METHOD FOR PRODUCE A STACK OF SOEC / SOFC SOLID OXIDES AND A STACK BONDED THEM

Description

TECHNICAL FIELD

[0001] The present invention relates to the general field of high temperature water electrolysis (HTE), in particular high temperature steam electrolysis (HTSE), respectively designated by the English terms "High Temperature Electrolysis" (HTE) and "High Temperature Steam Electrolysis" (HTSE), of carbon dioxide (CO2) electrolysis, or even of co-electrolysis of high temperature water (HTE) with carbon dioxide (CO2).

[0002] More specifically, the invention relates to the field of high-temperature solid oxide electrolyzers, usually designated by the acronym SOEC (for "Solid Oxide Electrolyzer Cell" in English).

[0003] It also concerns the field of high-temperature solid oxide fuel cells, usually referred to by the acronym SOFC (for "Solid Oxide Fuel Cells" in English).

[0004] Thus, more generally, the invention relates to the field of SOEC / SOFC type solid oxide stacks operating at high temperature.

[0005] More specifically, the invention relates to a method for making or assembling a SOEC / SOFC type solid oxide stack comprising a spot welding step on one face of each interconnector of the stack for fixing a contact layer, as well as an associated stack. PREVIOUS STATE OF THE ART

[0006] In a high-temperature solid oxide electrolyzer (SOEC), the process involves converting water vapor (H₂O) into hydrogen (H₂) and oxygen (O₂) using an electric current within the same electrochemical device, and / or converting carbon dioxide (CO₂) into carbon monoxide (CO) and oxygen (O₂). In a high-temperature solid oxide fuel cell (SOFC), the operation is reversed, producing both electricity and heat when supplied with hydrogen (H₂) and oxygen (O₂), typically from air and natural gas, such as methane (CH₄). For simplicity, the following description focuses on the operation of a high-temperature SOEC performing water electrolysis.However, this principle is applicable to the electrolysis of carbon dioxide (CO2), and even to the co-electrolysis of water at high temperature (EHT) with carbon dioxide (CO2). Furthermore, this principle can be transposed to the case of a high-temperature solid oxide fuel cell (SOFC).

[0007] To carry out the electrolysis of water, it is advantageous to do so at high temperature, typically between 600 and 1000°C, because it is more advantageous to electrolyze water vapor than liquid water and because part of the energy required for the reaction can be supplied by heat, which is cheaper than electricity.

[0008] To implement high-temperature water electrolysis (HTW), a high-temperature solid oxide electrolyzer (SOEC) consists of a stack of elementary units, each comprising a solid oxide electrolysis cell, or electrochemical cell, made up of three layers: anode, electrolyte, and cathode stacked one on top of the other, and interconnecting plates, often made of metallic alloys, also called bipolar plates or interconnectors. Each electrochemical cell is sandwiched 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 elementary units.Because this high-temperature technology is reversible, the same stack can operate in electrolysis mode and produce hydrogen and oxygen from water and electricity, or in fuel cell mode and produce electricity from hydrogen and oxygen.

[0009] Each electrochemical cell consists of an electrolyte / electrode assembly, typically a multilayer ceramic assembly where the electrolyte is formed by a central ion-conducting layer. This layer is solid, dense, and impermeable, sandwiched between two porous layers that form the electrodes. It should be noted that additional layers may exist, but these serve only to improve one or more of the layers already described.

[0010] Thus, for example, in a SOFC-type stack, it is known to provide a contact layer in the form of a nickel grid between the anode of each electrochemical cell and the adjacent interconnector. The article " Recent developments in anode supported thin fim SOFC at research center lulich" (XP009060695) published by Stover et.al ., The article "Thermal contact resistance in solid oxide fuel cell stocks" published by Dilling et al. discloses such stacks. The nickel grid can be spot-welded to the interconnector's contact ribs. JP2010-073631 also demonstrates the presence of a spot-welded nickel grid on the hydrogen side in a SOFC-type stack.

