High-temperature electrolysis reactor comprising a stack of cells and a receptacle for the stack filled with a material forming a gas barrier, and associated production method

Abstract

The invention essentially consists in integrating, into a receptacle (6), at least one electrochemical stack containing solid-oxide electrochemical cells (1), which stack is intended to operate at high temperature as an electrolysis or co-electrolysis reactor, a volume around the at least one electrochemical stack being filled with a material, at least one vitreous matrix of which material will act as a second gas-tight barrier, i.e. as an additional barrier to the barriers formed by the seals around the cathode and anode compartments of the stack.

Description

[0001] Description

[0002] Title :

[0003] HIGH TEMPERATURE ELECTROLYSIS REACTOR COMPRISING A STACK OF CELLS AND A CONTAINER FOR THE STACK FILLED WITH A MATERIAL FORMING A GAS BARRIER, AND ASSOCIATED PRODUCTION METHOD

[0004] Technical field

[0005] The present invention relates to the field of solid oxide fuel cells (SOFC, English acronym for "Solid Oxide Fuel Cell"), that of high temperature water electrolysis (EHT, or EVHT for high temperature water vapor electrolysis, or HTE English acronym for High Temperature Electrolysis, or HTSE English acronym for High Temperature Steam Electrolysis) also with solid oxides (SOEC, English acronym for "Solid Oxide Electrolyser Cell"), and that of high temperature co-electrolysis of water and another gas chosen from carbon dioxide CO2, nitrogen dioxide NO2.

[0006] The invention relates more particularly to the production of an electrochemical device constituting a high temperature water electrolysis or co-electrolysis (HTE) reactor of the SOEC type, and where appropriate operating in reversible mode in a SOEC type fuel cell, with a stack of elementary electrochemical cells.

[0007] The present invention aims firstly to make the operation of a hydrogen production system using one or more electrochemical devices more reliable and secure, by managing gas leaks likely to escape from the stack.

[0008] Although described with reference primarily to the application of high-temperature water electrolysis, the invention applies equally well to co-electrolysis of water and another gas selected from carbon dioxide CO2, as to a SOFC fuel cell.

[0009] Prior art

[0010] An SOFC fuel cell or an EHT electrolyzer is an electrochemical device consisting of a stack of elementary patterns, each comprising a solid oxide electrochemical cell, consisting of three layers superimposed on each other anode / electrolyte / cathode, and interconnection plates made of metal alloys also called bipolar plates, or interconnectors. The function of the interconnectors is 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 produced in an EHT electrolyzer; injected air and hydrogen and water produced in an SOFC cell) and to separate the anode and cathode compartments which are the gas circulation compartments on the anode and cathode sides of the cells respectively.

[0011] To carry out the electrolysis of water vapor at high temperature EHT, typically between 600 and 950°C, water vapor H2O is injected into the cathode compartment. Under the effect of the current applied to the cell, the dissociation of water molecules in vapor form is carried out at the interface between the hydrogen electrode (cathode) and the electrolyte: this dissociation produces dihydrogen gas H2 and oxygen ions. The dihydrogen is collected and evacuated at the outlet of the hydrogen compartment. The oxygen ions O2- migrate through the electrolyte and recombine into dioxygen at the interface between the electrolyte and the oxygen electrode (anode).

[0012] To operate a SOFC fuel cell, air (oxygen) is injected into the cathode compartment and hydrogen into the anode compartment. The hydrogen (H2) is transformed into H+ ions and releases electrons, which are captured by the anode. The H+ ions reach the cathode where they combine with O2- ions made 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.

[0013] 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 on top of each other, separating them by interconnectors. The assembly is positioned between two end connection plates, usually called terminal plates, one and / or the other of which supports the electrical power supplies and the gas supply / collection of an electrolyzer (electrolysis reactor) or a SOFC fuel cell.

[0014] Furthermore, to improve the quality of the electrical contacts established between the interconnectors and the electrodes, and therefore the performance of the aforementioned electrochemical devices, electrical contact elements are individually interposed 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 an SOFC cell), because it gives satisfactory results at low cost. All of these components form a stack that can be mechanically assembled and which is usually referred to by the English term "stack".

[0015] In a stack, it is necessary to ensure good sealing at each interconnector, between the anode and cathode compartments. This sealing depends on the design of the seals and the materials used for the various components opposite, but also on the gas pressure acting on the seal and the level of tightening of the stack.

[0016] Given the high operating temperature ranges of EHT electrolysers and SOFC fuel cells, typically 600°C to 1000°C, gaskets or seals are traditionally made from glass or glass-ceramic. A glass gasket is in a pasty state at operating temperature.

[0017] The multi-material nature, geometric complexity and thermomechanical constraints applied to this structure (stack) which works at high temperature impose enormous constraints for the production and maintenance of these seals.

[0018] In practice, it is observed that existing EHT stacks, by their design, have relatively high residual leak rates, compared to the very low leak rates theoretically achievable with vitroceramic seals.

[0019] Their operation is compatible with this provided that certain limits are not exceeded, generally set at around 1% of the H2 / H2O feed flow rate.

[0020] That being said, even with lower leak rates, observed as standard in operation, in a range estimated between 0.05 and 0.1% of the flow rate, the quantity of gas released by these external leaks can become significant for high-power stacks in which large flow rates circulate.

[0021] In current industrial concepts of high-power electrolyzer systems, a system comprises a set of modules, each module comprising an independent heating enclosure, commonly called a "hot box", containing several stacks aligned next to each other. The heating enclosure is swept by a constant air flow, which makes it possible to dilute the hydrogen emissions due to leaks from the stacks. This precaution is taken against the risk of localized accumulation of hydrogen pockets, but this type of operation has the disadvantage of being costly in terms of energy. The release of hydrogen in the enclosure under air flow, which self-ignites at high temperature, can also, if the leak is sufficiently localized, form a gas jet that causes a defect such as a through crack, and lead to the formation of a sustained flame and localized heating on the external walls of the stacks.

[0022] Such hotspots can have significant short-term consequences for the integrity of a stack.

[0023] Beyond the simple overall reduction of the gas leak rate from the stacks by improving the tightness of its structure, the management of leaks which generally appear following the formation of cracks is a technical problem to be overcome to make the operation and safety of high-temperature hydrogen production systems more reliable.

