Reactor for electrolysis or co-electrolysis of water (SOEC) or fuel cell comprising a stack of solid-oxides cells, having interconnectors instrumented by a removable probe for measuring voltage

Abstract

The invention essentially consists in integrating, into an electrochemical device comprising a stack of elementary electrochemical cells, on the periphery of at least one and preferably each interconnector between two adjacent cells in the stack, a mountable / dismountable probe by way of interface for measuring cell voltage, via simple and possibly manual insertion / removal into / from a mating shape within the interconnector.

Description

[0001] Description

[0002] Title: Water electrolysis or co-electrolysis reactor (SOEC) or fuel cell with solid oxide cell stack, with interconnectors instrumented by a removable electrical voltage measuring probe.

[0003] Technical field

[0004] The present invention relates to the field of solid oxide fuel cells (SOEC), that of high temperature water electrolysis (EHT), also using solid oxides (SOEC), and that of high temperature co-electrolysis of water and another gas chosen from carbon dioxide CO2 or nitrogen dioxide NO2.

[0005] The invention relates more particularly to the production of a high temperature water electrolysis or co-electrolysis (EHT) reactor of the SOEC type, or a fuel cell of the SOFC type, with a stack of elementary electrochemical cells which are each instrumented by a removable electrical voltage measurement interface.

[0006] Although described with reference primarily to the application of high-temperature water electrolysis, the invention applies equally well to co-electrolysis of water and another gas selected from carbon dioxide CO2 or nitrogen dioxide NO2, as to a SOFC fuel cell.

[0007] The invention applies to a SOFC fuel cell using either hydrogen or a hydrocarbon, for example methane CH4, as fuel.

[0008] Prior art

[0009] Electrolysis of water involves an electrolytic reaction that decomposes water into oxygen and hydrogen gases with the help of an electric current according to the reaction:

[0010] H2O H2+ 1 / 202.

[0011] To carry out the electrolysis of water, it is advantageous to carry it out at high temperature, typically between 600 and 950°C, because part of the energy required for the reaction can be provided by heat, which is cheaper than electricity, and the activation of the reaction is more efficient at high temperature and does not require a noble catalyst. To implement high-temperature electrolysis, it is known to use an SOEC type electrolyzer (acronym for "Solid Oxide Electrolyser Cell"), consisting of a stack of elementary patterns, each comprising a solid oxide electrolysis cell, consisting of three anode / electrolyte / cathode layers superimposed on each other, and interconnection plates made of metal alloys, also called bipolar plates, or interconnectors.The function of the interconnectors is to ensure both the passage of electric current and the circulation of gases in the vicinity of each cell (injected water vapor, hydrogen and oxygen extracted in an EHT electrolyzer; injected air and hydrogen and extracted water in an SOFC stack) and to separate the anode and cathode compartments which are the compartments for circulation of gases on the side of the anodes and cathodes of the cells respectively. To carry out the electrolysis of water vapor at high temperature EHT, water vapor H2O is injected into the cathode compartment. Under the effect of the current applied to the cell, the dissociation of water molecules in vapor form is carried out at the interface between the hydrogen electrode (cathode) and the electrolyte: this dissociation produces dihydrogen gas H2 and oxygen ions. The dihydrogen is collected and evacuated at the outlet of the hydrogen compartment. The oxygen ions O. 2' migrate through the electrolyte and recombine into oxygen at the interface between the electrolyte and the oxygen electrode (anode).

[0012] As shown schematically in Figure 1, each elementary electrolysis cell 1 is formed of a cathode 2 and an anode 4, placed on either side of a solid electrolyte 3 generally in the form of a membrane. The two electrodes (cathode and anode) 2, 4 are electrical conductors, made of porous material, and the electrolyte 3 is gas-tight, electronically insulating and ionically conductive. The electrolyte may in particular be an anionic conductor, more precisely an anionic conductor of O ions 2 ' and F electrolyser is then called an anionic electrolyser.

[0013] Electrochemical reactions take place at the interface between each of the electronic conductors and the ionic conductor.

[0014] At cathode 2, the half-reaction is as follows:

[0015] 2 H2O + 4 e' ^ 2 H2+ 2 O 2 '.

