Interconnectors for stacks of solid oxide cells of the SOEC / SOFC type containing different protruding elements

Abstract

The main object of the present invention is an interconnect for a stack of solid oxide cells of the SOEC / SOFC type, intended to be placed between two adjacent electrochemical cells, characterized in that it comprises a plane (P) on which at least a first group of identical first projecting elements (10a) and a second group of identical second projecting elements (10b) are formed, the first projecting elements (10a) having different geometric characteristics relative to the second projecting elements (10b), the height (H1) of each first projecting element (10a) being different from the height (H2) of each second projecting element (10b) and the contact width (D1) of each first projecting element (10a) being different from the contact width (D2) of each second projecting element (10b).

Description

[Technical Field]

[0001] The present invention relates generally to the field of high temperature electrolysis (HTE), in particular to high temperature steam electrolysis (HTSE), electrolysis of carbon dioxide (CO2), or even high temperature co-electrolysis of water vapor and carbon dioxide (CO2).

[0002] More precisely, the invention relates to the field of high temperature solid oxide electrolyzer cells (SOEC).

[0003] It also relates to the field of high temperature solid oxide fuel cells (SOFC).

[0004] More generally, the invention therefore relates to the field of stacks of solid oxide cells of the SOEC / SOFC type operating at high temperatures.

[0005] More precisely, the invention relates to an interconnect for a stack of solid oxide cells of the SOEC / SOFC type comprising a group of protruding elements of various geometric shapes, as well as to a stack of solid oxide cells of the SOEC / SOFC type comprising a plurality of such interconnects. [Background technology]

[0006] In the context of SOEC-type high-temperature solid oxide electrolyzers, this also relates to the conversion of water vapor (H2O) to dihydrogen (H2) or other fuels, such as methane (CH4), natural gas, or biogas, and to dioxygen (O2) using electric current, and / or the conversion of carbon dioxide (CO2) to carbon monoxide (CO) and dioxygen (O2) in the same electrochemical device. In the context of SOFC-type high-temperature solid oxide fuel cells, the reverse operation is used to generate electric current and heat, with dihydrogen (H2) and dioxygen (O2) typically supplied by air and natural gas, i.e., methane (CH4). For simplicity, the following description prioritizes the operation of SOEC-type high-temperature solid oxide electrolyzers performing the electrolysis of water vapor. However, this operation is also applicable to the electrolysis of carbon dioxide (CO2) or even the high-temperature co-electrolysis (HTE) of water vapor with carbon dioxide (CO2). In addition, this operation can be transposed to the case of SOFC-type high-temperature solid oxide fuel cells.

[0007] To perform water electrolysis, it is advantageous to do so at high temperatures, typically between 600 and 1,000°C, but it is advantageous to electrolyze water vapor rather than liquid water because part of the energy required for the reaction can be provided by heat, which is cheaper than electricity.

[0008] To implement high-temperature steam electrolysis (HTSE), a high-temperature solid oxide electrolyzer (SOEC) consists of a basic unit, each of which also contains a solid oxide electrolysis cell, or electrochemical cell, consisting of three anode / electrolyte / cathode layers stacked on top of each other, and a stack of interconnecting plates, often made of metal alloys and also called bipolar plates or interconnectors. Each electrochemical cell is tightly held between two interconnecting plates. A high-temperature solid oxide electrolyzer (SOEC) is therefore an alternating stack of electrochemical cells and interconnectors. A high-temperature solid oxide fuel cell (SOFC) consists of the same type of stack of basic units. This technology is reversible, so the same stack can operate in electrolysis mode to produce hydrogen and oxygen from water and electricity, or in fuel cell mode to produce electricity from hydrogen and oxygen.

[0009] Each electrochemical cell corresponds to an electrolyte / electrode junction, typically a ceramic multilayer junction, in which the electrolyte is formed by a central ion-conducting layer that is solid, dense, and leak-proof and is tightly held between two porous layers that form the electrodes. It should be noted that additional layers may be present, but are used only to improve one or more of the layers already described.

[0010] The electrical and fluidic interconnection device is, from an electrical point of view, an electronic conductor that ensures the connection of each electrochemical cell of a basic unit in a stack of basic units, ensuring electrical contact between one face and the cathode of the cell and the other face and the anode of the adjacent cell, and, from a fluidic point of view, ensuring the addition of reactants to and the evacuation of products from each of the cells. The interconnect thus ensures the function of delivering and collecting electrical current and defines gas circulation compartments for distribution and / or collection.

[0011] More precisely, the main function of the interconnector, besides the passage of electric current, is to ensure the circulation of gases within the vicinity of each cell (i.e.: for HTE electrolysis, injected water vapor, extracted hydrogen and oxygen; for SOFC cells, injected hydrogen and extracted water vapor, which are its air and fuel), and to separate the anode and cathode compartments of two adjacent cells, which are the gas circulation compartments on the anode and cathode side of the cell, respectively.

[0012] In particular, for high-temperature solid oxide electrolysers of the SOEC type, the cathode compartment contains water vapor and hydrogen produced from the electrochemical reaction, while the anode compartment contains exhaust gases, if present, and oxygen, which is another product of the electrochemical reaction.For high-temperature solid oxide fuel cells of the SOFC type, the anode compartment contains the fuel, while the cathode compartment contains the oxidant.

