable energy sources has introduced challenges for electrical grid stability, calling for increased demand and supply side flexibility and new energy storage and conversion technologies.

[0006] State of the art

[0007] An electrochemically active solid oxide cell can be used as a fuel cell or an electrolyser. A fuel cell produces electricity and heat from various fuels, and an electrolysis cell produces chemicals such as hydrogen, methane, ammonia and carbon monoxide from steam, CO2 and nitrogen, electricity, and heat. Such a cell that operates in both modes, as a fuel cell and electrolyser, is called a solid oxide electrochemical cell (SOEC) or reversible solid oxide cell (rSOC) or simply a solid oxide cell (SOC). Solid oxide cell (SOC) comprises a fuel electrode and an oxygen electrode and an electrolyte layer between them. In solid oxide fuel cells (SOFCs), oxygen is fed to the oxygen electrode and it is reduced to a negative oxygen ion by receiving electrons from the oxygen electrode. The negative oxygen ion is transported through the electrolyte layer to the fuel electrode where it reacts with fuel, producing typically water and carbon monoxide (CO) and carbon dioxide (CO2). Fuel electrode and oxygen electrode are connected through an external electric circuit comprising a load for the fuel cell operating mode withdrawing electrical energy out of the system. The fuel cells also produce heat to the reactant exhaust streams. In electrolysis operating mode, the current flow is reversed, and the solid oxide cells act as a load to which electricity is supplied. Depending on the electrolysis reaction operating conditions, the cell operation can be endothermic, exothermic, or thermoneutral.

[0008] Fuel cell reactions in the case of methane, carbon monoxide, and hydrogen fuel are shown below: fuel electrode: CF + H2O = CO + 3H2 (steam reforming reaction) CO + H2O = CO2 + H2 (water gas shift reaction) H2+ O2’ = H2O + 2e_(fuel cell anode reaction) oxygen electrode: O2 + 4e_= 2O2’ (fuel cell cathode reaction)

[0009] Net reactions: CF + 2O2 = CO2 + 2H2O

[0010] CO + 1 / 202 = CO2

[0011] H2+ 1 / 202 = H2O

[0012] In electrolysis operating mode the reaction is reversed, i.e., electrical energy from a source is supplied to the cell, where water and often also carbon dioxide are reduced on the fuel electrode, forming oxygen ions that move through the electrolyte layer to the oxygen electrode, where oxidation reaction takes place. It is possible to use the same solid oxide cell in both SOFC and SOEC modes. Prior art solid oxide electrolyser cells operate at temperatures that allow high temperature electrolysis reaction to take place, said temperatures being typically between 500 - 1040 °C, but even temperatures over 1040 °C may be useful. These operating temperatures are similar to those conditions of the solid oxide fuel cells (SOFCs). The net cell reaction produces hydrogen and oxygen gases. The reactions for one mole of water are shown below: fuel electrode: H2O + 2e — > 2 H2 + O2-(electrolysis cell cathode reaction) oxygen electrode: O2’ — > I / 2O2 + 2e_(electrolysis cell anode reaction)

[0013] Net reaction: H2O — > H2 + 1 / 202.

[0014] In case of co-electrolysis, carbonaceous species are supplied to the cell in addition to steam, typically in proportions favorable for subsequent refining of the resultant gas according to, e.g., the Fischer-Tropsch process. Carbon dioxide can be directly reduced to carbon monoxide or can interact with hydrogen through the reversed water-gas shift reaction to form carbon monoxide and steam. Solid oxide cell can also be used to produce other types of chemicals, either directly by electrochemical reactions or through chemical reactions. Such chemicals may include, e.g., methane and ammonia. Methane can be produced when steam and carbonaceous species are fed to a solid oxide electrolysis cell, and ammonia when steam and nitrogen are fed. The reaction rate of the chemical production is dependent on the supplied current, fuel and air side flow rates, fuel and air side gas concentrations, fuel and air side pressures, and fuel and air side temperatures.