[0016] At anode 4, the half-reaction is as follows: 2O 2 - ^ O2+ 4 e-,

[0017] The electrolyte 3 intercalated between the two electrodes 2, 4 is the place of migration of the O ions 2- ' under the effect of the electric field created by the potential difference imposed between the anode 4 and the cathode 2.

[0018] As illustrated in parentheses in Figure 1, the water vapor at the cathode inlet may be accompanied by hydrogen H2, and the hydrogen produced and recovered at the outlet may be accompanied by water vapor. Similarly, as illustrated in dotted lines, a draining gas, such as air, may also be injected at the inlet to evacuate the oxygen produced. The injection of a draining gas has the additional function of acting as a thermal regulator and facilitating the pressure regulation of the anode chamber.

[0019] An elementary electrolysis reactor consists of an elementary cell as described above, with a cathode 2, an electrolyte 3, and an anode 4 and two monopolar connectors which ensure the electrical, hydraulic and thermal distribution functions.

[0020] To increase the flow rates of hydrogen and oxygen produced, it is known to stack several elementary electrolysis cells on top of each other, separating them by interconnection devices, usually called interconnectors or bipolar interconnection plates. The assembly is positioned between two end interconnection plates which support the electrical supplies and gas supplies of the electrolyser (electrolysis reactor).

[0021] A high temperature water electrolyser (HTE) thus comprises at least one, generally a plurality of electrolysis cells stacked on top of each other, each elementary cell being formed of an electrolyte, a cathode and an anode, the electrolyte being intercalated between the anode and the cathode.

[0022] The fluidic and electrical interconnection devices which are in electrical contact with one or more electrodes generally provide the functions of supplying and collecting electric current and delimit one or more gas circulation compartments.

[0023] Thus, a so-called cathodic compartment has the function of distributing electric current and water vapor as well as recovering hydrogen at the cathode in contact.

[0024] A so-called anode compartment has the function of distributing the electric current as well as recovering the oxygen produced at the anode in contact, possibly using a draining gas.

[0025] Figure 2 represents an exploded view of elementary patterns of a high-temperature water vapor electrolyzer according to the state of the art. This EHT electrolyzer comprises a plurality of elementary electrolysis cells Cl, C2... of the solid oxide type (SOEC) stacked alternately with interconnectors 5. Each cell Cl, C2... consists of a cathode 2.1, 2.2,... and an anode 4.1, 4.2, between which an electrolyte 3.1, 3.2... is arranged. All of the electrolysis cells are supplied in series by the electric current and in parallel by the gases.

[0026] The interconnector 5 is a metal alloy component that ensures the separation between the cathode compartments CC and anode compartments CA, defined by the volumes between the interconnector 5 and the adjacent cathode 2.1 and between the interconnector 5 and the adjacent anode 4.2 respectively. It also ensures the distribution of gases to the cells. The injection of water vapor into each elementary unit is done in the cathode compartment CC. The collection of the hydrogen produced and the residual water vapor at the cathode 2.1, 2.2 ... is carried out in the cathode compartment CC downstream of the cell Cl, C2 ... after dissociation of the water vapor by the latter. The collection of the oxygen produced at the anode 4.2 is carried out in the anode compartment CA downstream of the cell Cl, C2 ... after dissociation of the water vapor into oxygen ions by the latter.

[0027] The interconnector 5 ensures the passage of current between the cells C1 and C2 by contact with the adjacent electrodes, i.e. between the anode 4.2 and the cathode 2.1.

[0028] In a state-of-the-art SOEC solid oxide fuel cell, the cells C1, C2, etc. and interconnectors 5 used are the same components, but the operation is the opposite of that of an EHT electrolyser as just explained with a reversed direction of current, with air supplying the compartments which have then become cathodic and hydrogen as fuel supplying the compartments which in turn have become anode.

[0029] Whether for an EHT electrolyser or a fuel cell stack, measuring the electrical voltage of each cell is essential, because this individual measurement makes it possible to assess the health of each cell and thus to choose the overall operating point of the electrolyser / battery based on the individual response of each cell. This individual measurement is therefore ideal for optimal operation.

[0030] However, it requires a lot of stack preparation work because each interconnector must be connected to a voltage measurement wire.