[0013] To perform high-temperature electrolysis (HTE) of water vapor, water vapor (HO) is injected into the cathode compartment. Under the influence of an electric current applied to the cell, dissociation of water molecules in the form of vapor occurs at the interface between the hydrogen electrode (cathode) and the electrolyte, which dissociation produces dihydrogen (H) gas and oxygen ions (O 2- ) is produced. Dihydrogen (H2) is collected and vented at the exit of the hydrogen compartment. Oxygen ions (O 2- ) migrates through the electrolyte and recombines into dioxygen (O) at the interface between the electrolyte and the oxygen electrode (anode). An exhaust gas, such as air, may be circulated at the anode, thus collecting the oxygen evolved in gaseous form at the anode.

[0014] To ensure the operation of a solid oxide fuel cell (SOFC), air (oxygen) is injected into the cathode compartment of the cell and hydrogen into the anode compartment. 2- The hydrogen dissociates into ions. These ions migrate through the electrolyte from the cathode to the anode and oxidize the hydrogen to form water, with the simultaneous production of electricity. In a SOFC cell, as in SOEC electrolysis, the water vapor resides in the dihydrogen (H2) compartment; only the polarity is reversed.

[0015] By way of example, Figure 1 shows a schematic diagram illustrating the operating principle of a high-temperature solid oxide electrolyzer of the SOEC type. The function of such an electrolyzer is to convert water vapor into hydrogen and oxygen according to the following electrochemical reaction: 2H2O→2H2+O2.

[0016] This reaction takes place electrochemically in the cells of an electrolytic cell. As shown schematically in Figure 1, each elementary electrolytic cell 1 is formed from a cathode 2 and an anode 4, placed on either side of a solid electrolyte 3. The two electrodes (cathode and anode) 2 and 4 are ionic and / or electronic conductors, made from porous materials, while the electrolyte 3 is gas-tight, an electronic insulator and an ionic conductor. In particular, the electrolyte 3 is an anion conductor, more precisely O 2-The anion conductor may be an ionic conductor, and the electrolyser is therefore known as an anion electrolyser, as opposed to a protonic electrolyte (H+).

[0017] An electrochemical reaction occurs at the interface between each of the electronic conductors and the ionic conductor.

[0018] At cathode 2, the half-reactions are: 2H2O+4e - →2H2+2O 2- .

[0019] At anode 4, the half-reactions are: 2O 2- →O2+4e - .

[0020] An electrolyte 3 inserted between two electrodes 2 and 4 is heated to O under the influence of an electric field created by a potential difference imposed between the anode 4 and the cathode 2. 2- This is the site of ion migration.

[0021] As illustrated in parentheses in Figure 1, water vapor at the cathode inlet may accompany hydrogen H2, and the hydrogen produced and recovered at the outlet may accompany water vapor. Also, as illustrated by the dotted line, an exhaust gas such as air may be further injected into the anode inlet to exhaust the produced oxygen. The injection of the exhaust gas has the additional function of acting as a temperature regulator.

[0022] The basic electrolyser, or electrolysis reactor, consists of a basic cell as described above, with a cathode 2, an electrolyte 3 and an anode 4, and two interconnectors that ensure the electrical and fluid distribution functions.

[0023] To increase the flow of hydrogen and oxygen produced, it is known to stack several elementary electrolysis cells on top of each other by separating them with interconnectors. The assembly is arranged between two end interconnection plates that support the electrical and gas supplies of the electrolyzer (electrolysis reactor).

[0024] A high-temperature solid oxide electrolyzer of the SOEC type therefore comprises at least one, and generally a number of, electrolytic cells stacked one on top of the other, each elementary cell being formed from an electrolyte, a cathode and an anode, the electrolyte being inserted between the anode and the cathode.

[0025] As indicated above, an electrical and fluidic interconnection device in electrical contact with one or more electrodes generally ensures functionality for delivering and collecting electrical current and defines one or more of the gas circulation compartments.

[0026] The function of the so-called cathode compartment is therefore to distribute the current and water vapor as well as to recover the hydrogen in contact with the cathode.

[0027] The function of the so-called anode compartment, in addition to distributing the current, is to recover the oxygen produced at the anode in contact with it, possibly using exhaust gases.

[0028] 2 shows an exploded view of a basic unit of a high-temperature solid oxide electrolyzer of the SOEC type according to the prior art. The electrolyzer comprises a number of basic electrolysis cells C1, C2 of the solid oxide cell (SOEC) type, stacked alternately with interconnects 5. Each cell C1, C2 consists of a cathode 2.1, 2.2 and an anode (only the anode 4.2 of cell C2 is shown), between which an electrolyte is provided (only the electrolyte 3.2 of cell C2 is shown).

[0029] The interconnector 5 is typically a metal alloy component that ensures the separation between the cathode compartment 50 and the anode compartment 51, defined by the volumes between the interconnector 5 and the adjacent cathode 2.1 and between the interconnector 5 and the adjacent anode 4.2, respectively. It also ensures the distribution of gases to the cells. The injection of water vapor into each basic unit is carried out in the cathode compartment 50. The hydrogen produced in the cathodes 2.1 and 2.2 and the residual water vapor are collected in the cathode compartment 50 downstream of the cells C1 and C2 after the dissociation of the water vapor by the cells C1 and C2. The oxygen produced in the anode 4.2 is collected in the anode compartment 51 downstream of the cells C1 and C2 after the dissociation of the water vapor by the cells C1 and C2. The interconnector 5 ensures the passage of current between the cells C1 and C2, i.e., between the anode 4.2 and the cathode 2.1, by direct contact with the adjacent electrodes.

[0030] As the operating conditions of high temperature solid oxide electrolyzers (SOECs) are very similar to those of solid state fuel cells (SOFCs), the same technical constraints are observed.

[0031] Therefore, the correct operation of such a stack of solid oxide cells of the SOEC / SOFC type operating at high temperatures requires that the following points be met:

[0032] First, electrical insulation between two successive interconnects is necessary, otherwise the electrochemical cell would be short-circuited, and also good electrical contact and a sufficiently large contact surface between the cell and the interconnect. The lowest possible ohmic resistance is required between the cell and the interconnect.

