Electrolysis or co-electrolysis reactor (SOEC) or fuel cell (SOFC) with stacked electrochemical cells incorporating mechanical reinforcement elements with temperature-dependent stiffness.

Abstract

Electrolysis or co-electrolysis reactor (SOEC) or fuel cell (SOFC) with a stack of electrochemical cells incorporating mechanical reinforcement elements with temperature-dependent stiffness. The invention relates to an electrochemical device formed by assembling, by alternating conventional stacking, electrochemical cells and electrical and fluidic interconnectors, in which at least one mechanical reinforcement element is placed at each stage to absorb the bending stresses that may occur in the stack during the initial thermomechanical treatment stage. Figure for the abstract: Fig. 6

Description

Title of the invention: Electrolysis or co-electrolysis reactor (SOEC) or fuel cell (SOFC) with stacked electrochemical cells incorporating mechanical reinforcement elements with temperature-dependent stiffness. technical field

[0001] The present invention relates to the field of solid oxide fuel cells (SOFCs), that of high-temperature water electrolysis (HTE, or HTSE), also with solid oxides (SOECs), and that of high-temperature co-electrolysis of water and another gas chosen from carbon dioxide (CO2) or nitrogen dioxide (NO2).

[0002] The invention relates more particularly to the realization of an electrochemical device constituting a high temperature water electrolysis or co-electrolysis reactor (HTE) of the SOEC type, or a SOFC type fuel cell, with a stack of elementary electrochemical cells.

[0003] The present invention aims primarily to improve the assembly of such a device and also its operation.

[0004] Although described with reference mainly to the application of high-temperature water electrolysis, the invention applies equally well to a co-electrolysis of water and another gas chosen from carbon dioxide CO2, as to a SOFC fuel cell.

[0005] The invention applies to a SOFC fuel cell using as fuel either hydrogen, or a hydrocarbon, for example methane CH4, or any other fuel such as NH3. Previous technique

[0006] A SOFC fuel cell or an EHT electrolyzer is an electrochemical device consisting of a stack of elementary units, each comprising a solid oxide electrochemical cell made up of three layers stacked one on top of the other (anode / electrolyte / cathode), and interconnecting plates made of metallic alloys, also called bipolar plates, or interconnectors. The interconnectors serve to ensure both the passage of electric current and the circulation of gases in the vicinity of each cell (injected water vapor, hydrogen, and oxygen). products in an EHT electrolyzer; injected air and hydrogen and water produced in a SOFC cell) and to separate the anodic and cathodic compartments which are the gas circulation compartments on the anode and cathode sides of the cells respectively.

[0007] To perform high-temperature steam electrolysis (HTE), typically between 600 and 950°C, steam (H₂O) is injected into the cathode compartment. Under the influence of the current applied to the cell, the dissociation of water molecules into vapor form occurs at the interface between the hydrogen electrode (cathode) and the electrolyte: this dissociation produces hydrogen gas (H₂) and oxygen ions. The hydrogen gas is collected and discharged from the hydrogen compartment. The oxygen ions (O₂⁻) migrate through the electrolyte and recombine into oxygen at the interface between the electrolyte and the oxygen electrode (anode).

[0008] To operate a SOFC fuel cell, air (oxygen) is injected into the cathode compartment and hydrogen into the anodic compartment. The hydrogen (H2) is transformed into H+ ions and releases electrons, which are captured by the anode. The H+ ions arrive at the cathode where they combine with O2- ions, formed from oxygen in the air, to form water. The transfer of H+ ions and electrons to the cathode produces a direct electric current from the hydrogen.

[0009] To increase the flow rates of hydrogen and oxygen produced in the case of EHT electrolysis or to increase the electrical power supplied in the case of a SOFC fuel cell, it is known to stack several elementary electrochemical cells one on top of the other, separating them by interconnectors. The assembly is positioned between two end connection plates that support the electrical power supplies and the gas supply / collection connections of an electrolyzer (electrolysis reactor) or an SOFC fuel cell.

[0010] Furthermore, to improve the quality of the electrical contacts established between the interconnectors and the electrodes, and thus the performance of the aforementioned electrochemical devices, electrical contact elements are individually intercalated and arranged on the electrodes. In an electrochemical device, a nickel grid is conventionally used for contact with the hydrogen electrode (cathode in an EHT reactor, anode in a SOFC cell), because it provides satisfactory results at low cost.