[0024] There is therefore a need to further improve stacked electrochemical devices each forming an SOEC type electrolysis reactor, operating where appropriate in reversible mode in a SOFC type fuel cell, in particular by reducing the release to the outside of gas leaks from the stacks without this harming the electrochemical operation of the devices.

[0025] The aim of the invention is to meet at least part of this need.

[0026] Statement of the invention

[0027] To do this, the invention firstly relates to an electrochemical device, constituting an SOEC electrolysis or co-electrolysis reactor, intended to operate at high temperature, and where appropriate a SOFC fuel cell in reversible mode comprising:

[0028] - at least one electrochemical stack comprising: a plurality of electrochemical cells based on solid oxides of the SOEC / SOFC type; a plurality of electrical and fluidic interconnectors, each consisting of at least one component made of electronically conductive and gas-tight material for supplying or collecting the electric current to the cells and for supplying, collecting and circulating gases on each electrode of each electrochemical cell; the interconnectors being arranged individually on either side of each of the electrochemical cells; a plurality of sealing gaskets each arranged between two adjacent interconnectors, around each gas inlet / outlet, to form a first gas-tight barrier; two plates called end plates between which the plurality of electrochemical cells, interconnectors and gaskets are arranged;

[0029] - a container arranged around the electrochemical stack and housing the latter by delimiting a volume filled at least partially with at least one material suitable for forming a second sealing barrier against gases likely to escape from the stack during operation at high temperature, the envelope being further arranged to allow compression of the stack during operation at high temperature.

[0030] According to an advantageous construction variant, the container consists of at least one peripheral wall and a bottom wall integral with or made integrally with the peripheral wall and against which one of the two end plates of the stack bears directly or indirectly, and the device comprises a means for distributing the compression force, arranged opposite the bottom wall, bearing directly or indirectly against the other of the two end plates of the stack to apply the compression clamping.

[0031] According to a first variant, the material is a glassy matrix whose glass transition temperature is less than or equal to the high operating temperature of the stack, the glassy matrix filling at least the part of the volume around the plurality of cells, interconnectors and seals.

[0032] Preferably, the vitreous matrix further covers at least the periphery of the end plate opposite that against the bottom wall, and where appropriate the force distribution means.

[0033] According to a second variant, the materials are a mineral powder filling at least the part of the volume around the plurality of interconnector cells and seals and a vitreous matrix whose glass transition temperature is less than or equal to the high operating temperature of the module, the vitreous matrix surmounting the mineral powder. The mineral powder may be composed of one or more vermiculite or talc type minerals of small particle size. Preferably, the particle size is less than 20 μm, more preferably between 5 and 10 μm. The advantage of this variant with two filling materials (mineral powder surmounted by a vitreous matrix) is to facilitate the removal of the stack and to allow possible reuse of the container.In fact, a layer of thin vitreous matrix can be deposited, which is easier to destroy and since the stack does not adhere to the mineral powder, it is easier to extract it from the container for removal.

[0034] Preferably, the glass matrix in its initial state is based on glass frit. Once at high temperature, the frit fuses to form a bath of molten glass. Once cooled, the glass matrix solidifies and forms a solid, compact block which constitutes the filling material of the container.

[0035] According to a first advantageous embodiment, the bottom wall of the container being provided with through openings forming the passages for the supply and outlet gases of the stack and the electrical supply connections and, where appropriate, for measuring the electrical voltage at each interconnector, the container further housing, between the bottom wall and the lower end plate of the stack, a support frame and a set of seals supported by the frame and ensuring sealing around the passages for the supply and outlet gases of the stack and the electrical supply connections.

[0036] Advantageously, the support frame and the set of seals form a single-piece sealing part, independent and housed in the container or pre-assembled with the stack, before the latter is housed in the container.

[0037] Advantageously, gas supply and outlet tubes are assembled with the bottom wall opposite its passages, forming a gas supply and outlet manifold.

[0038] In this first mode, rods forming the electrical power supply connections and, where appropriate, wires, preferably rigid, for measuring electrical voltage are preferably integrated into the stack and pass through the bottom wall of the container.

[0039] In an advantageous configuration where each interconnector is made up of three thin flat sheets, pierced with holes and elongated along two mutually orthogonal axes of symmetry, the flat sheets being laminated and assembled together by welding, an electrical voltage measuring wire is connected, in particular by welding, to the central sheet. In this first mode, the force distribution means may be a block bearing directly against the upper end plate of the stack and preferably incorporated in the glass matrix.

[0040] Advantageously, the block is in the form of a plate with a surface area enlarged compared to that of the stack so as to increase the path traveled in the glassy matrix by gas leaks likely to escape from the stack during operation at high temperature.

[0041] Advantageously, the lower edge of the enlarged plate, preferably incorporated in the glass matrix, has a frustoconical surface which widens from the upper end plate of the stack, so as to avoid the formation of gas pockets resulting from leaks.

[0042] Advantageously, the lateral edge of the enlarged plate, preferably incorporated in the glass matrix, is a wall which extends towards the interior of the glass matrix, so as to contain towards the interior any gas leaks likely to escape from the stack during operation at high temperature.

[0043] To further secure the device, several variants can be provided to deal with gas leaks that may escape from the stack during operation at high temperature.

[0044] According to a first variant, the enlarged plate is pierced at its periphery with one or more through holes, the device comprising:

[0045] - a cover fixed in a sealed manner to the container and / or to the enlarged plate, delimiting with the latter a volume (VI) in fluid communication with the through hole(s) of the enlarged plate, the cover being pierced, preferably in its center, with a passage,

[0046] - a tube for supplying a gas called inerting gas, assembled with the cover opposite its passage, forming a collector for supplying inerting gas to the volume (VI) into which gas leaks likely to escape from the stack during operation at high temperature arrive through the through hole(s).

[0047] By "inerting gas" is meant here and within the scope of the invention, a gas which will reduce or even eliminate the risks linked to gas leaks likely to escape from the stack. The volume of inerting gas is advantageously controlled and monitored. In the event of hydrogen leakage from the stack, two options are possible for the choice of inerting gas to supply the volume V 1:

[0048] - either a gas containing oxygen in which the escaping hydrogen will self-ignite on the surface of the glass as mentioned above,

[0049] - either an inert gas into which hydrogen can be released (mixed) without risk of ignition, provided that oxygen level monitoring is implemented and potentially gas renewal / purging is carried out, due to concomitant leaks of hydrogen and air from the stack.