[0015] In Solid Oxide Fuel Cell (SOFC) and Solid Oxide Electrolyser (SOE) stacks, where the flow direction of the fuel electrode gas is relative to the oxygen rich side gas internally in each cell as well as relative to the flow directions of the gases between adjacent cells, stacks are combined through different cell layers of the stack. Further, the fuel electrode gas, or the oxygen electrode gas, or both can pass through more than one cells before it is exhausted, and a plurality of gas streams can be split or merged after passing a primary cell and before passing a secondary cell. These combinations serve to increase the current density and minimize the thermal gradients across the cells and the whole stack.

[0016] The high operating temperature in the SOC cells and system introduces material related challenges with respect to thermomechanical forces, material properties, chemical stability, and uniformity of operating conditions. These aspects place practical constraints on feasible SOC cell, stack, and module sizes. Scaling the technology for large installations, typical to SOEC application, will thus primarily rely on the multiplication of cells, stacks, and SOC modules. Minimizing the cost of each multiplying unit at all levels is thus crucial for reducing the overall cost.

[0017] A SOFC delivers, in normal operation, a voltage of approximately 0.5 - 1 .2 V and a typical operation voltage of a SOE cell is about 0.9 - 1 .6 V. In order to increase the total voltage output, the SOCs are usually assembled in stacks in which the cells are electrically connected via metallic components (e.g. interconnector plates, bipolar plates, flow field plates). The desired level of voltage determines the number of cells needed.

[0018] Bipolar plates separate the anode and cathode sides of adjacent cell units, and at same the time enable electron conduction between anode and cathode. Interconnects, or bipolar plates, are normally provided with a plurality of channels for the passage of fuel gas on one side of an interconnect plate and oxidant gas on the other side. The flow direction of the fuel gas is defined as the substantial direction from the fuel inlet portion to the fuel outlet portion of a cell unit. Likewise, the flow direction of the oxidant gas (i.e., air) is defined as the substantial direction from the inlet portion to the outlet portion of a cell unit.

[0019] It is often necessary in prior art embodiments to apply protective coatings to metallic components to slow the corrosion of metal. Generally, three main corrosion mechanisms contribute to the aging of solid oxide fuel cells and electrolyser stacks. The first involves the formation of low-electrical- conductivity oxide layers on the metal surface. The second is the deposition of chromium compounds, which evaporate from the metal and settle on the active surfaces of the unit cell, where they react with electrochemically active materials, weakening their electrochemical, chemical, electrical conductivity, and / or gas permeability properties. The third mechanism is a change in the bulk metal composition, either through the depletion of at least one bulk metal component, such as chromium, or the inward transfer of a compound not originally present in the bulk metal, such as nickel from the fuel electrode or compounds from the sealing solution. Oxide structures are generally used as protective coatings to slow the diffusion of oxidants onto the metal surface and the diffusion of alloy atoms and compounds through the oxide layer.

[0020] The performance of protective coatings 104 in solid oxide cell stack (SOC) metallic components, e.g. interconnectors, is strongly linked to the chemical composition and microstructure of the deposited coatings. Since cathode degradation results from reactions between cathode materials and volatile chromium oxides and oxyhydroxides (e.g., CrOs, CrO2(OH)2, and CrO2(OH)), which are transported through the gas phase to the active electrode, these coatings must have a dense microstructure. A dense microstructure is crucial in harsh environments (high humidity and operating temperatures) to limit the growth of Cr-rich oxide scales, which can lead to uncontrolled breakaway oxidation and / or increased ohmic resistance in substrate-coating systems.

[0021] Over the years, coatings based on MnxCo3-xO4 (where 0 < x < 3) have been extensively researched. A common approach is to incorporate dopants (Cu, Ni, Fe) into the protective coating system to improve chemical, electrical and mechanical properties. However, research for cobalt-free spinel coatings for SOFCs and SOEs application it is not as extensively explored. As for cobalt- free protective coatings, there only a few compositions that has been reported to this day. For instance, Mn-Cu, Mn-Cu-Ni / Ce and Mn-O. Research on copper doped spinels within the Mn-Co-0 system have shown that copper has a positive effect on the sinterability of the coating, which is crucial for mitigating undesirable chromium evaporation. The notable physicochemical and catalytic properties of Cu-Mn-0 spinels are attributed to the presence of two Jahn-Teller ions, Mn3+and Cu2+, in the material.2In spinels like MnCozC , and Mn1.5Co1.5O4, the cubic phase remains stable within a specific composition range, influencing their properties. However, the range of composition and temperature where cubic phase exists in the Cu-Mn-0 systems is much narrower. Additionally, Cu-Mn-0 spinels are slightly less stable when compared to Mn-Co-0 systems due to their higher volatility of copper vapours, making it challenging to produce a spinel with desired composition. Any deviation from the stoichiometry, may lead to the formation of additional phases such as CuO or manganese oxides, which can significantly degrade electrical properties. Therefore, it's important to perform careful and appropriate synthesis method for Cu-Mn-0.3'2