[0011] Electrical and fluidic interconnecting devices are electronic conductors that, from an electrical standpoint, connect each electrochemical cell of elementary pattern within the stack of elementary patterns, ensuring electrical contact between one face and the cathode of one cell and between the other face and the anode of the next cell. From a fluidic standpoint, they combine the output of each cell. The interconnectors thus perform the functions of supplying and collecting electrical current and delineate gas circulation compartments for distribution and / or collection.

[0012] More specifically, the interconnectors have the main function of ensuring the passage of electric current but also the circulation of gases in the vicinity of each cell (namely: injected water vapor, extracted hydrogen and oxygen for EHT electrolysis; air and fuel including injected hydrogen and extracted water for a SOFC), and of separating the anodic and cathodic compartments of two adjacent cells, which are the gas circulation compartments on the anode and cathode sides of the cells respectively.

[0013] Specifically, for a high-temperature solid oxide electrolyzer (SOEC), the cathode compartment contains water vapor and hydrogen, products of the electrochemical reaction, while the anode compartment contains a drain gas, if present, and oxygen, another product of the electrochemical reaction. For a high-temperature solid oxide fuel cell (SOFC), the anode compartment contains the fuel, while the cathode compartment contains the oxidizer.

[0014] To perform high-temperature steam electrolysis (HTE), steam (H₂O) is injected into the cathode compartment. Under the influence of the electric current applied to the cell, the dissociation of water molecules into steam occurs at the interface between the hydrogen electrode (cathode) and the electrolyte. This dissociation produces hydrogen gas (H₂) and oxygen ions (O₂⁻). The hydrogen (H₂) is collected and discharged from the hydrogen compartment. The oxygen ions (O₂⁻) migrate through the electrolyte and recombine into oxygen (O₂) at the interface between the electrolyte and the oxygen electrode (anode). A draining gas, such as air, can circulate at the anode and thus collect the oxygen generated in gaseous form at the anode.

[0015] To operate a solid oxide fuel cell (SOFC), air (oxygen) is injected into the cathode compartment and hydrogen into the anodic compartment. The oxygen in the air dissociates into O2- ions. These ions migrate through the electrolyte from the cathode to the anode to oxidize the hydrogen and form water, simultaneously producing electricity. In an SOFC, as in SOEC electrolysis, water vapor is found in the hydrogen (H2) compartment. Only the polarity is reversed.

[0016] For example, the figure 1 represents a schematic view showing the operating principle of a high-temperature solid oxide electrolyzer of the SOEC type. The function of such an electrolyzer is to transform water vapor into hydrogen and oxygen according to the following electrochemical reaction: 2 H 2 O → 2 H 2 + O 2 .

[0017] This reaction is carried out electrochemically in the cells of the electrolyzer. As shown schematically on the figure 1 Each elementary electrolysis cell 1 consists of 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 electronic and / or ionic conductors, made of porous material, and the electrolyte 3 is gas-tight, an electronic insulator, and an ionic conductor. The electrolyte 3 can, in particular, be an anionic conductor, more precisely an anionic conductor of O2- ions, and the electrolyzer is then called an anionic electrolyzer, as opposed to proton electrolytes (H+).

[0018] Electrochemical reactions take place at the interface between each of the electronic conductors and the ionic conductor.

[0019] At cathode 2, the half-reaction is as follows: 2 H 2 O + 4 e -< → 2 H 2 + 2 O 2-< .

[0020] At anode 4, the half-reaction is as follows: 2 O 2-< → O 2 + 4 e -< .

[0021] Electrolyte 3, intercalated between the two electrodes 2 and 4, is the site of migration of O 2- ions under the effect of the electric field created by the potential difference imposed between the anode 4 and the cathode 2.

[0022] As illustrated in parentheses on the figure 1 The water vapor entering the cathode may be accompanied by hydrogen (H₂), and the hydrogen produced and recovered at the outlet may be accompanied by water vapor. Similarly, as illustrated by the dotted line, a draining gas, such as air, can also be injected at the inlet to remove the oxygen produced. The injection of a draining gas also serves as a thermal regulator.