[0050] In other words, this first variant consists of installing a sealed volume V 1 supplied with gas from the outside which will treat in said volume the gas leaks from the stack.

[0051] According to a second variant, the enlarged plate is pierced at its periphery with one or more through holes, the device comprising:

[0052] - a cover fixed in a sealed manner to the container and / or to the enlarged plate, delimiting with the latter a volume (V2) in fluid communication with the through hole(s) of the enlarged plate, the cover being pierced, preferably in its center, with a passage,

[0053] - a recovery tube assembled with the cover opposite its passage, forming a collector for recovering gas leaks likely to escape from the stack during operation at high temperature, which are recovered through the through hole(s).

[0054] In other words, this second variant consists of installing a sealed volume V2 which will collect gas leaks from the stack to evacuate them to the outside.

[0055] Advantageously, the through hole(s) is / are closed by a filter.

[0056] For fixing, the cover(s) is / are advantageously fixed to the container and / or to the enlarged plate by means of a plurality of bolts with the interposition of at least one sealing gasket between them. This gasket is preferably a flat or toric shaped gasket or a glass-metal type connection suitable for ensuring sealing at the high operating temperature of the stack.

[0057] According to a second embodiment, the bottom wall of the container is solid, the device further comprising a cover plate arranged above the stack, preferably being incorporated in the glassy matrix, the cover plate being provided with through openings forming the passages for the supply and outlet gases of the stack and the electrical supply connections and, where appropriate, electrical voltage measurement at each interconnector, the cover plate further forming a force distribution means.

[0058] In this second mode, gas supply and outlet tubes are preferably assembled with the cover plate opposite its passages, forming a gas supply and outlet manifold.

[0059] In this second mode also, the device comprises, as another means of force distribution, a rod in ball joint connection with the cover plate to achieve the clamping by compression.

[0060] The stack interconnectors and / or the container may each be made of one or more metal parts, preferably of ferritic steel with approximately 20% chromium, preferably of CROFER® 22APU or F18TNb, or of nickel-based steel such as Inconel® 600 or Haynes 230® or of stainless steel type 31 OS.

[0061] According to an advantageous configuration, the general shape of the stack and of the container is preferably axisymmetric. It is also possible to envisage a general oval, square or rectangular shape.

[0062] Thus, the invention essentially consists of integrating into a container at least one electrochemical stack with solid oxide electrochemical cells, intended to operate at high temperature as an electrolysis or co-electrolysis reactor, with a volume between them which is filled with a material including at least one glassy matrix which will act as a second gas-tight barrier, i.e. as an additional barrier to those of the seals around the cathode and anodic compartments of the stack. The formulation of the glass of the material guarantees in the temperature range a non-devitrified glassy matrix, i.e. which does not crystallize, remaining viscous. The glassy matrix which therefore coats at least the lateral edges of the stack is viscous at the high operating temperatures of the electrochemical stack.

[0063] In the event of a leak in the stack, the escaping gases bubble into the matrix which has become viscous, and the stack is thus protected from any risk of hot spots created by self-ignition of hydrogen on the lateral edges of the stack.

[0064] In other words, locally, if a gas jet forms following the appearance of a crack opening into the stack, bubbling in the viscous matrix will allow the gases to be released onto the free surface of this matrix.

[0065] The consequences of a hydrogen leak are thus limited. Indeed, the gas leak and the resulting hot spot, whose temperature can reach more than 1000°C, are of no consequence when created in the glass matrix.

[0066] The viscous matrix, by forming a second sealing barrier around the external walls of the electrochemical stack and by delaying gas diffusion, also contributes to the reduction of the overall mass leakage rate of the stack.

[0067] As indicated above, instead of a single filling material consisting of a vitreous matrix, the volume between the stack and the container can be filled with a powder of one or more mineral materials from a layer of vitreous matrix.

[0068] The mineral powder allows the evacuation of gases likely to come from leaks in the stack, by forming the second sealing barrier in which self-ignition of hydrogen cannot occur. After diffusion in the mineral layer, the gases are released onto the free surface of the glassy matrix in a viscous state.

[0069] Another advantage of the invention is to promote thermal exchanges with the exterior since the thermal exchanges are made by conduction from the stack passing through the filling material and through the container instead of natural convection with the surrounding air according to the state of the art. Thermal regulation of the electrochemical device is thus facilitated.

[0070] Another advantage of the invention is to use a filling material with electrical insulation properties. The invention benefits all high-temperature industrial hydrogen production systems in which the management and reduction of hydrogen leaks are major problems.

[0071] The invention also relates to a method for producing an electrochemical device as described above, comprising the following steps: a / housing the electrochemical stack with support against the bottom wall of the container, where appropriate with the interposition of the support frame and the set of seals supported by the frame; b / placing the force distributor means above the stack so as to apply the clamping force by compression of the stack; c / filling with the material(s) including at least the vitreous matrix in the liquid state of the volume between the stack and the container at least up to the upper end plate, preferably with incorporation of the force distributor means. Other advantages and characteristics will become more apparent upon reading the detailed description, given for illustrative and non-limiting purposes, with reference to the following figures.

[0072] Brief description of the drawings

[0073] [Fig 1] Figure 1 is a schematic cross-sectional view of an example of a state-of-the-art solid oxide electrochemical cell stack electrochemical device.

[0074] [Fig 2] Figure 2 is a schematic cross-sectional view of an example of an electrochemical device with a stack of solid oxide electrochemical cells according to the invention.

[0075] [Fig 3], [Fig 3A], [Fig 3B] Figures 3, 3A, 3B are schematic views respectively in perspective and in cross-section along two cutting axes of a container according to a first embodiment of an electrochemical device according to the invention.

[0076] [Fig 4], [Fig 4 A] Figures 4 and 4A are schematic exploded and top views respectively of a container according to Figures 3 to 3B in the bottom wall of which a single-piece sealing part is mounted. [Fig 5], [Fig 5A], [Fig 5B], [Fig 5C] Figures 5, 5A, 5B, 5C are schematic perspective and cross-sectional and detailed views respectively of an electrochemical stack according to the first embodiment of an electrochemical device according to the invention.