[0033] Moreover, it is necessary to have leak-tightness between the anode and cathode compartments, otherwise the gases produced will recombine, leading to a loss of efficiency and, above all, the appearance of hot spots which will damage the stack.

[0034] Finally, it is important to have a good distribution of gases at both the inlet and product collection points, otherwise there will be a loss of efficiency, non-uniformity of pressure and temperature within the various basic units, or even unacceptable degradation of the electrochemical cells.

[0035] To successfully increase the production efficiency and obtain good operating uniformity of stacks of solid oxide cells of the SOEC / SOFC type operating at high temperatures, the role of the interconnector is particularly important to obtain good electrical contact between the various parts of the stack and also to allow good distribution of gases within the electrochemical cell. The interconnector may be metallic and consist of three thin plates, as described in French patent application FR3024985A1.

[0036] These interconnectors are further described in French patent application FR2996065A1. In this application, the interconnector corresponds to a metal alloy substrate component, the base element of which is iron (Fe) or nickel (Ni), one of the main surfaces of which is coated with a thick ceramic or metal layer and grooved to define suitable channels for the distribution and / or collection of gases such as water vapor, HO, H2, O2, and exhaust gases. In particular, a thick ceramic contact layer based on strontium-doped lanthanum manganate may be provided on the oxygen electrode side (HTE anode, cathode in the case of SOFC cells). "Thick layer" refers to a layer whose thickness is greater than that of layers obtained by so-called "thin layer" techniques, typically between 2 and 15 μm. This allows for good performance and uniformity at low production costs in stacks of solid oxide cells of the SOFC / SOEC type.

[0037] Nevertheless, there is still a need to optimize such interconnects, especially from a fluidic and mechanical point of view. [Prior art documents] [Patent documents]

[0038] [Patent Document 1] French Patent Application Publication No. 3024985 [Patent Document 2] French Patent Application Publication No. 2996065 Summary of the Invention [Problem to be solved by the invention]

[0039] SUMMARY OF THE INVENTION It is an object of the present invention to at least partially remedy the above-mentioned needs and shortcomings associated with prior art embodiments.

[0040] It aims in particular to produce an optimized interconnect design for stacks of solid oxide cells of the SOEC / SOFC type, which makes it possible to obtain, for a given fastening, high electrical conductivity of the interconnect and good electrical or mechanical contact, while reducing the pressure loss for the passage of gases, in particular by means of specific machining of the contact layers of the interconnect. [Means for solving the problem]

[0041] The object of the present invention is therefore, according to one of its aspects, an interconnect for a stack of solid oxide cells of the SOEC / SOFC type operating at high temperatures, intended to be placed between two adjacent electrochemical cells of the stack, each electrochemical cell being formed from a cathode, from an anode and from an electrolyte inserted between the cathode and the anode, a plane surface on which at least one first group of first projecting elements identical to the plane surface and a second group of second projecting elements identical to the plane surface are formed; the first projecting element has a different geometric characteristic relative to the second projecting element; the height of each first protruding element, measured as the maximum perpendicular dimension of the first protruding element relative to the plane, is different from the height of each second protruding element, measured as the maximum perpendicular dimension of the second protruding element; An interconnector characterized in that the contact width of each first protruding element, measured as the maximum horizontal dimension relative to the plane of the outer contact end of each first protruding element opposite the inner end in contact with the plane, which is intended to contact the electrochemical cell, is different from the contact width of each second protruding element, measured as the maximum horizontal dimension relative to the plane of the outer contact end of each second protruding element opposite the inner end in contact with the plane, which is intended to contact the electrochemical cell.

[0042] The interconnector according to the present invention may further comprise one or more of the following features, taken alone or according to any possible technical combination:

[0043] The contact width of each first projecting element may be between 0.5 and 5 mm, preferably equal to 1 mm.

[0044] The contact width of each second protruding element may be between 0.005 mm and 0.5 mm, preferably equal to 100 μm.

[0045] The height of each first projecting element may be between 200 μm and 1,000 μm, preferably equal to 350 μm.

[0046] The height of each second projecting element may be between 250 μm and 1,050 μm, preferably equal to 400 μm.

[0047] The difference between the height of each second projecting element and the height of each first projecting element may be between 5 μm and 500 μm, preferably on the order of 50 μm.

[0048] Moreover, the interconnector may comprise N groups (N being an integer equal to or greater than 2, preferably between 2 and 50, also preferably equal to 5) of protruding elements formed on a plane, wherein the protruding elements of the same group are all identical and the protruding elements of different groups have different geometrical characteristics, i.e. different heights and different contact widths.

[0049] The protruding elements may be in the form of teeth or grooves arranged parallel to one another, the spaces between the protruding elements forming gas circulation channels.

[0050] The projecting elements may be in the form of pads, in particular of cylindrical shape, the spaces between the projecting elements forming a single serpentine gas circulation channel. Other shapes are also possible, for example parallelepiped shapes.

[0051] Furthermore, the projecting elements are regularly distributed over the plane according to at least one horizontal direction on the plane and are in particular equally spaced apart from one another at equal distances, in particular 50 μm to 5 mm, preferably 750 μm.

[0052] At least one region of the plane, in particular the central region, may be free of protruding elements.

[0053] Additionally, the protruding elements having the greatest width may be located around the periphery of the plane at a distance from other protruding elements and from gas circulation flow paths formed by spaces between the other protruding elements.