[0031] Each cell voltage is measured individually by connecting a voltage measuring device through the interconnectors via the wires.

[0032] Currently, each voltage measurement wire is connected to one of the stack's interconnectors by welding, particularly spot welding. These welds are performed manually and in situ in the stack's test equipment, making the operation time-consuming and delicate.

[0033] The soldering process is generally reliable, but measurement wires can break due to improper handling. Resoldering them is a delicate operation due to the formation of surface oxides. The wires also become brittle when left for long periods at the high operating temperatures of an EHT electrolyzer or SOFC fuel cell. The probability of breakage increases with the age of the wire.

[0034] This soldering operation is made easier if the interconnectors are thick, typically with a thickness greater than 1 mm, because a wire can be applied to the edge of an interconnector. Conversely, this operation is all the more complicated if the interconnectors are of a lesser thickness.

[0035] There is therefore a need to improve the implementation of means for measuring the electrical voltage cell by cell of a stack of an SOEC type electrolysis reactor or an SOFC type fuel cell, in particular in order to avoid welding operations, and this more particularly for interconnectors of the stack of low thickness.

[0036] The aim of the invention is to meet at least part of this need.

[0037] Statement of the invention

[0038] To this end, the invention relates, in one of its aspects, to an electrochemical device, in particular a high-temperature electrolysis reactor for water vapor H2O, or for co-electrolysis of water vapor H2O and carbon dioxide CO2, or a solid oxide fuel cell (SOFC), comprising: - a stack of n elementary electrochemical cells of the solid oxide type, each formed of a cathode, an anode and an electrolyte intercalated between the cathode and the anode, and a plurality of electrical and fluidic interconnectors each arranged between two adjacent elementary cells with one of its faces in electrical contact with the anode of one of the two elementary cells and the other of its faces in electrical contact with the cathode of the other of the two elementary cells;

[0039] - at least one electrical voltage measuring probe of at least one elementary cell, comprising a metal tab or a groove connected to an electric wire and of a shape adapted to be inserted and held with electrical contact in respectively a metal tab or a groove constituting a counterform arranged in the periphery of one of the two interconnectors in electrical contact with the elementary cell, forming a mountable and removable connection, the holding with electrical contact being established by the tab itself, once inserted, at ambient temperature and / or during the rise in temperature so as to be effective during operation of the device.

[0040] According to an advantageous embodiment, the device comprises a plurality of n measuring probes. Thus, each elementary electrochemical cell of the stack is instrumented by an individual probe.

[0041] The tongue can be made in the probe and the groove constituting the counterform can be provided in the thickness of an interconnector plate or between two thin interconnector plates or sheets.

[0042] According to a first advantageous embodiment configuration, the tab is flat and adapted to be inserted into the groove made in the central thin sheet of the interconnector F consisting of three flat thin sheets, pierced with holes and elongated along two mutually orthogonal axes of symmetry, the flat sheets being laminated and assembled together by welding. The probe can be in electrical contact with the central thin sheet but also with the upper and lower sheets, which maximizes the electrical contact potential, whatever the operating conditions of the device.

[0043] According to a second advantageous embodiment configuration, the tab is of decreasing thickness towards its free end and adapted to be inserted as a mechanical wedge into the thickness of the interconnector plate. Advantageously, the tab can be adapted to be inserted by fitting into the groove of complementary shape, according to a trajectory with a single fitting direction, or with at least two different fitting directions so that the extraction of the tab cannot be untimely, in particular under the effect of traction in one direction and therefore only carried out by following a predefined trajectory.

[0044] According to another embodiment of the invention, the tab is provided with at least one snap-on tab adapted to snap into the groove. This tab therefore snaps / clips into a groove of the F interconnector and thus ensures mechanical locking and electrical contact.

[0045] Preferably, the tongue and / or the edge of the groove is (are) coated with a paste made of electrically conductive material, preferably gold, or platinum. Thus, in the event of oxidation on an interconnector, however, it forms a layer of electrically conductive oxide, which allows the electrical connection of this interface layer. Adding a layer of electrically conductive paste ensures electrical contact in the event of problematic oxidation.

[0046] According to a first advantageous embodiment variant, the tab and the periphery of the connector are made of the same material.

