Monobloc electrical conductor

Abstract

The main object of the invention is an electrical conductor (70) comprising: an assembly (72) including a main conductive core (74) made of a first metallic material and a sheath (79) covering the main conductive core (74) and made of a second metallic material, having an electrical resistivity higher than that of the first metallic material; a connecting tab (78) connected to a first end (72a) of the assembly (72), comprising a conductive core of the connecting tab and a protective housing for the connecting tab, characterized in that the connecting tab (78) is made at least in part of the second metallic material, and in that the conductive core of the connecting tab (73) and the main conductive core (74) are formed as a single unit. Figure 17

Description

Title of the invention: Monobloc electrical conductor technical field

[0001] The present invention relates to the general field of high temperature 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 high temperature co-electrolysis of water vapor and carbon dioxide (CO2).

[0002] More specifically, the invention relates to the field of high-temperature electrochemical devices, such as high-temperature solid oxide electrolyzers, usually designated by the acronym SOEC (for "Solid Oxide Electrolysis Cell" in English), and high-temperature solid oxide fuel cells, usually designated by the acronym SOFC (for "Solid Oxide Fuel Cells" in English), but also high-temperature steam co-electrolyzers with carbon dioxide, reversible fuel cell and high-temperature electrolyzer systems, or even so-called medium-temperature fuel cells or electrolyzers, on the order of 400°C, also called PCFCs for "Proton Ceramic Fuel Cell" in English.

[0003] Thus, more generally, the invention relates to the field of SOEC / SOFC type solid oxide cell stacks operating at high temperature. These stacks can operate at atmospheric pressure or even under negative pressure.

[0004] Beyond such stacks of SOEC / SOFC type solid oxide cells, the invention is relevant to any system where there is a need for electrical conduction in an oxidizing environment at high temperature or under conditions leading to the rapid degradation of electrically conductive materials.

[0005] More particularly, the invention relates to the supply of electric current to a stack of electrochemical cells in the hot zone. PREVIOUS STATE OF THE ART

[0006] In the context of a high-temperature solid oxide electrolyzer of the SOEC type, the aim is to transform, by means of an electric current, within the same electrochemical device, water vapor (H2O) into dihydrogen (H2), or other fuels such as methane (CH4), natural gas, biogas, and into dioxygen (O2), and / or to transform carbon dioxide (CO2) into carbon monoxide (CO) and dioxygen (O2). In the context of a solid oxide fuel cell In a high-temperature SOFC (solid oxide fuel cell), the operation is reversed to produce an electric current and heat when supplied with dihydrogen (H2) and dioxygen (O2), typically from air and natural gas, namely methane (CH4). For simplicity, the following description focuses on the operation of a high-temperature SOEC (solid oxide electrolyzer) performing steam electrolysis. However, this operation is applicable to the electrolysis of carbon dioxide (CO2), and even to the co-electrolysis of high-temperature steam (HTS) with carbon dioxide (CO2). Furthermore, this operation can be transposed to the case of a high-temperature SOFC.

[0007] As is known per se, a high-temperature steam (H2O) electrolyzer, or EVHT electrolyzer, comprises a stack of several elementary solid oxide electrochemical cells. With reference to [Fig. 1], a solid oxide cell 10, or "SOC" (Anglo-Saxon acronym "Solid Oxide Cell"), comprises in particular: a) a first porous conductive electrode 12, or "cathode", intended to be supplied with steam for the production of dihydrogen; b) a second porous conductive electrode 14, or "anode", through which the dioxygen (O2) produced by the electrolysis of the water injected onto the cathode escapes; and c) a solid oxide membrane (dense electrolyte) 16 sandwiched between the cathode 12 and the anode 14, the membrane 16 being anionically conductive at high temperatures, usually temperatures above 600°C.

[0008] By heating the cell 10 at least to this temperature and by injecting an electric current 1 at the anode 14, there then occurs a reduction of water on the cathode 12, which generates dihydrogen (H2) at the cathode 12 and dioxygen (O2) at the anode 14.

[0009] A stack 20 of such cells, designed to produce a significant quantity of hydrogen, is illustrated by the schematic view in [Fig. 2]. In particular, the cells 10 are stacked one on top of the other, separated by interconnecting plates 18 or interconnectors. These plates serve both to ensure electrical continuity between the different electrodes of the cells 10, thus enabling their electrical connection in series, and to distribute the various gases necessary for the operation of the cells, as well as, where applicable, a carrier gas to aid in the removal of electrolysis products and / or the thermal management of the stack.

