WO2024121490A1

WO2024121490A1 - One-piece electrical conductor

Info

Publication number: WO2024121490A1
Application number: PCT/FR2023/051895
Authority: WO
Inventors: Michel Planque; Simon ALAMOME
Original assignee: Commissariat A L'energie Atomique Et Aux Energies Alternatives
Priority date: 2022-12-05
Filing date: 2023-12-01
Publication date: 2024-06-13
Also published as: FR3142768A1

Abstract

The main subject matter of the invention is an electrical conductor (70) comprising: an assembly (72) comprising a main conductive core (74) made of a first metal material and a sheath (79) covering the main conductive core (74) made of a second metal material, the electrical resistivity of which is higher than the electrical resistivity of the first metal material; a connection tab (78) connected to a first end (72a) of the assembly (72) comprising a conductive core of the connection tab and a housing for protecting the connection tab, characterised in that the connection tab (78) is at least partially made of the second metal material and in that the conductive core of the connection tab (73) and the main conductive core (74) are formed of one piece.

Description

DESCRIPTION

Title: One-piece electrical conductor

TECHNICAL AREA

The present invention relates to the general field of high temperature electrolysis (EHT), in particular the electrolysis of water vapor at high temperature (EVHT), respectively designated by the English names “High Temperature Electrolysis” (HTE). ) and “High Temperature Steam Electrolysis” (HTSE), the electrolysis of carbon dioxide (CO2), or even the co-electrolysis of water vapor and carbon dioxide (CO2) at high temperature.

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 batteries. solid oxide fuel cells at high temperature, usually referred to by the acronym SOFC (for “Solid Oxide Fuel Cells” in English), but also co-electrolyzers of water vapor at high temperature with carbon dioxide, reversible fuel cell and high temperature electrolyser systems, or even so-called medium temperature batteries or electrolysers, of the order of 400°C, also called PCFC for “Proton Ceramic Fuel Cell” in English.

Thus, more generally, the invention refers to the field of stacks of solid oxide cells of the SOEC/SOFC type operating at high temperature. These stacks can operate at atmospheric pressure or even under pressure.

Beyond such stacks of solid oxide cells of the SOEC/SOFC type, the invention concerns any system where a need exists for electrical conduction in an oxidizing medium at high temperature or in conditions leading to the rapid degradation of conductive materials. electricity.

More particularly, the invention relates to the supply of electric current to a stack of electrochemical cells in the hot zone. STATE OF PRIOR ART

In the context of a high temperature solid oxide electrolyzer of the SOEC type, it involves transforming, through 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 dioxygen (O2), and/or to transform carbon dioxide (CO2) into carbon monoxide ( CO) and dioxygen (O2). In the context of a high temperature solid oxide fuel cell of the SOFC type, the operation is reversed to produce an electric current and heat by being supplied with dihydrogen (H2) and dioxygen (O2), typically in air and natural gas, namely methane (CH4). For the sake of simplicity, the following description favors the operation of a high temperature solid oxide electrolyzer of the SOEC type carrying out the electrolysis of water vapor. However, this operation is applicable to the electrolysis of carbon dioxide (CO2), or even the co-electrolysis of high temperature water vapor (EVHT) with carbon dioxide (CO2). Furthermore, this operation can be transposed to the case of a high temperature solid oxide fuel cell of the SOFC type.

As is known per se, a high temperature water vapor (H2O) electrolyzer, or EVHT electrolyzer, comprises a stack of several elementary solid oxide electrochemical cells. Referring to Figure 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 water vapor for the production of hydrogen; 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 for high temperatures, usually temperatures above 600°C.

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

A stack 20 of such cells, or "stack", intended to produce a significant quantity of hydrogen, is illustrated by the schematic view of Figure 2. In particular, the cells 10 are stacked on top of each other while being separated by interconnection plates 18 or interconnectors. These plates have the function of both ensuring electrical continuity between the different electrodes of the cells 10, thus allowing them to be put in electrical series, and of distributing the different gases necessary for the functioning of the cells, as well as the case where appropriate a carrier gas to help evacuate the electrolysis products and/or thermal management of the stack.