[0022] Like manganese-cobalt spinels, the physicochemical properties of Mn-Cu-0 spinels can be enhanced through partial substitution with specific dopants. Mazur et al., explored the potential of substituting Cu with Fe in the spinel structure. The study found that a small amount of Fe (Mn-Cu-FexO , x = 0.1) does not significantly improve the properties.2However, a higher concentration of iron (x = 0.3 or 0.5) induces a phase transformation into tetragonal spinel due to the Jahn-Teller distortion at the octahedral sites. The increased level of dopant also stabilizes the spinel phase, as indicated by the reduced or absent CuO phase. Additionally, the study examined the effect of sintering temperature (900, 1000, or 1100°C) and observed that partially substituting Cu with Fe enhances the sinterability of the spinels and improves their thermochemical properties.2Nickel has also been studied as a dopant. It has also been previously used to synthesize Ni-doped Cu-Mn-0 spinels using a solid-state reaction method. The results showed that Ni could stabilize the cubic phase across a wider temperature range compared to iron.2'4 In terms of electrical conductivity at 800°C, a notable improvement was observed when Cu was substituted with Ni, resulting in the formation of (Mn,Ni,Cu)3O4 (~ 116 S / cm), compared to the original (Mn,Cu)3O4 (~60 S / cm). The study also demonstrated that a Ni-doped (Cu,Mn)sO4 spinel coating can effectively reduce the chromium diffusion rate. This is because Ni2+has a slightly lower preference for octahedral sites than Cr3+ions, but still higher than Cu2+ions. As a result, Ni2+ions can occupy octahedral sites more effectively than Cu2+ions, thereby reducing the diffusivity of Cr3+ions, which have a stronger preference for these sites. While Ni as a dopant in Cu-Mn-0 spinels has been explored in some studies, there is still limited information regarding its impact on microstructure.2'4

[0023] Protective coatings can be manufactured using various techniques, including thermal spraying methods such as plasma spraying, high-velocity oxy-fuel spraying, and flame spraying, which utilize dry powder, particle-containing suspensions, or liquid containing metallic salt precursors as feedstock. This coating feedstock is fed into the thermal flame, which melts the coating material and provides sufficient kinetic energy for the molten droplets to form a dense, well-adhered coating upon reaching the substrate.

[0024] Other methods include screen printing, dip coating, wet powder spraying, electrophoretic deposition, and painting, where a suspension is applied to the metallic component and then heat-treated. Heat treatment typically involves a two-step sintering process: the first sintering step is in a reducing environment to ensure good adhesion, followed by heat treatment in an aircontaining environment to restore the oxide structure. Alternatively, sintering can be performed solely in an air atmosphere if the primary particle size is small enough. Only the sub-micron particle range, allows sintering temperatures of 0.5-0.7 times the melting temperature of the coating material.

[0025] These publications are referred above e.g. by " material.2": 1 - Thaheem, I.; Joh, D. W.; Noh, T.; Im, H.-N.; Lee, K. T., Physico- Electrochemical Properties and Long-Term Stability of Mn1.45-o.5xC01.45- O.5XCUXYO.I04, Journal of Industrial and Engineering Chemistry, vol. 96, (2021), pp. 315-321.

[0026] 2 - Mazur, L.; Koszelow, D.; Zajusz, M.; Lapihski, M.; Bik, M.; Zaj^c, P.; Adamczyk, A.; Rutkowski, P.; Molin, S.; Brylewski, T., Comparison of Cu1.3Mn1.7O4 Spinels Doped with Ni or Fe and Synthesized via Wet Chemistry and Solid-State Reaction Methods, Designed as Potential Coating Materials for Metallic Interconnects. Journal of the European Ceramic Society, vol. 43, no. 13, pp. 5557-5574.

