Method for coating a part

Abstract

A method for producing a coated chromium-containing part is disclosed that includes providing a coating mixture of a solvent and a source of praseodymium and / or a source of terbium, contacting a surface of the part with the coating mixture, optionally drying, and heating the part in an oxidizing atmosphere at 450° C. or higher. Also disclosed are coated parts for devices, and electrochemical devices having coated parts, the parts having a surface coating that includes at least one layer that includes a praseodymium and / or terbium material. The method produces a coating that reduces chromium deposition and is useful as a barrier on the chromium-containing part.

Description

[Technical field]

[0001] The present invention relates to methods for producing coated parts, coated parts for use in devices and electrochemical devices including coated parts. [Background technology]

[0002] Coatings based on rare earth compounds have been used to reduce corrosion of substrates and to impart specific surface properties to substrates.

[0003] Yan Yan et al. (Surface and Coatings Technology; Vol. 272, (2015), pp. 415-427) disclose the fabrication of lanthanum, yttrium and cerium oxide coatings on porous stainless steel for use in metal-supported solid oxide fuel cells. The paper explains that the suitability of rare earth oxides as coatings is highly dependent on the rare earth oxide used.

[0004] US 2004 / 186201 discloses a corrosion resistant coating (including carbon pigments) for substrates that may contain rare earth metals. US 2005 / 0061664 discloses an electrolytic cell, more specifically an interconnected supported electrolytic cell assembly, a preform and a method for its manufacture. Spanish patent ES2359550 discloses a vitreous coating composition and a method for obtaining a vitreous coating obtained by a sol-gel process and stable at temperatures up to 250°C. Korean patent KR1020200131553 discloses a Pr x O 2x-δ Korean Patent KR1020200132500 discloses a battery module, which is an interconnector for a solid oxide battery having a coating.

[0005] WO 05 / 071021 discloses an anti-corrosion coating composition as a self-priming topcoat that contains a fluorinated resin and may include a corrosion-inhibiting rare earth compound.

[0006] US 2013 / 251942 and WO 2012 / 021822 each disclose a substrate having a hydrophobic coating of a rare earth material (oxide, carbide, nitride, fluoride and / or boride) having a dynamic water contact angle of at least about 90°.

[0007] Fontana et al. (Journal of Power Sources 171 (2007) pp. 652-662) disclose a corrosion resistance and electrical conductivity evaluation study for alloys using oxide coatings of La, Y and Nd deposited by metal organic chemical vapor deposition.

[0008] Electrochemical cells formed with oxide layers, which may include rare earth oxide layers (often known as solid oxide cells: SOCs), may be used as fuel cells or electrolyzer cells.

[0009] SOC fuel cell units generate electricity using an electrochemical conversion process that oxidizes fuel. SOC fuel cell units can also, or instead, operate as regenerative fuel cell (or reverse fuel cell) units, often known as solid oxide electrolyzer fuel cell units, for example to separate hydrogen and oxygen from water, or carbon monoxide and oxygen from carbon dioxide.

[0010] Solid oxide fuel cells (SOFCs) generate electrical energy through the electrochemical oxidation of a fuel gas (usually hydrogen-based); the devices are generally ceramic-based and use an oxygen-ion conducting metal oxide-containing ceramic as their electrolyte. Many ceramic oxygen-ion conductors (e.g., zirconium oxide- or cerium oxide-doped) have useful ionic conductivities at temperatures above 450° C. or 500° C. (for cerium oxide-based electrolytes) or above 650° C. (for zirconium oxide-based ceramics), so SOFCs tend to operate at high temperatures. The anode, electrolyte, and cathode of a SOC can each be formed of one or more layers to optimize operation.

[0011] During operation, the electrolyte of a SOFC guides oxygen ions from the cathode to the anode, located on the opposite side of the electrolyte. Fuel is in contact with the anode (usually known as the "fuel electrode"), and an oxidant, such as air or an oxygen-rich fluid, is in contact with the cathode (usually known as the "air electrode"). Conventional ceramic-supported (e.g. anode-supported) SOFCs have low mechanical strength and are vulnerable to fracture. Therefore, metal-supported SOFCs have been developed, which have active fuel cell component layers supported on a metal substrate. In these cells, the ceramic layers can be very thin since they only perform an electrochemical function: i.e., they are not free-standing, but rather are thin coatings / films laid down on and supported by a metal substrate. Such metal-supported SOFC stacks are more robust, lower cost, have better thermal properties than ceramic-supported SOFCs, and can be sealed using conventional metal welding techniques.

[0012] Applicant's WO 2015 / 136295 discloses a metal supported SOFC, where the metal support plate has a porous region surrounded by a non-porous region having an active layer deposited on the porous region, so that gas can pass through the pores from one side of the metal support plate to the other to access the active layer coated thereon. The porous region includes micro-apertures (holes through the metal foil substrate) that extend through the support plate.

[0013] WO 2016 / 128721 discloses interconnects for low temperature solid oxide fuel cells, in particular interconnects comprising a chromium oxide layer (chromium(III) oxide / chromia).

[0014] Components including metal supports and interconnects as well as other components in SOFCs (and other devices) may be formed of materials specific to SOFCs, including steel. However, it is desirable to use materials containing chromium, which may be low cost or have other beneficial properties. However, it has been observed that materials (e.g., metal alloys) may exhibit chromium volatility. Volatile chromium compounds may cause problems during fabrication and may contaminate SOFC electrodes during operation. There have been attempts to coat components (e.g., with alumina or CoCe) to reduce the chromium problem, but have not been entirely successful.