[0077] [Fig 6], [Fig 6A] Figures 6 and 6A are schematic top and detail views respectively of an interconnector of the stack with its connection to an electrical voltage measurement wire.

[0078] [Fig 7] Figure 7 is an exploded view showing an advantageous arrangement of the electrical voltage measuring wires of three adjacent interconnectors within an electrochemical stack of a device according to the invention.

[0079] [Fig 8A], [Fig 8B], [Fig 8C] Figures 8 A, 8B, 8C are schematic views respectively in perspective and in cross-section showing the steps of producing an electrochemical device according to the first embodiment of the invention.

[0080] [Fig 9], [Fig 9 A] Figures 9 and 9 A are schematic views respectively in perspective and in cross-section of an electrochemical device according to a second embodiment according to the invention.

[0081] [Fig 10] Figure 10 repeats Figure 9 showing a variant of filling with two materials the volume between container and stack of an electrochemical device according to the invention.

[0082] [Fig 11] Figure 11 is a cross-sectional view of a device according to a first alternative embodiment of the invention.

[0083] [Fig 12] Figure 12 is an exploded view of the device of Figure 11.

[0084] [Fig 13A], [Fig 13B] Figures 13A and 13B are partial sectional views of detail of a device according to Figures 11 and 12, according to two distinct alternatives.

[0085] [Fig 14], [Fig 14A] Figures 14 and 14A are schematic views in partial section and in detail of a device according to Figures 11 and 12, with an improvement in the evacuation of gases.

[0086] [Fig 15] Figure 15 is a cross-sectional view of a device according to a second alternative embodiment of the invention. [Fig 16], [Fig 16 A] Figures 16 and 14A are schematic views in partial section and in detail of a device according to Figure 15, with an improvement on the evacuation of gases.

[0087] [Fig 17A], [Fig 17B] Figures 17 A and 17B are partial sectional views of a detail of a device according to the invention, according to two distinct alternatives for producing sealing at the cover.

[0088] Detailed description

[0089] For the sake of clarity, the same elements of an electrochemical device according to the state of the art and of an electrochemical device according to the invention are designated by the same numerical references.

[0090] In the illustrated examples, the electrochemical devices 1 have a general axisymmetric shape around a central axis X.

[0091] The symbols and arrows for water vapor (H2O) supply, hydrogen distribution and recovery (H2) are shown for clarity and accuracy, to illustrate the operation of an electrochemical device operating as a high-temperature electrolysis reactor.

[0092] Throughout the present application, the terms "lower", "upper", "above", "below", "inner", "outer", "internal" "external" are to be understood with reference to an electrochemical device according to the invention in operating configuration, i.e. with its electrochemical stack vertical.

[0093] It is also specified that the electrochemical stack described is of the solid oxide type (SOEC, acronym for "Solid Oxide Electrolyte Cell") operating at high temperature. Thus, all the components (anode / electrolyte / cathode) of an electrolysis cell are ceramics. The high operating temperature of an electrolyzer (electrolysis reactor) which can operate in reversible mode in a SOFC fuel cell (acronym for "Solid Oxide Fuel Cell") is typically between 600°C and 1000°C.

[0094] Typically, the characteristics of a SOEC electrolysis cell suitable for the invention, of the cathode support type (CSC), may be those indicated as follows in Table 1 below. [Table 1]

[0095] Figure 1 shows an electrochemical device 1 according to the state of the art. Such a device 1 comprises an electrochemical stack 2 with electrochemical cells 20, based on solid oxides of the SOEC / SOFC type, which can operate reversibly as a high-temperature electrolyzer or SOFC fuel cell.

[0096] Within the stack, a plurality of electrical and fluidic interconnectors 21 are arranged individually on either side of each of the electrochemical cells. Each interconnector consists of at least one component made of electronically conductive and gas-tight material for supplying or collecting the electrical current to the cells and for supplying, collecting and circulating gases on each electrode of each electrochemical cell.

[0097] Finally, within the stack 2, a plurality of contact elements and sealing gaskets 22 around each gas inlet / outlet is arranged individually on each electrode of electrochemical cells.

[0098] At the ends of the stack 2, two end plates 3, 4 are arranged. The lower end plate 4 is provided with through openings 40, 41 forming the passages for the supply and outlet gases of the stack 2 so as to produce an electrical and fluidic connector for bringing or collecting the electric current from the electrochemical device to the outside and for bringing, collecting and circulating the gases from the electrochemical device to the outside. As shown in this figure 1, the through openings 40, 41 are respectively dedicated to the supply of water vapor and the recovery of the hydrogen produced. Other through openings not shown are dedicated to the supply of draining gas (air, oxygen), to the recovery of the oxygen O2 produced, and to the supply of the electric current.

[0099] A means for distributing the compression force 5, in the form of a support block, is arranged on the upper end plate 3 to apply a force for clamping the stack 2 by compression. For the assembly of this block 5, a guide and centering part 50 can be interposed between the upper plate 3 and the block. This part 50 guarantees the centering and blocking of the support block 5.

[0100] In such a device 1 according to the state of the art, the stack 2 is in the open air. As shown in Figure 1, even with very good quality seals 22, following the appearance of a through crack, there remains a risk of gas leaks into the open air, in particular of the hydrogen produced, which can therefore self-ignite on contact with the open air and create hot spots on the external lateral edges of the stack 2. A hot spot can cause serious irreversible damage to the external lateral edges of the stack 2.

[0101] To eliminate this risk, the inventors thought of housing the stack in a container 6 and coating it, that is to say filling the volume between stack 2 and container 6 with a glassy matrix 7 whose glass transition temperature is less than or equal to the high operating temperature of stack 2. Thus this matrix 7 is viscous at the high operating temperature of stack 2, forming a sealing barrier to gases likely to escape from the latter.

[0102] A first embodiment of such a device 1 with container 6 and glass matrix 7 is shown in 2 to 5C.

[0103] The container 6 consists of a wall of at least one peripheral wall 60 arranged around the stack 2 and a bottom wall 61 integral or made integrally with the peripheral wall 60. Preferably, as shown in detail in figures 3 to 3B, the container 6 is a single-piece metal part.

