A rigid electrical conductor having elements interconnected by TIG welding, a method for manufacturing such an electrical conductor, and the use of such an electrical conductor

Abstract

The subject of the present invention is a rigid electrical conductor (70). This rigid electrical conductor (70) comprises an assembly (72) having a rigid conductive rod (74) made of a first metallic material and a sheath (76) made of a second metallic material that covers the conductive rod (74) and has a higher electrical resistance than the electrical resistance of the first metallic material, and a first connection strip (78) that is at least partially formed of the second metallic material and is connected to a first end (72a) of the assembly (72). At the first end (72a) of the assembly (72), the conductive rod (74), the sheath (76), and the first connection strip (78) are joined together by TIG welding with the addition of a material made of the second metallic material.

Description

Technical Field

[0001] The present invention relates to the general field of high-temperature electrolysis (HTE), and more particularly to high-temperature steam electrolysis (HTSE), carbon dioxide (CO2) electrolysis, or co-electrolysis of high-temperature steam (HTE) and high-temperature carbon dioxide (CO2).

[0002] More particularly, the present invention relates to the field of high-temperature electrochemical devices such as high-temperature solid oxide electrolysis cells, commonly referred to using the acronym SOEC, and high-temperature solid oxide fuel cells, commonly referred to using the acronym SOFC, but further relates to high-temperature water co-electrolysis devices using carbon dioxide, reversible high-temperature fuel cells and electrolysis systems, or so-called intermediate-temperature cells or intermediate-temperature electrolysis devices at around 400 °C, also known as "proton ceramic fuel cells" or PCFCs.

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

[0004] In addition to such SOEC / SOFC type solid oxide cell stacks, the present invention relates to any system where electrical conduction is required in a high-temperature oxidizing environment or under conditions that result in rapid degradation of the electrically conductive material.

[0005] More particularly, the present invention relates to the current supply to a stack of electrochemical cells in a hot zone.

Background Art

[0006] In the case of a SOEC-type high-temperature solid oxide electrolyzer, the conversion of steam (H2O) to hydrogen (H2) and oxygen (O2), and / or the conversion of carbon dioxide (CO2) to carbon monoxide (CO) and oxygen (O2) by an electric current within the same electrochemical device is a problem. In the case of a SOFC-type high-temperature solid oxide fuel cell, the operation is reversed, and while being supplied with hydrogen (H2) or other fuels such as methane (CH4), natural gas, biogas, and oxygen (O2), typically while being supplied with air, an electric current and heat are generated. For the sake of simplicity, the following description prioritizes the operation of a SOEC-type high-temperature solid oxide electrolyzer that performs steam electrolysis. However, this operation is applicable to carbon dioxide (CO2) electrolysis or high-temperature steam co-electrolysis (HTE) using carbon dioxide (CO2). Furthermore, this operation can also be replaced in the case of a SOFC-type high-temperature solid oxide fuel cell.

[0007] As is well known, a high-temperature steam (H2O) electrolyzer, i.e., an HTSE electrolyzer, comprises a stack of a plurality of solid oxide basic electrochemical cells. Referring to FIG. 1, the solid oxide cell 10, i.e., the "SOC", specifically comprises a) a first porous conductive electrode 12, i.e., the "cathode", which is intended to be supplied with steam for hydrogen generation, b) a second porous conductive electrode 14, i.e., the "anode", into which oxygen (O2) generated by the electrolysis of water injected into the cathode flows, and c) a solid oxide film (dense electrolyte) 16 sandwiched between the cathode 12 and the anode 14. This film 16 is an anion conductor for high temperatures, usually at a temperature above 600°C.

[0008] By heating the cell 10 to at least this temperature and injecting an electric current I into the anode 14, reduction of water occurs at the cathode 12, whereby hydrogen (H2) is generated at the cathode 12 and oxygen (O2) is generated at the anode 14.

[0009] In the schematic diagram of FIG. 2, a stack 20 of such cells having the purpose of generating a large amount of hydrogen is shown. In particular, the cells 10 are separated by interconnecting plates 18, i.e., interconnectors, and stacked on top of each other. These plates provide electrical continuity between different electrodes of the cells 10, thus enabling the electrical series connection of those electrodes, and distribute the various gases necessary for the operation of the cells, and, where applicable, distribute a carrier gas for discharging electrolysis products and / or assisting in the thermal management of the stack.

[0010] For this purpose, the plate 18 is connected to a steam supply 22 for injecting this steam towards the cathode of the cell 10 according to a constant steam flow rate D set by a controllable valve 24. H2O Furthermore, the plate 18 is also connected to a gas manifold 26 for collecting the gases resulting from the electrolysis. An example of a stack and an interconnecting plate structure is described, for example, in international patent application WO2011 / 110676A1.

[0011] To effectively carry out the electrolysis by the stack 20, this stack is usually brought to a high heat above 600°C, which is a temperature between 650°C and 900°C, the gas supply is started at a constant flow rate, and a power supply 28 is connected between two terminals 30, 32 of the stack 20, where a current I circulates.