[0010] To this end, the plates 18 are connected to a steam supply 22 for injecting this steam onto the cathodes of the cells 10 according to a constant steam flow rate DH2o regulated by a controllable valve 24. The plates 18 are also connected to a gas collector 26 for collecting the gases from electrolysis. An example of stacking and interconnecting plate structure are described for example in international application WO 2011 / 110676 Al.

[0011] For the effective implementation of electrolysis by the stack 20, the stack is brought to a temperature above 600°C, usually a temperature between 650°C and 900°C, the gas supply is started at a constant flow rate and an electrical power supply 28 is connected between two terminals 30, 32 of the stack 20 in order to make a current 1 flow through it.

[0012] The intensity 1 of the electric current is usually on the order of a few hundred amperes, which generates significant heat losses due to the Joule effect in the electrical conductors. To optimize the energy efficiency of solid oxide electrochemical systems, it is necessary to limit these heat losses by developing, in particular, specific electrical conductors, also referred to as "current supply rods" (or "bus bars").

[0013] A current-supplying rod in the stack is generally in the form of a metal rod. Taking the example of a cylindrical rod, the electrical resistance R is expressed by the following formula:

[0014] Rp.l

[0015] where p is the resistivity of the rod (in Qm), l is the length of the rod (in m) and 5 is the cross-section of the rod (in m2).

[0016] Since Joule effect losses are proportional to the resistance R, to limit this effect, it is therefore necessary to reduce the electrical resistance of the current supply rod. Possible optimizations therefore consist of:

[0017] - limit the length of the stem,

[0018] - increase its cross-section,

[0019] - find a material with lower resistivity and stable at high temperature.

[0020] The first two possibilities are geometric choices that generally depend on the shape of the electrochemical system. Therefore, there are constraints concerning them and / or prior art rods are already optimized with respect to the electrochemical system. The last point concerns the material constituting the rod, which must be chosen with minimal resistivity to reduce ohmic losses.

[0021] The optimization of this last point has not been sufficiently taken into consideration. Indeed, for all laboratory developments of the technology, energy efficiency is not paramount. On the other hand, as explained below, a current-carrying rod is immersed in a highly corrosive environment, so the standard solution implemented consists of using solid stainless alloy rods, which therefore constitute the reference solution in all international publications. If the resistivity at room temperature (20°C) of these rods is already high, on the order of 75.108 Qm, it should be noted that this resistivity increases sharply with temperature.

[0022] Thus, at 900°C, which is a high operating temperature of a solid oxide electrolyzer, the electrical resistance of a stainless steel rod is equal to 117 x 10⁸ Qm, which generates a very significant ohmic loss. These aspects were notably described in French patent application FR 3 036 840 A1.

[0023] However, if the aim is to optimize electrical resistivity, the material generally recommended for electrical conductors subjected to high electric current is copper. An experimental study carried out by the Applicant determined the resistivity curve of copper as a function of temperature and confirmed that choosing copper reduces ohmic losses by at least a factor of 10 compared to the reference material over the entire operating temperature range of solid oxide systems.

[0024] However, one of the major constraints that needs to be taken into consideration is the corrosion problem related to the stacking environment.

[0025] Referring to [Fig. 3], the stack 20 is indeed enclosed in a so-called "thermal" chamber, the temperature of which is maintained between 650 and 900°C under air purging, a conventional electrochemical system thus comprising:

[0026] - the EVHT 20 electrolyzer, for example that described in relation to Figures 1 and 2 and comprising a set of conduits 52, 54, 56, 58 for supplying and collecting gases from the anodes and cathodes of the electrochemical cells of the electrolyzer;

[0027] - an enclosure 60 in which the electrolyzer 20, the conduits 52, 54, 56, are housed 58 passing through a wall of the enclosure 60 for their connection to gas supply and collection circuits (not shown). The enclosure 60 also includes an air inlet duct 62 and an air outlet duct 64, the enclosure 60 being, for example, everywhere else airtight to gases and liquids. The duct 62 is suitable for connection to an air supply circuit (not shown) so as to apply air sweeping to the hot zone surrounding the electrolyzer 20, the sweeping air being discharged through the outlet duct 64; and

[0028] - two electrical conductors 66, 68 connected to terminals 30, 32 of the stack 20 and passing through enclosure 60 for their connection to the power source 28.

