Fuel cell component

Abstract

Component for a fuel cell or electrolyser with a molten salt electrolyte provided with an anti-corrosion coating, as well as such a fuel cell or electrolyser with a molten salt electrolyte, the component comprising an electrically conductive substrate (31) and an anti-corrosion coating (32) deposited on at least one surface of the substrate (31), the anti-corrosion coating (32) comprising at least one main layer based on tantalum nitride doped with one or more doping elements chosen from the family of transition metals or lanthanides. Fig. 3.

Description

Title of the invention: Component for fuel cell Technical field

[0001] The present disclosure relates to a component for a fuel cell or molten salt electrolyte electrolyzer provided with an anti-corrosion coating, as well as such a fuel cell or molten salt electrolyzer.

[0002] Such a component, having an electrical conduction function, can in particular equip a molten carbonate fuel cell (MCFC: “Molten Carbonate Fuel Cell”), a molten carbonate electrolyzer (MCEC: “Molten Carbonate Electrolysis Cell”), a direct carbon fuel cell (DCFC: “Direct Carbon Fuel Cell”) or a direct urea fuel cell (DUFC: “Direct Urea Fuel Cell”)• Prior art

[0003] Conductive components, such as terminal plates, bipolar plates and interconnectors, used in fuel cells are exposed to both oxidizing conditions, due in particular to the presence of oxygen and / or water, and corrosive conditions, due in particular to acid effluents from the electrolyte, which are extremely harsh, leading, in the absence of adequate protection, to rapid deterioration leading to a loss of conductivity of these components as well as to pollution of the environment of the fuel cell, in particular of its electrolyte and / or its catalysts, by the products resulting from this corrosion.

[0004] These corrosion conditions are particularly severe in a fuel cell or an electrolyser with a molten salt electrolyte due, on the one hand, to the high operating temperature, generally around 650°C, and, on the other hand, to the presence of molten salts from the electrolyte.

[0005] In order to limit this corrosion, a first option is to use very specific alloys that naturally have a high resistance to corrosion. This could be Inconel 625. However, such special alloys are expensive. In addition, their natural resistance to corrosion may prove insufficient in certain applications.

[0006] A second option is to use more conventional materials for such conductive components but to protect them using an anti-corrosion coating. Many materials have thus been tested in the scientific literature, including coatings of graphite or conductive metal oxides.

[0007] However, in addition to very good corrosion protection properties, this anti-corrosion coating must have good stability and conductivity. sufficient electrical conductivity so as not to hinder the electrical operation of the fuel cell. In particular, the conductivity of the coating must remain above 100 S / cm. In addition, the coating must be sufficiently thin, for example less than 5 pm, so as not to modify the geometry of the component, particularly when the latter includes channels.

[0008] However, to date, both in the field of molten salt electrolyte fuel cells, the only known solution enabling a lifetime greater than 5000 h and an acceptable degradation rate (less than 40 pV / h) to be achieved is the pure gold coating, with a thickness of 200 to 500 nm.

[0009] However, it will be easily understood that such a pure gold coating significantly increases the cost of the fuel cell. Thus, when all the conductive components of the fuel cell are equipped with such a coating, the cost of this coating alone can represent up to half of the total cost of the fuel cell. In addition, even the pure gold coating eventually wears off in part, thus polluting the environment of the fuel cell: in particular, gold particles can be deposited on certain components of the fuel cell and create electrical connections in undesired locations, which reduces the efficiency of the fuel cell.

[0010] There is therefore a real need for a component for a fuel cell or molten salt electrolyte electrolyzer, as well as for a fuel cell or molten salt electrolyte electrolyzer comprising such a component, which are free, at least in part, from the drawbacks inherent in the aforementioned known configurations. Statement of the invention

[0011] The present disclosure relates to a component for a fuel cell or molten salt electrolyte electrolyzer, comprising an electrically conductive substrate and an anti-corrosion coating deposited on at least one surface of the substrate, in which the anti-corrosion coating comprises at least one main layer based on tantalum nitride doped with one or more doping elements chosen from the family of transition metals or lanthanides.

[0012] As will be specified below in the detailed description, such a layer of tantalum nitride doped in this way offers very good protection against corrosion while benefiting from good electrical conductivity. In particular, the inclusion of one or more dopants makes it possible to increase the chemical stability of tantalum nitride, which is usually metastable, by forming solid solutions.

[0013] The component thus obtained is therefore capable of ensuring its current conduction function efficiently and durably, despite the highly oxidizing conditions prevailing in the fuel cell or the electrolyser.

[0014] In particular, thanks to the high stability of the doped tantalum nitride, the coating practically does not degrade over time: this reduces the risk, on the one hand, of seeing the conductivity of the component decrease over time and, on the other hand, of polluting the environment of the fuel cell or the electrolyser, in particular its electrolyte or its catalysts, and therefore of reducing its efficiency. Thus, such a coating makes it possible to achieve an extremely long service life for the component, of the order of 20,000 to 30,000 hours.