[0047] According to a second advantageous embodiment variant, the tab is made of a material with a thermal expansion coefficient greater than that of the periphery of the interconnector F so that when the temperature rises, the inserted tab is tightly fitted in the groove.

[0048] Materials are chosen based on their expansion rate and their electrical characteristics at high temperatures.

[0049] Advantageously, the interconnectors and / or the tab(s) are made of steel, more preferably ferritic steel with approximately 20% chromium or 310 stainless steel, preferably CROFER® 22APU or F18TNb, or nickel-based such as Inconel® 600 or Haynes 230® or metallic material which oxidizes to form a conductive spinel.

[0050] According to an advantageous application, the device is intended to operate reversibly by constituting a reactor or a fuel cell, respectively in electrolysis or co-electrolysis mode, where appropriate with in situ methanation or in fuel cell mode, where appropriate with internal reforming of methane.

[0051] The invention essentially consists of integrating into an electrochemical device with a stack of elementary electrochemical cells, at the periphery of at least one, preferably of each, interconnector between two adjacent cells in the stack, a probe which can be mounted / removed as an interface for measuring the electrical voltage of the cell, by simple insertion / disinsertion which can be manual, into a counterform within the interconnector.

[0052] The male form can be that of the probe or of the F interconnector and the counterform (female form) can be that of the F interconnector or of the probe respectively. In the case where the F interconnector is the male part of the interface, it is possible to use all or part of the number of plates composing the F interconnector in order to realize the form of the probe.

[0053] In this case, the counter-form, which will be the removable part of the system, can be produced advantageously by taking up all the design principles listed in the case where the counter-form is internal to the interconnector.

[0054] The electrical voltage measurement carried out by the probe according to the invention is said to be "currentless", that is to say that only a punctual mechanical and therefore electrical contact is required to carry out the measurement. Preferably, the contact is made over a few square millimeters, in order to avoid any false contact during possible movements.

[0055] The device for measuring electrical voltage can be made up of a device already marketed, such as the one under the trade name Keithley 2750. Typically, the inventors used such a device with an impedance of 10 gigaOhm, which allows us to make a measurement without current. Any multiplexed digital multimeter type device can also be considered.

[0056] A voltage probe and associated housing groove within an interconnector are made in such a way that electrical contact is permanent even in the event of expansion / contraction, rotation, traction or any other mechanical action on the probe.

[0057] A voltage probe according to the invention may have a planar shape adapted to the structure of an interconnector or a 3-dimensional shape in order to establish electrical contact in all directions. A voltage probe may be made of a metallic material having a coefficient of expansion greater than that of F interconnector, in order to achieve a tight fit between and F interconnector, so as to guarantee electrical contact at the high operating temperatures of the device, in particular EHT electrolyzer or SOFC fuel cell.

[0058] The advantages of the invention are numerous, among which we can cite:

[0059] - a probe according to the invention makes it possible not to add additional electrical interface resistances between an electrical wire dedicated to the measurement and the interconnector in which the probe is inserted;

[0060] - the possibility of carrying out a probe installation according to the invention, cold but allowing the measurement of cell voltages or ohmic resistance between the interconnectors cold as well as hot;

[0061] - the fact that each probe can be dismantled quickly and at will makes it easier and quicker to dismantle the electrochemical device from its test station at the end of the assembly line. Its transport and its reassembly in situ at the place of use are also faster, more practical and more reliable than according to the state of the art.

[0062] Other advantages and characteristics of the invention will become more apparent upon reading the detailed description of examples of implementation of the invention given by way of illustration and not limitation with reference to the following figures.

[0063] Brief description of the drawings

[0064] [Fig 1] Figure 1 is a schematic view showing the working principle of a high temperature water electrolyzer.

[0065] [Fig 2] Figure 2 is an exploded schematic view of a portion of a SOEC type high temperature (HTE) steam electrolyzer including state-of-the-art interconnectors.

[0066] [Fig 3] Figure 3 is a partial perspective view and transparency showing a first example of an electrical voltage measurement probe according to the invention, in its configuration mounted (inserted) in an interconnector of an electrochemical device with a stack of elementary electrochemical cells. [Fig 4] Figure 4 is a top view of a second example of an electrical voltage measurement probe according to the invention.