[0029] Under these conditions, two conductors 66, 68 in the form of copper rods, at least a portion of which is contained within the enclosure 60, will oxidize very rapidly. Furthermore, copper does not resist oxidation at high temperatures because the oxide formed on the surface is not sufficiently impermeable and adherent to protect the underlying metal. Materials known to resist oxidation at high temperatures are chromium and aluminum alloys such as stainless steels and nickel alloys. They are stainless because they form chromium and / or alumina, which are much more protective oxides. However, as mentioned above, these alloys have such high electrical resistivity that their use results in significant energy losses.

[0030] A high-temperature solid oxide fuel cell (SOFC) experiences similar problems. Indeed, an EVHT electrolyzer and an SOFC are identical structures, differing only in their operating mode. The electrolyzer operates in carbon dioxide (CO2) reduction mode or in co-electrolysis mode, that is, with a gas mixture at the cathodic inlet composed of water vapor (H2O) and carbon dioxide (CO2). The mixture at the cathodic outlet is then composed of hydrogen (H2), water vapor (H2O), carbon monoxide (CO), and carbon dioxide (CO2). Referring to [Fig.4], an electrochemical cell constituting an SOFC cell comprises the same elements (anode 12, cathode 14, electrolyte 16) as an electrolyzer cell, the cell of the cell however being supplied, with constant flow rates, on its anode by dihydrogen and on its cathode by dioxygen, and connected to a load C to deliver the electric current produced.Given the electric current produced, which is several amperes, the battery therefore experiences the same problems as the electrolyzer.

[0031] One solution would be to protect a copper rod (or any other metal deemed suitable in terms of electrical resistivity) with a coating to give it good oxidation resistance, for example, a chromium or alumina coating. This presents several problems. First, the coating's seal and adhesion to the copper substrate during heating must be guaranteed. It should be emphasized that copper has a high coefficient of thermal expansion, and strong differential thermal expansion stresses can occur and damage the coating and / or the re-coating / copper interface. Furthermore, at the hot end of the rod, an electrical connection to the stack must be made without exposing the copper. The connection must therefore be made on the coating without damaging it, which is technically difficult.

[0032] Another solution is to encase the copper rod in a sheath of oxidation-resistant material. In this way, the problem of resistance to differential thermal expansion stresses is solved since the two materials are not bonded. Such an assembly (copper + stainless steel sheath) is already known from the prior art for other application areas (e.g., a strong acid environment at low temperature, 50-80°C), notably from Chinese document CN 202608143 U, which describes a copper bar that is simply threaded into a steel tube. This type of conductor performs satisfactorily at low temperatures, but it has been observed that it is not suitable as is for solid oxide systems. Indeed, the The poor contact between the conductor and the sheath results, given the high temperature, in the deterioration of the electrical contact between the two materials and an increase in ohmic losses. In other words, there is no optimized electrical conduction system in the prior art suitable for high electric currents and capable of withstanding significant thermal cycling in an oxidizing environment.

[0033] French patent application FR 3 036 840 Al is known an electrical conductor suitable for currents of several hundred amperes, resistant to oxidation at high temperature and able to withstand thermal cycling up to 900°C. This electrical conductor comprises a rod made of a first metallic material and a sheath, completely covering the rod, made of a second metallic material, the two being welded to each other using hot isostatic compression (HIC).

[0034] More specifically, this application proposes to shape a rod composed of a copper core protected by a sheath of Inconel® 600 steel tubing, with a "whistle" made of Inconel® 600 steel which serves as the connection terminal, and a closing tip also made of Inconel® 600 steel through which a vacuum is drawn. These parts are assembled by TIG (Tungsten Inert Gas) arc welding. The resulting rod then undergoes a hot isostatic pressing (HIP) process, which allows for diffusion welding of the different materials without the addition of filler metal.

[0035] This solution, however, has a drawback. The copper core stops at the whistle, which is made of Inconel® 600. Consequently, the current must pass through a significant length of electrically inefficient material, thus increasing the electrical resistance of the current-carrying rod. Description of the invention

[0036] The invention aims to remedy at least partially the needs mentioned above and the disadvantages relating to the achievements of the prior art.

[0037] The invention thus relates, according to one of its aspects, to an electrical conductor comprising:

[0038] - an assembly comprising:

[0039] - a main conductive core made of a first metallic material,

[0040] - a sheath covering the main conductive core and consisting of a second metallic material, particularly stainless or refractory, with an electrical resistivity higher than the electrical resistivity of the first metallic material,

[0041] - a connecting tab attached to a first end of the assembly, including a conductive core for the connecting leg and a protective housing for the connecting leg,

[0042] characterized in that the connecting lug is constituted at least in part by the second metallic material, in particular the protective housing being made of the second metallic material, the conductive core of the connecting tab being made in particular of the first metallic material, and in that the conductive core of the connecting tab and the main conductive core are made in one piece.