[0054] The interconnector may comprise a metal alloy substrate, in particular of a ferritic steel of the chromia-forming type, in particular of the Uginox® K41 or VDM® Crofer type, whose base element is iron or nickel, having two main planes, one of which is provided with a first coating layer forming a first contact layer with the electrochemical cell and the other of which is provided with a second coating layer forming a second contact layer with the electrochemical cell, the first coating layer and / or the second coating layer comprising a plane and protruding elements formed thereon, in particular by machining.

[0055] The first coating layer may be a thick ceramic coating layer, whether porous or not, wherein the ceramic material has the formula La 1-x Sr x In MO3, M (transition metal) = nickel (Ni), iron (Fe), cobalt (Co), manganese (Mn), chromium (Cr), alone or in mixtures thereof, is particularly selected from layered structure materials such as lanthanum manganates or lanthanide nickelates of formula Ln2NiO4 (Ln = lanthanum (La), neodymium (Nd), praseodymium (Pr)), or other electrically conductive perovskite oxides.

[0056] The second coating layer may be a thick metallic coating layer, in particular of lattice type or dense material, the metallic material being in particular selected from nickel (Ni) and its alloys or chromia-forming alloys whose base element is iron (Fe), in particular ferritic steels of the Uginox® K41 or VDM® Crofer type.

[0057] Moreover, another object of the present invention, according to another of its aspects, is a stack of solid oxide cells of the SOEC / SOFC type operating at high temperature, comprising a plurality of electrochemical cells each formed from a cathode, an anode and an electrolyte interposed between the cathode and the anode, and a plurality of interconnects as defined above, each interposed between two adjacent electrochemical cells.

[0058] The invention can be better understood on reading the following detailed description, on non-limiting examples of its implementation, and on studying the accompanying schematic and partial drawings. [Brief explanation of the drawings]

[0059] [Figure 1] FIG. 1 is a schematic diagram illustrating the operating principle of a high temperature solid oxide electrolyzer (SOEC). [Figure 2] 1 is an exploded schematic view of a portion of a high temperature solid oxide electrolyzer (SOEC) with an interconnect according to the prior art; FIG. [Figure 3] 1 is a schematic front view of a prior art interconnect for a stack of high temperature solid oxide electrolysis cells (SOEC) or fuel cells (SOFC) operating at high temperature. [Figure 3A] FIG. 4 is a detailed cross-sectional view of the interconnector according to FIG. 3. [Figure 3B] FIG. 4 is a view similar to that of FIG. 3 illustrating current lines passing through the interconnector. [Figure 4] FIG. 1 illustrates in graphical form the height, in mm, of the interconnect teeth as a function of the length, in mm, for pre-clamped and post-clamped configurations of a stack of high-temperature electrolysis cells (SOECs) or high-temperature fuel cells (SOFCs). [Figure 5] FIG. 10 graphically illustrates polarization curves for three different configurations with two different tooth geometries and two different clamping forces. [Figure 6] 1 is a cross-sectional view of two teeth and channels of a conventional interconnect for a stack of high-temperature solid oxide cells of the SOEC / SOFC type. [Figure 7] FIG. 1 is a cross-sectional view of five teeth and four channels of an interconnect according to the invention for a stack of high-temperature solid oxide cells of the SOEC / SOFC type before clamping. [Figure 8] FIG. 8 is a cross-sectional view of the configuration of FIG. 7 after tightening. [Figure 9] FIG. 9 is a top view of the configuration of FIGS. 7 and 8. [Figure 10] 8 is an alternative embodiment of the configuration of FIG. 7. [Figure 11] FIG. 11 is a top view of the configuration of FIG. 10. [Figure 12] 12 is an alternative embodiment to the configuration of FIG. 11. [Figure 13] 10 is an alternative geometric embodiment of the configuration of FIG. 9. [Figure 14] 14 is an alternative embodiment of the configuration of FIG. 13. [Figure 15] 1 shows an assembly comprising a stack of solid oxide cells of the SOEC / SOFC type with an interconnect according to the invention and a clamping system for the stack, viewed from a perspective and from above; FIG. DETAILED DESCRIPTION OF THE INVENTION

[0060] In all of these figures, the same references may indicate the same or similar elements.

[0061] In addition, in order to make the figures more readable, the various parts shown in the figures are not necessarily to a uniform scale.

[0062] Figures 1 and 2 have already been described above in the section relating to the prior art. With respect to Figures 1 and 2, it is noted that the symbols and H2O steam supply arrows for distributing and recovering dihydrogen H2, oxygen O2, air and current are shown for the purposes of clarity and precision to illustrate the operation of the illustrated apparatus.

[0063] Furthermore, it should be noted that all of the components (anode / electrolyte / cathode) of a given electrochemical cell are preferably ceramic. The operating temperatures of high-temperature SOEC / SOFC type stacks are also typically between 600 and 1,000°C.

[0064] In addition, the possible terms "upper" and "lower" are to be understood here according to the normal direction of operation of a stack of the SOEC / SOFC type when it is in its use configuration.

[0065] The interconnector 5 may have a particular geometric shape, in particular a grooved shape due to the presence of teeth and channels. For example, as described in French patent application FR 2 996 065 A1, the interconnector 5 may consist of a component including a metal alloy substrate of a ferritic steel of the chromia-forming type, in particular of the Uginox® K41 type or VDM® Crofer type, in particular with iron or nickel as the base element, this substrate having two main planes, one of which is coated with a coating including a thick ceramic layer and grooved by defining channels and teeth for gas distribution and / or collection, this layer also being referred to as the "contact layer". The teeth and channels may therefore be formed in the contact layer. In addition, in the following description, it will be understood that the teeth and channels of the interconnector 5, or more generally, reliefs, may be formed from the contact layer of this interconnector 5.