[0104] The walls 60 and 61 of the container may be made of steel, preferably ferritic steel with approximately 20% chromium, preferably CROFER® 22APU or F18TNb, or nickel-based steel such as Inconel® 600 or Haynes 230® or 310S stainless steel. Other materials may be considered. In general, the container material must be compatible, primarily in terms of corrosion, with high-temperature operation.

[0105] The bottom wall 61 is provided with through openings 62, 63 forming the passages for the supply and outlet gases of the stack 2. Advantageously, gas supply and outlet tubes 64, 65 are assembled with the bottom wall 61 opposite its passages 62, 63, forming a gas supply and outlet collector.

[0106] Furthermore, the bottom wall 61 is provided with through openings 66 to allow the passage of the electrical power supply and electrical voltage measurement connections respectively to each interconnector 21 of the stack 2.

[0107] The lower end plate 4 of the stack 2 bears indirectly against the bottom wall 61. Indeed, as shown in FIGS. 4 and 4A, a single-piece sealing part 8 is interposed between the lower end plate 4 of the stack 2 and the bottom wall 61. This single-piece sealing part 8 can be pre-assembled with the stack 2 or mounted against the bottom wall 61 of the container 6 before housing the stack 2.

[0108] This one-piece sealing part 8 consists of a support frame 80 and a set of seals 81 supported by the frame 80. The set of seals 81 is located around through openings 82, 83 in the frame which ensure sealing respectively around the passages for the supply and outlet gases of the stack and the electrical supply connections. In addition, the frame 80 may comprise through openings 83 for the passage of electrical voltage measurement wires to each interconnector. Each of these through openings 82, 83 of this one-piece sealing part 8 is therefore opposite respectively one of the corresponding through openings 62, 63, 66 of the bottom wall 61 of the container 6.

[0109] Furthermore, the device 1 comprises a block 5 for distributing compression force, arranged opposite the bottom wall, bearing directly against the upper end plate of the stack 2 to apply a compression clamping of the latter.

[0110] Thus, as symbolized in Figure 2, surrounded by the glassy matrix 7 contained between the container 6 and the stack 2, the latter is protected from any risk of hot spots created by self-ignition of the hydrogen on these external lateral edges.

[0111] Indeed, in the event of a leak from the stack 2 in operation at high temperature, the gases which escape from it bubble in a way in the vitreous matrix 7 which is in a viscous state. Locally, if a jet of gas forms following the appearance of a through crack in the stack 2, the bubbling produced in the matrix 7 will allow the gases to be released onto the free surface of the glass, that is to say at a distance from the stack.

[0112] The consequences of a hydrogen leak are thus limited, the leak and the resulting hot spot whose temperature can reach more than 1000°C is of no consequence because it is created on the free surface of the matrix 7, unlike a device 1 according to the state of the art, as shown in figure 1 where a hot spot can cause serious irreversible damage to the lateral edges of the stack 2 in the open air.

[0113] Figures 5 to 5C show a variant of simplification of the interface between a stack 2 and the bottom wall 61 of the container 6. In this variant, the stack 2 integrates the connections 24 to the current leads and 25 to the voltage measurements made individually on each interconnector 21, which are arranged and fixed inside the structure of the stack 2, in passages which are respectively dedicated to them from through openings 42, 43 in the lower end plate 41. The passages 200, 201 within the stack, respectively for supplying gas and for recovering produced gas, are free of any object.

[0114] The integration in the stack 2 of the connections 25, in the form of wires, of voltage measurements makes it possible to protect them and limits the stresses on these wires during phase changes (solid / glassy) of the glass. The voltage measurement wires are preferably nickel wires with a diameter not exceeding 0.5 mm.

[0115] Figures 6 and 6 A show an advantageous integration in the case of an interconnector 21 with three thin flat sheets 210, 211, 212, which are pierced with holes and elongated along two mutually orthogonal axes of symmetry, the flat sheets being laminated and assembled together by welding. To better understand the production of the interconnectors 21 with three thin sheets, reference may advantageously be made to patent application FR3040061A1.

[0116] The thin sheets are preferably made of steel, preferably ferritic steel with approximately 20% chromium, preferably CROFER® 22APU or F18TNb.

[0117] An electrical voltage measuring wire 25 is directly welded to a protruding tab 213 of the central sheet 211 which opens into a through opening 214 opposite the dedicated opening 43 of the relatively fragile lower terminal plate 4, which are pointed at the middle plate of the interconnectors.

[0118] As shown in Figure 7, to facilitate mounting at each stage of the stack 2, an interconnector 21.2 of a given stage is mounted by being oriented 180° relative to an interconnector 21.1 of an adjacent stage, so that the legs 213 have an opposite position from one stage to the other and thus alternate the position of the voltage measurement wires 25.

[0119] A good spacing of these measuring wires 25 between the interconnectors is guaranteed. In other words, the risk of two measuring wires 25 being too close to each other is avoided, which could distort the individual electrical voltage measurements interconnector by interconnector of the stack, and create a parasitic electrical contact between two interconnectors. A method of assembling an electrochemical device 1 according to the first embodiment of the invention is now described with reference to FIGS. 8 A to 8C. The electrochemical stack 2 is housed with support against the bottom wall

[0120] 61 of the container 6, with the interposition of the single-piece sealing part 8 consisting of the support frame 80 and the set of seals 81 supported by the frame (figure 8A). In the variant of a stack 2 which integrates the electrical connections 24 and the electrical voltage measuring wires 25, care is taken to ensure that these pass through the openings 66 of the bottom wall 6 provided for this purpose.

[0121] The force distributor block 5 is put in place by guiding and centering it on the upper end plate 3 above the stack so as to apply the clamping force by compression of the stack 2 (figure 8B). The volume between the stack 2 and the container 6 is then filled with the glass matrix 7 based on glass frit in its initial state, at least up to the upper end plate 3 (figure 8C). Preferably, the force distributor block 5 is incorporated in the glass matrix 7.

[0122] The frit can be a powder of crushed glass in its initial state. When it is heated, once past the melting point, lower than the operating temperature of stack 2, this frit liquefies and transforms into a viscous paste which forms a gangue around stack 2. When the glass cools and returns below its glass transition temperature, it solidifies and forms a solid block.