[0015] Therefore, there is a need to reduce or prevent the problems associated with the use of chromium-containing materials.

[0016] It is an object of the present invention to address this need. Summary of the Invention

[0017] Thus, the present invention provides in a first aspect a method for producing a coated part, the method comprising: a) providing a chromium-containing part; b) providing a coating mixture comprising at least one solvent and a source of praseodymium and / or a source of terbium; c) contacting at least one surface of the part with the coating mixture; d) optionally drying the part; and e) heating the part in an oxidizing atmosphere at a temperature of 450° C. or higher.

[0018] As a result, in a method using a source of praseodymium, a method for producing a coated part is provided that includes: a) providing a chromium-containing part; b) providing a coating mixture including at least one solvent and a source of praseodymium; c) contacting at least one surface of the part with the coating mixture; d) optionally drying the part; and e) heating the part in an oxidizing atmosphere at 450° C. or greater.

[0019] Such a method is advantageous because it produces a chromium-containing component having at least one surface coated with a coating that includes at least one layer that includes a Pr or Tb material, and it has been surprisingly observed that problems with the chromium-containing component are reduced.

[0020] The coating has the advantage that it may act as a barrier to reduce or prevent volatilization of chromium.

[0021] The heating step may be for decomposition of a source of Pr and / or a source of Tb coating and for oxidation of the coating to produce a coating having the properties of a barrier layer in a single heating step. Alternatively, the method may further include one or more additional heating steps, optionally in an oxidizing atmosphere. Thus, the method may further include further heating the part at a temperature between 450°C and 950°C, optionally between 450°C and 910°C, optionally between 450°C and 870°C, optionally between 450°C and 810°C, optionally between 450°C and 620°C. The additional heating steps may occur during operation of the part.

[0022] The praseodymium source and / or terbium source may be a source of Pr(III) and / or Tb(III). Typically, the praseodymium source and / or terbium source may be a source of Pr(III) or Tb(III), thereby producing a coating that includes a Pr or Tb-containing material. However, in some applications, the praseodymium source and / or terbium source may be a mixed source of praseodymium and terbium, thereby producing a mixed material that includes both Pr and Tb.

[0023] The method may further include repeating steps a) through c), and possibly d) and e), thereby producing a coated part having a coating comprising multiple layers, which may be advantageous if a thicker coating is desired.

[0024] The method according to the invention is advantageous because it renders the coating continuous (eg, to form a substantially continuous coating). Furthermore, it has been found that the coating may be electrically conductive.

[0025] In general, the coating may have a thickness in the range of 50 nm to 1 μm, preferably the coating has a thickness in the range of 50 nm to 500 nm, more preferably 50 nm to 200 nm.

[0026] The part may be uncoated, ie, the coating may be placed directly on the surface of the part without an intervening layer.

[0027] The component may include a metal alloy containing chromium. Such alloy may be selected from Ni and / or Co superalloys.

[0028] The alloy typically comprises an iron with chromium (ie, iron-containing) alloy.

[0029] The component may comprise stainless steel, for example a ferritic stainless steel.

[0030] The alloy may contain 11%wt or more of Cr; in some cases 15%wt or more of Cr; in some cases 17%wt or more of Cr; in some cases 19%wt or more of Cr.

[0031] The alloy may have lanthanum or zirconium in an amount less than 0.08 wt%.

[0032] Preferably, the coating mixture is in a liquid state and preferably comprises a coating solution.

[0033] The solvent may include an alcohol, optionally a C1-C6 alcohol. The solvent may be selected from one or more of ethanol, propanol, and / or methoxypropanol.

[0034] A liquid coating method may be used. For example, contacting at least one surface of the component with the coating mixture may include dip-coating the component in the coating mixture and / or spray-coating the component with the coating mixture.

[0035] If the method includes dip coating, the step of dip coating the part may be performed at a controlled dip speed to help control the thickness and other characteristics of the coating.

[0036] When the method is a spray, the method may include atomization spray, optionally using a sonic or ultrasonic atomizer.

[0037] The step of contacting at least one surface of the part with the coating mixture may be carried out at a part temperature in the range of 10° C. to 100° C., optionally 12° C. to 50° C., and optionally at about room temperature.

[0038] Before the surface of the part is contacted with the coating mixture, the surface of the part may be cleaned / polished.

[0039] Heating the part in an oxidizing atmosphere may include heating the part to a temperature of 480°C or higher, in some cases to a temperature of 500°C or higher, in some cases to a temperature of 520°C or higher, and in some cases to a temperature of 550°C or higher.

[0040] Heating the component in an oxidizing atmosphere may include heating the component to a temperature of 580°C, 610°C, 650°C, 670°C, 720°C, 770°C, 820°C, 870°C, 900°C, 910°C or higher.

[0041] The oxidizing atmosphere may include oxygen, typically air.

[0042] The source of praseodymium and / or the source of terbium may include a Pr(III) salt and / or a Tb(III) salt, which may typically be Pr(III) nitrate and / or Tb(III) nitrate.

[0043] The source of praseodymium and / or the source of terbium may include chelated Pr(III) and / or chelated Tb(III). In some cases, the chelated Pr(III) and / or chelated Tb(III) may include a bidentate ligand (e.g., acetylacetonate (acac) or ethylenediamine) or a tridentate or tetradentate ligand.

[0044] The source of praseodymium and / or the source of terbium may include a mixture of Pr(III) salts and chelated Pr(III); and / or a mixture of Tb(III) salts and chelated Tb(III).