[0023] An elementary electrolyzer, or electrolysis reactor, consists of an elementary cell as described above, with a cathode 2, an electrolyte 3, and an anode 4, and two interconnectors which provide the electrical, hydraulic and thermal distribution functions.

[0024] To increase the flow rates of hydrogen and oxygen produced, it is known to stack several elementary electrolysis cells on top of each other, separated by interconnectors. The assembly is positioned between two end interconnection plates that support the electrical and gas supplies for the electrolyzer (electrolysis reactor).

[0025] A high-temperature solid oxide electrolyzer of the SOEC type thus comprises at least one, usually a plurality of electrolysis cells stacked one on top of the other, each elementary cell being formed of an electrolyte, a cathode and an anode, the electrolyte being intercalated between the anode and the cathode.

[0026] As previously stated, fluid and electrical interconnection devices that are in electrical contact with one or more electrodes generally provide the functions of supplying and collecting electrical current and delimit one or more gas circulation compartments.

[0027] Thus, the so-called cathodic compartment has the function of distributing the electric current and water vapor as well as recovering hydrogen at the cathode in contact.

[0028] The so-called anodic compartment has the function of distributing the electric current as well as recovering the oxygen produced at the anode in contact, possibly with the help of a draining gas.

[0029] There figure 2 represents an exploded view of elementary motifs of a high-temperature solid oxide electrolyzer of the SOEC type according to the prior art. This electrolyzer comprises a plurality of elementary electrolysis cells C1, C2, of the solid oxide type (SOEC), stacked alternately with interconnectors 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 is disposed an electrolyte (only the electrolyte 3.2 of cell C2 is shown).

[0030] The interconnector 5 is typically a metal alloy component that separates 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. Water vapor is injected into each element in the cathode compartment 50. The hydrogen produced and residual water vapor at cathodes 2.1 and 2.2 are collected in the cathode compartment 50 downstream of cell C1 and C2 after the water vapor has been dissociated by the cell. The oxygen produced at anode 4.2 is collected in the anode compartment 51 downstream of cell C1 and C2 after the water vapor has been dissociated by the cell.Interconnector 5 ensures the passage of current between cells C1 and C2 by direct contact with adjacent electrodes, i.e. between anode 4.2 and cathode 2.1.

[0031] Since the operating conditions of a high-temperature solid oxide electrolyzer (SOEC) are very close to those of a solid oxide fuel cell (SOFC), the same technological constraints are found.

[0032] Thus, the proper functioning of such SOEC / SOFC type solid oxide stacks operating at high temperature mainly requires meeting the points stated below.

[0033] First, electrical insulation is necessary between two successive interconnectors to avoid short-circuiting the electrochemical cell. Good electrical contact and sufficient contact surface area between a cell and an interconnector are also essential. The lowest possible ohmic resistance is desired between cells and interconnectors.

[0034] Furthermore, a seal must be in place between the anodic and cathodic compartments, otherwise the produced gases will recombine, leading to a decrease in efficiency and, above all, the appearance of hot spots that damage the stack.

[0035] Finally, it is essential to have good gas distribution both in the input and in the recovery of the products, otherwise there will be loss of efficiency, inhomogeneity of pressure and temperature within the different elementary motifs, or even prohibitive degradation of the electrochemical cells.

[0036] To increase production efficiency and achieve good operational homogeneity in SOEC / SOFC solid oxide stacks operating at high temperatures, the role of interconnectors is essential, particularly for ensuring good electrical contact between the different parts of the stacks and also for ensuring proper gas distribution within the electrochemical cells. Interconnectors can be metallic and composed of three thin plates, also called sheets or strips, welded together, as described in French patent application FR 3 024 985 A1.

[0037] There figure 3 This represents, according to an exploded view, an example of interconnector 5 formed by the assembly of three thin metal sheets 21 to 23 assembled and laminated.

[0038] The three sheets 21, 22, 23 are elongated along two axes of symmetry X and Y orthogonal to each other, the sheets being laminated and joined together by welding. A central sheet 22 is inserted between a first end sheet 21 and a second end sheet 23.