[0043] The electrical conductor according to the invention may further comprise one or more of the following characteristics taken individually or in any possible technical combinations.

[0044] The electrical conductor may be a rigid electrical conductor. In particular, the main conductive core may be a rigid conductive core.

[0045] By "rigid" electrical conductor, we mean a conductor acting mechanically within a main connection and not necessarily connected to a stack, as opposed to a "flexible" electrical conductor used for connection to the stack, capable of preventing the transmission of vibrations, expansion, and other parasitic movements between the stack and its environment, and allowing for a possible electrical connection between stacks without mechanical transition. A rigid electrical conductor has sufficient rigidity to remain in place.

[0046] The electrical conductor may include a closing tip made at least partly of the second metallic material and connected to a second end of the assembly, the closing tip including in particular a central channel for vacuuming.

[0047] In addition, the sheath may include a tip, at the first end of the assembly, which comes into contact with the connecting tab.

[0048] The conductive core of the connecting tab can be inserted into the housing of the connecting tab, which is made at least partially of the second metallic material. The housing and the conductive core of the connecting tab can be drilled to form a passage accommodating a tube made at least partially of the second metallic material.

[0049] The main conductive core and the conductive core of the connecting tab, made of the first metallic material, may be made of copper, nickel, or silver and / or alloys of copper, nickel, or silver, or any other metal or alloy with good electrical conductivity. In particular, any other metal or alloy with good electrical conductivity that is sensitive to oxidation at high temperatures, on the order of 900°C, such as, for example, brass or bronze.

[0050] Furthermore, the sheath, the casing, the possible closing tip and the possible tube, made of the second metallic material, may be made of stainless or refractory metal and / or metallic or refractory alloys, in particular of stainless or refractory steel, for example nickel, chromium or cobalt based, especially Inconel®, for example Inconel® 600 or 625, or any other metal or alloy resistant to high temperature oxidation, for example 316L stainless steel.

[0051] In addition, the invention also relates, according to another of its aspects, to a method of manufacturing an electrical conductor as defined above, characterized in that it includes the step of manufacturing the conductive core of the connecting tab by forging or die-making.

[0052] The process may include the following steps:

[0053] - forging or die-casting one end of a metal rod, in particular of the shape cylindrical and circular in section, made of the first metallic material to form the conductive core of the connecting tab,

[0054] - rolling of the remaining part of the metal rod to form the conductive core main and thus obtain the main conductive core and the conductive core of the connecting leg formed in one piece made of the first metallic material.

[0055] The process may further include the following additional steps:

[0056] - insertion of the main conductive core into the sheath, including in particular a pre-machined end piece designed to be in contact with the connecting tab,

[0057] - insertion of the conductive core of the connecting leg into the leg housing connecting element, consisting at least in part of the second metallic material, notably obtained by stamping or bending,

[0058] - TIG welding (acronym for "Tungsten Inert Gas" in English) of the sheath and casing, especially around the entire circumference.

[0059] Furthermore, the process may include the following additional steps:

[0060] - drilling of the housing of the connecting leg and of the conductive core of the leg connection for obtaining a fixing passage,

[0061] - insertion of a tube made of the second metallic material into the passage and TIG welding of the tube to the housing

[0062] - attachment of a closing tip to the second end of the assembly.

[0063] The manufacturing process according to the invention may include the step of applying a Hot Isostatic Compression (HIC) diffusion welding cycle.

[0064] The Hot Isostatic Compression (HIC) diffusion welding cycle can be carried out under the following operating conditions:

[0065] - heat the assembly to a temperature between 600°C and 1060°C, preferably between 800°C and 1000°C, including a temperature of 920°C,

[0066] - apply a pressure of between 500 bar and 1500 bar to the sheath, Preference is given to pressures between 800 bar and 1200 bar, specifically a pressure of 1020 bar.

[0067] - apply a pressure and temperature plateau lasting 30 minutes to several hours, preferably 1 to 3 hours, especially 2 hours

[0068] - allow the assembly to cool down and depressurize.

[0069] Furthermore, the invention also relates, according to another aspect, to the use of at least one electrical conductor as defined above, as an electrical conductor of an electrochemical system comprising:

[0070] - an enclosure for air circulation within the volume delimited by it,

[0071] - an electrochemical device housed within the enclosure, comprising:

[0072] - a stack of solid oxides of the SOEC / SOFC type operating at high temperature temperature, of elementary electrochemical cells each comprising an electrolyte interposed between a cathode and an anode and connected in series between two electrical terminals, and

[0073] - said at least one electrical conductor connected to at least one of the two terminals electric.