[0067] [Fig 5] Figure 5 is a top view of a third example of an electrical voltage measuring probe according to the invention with an interconnector F in which a corresponding groove is provided suitable for receiving the probe.

[0068] [Fig 6] Figure 6 is a partial perspective view in transparency showing a fourth example of an electrical voltage measuring probe according to the invention, in its configuration mounted (inserted) in an interconnector of an electrochemical device with a stack of elementary electrochemical cells.

[0069] Detailed description

[0070] For the sake of clarity, the same elements of an EHT electrolysis reactor according to the state of the art and of an EHT electrolysis reactor according to the invention are designated by the same numerical references.

[0071] In Figures 1 and 2, the symbols and arrows for the supply of water vapor H2O, distribution and recovery of dihydrogen H2, oxygen 02, air and electric current, as well as the balancing gas are shown for clarity and precision, to illustrate the operation of a high-temperature electrolysis reactor.

[0072] It is specified here throughout the present application that the terms "lower", "upper", "above", "below", "inner", "outer", "internal" and "external" are to be understood with reference to a reactor or a fuel cell according to the invention in operating configuration, i.e. the cells being stacked vertically.

[0073] Figures 1 and 2 relating to the state of the art have already been commented on in the preamble. They are therefore not detailed below.

[0074] Nor is the structure or operation of a stack constituting an EHT reactor or electrolyser or fuel cell in which an electrical voltage measuring probe 6 is inserted detailed.

[0075] It is an electrochemical device with a stack of n elementary electrochemical cells of the solid oxide type, each formed of a cathode, an anode and an electrolyte intercalated between the cathode and the anode, and a plurality of electrical and fluidic interconnectors each arranged between two adjacent elementary cells with one of its faces in electrical contact with the anode of one of the two elementary cells and the other of its faces in electrical contact with the cathode of the other of the two elementary cells.

[0076] Figure 3 shows a first example of a probe 6 as it is inserted into an interconnector 5 of the stack.

[0077] The probe consists of a flat tab 6 with a rectangular portion 60 offset to the periphery of the interconnector F and extended by a circular portion 61, which in the position inserted into the groove 510 of the interconnector F is in electrical contact with the latter.

[0078] The interconnector 5 is here made up of three thin flat sheets 50, 51, 52, pierced with holes and elongated along two mutually orthogonal axes of symmetry, the flat sheets being laminated and assembled together by welding. To better understand the production of the interconnectors 5 with three thin sheets 50, 51, 52, it is advantageous to refer to patent application FR 3040061 AL

[0079] The thin sheets are preferably made of steel, preferably ferritic steel with approximately 20% chromium, preferably CROFER® 22APU or F18TNb, or nickel-based steel such as Inconel® 600 or Haynes 230®.

[0080] As shown in this figure 3, the probe is therefore inserted by fitting with electrical contact, with its circular portion 61 in a groove 510 of circular portion shape complementary to the central sheet 51. The advantage of this configuration is that the probe can be in contact with a large contact surface (the circular portion 61), with each of the three sheets 50, 51, 52 of the interconnector. Another advantage is that, in its mounted position, the probe can be moved in rotation according to the constraints.

[0081] Figure 4 shows a second example of a probe 6 formed by a tab. The rectangular elongated portion 60 is provided with snap-on tabs 62 on its longitudinal edges. Thus, the mounting of the probe 6 in the interconnector groove 5 is carried out by snap-on / clipping. Thus, the probe 6 is compressed in the interconnector groove F. It is possible to add an elastic element and / or another snap-on tab which extends in a third dimension, in order to increase the electrical contact. Figure 5 illustrates a third example of a probe 6 in the form of a tab. The rectangular elongated portion 60 is extended by an arrow 63 which extends in a direction other than the portion 60.

[0082] Thus, the tongue 60, 63 can be inserted by fitting into the groove 53 of complementary shape, along a trajectory with at least two different fitting directions so that the extraction of the tongue can only be done by following the trajectory. Thus, in this configuration, in the event of traction on the probe 6, the latter remains stuck in the groove 53.