[0039] The central plate 22 here has a central stamped portion 70 defining raised or embossed elements 10. Alternatively, the central plate 22, and therefore the central portion 70, may be smooth. Furthermore, it is pierced around the periphery of its central portion 70 with four openings 71, 72, 73, 74. By "opening," we mean a hole opening on either side of a metal plate.

[0040] One of the flat end plates 21 has a flat central part 69 and is pierced, at the periphery of its central part 69, by four openings 61, 62, 63, 64. The first end plate 21 also has two slots 67, 68, openings arranged symmetrically on either side of the Y axis. They are elongated over a length corresponding approximately to the length of the central part 69 along the Y axis.

[0041] The other of the flat end plates 23 has a central part 89 hollowed out and pierced, at the periphery of its central part 89, with four openings 81, 82, 83, 84.

[0042] The openings 61, 71, 81, 63, 73, 83 of each sheet are elongated over a length corresponding substantially to the length of the central part 69, 70, 89 along the X axis, while the openings 62, 72, 82, 64, 74, 84 of each sheet are elongated over a length corresponding substantially to the length of the central part 69, 70, 89 along the Y axis.

[0043] The openings 71 to 74 in the central plate 22 are enlarged relative to the openings 61, 81, 62, 82, 63, 83, 64, 84, and their enlarged portion includes sheet metal tabs 710, 720, 730, 740 spaced apart to form a comb. Each of the slots 711, defined between the edge of the enlarged opening 71 and a tab 710 or between two successive tabs 710, opens onto the channels 11 defined by the raised or embossed features 10. The same applies to the slots made on the side of the openings 72, 73, 74.

[0044] Sheets 21, 22, 23 are typically ferritic steel with around 20% chromium, preferably CROFER ®< 22 (APU or H) or K41 (ASI 441) or FT18TNb, nickel-based Inconel ®< 600 or Haynes ®< in thicknesses typically between 0.1 and 1 mm.

[0045] These interconnectors can also be as described in French patent application FR 2 996 065 A1. In this application, the interconnector corresponds to a component with a metallic alloy substrate, the basic element of which is Iron (Fe) or Nickel (Ni), with one of the main flat faces coated with a thick ceramic layer, grooved to delimit channels suitable for the distribution and / or collection of gases, such as water vapor H2O, H2; Air, and the other of the main flat faces coated with a thick metallic layer, grooved to delimit channels suitable for the distribution and / or collection of gases, such as water vapor H2O, H2; O2, draining gas.In particular, a thick ceramic contact layer based on strontium-doped lanthanum manganite can be provided on the side of the oxygen electrode (anode in EHT, cathode for a SOFC cell), on the end plate 23, which is thermo-pressed according to the principle of FR 2 996 065 A1, and a thick metallic contact layer based on nickel can be provided on the side of the hydrogen electrode (cathode in EHT, anode for a SOFC cell), on the end plate 21, and may be in particular in the form of a nickel grid.

[0046] By "thick film," we mean a layer whose thickness is greater than that of a layer obtained by a so-called "thin film" technology, typically a thickness between 2 and 15 µm. This results in good performance with good homogeneity in SOFC / SOEC type solid oxide stacks with low manufacturing costs.

[0047] The manufacturing and assembly of the stack, namely the set of electrochemical cells 1 and interconnectors 5, is carried out in a specific way, taking into account the geometry of the plates and the technical design choices made. The successive layers are stacked in the following sequence: interconnector, then ceramic contact layer, then electrochemical cell, then metallic contact layer, then interconnector, etc.

[0048] Also, there are still needs to optimize the stacking of such successive layers to form the stack, and in particular to obtain a solid assembly so as to avoid any movement during the assembly and stacking phases enabling the manufacture of the stack. DESCRIPTION OF THE INVENTION

[0049] The invention aims to remedy at least partially the needs mentioned above and the drawbacks related to prior art achievements.

[0050] It aims in particular at the realization of an interconnector / contact layer / electrochemical cell assembly for SOEC / SOFC type solid oxide stacks which is stable and rigid to facilitate the manufacture of the stack.