[0045] Thus, the source of Pr(III) may include chelated Pr(III) and / or the source of Tb(III) may include chelated Tb(III).

[0046] The method according to the first aspect produces coated parts having a variety of uses, including for use in devices, possibly operating at temperatures of 450° C. or higher.

[0047] In a second aspect, the present invention may provide a coated part obtainable by the method described above.

[0048] Thus, in a third aspect, the present invention provides a coated part for a device, the part comprising a chromium-containing part and having at least one surface carrying a coating comprising at least one layer comprising a praseodymium material and / or a terbium material.

[0049] Thus, there is provided a coated part for a device, wherein the coating comprises at least one layer comprising a praseodymium material, the coated part comprising a chromium-containing part, the part having at least one surface carrying the coating comprising at least one layer comprising a praseodymium material.

[0050] Preferably the device is for operation at temperatures of 450° C. or higher.

[0051] The coating may include two or more layers, each layer including a praseodymium material and / or a terbium material. The coating may include three or more layers, each layer including a praseodymium material and / or a terbium material.

[0052] In some cases, the coating may be in direct contact with (i.e., directly adjacent to) the metal surface of the component, and thus the coating may be on an exposed or otherwise uncoated surface of the component.

[0053] The coatings described herein may form a barrier coating on chromium-containing components that reduces or prevents volatility of chromium and acts to protect components that may be susceptible to chromium contamination, especially when these susceptible components are in fluid communication with the chromium-containing components in systems that include, for example, a stack of electrochemical cells.

[0054] In a preferred embodiment, the device may include an electrochemical cell, and thus the components may include interconnects, spacers, metal plates or substrates.

[0055] The device may be a system including a stack of electrochemical cells, and thus the component may include a system component, such as a tube fitting, a fastener, a valve component, a pipe, or a heat exchanger.

[0056] Thus, in a fourth aspect, the present invention provides an electrochemical device comprising a coated component, the coated component comprising a chromium-containing component having at least one surface carrying a coating comprising at least one layer comprising a praseodymium material and / or a terbium material.

[0057] Thus, there is provided an electrochemical device including a coated component, the coating including at least one layer including a praseodymium material, the coated component including a chromium-containing component having at least one surface bearing a coating including at least one layer including a praseodymium material.

[0058] The electrochemical device can be a system including a stack of electrochemical cells.

[0059] The electrochemical device may be (or may include) an electrolyser, an oxygen separator, a sensor or a fuel cell, preferably a SOFC. Preferably, the electrochemical cell is for operation at a temperature of 450° C. or higher.

[0060] In all aspects of the invention relating to methods, coated parts, electrochemical devices and uses, preferably the coating is not an active electrochemical layer, for example is not an electrode or electrolyte layer.

[0061] The coating acts as a barrier coating on the parts, reducing or preventing the volatilization of chromium.

[0062] Thus, in a fifth aspect, there is provided the use of a coating as a barrier coating on a chromium-containing component in an electrochemical device, the coating comprising at least one layer comprising a praseodymium material and / or a terbium material.

[0063] Thus, there is provided the use of a coating as a barrier coating on a chromium-containing component in an electrochemical device, the coating comprising at least one layer comprising a praseodymium material, the coating comprising at least one layer comprising a praseodymium material.

[0064] Preferably, the coating is adjacent to, i.e., directly on, the surface of the component.

[0065] The present invention in various embodiments is advantageous because it may protect substrates, components and devices (including electrochemical cells) from contamination with chromium, which may evaporate from components (including stainless steel components) at higher temperatures and may react to form stable chromate phases on active surfaces of the components (e.g., on electrodes in electrochemical cells).

[0066] definition As used herein, the term "source of" an element, compound or other material refers to a material that contains the element, compound or other material, whether or not it is chemically bound within the source. The source of the element, compound or other material may be an elemental source (e.g., Pr, Tb or O2), or may be in the form of a compound or a mixture that includes the element, compound or other material that contains one or more of these elements, compounds or materials.

[0067] References herein to a source of praseodymium and / or a source of terbium may refer to a source of praseodymium or a source of terbium; or to a source of praseodymium and a source of terbium (e.g., a mixture of a source of praseodymium and a source of terbium). Similarly, references herein to a praseodymium material and / or a terbium material may refer to a praseodymium material or a terbium material; or to a praseodymium material and a terbium material (e.g., a mixture of a praseodymium material and a terbium material).

[0068] References herein to electrochemical cells, SOCs, SOFCs and SOECs may refer to cylindrical or planar cells. The electrochemical cell units may be cylindrical or planar in configuration. Planar fuel cell units may be arranged on top of each other in a stacked arrangement, for example 100-200 fuel cell units in a stack, with the individual fuel cell units being electrically arranged in series.

[0069] An electrochemical cell can be a fuel cell, a reversible fuel cell or an electrolyzer cell. In general, these cells may have the same structure and a reference to an electrochemical cell may refer to any of these types of cells (unless the context suggests otherwise). The cell may be based on a solid oxide electrolyte, possibly a metal-supported solid oxide battery. In fuel cell mode, the fuel is in contact with the anode (fuel electrode) and an oxidant such as air or an oxygen-rich fluid is in contact with the cathode (air electrode), so that in fuel cell mode operation, the air electrode is the cathode. A solid oxide electrolyzer cell (SOEC) may have the same structure as a SOFC, but is essentially a SOFC that operates in reverse or in regenerative mode, using a solid oxide electrolyte to achieve electrolysis of water and / or carbon dioxide to produce hydrogen gas and / or carbon monoxide and oxygen.