[0066] Figures 3, 3A and 3B illustrate interconnectors 5 commonly used in high temperature SOEC / SOFC type stacks. The delivery or collection of current at the electrodes is done by teeth 10 or ribs, which are in direct mechanical contact with the electrodes involved. The delivery of water vapor at the cathode or exhaust gas at the anode in an HTE electrolyser, and of dioxygen at the cathode or hydrogen at the anode in an SOFC cell are represented by arrows F1 which can be seen in Figure 3.

[0067] The collection of hydrogen produced at the cathode or oxygen produced at the anode in HTE electrolysers, and of water produced at the cathode or excess hydrogen at the anode in SOFC cells is carried out by channels 11 leading to fluid connections, commonly known as manifolds, that are common to the stack of cells. The structure of these interconnects 5 allows a compromise between the two functions of (gas / current) delivery and collection.

[0068] In order to obtain good electrical conductivity between the interconnect 5, in particular the contact layer, and the electrochemical cell, the teeth 10 should be spaced fairly close together, however this would therefore tend to have a small passage surface for the gas, which could lead to significant pressure losses during operation.

[0069] Moreover, the interconnector 5 should allow the gas to circulate correctly and have low pressure losses, which can be achieved using wide flow channels 11. Nevertheless, this leads to the teeth 10 being spaced apart from each other, which is detrimental to electrical conductivity.

[0070] Furthermore, the geometry of the teeth 10 and channels 11 should allow them to adapt to surface imperfections, in particular of the cells and interconnects 5. For this, they must be able to be easily crushed. This can be obtained, for example, by creating narrow teeth 10. However, if the teeth 10 are crushed significantly, the height of the channels 11 will be significantly reduced and the passage surface for the gas will thereby be reduced, leading to greater pressure losses. By way of example, FIG. 4 illustrates in graphical form the height H, expressed in mm, of the teeth 10 as a function of the length L, expressed in mm, for a configuration C1 before clamping and a configuration C2 after clamping.

[0071] The forces applied to a stack of solid oxide cells of the SOEC / SOFC type, or to a stack, make it possible to calculate the local clamping stresses. For this purpose, a force F of 1,000 N is applied and the bearing surface S is 100 cm 2 If the contact is made using the teeth 10 of the contact layer of the interconnect 5, which in particular represents half of the surface, the F / S stress is 0.4 MPa.

[0072] 100cm 2 Three actual experiments (E1, E2, E3) for hydrogen production from a SOEC-type stack with five cells of surface area of ​​12 Nml / min / cell / cm were carried out with two geometries of the interconnector (tooth A and tooth B) and two different clamping forces (force A and force B). The total flow rate was 12 Nml / min / cell / cm. 2 A mixture of water vapor and hydrogen was delivered. The H2O / H2 mixture was 90% H2O and 10% H2. The stack temperature was 800°C.

[0073] A / cm 2 By gradually increasing the current i, denoted by , and measuring the voltage E, denoted by V, of the relevant cell, polarization curves (tooth A, E1 for force A; tooth B, E2 for force A; tooth B, E3 for force B) are carried out each time. These curves make it possible to measure the area specific resistance (ASR) coming from the cells, interconnects, interfaces, connection systems, etc., as well as the maximum utilization rate t of water vapor.

[0074] The reference interconnect geometry comprises an interconnect, in particular a contact layer, with teeth 10 (tooth A) of width A. A second interconnect geometry has been created with teeth 10 (tooth B) of width B, which is three times narrower than width A. The applied force may be reference force A (force A) or force B, which is three times smaller than force A.

[0075] Figure 5 illustrates in graphical form the polarization curves E1, E2, E3 obtained for three stacks of two interconnect geometries (tooth A, tooth B) and two different forces (force A, force B). Additionally, Table 1 below shows the relative pressure drop obtained for the O2 chamber.

[0076] [Table 1]

[0077] Therefore, by maintaining the same clamping force (Force A), if the teeth are narrower (Tooth B), the ASR is lower and therefore performance is improved, but the pressure drop increases. Collapsing of the teeth reduces the passage surface for gas. If the teeth are narrower (Tooth B) but the force is reduced (Force B), performance deteriorates (higher ASR and reduced maximum duty cycle), but the pressure drop is significantly reduced.

[0078] The principles of the present invention will now be described with reference to Figures 7 to 14, with the aim of optimizing these aspects and in particular obtaining a design of the interconnects, in particular the contact layers, that makes it possible to have good collapse of the teeth 10 and also to maintain a significant volume of gas circulation channels 11.

[0079] The interconnect 5 for a stack of solid oxide cells of the SOEC / SOFC type operating at high temperatures is intended to be placed between two adjacent electrochemical cells 1 of the stack, each cell being formed from the cathode, the anode, and an electrolyte inserted between the cathode and the anode. The interconnect usually has a regular geometric shape. In particular, the contact layer forming the coating on one of the faces of the metal alloy substrate of the interconnect 5 conventionally comprises teeth 10 and channels 11 of regular geometric shape. Therefore, all the teeth 10 have the same dimensions (height and width), and all the channels 11 have the same width. The main features of the teeth 10 and channels 11 are detailed in the cross-sectional view in FIG. 6. Therefore, the contact width of the teeth 10 is designated D, the upper width of the channels 11 is designated Ch, while the lower width of the channels 11 is designated Cb, and the height of the teeth 10 is designated H.

[0080] According to the invention, the geometry of the interconnect 5, in particular of the contact layer, is varied to obtain a non-uniformity that allows both an optimum electrical contact and a gas distribution that provides little resistance during the passage of gas and therefore little overpressure. In particular, non-uniform machining is performed to obtain teeth and channels with different characteristics on the same interconnect 5, in particular on the same contact layer of this interconnect 5.