[0027] 3 - Wang, Y. Structure and Electrical Conductivity of Mn-Based Spinels Used as Solid Oxide Fuel Cell Interconnect Coatings, McMaster University, Hamilton, Ontario, 2013. http: / / hdl.handle.net / 11375 / 13354

[0028] 4 - Joshi, S.; Petrie, A., Nickel Substituted CuMnzO4 Spinel Coatings for Solid Oxide Fuel Cell Interconnects, International Journal of Hydrogen Energy, vol. 42, no. 8, pp. 5584-5589.

[0029] Brief description of the invention

[0030] An object of the invention is to produce a protective coating where at least three principal elements have the same atomic ratio. This is achieved by a protection arrangement of solid oxide cell stacks, each solid oxide cell stack being used in at least one of a fuel cell system and an electrolysis system, and the solid oxide cell stack comprising of at least one metallic component in an oxygen rich gas side to arrange gas flow for at least one solid oxide cell and to transfer current and heat to and from the solid oxide cell, the solid oxide cell comprising of a fuel gas electrode, an oxygen rich gas electrode, and an electrolyte between the fuel gas electrode and the oxygen rich gas electrode. The protection arrangement comprises protective coating applied on at least one metallic component and the protective coating being comprised of oxygen and at least three cations comprising as principal elements at least three of an Al, Ce, Cu, Co, Cr, Fe, Gd, La, Mg, Mn, Mo, Nb, Ni, Sc, Si, Sm, Sn, Sr, Ta, Ti, Y, V, W, Zn, and Zr which has a same kind of atomic fraction.

[0031] The invention is based on that the protective coating is comprised of oxygen and at least three cations comprising as principal elements at least three of an Al, Ce, Cu, Co, Cr, Fe, Gd, La, Mg, Mn, Mo, Nb, Ni, Sc, Si, Sm, Sn, Sr, Ta, Ti, Y, V, W, Zn, and Zr which has a same kind of atomic fraction.

[0032] Benefit of the invention is that by adjusting the combination and quantity of these cation elements, the coating can be tailored to offer specific benefits such as enhanced corrosion resistance, and low electrical resistance.

[0033] Brief description of the drawings

[0034] Figure 1 presents a solid oxide cell structure.

[0035] Figure 2 presents an exemplary arrangement according to the present invention.

[0036] Figure 3 presents another exemplary arrangement according to present invention.

[0037] Detailed description of the invention

[0038] The present invention is focused on a protective coating 104 with a unique composition that ensures optimal performance by maintaining at least three, four or five metallic cations an equal atomic ratio. The protective coating can have a wide range of compositions, which is not limited to any single combination of elements but rather emphasizes atomic ratio consistency across at least three elements. The protective coating 104 comprises oxygen and a minimum of three or more, e.g. five, principal elements. These cation elements are selected from a broad range of metals, including e.g. Al, Ce, Cu, Co, Cr, Fe, Gd, La, Mg, Mn, Mo, Nb, Ni, Sc, Si, Sm, Sn, Sr, Ta, Ti, Y, V, W, Zn, and Zr. This flexibility in the number and type of cation elements allows for the development of protective coatings with highly customizable properties to meet various performance and durability requirements. By adjusting the combination and quantity of these cation elements, the protective coating can be tailored to offer specific benefits such as enhanced corrosion resistance, and low electrical resistance.

[0039] In addition, a doping element, such as La, Sr, Y, Zr, Sc, Sm, Mo, V, W, Nb, Ti and Ce is included to further enhance the protective qualities of the coating. The combination of these elements provides excellent resistance to oxidation and other forms of degradation.