[0011] During the entire preparation of an electrochemical device, it is necessary that each layer of the stack and each stage be positioned very precisely and that this position be maintained.

[0012] Before the operation of the aforementioned electrochemical device, it is necessary to subject its stack to at least one heat treatment step called reduction, in order to put the electrochemical cells into their reduced form, and not not oxidized as they are initially.

[0013] This reduction step can be a thermomechanical cycle under a reducing gas for the hydrogen electrode and air or neutral gas for the oxygen electrode.

[0014] A particular heat treatment step has been described in patent EP2870650B1.

[0015] The stacks implemented to date generally use, at each of their stages, seals that must guarantee the seal between two distinct, adjacent gas circulation compartments, i.e., an anodic compartment and a cathodic compartment. Advantageous seals have been described in patent EP3078071B1. These seals have the particularity of requiring thermal conditioning during which they are compressed.

[0016] The contact elements, such as the layers described in patent application EP2900846A1 or the nickel grids, are also compressed during heat conditioning and operation of the electrochemical device, which ensures their proper alignment. The elements that serve as contact elements in the hydrogen chamber are also compressed. In other words, during the heat conditioning step, a stack of the aforementioned electrochemical device is compressed, typically by several centimeters. To date, this compression process has been successful.

[0017] However, in some SOEC / SOFC stacks, the inventors observed detrimental deformations during the pre-operation heat treatment stage. These deformations reduce the contact areas between electrochemical cells and electrical contact elements.

[0018] This undesirable situation is shown in Figures 1 and 2, with an electrochemical device 1 consisting of a stack of electrochemical cells 2 based on SOEC / SOFC-type solid oxides and electrical and fluidic interconnectors 3 made of electronically conductive and gas-tight material for supplying or collecting electric current to the cells and for supplying, collecting, and circulating gases over each electrode of each electrochemical cell. Each electrochemical cell consists of a first electrode forming a cathode, a second electrode forming an anode, and an electrolyte intercalated between the two electrodes.

[0019] For the sake of clarity, in these figures 1 and 2, only one electrochemical cell 2 is shown as arranged between two interconnectors 3.

[0020] A first electrical contact element 4 is arranged in contact with an electrode of the cell 2 opposite an interconnector 3. This element can be in the form of a nickel grid, preferably openwork as described in patent application FR2213927 and which can incorporate glass in the form of cord(s) to guide the gases, as described in patent EP3156721B1.

[0021] A second electrical contact element 5 is arranged in contact with another in Interconnector 3 is positioned opposite the other electrode of cell 2. This element can be a conductive ceramic layer, particularly grooved. It can also be a strontium-doped lanthanum manganite (LSM) strip, which has been previously cut and is bonded or heat-pressed directly onto the interconnector 3. The bonding can be carried out without residue, as described in patent application WO2022 / 234214. The LSM strip can also be bonded by heat-pressing to one face of the interconnector 3, as described in EP2900846B1.

[0022] As shown at the end of the stack, an electrical contact element 5, in particular identical to that in contact with an interconnector, can be fixed to the inner face of a so-called terminal plate 6 of the stack 1.

[0023] Sealing gaskets 7, preferably made of glass-ceramic, are interposed around the cell 2 and the gas passages, being in contact with the cell 2 or either of the electrical contact elements 4, 5. The gaskets 7 between two adjacent interconnectors 3 within the stack can be supported by a sealing frame 8 made of electrically insulating material, preferably mica.

[0024] In this configuration, initially the metal elements (terminal plates 6, interconnectors 3) rest on the sealing gaskets 7, as shown in [Fig.1].

[0025] The clamping of the stack 1 is carried out cold between a support point P and an axial load C, applied vertically. During the initial temperature rise, the mechanical resistance of the metallic elements 6, 3 decreases, while that of the seals 7 does not change before, typically at 650°C or even 700°C, when the latter are made of glass-ceramic.

[0026] However, it can happen that the bending load applied to the metal elements 3, 6 leads to their irreversible deformation ([Fig. 2]), which is detrimental to subsequent electrical contacts. Indeed, as schematically shown, the flat faces of the metal elements, which should ideally be in direct contact on all their surfaces, are no longer so.