[0012] The intensity I of the current is usually about several hundred amperes, which causes significant heat losses due to the Joule effect in the electrical conductor. To optimize the energy efficiency of the solid oxide electrochemical system, it is necessary to limit these heat losses, especially by developing special electrical conductors, sometimes referred to by the expression "bus bar".

[0013] The bus bars within the stack are generally provided in the form of metal rods. Taking a cylindrical rod as an example, the electrical resistance R is expressed by the following formula.

[0014] [Number]

[0015] Here, ρ is the resistance of the rod (Ω·m), l is the length of the rod (m), and S is the cross-sectional area of the rod (m 2 ²).

[0016] Since the loss due to the Joule effect is proportional to the resistance R, therefore, to limit this effect, it is necessary to reduce the electrical resistance of the busbar. Therefore, the possible optimizations consist of the following. - Limit the length of the rod. - Increase the cross-sectional area. - Find a material with low resistance and stable at high temperatures.

[0017] The first two options are generally shape selections that depend on the shape of the electrochemical system. Therefore, there are constraints regarding the electrochemical system and / or the conventional busbar is pre-optimized regarding the electrochemical system. The last point relates to the constituent material of the rod that should be selected to have the minimum resistance to reduce the resistance loss.

[0018] The optimization of this last point has not been fully considered. In fact, in all laboratory developments of this technology, energy efficiency is not a fundamental issue. On the other hand, as will be explained later, since the busbar is immersed in a highly corrosive environment, the standard solution implemented consists of the use of solid non-oxidizing alloy rods, and thus corresponds to the standard solution in all international publications. The resistance of these rods at the ambient temperature (20 °C) is pre-high, about 75×10 -8 Ω·m, but note that this resistance increases significantly with temperature.

[0019] Therefore, at 900 °C, which is the operating temperature of the high-temperature solid oxide electrolyzer, the electrical resistance of the stainless-steel rod is 117×10 -8Equal to Ω.m, which causes very large resistive losses. These points are specifically described in French patent application FR3036840A1.

[0020] While it is required to optimize the electrical resistance, the material generally recommended for electrical conductors subject to high current intensities is copper. Experimental research conducted by the applicant has made it possible to determine the resistance curve of copper as a function of temperature and to confirm that by selecting copper, the resistive losses can be reduced to at least one-tenth with respect to the reference material over the entire operating temperature range of the solid oxide system.

[0021] However, one of the important constraints that needs to be considered is the problem of corrosion related to the stack environment.

[0022] Referring to Figure 3, stack 20 is actually surrounded within a so-called "thermal" chamber, and the temperature of this thermal chamber is maintained between 650 and 900 °C under air scavenging. Therefore, a conventional electrochemical system comprises the following. - An HTSE electrolyzer 20, as described with reference to Figures 1 and 2 for example, and comprising a set of ducts 52, 54, 56, 58 for supplying and collecting gases from the anode and cathode of the electrochemical cell of the electrolyzer. - A chamber 60 in which the electrolyzer 20 is housed. Ducts 52, 54, 56, 58 penetrate the wall of chamber 60 for connection to a gas supply and collection circuit (not shown). Furthermore, chamber 60 comprises an air inlet duct 62 and an air outlet duct 64, and chamber 60 is sealed with respect to gases and liquids in all other places, for example. Duct 62 is connected to an air supply circuit (not shown) and is capable of performing air scavenging of the hot zone around electrolyzer 20, and this scavenging air is discharged through outlet duct 64. - Two electrical conductors 66, 68 connected to the terminals 30, 32 of stack 20 and passing through chamber 60 for connection to a current source 28.

[0023] Under these conditions, the two conductors 66, 68 in the form of copper wires, at least a part of which is included in the chamber 60, oxidize very rapidly. Furthermore, copper cannot withstand oxidation at high temperatures because the oxide formed on the surface does not have sufficient impermeability and adhesiveness to protect the underlying metal. Materials known to withstand oxidation at high temperatures are chromia-forming alloys and alumina-forming alloys such as, for example, stainless steel and non-oxidizing nickel alloys because these chromia-forming alloys and alumina-forming alloys form chromia and / or alumina, which are oxides with much higher protective properties. However, as described above, these alloys have an electrical resistivity such that significant energy losses occur when used.

[0024] High-temperature solid oxide fuel cells (SOFCs) have similar problems. In fact, HTSE electrolyzers and SOFC cells have the same structure and only differ in their operating modes. The electrolyzer operates in a carbon dioxide (CO2) reduction mode or a co-electrolysis mode, i.e., using a gas mixture consisting of steam (H2O) and carbon dioxide (CO2) at the cathode input. The mixture at the cathode outlet consists of hydrogen (H2), steam (H2O), carbon monoxide (CO), and carbon dioxide (CO2). Referring to FIG. 4, an electrochemical cell consisting of an SOFC cell comprises the same elements as the electrolytic cell (cathode 12, anode 14, electrolyte 16), but in the fuel cell, a hydrogen binary gas is supplied to the anode and an oxygen binary gas is supplied to the cathode at a constant flow rate and is connected to a load C to deliver the generated current. Therefore, in relation to the generated current being a few amperes, the fuel cell has the same problems as the electrolyzer.