[0040] The protective coating 104 can have various structures depending on the selected elements used. The typical structures that can form include, but are not limited to, the following combinations: (Mn,Co,Cu)3O4, (Mn,Co,Fe)3O4, (Mn,Cu,Fe)3O4, (Mn,Cu,Cr)3O4, (Mn,Cu,Ni)3O4, (Mn,Cu,Fe,Ni)3O4, (Mn,Co,Fe,Ni)3O4, (Mn,Cr,Fe,Ni)3O4, (Mn,Cu,Fe,Ni,Ce)3O4, and (Mn,Cu,Fe,Ni,Y)3O4.

[0041] It should be noted that the composition of the raw materials and precursors used in the preparation of the protective coating may differ significantly from the final composition of the coating itself. This discrepancy is influenced by factors such as the specific coating method employed and the properties of the raw materials. For example, methods like plasma spraying or chemical vapor deposition may lead to variations in the final elemental distribution and structure of the protective coating.

[0042] The protective coating 104 exhibits exceptional electrochemical performance, with an area-specific resistance (ASR) value of less than 5 mOhm*cm2after 2000 hours of operation at about 650 °C. This low ASR value highlights the protective coating’s ability to minimize electrical resistance and optimize energy efficiency over extended periods.

[0043] The protective coating 104 is specifically engineered to withstand single and dual atmospheric conditions at temperatures exceeding 400°C. This makes it particularly suitable for applications where metallic components are exposed to varying oxidative and reductive environments, ensuring durability and consistent performance across different operational scenarios.

[0044] The metallic components 103 can be manufactured using various process steps in alternating order. Depending on the metallic component design, the protective coating 104 can be applied at any point in the manufacturing process. The metallic component can be flat and protectively coated to operate in dual-atmosphere conditions and combined with a formed and perforated coated structure for single-atmosphere conditions. The second option is a formed and coated structure operating in dual-atmosphere conditions. The third option is a formed and coated structure operating in dual-atmosphere conditions combined with perforated and coated structure operated in single-atmosphere conditions. The fourth option is a formed and coated structure operating in dual-atmosphere conditions, combined with a coated or non-coated metallic mesh structure operating in single-atmosphere conditions.

[0045] After the metallic component forming process, the plates are washed to remove forming chemicals that could reduce the adhesion of the protective coating. The formed structure can be annealed at elevated temperatures above 400 °C to restore mechanical properties for example grain size, grain size distribution and the crystallographic texture to a state close to its condition prior to forming. Annealing can also be part of the stack conditioning process, where the stack is held at a specific temperature for a fixed time to recover internal stresses and restore grain size distribution and the crystallographic structure. Depending on the metallic component design, welding can be performed either before or after the coating process to connect different elements 103a, 103b and 103c in the metallic component design . In addition to welding, diffusion bonding can be used to connect different elements 103a, 103b and 103c in the metallic component design. The process may vary depending on whether the protective coating is in a metallic or oxide state. Diffusion bonding is carried out at temperatures between 900-1050 °C in inert or reducing atmospheres. Therefore, similar changes in grain size distribution and crystallographic texture occur as in separate annealing steps.

[0046] The conditioning process is a manufacturing step where the assembled stack is heated to specific temperature steps to achieve gas-tight stack structure and electrochemically active layers.

[0047] A typical conditioning process includes an annealing phase at temperatures between 400-700 °C in air, inert, or reducing atmospheres. This phase restores mechanical properties, grain size distribution, and crystallographic texture of the metallic components. The annealing step typically lasts between 0.5-6 hours.

[0048] After the annealing phase, the stack is heated to sufficiently high temperatures to melt the sealing glass. This temperature is generally higher than typical operating conditions and defined by the glass composition, ranging between 700-900 °C. Under these conditions, the glass layer melts and forms a gas-tight repeating unit and stack structure. This step is typically carried out in oxidizing or inert conditions, allowing for the effective burnout of organics used in sealing components and glass layers. The burnout of the organics typically starts already when temperature exceeds 200 °C. The stack sealing phase usually lasts 0.5-4 hours.

[0049] Once a gas-tight structure is achieved, the fuel-side electrode is reduced to create an electrochemically active layer. This step is conducted at temperatures ranging from 600-750 °C, with hydrogen-containing gas fed into the fuel electrode structure while air is supplied to the oxygen electrode structure. During this phase NiO particles in the fuel-side electrode are reduced to metallic Ni, rendering the ceramic cell to be electrochemically active. This step generally lasts between 1-4 hours.