[0081] Therefore, the interconnector 5 of the present invention includes a plane P on which at least a first group of identical first protrusion elements 10a and a second group of identical second protrusion elements 10b are formed, and the first protrusion elements 10a and the second protrusion elements 10b have different geometric characteristics.

[0082] 7 and 8 illustrate an example embodiment with two different machining geometries before and after crushing, however, many different geometries may be provided for the interconnect 5 within the scope of the present invention.

[0083] Therefore, the height H1 of each first protruding element 10a, measured as the maximum vertical dimension of the first protruding element 10a with respect to the plane P, is different from the height H2 of each second protruding element 10b, measured as the maximum vertical dimension of the second protruding element 10b. Similarly, the contact width D1 of each first protruding element 10a, measured as the maximum horizontal dimension with respect to the plane P of the outer contact end 10ae of each first protruding element 10a, which is intended to contact the electrochemical cell 1, opposite the inner end 10ai that contacts the plane P, is different from the contact width D2 of each second protruding element 10b, which is measured as the maximum horizontal dimension with respect to the plane P of the outer contact end 10be of each second protruding element 10b, which is intended to contact the electrochemical cell 1, opposite the inner end 10bi that contacts the plane P.

[0084] In particular, the contact width D1 of each first projecting element 10a is between 0.5 and 5 mm, preferably equal to 1 mm. This large width makes it possible to support the clamping constraint and to act as a crushing limiter.

[0085] The contact width D2 of each second protruding element 10b is between 0.005 mm and 0.5 mm, preferably equal to 100 μm. This narrow width makes it possible to have regular contact points around the entire contact surface of the electrochemical cell 1 without impeding fluid flow.

[0086] Moreover, the height H1 of each first protruding element 10a is less than the height H2 of each second protruding element 10b, which are 350 and 400 μm, respectively, so that the narrow width D2 of the protruding elements 10b ensures electrical contact.

[0087] It should be noted that in this example of Figures 7 and 8, as well as in Figures 10 to 12, the protruding elements 10a, 10b, 10c are in the form of teeth or grooves arranged parallel to one another. However, the protruding elements may have any shape that ensures electrical contact and gas circulation. The spaces between the protruding elements 10a, 10b, 10c thus form gas circulation channels 11.

[0088] Moreover, the protruding elements 10a, 10b are here regularly distributed across the plane P. To be precise, they are equally spaced apart from one another according to at least one horizontal direction DH across the plane P at the same distance Cb, in particular 50 μm to 5 mm, preferably 750 μm. The spacing between the protruding elements 10a, 10b is therefore constant, allowing a good distribution of the current within the electrodes of the electrochemical cell 1. The value of the spacing may depend on the electrochemical cell 1 used.

[0089] During tightening, the protruding elements 10b collapse first since they are taller. The collapse is more pronounced due to the narrow contact width D2. This then allows for good accommodation of geometrical imperfections.

[0090] This collapse continues until the height H2 of the protruding element 10b reaches the height H1 of the protruding element 10a. The contact surface thus increases sharply, stopping the collapse. This cessation of the collapse allows a significant space for the gas circulation channel 11 to be maintained. Therefore, pressure losses can remain low. In addition, the relatively small spacing Cb between the protruding elements 10a, 10b ensures good electrical conductivity.

[0091] Advantageously, the present invention does not require precise adjustment of the clamping force to stop the collapse: in fact, the significant increase in the surface when contact is established with the protruding elements 10a makes it possible to significantly reduce the stress and limit the effect of the initial force.

[0092] FIG. 9 makes it possible to see the regular distribution of the first and second projecting elements 10a, 10b of the examples of FIGS.

[0093] Since the manufacture of the interconnector 5 and the electrochemical cell 1 is irregular, it may further be advantageous to have the interconnector 5, in particular the contact layer of the interconnector 5, equipped with protruding elements, the collapse of which can be adjusted during operation.

[0094] Thus, by creating N different geometric shapes, an easily accessible crushing stage can be obtained even during testing. In other words, the interconnect may more generally comprise N (N being an integer greater than or equal to 2, preferably between 2 and 50, also preferably equal to 5) groups of projecting elements formed in a plane P, the projecting elements of the same group being all identical and the projecting elements of different groups having different geometric characteristics, i.e. different heights and different contact widths.

[0095] 10 and 11 make it possible to illustrate the case for N=3, which is merely an illustrative and non-limiting example of the invention. The interconnect 5 thus comprises a first protruding element 10a of contact width D1 and height H1, a second protruding element 10b of contact width D2 and height H2, and a third protruding element 10c of contact width D3 and height H3. The values ​​chosen are such that D3>D1>D2 and H2>H1>H3.

[0096] This possibility makes it possible to have several possible crushing levels. It is therefore possible to have a crushing with Force 1 which only crushes protruding element 10b. If this is not sufficient, because the geometrical defects to be compensated for are significant, it is possible to change to Force 2, which is greater than Force 1, in order to crush protruding element 10a to height H3 of protruding element 10c. The crushing and contact can therefore be adjusted as needed.

[0097] It is therefore possible to envisage N different geometries with increasing contact widths, if required. A successive increase in the clamping force allows the projecting elements to be crushed step by step and then stopped as soon as the contact is good and for optimal crushing, thus resulting in an interconnect 5, or its contact layer, that is adapted to all geometries.

[0098] FIG. 12 illustrates the possibility of having a protruding element 10c with a maximum contact width D3 located around the perimeter Pi of the plane P at a distance from the other protruding elements 10a, 10b and from the gas circulation channel 11.