[0051] The invention thus relates, according to one of its aspects, to a method for producing a high-temperature SOEC / SOFC type solid oxide stack, comprising a plurality of electrochemical cells each formed of a cathode, an anode and an electrolyte intercalated between the cathode and the anode, and a plurality of metallic interconnectors each arranged between two adjacent electrochemical cells, each interconnector having two main flat faces, a first face of the two main flat faces comprising a metallic coating layer in the form of a grid forming a contact layer with an electrochemical cell, the process comprising the step of spot welding the metallic coating layer on the first face of the interconnector to enable its fixing, and the step of depositing an adhesive around the periphery of the coating layer (GN), outside the active area and away from the gas supplies, intended to fix the electrochemical cell (1), the adhesive comprising between 5% and 50% by mass of polyvinyl butyral (PVB), between 5% and 50% by mass of terpineol and between 5% and 95% by mass of ethanol.

[0052] The manufacturing process according to the invention may further include one or more of the following characteristics taken individually or in any possible technical combinations.

[0053] The metallic material of the coating layer can be chosen from Nickel and its alloys, the coating layer being notably in the form of a Nickel grid, or chromium-forming alloys whose basic element is Iron.

[0054] In addition, several weld points can be made, in particular at least four, or even at least eight, being regularly distributed around the periphery of the coating layer, being present in particular at the corners of the coating layer.

[0055] Furthermore, the manufacturing process may include the step of depositing a layer of glass on the coating layer before the step of depositing glue.

[0056] In addition, each interconnector having two main flat faces, a second face of the main flat faces may comprise a thick ceramic coating layer, forming a contact layer with an electrochemical cell, the ceramic material being notably chosen from a strontium-doped lanthanite of formula La 1-x Sr x MO 3 with M (transition metals) = Nickel, Iron, Cobalt, Manganese, Chromium, alone or in mixture, or lamellar structure materials such as lanthanide nickelates of formula Ln 2 NiO 4 (Ln = Lanthanum, Neodymium, Praseodymium), or another electrically conductive perovskite oxide.

[0057] Furthermore, each interconnector can be formed by assembling at least three elongated plates along a first axis of symmetry and a second axis of symmetry orthogonal to each other, a central plate being interposed between a first end plate and a second end plate.

[0058] Furthermore, the invention also relates, according to another aspect, to a high-temperature SOEC / SOFC type solid oxide stack, obtained by means of an embodiment process as defined above, comprising a plurality of electrochemical cells each formed of a cathode, an anode and an electrolyte intercalated between the cathode and the anode, and a plurality of metallic interconnectors arranged each between two adjacent electrochemical cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The invention will be better understood upon reading the detailed description that follows, the non-limiting examples of its implementation, and upon examination of the schematic and partial figures in the attached drawing, on which: There figure 1 This is a schematic view showing the operating principle of a high-temperature solid oxide electrolyzer (SOEC). figure 2is a schematic exploded view of part of a high-temperature solid oxide electrolyzer (SOEC) including interconnectors according to the prior art, The figure 3 is an exploded view of a high-temperature SOEC / SOFC type solid oxide stacking interconnector, corresponding to the assembly of three thin sheets or plates, The figure 4 is a partial front view of a high-temperature SOEC / SOFC type solid oxide stacking interconnector sheet illustrating the spot welding step of the embodiment according to the invention, The figure 5 illustrates graphically the thermogravimetric analysis (TGA) of the adhesive from the manufacturing process according to the invention under different atmospheres. figures 7 And 8 are two partial front views of the interconnector sheet metal of the figure 4 illustrating the glue application step of the manufacturing process according to the invention, The figure 8is a partial front view of the interconnector sheet metal of the figure 4 illustrating the step of bonding the electrochemical cell after deposition of the glue shown in Figures 6 and 7 , and La figure 9 represents, in perspective and by observation from above, an assembly comprising a SOEC / SOFC type solid oxide stack with a stack of electrochemical cells and interconnectors obtained by the manufacturing process according to the invention, and a stack clamping system.