[0015] Furthermore, the cost of obtaining a doped tantalum nitride coating is significantly lower than that of a pure gold coating, which makes it possible to significantly reduce the overall cost of the fuel cell or electrolyser.

[0016] Tantalum nitride also has the advantage of remaining stable up to approximately 3000°C, which allows its use in a very wide spectrum of applications, including at very high temperatures.

[0017] In certain embodiments, the main layer is made essentially of tantalum nitride doped with one or more doping elements chosen from the family of transition metals or lanthanides. The main layer is thus essentially uniform.

[0018] In some embodiments, the main layer is two-phase or multi-phase. In particular, the main layer may have a composition gradient, for example in the direction perpendicular to the substrate.

[0019] In some embodiments, the main layer is made essentially of tantalum nitride. On the other hand, the main layer may have a variation in composition affecting the crystalline structure and / or the doping of the tantalum nitride. In particular, a gradient in crystalline structure has the advantage of improving the accommodation of stresses between the coating and its substrate, which improves the mechanical properties of the complete system, by limiting cracks and / or delamination of the coating.

[0020] In some embodiments, the electrolyte of the fuel cell or electrolyzer comprises one or more molten salts, preferably sodium carbonate NaCO3, potassium carbonate K2CO3 and / or lithium carbonate Li2CO 3-

[0021] In some embodiments, the electrolyte of the fuel cell or electrolyzer comprises a porous matrix of oxide, preferably lithium aluminum oxide.

[0022] In some embodiments, the component has an electrical conduction function within the fuel cell or the electrolyzer. In particular, the component may be a terminal plate, a bipolar plate or even an interconnector for a fuel cell or electrolyzer.

[0023] In some embodiments, the substrate is metallic.

[0024] In some embodiments, the substrate is made of steel. It may in particular be stainless steel, for example 316L stainless steel. In fact, thanks to the anti-corrosion protection offered by the anti-corrosion coating, it is possible to use a relatively inexpensive material for the substrate, which is particularly the case with stainless steel, even if it does not intrinsically have very high anti-corrosion properties.

[0025] In some embodiments, the substrate is made of titanium, aluminum, nickel, or an alloy based on at least one of these elements. These metals are also relatively inexpensive.

[0026] In certain embodiments, the substrate is non-metallic. It may in particular be made of graphite or a composite material, for example with an organic or ceramic matrix.

[0027] In some embodiments, the crystal system of the tantalum nitride of the main layer is hexagonal. Indeed, in addition to excellent corrosion resistance, hexagonal tantalum nitride benefits from a conductivity almost as good as that of gold.

[0028] In some embodiments, the crystal system of the tantalum nitride of the main layer is cubic. Indeed, although a little less conductive than hexagonal tantalum nitride, cubic tantalum nitride also benefits from excellent corrosion resistance, particularly when it is doped as is the case here.

[0029] In certain embodiments, the total dopant content within the main layer is between 1 ppm and 10 at%, preferably between 10 ppm and 1 at%, more preferably between 0.2 and 0.5 at%.

[0030] In some embodiments, the main doping element is selected from zirconium, hafnium, chromium, titanium, vanadium, niobium or molybdenum.

[0031] In certain embodiments, the doping element used, preferably only one, is chromium (Cr). Indeed, given the critical oxidizing conditions prevailing in a fuel cell or an electrolyzer with molten salt electrolyte(s), minimal oxidation of the coating is practically inevitable, whatever the resistance properties of the coating. Therefore, the choice of an element benefiting from good electrical conduction such as chromium makes it possible to maintain a good level of conduction within the fuel cell or the electrolyzer, even in the event of pollution by this doping element.

[0032] In certain embodiments, the doping element used, preferably only one, is vanadium (V). Indeed, vanadium very easily forms a solid solution with tantalum nitride, which increases its stability. In addition, vanadium is difficult to oxidize: consequently, even if a small fraction of vanadium is released into the medium of the fuel cell or the electrolyzer, its impact on the electrolyte or the catalysts will be very low.

[0033] In certain embodiments, the content of the main dopant within the main layer is between 1 ppm and 10 at%, preferably between 10 ppm and 1 at%, more preferably between 0.2 and 0.5 at%.

[0034] In certain embodiments, the thickness of the anti-corrosion coating is between 5 nm and 5 μm, preferably between 10 nm and 1 μm, more preferably between 100 nm and 300 nm.

[0035] In some embodiments, the anti-corrosion coating comprises several superimposed layers, preferably between 2 and 10 layers, the material of the main layer constituting a main material, and the anti-corrosion coating comprising at least one secondary layer based on a secondary material different from the main material. Such a multi-layer structure makes it possible to reinforce the mechanical resistance of the coating, each interface between two distinct layers contributing to deflecting any cracks appearing in the material. As a result, it is possible to reduce the risk of a crack propagating to the substrate, thus allowing the substrate to remain protected against corrosion.