To do this, the plates 18 are connected to a water vapor supply 22 for the injection of this steam onto the cathodes of the cells 10 in accordance with a constant flow rate of DH2O water vapor regulated by a controllable valve 24. The plates 18 are also connected to a gas collector 26 for collecting gases resulting from electrolysis. An example of stacking and interconnection plate structure are for example described in international application WO 2011/110676 Al.

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 switched on. in operation at constant flow rate and an electrical power source 28 is connected between two terminals 30, 32 of the stack 20 in order to circulate a current /.

The intensity/of the electric current is usually of the order of a few hundred amperes, which generates significant thermal losses by Joule effect in the electrical conductors. To optimize the energy efficiency of solid oxide electrochemical systems, it is necessary to limit these thermal losses by developing electrical conductors in particular, also referred to by the expression “current supply rods” (or even “bus-bars”). ), specific. A current supply 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:

where p is the resistivity of the rod (in Qm), l is the length of the rod (in m) and S is the section of the rod (in m ² ).

The Joule effect losses being proportional to the resistance R, to limit this effect, it is therefore necessary to reduce the electrical resistance of the current supply rod. The possible optimizations therefore consist of:

- limit the length of the rod,

- increase its section,

- find a material with lower resistivity and stable at high temperatures.

The first two possibilities are geometry choices that generally depend on the shape of the electrochemical system. There are therefore constraints concerning them and/or the rods of the state of the art are already optimized with respect to the electrochemical system. The last point concerns the material constituting the rod which must be chosen with minimum resistivity to reduce ohmic losses.

The optimization of this last point has not been sufficiently taken into consideration. Indeed, for all laboratory developments in technology, energy efficiency is not paramount. On the other hand, as explained below, a current supply rod is immersed in a very corrosive environment, so that 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, of the order of 75.10 ^-8 Qm, you should know that this resistivity increases sharply with temperature.

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. 10 ^-8 Qm, which generates a very significant ohmic loss. These aspects have been described in particular in French patent application FR 3 036 840 Al.

However, if we seek to optimize electrical resistivity, the material generally recommended for electrical conductors subjected to a high intensity of electrical current is copper. An experimental study carried out by the Applicant made it possible to determine the resistivity curve of copper as a function of temperature and to confirm that the choice of copper makes it possible to reduce the ohmic losses by at least a factor of 10 compared to the reference material over all the operating temperature range of solid oxide systems.

However, one of the strong constraints that must be taken into consideration is the problem of corrosion linked to the stack environment.

Referring to Figure 3, the stack 20 is in fact enclosed in a so-called “thermal” enclosure, the temperature of which is maintained between 650 and 900°C under air sweeping, a classic electrochemical system thus comprising:

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

- an enclosure 60 in which the electrolyser 20 is housed, the pipes 52, 54, 56, 58 passing through a wall of the enclosure 60 for their connection to supply and gas collection circuits (not shown). The enclosure 60 also includes an air inlet pipe 62, and an air outlet pipe 64, the enclosure 60 being for example everywhere else hermetic to gases and liquids. The pipe 62 is capable of being connected to an air supply circuit (not shown) so as to apply an air sweep of the hot zone surrounding the electrolyser 20, the sweeping air being evacuated by the pipe output 64; And

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

Under these conditions, two conductors 66, 68 in the form of a copper rod, at least part of which is included in the enclosure 60, will oxidize very quickly. In Additionally, copper does not resist oxidation at high temperatures because the oxide formed on the surface is not sufficiently waterproof and adherent to protect the underlying metal. Materials known to resist oxidation at high temperatures are chromino and alumino forming alloys such as stainless steels and stainless nickel alloys as these form chromine and/or alumina which are oxides much more protective. However, as said above, these alloys have an electrical resistivity such that their use results in significant energy losses.