[0025] One solution is to provide good oxidation resistance by protecting a copper (or any other metal considered suitable from the perspective of electrical resistance) rod with a coating such as a chromia coating or an alumina coating. This presents several problems. First, it is necessary to ensure the impermeability of the coating during heating and its stability on the copper substrate. It must be emphasized that since copper has a high coefficient of thermal expansion, high thermal expansion differential stresses can occur, which may cause damage to the coating and / or the coating / copper interface. Furthermore, at the high-temperature end of the rod, it is necessary to make an electrical connection to the stack without exposing the copper. Therefore, this connection must be made without damaging the coating, which is technically difficult.

[0026] Another solution is to coat a copper rod located within a sheath of oxidation-resistant material. By doing so, since the two materials are not rigidly connected, the problem of resistance to thermal expansion differential stresses is eliminated. Such an assembly (copper + non-oxidizing sheath) is already known in the prior art for other application fields (such as a strong acid environment at low temperatures of 50 to 80 °C), specifically in the Chinese document CN202608143U, which describes a copper rod simply screwed into a steel pipe. Conductors of this type are satisfactory at low temperatures and at certain low temperatures, but have been found to be unsuitable as they are for solid oxide systems. In fact, due to the weak contact between the conductor core and the sheath, the electrical contact between the two materials decreases as a result at high temperatures, leading to an increase in resistance losses. In other words, in the prior art, there is no optimized electrical conduction system adapted to high currents and resistant to high heat in an oxidizing environment.

[0027] According to patent application FR3036840A1, an electrical conductor is known that is adapted to currents of several hundred amperes, has resistance to oxidation at high temperatures, and can withstand thermal cycles up to 900 °C. This electrical conductor comprises a rod made of a first metallic material and a sheath made of a second metallic material that entirely covers the rod, and both the rod and the sheath are welded to each other using hot isostatic pressing (HIP).

[0028] More specifically, this application proposes forming a rod consisting of a circular copper core protected by a sheath of Inconel® 600 type steel. This copper core has a portion called a "scarf joint" which is a connection terminal made of Inconel® 600 type steel, and a closed end piece also made of Inconel® 600 type steel where the exhaust is carried out. These parts are assembled using TIG (tungsten inert gas) type arc welding. The resulting busbar is then subjected to the hot isostatic pressing (HIP) process, which enables diffusion bonding of different materials together without adding filler metal.

[0029] However, this solution has several drawbacks. Specifically, the use of hot isostatic pressing (HIP) is a costly method and can only be implemented by certain companies when operating at temperatures of around 900 °C and pressures of around 1000 bar with cycle times of several hours.

[0030] Furthermore, the busbar is composed of a single high-temperature connection area, which makes it impossible to achieve internal connections in the high-temperature zone.

Prior Art Documents

Patent Documents

[0031]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0032] The object of the present invention is to at least partially eliminate the above-mentioned needs and the drawbacks associated with the embodiments of the prior art.

Means for Solving the Problems

[0033] Accordingly, the subject matter of the present invention is, according to one of its aspects, a rigid electrical conductor. This rigid electrical conductor is - an assembly comprising - a rigid conductive rod made of a first metal material, and - a sheath covering the conductive rod and made of a second metal material, in particular non-oxidizing or refractory, having a higher electrical resistance than the electrical resistance of the first metal material and, - a first connection strip at least partially formed of the second metal material and connected to the first end of the assembly and - at the first end of the assembly, the conductive rod, the sheath, and the first connection strip are joined together by TIG (acronym for Tungsten Inert Gas) welding, in particular along the entire outer periphery, with the addition of a material made of the second metal material.

[0034] A "rigid" electrical conductor means a conductor that acts mechanically within the main link and is not necessarily connected to the stack, as opposed to a "flexible" electrical conductor used for connection to the stack. This conductor prevents the transmission of vibrations, expansions, and other parasitic movements between the stack and its environment and enables any electrical connection between stacks without mechanical transitions. The rigid electrical conductor has sufficient rigidity to hold its position.

[0035] The electrical conductor according to the present invention may further comprise one or more of the following features, either individually or in any possible technical combination.

[0036] Advantageously, the electrical conductor may be at least partially formed of a second metal material and comprise a second connection strip connected to the second end of the assembly. At the second end of the assembly, the conductive rod, the sheath, and the second connection strip may be joined together by TIG welding with the addition of a material made of the second metal material. The TIG welds at both ends of the assembly and on the sheath may completely cover the conductive rod over its entire length.

[0037] Furthermore, at least one gap may exist between the outer surface of the conductive rod and the inner surface of the sheath along at least a portion of the length of the conductive rod.

[0038] The conductive rod, i.e., the first metal material, may be made of copper, nickel, silver, and / or copper alloy, nickel alloy, silver alloy, or any other metal or alloy that is a good electrical conductor. Specifically, for example, any other metal or alloy that is a good electrical conductor and is susceptible to oxidation at a high temperature of about 900 °C, such as brass or bronze.