[0070] In this specification, area specific resistance (ASR; Ωcm 2 or mΩcm if not normalized 2 ) refers to the internal resistance of an electrochemical cell normalized to the cell active surface area (commonly used to allow direct comparison of cells of different active surface areas). ASR is a function of current density (Acm -2 When multiplied by this, it is equivalent to the voltage drop due to the internal resistance of the cell.

[0071] The secant ASR comes from the voltage drop from open circuit to the cell operating voltage divided by the applied current density (so a cell with a lower ASR has a higher operating voltage and power output at any given applied current density).

[0072] Ohmic resistance / series resistance (Rs) is the component of the cell internal resistance that has no associated capacitance (the resistance of oxide scale on steel parts may be accounted for by Rs).

[0073] It is understood that the term "fluid flow path" is used to define the fluid flow paths between various components, and therefore that these components are in fluid communication with each other.

[0074] As will be appreciated by those skilled in the art, the various features of the aspects of the disclosure described herein may be used in combination with any other feature in the same or other aspects of the disclosure, mutatis mutandis, if necessary.

[0075] Furthermore, it is to be understood that every aspect of the present invention or disclosure "comprises" the features described in relation to that aspect, but may specifically "consist" or "consist essentially of" those features outlined in the claims.

[0076] The invention will now be described with reference to the accompanying drawings and examples. [Brief description of the drawings]

[0077] [Figure 1] FIG. 1 shows a graph of normalized series resistance as a function of temperature for a coated stainless steel interconnect. [Diagram 2] FIG. 2 shows a graph of secant ASR as a function of temperature normalized to a standard SOFC cell for a stainless steel (having 22-23% Cr and 0.1% La) SOFC substrate coated according to the present invention. [Diagram 3] FIG. 3 shows a graph of Rs as a function of temperature normalized to a standard SOFC cell for a stainless steel SOFC substrate coated as in FIG. [Figure 4] FIG. 4 shows a graph of SecASR as a function of temperature normalized to a standard SOFC cell for a stainless steel SOFC substrate coated as in FIG. [Diagram 5] FIG. 5 shows a schematic flow diagram of this method. [Figure 6] FIG. 6 shows a schematic diagram of a fuel cell system illustrating the fluid flow paths. [Figure 7]FIG. 7 shows a schematic (not to scale) cross-section of a coated part. [Figure 8] FIG. 8 shows a graph of cumulative chromium evaporation from the coated stainless steel coupon as a function of time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0078] FIG. 5 shows a schematic flow diagram illustrating a method of providing a coating on a part as an example. In FIG. 5, dashed arrows indicate optional steps. A coating mixture 320 is provided, containing a solvent and a source of Pr, such as a mixture of Pr nitrate and Pr acac. The coating mixture 320 is applied to a part (which may be made of stainless steel) 310 in step 330. After applying the coating mixture 320 (330), the part is optionally dried (340) and then heated (350) at 450° C. or higher in an oxidizing atmosphere. The coating step is optionally repeated (360) after step 330, after the optional drying step 340, or after the heating step 350 to form additional layers and thicker coatings.

[0079] Chromium contamination may affect electrochemically active components in a fuel cell system, particularly chromium-containing components that are in fluid communication with the electrochemically active components. The coatings described herein may form a barrier coating on the chromium-containing components that acts to reduce or prevent volatility of chromium and protect components that may be susceptible to chromium contamination (e.g., in fluid communication with the chromium-containing components).

[0080] Thus, referring to FIG. 6, the fuel cell system 10 is an intermediate temperature solid oxide fuel cell (IT-SOFC) system. As taught in WO 2015 / 004419, the fuel cell stack 20 is a metal supported IT-SOFC fuel cell stack. The fuel cell system 10 has a steady state 1 kW electrical output from the fuel cell stack 20 and includes 121 metal supported IT-SOFC fuel cells 30. Each fuel cell 30 has an anode side 40, an electrolyte layer 50, and a cathode side 60. Each fuel cell layer in the fuel cell stack is separated by an electrically conductive gas impermeable metal interconnect plate (interconnector) (not shown). Fuel cell stack end plates and compression means (not shown) are also provided.

[0081] In this specification, reference to fuel cells 30 refers to the entire set of 121 fuel cells 30 .

[0082] An electrical load L is disposed across the fuel cell 30 .

[0083] The fuel cell stack anode inlet 41 is in fluid communication with the fuel cell anode inlet 41A for the flow of anode inlet gas to the anode side 40 of the fuel cell 30. The fuel cell anode outlet 42A is in fluid communication with the fuel cell stack anode off-gas outlet 42 for the flow of anode off-gas.

[0084] The fuel cell stack cathode inlet 61 is in fluid communication with the fuel cell cathode inlet 61A for the flow of cathode inlet gas to the cathode side 60 of the fuel cell 30. The fuel cell cathode outlet 62A is in fluid communication with the fuel cell stack cathode off-gas outlet 62 for the flow of cathode off-gas.

[0085] The steam reformer 70 includes a reformer inlet 71 for the anode inlet gas and a reformer outlet 72 for exhausting the anode inlet gas.

[0086] The tail gas burner 80 is in fluid communication with the fuel cell stack anode and cathode off-gas outlets 42, 62 and has a tail gas burner exhaust 81, an anode off-gas inlet 82 and a cathode off-gas inlet 83. The tail gas burner 80 defines a fluid flow path from the fuel cell stack anode and cathode off-gas outlets 42, 62 to the tail gas burner exhaust 81 and is configured to combust the anode and cathode off-gas and produce tail gas burner off-gas.