A high-temperature solid oxide fuel cell (SOFC) has similar problems. Indeed, an EVHT electrolyser and a SOFC cell are identical structures, only their mode of operation being different, the electrolyser operating in carbon dioxide (CO2) reduction mode or even in co-electrolysis mode, i.e. say with a mixture of gases at the cathode input composed of water vapor (H2O) and carbon dioxide (CO2). The mixture at the cathode output is then composed of hydrogen (H2), water vapor (H2O), carbon monoxide (CO) and carbon dioxide (CO2). Referring to Figure 4, an electrochemical cell constituting a SOFC battery comprises the same elements (anode 12, cathode 14, electrolyte 16) as an electrolyzer cell, the cell of the battery being however powered, with constant flow rates, on its anode with dihydrogen and on its cathode with dioxygen, and connected to a load C to deliver the electric current produced. Considering the electric current produced, of several amperes, the battery therefore experiences the same problems as the electrolyser.

One solution would be to protect a copper rod (or any other metal deemed appropriate in terms of electrical resistivity) with a coating to give it good resistance to oxidation, for example a chromine or alumina coating. This poses several problems. First of all, it is necessary to guarantee the waterproofness of the coating and its resistance to the copper substrate during heating. It should be noted that since copper has a high coefficient of thermal expansion, strong differential thermal expansion stresses can appear and damage the coating and/or the coating/copper interface. Additionally, at the hot end of the rod it is necessary to carry out an electrical connection with the stack without exposing the copper. The connection must therefore be made on the covering, without damaging it, which is technically difficult.

Another solution is to coat 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 united. Such an assembly (copper + stainless sheath) is already known from the state of the art for other fields of application (e.g. a strong acid environment at low temperature, 50-80°C), in particular from the Chinese document CN 202608143 U which describes a copper bar which is simply threaded into a steel tube. This type of conductor is satisfactory at low temperatures and with low temperature, but it has been observed that it is not suitable as it is for solid oxide systems. Indeed, the weak contact between the conductive core 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 state of the art adapted to a strong electric current and supporting significant thermal cycling in an oxidizing environment.

We know from patent application FR 3 036 840 Al an electrical conductor suitable for currents of several hundred amperes, resistant to oxidation at high temperatures and supporting 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 (CIC ).

More precisely, this request proposes to shape a rod composed of a copper round core protected by a sheath in Inconel® 600 type steel tube, with a part called a “whistle” in Inconel® 600 type steel. which is the connection terminal, and a closing end also made of Inconel® 600 type steel through which the vacuum is drawn. The assembly of these parts is done by TIG type arc welding (for “Tungsten Inert Gas” in English). The cane obtained then passes through a hot isostatic compression (CIC) process, which allows, without adding filler metal, to carry out diffusion welding of the different materials together. This solution, however, has a drawback. In fact, the copper core stops at the level of the whistle, which is made of Inconel® 600. Consequently, the current must pass through a significant length of material that is not very electrically conductive, which increases the electrical resistance of the cane. current supply.

STATEMENT OF THE INVENTION

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

The subject of the invention is, according to one of its aspects, an electrical conductor, comprising:

- a set including:

- a main conductive core made of a first metallic material,

- a sheath covering the main conductive core and made up of a second metallic material, in particular stainless or refractory, of electrical resistivity greater than the electrical resistivity of the first metallic material,

- a connection tab connected to a first end of the assembly, comprising a conductive core of the connection tab and a protective housing of the connection tab, characterized in that the connection tab is constituted at least in part by the second metallic material, in particular the protective casing being constituted by the second metallic material, the conductive core of the connection tab being in particular constituted by the first metallic material, and in that the conductive core of the connection tab and the main conductive core are made in one piece.

The electrical conductor according to the invention may also include one or more of the following characteristics taken individually or in any possible technical combination.

The electrical conductor may be a rigid electrical conductor. In particular, the main conductive core may be a rigid conductive core. By “rigid” electrical conductor is meant 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 avoiding the transmission of vibrations, expansions and other parasitic movements between the stack and its environment and making it possible to make a possible electrical connection between stacks without mechanical transition. A rigid electrical conductor has sufficient rigidity to hold itself in place.

The electrical conductor may include a closure end piece constituted at least in part by the second metallic material and connected to a second end of the assembly, the closure end piece comprising in particular a central channel for vacuum extraction.

In addition, the sheath may include an end piece, at the first end of the assembly, coming into contact with the connection tab.