[0050] In addition to the reduction of the fuel electrode layer, a similar conditioning process can be applied to the oxygen electrode to enhance its properties, typically involving changes in phase structures and porosity. This process can be carried out in various gas compositions, ranging from oxidizing to reducing atmospheres. The oxygen electrode can also be sintered using electrical current. When the stack becomes electrochemically active, the increased current density at contact points raises the local temperature, promoting the sintering of particles.

[0051] After the fuel electrode reduction phase is completed, the stack can operate under normal conditions. Typically, the final step of the stack conditioning process involves end-of-line testing. During this testing, parameters such as the current-voltage profile (l-V), open circuit voltage (OCV), electrochemical impedance measurements (EIS), gas leakage test, shut-down tests, fuel utilization (Fll), and oxygen utilization are evaluated to ensure stack quality control. The mentioned measurements can be conducted either in fuel cell or electrolysis modes.

[0052] Once the high-temperature conditioning process is completed, roomtemperature leakage test, 3D measurements, and resistance measurements can be performed to further validate stack quality control data. Depending on the stack design, transfer compression rods and springs can be added to ensure the mechanical stability of the stack. The conditioned stack can be packed by sealing it in a protective gas package or vacuum packing to ensure long-term transport and storage.

[0053] The conditioning process can also alter the structure of the protective coating 104. The elevated temperatures facilitate the formation of stable protective coating structures, transitioning the metastable phases into phases, which may include cubic, tetragonal, or monoclinic structures. Additionally, metallic layers are converted into oxide layers through oxidation. The conditioning process can also modify the protective coating microstructure, resulting in a denser protective coating with improved adhesion properties.

[0054] An object of the invention is to have protection arrangement and method to form protective oxide layer 104 with a dense microstructure which is able to sinter and densify when energy (i.e. heat) is induced to prevent corrosion in single and dual-atmosphere conditions and to improve lifetime and electrical efficiency of the metal component.

[0055] The method of manufacturing protective coating 104 onto a substrate can be performed by using one or more of the following coating techniques: thermal spraying using coating feedstock selected from dry powder, suspension, or liquid-based materials, screen printing, wet powder spraying; painting; suspension coating; electrophoretic deposition (EPD); anodizing, thin-film deposition techniques including physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), and magnetron sputtering.

[0056] Protective coating 104 can be deposited using thermal spraying or high- temperature spray pyrolysis through liquid-state synthesis, so that metallic salts are homogeneously diluted in liquid precursors. Liquid precursor is formed from at least metal nitrates and metal acetates and from solvent formed by at least one organic compound and water. An amount of metallic salts can be adjusted so that cationic concentration for precursors is between 1 ...4.5 mol / L.

[0057] Exothermic properties of the liquid precursor can be adjusted using citric acid, glycine, carbamide, polyvinyl alcohol.

[0058] A dense protective coating 104 is formed from submicron particles in a metastable state, which subsequently transform into cubic, tetragonal, or monoclinic crystallographic phase structure at elevated temperatures which can be the conditioning or stack operation step. Chemical composition can alter from the initial precursor as it depends on the oxidizing environment (temperature and gas conditions).

[0059] High temperature and high velocity thermal flame in thermal spraying deposition process can be accomplished e.g. by combusting hydrocarbons either propane, propylene, hydrogen, ethylene, acetylene, kerosene or mixture of hydrocarbons with oxygen.

[0060] The protective coating 104 layers can be produced using physical vapor deposition (PVD) techniques such as thermal evaporation, electron beam evaporation, DC sputtering, RF sputtering, magnetron sputtering, high-power impulse magnetron sputtering (HiPIMS), cathodic arc deposition, ion plating, pulsed laser deposition (PLD), plasma-enhanced PVD (PEPVD), and chemically assisted PVD. The targets used in these processes can be tailored to achieve the desired coating composition, in both metallic and oxide forms.