[0087] An anode inlet gas flow path A defines a path from the fuel source 90 to the evaporator 100 to the steam reformer 70 to the fuel cell stack anode inlet 41 to the fuel cell anode inlet 41A, ie, the components are in fluid communication with each other.

[0088] The anode off-gas fluid flow path B is defined from the fuel cell anode outlet 42A to the fuel cell stack anode off-gas outlet 42, to the anode off-gas heat exchanger 110 (HX-AOG), to the condenser heat exchanger 120, to the separator 130, and to the anode off-gas inlet 82 of the tail gas burner 80.

[0089] The main cathode inlet gas flow passage 230 and the air bypass inlet gas flow passage 240 have many common components and share a common flow passage, marked cathode inlet gas fluid flow passage C, in many places.

[0090] The main cathode inlet gas flow path 230 defines the flow from the oxidant inlet 140 to the blower 210, to the valve / separator 220, to the anode off-gas heat exchanger 110, to the air preheater heat exchanger 150 (HX-APH), to the reformer heat exchanger 160 (HX-Ref), to the fuel cell stack cathode inlet 61, to the fuel cell cathode inlet 61A.

[0091] An air bypass inlet gas flow path 240 defines from the oxidant inlet 140 to the blower 210 to the valve / separator 220 to the air bypass inlet 190 to the reformer heat exchanger 160 to the fuel cell stack cathode inlet 61 to the fuel cell cathode inlet 61A.

[0092] The valve / separator 220 is controlled by a control means 200 to split the inlet air flow between the main cathode inlet gas passage 230 and the air bypass inlet gas passage 240 .

[0093] Thus, the air bypass inlet gas flow path 240 bypasses the anode off-gas heat exchanger 110 and the air preheater heat exchanger 150 .

[0094] Thus, in this embodiment, the common portions of gas flow paths 230 and 240 (cathode inlet gas fluid flow path C) are (a) from the oxidant inlet 140 to the blower 210 to the valve / separator 220, and (b) from the reformer heat exchanger 160 to the fuel cell stack cathode inlet 61 to the fuel cell cathode inlet 61A.

[0095] A cathode off-gas fluid flow path D is defined from the fuel cell cathode outlet 62 A to the fuel cell stack cathode off-gas outlet 62 to the cathode off-gas inlet 83 of the tail gas burner 80 .

[0096] A tail gas burner off-gas fluid flow path E defines a tail gas burner exhaust 81 to the air preheater heat exchanger 150 to the evaporator heat exchanger 170 (HX-Evap) to the fuel cell system exhaust 180 .

[0097] The anode off-gas heat exchanger 110 is fluidly connected to (i) the fuel cell stack anode off-gas outlet 42 (i.e., having the fuel cell anode outlet 42A) and the tail gas burner anode off-gas inlet 82, and (ii) the oxidant inlet 140 and the fuel cell stack cathode inlet 61 (i.e., having the fuel cell cathode inlet 61A), and is positioned to exchange heat between the anode off-gas from the fuel cell stack 20 and the cathode inlet gas to the fuel cell stack 20.

[0098] The air preheater heat exchanger 150 is in fluid communication with (i) the tail gas burner exhaust 81 and the fuel cell system exhaust 180, and (ii) the oxidant inlet 140 and the fuel cell stack cathode inlet 61 (i.e., having the fuel cell cathode inlet 61A), and is positioned to exchange heat between the tail gas burner 81 off-gas and the cathode inlet gas to the fuel cell stack 20.

[0099] The reformer heat exchanger 160 is a parallel-flow heat exchanger that is fluidly connected to (i) the oxidant inlet 140 and the fuel cell stack cathode inlet 61 (i.e., having a fuel cell cathode inlet 61A), and (ii) the fuel source 90 and the fuel cell stack anode inlet 41 (i.e., having a fuel cell anode inlet 41A), and is positioned to exchange heat between the cathode inlet gas and the anode inlet gas.

[0100] The evaporator 100 has a fuel inlet 101 for anode inlet gas from the fuel source 90, a water inlet 102 for water from a water supply 103, and an evaporator exhaust 104 for exhausting the anode inlet gas from the evaporator 100, and is disposed in the anode inlet gas fluid flow path between the fuel source 90 and the steam reformer 70. The evaporator 100 further includes an evaporator heat exchanger 170 disposed in the tail gas burner off-gas fluid flow path E between the air preheater heat exchanger 150 and the fuel cell system exhaust 180.

[0101] The evaporator heat exchanger 170 is in fluid communication with (i) the tail gas burner exhaust 81 and the fuel cell system exhaust 180, and (ii) the fuel source 90 and the water supply 103 and the fuel cell stack anode inlet 41 (i.e., having the fuel cell anode inlet 41A) and is positioned to exchange heat between the tail gas burner off-gas, the anode inlet gas and the water to generate a steam fuel mixture for the anode inlet gas to the steam reformer 70.

[0102] The condenser heat exchanger 120 is fluidly connected to (i) the fuel cell stack anode off-gas outlet 42 (i.e., having the fuel cell anode outlet 42A) and the tail gas burner anode off-gas inlet 82, and (ii) the cooling circuit 121, and is positioned to exchange heat between the anode off-gas from the fuel cell stack 20 and the cooling fluid in the cooling circuit 121.

[0103] The separator 130 is disposed in the anode off-gas fluid flow path between the condenser heat exchanger 120 and the tail gas burner 80, has a separator condensate outlet 131, and is adapted to separate condensate from the anode off-gas fluid flow path and discharge the condensate via the condensate outlet 131.