The conductive core of the connection tab can be inserted into the housing of the connection tab constituted at least in part by the second metallic material. The housing and the conductive core of the connection tab can be pierced to form a passage housing a tube constituted at least in part by the second metallic material.

The main conductive core and the conductive core of the connection 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 that is a good electrical conductor. In particular, any other metal or alloy that is a good electrical conductor sensitive to oxidation at high temperatures, of the order of 900°C, such as for example brass or bronze.

In addition, the sheath, the housing, the possible closure end piece and the possible tube, made of the second metallic material, can be made of stainless or refractory metal and/or of metallic or refractory alloys, in particular stainless steel or refractory, for example based on nickel, chromium or cobalt, in particular Inconel®, for example Inconel® 600 or 625, or any other metal or alloy resistant to oxidation at high temperatures, for example 316L stainless steel. Furthermore, 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 comprises the step of manufacturing the conductive core of the connection tab by forging or stamping.

The process may include the following steps:

- forging or stamping of one end of a metal rod, in particular of cylindrical shape and circular section, made of the first metallic material to form the conductive core of the connection tab,

- rolling the remaining part of the metal rod to form the main conductive core and thus obtain the main conductive core and the conductive core of the connection tab formed in one piece made of the first metallic material.

The process may also include the following additional steps:

- insertion of the main conductive core into the sheath, including in particular a previously machined endpiece intended to be in contact with the connection tab,

- insertion of the conductive core of the connection tab into the housing of the connection tab, made at least partly of the second metallic material, in particular obtained by stamping or folding,

- TIG welding (acronym for “Tungsten Inert Gas” in English) of the sheath and the housing, in particular over the entire circumference.

In addition, the process may include the following additional steps:

- drilling the housing of the connection tab and the conductive core of the connection tab to obtain a fixing passage,

- insertion of a tube made of the second metallic material in the passage and welding by TIG welding of the tube with the housing,

- fixing a closure end at the second end of the assembly.

The manufacturing process according to the invention may include the step of applying a diffusion welding cycle by Hot Isostatic Compression (CIC). The Hot Isostatic Compression (HIC) diffusion welding cycle can be carried out with the following operating conditions:

- bring the assembly to a temperature between 600°C and 1060°C, preferably between 800°C and 1000°C, in particular a temperature of 920°C,

- apply to the sheath a pressure of between 500 bars and 1500 bars, preferably between 800 bars and 1200 bars, in particular a pressure of 1020 bars,

- apply a pressure and temperature level lasting from 30 minutes to several hours, preferably 1 hour to 3 hours, especially 2 hours,

- let everything cool and depressurize.

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

- an enclosure for the circulation of air in the volume delimited by it,

- an electrochemical device housed in the enclosure, comprising:

- a stack, with solid oxides of the SOEC/SOFC type operating at high 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

- said at least one electrical conductor connected to at least one of the two electrical terminals.

Furthermore, the invention also relates, according to another of its aspects, to an electrochemical system comprising:

- an enclosure for the circulation of air in the volume delimited by it,

- an electrochemical device housed in the enclosure, comprising:

- at least one electrical conductor as defined previously, connected to at least one of the two electrical terminals. BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood on reading the detailed description which follows, non-limiting examples of its implementation, as well as on examining the schematic and partial figures of the appended drawing, on which :

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

[Fig. 2] is a schematic view of a stack of cells according to [Fig. 1],

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

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

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

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

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

In all of these figures, identical references can designate identical or similar elements.

Furthermore, the different parts represented in the figures are not necessarily on a uniform scale, to make the figures more readable.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

Figures 1 to 4 have already been described previously in the section relating to the state of the prior art and the technical context of the invention.

With reference to Figures 5 and 6, an example of electrical conductor 70 according to the invention is shown.

The electrical conductor 70 comprises an assembly 72 composed of a main conductive core 74 made of a first metallic material, here copper, inserted in a sheath 79, made of a second metallic material, here a stainless alloy, in particular Inconel® 600, for prevent the oxidation of the first metallic material otherwise to have lowered electrical conductivity performance, having an electrical resistivity greater than the electrical resistivity of the first metallic material.

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.