[0061] In the following is presented preferred embodiments according to the present invention as referred to the attached figures 1 -3. In a protection arrangement of solid oxide cell stacks, each solid oxide cell stack comprises at least two metallic components 103 made of metal to arrange gas flows 105, 106 for at least one solid oxide cell. The solid oxide cell comprises a fuel gas side 100, an oxygen rich gas side 101 , and an electrolyte element 102 between the fuel gas side and the oxygen rich gas side. The protection arrangement comprises protective coating 104 applied on the metallic components 103, which protective coating 104 is comprised of oxygen and at least three cations comprising as principal elements at least three of an Al, Ce, Cu, Co, Cr, Fe, Gd, La, Mg, Mn, Mo, Nb, Ni, Sc, Si, Sm, Sn, Sr, Ta, Ti, Y, V, W, Zn, and Zr, which each has a same kind of atomic fraction.

[0062] In one exemplary embodiment according to the present invention the protective coating 104 can comprise at least one of an doping element La, Sr, Y, Zr, Sc, Sm, Mo, V, W, Nb, Ti and Ce, which amount is less than of the principal elements. In another exemplary embodiment according to the present invention the protection arrangement can comprise a protective coating 104 combining oxygen and three principal cation elements, each having an atomic fraction of 20 - 47 % in respect to other principal cation elements, and optionally at least one doping element used in atomic fraction of below 12.5 % in respect to the total cation elements. The protection arrangement can also comprise a protective coating 104 combining oxygen and four principal cation elements, each having an atomic fraction of 15 - 35 % in respect to other principal cation elements, and at least one doping element used in atomic fraction of below 10 % in respect to the total cation elements. In a further exemplary embodiment according to the present invention the protection arrangement can comprise a protective coating 104 combining oxygen and five principal cation elements, each having an atomic fraction of 12 - 28 % in respect to other principal cation elements, and at least one doping element used in atomic fraction of below 7.5 % in respect to the total cation elements.

[0063] The protection arrangement can preferably comprise a protective coating 104 having dense microstructure with a porosity less than 30 %.

[0064] In a preferred exemplary method of manufacturing protective coating 104 according to the present invention the protective coating 104 is manufactured in a solid-state synthesis. Reactants are selected from at least one of oxidebased and carbonate-based materials added in stoichiometric proportions, and calcinated at a temperature above 600°C to form a homogenous mixture of elements.

[0065] Metallic salts are dissolved in a liquid precursor comprising at least one metal nitrate, one metal acetate, and a solvent formed of at least one organic compound and water. The metallic salts are adjusted so that the cationic concentration of the precursor is between 1 mol / L and 4.5 mol / L.

[0066] According to the present invention the metallic component can comprise an oxidized protective coating 104 being heat treated in a process to stabilize the coating structure. In another embodiment according to the present invention the metallic component 103 can comprise a metallized protective coating 104 being heat treated in a process to form an oxidized coating structure.

[0067] In an exemplary embodiment according to the present invention an oxide powder feedstock to produce protective coating 104 can be manufactured in solid-state or in liquid phase synthesis or in both of them to select reactants from at least one of metal oxide, metal carbonate, metal nitrate, and metal acetate materials. The reactants can be added in a same kind of cation proportions, and calcinated to form a mixture of oxides. Cation proportion is defined as atomic fraction of principal and doping elements.

[0068] In another exemplary embodiment according to the present invention a coating feedstock can be manufactured in a liquid-state synthesis, wherein metallic salts are dissolved in a solvent. The coating feedstock can comprise metal nitrate or metal acetate materials or both of them, at least one compound containing carbon. The metallic salts can be added in a same kind of cation proportions.

[0069] The present protection arrangement can comprise a protective coating 104 which gives corrosion resistance at single and dual atmospheric conditions in fuel cell and electrolysis modes at temperatures more than 400 °C.

[0070] According to the present invention the concentration of the starting materials can differ considerably from the composition of the final coating. This is influenced by e.g. a used coating method and starting materials.

[0071] Figure 3 presents another arrangement according to present invention, in which a fuel side coating 107 is on a separator plate 103b of a fuel flow plate structure 103 which comprises also an air side flow structure 103a and a fuel side flow structure 103c. The air side flow structure 103a can also contain protective coating 104. The separator plate 103b can contain protective coating 104 on its first side and fuel side coating 107 on its second side. Structures 103a, 103b, 103c can be for example at least one of perforated, mesh, corrugated and porous foam structure. Structures 103a, 103b, 103c can be for example made of ferritic stainless steel, austenitic stainless steel, single, metal mixtures and alloyed metal composition for example Ni, Ni-Sn and super alloys.