[0123] Prior to step a / , the thermomechanical conditioning of stack 2 is carried out.

[0124] To do this, a thermomechanical treatment is applied to the stack produced in order to finalize at least the installation of electrical contact elements and sealing joints within the stack. This thermomechanical treatment may also include the reduction of the electrochemical cells.

[0125] The temperatures are determined by the temperatures required for the installation of seals, typically made of glass or glass-ceramic, for example, between 850 and 950°C for a period of time adapted to the type / geometry of the seal and the glass. The temperature increase can be made for a given module up to a value that prevents the formation of thermal gradients.

[0126] The reduction of electrochemical cells can be done from 650°C or advantageously at 800°C for a period of one hour to several days depending on the hydrogen flow rates sent.

[0127] When the solid block 7 is formed, the high temperature operation of the device 1 can take place for the production of hydrogen.

[0128] When the temperature rises, the glass frit constituting the matrix 7 then transforms into a viscous fluid which covers the lateral edges of the stack 2 and preferably covers the upper end plate 3. This fluid, as long as it is maintained at a temperature above the glass transition temperature, has a viscosity ensuring the coating of the stack 2 without transmitting mechanical stresses to it, in particular linked to the differential expansions of the materials.

[0129] During cooling of the device 1, when the matrix 7, which has not devitrified when hot, becomes solid again, the formation of cracks within the matrix remains without consequence, the glass not having in this operational phase a sealing function to ensure, because at these cooling temperatures, no gas passes through the stack.

[0130] When the device 1 is reheated for a new operating cycle, as soon as the matrix 7 becomes viscous again, it then regains its fluidic properties and can once again fulfill its role as a gas-tight barrier.

[0131] A second embodiment of an electrochemical device 1 according to the invention is shown in Figures 9 and 9A.

[0132] The bottom wall 61 of the container 6 and the end plate 4 of the stack 2 are solid here.

[0133] A cover plate 9 is arranged above the upper end plate 3 of the stack 2, preferably being incorporated into the glass matrix 7.

[0134] The cover plate is provided with through openings 90, 91, 92 respectively forming the passages for the supply and outlet gases of the stack and the electrical supply connections 24 and the electrical voltage measurement wires 25 to each interconnector. These passages 90, 91, 92 are opposite the corresponding passages 30, 31 of the upper end plate 3 of the stack 2.

[0135] This cover plate 9 further forms a force distribution means on which a rod 10 preferably rests in a ball joint connection as another force distribution means to achieve compression of the stack 2.

[0136] Gas supply and outlet tubes 93, 94 are advantageously assembled with the cover plate 9 opposite its passages 90, 91, forming a gas supply and outlet manifold.

[0137] Thus, in the assembly according to this second mode, the container is simplified and only has a container function to ensure, the gas collector function being ensured by the covering part 9.

[0138] For mounting the stack 2 in the container 6, a guide and centering part 11 can be installed on the bottom wall 61.

[0139] As illustrated in Figure 10, instead of a filling material consisting solely of a vitreous matrix 7, the volume between stack 2 and container 6 can be filled with a layer of powder of mineral materials 70, for example of the vermiculite or talc type of low granularity, preferably compacted, covered with a layer of vitreous matrix 71.

[0140] The layer of mineral powder 70 allows the evacuation of gases likely to escape from the stack 2, by forming a second sealing barrier in which self-ignition of hydrogen cannot occur. The gases then come after diffusion in the mineral layer 70 to be released on the free surface of the layer of vitreous matrix 71. This variant makes it easier to remove a stack 2 and to allow possible reuse of the container 6. Indeed, it is possible to dimension a layer of vitreous matrix 70 sufficiently thin so that when it is cold it can be easily destroyed to easily dismantle the stack 2 from the container 6, because in fact the stack is not adherent to the mineral powder 70.

[0141] Although illustrated in Figure 10, in relation to the second embodiment, this variant with two superimposed layers, respectively of mineral powder 70 and of vitreous matrix 71 can be implemented in a device according to the first embodiment. In the event of gas leakage from the stack and which can escape through the vitreous matrix, additional safety measures can be provided, in particular by installing volumes for treatment or collection and evacuation of these gas leaks.

[0142] A first variant embodiment of a device is shown in Figures 11 to 14A.

[0143] The device 1 as a whole according to this first variant is shown in figures 11 and 12.

[0144] According to this variant, the support block 5 is in the form of a plate with a surface area enlarged compared to that of the stack, so as to increase the path traveled in the vitreous matrix by gas leaks likely to escape from the stack during operation at high temperature.

[0145] The geometry of this enlarged plate makes it possible to slow down the leaks emitted by the stack 2 and bubbling in the glass matrix 7 by increasing the length of the leak path. The greater the difference in diameter between the enlarged plate 5 and the stack 2, the greater the distance that must be traveled in the glass for gas leaks.

[0146] This enlarged plate 5 is pierced at its periphery with one or more through holes 53. These holes 53 are of small diameter to protect against the risk of accumulation of gases. In addition, the diameter of these holes 53, preferably distributed regularly around the periphery of the plate 5, is small, typically of the order of a millimeter, so that the glass of the matrix 7, the viscosity of which is very high compared to that of the gases, cannot rise by capillary effect.

[0147] A cover 12 is fixed in a sealed manner to the container 6, delimiting with the latter a volume (VI) in fluid communication with the through holes 53, the cover being pierced, preferably in its center, with a passage.

[0148] A tube 13 for supplying a gas called inerting gas, assembled with the cover opposite its passage, forming a collector for supplying inerting gas to the volume (VI) in which gas leaks likely to escape from the stack during operation at high temperature arrive through the through holes.

[0149] As illustrated 13B, the lower edge 51 of the enlarged plate 5, incorporated in the vitreous matrix, has a frustoconical surface which widens from the upper end plate 3 of the stack, so as to avoid the formation of gas pockets resulting from leaks, as symbolized in FIG. 13A in the case of a horizontal lower edge 51.