In addition, the electrical conductor 70 comprises a connection tab 78, comprising a protective housing 76 and a conductive core of the connection tab 73 advantageously made of the first metallic material and connected to a first end 72a of the assembly 72. In order to to guarantee electrical continuity, especially the length, the conductive core of the connection tab 73 and the main conductive core 74 are made in one piece. In other words, they form only one piece, here in copper, so as to obtain a one-piece current rod.

The connection tab 78 hermetically obstructs the end 72a of the assembly 72, and thus prevents the passage of gas. It allows you to create an electrical connection terminal. It has a complementary shape to the plate of the electrolyzer on which the tab 78 is fixed for the electrical connection of the electrolyzer.

The shape or geometry of the connection tab 78 can be the usual shape of a lug, as shown here, or any other different shape, for example cylindrical and intended to enter a drilling or clamped between two half-shells secured to the device to feed.

Furthermore, the electrical conductor 70 also includes a closure end 80 at the second end 72b of the assembly 72. This closure end 80 makes it possible to draw the assembly 72 to the level of its end 72b. It is for example made of the second metallic material, in particular a stainless alloy, for example Inconel® 600. The end piece 80 makes it possible to hermetically obstruct the end 72b of the assembly 72 apart from a central channel 84 which passes through it on either side. part and which is intended to be in communication with a vacuum tube. The conductive core of the connection tab 73 can advantageously be obtained by forging or by stamping, in particular from a round copper bar, for example of the CuCl type.

Forging is a technique for obtaining a mechanical part by applying a significant force to a metal bar, cold or hot, in order to force it to conform to the desired shape. Forging involves a striking device, such as hammer, sledgehammer, flogger or sledgehammer, and a support, such as anvil or die. Forging does not allow the same tolerance margins to be obtained as machining, which reserves it for parts requiring high strength but low precision such as bolts or tools. The parts obtained are more resistant to mechanical stress because the deformation of metals generates a large number of metallurgical phenomena, both at the microscopic and macroscopic level. Among these phenomena, we find in particular wrought, which itself is at the origin of the fibering of the metal.

Forging, or forging by forging, consists of forming by plastic deformation after heating raw parts made of alloys such as aluminum, copper, titanium, nickel alloys, etc. The stamping of steels is called “stamping”. Forging is a forging operation carried out using tools called dies, typically an upper half-die and a lower half-die. The dies then bear the shape of the part.

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

Thus, Figure 7 illustrates a metal rod 90, made of the first metallic material, for example of cylindrical shape and circular section, here with a diameter of 14 mm. It is in particular a copper round of the CuCl type. This metal rod 90 is intended to form the conductive core of the connection tab 73 and the main conductive core 74 made in one piece.

Starting from this metal rod 90, the volume of the conductive core of the connection tab 73, produced by forging or here by stamping, will depend on the volume of the rod 90 used. In order to obtain a usual volume, i.e. of the order of 6400 mm ³ with a section of 160 mm ² , the diameter of the rod 90 will have a section equivalent to 160 mm ² , i.e. a diameter of around 14 mm.

After stamping operation on the metal rod 90, we then obtain a conductive core of the connection tab 73, here of parallelepiped shape at the end of the metal rod 90.

A following operation, illustrated in Figure 9, then consists of bringing the remainder of the metal rod 90 to the desired diameter by rolling in order to obtain the main conductive core 74. We then go from a diameter of 14 mm to a diameter of 10 mm so as to subsequently allow its introduction into the sheath 79, in particular in the form of an Inconel® 600 tube with a diameter of 10/12. Between 4 and 6/ ^10th of clearance will be required between the internal diameter of the sheath 79 and the external diameter of the main conductive core 74 obtained by rolling.

Rolling is a manufacturing process by plastic deformation. It concerns different materials such as metal or any other material in pasty form such as paper or pasta. This deformation is notably obtained by continuous compression passing between two contra-rotating cylinders called “rolling mills”.

At this stage shown in Figure 9, we have therefore obtained the one-piece part comprising the main conductive core 74 and the conductive core of the connection tab 73, both made of copper.

In a following step illustrated in Figure 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 connection tab 73.