[0072] Calcinated mixture of oxides is grinded to form a powder that is used to produce protective coating. The primary particle size in the powder is preferably less than 20 pm but can be also larger. The powder can be used as such in a coating process or can be mixed with liquid to form a suspension that is used in a coating process.

[0073] Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the invention may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements which perform substantially the same results are within the scope of the invention. Substitutions of the elements from one described embodiment to another are also fully intended and contemplated. It is also to be understood that the drawings are not necessarily drawn to the scale, but they are merely conceptual in nature. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

Claims1 . Protection arrangement of solid oxide cell stacks, each solid oxide cell stack being used in at least one of a fuel cell system and an electrolysis system, and the solid oxide cell stack comprising of at least one metallic component (103) in an oxygen rich gas side to arrange gas flow (105) for at least one solid oxide cell and to transfer current and heat to and from the solid oxide cell, the solid oxide cell comprising of a fuel gas electrode (100), an oxygen rich gas electrode (101 ), and an electrolyte (102) between the fuel gas electrode and the oxygen rich gas electrode, characterized by that the protection arrangement comprises protective coating (104) applied on at least one metallic component (103) and the protective coating being comprised of oxygen and at least three cations comprising as principal elements at least three of an Al, Ce, Cu, Co, Cr, Fe, Gd, La, Mg, Mn, Mo, Nb, Ni, Sc, Si, Sm, Sn, Sr, Ta, Ti, Y, V, W, Zn, and Zr which has a same kind of atomic fraction.

2. Protection arrangement of solid oxide cell stacks according to the claim 1 , characterized by that the protective coating comprising at least one of a doping element La, Sr, Y, Zr, Sc, Sm, Mo, V, W, Nb, Ti and Ce, which amount is less than of the principal elements.

3. Protection arrangement of solid oxide cell stacks according to the claim 1 , characterized by that the protection arrangement comprises a protective coating combining oxygen and three principal cation elements, each having an atomic fraction of 20 - 47 % in respect to other principal cation elements, and optionally at least one doping element used in atomic fraction of below 12.5 % in respect to the total cation elements.

4. Protection arrangement of solid oxide cell stacks according to the claim 1 , characterized by that the protection arrangement comprises a protective coating combining oxygen and four principal cation elements, each having anatomic fraction of 15 - 35 % in respect to other principal cation elements, and optionally at least one doping element used in atomic fraction of below 10 % in respect to the total cation elements.

5. Protection arrangement of solid oxide cell stacks according to the claim 1 , characterized by that the protection arrangement comprises a protective coating combining oxygen and five principal cation elements, each having an atomic fraction of 12 - 28 % in respect to other principal cation elements, and optionally at least one doping element used in atomic fraction of below 7.5 % in respect to the total cation elements.

6. Protection arrangement of solid oxide cell stacks according to the claim 1 , characterized by that the protection arrangement comprises oxide coating having dense microstructure with a porosity less than 30 %.

7. Protection arrangement of solid oxide cell stacks according to the claim 1 , characterized by that an oxide powder feedstock to produce protective coating is manufactured in at least one of a solid state and liquid phase synthesis, in which reactants are selected from at least one of metal oxide, metal carbonate, metal nitrate, and metal acetate materials, and are added in a same kind of cation proportions, and calcinated to form a mixture of oxides.

8. Protection arrangement of solid oxide cell stacks according to the claim 1 , characterized by a coating feedstock is manufactured in a liquid phase synthesis, wherein metallic salts are dissolved in a solvent, feedstock comprising at least one of metal nitrate and metal acetate materials, at least one compound containing carbon, and the metallic salts are added in a same kind of cation proportions.

9. Protection arrangement of solid oxide cell stacks according to the claim 1 , characterized by that the protection arrangement is being heat treated to perform at least one of stabilizing and forming oxide phase structure.

10. A metallic component, characterized by that the metallic component being protectively coated according to claim 1 .

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