[0150] As illustrated in Figures 14 and 14A, the lateral edge of the enlarged plate, preferably incorporated in the glass matrix 7, is a wall 52 or blade which extends towards the inside of the glass matrix, so as to contain towards the inside the gas leaks likely to escape from the stack during operation at high temperature. In other words, this wall or blade 52 plunging into the glass matrix 7 forms a baffle which makes it possible to channel the leaks coming from the stack 2 towards the cover 12.

[0151] Thus, according to this first variant, the cover 12 is installed to form a sealed enclosure delimiting a volume VI in its upper part into which an inerting gas is brought, the stack 2 being immersed in the lower part of the enclosure, in the vitreous matrix 7.

[0152] The inerting gas is either an oxygen-containing gas in which hydrogen leaks from stack 2 can self-ignite on the surface of the glass of matrix 7, or an inert gas in which hydrogen leaks can mix without risk of ignition. Preferably, in the latter case, monitoring of the oxygen level and potentially renewal / purging of the gas is implemented, since concomitant leaks of hydrogen and air from the stack are possible. Generally speaking, monitoring of the inerting gas (pressure / temperature, hydrogen level) is an indirect method that makes it possible to quantify or at least detect possible leaks from the stack to the outside. The appearance of a leak will in fact generate an overpressure of the cover gas informing of the appearance of a gas leak from stack 2.

[0153] Thus, in the event of gas leaks from the stack, the escaping gases bubble into the vitreous glass of the matrix 7. The longer the time required for the gas to pass through this second sealing barrier 7, the lower the leak rate. The addition of the cover 12 on the stack makes it possible to increase the distance of glass to be crossed by a leak that would bubble into the vitreous matrix.

[0154] Whatever the inerting gas solution chosen, the main function of the glass matrix to provide a second barrier and protect the external walls of the stack in the event of a localized hydrogen leak is therefore retained. A second safety embodiment variant of a device 1 is shown in Figures 15 to 16A.

[0155] Here, a cover 16 pierced in its center with a passage, is fixed in a sealed manner to the enlarged plate 5 by delimiting with the latter a volume NI in fluid communication with the through holes 53.

[0156] A recovery tube 17 is assembled with the cover 16 opposite its passage, forming a collector for recovering gas leaks likely to escape from the stack during operation at high temperature, which are recovered through the holes 53.

[0157] Here, the collection of the escaping gases is therefore achieved by forming a cavity closed to the volume V2, above the stack 2. This volume V2 can be subjected to a slight depression. Just as for the first variant, the diameter of the holes 53 is small, typically so that the glass of the matrix 7 cannot rise by capillary effect.

[0158] Small diameter holes 53 can be enlarged by being individually closed with a filter. This can be a standard filter, such as that marketed in the form of a disc under the name PORAL®

[0159] As with the first variant, the lower edge 51 of the widened plate 5 is preferably a truncated cone shape that widens outward to prevent gas pockets. Also to best confine leaks and direct them toward the holes, the edge of the widened wall includes a vertical wall or blade 52.

[0160] Finally, an additional cover 12, like that of the first variant, pierced to allow the gas evacuation tube 13 to pass through, can be fixed above, in particular directly to the container 6, and preferably in a sealed manner.

[0161] As shown in Figures 17A and 17B, the cover 12 is advantageously fixed to the container 6 in their peripheral parts in the form of flanges, by means of a plurality of bolts 14 preferably distributed regularly around the flanges.

[0162] To ensure the seal between them, a seal 15 is interposed between them, in particular in an annular groove provided for this purpose in the container 6. The seal 15 can be a flat-shaped (figure 17A) or toric (figure 17B) seal or a glass-metal type connection adapted to ensure the seal at the high operating temperature of the stack. The prerequisites in terms of sealing on the interface between cover 12 and container 6, subjected to a very low pressure gradient, can remain modest. The pressure and the supply of the cover gas are controlled with a supply that can, if necessary, continuously compensate for any leakage. With a judicious choice of seals and mechanical assembly, the mechanical forces to be applied to the assembly to ensure the seal at the interfaces can be reduced.

[0163] The enlarged plate 5 can be mounted integrally or not with the end plate 3 via a mechanical connection blocking the relative vertical movements of the two parts. A part 50 guaranteeing the centered position of the centering pin type cover is however required to block the relative horizontal movements between the two parts.

[0164] The invention is not limited to the examples which have just been described; in particular, it is possible to combine characteristics of the illustrated examples within non-illustrated variants.

[0165] Other variations and improvements may be envisaged without departing from the scope of the invention.

[0166] If in all the examples illustrated, the shapes of stack and container forming an electrochemical device are axisymmetric around a central axis, it is possible to envisage implementing the invention on other shapes, such as stacks and containers of square or rectangular section. In general, the invention can be implemented for any stack geometry, because the container has the sole function of being a stack container and the material forming the gas-tight barrier. Such a container therefore remains subject to low thermomechanical constraints and its geometry can easily adapt to that of the stacks.

[0167] As illustrated, the integration of electrical connections and electrical voltage measurement wires in a stack or in a cover plate simplifies its integration in a container. However, other embodiments are possible: in fact, the glass matrix having electrical insulating properties, more conventional assemblies, with current leads made by current rods connected to the periphery of the terminal plates of the stack and voltage measurement wires connected in the corners of the interconnectors, are conceivable.

Claims

Claims 1. Electrochemical device (1), constituting an electrolysis or co-electrolysis reactor SOEC, intended to operate at high temperature, and where appropriate an SOFC fuel cell in reversible mode comprising: - at least one electrochemical stack (2) comprising: a plurality of electrochemical cells (20) based on solid oxides of the SOEC / SOFC type; a plurality of electrical and fluidic interconnectors (21), each consisting of at least one component made of electronically conductive and gas-tight material for supplying or collecting the electric current to the cells and for supplying, collecting and circulating gases on each electrode of each electrochemical cell; the interconnectors being arranged individually on either side of each of the electrochemical cells by defining cathode and anodic compartments; a plurality of sealing gaskets (22) each arranged between two adjacent interconnectors, around each gas inlet / outlet, to form a gas-tight barrier; two plates called end plates (3, 4) between which the plurality of electrochemical cells, interconnectors and gaskets are arranged; - a container (6), arranged around the electrochemical stack and housing the latter by delimiting a volume filled at least partially with at least one material (7; 70, 71) adapted to form an additional barrier to that of the seals around the cathode and anodic compartments of the stack to gases likely to escape from the stack during operation at high temperature, the envelope being further arranged to allow compression of the stack during operation at high temperature, the container consisting of at least one peripheral wall (60) and a bottom wall (61) integral or made integrally with the peripheral wall and against which one of the two end plates of the stack bears directly or indirectly, the device comprising a means for distributing compression force (5), arranged opposite the bottom wall, bearing directly or indirectly against the other of the two end plates of the stack to apply the compression clamp, the material being a glassy matrix whose glass transition temperature is less than or equal to the high operating temperature of the stack, the glassy matrix filling at least the part of the volume around the plurality of cells, interconnectors and seals.