[0039] Furthermore, the sheath, i.e., the second metal material, may be made of a non-oxidizing or refractory metal and / or metal alloy or refractory alloy, particularly stainless steel or refractory steel based on, for example, nickel, chromium, or cobalt, particularly Inconel® 600 or 625, or any other metal or alloy that is resistant to oxidation at high temperatures, such as 316L stainless steel.

[0040] The first connection strip and / or the second connection strip may be made entirely of the second metal material.

[0041] Alternatively, in order to limit the electrical losses, each of the first connection strip and / or the second connection strip may comprise a conductive connection core made of a first metal material and a connection sheath that completely covers the connection core over its entire length and is made of a second metal material.

[0042] The connection sheath may have a thickness of about 0.5 mm.

[0043] Furthermore, the subject matter of the present invention is, according to another aspect thereof, a method for manufacturing an electrical conductor as defined above. This method is characterized by including the following steps. - Cleaning the surface, in particular with a detergent and / or a solvent, of the surface that is particularly intended to be adhered, i.e., the electrical conduction surface and the surface necessary for the impermeability of the electrical conductor. - Inserting a conductive rod into the sheath. - Joining between the conductive rod and the first connection strip by TIG welding. - Joining between the sheath and the first connection strip by TIG welding. - Optionally, evacuating the sheath by pumping.

[0044] As described above, the electrical conductor may be at least partially formed of a second metal material and comprise a second connection strip connected to the second end of the assembly. This method may include the following steps after the step of joining between the sheath and the first connection strip by TIG welding, i.e., - Joining between the conductive rod and the second connection strip by TIG welding, and - Joining between the sheath and the second connection strip by TIG welding may be included.

[0045] This manufacturing may be carried out in an ambient atmosphere (air) or a neutral atmosphere such as argon, for example.

[0046] The first connection strip and / or the second connection strip may be formed by assembling a conductive connection core and a connection sheath that completely covers the connection core. The connection core may be manufactured by swaging. However, it is also possible to use methods other than swaging, such as machining or forging. The connection sheath may be manufactured by drawing or assembling several components formed of a second metal material.

[0047] Furthermore, the assembly of the first connection strip and / or the second connection strip may at least include the following steps. - A step of cleaning the components of the connection strip, particularly using a detergent or a solvent. - A step of inserting the connection core into the connection sheath. - A step of evacuating the connection strip. - A step of applying a hot isostatic pressing (HIP) diffusion bonding cycle.

[0048] The hot isostatic pressing (HIP) diffusion bonding cycle may be carried out under the following operating conditions. - Conditions for setting the assembly formed from the connection core and the connection sheath to a temperature between 600 °C and 1060 °C, preferably between 800 °C and 1000 °C, particularly to a temperature of 920 °C. - Conditions for applying a pressure between 500 bar and 1500 bar to the connection sheath, preferably a pressure between 800 bar and 1200 bar, particularly a pressure of 1020 bar. - Conditions for applying a pressure plateau and a temperature plateau over a period of 30 minutes to several hours, preferably 1 hour to 3 hours, particularly 2 hours. - Conditions for cooling and depressurizing the assembly.

[0049] Furthermore, in order to ensure good electrical conductivity, the conductive rod and the connection core of the first connection strip and / or the second connection strip may be connected together by a high-temperature brazing welding method or a brazing method.

[0050] Furthermore, a further subject matter of the invention according to another aspect of the invention is - a chamber for circulating air within a volume defined by itself, and - an electrochemical device housed within the chamber, wherein - a SOEC / SOFC type solid oxide stack of basic electrochemical cells operating at high temperature, each basic electrochemical cell comprising an electrolyte inserted between a cathode and an anode, the SOEC / SOFC type solid oxide stack being connected in series between two electrical terminals, and - at least one electrical conductor connected to at least one of the two electrical terminals comprising an electrochemical device Use of at least one electrical conductor as defined above as an electrical conductor of an electrochemical system comprising

[0051] Furthermore, a further subject matter of the invention according to another aspect of the invention is - a chamber for circulating air within a volume defined by itself, and - an electrochemical device housed within the chamber, wherein - a SOEC / SOFC type solid oxide stack of basic electrochemical cells operating at high temperature, each basic electrochemical cell comprising an electrolyte inserted between a cathode and an anode, the SOEC / SOFC type solid oxide stack being connected in series between two electrical terminals, and - at least one electrical conductor as defined above connected to at least one of the two electrical terminals comprising an electrochemical device An electrochemical system comprising

[0052] The invention will be better understood by reading the following detailed description of non-limiting implementation forms of the invention and by considering the schematic and partial views of the accompanying drawings.

Brief Description of the Drawings

[0053]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0054] In any of these drawings, the same reference numerals may refer to the same or equivalent elements.

[0055] Furthermore, in order to make the drawings easier to read, the various parts shown in the figures are not necessarily drawn to a uniform scale.

[0056] FIGS. 1 to 4 have already been described above in relation to the prior art and the technical background of the present invention.

[0057] Referring to FIGS. 5 and 6, an example of an electrical conductor 70 according to the present invention will be described. Thus, this electrical conductor 70 comprises an assembly 72 in which a conductive rod 74 made of a first metallic material, which is copper in this case, is inserted into a sheath 76 made of a second metallic material, which is a non-oxidizing alloy such as Inconel (registered trademark) in this case. This second metallic material has a higher electrical resistance than the first metallic material.