[0074] Furthermore, the invention also relates, according to another aspect, to an electrochemical system comprising:

[0075] - an enclosure for air circulation within the volume delimited by it,

[0076] - an electrochemical device housed within the enclosure, comprising:

[0077] - a stack of solid oxides of the SOEC / SOFC type operating at high temperature temperature, of elementary electrochemical cells each comprising an electrolyte interposed between a cathode and an anode and connected in series between two electrical terminals, and

[0078] - at least one electrical conductor as defined above, connected to the minus one of the two electrical terminals. Brief description of the drawings

[0079] 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 accompanying drawing, in which:

[0080] [Fig.1] is a schematic view of an elementary electrochemical cell of an EVHT electrolyzer,

[0081] [Fig.2] is a schematic view of a cell stacking according to [Fig.1],

[0082] [Fig.3] is a schematic view of a system incorporating a stacking according to [Fig.2],

[0083] [Fig.4] is a schematic view of an electrochemical cell of a SOFC battery,

[0084] [Fig.5] is a schematic view of an electrical conductor according to the invention,

[0085] [Fig.6] is a schematic cross-sectional view along plane VLVI of [Fig.5], and

[0086] [Fig.7] to [Fig. 17] are perspective views illustrating steps in the process of manufacturing an electrical conductor according to the invention.

[0087] Throughout these figures, identical reference numerals may designate identical or similar elements.

[0088] Furthermore, the different parts represented in the figures are not necessarily shown on a uniform scale, in order to make the figures more legible.

[0089] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0090] Figures 1 to 4 have already been described previously in the part relating to the prior art and the technical context of the invention.

[0091] With reference to figures 5 and 6, an example of an electrical conductor 70 according to the invention is shown.

[0092] The electrical conductor 70 comprises an assembly 72 consisting of a main conductive core 74 in a first metallic material, here copper, inserted in a sheath 79, in a second metallic material, here stainless alloy, in particular Inconel® 600, to prevent oxidation of the first metallic material under penalty of having lowered electrical conductivity performance, exhibiting an electrical resistivity higher than the electrical resistivity of the first metallic material.

[0093] It should be noted that the main conductive core 74 is here made of copper, but the invention applies to other metals that are good electrical conductors but sensitive to oxidation, for example nickel, silver, brass, bronze and / or copper alloys, such as those hardened by dispersoids.

[0094] Furthermore, the electrical conductor 70 includes a connecting tab 78, comprising a protective housing 76 and a conductive core of the connecting tab 73 advantageously made of the first metallic material and connected to a first end 72a of the assembly 72. In order to ensure electrical continuity along its entire length, the conductive core of the connecting tab 73 and the main conductive core 74 are made in one piece. In other words, they form a single piece, here made of copper, so as to obtain a single-piece current conductor.

[0095] The connecting tab 78 hermetically seals the end 72a of the assembly 72, thus preventing the passage of gas. It provides an electrical connection terminal. It has a shape complementary to the electrolyzer plate to which the tab 78 is fixed for the electrical connection of the electrolyzer.

[0096] The shape or geometry of the connecting tab 78 can be the usual shape of a lug, as shown here, or any other different shape, for example cylindrical and intended to fit into a bore or clamped between two half-shells attached to the device to be powered.

[0097] Furthermore, the electrical conductor 70 also includes a closing tip 80 at the second end 72b of the assembly 72. This closing tip 80 allows the assembly 72 to be evacuated at its end 72b. It is by example made in the second metallic material, in particular in stainless alloy, for example in Inconel® 600. The tip 80 allows the end 72b of the assembly 72 to be hermetically sealed except for a central channel 84 which passes through it and which is intended to be in communication with a vacuum pulling tube.

[0098] The conductive core of the connecting leg 73 can advantageously be obtained by forging or by die-making, in particular from a round copper bar, for example of the CuCl type.

[0099] Forging is a technique for obtaining a mechanical part by applying significant force to a metal bar, either hot or cold, to force it into the desired shape. Forging involves a striking device, such as a hammer, sledgehammer, trip hammer, or drop hammer, and a support, such as an anvil or die. Forging does not allow for the same tolerances as machining, which limits its use to parts requiring high strength but low precision, such as bolts or tools. The resulting parts are more resistant to mechanical stresses because the deformation of the metals generates a large number of metallurgical phenomena, both microscopic and macroscopic. Among these phenomena is forging, which itself leads to the formation of grain in the metal.