2. Electrochemical device according to claim 1, the vitreous matrix further covering at least the periphery of the terminal plate opposite that against the bottom wall, and where appropriate the force distribution means.

3. An electrochemical device according to claim 1 or 2, the materials being a mineral powder (70) filling at least the portion of the volume around the plurality of cells, interconnectors and seals and a glassy matrix (71) whose glass transition temperature is less than or equal to the high operating temperature of the module, the glassy matrix overlying the mineral powder.

4. Electrochemical device according to one of the preceding claims, the vitreous matrix being in its initial state, based on glass frit.

5. Electrochemical device according to one of the preceding claims, the bottom wall of the container being provided with through openings (62, 63, 66) forming the passages for the supply and outlet gases of the stack and the electrical supply connections and, where appropriate, for measuring the electrical voltage at each interconnector, the container further housing, between the bottom wall and the lower end plate of the stack, a support frame (80) and a set (81) of seals supported by the frame and ensuring sealing around the passages for the supply and outlet gases of the stack and the electrical supply connections.

6. Electrochemical device according to claim 5, the support frame and the set of seals forming a single-piece sealing part (8), independent and housed in the container or pre-assembled with the stack, before housing the latter in the container.

7. Electrochemical device according to claim 5 or 6, gas supply and outlet tubes (64, 65) being assembled with the bottom wall opposite its passages, forming a gas supply and outlet manifold.

8. Electrochemical device according to one of claims 5 to 7, rods (24) forming the electrical power supply connections and where appropriate wires (25), preferably rigid, for measuring electrical voltage being integrated into the stack and passing through the bottom wall of the container.

9. Electrochemical device according to claim 8, each interconnector being made up of three thin flat sheets (210, 211, 212), pierced with holes and elongated along two mutually orthogonal axes of symmetry, the flat sheets being laminated and assembled together by welding, an electrical voltage measuring wire being connected, in particular by welding, to the central sheet.

10. Electrochemical device according to one of claims 5 to 9, the force distribution means being a block (5) bearing directly against the upper end plate of the stack and preferably incorporated into the glass matrix.

11. Electrochemical device according to claim 10, the block being in the form of a plate with a surface area enlarged relative to that of the stack so as to increase the path traveled in the glassy matrix by gas leaks likely to escape from the stack when operating at high temperature.

12. Electrochemical device according to claim 11, the lower edge (51) of the widened plate, preferably incorporated in the glassy matrix, having a frustoconical surface which widens from the upper end plate of the stack, so as to avoid the formation of pockets of gas from leaks.

13. Electrochemical device according to claim 11 or 12, the lateral edge of the enlarged plate, preferably incorporated in the glassy matrix, being a wall (52) which extends towards the interior of the glassy matrix, so as to contain towards the interior the gas leaks likely to escape from the stack in operation at high temperature.

14. Electrochemical device according to one of claims 10 to 13, the enlarged plate being pierced at its periphery with one or more through holes (53), the device comprising: - a cover (12) fixed in a sealed manner to the container and / or to the enlarged plate, delimiting with the latter a volume (VI) in fluid communication with the through hole(s) of the enlarged plate, the cover being pierced, preferably in its center, with a passage, - a tube (13) for supplying a gas called inerting gas, assembled with the cover opposite its passage, forming a collector for supplying inerting gas to the volume (VI) in which gas leaks likely to escape from the stack during operation at high temperature arrive through the through hole(s).

15. Electrochemical device according to one of claims 10 to 13, the enlarged plate being pierced at its periphery with one or more through holes (53), the device comprising: - a cover (16) fixed in a sealed manner to the container and / or to the enlarged plate, delimiting with the latter a volume (V2) in fluid communication with the through hole(s) of the enlarged plate, the cover being pierced, preferably in its center, with a passage, - a recovery tube (17) assembled with the cover opposite its passage, forming a collector for recovering gas leaks likely to escape from the stack during operation at high temperature which are recovered by the through hole(s).

16. Electrochemical device according to claim 15, the through hole(s) being closed by a filter.

17. Electrochemical device according to one of claims 10 to 16, the cover(s) being fixed to the container and / or to the enlarged plate by means of a plurality of bolts (14) with the interposition of at least one sealing gasket (15) between them.

18. Electrochemical device according to one of claims 10 to 17, the seal (15) being a flat or toric shaped seal or a glass-metal type connection suitable for guaranteeing sealing at the high operating temperature of the stack.

19. Electrochemical device according to one of claims 1 to 4, the bottom wall of the container being solid, the device further comprising a cover plate (9) arranged above the stack, preferably being incorporated in the glassy matrix, the cover plate being provided with through openings (90, 91, 92) forming the passages for the supply and outlet gases of the stack and the electrical supply connections and, where appropriate, electrical voltage measurement at each interconnector, the cover plate further forming a force distribution means.

20. Electrochemical device according to claim 19, gas supply and outlet tubes (93, 94) being assembled with the cover plate opposite its passages, forming a gas supply and outlet collector.

21. Electrochemical device according to claim 19 or 20, comprising as another force distribution means, a rod (10) in ball joint connection with the cover plate to achieve the compression clamping.

22. Method for producing an electrochemical device according to one of the preceding claims, comprising the following steps: a / housing the electrochemical stack with support against the bottom wall of the container, where appropriate with the interposition of the support frame and the set of seals supported by the frame; b / placing the force distributor means above the stack so as to apply the clamping force by compression of the stack; c / filling with the material(s) including at least the glassy matrix in the liquid state of the volume between the stack and the container at least up to the upper end plate, preferably with incorporation of the force distributor means.

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