[0058] In this case, the conductive rod 74 is made of copper, but it should be noted that the present invention is also applicable to other metals which are good electrical conductors but are susceptible to the effects of oxidation, such as nickel, silver, brass, bronze, and / or copper alloys such as those hardened by a dispersoid for example.

[0059] Furthermore, the electrical conductor 70 comprises a first connection strip 78 made of the second metallic material and connected to the first end 72a of the assembly 72, and a second connection strip 78 made of the second metallic material and connected to the second end 72b of the assembly 72.

[0060] In this case, the connection strips 78, which are of the Inconel (registered trademark) type non-oxidizing alloy, i.e. "scarf joints", seal the ends 72a and 72b of the assembly 72 and thus prevent the passage of gas. These strips 78 can form electrical connection terminals. These strips 78 have a shape complementary to that of an electrolytic cell plate to which the strip 78 is attached for the electrical connection of the electrolytic cell.

[0061] The shape or geometry of the connection strip 78 may be the usual lug shape as shown here, or any other different shape such as cylindrical for example, and may be intended to enter a hole which is clamp-fixed between two half-shells rigidly connected to the device to be supplied.

[0062] At the first end 72a of the assembly 72, the conductive rod 74, the sheath 76, and the first connection strip 78 are joined together by TIG welding, such as orbital welding, while adding a material made of a second metal material over the entire outer periphery shown as P in FIG. 6. Similarly, at the second end 72b of the assembly 72, the conductive rod 74, the sheath 76, and the second connection strip 78 are joined together by TIG welding (reference numeral P) while adding a material made of a second metal material. The TIG welds at the positions of the two ends 72a and 72b of the assembly 72 and the sheath 76 completely cover the conductive rod 74 along its entire length L as can be seen in FIG. 6. The TIG welds make it possible to protect the conductive rod 74 from oxidation. In fact, this welding is performed to render the connection between the scarf joint 78 and the sheath 76 impermeable.

[0063] As schematically shown in FIG. 6, one or more gaps J may exist between the outer surface of the conductive rod 74 and the inner surface of the sheath 76 along at least a portion of the length L of the conductive rod 74. Specifically, an atmosphere such as air or an inert atmosphere such as argon, for example, may be trapped between the conductive rod 74 and the sheath 76.

[0064] When air is trapped between the sheath 76 and the conductive rod 74, especially during use at high temperatures, this air is consumed by the oxidation of copper and Inconel®. However, since the volume of air is small and non-replenishable (the welds are impermeable), the oxide layer remains very small. In the case of a neutral atmosphere, the formation of the oxide layer may be prevented, for example, by argon purging.

[0065] Also, it is possible to exhaust the assembly 72 through a tube added for this purpose. Then, a degassing tube is added at one end, and the sheath is exhausted by pumping through the tube. Then, pinching may be performed to completely retain the vacuum, thereby making it possible to seal the tube hermetically and completely. Further, such an exhaust step can also perform an impermeability check.

[0066] The non-oxidizing alloy of the sheath 76 and the connection strip 78 is selected according to the thermal stress to which the electrical conductor 70 is exposed. Specifically, for a temperature range up to 900 °C at most, the sheath 76 and the strip 78 may be made of Inconel® 600. The conductive rod 74 may have a diameter of several tens of millimeters. However, its cross-section may be modified as necessary, for example, with respect to current, voltage drop, etc.

[0067] Therefore, the present invention proposes to form a rod 74 made of copper (or any other metal considered sufficient in terms of electrical resistance) protected by a sheath 76 made of a non-oxidizing metal or a refractory metal, particularly stainless steel or a non-oxidizing nickel alloy, and the whole being joined by TIG welding in the presence of two connection strips 78. Therefore, the present invention can be implemented without using the hot isostatic pressing (HIP) method in order to enable the assembly between the rod 74, the sheath 76, and the connection strip 78.

[0068] Therefore, advantageously, the present invention can bring about a reduction in manufacturing cost and also manufacturing simplicity that enables direct shaping and even length adjustment on-site (shaping, length cutting, scarf joint welding). The electrical conductor 70 (bus bar) may be used entirely within the high-temperature zone, and further, by being used within the partition bushing, it may enable a link between the high-temperature zone and the ambient temperature zone.

[0069] A method for manufacturing such an electrical conductor 70, intended to be used as an electrical conductor for current distribution in an electrochemical system such as those of FIGS. 1 to 4, for example, includes the following steps. - The step of manufacturing the above-mentioned parts (rods, sheaths, strips). - The step of cleaning the parts, in particular the surfaces to be joined, i.e., the electrically conductive surfaces and the surfaces necessary for the impermeability of the electrical conductor, with a detergent and / or a solvent or any other means. - The step of inserting the conductive rod 74 into the sheath 76. - The step of joining between the conductive rod 74 and the first connection strip 78 by TIG welding. - The step of joining between the sheath 76 and the first connection strip 78 by TIG welding. - The step of joining between the conductive rod 74 and the second connection strip 78 by TIG welding. - The step of joining between the sheath 76 and the second connection strip 78 by TIG welding. - The step of evacuating the sheath 76 by pumping, if necessary and applicable.