[0100] Die forging, or die forging, consists of forming, by plastic deformation after heating, blanks made of alloys such as aluminum, copper, titanium, nickel, etc. Die forging of steels is called "stamping." Die forging is a forging operation performed using tools called dies, typically an upper half-die and a lower half-die. The dies then imprint the shape of the part.

[0101] Figures 7 to 17 illustrate, according to perspective views, steps in the manufacturing process of an electrical conductor 70 according to the invention.

[0102] Thus, [Fig. 7] illustrates a metal rod 90, made of the first metallic material, for example cylindrical in shape and circular in cross-section, here with a diameter of 14 mm. In particular, it is a copper rod of the CuCl type. This metal rod 90 is intended to form the conductive core of the connecting tab 73 and the main conductive core 74, which are made in one piece.

[0103] Starting from this metal rod 90, the volume of the conductive core of the connecting lug 73, produced by forging or, in this case, by die-casting, will depend on the volume of the rod 90 used. In order to obtain a typical volume, on the order of 6400 mm³ with a cross-section of 160 mm², the diameter of the rod 90 will have a cross-section equivalent to 160 mm², or a diameter of approximately 14 mm.

[0104] After a die-forging operation on the metal rod 90, a conductive core of the connecting lug 73 is obtained, here of parallelepiped shape in end of the metal rod 90.

[0105] A subsequent operation, illustrated in [Fig. 9], consists of rolling the remaining metal rod 90 to the desired diameter to obtain the main conductive core 74. The diameter is thus reduced from 14 mm to 10 mm to allow its subsequent insertion into the sheath 79, particularly in the form of an Inconel® 600 tube with a diameter of 10 / 12 mm. A clearance of between 0.4 and 0.6 mm is required between the inner diameter of the sheath 79 and the outer diameter of the main conductive core 74 obtained by rolling.

[0106] Rolling is a manufacturing process involving plastic deformation. It applies to various materials such as metal or any other material in a paste-like form such as paper or pasta. This deformation is notably achieved by continuous compression as the material passes between two counter-rotating cylinders called "rolling mills".

[0107] At this stage represented in [Fig.9], we have therefore obtained the one-piece part comprising the main conductive core 74 and the conductive core of the connecting leg 73, both made of copper.

[0108] In a subsequent step illustrated in [Fig.10], the sheath 79, here made of Inconel® 600 with a diameter of 12 / 10 mm, is introduced around the part formed of the main conductive core 74 and the conductive core of the connecting tab 73.

[0109] The end piece 77, shown in an enlarged view in [Fig.1 1], of the sheath 79 has been previously machined to obtain a shape intended to fit the heel of the conductive core of the connecting tab 73. This end piece 77 may, for example, have a parallelepiped shape, as seen in [Fig.1 1], but any other shape is possible.

[0110] Subsequently, as shown in [Fig.12], a housing for the connecting leg 76, here made of Inconel® 600, with a thickness of for example between 0.5 mm and 1 mm, previously manufactured, covers the conductive core of the connecting leg 73. This housing 76 is thus closed at one end and open at the other opposite end to allow the insertion of the conductive core of the connecting leg 73.

[0111] The housing 76 can be obtained by stamping or by bending. Advantageously, its thickness will be as thin as possible, while still allowing welding, in order to offer the least possible resistance to the electric current.

[0112] Deep drawing is a manufacturing technique that allows an object whose shape cannot be developed to be obtained from a flat, thin sheet of metal. This technique can be considered for the mass production of such housings 76.

[0113] At the first end 72a of the assembly 72 thus formed, the sheath 79 and the housing 76 are then welded by means of TIG welding over the entire circumference conference, represented by S in [Fig. 13], for example an orbital weld, with a filler material preferably composed of the second metallic material. In this way, the housing 76 is linked to the sheath 79, by means of TIG welding around its entire periphery, so as to make the joint airtight.

[0114] A drilling or boring is then carried out in the conductive core of the connecting lug 73 and the housing 76, as seen in [Fig. 14], to create a passage 91 for the bolt which will allow the current rod to be linked to the connecting lug of the stack.

[0115] Then, as illustrated in [Fig. 15], following the same logic of protecting the copper against oxidation, the passage 91 thus formed is lined with a tube 92, here made of stainless steel, specifically Inconel® 600, inserted into the passage 91. A TIG weld is then performed around the circumference of this tube 92 with the housing 76 on both sides, schematically represented by reference S in [Fig. 16]. The internal diameter of this tube 92 must allow the connecting bolt between the current rod and the stack connection lug to pass through.