[0027] There is therefore a need to further improve electrochemical devices with stacks of electrochemical cells, forming an SOEC type electrolysis reactor or a SOFC type fuel cell, in particular to avoid the consequences of irreversible, undesired deformations of electrical contact elements within the stack, which can appear in the transient phase of first temperature rise during thermal conditioning before the first operating cycle. Description of the invention

[0028] To this end, the invention first relates to an electrochemical device, constituting an electrolysis or SOEC co-electrolysis reactor or a co-cell SOFC fuel, designed to operate at high temperatures, comprising:

[0029] - a stack of SOEC-type solid oxide-based electrochemical cells / SOFC and electrical and fluidic interconnectors arranged individually on either side of each of the electrochemical cells, each interconnector comprising at least one component made of electronically conductive and gas-tight material to bring or collect electric current to the cells and to bring, collect and circulate gases over each electrode of each electrochemical cell;

[0030] - two plates, called terminal plates, arranged at the ends of the stack;

[0031] - a plurality of electrical contact elements, each arranged with contact with one face of one of the terminal plates or with an electrode of the electrochemical cells or with one face of an interconnector;

[0032] - a plurality of sealing gaskets, each arranged around each of the or through-holes to ensure sealing around each gas inlet / outlet within the stack;

[0033] - a plurality of mechanical reinforcement elements, each arranged with contact with one face of one of the terminal plates or with an electrode of the electrochemical cells or with one face of an interconnector, the mechanical reinforcement elements being made of an electrically insulating material and having a rigidity that varies according to temperature and is substantially equal to that of the sealing joints so that during an initial temperature rise of the device, before its operation, the reinforcement elements soften and then melt simultaneously with the sealing joints, limiting the flexing of the terminal plates and the interconnectors.

[0034] Preferably, the mechanical reinforcement elements are made of the same constituent material as the sealing gaskets, preferably a glass-ceramic.

[0035] Advantageously, the mechanical reinforcement elements are in the form of cords, preferably closed on themselves, and / or solid pellets.

[0036] Advantageously, at least some of the mechanical reinforcement elements are arranged at the center of the faces of the terminal plates or the electrodes of the electrochemical cells or the faces of the interconnectors. When located at the center of the stack components, the position of the load transfer by the reinforcement elements reduces the bending moment by a factor of 4, since the bending moment depends on the square of the length. A mechanical reinforcement element according to the invention can be a point support at the center of the part or any other geometric shape that reduces the bending moment.

[0037] The material used for the shim ensuring the load transfer is advantageously made of the same material as the sealing gasket so that the change in rigidity occurs concomitantly when the softening / melting temperature is reached.

[0038] Preferably, the surface area of ​​a mechanical reinforcement element is between 0.1 and 10cm2, preferably even more than 0.5 cm2.

[0039] According to a first advantageous embodiment, the electrical contact elements comprise at least one electrically conductive grid, preferably made of gold.

[0040] A gold grid can have a surface area between 0.5 and 5 cm², preferably on the order of 2 cm², with a mesh count of 100 to 3600 meshes / cm². A nickel grid can also be considered. In this case, care must be taken to ensure a seal around the grid to prevent oxidation. A copper grid can also be considered. A conductive ceramic grid can also be considered. Ferritic steel grids, preferably ferritic steel with approximately 20% chromium, preferably CROFER® or K41 (441 steel), can be used if they are in grid form. Indeed, these high-chromium steels are highly resistant to corrosion and are good electrical conductors.

[0041] Grids made of precious metals, such as platinum, can also be considered.

[0042] The number of grids supported per face of the interlayer plate can be between 1 and 10, preferably 5. With a single grid, the amount of material is limited, but the mechanical equilibrium within a stack may not be optimal. With 10 grids, mechanical equilibrium is ensured, but the amount of material used can be significant.

[0043] Preferably, the surface area of ​​a grid is between 0.5 and 5cm2, preferably on the order of 2cm, for a sheet metal surface area of ​​the order of 500 cm2.

[0044] Preferably, the grid(s) is / are welded directly to one face of an interconnector and / or a terminal plate. The weld may be by spot welding.

[0045] According to an advantageous embodiment, a mechanical reinforcement element is in the form of a solid disc arranged in an opening made in the center of the grid.

[0046] According to an advantageous embodiment, five grids are provided in contact with a cell electrode, distributed in a square or rectangle with one of them in the center of the square or rectangle.

[0047] According to this method and an advantageous configuration, a mechanical reinforcement element is in the form of a cord closed on itself by surrounding the grid at the center of the square or rectangle.