[0070] Furthermore, a welding X-ray imaging step may be performed to confirm the quality of the welds from a mechanical, electrical, and impermeability perspective.

[0071] The end portion provided with the strip 78 is a hot end that can be perforated in a direction perpendicular to the axis of the sheath 76 so as to be screwed onto the stack, as can be seen in FIGS. 5 and 6.

[0072] Advantageously, the TIG welds are made by a person skilled in the art to ensure a good electrical connection, specifically in the case of welding between copper and Inconel® and to ensure an impermeable weld in the case of welding between Inconel® and Inconel®.

[0073] In the following Table 1, when the electrical conductor 70 with a diameter of 12 mm is completely made of Inconel (registered trademark) 600 (prior art embodiment), and when the electrical conductor 70 with a diameter of 12 mm is manufactured using a sheath 76 made of Inconel (registered trademark) 600 and a core 74 made of copper (embodiment according to the present invention), by comparing the resistance obtained for 1 m of the electrical conductor 70, it can be seen that the present invention can reduce the electrical loss by one-tenth at a use temperature of 800°C.

[0074]

Table 1

[0075] In the case of the results in this Table 1, the resistance of copper is 17.24×10 -9 Ω·m at cold (20°C) and 70×10 -9 Ω·m at 800°C. The resistance of Inconel (registered trademark) 600 is 1.03×10 -6 Ω·m at cold (20°C) and 1.13×10 -6 Ω·m at 800°C.

[0076] The rigid electrical conductor 70 obtained according to the principle of the present invention is an electrical conductor adapted to the high temperature and high current of a stack of SOEC / SOFC type solid oxide cells. However, electrical losses may occur in the connection strips 78, and it is possible to modify the design of these connection strips 78 to limit these losses.

[0077] Figures 7 to 10 relate to another embodiment of the rigid electrical conductor 70 according to the present invention, where the connection strip 78 has a different design and in this case is called a "high conductivity" connection strip 78 or a scarf joint 78.

[0078] Specifically, each of the first connection strip 78 and the second connection strip 78 includes a conductive connection core 80 made of a first metal material, which is copper here but can be any of the other metals mentioned above, and a connection sheath 81 made of a second metal material that completely covers the connection core 80 over its entire length l, which is Inconel® 600 here but can be any of the other metals mentioned above. Advantageously, the connection sheath 81 has a thickness e g as shown in FIG. 9, which is about 0.5 mm. Obtaining a thin thickness e g greatly contributes to reducing electrical losses.

[0079] Furthermore, each connection strip 78 includes a tube-forming sleeve 82 inserted into a corresponding bore of the connection core 80 and a connection sheath 81 that enables attachment to the stack, as can be seen in FIGS. 9 and 10.

[0080] As shown in FIGS. 9 and 10, the resulting connection strip 78 can reduce electrical losses in the connection strip 78 by replacing a portion of the second metal material with the first metal material having good electrical conductivity. In fact, by leaving a connection sheath 81 made of Inconel® to protect the copper-made connection core 80 from oxidation, it is possible to reduce the electrical losses of the scarf joint 78. However, since such a scarf joint 78 is a connection point, electrical continuity is required across the entire connection surface between the connection sheath 81 and the connection core 80. For this purpose, the method for manufacturing such a scarf joint 78 described hereinafter uses the hot isostatic pressing (HIP) method, which is only used in the present invention for manufacturing such a "high-conductivity" scarf joint 78, to ensure welding across the entire connection surface between the connection core 80 and the connection sheath 81.

[0081] Therefore, since the electrical conductor 70 of the embodiments of FIGS. 7 and 8 uses a "high conductivity" connection strip 78, it has better conductivity than that described with reference to FIGS. 5 and 6. Specifically, the "high conductivity" connection strip 78 may have only about 10 percent of the resistance compared to a connection strip 78 made entirely from a second metal material.

[0082] To manufacture the "high conductivity" connection strip 78, the connection core 80 may be obtained by swaging. Swaging forging consists of plastically deforming a raw part made from an alloy such as, for example, an aluminum alloy, a copper alloy, a titanium alloy, a nickel alloy, etc. after heating. The swaging of steel is also known as "stamping". Swaging is a forging operation carried out using a tool called a "die", in particular an upper and a lower half die. These dies have the cavity shape of the part to be manufactured.

[0083] Furthermore, the connection sheath 81 can be obtained by drawing or assembling a plurality of parts made from a second metal material. This drawing manufacturing technique makes it possible to obtain an object having a shape that cannot be developed from a flat sheet-like metal plate. This technique is adapted for continuous production.