[0036] In some embodiments, the anti-corrosion coating comprises at least three layers each comprising a different material.

[0037] In some embodiments, each layer of the coating comprises a thickness of between 1 and 500 nm, preferably between 10 and 100 nm.

[0038] In some embodiments, the topmost layer of the anti-corrosion coating is a primary layer made of the main material. The first line of protection is thus provided by the main material, which is generally the one with the best anti-corrosion properties. However, in other embodiments, the topmost layer of the anti-corrosion coating could be a secondary layer.

[0039] In certain embodiments, the main material constitutes at least 30% by volume, preferably at least 50% by volume, of the anti-corrosion coating. This provides, overall, particularly high anti-corrosion protection.

[0040] In some embodiments, the anti-corrosion coating comprises alternating layers based alternately on the primary material and the secondary material. Such alternation is particularly effective in stopping cracks before reaching the substrate.

[0041] In some embodiments, the secondary material is crystallographic tantalum nitride having a different crystal system and / or doping from the main material. In particular, the secondary material may comprise one or more different doping elements, or may be undoped. In this way, the secondary material has anti-corrosion properties that remain very high, which makes it possible to ensure satisfactory anti-corrosion protection even in the event of cracking of the main layer.

[0042] In some embodiments, the secondary layer consists essentially of the secondary material.

[0043] In some embodiments, the secondary layer is two-phase or multi-phase. In particular, the secondary layer may have a composition gradient, for example in the direction perpendicular to the substrate.

[0044] In certain embodiments, the secondary layer is made essentially of tantalum nitride. On the other hand, the secondary layer may have a variation in composition affecting the crystalline structure and / or the doping of the tantalum nitride. In particular, layers with a gradient in crystalline structure have the advantage of improving the accommodation of stresses between a given layer and the lower layer, which improves the mechanical properties of the complete system, by limiting cracks and / or delamination of the coating at the interfaces. The doping gradient can similarly make it possible to best accommodate two successive layers, avoiding a sudden change in composition which could generate a more mechanically fragile interface.

[0045] In certain embodiments, the main layer is deposited using a co-sputtering method. This co-sputtering method may in particular combine high-power pulsed magnetron sputtering (referred to by the acronym “HiPIMS” in the English literature for “High-Power Impulse Magnetron Sputtering”) using a tantalum target and magnetron sputtering using a target comprising the doping element. Examples of high-power pulsed magnetron sputtering methods are in particular described in document FR 3 097 237.

[0046] The present disclosure also relates to a fuel cell or an electrolyser, with acid electrolyte, comprising at least one component according to any one of the preceding embodiments.

[0047] In some embodiments, the fuel cell is of the molten carbonate fuel cell (MCFC) type.

[0048] In some embodiments, the electrolyzer is of the molten carbonate electrolyzer (MCEC) type.

[0049] In some embodiments, the fuel cell is of the direct carbon fuel cell (DCFC) type.

[0050] In some embodiments, the fuel cell is of the direct urea fuel cell (DUFC) type.

[0051] In some embodiments, the fuel cell is configured to be supplied with gaseous fuel.

[0052] In certain embodiments, the fuel cell is configured to be supplied with dihydrogen H2, ammonia NH3, methane CH4.

[0053] In some embodiments, the fuel cell is configured to be powered by a carbon-rich fuel C, preferably based on coal or biomass.

[0054] In some embodiments, the fuel cell is configured to be supplied with urea CO(NH2)2.

[0055] In the present disclosure, it is considered that a part or part of a part is made from a given material when this material represents the majority material, by mass, in the composition of the part or part of the part.

[0056] In the present disclosure, it is considered that a part or part of a part is made essentially of a given material when it is formed at least 80%, preferably 90%, more preferably 99%, by this material.

[0057] The above-mentioned features and advantages, as well as others, will become apparent upon reading the following detailed description of exemplary embodiments of the proposed component and fuel cell. This detailed description refers to the attached drawings. Brief description of the drawings

[0058] The attached drawings are schematic and are intended primarily to illustrate the principles of the disclosure.

[0059] In these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference signs. In addition, elements (or parts of elements) belonging to different embodiments but having a similar function are identified in the figures by numerical references incremented by 100, 200, etc.

[0060] [Fig.l] [Fig.l] is a schematic view of a fuel cell according to the disclosure.

[0061] [Fig.2] [Fig.2] is a diagram of a cell of the fuel cell of [Fig.l].

[0062] [Fig.3] [Fig.3] is a schematic view of a first example of a component.

[0063] [Fig.4] [Fig.4] schematically illustrates a device allowing the realization of a coating according to the description.

[0064] [Fig.5] [Fig.5] is a graph illustrating corrosion test results in the first example.