[0104] The control means 200 is connected to the fuel cell stack cathode inlet gas temperature sensor T1, the fuel cell stack cathode off-gas temperature sensor T2, the blower 210 and the valve / separator 220. The control means 200 is configured to maintain the temperatures determined by the temperature sensors T1 and T2 at or near a desired temperature during steady state operation of the fuel cell system.

[0105] The control means 200 is adapted to operate two independent control loops operating on the cathode inlet gas passing through the cathode inlet gas fluid flow passage C.

[0106] A first control loop controls the heating of the cathode inlet gas, and a second control loop controls the mass flow rate of the cathode inlet gas.

[0107] In use, the fuel cell system 10 goes through three phases: start-up, steady state, and shutdown. In the start-up phase, the fuel cell stack 20 is cold (or at least below its steady state operating temperature) and therefore needs to be heated to achieve an operating state. In the steady state phase, the fuel cell stack 20 is maintained at the operating temperature, as determined by sensors T1 and T2. Electricity is generated and used by the load L across the fuel cell 30. The temperature detected by temperature sensors T1 and T2 changes and the control means 200 varies the inlet air mass flow rate and the division of air between flow paths 230 and 240 accordingly. In the shutdown phase, power from the fuel cell system 10 is no longer needed and a controlled shutdown procedure is initiated. The power demand from the fuel cell stack 20 drops to zero and the temperature setpoint for the fuel cell stack air inlet T1 is reduced, while the air flow rate from the blower 210 is increased.

[0108] 7 shows a schematic cross-section of a coated part. A stainless steel (chromium-containing) part 402, which may be an interconnect, a substrate or other metallic part, is coated with a Pr-containing coating deposited on the surface of the part using the method detailed below.

[0109] Working Example In the examples, the parts were coated by a sol-gel coating technique (dip coating) using a coating solution having a mixture of rare earth metal (La or Pr or Tb) salts and chelates (acac).

[0110] The coating solution used is a mixture of 75% rare earth metal acetylacetonate (Pr or La or Tb) and 25% rare earth metal (Pr or La or Tb) nitrate in a 90% vol ethanol / 10% vol methoxypropanol mixture.

[0111] Metal parts were dip-coated in the solution and then hung to allow the excess to drain off and dry, leaving a thin film of rare earth oxide precursor, which was decomposed to the oxide by heating to >400° C. This deposition process may be repeated one or more times.

[0112] After coating, optional drying and decomposition, the metal parts were exposed to high temperatures in air to cause the coating to react with the native oxide scale to form a passivation layer.

[0113] The metal parts used were stainless steel with 23% Cr (a high La stainless steel developed specifically for use in SOFCs), ferritic stainless steel with 22% Cr, SS441 and SS316 stainless steel parts.

[0114] The Cr composition of the stainless steel can be: SS441: Chromium 17.5~18.5%; Carbon 0.03%; Si 1.00%; Mn 1.00%; P 0.04%; S 0.015%; Ti 0.1~0.6%; Niobium (3×C+0.3)~1.00%; balance Fe. Ferritic stainless steel with 22% Cr: 22.1% chromium. SS316 Chromium 18.2%; Molybdenum 2.2%; Carbon 0.05%; Nickel 10% Stainless steel with 23%Cr: 22-23% chromium; 0.1% lanthanum.

[0115] It would be desirable to use lower cost ferritic stainless steels for the cell substrate. However, it has been observed by the inventors that potentially lower cost steels not specifically designed for SOFC applications, such as ferritic stainless steels with 22% Cr, have a higher chromium volatility at high temperatures. This could lead to problems either in cell manufacturing or potential cathode poisoning during operation. We hypothesize (without wishing to be bound) that this is due to the absence of highly reactive alloying elements in the steel, such as lanthanum or zirconium, present in SOFC specific steels.

[0116] The inventors have surprisingly discovered that oxide scale growth and chromium evaporation can be strongly inhibited on ferritic stainless steels having 22% Cr during simulated electrolyte firing by coating the surface with a thin film of praseodymium oxide prior to high temperature oxidation. As previously described, a continuous film was formed by sol-gel dip coating using a solution of praseodymium acetylacetonate and praseodymium nitrate dissolved in a 90:10 ethanol / methoxypropanol solution, followed by heat treatment to decompose the sol-gel film into the oxide.

[0117] In standard SOFC interconnects, a CoCe coating is deposited to inhibit corrosion and chromium evaporation.

[0118] The inventors have surprisingly discovered that the inventive sol-gel coating of praseodymium oxide deposited on uncoated SS441 interconnect appears to inhibit oxidation of the steel during subsequent heat treatment and prevent the formation of iron oxide nodules at the surface. Without wishing to be bound, it is believed that these REO coatings can achieve the same results at a much lower cost than the post-formation of a CoCe coating, since REO forms an outer oxide layer of RE chromite / manganite that has a much lower chromium vapor pressure than the natural oxide scale. Furthermore, it is expected that the resistivity of this protective oxide is lower than standard coatings, potentially improving performance and reducing degradation.

[0119] Additionally, coating stainless steels such as SS316 with thin sol-gel coatings of rare earth oxides (e.g. lanthanum oxide or praseodymium oxide or terbium oxide) greatly enhances their resistance to high temperature corrosion after simply dip-coating the parts in solution and drying before heat treatment. This is likely to be applicable to balance of stacks and balance of plant parts, especially since it is likely to reduce chromium evaporation from surfaces upstream of the stack in a process that is much lower cost and less complex than aluminizing the alloy. Additionally, this may be more generally applicable in industry (e.g. automotive exhaust systems or piping in chemical plants).