[0060] Throughout these figures, identical references may designate identical or analogous elements.

[0061] Furthermore, the different parts represented in the figures are not necessarily shown on a uniform scale, in order to make the figures more legible. DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0062] THE figures 1 to 3have already been described previously in the section relating to the prior art and the technical context of the invention. It is specified that, for the figures 1 and 2 The symbols and arrows for supplying water vapor H2O, distributing and recovering dihydrogen H2, oxygen O2, air and electric current, are shown for clarity and accuracy, to illustrate the operation of the devices shown.

[0063] Furthermore, it should be noted that all the components (anode / electrolyte / cathode) of a given electrochemical cell are preferentially ceramics. The operating temperature of a high-temperature SOEC / SOFC stack is also typically between 600 and 1000°C.

[0064] Furthermore, the possible terms "upper" and "lower" are to be understood here according to the normal orientation of a SOEC / SOFC type stack when in its usage configuration.

[0065] There figure 3 described above relates to an interconnector 5 formed by the assembly of three thin metal sheets 21 to 23.

[0066] The method for implementing the invention will be described with reference to figures 4 to 8 , THE figures 4 And 6 à 8 partially representing sheet metal 21 of interconnector 5 of the figure 3 Therefore, the elements already described will not be described again.

[0067] It should be noted that the interconnector 5 may include a metallic alloy substrate, in particular of the chromino-forming type whose basic element is Iron (Fe) or Nickel (Ni), having two main flat faces P1 and P2, as described in French patent application FR 2 996 065 A1.

[0068] Thus, as can be seen on the figure 3 The interconnector 5 has two main flat faces, P1 and P2. The first main flat face, P1, is intended to be covered by a layer of metallic coating GN, visible on the figure 4 forming a contact layer with an electrochemical cell 1, and provided in particular on the side of the hydrogen electrode. The material of this metallic coating layer GN is preferably chosen from nickel and its alloys or chromium-forming alloys whose basic element is iron (Fe). In particular, this metallic coating layer GN is in the form of a nickel grid, as seen in the figures 4 , 6 and 7 .

[0069] The manufacturing process according to the invention aims to enable optimal assembly between the interconnector 5 and the electrochemical cell 1, and in particular between the end plate 21 and the Nickel grid GN.

[0070] Thus, the process includes the step of spot welding S the metallic coating layer GN onto the first face P1 of the interconnector 5 to allow its attachment. As seen on the figure 4 This welding is carried out using an OS welding tool, specifically a spot welding device.

[0071] The Nickel GN grid is positioned on the central part 69 of the end plate 21, the openings of which 62 and 63 are visible on the figure 4 , and solder points S are made all around the periphery of the Nickel GN grid to allow its attachment to the first main flat face P1.

[0072] Specifically, in this case, eight S-weld points are made in the peripheral area of ​​the Nickel GN grid: four S-weld points at the four corners of the Nickel GN grid and four points in the middle of each side of the Nickel GN grid. These S-weld points are evenly spaced around the perimeter of the Nickel GN grid. It is possible to have a larger number of S-weld points, but this would lengthen the time required for this step in the manufacturing process.

[0073] Advantageously, this spot welding allows the Nickel GN grid to be held in place without deforming it and without adding any filler material, thus limiting possible contamination, unlike prior art solutions which do not provide any means of fixing the Nickel GN grid to the end plate 21.

[0074] Furthermore, as illustrated by the Figures 6 and 7The manufacturing process according to the invention includes a step of depositing an adhesive C on the Nickel grid GN to prepare it to receive the electrochemical cell 1 and to allow optimal fixation of the electrochemical cell 1 on the interconnector 5 by means of the contact layer formed by the Nickel grid GN.

[0075] The glue used, C, or adhesive, has a very precise composition to allow optimized fixation on the Nickel GN grid and to avoid leaving any residue when passing through high temperatures.