[0099] These protruding elements 10c form the crushing limits since they have a maximum contact width D3. They may be located outside the effective area. In this way, a maximum surface is reserved for the passage of gas.

[0100] Furthermore, any shape is possible for the protruding elements 10a, 10b, 10c, they do not necessarily have to be tooth-shaped as described above.

[0101] 13 and 14 thus illustrate the possibility of having protruding elements 10a, 10b in the form of pads, in particular cylindrical in shape. Other shapes are also possible, for example parallelepiped shapes. The spaces between the protruding elements 10a, 10b then form a single serpentine gas circulation channel 11.

[0102] Advantageously, this may allow for more precise tailoring of stresses at appropriate surfaces to optimize gas passage.

[0103] 14 illustrates the possibility of having at least one region Z of the plane P, here the central region Z, free of protruding elements. Indeed, heat generation due to a surface of an electrochemical cell 1 that is too large may cause overheating problems, especially in the center of the cell 1, where the heat is difficult to evacuate. Therefore, it is possible to intentionally limit the reaction in the core of the cell 1 by reducing the conductivity in a particular central region Z and thereby intentionally eliminating electrical contact.

[0104] It should be noted that the interconnector 5 according to the invention may advantageously comprise a metal alloy substrate having two main planes, in particular of a ferritic steel of the chromia-forming type, in particular of the Uginox® K41 type or VDM® Crofer type, in which the base element is iron (Fe) or nickel (Ni), as described in French patent application FR 2 996 065 A1.

[0105] One of the main surfaces is provided with a first coating layer that forms a first contact layer with the electrochemical cell 1, and the other of the main surfaces is provided with a second coating layer that forms a second contact layer with the electrochemical cell 1.

[0106] The first coating layer and / or the second coating layer may comprise a plane P and protruding elements 10a, 10b, 10c formed thereon, in particular by machining, as described above.

[0107] When these two coating layers are provided with such protruding elements, these protruding elements may or may not be identical in the first and second coating layers, and their distribution may or may not be identical in the first and second coating layers.

[0108] The first coating layer may be a first thick ceramic coating layer, whether porous or not, in particular based on strontium-doped lanthanum manganate, which may be applied to the oxygen electrode side.

[0109] The second covering layer may in particular be a second thick metallic, in particular nickel-based, contact layer, which may be applied on the hydrogen electrode side.

[0110] This second layer may in particular comprise at least two different types of nickel lattices. 2 The mesh number and wire diameter per mesh may be adjusted. For example, it is possible to use a grid A with a mesh number Na and height Ha forming the protruding elements, and a second grid B with a mesh number Nb smaller than the mesh number Na and height Hb smaller than the height Ha forming the protruding elements, so that it allows significant collapse and acts as a collapse limit.

[0111] Moreover, FIG. 15 illustrates a stack 20 of solid oxide cells of the SOEC / SOFC type operating at high temperatures according to the present invention.

[0112] More precisely, FIG. 15 illustrates an assembly 80 comprising a stack 20 of solid oxide cells of the SOEC / SOFC type and a clamping system 60 .

[0113] This assembly 80 has a structure similar to that of the assembly described in French patent application FR3045215A1.

[0114] The stack 20 comprises a plurality of electrochemical cells 1 each formed from a cathode, from an anode and from an electrolyte inserted between the cathode and anode, and a plurality of interconnectors 5 according to the present invention each disposed between two adjacent electrochemical cells 1. This assembly of electrochemical cells 1 and interconnectors 5 may also be referred to as a "stack".

[0115] Additionally, stack 20 includes an upper terminal plate 43 and a lower terminal plate 44, also known as upper stack terminal plate 43 and lower stack terminal plate 44, respectively, between which the plurality of electrochemical cells 1 and the plurality of interconnectors 5 are clamped or between which the stack is located.

[0116] Moreover, the assembly 80 also includes a clamping system 60 for the stack 20 of solid oxide cells of the SOEC / SOFC type, comprising an upper clamping plate 45 and a lower clamping plate 46 between which the stack 20 of solid oxide cells of the SOEC / SOFC type is clamped.

[0117] Each clamping plate 45, 46 of the clamping system 60 includes four clamping openings 54. In addition, the clamping system 60 further includes four clamping rods 55 or tie rods that extend through the clamping openings 54 of the upper clamping plate 45 and through corresponding clamping openings 54 of the lower clamping plate 46, allowing the upper clamping plate 45 and the lower clamping plate 46 to be assembled to one another. In addition, the clamping system 60 includes clamping means 56, 57, 58 that cooperate with the clamping rods 55 in each clamping opening 54 of the upper clamping plate 45 and the lower clamping plate 46, allowing the upper clamping plate 45 and the lower clamping plate 46 to be assembled to one another. More precisely, the clamping means include, in each clamping opening 54 of the lower clamping plate 46, a first clamping nut 56 that cooperates with a corresponding clamping rod 55 inserted through the clamping opening 54. Additionally, the clamping means includes, in each clamping opening 54 of the upper clamping plate 45, a second clamping nut 57 associated with a clamping washer 58, which cooperates with a corresponding clamping rod 55 inserted through the clamping opening 54. The clamping washer 58 is located between the second clamping nut 57 and the upper clamping plate 45.