[0048] According to a second advantageous embodiment, the electrical contact elements comprise at least one layer of a conductive ceramic material.

[0049] According to this second variant, the conductive ceramic material is advantageously chosen from the group consisting of:

[0050] - Lao,6Sro,4Coo,8Feo,203 (LSCF) ; - Lao,sSro,2Cuo,9Feo,16)2,5 (LSCuF) ; - Laoj7Sr0j3Co03 (LSC) ; - Sm0j5Sr0j5CoO3 (SSC) ; - SmBaoj5Sr0j5Co205 (SBSC) ; - GdSrCo2O5 (GSC); - La0j65Sr0j3MnO3 (LSM) ; - LaBaCo2O5 (LBC); - YBaCo2O5 (YBC) ; - Ndlj8Ce0j2CuO4 (NCC) ; ■ Lao>8Sro,2Coo,3 Mn03 Fe0>6O3 (LSCMF) ; ■ Lao^Nio^Feo^O;; (LNF) ; - Lalj2Sr0j8NiO4 (LSN) ; - La0j7Sr0j3FeO3 (LSF) ; - La2Nio,6Cu0,404 (LNC).

[0051] Avantageusemente encore, the ceramic material conductrice is chosen in the group constituted by the LSM, the LSC, the LNF, and the LSCF.

[0052] Preferably, the conductive ceramic material layer is hollowed out over at least part of its thickness. The hollowing may consist of grooves, holes, or any other shape. Hollowing out, and in particular grooving, the contact layer allows, for the same crushing force, an increase in stress and therefore greater compression of the layer, thus better correcting surface defects. In other words, grooving a contact layer improves its crushing capacity. Conversely, a solid contact layer promotes electrical contact due to a larger current-carrying surface area.

[0053] Advantageously, the conductive ceramic material layer is bonded, preferably by heat pressing or by means of an adhesive, or by heat pressing through the sheet metal, which has been preheated by Joule heating through current flow or induction. Reference may be made to the advantageous heat pressing methods described in patent EP2900846B1 or to the residue-free bonding method described in patent application WO2022 / 234214. Inductive heat pressing consists of heating the interconnector or terminal plate sheet(s) by Joule heating and then directly applying the ceramic material layer to the desired location.

[0054] Advantageously still, the thickness of the conductive ceramic material layer on each face of the sheet is between 100 pm and 5 mm.

[0055] Furthermore, care is taken to minimize the surface area of ​​a ceramic material layer so as to increase the local clamping stresses applied to the stack. Indeed, the applied clamping force is constant. Therefore, by reducing the surface area of ​​the contact layer, the stress (F / S) will be increased. For example, with the same force and a ceramic material layer whose surface area is two The smaller the unit, the more the stress is twice as high.

[0056] Thus, the invention essentially consists of an electrochemical device formed by assembling by usual alternating stacking of electrochemical cells and electrical and fluidic interconnectors in which at each stage at least one mechanical reinforcement element is put in place which will take up the bending forces which are likely to appear in the stacking during the initial thermomechanical treatment stage.

[0057] This treatment serves to finalize at least the placement of the electrical contact elements and sealing gaskets within the stack.

[0058] And, in stacks according to the state of the art, during the initial temperature rise phase, due to the softening of the sealing joints, flexures appear.

[0059] Implementing mechanical reinforcements made with materials with variable rigidity depending on the temperature allows said reinforcements to act by taking up the forces during the first temperature rise.

[0060] These reinforcements, advantageously in the same material as the seals, more particularly in glass-ceramic, will remain rigid until their softening / melting temperature is identical to the seals.

[0061] Once this temperature is reached, all mechanical forces are transmitted uniformly to the electrical contact elements.

[0062] In the end, the invention has many advantages, among which we can mention: - the elimination of deformations in SOEC / SOFC stacks, which can reduce the contact areas between electrochemical cells and electrical contact elements; - as a corollary, obtaining greater control over the level of electric current passing through SOEC / SOFC stacks; - simplicity and speed of implementation of the mechanical reinforcement elements which are installed during the step of removing the sealing joints; - a low additional cost as it can consist of a simple addition of cords and / or solid pellets in the same material as the sealing gaskets.