The end piece 77, shown in an enlarged view in Figure 11, of the sheath 79 has been previously machined in order to obtain a shape intended to match the heel of the conductive core of the connection tab 73. This end piece 77 can for example present a parallelepiped shape, as visible in Figure 11, but any other shape is possible.

Subsequently, as shown in Figure 12, a housing of the connection tab 76, here in Inconel® 600, whose thickness is for example between 0.5 mm and 1 mm, previously manufactured, comes to cover the conductive core of the tab connection 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 connection tab 73.

The housing 76 can be obtained by stamping, or by folding. Advantageously, its thickness will be as thin as possible, while allowing welding, in order to oppose the electric current with as little resistance as possible.

Stamping is a manufacturing technique that makes it possible to obtain, from a sheet of flat, thin sheet metal, an object whose shape cannot be developed. This technique can be considered for mass production of such boxes 76.

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, represented by S in FIG. 13, for example a weld orbital, with a contribution of material preferably composed of the second metallic material. In this way, the housing 76 is linked to the sheath 79, thanks to TIG welding over the entire periphery, so as to make the junction hermetic.

A drilling or reaming is then made in the conductive core of the connection lug 73 and the housing 76, as visible in Figure 14, to create a passage 91 for the bolt which will allow the current rod to be connected to the lug. connection of the stack.

Then, as illustrated in Figure 15, in the same logic of protecting the copper against oxidation, the passage 91 thus formed is lined using a tube 92, here made of stainless steel, in particular Inconel® 600, introduced into passage 91. TIG welding is then carried out around the perimeter of this tube 92 with the housing 76 on both faces, schematized by the reference S in Figure 16. The internal diameter of this tube 92 must make it possible to allow the connecting bolt to pass between the current rod and the stack connection tab.

Finally, as illustrated in Figure 17, the closure end 80 is attached by welding to the second end 72b of the assembly 72 to obtain the electrical conductor 70. It is thus possible to vacuum the assembly 72 by the through a tube added for this purpose. A degassing tube is then added to the end 72b and the evacuation of the sheath 79 is carried out by pumping via the tube. A tailing can then be carried out in order to permanently maintain the vacuum, making it possible to close the tube in a manner airtight and definitive. Such a vacuum step can also make it possible to carry out a tightness check. The cane then undergoes a CIC (Hot Isostatic Compression) cycle as described in patent application FR 3 036 840 Al.

The stainless alloy of the sheath 79, the housing 76, the tube 92 and the closure end 80 is chosen according to the thermal constraints 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 sections of these elements can be chosen according to needs, for example in terms of current, voltage drop, etc.

The method of manufacturing such an electrical conductor 70, intended to be used as an electrical conductor for supplying a current in an electrochemical system, for example that of Figures 1 to 4, may further comprise for example a or more of the following steps:

- manufacture the parts previously described (core, sheath, tab),

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

- x-ray of the welds in order to confirm the quality of the welds from a mechanical, electrical and sealing point of view.

By comparing, in Table 1 below, the resistance obtained for a main conductive core 74 in copper of 1 m and diameter 14 mm, the resistance of a reference whistle 78 in Inconel® 600 (made according to the prior art) and the resistance of a whistle 78 (conductive core of the connection tab 73 and the housing 76) according to the invention, we see that, at 800°C, the resistance of the reference whistle 78 represents approximately a third of the complete current rod for a main conductive core of only 1 m. Switching to the conductive core 73 + housing 76 version of the whistle 78 makes it possible to reduce its resistance by a factor of 12 at 800°C and even by a factor of 41 at room temperature (20°C).

Table 1

For the results in this Table 1, the resistivity of copper is 17.24.10 ^-9 Qm at cold (20°C) and 70.10 ^-9 Qm at 800°C. The resistivity of Inconel® 600 is 1.03.10 ^-6 Qm at cold (20°C) and 1.13.10' ⁶ Qm at 800°C.

The electrical conductor 70 obtained according to the principle of the invention is thus an electrical conductor adapted to the high temperature and the high current of stacks of solid oxide cells of the SOEC/SOFC type. It advantageously makes it possible to limit electrical losses at the level of the connection tab(s) 78 by avoiding any phenomenon of interruption of electrical continuity between the main conductive core 74 and a conductive core of the connection tab 73.