[0116] Finally, as illustrated in [Fig. 17], the closing tip 80 is welded to the second end 72b of the assembly 72 to obtain the electrical conductor 70. The assembly 72 can then be evacuated via a tube added for this purpose. A degassing tube is then added to the end 72b, and the sheath 79 is evacuated by pumping through the tube. A swaging can then be performed to permanently maintain the vacuum, allowing the tube to be sealed airtight and permanently. This evacuation step can also be used to perform a leak test. The rod then undergoes a CIC (Hot Isostatic Compression) cycle as described in patent application FR 3 036 840 AL

[0117] The stainless alloy of the sheath 79, the housing 76, the tube 92 and the end cap 80 is chosen according to the thermal stresses to which the electrical conductor 70 is exposed. In particular, for a temperature range up to 900°C, they can be made of Inconel® 600. In addition, the cross-sections of these elements can be chosen according to requirements, for example in terms of current, voltage drop, etc.

[0118] The method for manufacturing such an electrical conductor 70, intended for use as an electrical conductor for supplying current in an electrochemical system, for example that of Figures 1 to 4, may further include, for example, one or more of the following steps:

[0119] - manufacture the parts described above (core, sheath, leg),

[0120] - cleaning of parts and in particular of surfaces intended to be welded, namely the electrical conduction surfaces and the surfaces necessary for sealing the electrical conductor, by means of a detergent and / or solvent, or any other means,

[0121] - radiography of welds to confirm the quality of welds at a point mechanical, electrical and sealing view.

[0122] By comparing, in Table 1 below, the resistance obtained for a main conductive core 74 made of 1 meter of copper with a diameter of 14 mm, the resistance of a reference whistle 78 made of Inconel® 600 (prior art design) and the resistance of a whistle 78 (conductive core of the connecting tab 73 and the housing 76) according to the invention, it can be seen that, at 800°C, the resistance of the reference whistle 78 represents approximately one-third of the complete current rod for a main conductive core of only 1 m. Switching to the version with a conductive core 73 + housing 76 of the whistle 78 reduces its resistance by a factor of 12 at 800°C and even by a factor of 41 at room temperature (20°C). Temperature (°C) Main conductor resistance 74 in copper (Q) Reference whistle resistance 78 in Inconel® 600 (Q) (8x20x38 mm) Whistle resistance 78 (conductive conductor 73 + casing 76) 0.5 mm thick invention (Q) Ratio between reference whistle resistance 78 and invention resistance 20 112.106 245.106 5.95.106 41 800 455.106 268.106 21.9.106 12

[0123] Table 1

[0124] For the results in Table 1, the resistivity of copper is 17.24 x 10⁹ Qm at cold temperatures (20°C) and 70 x 10⁹ Qm at 800°C. The resistivity of Inconel® 600 is 1.03 x 10⁶ Qm at cold temperatures (20°C) and 1.13 x 10⁶ Qm at 800°C.

[0125] The electrical conductor 70 obtained according to the principle of the invention is thus an electrical conductor adapted to the high temperature and high current of SOEC / SOFC type solid oxide cell stacks. It advantageously limits electrical losses at the connection lug(s) 78 by preventing any interruption of electrical continuity between the main conductive core 74 and a conductive core of the connection lug 73.

[0126] The invention can be applied to a high-temperature steam electrolyzer, to a high-temperature co-electrolyzer fed with a mixture of steam (H2O) and carbon dioxide (CO2), to a high-temperature solid oxide fuel cell, to a reversible system, fuel cell and high-temperature electrolyzer temperature, to the "medium temperature" battery or electrolyzer, i.e. 400°C, or PCFC for "Proton Ceramic Fuel Cell" in English, as described previously.

[0127] The invention applies to the systems described above operating at atmospheric pressure but also to systems under pressure.

[0128] Outside the technical field of solid oxide electrochemical systems, the invention applies to all fields for which there is a need for electrical conduction in an oxidizing environment at high temperature or under conditions leading to the rapid degradation of electrically conductive materials.

[0129] Of course, the invention is not limited to the embodiments just described. Various modifications can be made to them by a person skilled in the art.

Claims

Demands

1. An electrical conductor (70) comprising: - an assembly (72) including a main conductive core (74) made of a first metallic material, and a sheath (79) covering the main conductive core (74) and made of a second metallic material, having an electrical resistivity greater than the electrical resistivity of the first metallic material, - a connecting tab (78) connected to a first end (72a) of the assembly (72), comprising a conductive core of the connecting tab (73) and a protective housing for the connecting tab (76), characterized in that the connecting tab (78) is made at least in part by the second metallic material, in particular the protective housing (76) being made of the second metallic material, the conductive core of the connecting tab (73) being in particular made of the first metallic material,and in that the conductive core of the connecting lug (73) and the main conductive core (74) are made in one piece.