[0065] [Fig.6] [Fig.6] illustrates, in section and from the front, the microstructure of a cubic TaN coating deposited by a high-power pulsed magnetron sputtering process.

[0066] [Fig.7] [Fig.7] is a graph illustrating the results of corrosion tests in a second example.

[0067] [Fig.8] [Fig.8] is a schematic view of a third example component.

[0068] [Fig.9] [Fig.9] is a graph illustrating results of corrosion tests in the frame of the third example.

[0069] [Fig. 10] [Fig. 10] illustrates, in section and from the front, the microstructure of a hexagonal TaN coating deposited by a high-power pulsed magnetron sputtering process.

[0070] [Fig. 11] [Fig. 11] illustrates comparatively, in section and from the front, the microstructure of a hexagonal TaN coating deposited by a conventional magnetron sputtering process. Description of the embodiments

[0071] In order to make the disclosure more concrete, examples of components and fuel cells are described in detail below, with reference to the accompanying drawings. It is recalled that the invention is not limited to these examples.

[0072] [Fig. 1] schematically illustrates a fuel cell 1 according to the invention. Such a fuel cell comprises two terminal plates 11, 12 between which cells 20 are stacked in a stacking direction X. Each cell 20 comprises, in order (from left to right in [Fig. 1]), a first bipolar plate 21, a first diffusion layer 22, a first electrode 23, an electrolyte 24, a second electrode 25, a second diffusion layer 26 and a second bipolar plate 27.

[0073] The bipolar plates 21, 27 have the function of distributing the reactants and, where appropriate, the heat transfer fluid which cools the cell when said cell has reached its nominal operating speed: the bipolar plates 21, 27 are thus provided with a network of channels 21a, 27a on each of their faces. The bipolar plates 21, 27 also have the function of conducting an electric current between the successive cells 20. Thus, each bipolar plate 21, 27 is located at the interface between two successive cells 20, the second bipolar plate 27 of the Nth cell 20 constituting the first bipolar plate 21 of the (N+1)th cell 20, thus electrically connecting the Nth and (N+1)th cells 20 in series.

[0074] The end plates 11, 12 play the same role as the bipolar plates 21, 27 except that they are provided at the ends of the stack, thus respectively closing the left side of the first cell 20 and the right side of the last cell 20: the terminal plates 11, 12 therefore only have a network of channels 11a, 12a on one of their faces. Also conductive, they constitute the terminals of the fuel cell as a whole: thus, the terminals of the electrical load 2 to be supplied, for example a motor, can be connected to each of the terminal plates 11, 12.

[0075] The diffusion layers 22, 26 have the function of allowing the diffusion of the reactants from the bipolar plate 21, 27 towards the electrode 23, 25 concerned, and of the reaction products, from this same electrode 23, 25 towards the bipolar plate 21, 27. This diffusion can in particular be made possible by grooves or a network of porosities for example.

[0076] The electrodes 23, 25 are the seat of the electrochemical half-reactions ensuring the operation of the fuel cell 1: the first electrode 23 thus forms the anode while the second electrode 25 forms the cathode. The electrodes 23, 25 are porous, preferably microporous, in order to allow access to the reactants and the evacuation of the reaction products. The first electrode 23 and / or the second electrode 25 is provided with a catalyst making it possible to catalyze the electrochemical half-reaction in question.

[0077] The electrolyte 24 has the function of allowing the migration of certain ions between the anode 23 and the cathode 25 while preventing the passage of electrons resulting from the oxidation half-reaction at the anode 23. The electrons e thus formed are then conducted towards the cathode 25 of the immediately preceding cell 20 where they are consumed by the reduction half-reaction. The electrons formed by the first cell 20 are for their part collected by the first terminal plate 11, supply the load 2, and join the cathode 25 of the last cell 20 via the second terminal plate 12.

[0078] [Fig. 2] illustrates more precisely the operation of a cell 20 in the context of a first exemplary embodiment. In this first example, the fuel cell 1 is a molten carbonate fuel cell.

[0079] In such a fuel cell 1, the fuel supplied to the anode 23 is dihydrogen H2 while air is supplied to the cathode 25. The electrolyte 24 is a molten mixture of lithium carbonates Li2CO3 and potassium K2CO3, forming a eutectic, in a porous matrix of aluminum oxide and lithium: this electrolyte 24 is capable of allowing the CO32 ions to pass through while retaining the electrons e. The electrolyte 24 also prevents the passage of any gas. Due to the high operating temperature of such a cell, greater than 500°C, it is possible to choose a non-precious metal as catalyst.