[0084] The method of assembling the "high conductivity" connection strip 78, i.e., the "high conductivity" scarf joint, includes the following steps. - Cleaning the components of the scarf joint 78 using, for example, a detergent, a solvent, or other suitable means. - Inserting the connection core 80 into the connection sheath 81. - Inserting a tube-forming sleeve 82 made from a first metal material. - Optionally, with the addition of a material consisting especially of stainless steel, joining the connection sheath 81 and the tube forming the sleeve 82 by TIG welding to impart impermeability to the joints on each side. - The step of adding a closing cover 85 formed by a closing plate 83 and a pinching tube 84 as shown in FIG. 9. - The step of joining the connection sheath 81 and the closing cover 85 by TIG welding to impart impermeability to the joint. - The step of evacuating the scarf joint 78 and connecting the tube 84 for a vacuum pump to generate a vacuum inside the connection sheath 81, and then performing pinching of the tube 84 to seal the tube 84 tightly and surely.

[0085] Thereafter, the application of a hot isostatic pressing (HIP) diffusion bonding cycle is carried out under the following operating conditions. - In particular, the assembly 78 formed from the connection core 80 and the connection sheath 81 is brought to a temperature of 600 °C to 1060 °C, preferably to a temperature of 800 °C to 1000 °C, and in particular to a temperature of 920 °C. - A pressure between 500 bar and 1500 bar is applied to the connection sheath 81, preferably a pressure between 800 bar and 1200 bar, and in particular a pressure of 1020 bar. - A pressure plateau and a temperature plateau are applied for a period of 30 minutes to several hours, preferably 1 hour to 3 hours, and in particular 2 hours. - The assembly is cooled and depressurized.

[0086] Finally, each "high conductivity" connection strip 78 may be machined so that direct connection of the connection core 80 is possible, and a scarf joint 78 as shown in FIG. 10 is obtained. Note that the two end zones ZE as shown in this FIG. 10 may be retained or machined.

[0087] Next, a "high-conductivity" scarf joint 78 is connected to the assembly 72 by a low-resistance connection. Specifically, the conductive rods 74 and the connection cores 80 of each connection strip 78 can be connected by brazing welding or high-temperature brazing. In this way, a high-conductivity electrical connection is realized. By choosing the filler material, it is possible to guarantee the connection up to a maximum operating temperature of about 900 °C. This attachment can be carried out, for example, using commercially available solder Castolin® 146 and the recommended 146M flux. This solder is composed of 60% copper, 39% zinc, and 1% tin manganese.

[0088] Next, as described above, mechanical connection and impermeability are obtained by TIG welding over the entire outer periphery at location P as shown in FIG. 8, with the addition of a material made of a second metallic material. Any evacuation step may be carried out, and as described above, an X-ray imaging step for welding and soldering may also be carried out.

[0089] The embodiments described above with reference to FIGS. 5 to 10 enable the realization of rigid electrical conductors adapted to the high temperature and high current of a solid oxide cell stack based on the use of busbars. With these rigid electrical conductors, it becomes possible to transmit the current of the main link with the lowest possible losses.

[0090] As described above, the present invention can be applied to a high-temperature steam electrolyzer, a high-temperature co-electrolyzer to which a mixture of steam (H2O) and carbon dioxide (CO2) is supplied, a high-temperature solid oxide fuel cell, a reversible system, a high-temperature fuel cell and electrolyzer, a "mid-temperature" i.e. 400 °C fuel cell or electrolyzer, or a proton ceramic fuel cell (PCFC).

[0091] The present invention is applicable not only to the systems described above operating at atmospheric pressure but also to pressurized systems.

[0092] The present invention is applicable not only to the technical field of solid oxide electrochemical systems but also to any field where electrical conduction is required in a high-temperature oxidation environment or under conditions that result in rapid degradation of an electrically conductive material.

[0093] It is obvious that the present invention is not limited to the above-described embodiments. Various modifications may be made to these embodiments by those skilled in the art.

Explanation of Reference Numerals

[0094] 10 Solid oxide cell 12 First porous conductive electrode, cathode 14 Second porous conductive electrode, anode 16 Solid oxide film (high-density electrolyte) 18 Interconnecting plate 20 Stack, HTSE electrolyzer, electrolytic cell 22 Steam supply section 24 Controllable valve 26 Gas manifold 28 Power source, current source 30 Terminal 33 Duct 54 Duct 56 Duct 58 Duct 60 Chamber 62 Air inlet duct 64 Air outlet duct 66 Electrical conductor 68 Electrical conductor 70 Rigid electrical conductor 72 Assembly 72a First end 72b Second end 74 Conductive rod, core 76 Sheath 78 First connection strip, second connection strip, assembly, scarf joint 80 Conductive connection core 81 Connection sheath 82 Tube-forming sleeve 83 Closing plate 84 Pinching Tube 85 Closing Cover ZE End Zone e g Thickness

Claims

1. An assembly (72) comprising: a rigid conductive rod (74) made of a first metal material; and a sheath (76) made of a second metal material that covers the conductive rod (74) and has a higher electrical resistance than the electrical resistance of the first metal material is provided, and an assembly (72); a first connection strip (78) at least partially formed of the second metal material and connected to a first end (72a) of the assembly (72); In a rigid electrical conductor (70) comprising: At the first end (72a) of the assembly (72), the conductive rod (74), the sheath (76), and the first connection strip (78) are joined together by TIG welding with the addition of a material made of the second metal material. A rigid electrical conductor (70).