2. Conductor according to claim 1, characterized in that it comprises: - a closing tip (80) made at least in part by the second metallic material and connected to a second end (72b) of the assembly (72), the closing tip (80) comprising in particular a central channel (84).

3. Conductor according to claim 1 or 2, characterized in that the sheath (79) has an end piece (77), at the first end (72a) of the assembly (72), coming into contact with the connecting tab (78).

4. Conductor according to any one of the preceding claims, characterized in that the conductive core of the connecting leg (73) is inserted into the housing of the connecting leg (76) made at least in part of the second metallic material.

5. Conductor according to claim 4, characterized in that the housing (76) and the conductive core of the connecting tab (73) are drilled to form a passage (91) housing a tube (92) made at least in part by the second metallic material.

6. Conductor according to any one of the preceding claims, characterized in that the main conductive core (74) and the connecting tab (78) are made of copper, nickel or silver and / or of copper, nickel or silver alloys.

7. Conductor according to any one of the preceding claims, characterized in that the sheath (79) is made of stainless or refractory metal and / or metallic or refractory alloys, in particular stainless or refractory steel.

8. A method for manufacturing an electrical conductor (70) according to any one of the preceding claims, characterized in that it comprises the step of manufacturing the conductive core of the connecting tab (73) by forging or die-casting.

9. A method according to claim 8, characterized in that it comprises the following steps: - forging or die-casting one end of a metal rod (90), in particular of cylindrical shape and circular cross-section, made of the first metallic material to form the conductive core of the connecting tab (73), - rolling the remaining part of the metal rod (90) to form the main conductive core (74) and thus obtain the main conductive core (74) and the connecting tab (78) formed in one piece made of the first metallic material.

10. The method according to claim 9, characterized in that it comprises the following additional steps: - insertion of the main conductive core (74) into the sheath (79), including in particular a previously machined end piece (77) intended to be in contact with the connecting tab (78), - insertion of the conductive core of the connecting tab (73) into the housing of the connecting tab (76), made at least in part of the second metallic material, in particular obtained by stamping or bending, - TIG welding of the sheath (79) and the housing (76).

11. The method according to claim 10, characterized in that it comprises the following additional steps: - drilling the housing of the connecting tab (76) and the conductive core of the connecting tab (73) to obtain a fixing passage (91), - insertion of a tube (92) made of the second metallic material into the passage (91) and TIG welding of the tube (92) to the housing (76), - fixing of a closing end cap (80) to the second end (72b) of the set (72).

12. A method according to any one of claims 8 to 11, characterized in that it comprises the step of applying a Hot Isostatic Compression (HIC) diffusion welding cycle.

13. The method according to claim 12, characterized in that the Hot Isostatic Compression (HIC) diffusion welding cycle is carried out with the following operating conditions: - bringing the assembly (72) to a temperature between 600°C and 1060°C, preferably between 800°C and 1000°C, in particular a temperature of 920°C, - applying a pressure between 500 bar and 1500 bar to the sheath (79), preferably between 800 bar and 1200 bar, in particular a pressure of 1020 bar, - applying a pressure and temperature plateau for a period of 30 minutes to several hours, preferably 1 hour to 3 hours, in particular 2 hours, - allowing the assembly to cool and depressurize.

14. Use of at least one electrical conductor (70) according to any one of claims 1 to 7, as an electrical conductor of an electrochemical system comprising: - an enclosure (60) for the circulation of air in the volume delimited thereby, - an electrochemical device housed in the enclosure (60), comprising: - a stack (20), of SOEC / SOFC type solid oxides operating at high temperature, of elementary electrochemical cells (10) each comprising an electrolyte (16) intercalated between a cathode (12) and an anode (14) and connected in series between two electrical terminals (30, 32), and - said at least one electrical conductor (70) connected to at least one of the two electrical terminals (30, 32).

15. Electrochemical system comprising: - an enclosure (60) for air circulation within the volume delimited thereby, - an electrochemical device housed within the enclosure (60), comprising: - a stack (20), of SOEC / SOFC type solid oxides operating at high temperature, of elementary electrochemical cells (10) each comprising an electrolyte (16) interposed between a cathode (12) and an anode (14) and connected in series between two terminals electric (30, 32), and - at least one electrical conductor (70) according to any one of claims 1 to 7, connected to at least one of the two electrical terminals (30, 32).

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