[0080] Anode 23 is thus the seat of the following oxidation half-reaction: H2 + CO32 -> H2O + CO2 + 2e

[0081] Cathode 25 is for its part the seat of the following reduction half-reaction: O2+ 2CO2 + 4e -> 2CO32

[0082] Thus, overall, the operating equation of the fuel cell 1 is as follows: 2H2 + O2 2H2O

[0083] Since the reduction half-reaction requires the consumption of carbon dioxide CO2 at the cathode 25 while the same amount of carbon dioxide CO2 is produced by the oxidation half-reaction at the anode 23, a recirculation line 28 is provided between the two diffusion layers 22 and 26 in order to conduct the carbon dioxide CO2 produced at the anode 23 to the cathode 25. If necessary, additional carbon dioxide CO2 can also be supplied from outside, in particular to initiate the process.

[0084] Due to this highly corrosive environment, the end plates 11, 12 and the bipolar plates 21, 27 must be able to resist corrosion while continuing to perform their electrical conduction function.

[0085] [Fig. 3] then schematically represents such a component, designated by the generic reference 30, according to the first embodiment. The component 30 thus comprises a substrate 31, made for example of 316L stainless steel, and an anti-corrosion coating 32 deposited on the substrate 31, the anti-corrosion coating 32 having a thickness ei of 380 nm.

[0086] In this first example, the anti-corrosion coating 32 comprises a single layer made of tantalum nitride TaN doped with zirconium Zr. This compound, of formula TabxZrxN (with 0 < X ​​< 1), has a stable crystalline structure in which the zirconium atoms replace tantalum atoms Ta, thus forming a solid solution.

[0087] In the present example, the crystal system of this compound is cubic, more precisely having a face-centered cubic lattice. However, this compound is also capable of crystallizing in a hexagonal form, which is also quite suitable.

[0088] In the present example, zirconium is present at 5.8 + / - 0.6% at within this compound.

[0089] Such an anti-corrosion coating 32 can be deposited on the substrate 31 using the device 50 shown schematically in [Fig.4]. This device 50 makes it possible to carry out co-sputtering by high-power pulsed magnetron cathode sputtering.

[0090] The device 50 comprises a chamber 51 intended to receive a plasma gas, for example consisting of a mixture of argon and nitrogen. The device further comprises a source of plasma gas (not shown) in communication with the chamber 51. The pressure in the chamber 51 is set between 0.1 and 7 Pa; the gas mixture comprises between 1 and 95% at nitrogen. In the present example, the pressure is set at 0.15 Pa and the gas mixture of argon and nitrogen comprises 10% nitrogen.

[0091] The chamber 51 comprises a tantalum target 52, constituting a first cathode, and a zirconium target 53, constituting a second cathode. The two targets 52 and 53 are arranged on the same side of the chamber 51, forming an angle of 90° with respect to each other.

[0092] The substrate 31 to be covered, constituting the anode, is arranged within the chamber 51 opposite the targets 52, 53, perpendicularly and centered relative to the bisector of the two targets 52, 53.

[0093] In the present example, the first target 52 comprises tantalum in an amount of more than 99% in atomic percentages, and preferably in an amount of more than 99.9% in atomic percentages. The second target 53 comprises zirconium in an amount of more than 99% in atomic percentages, and preferably in an amount of more than 99.9% in atomic percentages.

[0094] During the coating, the tantalum target 52 is polarized by superimposing a DC polarization and a pulsed polarization. The polarization of the first target 52 is imposed by a first electrical power supply device 54 comprising a voltage pulse generator and a DC voltage generator electrically connected to the target 52. The voltage pulse generator makes it possible to impose the pulsed polarization on the tantalum target 52. The DC voltage generator makes it possible to impose the DC polarization on the target 52. Such a configuration is notably described in the document FR 3 097 237. The width of the pulses can be between 1 and 500 ps; their frequency between 100 and 5000 Hz; and their voltage between 300 and 2000 V. In this example, the pulse width is equal to 30 ps, ​​their frequency is equal to 1000 Hz and their voltage is equal to 1000 V.

[0095] Similarly, the zirconium target 53 is polarized using a second electrical power supply device 55 configured to provide radiofrequency polarization.

[0096] In the chamber 51, the application of a voltage between the target 52 and the substrate 31 in the presence of an atmosphere comprising nitrogen makes it possible to create a plasma. Electrons are generated by the target 52 and can ionize by collision the atoms constituting the plasma. It is possible to introduce into the chamber 51 in the vicinity of the target 52 one or more permanent magnets, not shown, whose magnetic field confines the electrons generated in the vicinity of the target 51 and increases the probability that the collision between an electron and an atom of the plasma takes place there. When such a collision takes place, a high-energy species is generated, and the latter can bombard the target 52 and tear off, by elastic impact, particles from the target 52. The particles of the target 52 thus torn off can then be deposited on the substrate 31 to form the coating 32.

[0097] Similarly and simultaneously, particles of the target 53 are also torn from the target 53 and sprayed onto the substrate 31. It is possible to adjust the quantity of doping particles, here zirconium, in the coating 32 by adjusting the electrical power supplied to the second target 53. For example, in the present example, a power of 5W is applied to the zirconium target 53.