[0063] Other advantages and features will become clearer upon reading the detailed description, given by way of illustration and not limitation, with reference to the following figures. Brief description of the drawings

[0064] [Fig.1] [Fig.1] is a schematic longitudinal cross-sectional view of part of a state-of-the-art electrochemical stacking device of solid oxide cells, once the stacking step of the different components has been carried out.

[0065] [Fig.2] [Fig.2] reproduces [Fig.1] and illustrates the bending deformations that can occur during the first temperature rise during the initial thermomechanical treatment step applied to the device.

[0066] [Fig.3] [Fig.3] is a schematic longitudinal sectional view at the level of a terminal plate forming a lid of a state-of-the-art electrochemical device with stacked solid oxide cells.

[0067] [Fig.4A], [Fig.4B] Figures 4A and 4B are schematic longitudinal section views tudinal at the level of a terminal plate forming a cover of an electrochemical device with stacked solid oxide cells according to the invention, respectively before and after the concomitant placement of the sealing gaskets and the mechanical reinforcement elements according to the invention.

[0068] [Fig.5] [Fig.5] is a photographic reproduction showing a sheet of mica supporting sealing joints and a mechanical reinforcement element, placed on a terminal plate of an electrochemical device according to the invention.

[0069] [Fig.6] [Fig.6] is a photographic reproduction of an interlayer according to the invention supporting electrical contact elements and a mechanical reinforcement element.

[0070] [Fig. 7] [Fig. 7] is a schematic longitudinal cross-sectional view of part of another example of a stacked solid oxide cell electrochemical device according to the invention, once the stacking step of the different components has been completed. Detailed description

[0071] For the sake of clarity, the same elements of an electrochemical device according to the prior art and of an electrochemical device according to the invention are designated by the same numerical references.

[0072] Throughout this application, the terms "lower", "upper", "above", "below", "inside", "outside", "internal" "external" are to be understood by reference to an electrochemical device according to the invention in its operating configuration, i.e. the modules being stacked vertically.

[0073] It is also specified that the electrolyzers or fuel cells described are of the solid oxide type (SOEC, English acronym for "Solid Oxide Electrolyte Cell" or SOFC, English acronym for "Solid Oxide Fuel Cell") operating at high temperature.

[0074] Thus, all the constituents (anode / electrolyte / cathode) of an electrolysis cell or battery are ceramics.

[0075] The high operating temperature of an electrolyzer (electrolysis reactor) or a battery is typically between 600°C and 1000°C.

[0076] Typically, the characteristics of a suitable SOEC electrolysis cell of the cathode support (CSC) type, according to the invention, may be those indicated as follows: in Table 1 below.

[0077] [Tables 1] Electrolysis Cell Unit Value Cathode Constituent material Ni-YSZ Thickness µm 400 Thermal conductivity W m1K 1 13.1 Electrical conductivity Q1 m1 105 Porosity 0.37 Permeability m2 1013 Tortuosity 4 Current density A.m2 5300 Anode Constituent material LSM, LSC Thickness µm between 10 and 50 Thermal conductivity W m1K 1 9.6 Electrical conductivity Q1 m1 1 104 Porosity 0.37 Permeability m2 1013 Tortuosity 4 Current density A.m2 2000 Electrolyte Constituent material YSZ Thickness µm <10 Resistivity Qm 0.42

[0078] Figures 1 and 2 relating to an electrochemical device 1 according to the prior art have been described in the preamble. They are therefore not discussed below.

[0079] Having observed detrimental deformations at electrical contacts in a stack of an electrochemical device according to the prior art, the inventors conceived of incorporating mechanical reinforcement elements into this type of stack. The role of these elements is to absorb the mechanical stresses in order to minimize the bending moments during the initial temperature rise of the stack necessary to achieve the Installation of the sealing gaskets.

[0080] In order to best follow the deformation of these joints, the inventors considered making these reinforcement elements in the same constituent material, typically in a sealing glass-ceramic.

[0081] The glass-ceramic of the reinforcing elements will thus remain rigid until its softening / melting temperature, then all the mechanical clamping forces will be transmitted to the electrical contact elements.

[0082] Thus, the reinforcing elements, made of the same material as the sealing gaskets, act as load-bearing shims. Load transfer therefore occurs as long as the bending moment is present and decreases as soon as the bending moment diminishes.

[0083] A first example of the realization of the mechanical reinforcement elements is shown in relation to a plate 9 forming the cover of an electrochemical device with stacked cells 2.