[0120] SOFC interconnect coating SOFC interconnects were coated with PrOx and La2O3 sol-gel coatings and then calcined at 870°C or 910°C for 2 h in dry air.

[0121] The process was as follows: 1) Dip coat the parts in a metal-organic solution of rare earth metal salts in ethanol / methoxypropanol; 2) Allow the parts to dry vertically at room temperature to allow excess solution to drain off; 3) Heat the part at >450°C to decompose the salt coating into its oxide; 4) Repeat as necessary

[0122] The samples produced are shown in Table 1, which also shows the durability data for the coatings in terms of voltage degradation rate (in % / kh). The interconnects were tested at 610°C for 1000 hours in an operating SOFC stack. The voltage degradation appears to be mostly related to the increase in ohmic resistance of the oxide scale in the interconnects. The lanthanum coatings degrade more.

[0123] [Table 1]

[0124] The interconnect was incorporated into a stack of standard SOFC cells and the resistance was normalized relative to a standard cell as a function of the determined temperature, the results of which are shown in Figure 1.

[0125] PrOx coated parts fired at 870°C have a resistance comparable to the standard parts; parts fired at 910°C generally have a higher resistance.

[0126] La2O3 coated parts, especially those fired at 910°C, generally have higher resistivity.

[0127] Coating of SOFC substrate (23% chromium) Generally, as shown above for interconnects, stainless steel (23% chromium with 0.1% lanthanum) substrates are coated with La2O3, or PrOx (double coating with IR heating between steps), or TbO x was coated with.

[0128] The substrate was incorporated into a stack of standard SOFC cells and the performance as a function of temperature was determined. The results of the tests are shown in Figures 2-4.

[0129] Figure 2 shows the secant ASR as a function of temperature normalized to a standard cell. The La2O3 coated substrate (curve 1) exhibits a higher resistance over the entire temperature range, while the PrO x The coated substrate (curve 2) performs poorly at low temperatures but is comparable or even better at >600 °C. x The coated substrate (curve 3) performs better. These results are consistent with those for the interconnects.

[0130] FIG. 3 shows the resistance as a function of temperature normalized to a standard cell.

[0131] The La2O3 coated substrate (curve 1) shows an increase in resistance at higher temperatures.

[0132] The PrOx coated substrate (curve 2) has a lower Rs than the standard cell over the entire temperature range; the difference increases as the temperature increases.

[0133] TbO x The coated substrate (curve 3) generally performs better.

[0134] Figure 4 shows the SecASR as a function of temperature normalized to the standard cell. Both the La2O3-coated substrate (curve 1) and the PrOx-coated substrate (curve 2) show higher polarization resistance than the standard cell; x The coated substrate (curve 3) has good or very good performance.

[0135] PrO x appears to give improved results for SOFC applications over La2O3, which appears to form a resistive oxide scale. x forms a more stable deposition solution. Due to its similar chemical properties (Tb forms the electronically conducting mixed-valence oxide Tb4O7), terbium is expected to perform better with similar advantages in general.

[0136] Coating of SOFC substrate (22% chromium) As generally described above for the interconnects, substrates of ferritic stainless steel with 22% chromium were coated with La2O3 or PrOx.

[0137] The substrate was incorporated into a stack of standard SOFC cells and the ohmic cell resistance, normalized to the uncoated substrate (the same stainless steel), was determined at 610 °C. x The coating result was 0.918 and the La2O3 coating was 0.921. Thus, coating the substrate results in a decrease in ohmic resistance compared to the uncoated substrate.

[0138] Comparison of chromium evaporation rates. Chromium evaporation rate measurements were performed using the method described by Froitzheim et al, J. Electrochem. Soc., 157(9), B1295 (2010) to measure chromium evaporation from three ferritic stainless steel (23% Cr, 0.1% La) coupons. The method involved a denuder tube coated with Na2CO3 placed in fluid communication with the sample. CrO2(OH)2 evaporated from the sample was collected on the denuder and converted to thermally stable Na2CrO4. The chromate was then dissolved in water and quantitatively determined.

[0139] The samples investigated were: a) Uncoated coupon pre-oxidized at 850°C for 2 hours (h) in air; b) La-coated coupon pre-oxidized at 850 °C for 2 h in air; c) Pr-coated coupon pre-oxidized at 850 °C for 2 h in air

[0140] The coatings were applied to the coupons generally as described above.

[0141] The measurements were carried out in an air stream containing 3% water vapor at 600° C. (instead of 850° C. as described by Froitzheim et al.) for 1000 h, and the results are shown in FIG.

[0142] Chromium evaporation from both coated coupons was significantly reduced compared to the uncoated coupons, with the praseodymium coating being particularly effective. [Explanation of symbols]