[0098] The substrate 31 may be heated during the coating by a heating member not shown. Alternatively, the substrate 31 may not be heated during the coating. The temperature of the substrate may for example be greater than or equal to 20°C during the coating, for example between 20°C and 600°C, or even between 30°C and 500°C. The temperature makes it possible to provide the substrate with thermal energy, and thus to allow a certain mobility of the atoms promoting the recombination of the atoms deposited on the surface of the substrate 31.

[0099] [Fig. 5] now illustrates the results of corrosion tests concerning this first embodiment. This cyclic voltammetry test was carried out in the laboratory, at room temperature, by immersing a working electrode made of the material to be tested and a platinum counter-electrode in a bath of 0.5 mol / L phosphoric acid, by varying the potential applied to the working electrode relative to the counter-electrode and by recording its current response.

[0100] Curve 61 then corresponds to a working electrode made of 316L stainless steel, i.e. the material of the substrate 31. Curve 62 corresponds to a working electrode made of 316L stainless steel completely covered with a coating of cubic tantalum nitride doped at a height of 5.8 + / - 0.6 at% with zirconium Zr, i.e. a coating 32 according to the first embodiment. Curve 63 corresponds to a working electrode made of 316L stainless steel completely covered with a coating of cubic tantalum nitride doped at a height of 6.0 + / - 0.4 at% with zirconium Zr, i.e. a coating 32 according to an alternative embodiment.

[0101] It can thus be seen in [Fig. 5] that curves 62 and 63, corresponding to the anti-corrosion coatings 32 according to the first exemplary embodiment and its variant, have significantly wider stability levels than curve 61 corresponding to the material of the substrate 31, thus confirming the protection of the substrate 31 by the anti-corrosion coating 32.

[0102] This test also makes it possible to measure the corrosion potential and current for these different samples:

[0103] [Tableauxl] 316L TabxZrxN - 5.8% TabxZrxN - 6.0% Ecoir (V / Pt) 0.4 0.6 0.6 ICOIT (pA / cm2) 27.2 18.4 17.5

[0104] It is thus noted that the ICOIT corrosion current of the anticorrosion coatings 32 according to the present exemplary embodiment and its variant is more than 30% lower than that of the comparative sample of the substrate 31, thus confirming the excellent anticorrosion properties of these coatings.

[0105] Furthermore, [Fig.6] illustrates the microstructure of a cubic tantalum nitride coating, in section and from the front, deposited by a high-power pulsed magnetron sputtering process in accordance with the present example. The scale shown at the bottom of each view corresponds to Ipm. It can be seen from these two views that the microstructure of the coating is fine and homogeneous, which implies good mechanical strength with, in particular, good resistance to crack propagation within the coating. For comparison, such a coating deposited by a conventional magnetron sputtering process results in a columnar microstructure that is easily fracturable.

[0106] It is also important to note that the anti-corrosion coatings 32 according to the first embodiment and its variant benefit from a conductivity well above 100 S / cm, which ensures sufficient conductivity for conducting electrons satisfactorily within the fuel cell or the electrolyser. Indeed, at 160°C, the conductivity of the cubic tantalum nitride deposited by high-power pulsed magnetron sputtering is equal to 538 S / cm.

[0107] In this first example, the tantalum nitride TaN forming the anti-corrosion coating 32 is doped using zirconium. However, in other examples, other doping elements, derived from transition metals or lanthanides, could be used instead of or in addition to zirconium.

[0108] In particular, in a second exemplary embodiment, the anti-corrosion coating comprises a single layer made of tantalum nitride TaN doped with hafnium Hf. This compound, of formula TabxHfxN, has a stable crystalline structure in which the zirconium atoms replace tantalum Hf atoms, thus forming a solid solution.

[0109] In this second example, the crystal system of this compound is also cubic, more precisely having a face-centered cubic lattice. However, this compound is also capable of crystallizing in a hexagonal form, which is also quite suitable.

[0110] In this second example, hafnium is present at 5.7 + / - 0.5% at within this compound.

[0111] A process entirely analogous to that of the first example can be used to deposit this anti-corrosion coating on the substrate, by replacing the zirconium 53 target with a hafnium target.

[0112] Similarly to [Fig.5], [Fig.7] illustrates corrosion test results for this second embodiment. This cyclic voltammetry test was carried out under the same conditions as the test carried out for the first embodiment.

[0113] Curve 161 then corresponds to a working electrode made of 316L stainless steel, i.e. the substrate material. Curve 162 corresponds to a working electrode made of 316L stainless steel completely covered with a coating of cubic tantalum nitride doped at a height of 5.7 + / - 0.7 at% with hafnium Hf, i.e. a coating according to the second embodiment. Curve 163 corresponds to a working electrode made of 316L stainless steel completely covered with a coating of cubic tantalum nitride doped at a height of 5.3 + / - 0.5 at% with hafnium Hf, i.e. a coating according to an alternative embodiment of the second example.