[0083] Figure 6 illustrates another example of probe 6 in the form of a tab. Here, the tab is of decreasing thickness from its portion 60 on the outside towards its free end 64. Thus, the probe 6 is inserted as a mechanical wedge in the thickness of the plate of an interconnector 5. This example is rather dedicated to interconnectors in the form of thick plates, typically of thickness greater than or equal to 1 mm.

[0084] The invention is not limited to the examples which have just been described; in particular, it is possible to combine characteristics of the illustrated examples within non-illustrated variants.

[0085] Other variants and embodiments may be envisaged without departing from the scope of the invention.

[0086] Other probe and counterform shapes can be considered in an interconnector than those in the examples illustrated.

[0087] For example, one can consider a probe shape with a round, square, or other cross-section and a countershape of complementary geometric shape in an interconnector.

[0088] If in the examples illustrated, the male shape is that of the probe and the counter-shape (female shape) is that of the interconnector F, the reverse can very well be envisaged within the framework of the invention, that is to say a male shape produced in the interconnector F and a counter-shape (female shape) formed in the probe.

Claims

Claims 1. Electrochemical device, in particular a high-temperature electrolysis reactor for water vapor H2O, or for co-electrolysis of water vapor H2O and carbon dioxide CO2, or a solid oxide fuel cell (SOFC), comprising: - a stack of n elementary electrochemical cells of the solid oxide type, each formed of a cathode, an anode and an electrolyte intercalated between the cathode and the anode, and a plurality of electrical and fluidic interconnectors each arranged between two adjacent elementary cells with one of its faces in electrical contact with the anode of one of the two elementary cells and the other of its faces in electrical contact with the cathode of the other of the two elementary cells; - at least one electrical voltage measuring probe of at least one elementary cell, comprising a metal tab or a groove connected to an electric wire and of a shape adapted to be inserted and held with electrical contact in respectively a groove or a metal tab constituting a counterform arranged in the periphery of one of the two interconnectors in electrical contact with the elementary cell, forming a mountable and removable connection, the holding with electrical contact being established by the tab itself, once inserted in the groove, at ambient temperature and / or during the rise in temperature, so as to be effective during operation of the device.

2. Device according to claim 1, comprising a plurality of n measuring probes.

3. Device according to claim 1 or 2, the tongue being produced in the probe, the groove constituting the counterform being formed in the thickness of an interconnector plate or between two thin interconnector plates or sheets.

4. Device according to claim 3, the tongue being flat and adapted to be inserted into the groove made in the central thin sheet of the interconnector F consisting of three flat thin sheets, pierced with holes and elongated along two axes of symmetry orthogonal to each other, the flat sheets being laminated and assembled together by welding.

5. Device according to claim 3, the tab being of decreasing thickness towards its free end and adapted to be inserted as a mechanical wedge into the thickness of the interconnector plate.

6. Device according to one of the preceding claims, the tongue being adapted to be inserted by fitting into the groove of complementary shape, according to a trajectory with a single fitting direction.

7. Device according to one of claims 1 to 5, the tongue being adapted to be inserted by fitting into the groove of complementary shape, along a trajectory with at least two different fitting directions so that the extraction of the tongue cannot be done untimely, in particular under the effect of traction in one direction and therefore only done by following a predefined trajectory.

8. Device according to one of the preceding claims, the tongue being provided with at least one snap-on tab adapted to snap into the groove.

9. Device according to one of the preceding claims, the tongue and / or the edge of the groove being coated with a paste of electrically conductive material, preferably gold or platinum.

10. Device according to one of the preceding claims, the tab and the periphery of the connector being made of the same material.

11. Device according to one of claims 1 to 9, the tab being made of a material with a coefficient of thermal expansion greater than that of the periphery of the interconnector so that when the temperature rises, the inserted tab is tightly fitted in the groove.

12. Device according to one of the preceding claims, the interconnectors and / or the tab(s) being made of steel, more preferably ferritic steel with approximately 20% chromium or 310 stainless steel, preferably CROFER® 22APU or F18TNb, or nickel-based such as Inconel® 600 or Haynes 230® or metallic material which oxidizes to form a conductive spinel.

13. Device according to one of the preceding claims, intended to operate reversibly by constituting a reactor or a fuel cell, respectively in electrolysis or co-electrolysis mode, where appropriate with in situ methanation or in fuel cell mode, where appropriate with internal reforming of methane.

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