[0143] 1 - La-based coating curve 2 - Curve of Pr-based coating 3 - Tb-based coating curves 10 - Fuel Cell Systems 20 - Fuel Cell Stack 30 - fuel cell 41 - Anode side fuel cell stack anode inlet 41A - Fuel cell anode inlet 42 - Fuel cell stack anode off-gas outlet 42A - Fuel cell anode outlet 50 - electrolyte layer 60 - Cathode side 61 - Fuel cell stack cathode inlet 61A - Fuel cell cathode inlet 62 - Fuel cell stack cathode off-gas outlet 62A - Fuel cell cathode outlet 70 - Steam reformer 71 - Reformer inlet 72 - Reformer outlet 80 - Tail gas burner 81 - Tail gas burner exhaust 82 - Anode off-gas inlet 83 - Cathode off-gas inlet 90 - Fuel source 100 - Evaporator 101 - Fuel inlet 102 - Water inlet 103 - Water supply 104 - Evaporator exhaust 110 - Anode off-gas heat exchanger 120 - Condenser heat exchanger 121 - Cooling circuit 130 - Separator 131 - Separator condensate outlet 140 - Oxidizer inlet 150 - Air preheater heat exchanger 160 - Reformer Heat Exchanger 161 - Reformer heat exchanger oxidant inlet 162 - Reformer heat exchanger oxidant outlet 170 - Evaporator heat exchanger 180 - Fuel cell system exhaust 190 - Air bypass inlet 200 - Control Means 210 - Blower 220 - Valves / Separators 230 - Main cathode inlet gas passage 240 - Air bypass inlet gas flow path 250 - Fuel source 260 - Air bypass inlet gas flow path A - Anode inlet gas flow passage B - Anode off-gas fluid flow path C - Cathode inlet gas flow passage D - Cathode off-gas fluid flow path E - Tail gas burner off-gas fluid flow path G - Reformer cathode off-gas fluid flow path L – Electrical load T1 - Fuel cell stack cathode inlet gas temperature sensor T2 - Fuel Cell Stack Cathode Offgas Temperature Sensor T3 - Fuel cell stack anode inlet gas temperature sensor 310 - Stainless Steel Parts 320 - Coating Mixture 330 - Applying the coating mixture 340 - (Sometimes) Dry 350 - heating 360 - (Optional) Repeat step 401 - Pr-containing coating 402 - Stainless Steel Parts

[0144] All publications mentioned in the above specification are incorporated herein by reference. Although illustrative embodiments of the present invention have been described in detail herein with reference to the accompanying drawings, it is understood that the present invention is not limited to the precise embodiments, and that those skilled in the art can make various changes and modifications without departing from the scope of the present invention as defined by the appended claims and their equivalents.

Claims

1. A method for producing coated parts, a) Prepare chromium-containing parts. b) Prepare a coating mixture comprising at least one solvent, and a source of praseodymium and / or a source of terbium. c) bringing at least one surface of the component into contact with the coating mixture. d) In some cases, drying the aforementioned parts, and e) Heating the component in an oxidizing atmosphere at a temperature of 450°C or higher. Methods that include...

2. The method according to claim 1, wherein the source of praseodymium and / or the source of terbium is a source of Pr(III) and / or Tb(III).

3. The method according to claim 2, wherein the source of Pr(III) comprises a Pr(III) salt and / or chelated Pr(III), and / or the source of Tb(III) comprises a Tb(III) salt and / or chelated Tb(III).

4. The method according to claim 1, further comprising repeating steps a) to c), optionally d) and e), thereby producing a coated component having a coating comprising multiple layers.

5. The method according to claim 1, wherein the coating is conductive.

6. The method according to claim 1, wherein the coating has a thickness in the range of 50 nm to 1 μm, preferably in the range of 50 nm to 500 nm.

7. The method according to claim 1, wherein the component includes a metal alloy containing chromium.

8. The method according to claim 7, wherein the component comprises an iron alloy containing chromium.

9. The method according to claim 8, wherein the component includes stainless steel.

10. The method according to claim 7, wherein the alloy comprises 11% wt or more of Cr; optionally 15% wt or more of Cr; optionally 17% wt or more of Cr; optionally 19% wt or more of Cr.

11. The method according to claim 1, wherein the coating mixture is in a liquid state and preferably includes a coating solution.

12. The solvent is an alcohol, and possibly C １ ~C ６ The method according to claim 1, comprising alcohol.

13. The method according to claim 1, wherein the solvent is selected from one or more of ethanol, propanol, and methoxypropanol.

14. The method according to claim 1, wherein bringing at least one surface of the component into contact with the coating mixture comprises dipping the component in the coating mixture and / or spray-coating the component with the coating mixture.

15. The method according to claim 1, wherein heating the component in an oxidizing atmosphere includes heating the component to a temperature of 500°C or higher, and in some cases to a temperature of 550°C or higher.

16. The method according to claim 1, wherein the oxidizing atmosphere includes air.

17. The method according to claim 1, wherein the covering component includes a covering component for use in a device, which may be for operation at a temperature of 450°C or higher.

18. A covering component for a device, which can be obtained by the method described in claim 1.

19. A coating component for a device, comprising a chromium-containing component and having at least one surface that holds a coating comprising at least one layer containing praseodymium material and / or terbium material.

20. The covering component according to claim 19, wherein the device is for operation at a temperature of 450°C or higher.

21. The coated component according to claim 19, wherein the coating comprises two or more layers, each layer comprising a praseodymium material and / or a terbium material.

22. A covering component for the device according to claim 18, wherein the device includes an electrochemical cell.

23. A covering component for the device according to claim 22, wherein the component includes an interconnect, a spacer, a metal plate, or a substrate.

24. A covering component for the device according to claim 18, wherein the device includes a system comprising a stack of electrochemical cells.

25. A covering component for the device according to claim 24, wherein the component includes a pipe fitting, a fastener, a valve component, a pipe, or a heat exchanger.

26. An electrochemical device including a coated component, wherein the coated component includes a chromium-containing component having at least one surface that holds a coating comprising at least one layer of praseodymium material and / or terbium material, and is optionally intended for operation at a temperature of 450°C or higher.

27. Use of a coating as a barrier on a chromium-containing component in an electrochemical device, wherein the coating comprises at least one layer containing a praseodymium material and / or a terbium material.

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