[0114] It can thus be seen in [Fig.7] that curves 162 and 163, corresponding to the anti-corrosion coatings according to the second embodiment and its variant, have significantly wider stability levels than curve 161 corresponding to the substrate material, thus confirming the protection of the substrate by the anti-corrosion coating.

[0115] This test also makes it possible to measure the corrosion potential and current for these different samples:

[0116] [T ableaux2] 316L TabxHfxN - 5.3% TabxHfxN - 5.7% Ecoir (V / Pt) 0.4 0.6 0.5 ICOIT (pA / cm2) 27.2 22.1 23.7

[0117] It is thus observed that the corrosion current Icotr of the anticorrosion coatings according to the second embodiment example and its variant is more than 10% lower than that of the comparative sample of the substrate, thus confirming the excellent anticorrosion properties of these coatings.

[0118] [Fig. 8] schematically represents a component 230 according to a third exemplary embodiment. Again, the component 230 comprises a substrate 231, made for example of 316L stainless steel, and an anti-corrosion coating 232 deposited on the substrate 231.

[0119] In this third example, the anti-corrosion coating 232 comprises a plurality of superimposed layers 233, more precisely ten layers in the present example, each having a thickness of 50 nm for a total coating thickness of 500 nm.

[0120] In this third example, the anti-corrosion coating 232 comprises two types of layers 233 deposited alternately: main layers 233a, made of a main material, and secondary layers 233b, made of a secondary material. Here, the uppermost layer of the anti-corrosion coating 232, exposed to the environment, is a main layer 233a.

[0121] In this third example, the main material, i.e. the material of the main layers 233a, is cubic tantalum nitride TaN doped with zirconium Zr. In particular, this main material may correspond to the material of the anti-corrosion coating 32 of the first embodiment.

[0122] In this third example, the secondary material, i.e. the material of the secondary layers 233b, is undoped hexagonal tantalum nitride TaN.

[0123] This multilayer anticorrosion coating 232 can be deposited on the substrate 231 using the same device 50 shown schematically in [Fig.4] and described in the context of the first embodiment. Indeed, the main layers 233a can be deposited by co-sputtering as described above; the secondary layers 233b can for their part be deposited by high-power pulsed magnetron cathode sputtering using the first target 52 alone, that is to say by applying no power to the second target 53.

[0124] Thus, it is possible to produce all of the layers 233 of the coating 232 in a single step and using a single device 50, by controlling over time the electrical polarizations applied to each of the targets 52, 53.

[0125] In particular, in this third example, the pressure in the chamber 51 is set at 5 mTorr, or approximately 0.7 Pa; the gas mixture is composed of argon and nitrogen with 25% at nitrogen. The main layers are deposited with the same pulse parameters as those of the first embodiment. The secondary layers are deposited with the following pulse parameters: pulse width equal to 50 ps; pulse frequency equal to 1000 Hz; and pulse voltage equal to 700V.

[0126] The anti-corrosion performance of the main material has been described in the context of the first embodiment. [Fig.9] illustrates the results of corrosion tests concerning the secondary material. This cyclic voltammetry test was carried out under the same conditions as the test carried out for the first embodiment, except that the working electrode was tested in several phosphoric acid baths at increasing concentrations: 0.1 mol / L; 0.5 mol / L; and 1 mol / L.

[0127] The three curves 261, 262 and 263 thus correspond to the same working electrode made of 316L stainless steel completely covered with an undoped hexagonal tantalum nitride coating. Curve 261 corresponds to a bath concentration of 0.1 mol / L; Curve 262 corresponds to a bath concentration of 0.5 mol / L; and Curve 263 corresponds to a bath concentration of 1 mol / L.

[0128] It can thus be seen in [Fig.9] that curves 261, 262 and 263, corresponding to the secondary material, also have significantly wider stability levels than that of the substrate 231 in 316L stainless steel.

[0129] This test also allows the corrosion potential and current to be measured for 316L stainless steel (Table 3) and undoped hexagonal tantalum nitride (Table 4) for these different bath concentrations.

[0130] [Tables3] 0.1 mol / L 0.5 mol / L 1 mol / L Ecoir (V / Pt) 0.9 0.4 0.5 Lorr (pA / cm2) 14 27.2 49.7 Stability range (V) 2.1 1.4 1.4

[0131] [Tables4] 0.1 mol / L 0.5 mol / L 1 mol / L Ecoir (V / Pt) 0.4 0.4 0.4 Lorr (pA / cm2) 17.6 22.2 35.2 Stability range (V) 2.2 2.1 2.1

[0132] It is thus observed that the ICOIT corrosion current of undoped hexagonal tantalum nitride increases much less quickly than that of 316L stainless steel with the increase in the acidity of the medium, thus revealing better resistance to corrosion.