The invention can be applied to a high temperature water vapor electrolyzer, to a high temperature co-electrolyzer supplied with a mixture of water vapor (H2O) and carbon dioxide (CO2), to a fuel cell with solid oxides at high temperature, with a reversible system, fuel cell and high temperature electrolyzer, with “medium temperature” battery or electrolyzer, i.e. 400°C, or even PCFC for “Proton Ceramic Fuel Cell” in English, as described previously.

The invention applies to the systems previously described operating at atmospheric pressure but also to systems under pressure.

Outside the technical field of electrochemical systems with solid oxides, the invention applies to all fields for which there is a need for electrical conduction in an oxidizing medium at high temperature or in conditions leading to the rapid degradation of conductive materials. electricity. Of course, the invention is not limited to the embodiments which have just been described. Various modifications can be made there by those skilled in the art.

Claims

1. Electrical conductor (70) comprising:

- an assembly (72) comprising 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, of greater electrical resistivity to the electrical resistivity of the first metallic material,

- a connection tab (78) connected to a first end (72a) of the assembly (72), comprising a conductive core of the connection tab

(73) and a protective housing for the connection tab (76), characterized in that the connection tab (78) is constituted at least in part by the second metallic material, in particular the protective housing (76) being constituted by the second metallic material, the conductive core of the connection tab (73) being in particular constituted by the first metallic material, and in that the conductive core of the connection tab (73) and the main conductive core

(74) are made in one piece.

2. Conductor according to claim 1, characterized in that it comprises:

- a closure tip (80) constituted at least in part by the second metallic material and connected to a second end (72b) of the assembly (72), the closure tip (80) comprising in particular a central channel (84 ).

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

4. Conductor according to one of the preceding claims, characterized in that the conductive core of the connection tab (73) is inserted in the housing of the connection tab (76) constituted at least in part by the second metallic material . 5. Conductor according to claim 4, characterized in that the housing (76) and the conductive core of the connection tab (73) are pierced to form a passage (91) housing a tube (92) constituted 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 connection tab (78) are made of copper, nickel or silver and/or alloys of copper, nickel or silver.

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 of metal or refractory alloys, in particular stainless or refractory steel.

8. Method of 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 connection tab (73) by forging or stamping.

9. Method according to claim 8, characterized in that it comprises the following steps:

- forging or stamping of one end of a metal rod (90), in particular of cylindrical shape and circular section, made of the first metallic material to form the conductive core of the connection tab (73),

- rolling of 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 connection tab (78) formed in one piece made of the first metallic material.

10. 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), comprising in particular a previously machined end piece (77) intended to be in contact with the connection tab (78),

- insertion of the conductive core of the connection tab (73) into the housing of the connection tab (76), made at least partly of the second metallic material, in particular obtained by stamping or folding,

- TIG welding of the sheath (79) and the housing (76).

11. Method according to claim 10, characterized in that it comprises the following additional steps:

- drilling the housing of the connection tab (76) and the conductive core of the connection tab (73) to obtain a fixing passage (91),

- insertion of a tube (92) made of the second metallic material in the passage (91) and TIG welding of the tube (92) with the housing (76),

- fixing a closure end (80) to the second end (72b) of the assembly (72).

12. Method according to one of claims 8 to 11, characterized in that it comprises the step of applying a diffusion welding cycle by Hot Isostatic Compression (CIC).

13. Method according to claim 12, characterized in that the Hot Isostatic Compression (CIC) diffusion welding cycle is carried out with the following operating conditions:

- bring 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, - apply to the sheath (79) a pressure of between 500 bars and 1500 bars, preferably between 800 bars and 1200 bars, in particular a pressure of 1020 bars,

- let everything 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 by it,

- an electrochemical device housed in the enclosure (60), comprising:

- a stack (20), with solid oxides of the SOEC/SOFC type 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 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 the circulation of air in the volume delimited by it,

- an electrochemical device housed in the enclosure (60), comprising:

- 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).