[0118] Of course, the invention is not limited to the example embodiments just described, as various modifications can be made by those skilled in the art. [Explanation of symbols]

[0119] 1. Electrochemical cell 2 cathodes 3 Solid electrolyte 4 anodes 5 Interconnector 10 teeth 10a First protruding element 10ae outer contact end 10ai inner edge 10b Second protruding element 10be outer contact end 10bi inner edge 10c Third projecting element 11 Flow path 20 stacks 43 Upper terminal board 44 Lower terminal board 45 Upper clamping plate 46 Lower tightening plate 54 Fastening opening 55 Clamping rod 56 First fastening nut, fastening means 57 Second fastening nut, fastening means 58 Fastening washer, fastening means 60 Fastening System 80 Assembly P plane Pi surroundings Z area

Claims

1. An interconnector (5) for a stack (20) of solid oxide cells of the SOEC / SOFC type operating at high temperatures, intended to be placed between two adjacent electrochemical cells (1) of said stack (20), each electrochemical cell (1) being formed from a cathode, from an anode and from an electrolyte inserted between said cathode and said anode, a plane (P) on which at least one first group of first protruding elements (10a) relative to said plane (P) and at least one second group of second protruding elements (10b) relative to said plane (P) are formed, said first projecting elements (10a) having a different shape relative to said second projecting elements (10b); a height (H1) of each first projecting element (10a), measured as the maximum perpendicular dimension of said first projecting element (10a) relative to said plane (P), is different from a height (H2) of each second projecting element (10b), measured as the maximum perpendicular dimension of said second projecting element (10b); a contact width (D1) of each first projecting element (10a), measured as the maximum horizontal dimension, relative to the plane (P), of an outer contact end (10ae) of each first projecting element (10a), intended to be in contact with the electrochemical cell (1), opposite its inner end (10ai) in contact with the plane (P), differs from a contact width (D2) of each second projecting element (10b), measured as the maximum horizontal dimension, relative to the plane (P), of an outer contact end (10be) of each second projecting element (10b), intended to be in contact with the electrochemical cell (1), opposite its inner end (10bi) in contact with the plane (P); The interconnector (5) comprises a metal alloy substrate having two main surfaces, one of which is provided with a first coating layer forming a first contact layer with the electrochemical cell (1), and the other of which is provided with a second coating layer forming a second contact layer with the electrochemical cell (1); The first coating layer and / or the second coating layer comprises the plane (P) and the first and second projecting elements (10a, 10b) formed thereon. An interconnector comprising:

2. 2. An interconnector according to claim 1, characterized in that the contact width (D1) of each first projecting element (10a) is between 0.5 and 5 mm.

3. An interconnector according to claim 1 or 2, characterized in that the contact width (D2) of each second projecting element (10b) is between 0.005 mm and 0.5 mm.

4. Interconnector according to any one of claims 1 to 3, characterized in that the height (H1) of each first projecting element (10a) is between 200 μm and 1,000 μm.

5. Interconnector according to any one of claims 1 to 4, characterized in that the height (H2) of each second projecting element (10b) is between 250 μm and 1,050 μm.

6. An interconnector according to any one of claims 1 to 5, characterized in that the difference between the height (H2) of each second protruding element (10b) and the height (H1) of each first protruding element (10a) is 5 μm to 500 μm.

7. 7. The interconnector according to claim 1, characterized in that the interconnector comprises N groups of protruding elements (N being an integer greater than or equal to 2) formed on the plane (P), the protruding elements of the same group are all identical, and the protruding elements of different groups have different shapes, i.e., different heights and different contact widths.

8. 8. An interconnector according to any one of claims 1 to 7, characterized in that the protruding elements are in the form of teeth or grooves arranged parallel to one another, the spaces between the protruding elements forming gas circulation channels (11).

9. 8. An interconnector according to any one of claims 1 to 7, characterized in that the protruding elements are in the form of pads, thus defining spaces between them, said spaces forming a single serpentine gas circulation flow path (11).

10. 10. An interconnect according to any one of the preceding claims, characterized in that the protruding elements are evenly distributed over said plane (P) according to at least one horizontal direction (DH) on said plane (P).

11. Interconnect according to any one of claims 1 to 10, characterized in that at least one region (Z) of said plane (P) is free of protruding elements (10a, 10b, 10c).

12. 10. An interconnector according to claim 8 or 9, characterized in that the protruding elements (10c) having the greatest width (D3) are located around the periphery (Pi) of the plane (P) at a distance from the other protruding elements (10a, 10b) and from the gas circulation flow paths (11) formed by the spaces between the other protruding elements (10a, 10b).

13. 13. The interconnector according to any one of claims 1 to 12, characterized in that the metal alloy substrate is of the chromia-forming type, the base element of which is iron (Fe) or nickel (Ni).

14. The first coating layer is a thick ceramic coating layer, whether porous or not, and the ceramic material is of the formula La １－ｘ Sr ｘ MO ３ , M (transition metal) = nickel (Ni), iron (Fe), cobalt (Co), manganese (Mn), chromium (Cr) alone or in mixture, or lanthanum manganate of the formula Ln ２ NiO ４ 14. The interconnector according to any one of claims 1 to 13, characterized in that the material is selected from the group consisting of lanthanide nickelates (Ln = lanthanum (La), neodymium (Nd), praseodymium (Pr)) or other electrically conductive perovskite oxide layer structure materials.

15. 15. An interconnector according to any one of claims 1 to 14, characterized in that the second coating layer is a thick metallic coating layer, the metallic material being selected from nickel (Ni) and its alloys or chromia-forming alloys whose base element is iron (Fe).

16. 16. A stack (20) of solid oxide cells of the SOEC / SOFC type operating at high temperature, comprising a plurality of electrochemical cells (1), each formed from a cathode, an anode, and an electrolyte inserted between the cathode and the anode, and a plurality of interconnects (5) according to any one of claims 1 to 15, each arranged between two adjacent electrochemical cells (1).

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