[0133] Furthermore, [Fig. 10] illustrates the microstructure of a hexagonal tantalum nitride coating, in section and from the front, deposited by a high-power pulsed magnetron sputtering process in accordance with the present example. The scale shown at the bottom of each view corresponds to Ipm. It can be seen from these two views that, in the same way as for its cubic counterpart in [Fig. 6], the microstructure of the coating is fine and homogeneous, which implies good mechanical strength with, in particular, good resistance to the propagation of cracks within the coating. For comparison, such a coating deposited by A conventional magnetron sputtering process results in an easily fracturable columnar microstructure, as seen in [Fig.l 1].

[0134] Furthermore, the inventors determined that the cubic and hexagonal phases of tantalum nitride possess significantly different Young's moduli. Indeed, the Young's modulus measured by nano-indentation of the cubic phase is 430 GPa while that of the hexagonal phase is 560 GPa.

[0135] Consequently, the cracks tend to be deflected at the interface between a main layer 233a and a secondary layer 233b. Therefore, the superposition of several alternating main layers 233a and secondary layers 233b makes it possible to significantly slow down the propagation of cracks within the coating 232.

[0136] Finally, it is important to note that hexagonal tantalum nitride benefits from an even higher conductivity than cubic tantalum nitride, which further improves its electrical conduction function. Thus, at 160°C, the conductivity of cubic tantalum nitride deposited by high-power pulsed magnetron sputtering is equal to 4,045 S / cm.

[0137] In this third example, the primary material is doped cubic tantalum nitride while the secondary material is undoped hexagonal tantalum nitride. However, other multilayer configurations are also conceivable.

[0138] For example, the main material may be hexagonal tantalum nitride, or two-phase tantalum nitride, either cubic or hexagonal. The main material may also include a different doping element or one or more additional doping elements.

[0139] For example, the secondary material may also be doped. However, if the crystal system of the second material is the same as that of the main material, the doping will preferably be different from that of the main material.

[0140] Thus, in particular, in a fourth exemplary embodiment, the coating comprises alternating layers of doped hexagonal tantalum nitride and undoped hexagonal tantalum nitride.

[0141] In a fifth embodiment, the coating comprises alternating layers of doped hexagonal tantalum nitride and cubic tantalum nitride, doped or not.

[0142] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0143] It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a method.

Claims

Claims

1. Component for a fuel cell or molten salt electrolyte electrolyzer, comprising an electrically conductive substrate (31) and an anti-corrosion coating (32) deposited on at least one surface of the substrate (31), in which the anti-corrosion coating (32) comprises at least one main layer based on tantalum nitride doped with one or more doping elements chosen from the family of transition metals or lanthanides, in which the total dopant content within the main layer (32) is between 10 ppm and 10 at.%.

2. Component for a fuel cell or acid electrolyser, comprising an electrically conductive substrate (31) and an anti-corrosion coating (32) deposited on at least one surface of the substrate (31), wherein the anti-corrosion coating (32) comprises at least one main layer based on tantalum nitride doped with one or more doping elements chosen from the family of transition metals or lanthanides, wherein the anti-corrosion coating (232) comprises several superimposed layers (233a, 233b), preferably between 2 and 10 layers, wherein the material of the main layer (233a) constitutes a main material, and wherein the anti-corrosion coating (232) comprises at least one secondary layer (233b) based on a secondary material which is tantalum nitride having a crystal system and / or doping different from the main material.

3. A component according to claim 2, wherein the main material constitutes at least 30% by volume, preferably at least 50% by volume, of the anti-corrosion coating.

4. A component according to claim 2 or 3, wherein the anti-corrosion coating comprises alternating layers based alternately on the primary material and the secondary material.

5. Component according to any one of claims 1 to 4, wherein the substrate (31) is metallic, preferably steel.

6. A component according to any one of claims 1 to 5, wherein the crystal system of the tantalum nitride of the main layer (32) is hexagonal or cubic.

7. Component according to any one of claims 1 to 6, wherein the total dopant content within the main layer (32) is between 1 ppm and 10 at%, preferably between 10 ppm and 1 at%, more preferably between 0.2 and 0.5 at%.

8. A component according to any one of claims 1 to 7, wherein the main doping element is selected from zirconium, hafnium, chromium, titanium, vanadium, niobium or molybdenum.

9. Component according to any one of claims 1 to 8, wherein the thickness of the anti-corrosion coating (32) is between 5 nm and 5 pm, preferably between 10 nm and 1 pm, more preferably between 100 nm and 300 nm.

10. Fuel cell or electrolyzer, with molten salt electrolyte, comprising at least one component (30) according to any one of claims 1 to 9.

11. Fuel cell or electrolyzer according to claim 10, of the molten carbonate fuel cell (MCFC) type, of the molten carbonate electrolyzer (MCEC) type, of the direct carbon fuel cell (DCFC) type or of the direct urea fuel cell (DUFC) type.

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