[0084] As shown in [Fig.3], a cover 9 of a device 1 according to the state of the art, i.e. without implantation of a reinforcement element for the transfer of force, is supported on glass-ceramic seals 7 arranged at the periphery which can also be supported by a support 8 generally in the form of a mica sheet.

[0085] When subjected to a clamping load C, such a cover 9 is therefore subjected to bending stresses that can lead to its plastic deformation. Indeed, the seals 7 remain rigid up to high temperatures, typically around 650 to 700°C, before softening, then melting and settling into place. The temperatures and cycles required for the settling of seals typically made of glass or glass-ceramic can vary depending on the composition. Typically, temperatures can range from 750 to 900°C for a duration of 1 to 48 hours, depending on one or more cycles. The temperature rise can be achieved for a device 1 at up to 10°C / min.

[0086] With a mechanical reinforcement element 10, for example in the form of a glass-ceramic washer in the center of the cover 6, preferably in an opening 80 made in the mica support 8, as illustrated in [Fig.4A], then the bending stresses are drastically reduced before the glass-ceramic melts.

[0087] As shown in [Fig.4B], due to the melting of the glass-ceramic both for the seals 7 and for the washer 10 forming a load-bearing wedge, there is no longer any bending stress.

[0088] Fig. 5 shows a concrete example of the realization of a plate 9 forming a cover with a sheet of mica 8 supporting both the sealing gaskets 7 at the periphery around the openings 90 which are in view of the gas passages, and the load-bearing washer 10 in a central opening 80 of the sheet 8.

[0089] Fig. 6 shows another example of integration of a reinforcing element 10 for load transfer on one face of an interconnector 3.

[0090] The face of the interconnector 3 supports, as electrical contact elements 4, five gold grids arranged in a square with one in the center of the square. These grids 4 are preferably welded directly to the face of the outer sheet metal of the interconnector 3. Sealing gaskets 7 have been deposited in the form of beads around each through-hole 30 dedicated to the passage of gases in a device 1.

[0091] A glass-ceramic cord 10, closed on itself by forming a circular ring around the center grid 4, forms a mechanical reinforcement element which will reduce the bending moments which the interconnector 3 could undergo during the first temperature rise.

[0092] Fig. 7 shows yet another example of implementation of the mechanical reinforcement elements 10, in glass-ceramic.

[0093] As illustrated, a solid ceramic disc 10 can be arranged in the center of each of the electrical contact layers 5, in particular in LSM in an opening 50 made for this purpose.

[0094] Solid ceramic discs 10 can also be placed in an opening 40 of an electrical contact grid 4, in particular made of nickel.

[0095] This minimizes the bending force at every point of an electrochemical device 1 with a stack of solid oxide cells.

[0096] Regardless of its placement within a device 1, care is taken to ensure that the surface area of ​​a mechanical reinforcement element 10 is not too large to avoid excessively reducing the active electrochemical surfaces of the cells 2. Advantageously, the surface area of ​​a reinforcement element 10 is between 0.1 and 10cm2, preferably even 0.5 cm2.

[0097] The invention is not limited to the examples just described; in particular, features of the illustrated examples can be combined in unillustrated variants.

[0098] Other variants and improvements may be envisaged without departing from the scope of the invention.

[0099] A mechanical reinforcement element 10 made of glass-ceramic material according to the invention can preferably be arranged in the center between two constituents of the stack forming an electrochemical device.

[0100] The plate 9 forming the lid can be an end plate, arranged at the top end of a stack and whose primary function is to stiffen it, to allow current to be carried over a thick plate, and to absorb the stresses during the return from cold. In this case, the end plate is not open because it does not have not the function of passing gases through the stack.

[0101] In a stack where the top terminal plate is to be through-hole, as in patent application EP3955353A1, then the lid is formed by an additional non-through plate.