[0076] Specifically, adhesive C contains between 5% and 50% by mass of polyvinyl butyral (PVB), between 5% and 50% by mass of terpineol, and between 5% and 95% by mass of ethanol. Preferably, adhesive C contains 17% by mass of polyvinyl butyral (PVB), 28% by mass of terpineol, and between 55% by mass of ethanol. The composition of adhesive C can therefore vary, but its viscosity will change depending on the mixing ratios.

[0077] The advantage of this bonding step is that it prevents movement of the electrochemical cell 1 during subsequent stacking or assembly phases, and also flattens the electrochemical cell 1 in the common case where it is bent. Furthermore, the specific composition of the proposed adhesive C avoids the drawbacks of conventional adhesives that leave residues after heating, thus creating pollution detrimental to the durability of the SOFC / SOEC stack.

[0078] There figure 7 This graph illustrates the evolution of the PM mass loss, expressed as a percentage (%), as a function of temperature T, expressed in degrees Celsius (°C). It represents a thermogravimetric analysis (TGA) of adhesive C. Three curves, C1, C2, and C3, are shown, corresponding to three different atmospheres. It can be observed that, regardless of the atmosphere, no residual mass is obtained above 500°C. Thus, the specific composition of adhesive C used ensures the absence of residue after heating.

[0079] Advantageously, adhesive C is deposited around the periphery of the Nickel GN grid, outside the active zone and away from the gas supply. As seen on the Figures 6 and 7 , glue C is thus disposed, by means of a glue deposition tool OC, in peripheral glue deposition zones ZC in order to avoid blocking any gas circulation.

[0080] Once glue C has been applied, the electrochemical cell 1 is put in place, as illustrated in the figure 8 and a load is positioned for a few hours so that glue C can dry and to maintain the electrochemical cell 1 even if it was initially deformed.

[0081] However, prior to the application of the adhesive C, the manufacturing process according to the invention may include the step of applying a glass layer V, visible on the figure 8 , on the Nickel GN grid. This glass V deposition increases fluidic distribution, as described in French patent application FR 3 056 337 A1. Furthermore, bonding after the glass V deposition results in a glass V layer that is even more flexible because it is not completely dry.

[0082] It should also be noted that, as can be seen on the figure 3, the interconnector 5 has a second face P2 which includes a thick ceramic coating layer, provided in particular on the side of the oxygen electrode, forming a contact layer with an electrochemical cell 1. The ceramic material can be chosen from a strontium-doped lanthanite of formula La 1-x Sr x MO 3 with M (transition metals) = Nickel (Ni), Iron (Fe), Cobalt (Co), Manganese (Mn), Chromium (Cr), alone or in mixture, or lamellar structure materials such as lanthanide nickelates of formula Ln 2 NiO 4 (Ln = Lanthanum (La), Neodymium (Nd), Praseodymium (Pr)), or another electrically conductive perovskite oxide.

[0083] The various steps of the manufacturing process according to the invention are repeated for all interconnectors 5 and electrochemical cells 1 so as to obtain a stack 20 of solid oxides of the SOEC / SOFC type operating at high temperature.

[0084] There figure 9represents such a stack of 20 solid oxides of the SOEC / SOFC type operating at high temperature according to the invention.

[0085] More specifically, the figure 9 shows an 80 assembly comprising the 20 SOEC / SOFC type solid oxide stack and a 60 clamping system.

[0086] This set 80 has a structure similar to that of the set described in French patent application FR 3 045 215 A1.

[0087] The stack 20 comprises a plurality of electrochemical cells 1, each consisting of a cathode, an anode, and an electrolyte interposed between the cathode and the anode, and a plurality of metallic interconnectors 5, each arranged between two adjacent electrochemical cells 1. This assembly of electrochemical cells 1 and interconnectors 5 is designated as the "stack" and is obtained by the embodiment according to the invention, described above.

[0088] In addition, the stack 20 includes an upper terminal plate 43 and a lower terminal plate 44, respectively also referred to as upper stack terminal plate 43 and lower stack terminal plate 44, between which the plurality of electrochemical cells 1 and the plurality of interconnectors 5 are sandwiched, i.e. between which lies the stack.