2. A second connection strip (78) at least partially formed of the second metal material and connected to a second end (72b) of the assembly (72) is provided, At the second end (72b) of the assembly (72), the conductive rod (74), the sheath (76), and the second connection strip (78) are joined together by TIG welding with the addition of a material made of the second metal material. The TIG welds at both ends (72a, 72b) of the assembly (72) and in the sheath (76) completely cover the conductive rod (74) over its entire length (L). The conductor according to claim 1, characterized in that

3. At least one gap (J) is present between the outer surface of the conductive rod (74) and the inner surface of the sheath (76) along at least a portion of the length (L) of the conductive rod (74). The conductor according to claim 1 or 2, characterized in that

4. The conductive rod (74) is made of copper, nickel, silver, and / or a copper alloy, a nickel alloy, or a silver alloy. The conductor according to any one of claims 1 to 3, characterized in that

5. The sheath (76) is made of a non-oxidizing or refractory metal and / or a metal alloy or a refractory alloy, particularly stainless steel or refractory steel. The conductor according to any one of claims 1 to 4, characterized in that

6. Each of the first connection strip (78) and / or the second connection strip (78) comprises a conductive connection core (80) made of the first metal material, and a connection sheath (81) made of the second metal material that completely covers the connection core (80) over its entire length (l). The conductor according to any one of claims 1 to 5 is characterized by this.

7. In a method for manufacturing an electrical conductor (70) according to any one of claims 1 to 6, a step of cleaning the surface, in particular with a detergent and / or a solvent, a step of inserting the conductive rod (74) into the sheath (76), a step of joining between the conductive rod (74) and the first connection strip (78) by TIG welding, a step of joining between the sheath (76) and the first connection strip (78) by TIG welding, optionally, a step of evacuating the sheath (76) by pumping and is characterized by including this.

8. In the method according to claim 7, the electrical conductor (70) is at least partially formed of the second metal material and comprises a second connection strip (78) connected to the second end (72b) of the assembly (72). After the step of joining between the sheath (76) and the first connection strip (78) by TIG welding, the method includes a step of joining between the conductive rod (74) and the second connection strip (78) by TIG welding, and a step of joining between the sheath (76) and the second connection strip (78) by TIG welding. The method is characterized by this.

9. The first connection strip (78) and / or the second connection strip (78) is formed by assembling a conductive connection core (80) and a connection sheath (81) that completely covers the connection core (80). The connection core (80) is manufactured by swaging, and the connection sheath (81) is manufactured by drawing. The method according to claim 7 or 8 is characterized by this.

10. The assembly of the first connection strip (78) and / or the second connection strip (78) includes a step of cleaning the components of the connection strip (78), in particular using a detergent or a solvent, The step of inserting the connection core (80) into the connection sheath (81); The step of evacuating the connection strip (78); The step of applying a hot isostatic pressing (HIP) diffusion bonding cycle; The method according to claim 9, characterized by comprising at least the above steps.

11. The hot isostatic pressing (HIP) diffusion bonding cycle is carried out under the following operating conditions, namely: Condition of bringing the assembly formed from the connection core (80) and the connection sheath (81) to a temperature between 600 °C and 1060 °C, preferably between 800 °C and 1000 °C, particularly at a temperature of 920 °C; Condition of applying a pressure between 500 bar and 1500 bar to the connection sheath (81), preferably between 800 bar and 1200 bar, particularly at a pressure of 1020 bar; Condition of applying a pressure plateau and a temperature plateau for a period of 30 minutes to several hours, preferably 1 hour to 3 hours, particularly 2 hours; Condition of cooling and depressurizing the assembly; The method according to claim 10, characterized by being carried out under the above conditions.

12. The method according to any one of claims 9 to 11, characterized in that the conductive rod (74) and the connection core (80) of the first connection strip (78) and / or the second connection strip (78) are connected together by a high-temperature brazing welding method or a brazing method.

13. A chamber (60) for circulating air within a volume defined by itself; An electrochemical device housed within the chamber (60), An SOEC / SOFC type solid oxide stack (20) of basic electrochemical cells (10) operating at high temperature, each basic electrochemical cell (10) comprising an electrolyte (16) inserted between a cathode (12) and an anode (14), and being connected in series between two electrical terminals (30, 32), the SOEC / SOFC type solid oxide stack (20), and At least one electrical conductor (70) connected to at least one of the two electrical terminals (30, 32); An electrochemical device comprising; Use of at least one electrical conductor (70) according to any one of claims 1 to 6 as an electrical conductor of an electrochemical system comprising.

14. A chamber (60) for circulating air within a volume defined by itself; An electrochemical device housed within the chamber (60), an SOEC / SOFC type solid oxide stack (20) of basic electrochemical cells (10) that operates at high temperatures, each basic electrochemical cell (10) comprising an electrolyte (16) inserted between a cathode (12) and an anode (14), the SOEC / SOFC type solid oxide stack (20) being connected in series between two electrical terminals (30, 32), and at least one electrical conductor (70) according to any one of claims 1 to 6, connected to at least one of the two electrical terminals (30, 32) comprising an electrochemical device and comprising an electrochemical system.

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