Claims

Demands

1. An electrochemical device (1) constituting an SOEC electrolysis or co-electrolysis reactor or a SOFC fuel cell, intended to operate at high temperature, comprising: - a stack of SOEC / SOFC type solid oxide electrochemical cells (2) and electrical and fluidic interconnectors (3) individually arranged on either side of each of the electrochemical cells, each interconnector comprising at least one component of electronically conductive and gas-tight material for bringing or collecting electric current to the cells and for bringing, collecting and circulating gases over each electrode of each electrochemical cell; - two plates (6), called terminal plates, arranged at the ends of the stack;- a plurality of electrical contact elements (4, 5), each arranged to contact one face of one of the terminal plates or an electrode of the electrochemical cells or one face of an interconnector; - a plurality of sealing gaskets (7), each arranged around each of the through openings to ensure sealing around each gas inlet / outlet within the stack;- a plurality of mechanical reinforcement elements (10), each arranged in contact with a face of one of the terminal plates or with an electrode of the electrochemical cells or with a face of an interconnector, the mechanical reinforcement elements being made of an electrically insulating material and having a rigidity that varies according to the temperature and is substantially equal to that of the sealing gaskets so that during an initial temperature rise of the device, before its operation, the reinforcement elements soften and then melt simultaneously with the sealing gaskets, limiting the flexing of the terminal plates and the interconnectors.

2. Electrochemical device according to claim 1, the mechanical reinforcement elements being in the same constituent material as the sealing joints, preferably a glass-ceramic.

3. Electrochemical device according to claim 1 or 2, wherein at least a portion of the mechanical reinforcement elements are arranged in the center of the faces of the terminal plates or electrodes of the electro- cells chemical or interconnector faces.

4. Electrochemical device according to any one of the preceding claims, the surface area of ​​a mechanical reinforcement element being between 0.1 and 10cm2, preferably even 0.5 cm2.

5. Electrochemical device according to any one of the preceding claims, the mechanical reinforcement elements being in the form of cords, preferably closed on themselves, and / or solid pellets.

6. Electrochemical device according to any one of the preceding claims, the electrical contact elements comprising at least one electrically conductive grid, preferably made of gold.

7. Electrochemical device according to claim 6, the number of grids in contact with a cell electrode being between 1 and 10, preferably equal to 5.

8. Electrochemical device according to claim 6 or 7, the surface area of ​​a grid being between 0.5 and 5cm2, preferably on the order of 2cm2.

9. Electrochemical device according to any one of claims 6 to 8, the grid(s) being welded directly to one face of an interconnector and / or a terminal plate.

10. Electrochemical device according to any one of claims 6 to 9 in combination with claim 5, a mechanical reinforcement element being in the form of a solid pellet arranged in an opening made in the center of the grid.

11. Electrochemical device according to any one of claims 6 to 10, comprising a number of five grids in contact with a cell electrode, distributed in a square or rectangle with one of them in the center of the square or rectangle.

12. Electrochemical device according to claim 11 in combination with claim 5, a mechanical reinforcement element being in the form of a cord closed on itself by surrounding the grid at the center of the square or rectangle.

13. Electrochemical device according to any one of claims 1 to 5, the electrical contact elements comprising at least one layer of a conductive ceramic material.

14. Electrochemical device according to claim 13, the conductive ceramic material being selected from the group consisting of: - Lao,6Sro,4Coo,8Feo,203 (LSCF); - Lao,8Sro,2Cuo,9Feo,101,5 (LSCuF); - Laoj7Sr0j3Co03 (LSC); - Sm0j5Sr0j5CoO3 (SSC); - SmBaoj5Sr0j5Co205 (SBSC); - GdSrCo2O5 (GSC); - La0j65Sr0j3MnO3 (LSM); - LaBaCo2O5 (LBC); - YBaCo2O5 (YBC); - Ndlj8Ce0j2CuO4 (NCC); ■ Lao>8Sro,2Coo,3 Mn03 Fe0j6O3 (LSCMF); ■ Lao^Nio^Feo^O;; (LNF); - La1>2Sr0j8NiO4 (LSN); - La0j7Sr0j3FeO3 (LSF); - La2Nio.6Cu0.404 (LNC).

15. Electrochemical device according to any one of claims 13 or 14, the layer of conductive ceramic material being hollowed out over at least part of its thickness.

16. Electrochemical device according to any one of claims 13 to 15, the layer of conductive ceramic material being bonded, preferably by heat pressing or by means of an adhesive or by heat pressing, to the interconnector sheet(s) preheated by Joule effect by current passage or inductively.

17. Electrochemical device according to any one of claims 13 to 16, the thickness of the conductive ceramic material layer being between 100 pm and 5 mm.

18. Electrochemical device according to any one of claims 13 to 17 in combination with claim 5, a mechanical reinforcement element being in the form of a solid pellet arranged in an opening made in the center of the ceramic layer.

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