[0089] Furthermore, the assembly 80 also includes a clamping system 60 for the SOEC / SOFC type solid oxide stack 20, comprising an upper clamping plate 45 and a lower clamping plate 46, between which the SOEC / SOFC type solid oxide stack 20 is clamped.

[0090] Each clamping plate 45, 46 of the clamping system 60 has four clamping holes 54. Furthermore, the clamping system 60 also includes four clamping rods 55, or tie rods, extending through a clamping hole 54 of the upper clamping plate 45 and through a corresponding clamping hole 54 of the lower clamping plate 46 to allow the upper clamping plates 45 and lower clamping plates 46 to be joined together. The clamping system 60 further includes clamping means 56, 57, 58 at each clamping hole 54 of the upper clamping plates 45 and lower clamping plates 46 that cooperate with the clamping rods 55 to allow the upper clamping plates 45 and lower clamping plates 46 to be joined together.More specifically, the clamping means comprise, at each clamping hole 54 of the upper clamping plate 45, a first clamping nut 56 cooperating with the corresponding clamping rod 55 inserted through the clamping hole 54. In addition, the clamping means comprise, at each clamping hole 54 of the lower clamping plate 46, a second clamping nut 57 associated with a clamping washer 58, these cooperating with the corresponding clamping rod 55 inserted through the clamping hole 54. The clamping washer 58 is located between the second clamping nut 57 and the lower clamping plate 46.

[0091] Of course, the invention is not limited to the examples of implementation that have just been described. Various modifications can be made to it by a person skilled in the art.

Claims

1. A method for making a SOEC / SOFC-type solid oxide stack (20) operating at high temperature, including a plurality of electrochemical cells (1) each formed of a cathode, an anode and an electrolyte interposed between the cathode and the anode, and a plurality of metal interconnectors (5) each arranged between two adjacent electrochemical cells (1), each interconnector (5) having two main planar faces, a first face (P1) of the two main planar faces comprising a metal coating layer (GN) in the form of a grid forming a contact layer with an electrochemical cell (1), the method including the step of spot-welding (S) the metal coating layer (GN) on the first face (P1) of the interconnector (5) to enable fastening thereof, and the step of depositing a glue at the periphery of the coating layer (GN), off the active area and at a distance from the gas supplies, intended to fasten the electrochemical cell (1), the glue comprising between 5% and 50% by weight of polyvinyl butyral (PVB), between 5% and 50% by weight of terpineol and between 5% and 95% by weight of ethanol.

2. The method according to claim 1, characterised in that the metallic material of the coating layer (GN) is selected from among nickel (Ni) and its alloys, the coating layer being in particular in the form of a Nickel grid (GN), or the chromia-forming alloys whose base element is Iron (Fe).

3. The method according to claim 1 or 2, characterised in that several welding spots (S) are made, in particular at least four, and possibly at least eight, by being evenly distributed at the periphery of the coating layer (GN), being in particular present at the angles of the coating layer (GN).

4. The method according to any one of the preceding claims, characterised in that it includes the step of depositing a glass layer (V) over the coating layer (GN) before the glue deposition step.

5. The method according to any one of the preceding claims, characterised in that, each interconnector (5) having two main planar faces, a second face (P2) of the main planar faces comprises a thick ceramic coating layer, forming a contact layer with an electrochemical cell (1), the ceramic material being selected in particular from a strontium-doped lanthanide of formula La1-xSrxMO3 with M (transition metals) = Nickel (Ni), Iron (Fe), Cobalt (Co), Manganese (Mn), Chromium (Cr), alone or as a mixture, or lamellar structure materials such as lanthanide nickelates of formula Ln2NiO4 (Ln = Lanthanum (La), Neodymium (Nd), Praseodymium (Pr)), or another electrically-conductive perovskite oxide.

6. The method according to any one of the preceding claims, characterised in that each interconnector (5) is formed by the assembly of at least three plates (21, 22, 23) elongated according to a first axis of symmetry (X) and a second axis of symmetry (Y) orthogonal to each other, a central plate (22) being interposed between a first end plate (21) and a second end plate (23).