Methods for co-electrolysis of water and CO.SUB.2 .(SOEC) or for high-temperature electricity production (SOFC) optionally promoting catalytic reactions inside the H.SUB.2 .electrode

Abstract

The invention essentially consists of proposing a novel reactor or fuel cell architecture having an active section of the catalytic material for methanation or reforming reaction integrated into the electrode which varies with the composition of the gases, as they are distributed in accordance with the electrochemistry on said electrode.

Claims

1. A method comprising co-electrolyzing steam H.sub.2O and carbon dioxide CO.sub.2, in a reactor comprising a stack of individual electrolysis cells of solid oxide type, with a rectangular or square area, each formed of a cathode comprising material configured to catalyze a methanation reaction, of an anode and of an electrolyte inserted between the cathode and the anode, a plurality of electrical and fluid interconnectors each comprising a first gas flow sector and a second gas flow sector arranged on a same side of the interconnector and each being arranged between two adjacent individual electrolysis cells of the stack of individual electrolysis cells with one face in electrical contact with the anode of one of the two adjacent individual electrolysis cells and the other face in electrical contact with the cathode of a second individual electrolysis cell of the two adjacent individual electrolysis cells, and a plurality of electrical contact and gas distribution elements, each arranged between the cathode of one of the individual electrolysis cells and one of the plurality of electrical and fluid interconnectors, wherein: a first zone and a second zone of each of the plurality of electrical and fluid interconnectors are supplied independently with a mixture of steam H.sub.2O and of carbon dioxide CO.sub.2 and the mixture is distributed to the cathode of each of the individual electrolysis cells, then a synthesis gas produced is recovered within the cathode of each of the individual electrolysis cell, in a third zone and a fourth zone of each of the plurality of electrical and fluid interconnectors in fluid communication respectively with the first zone and the second zone; each of the plurality of electrical contact and gas distribution elements integrating a sealing bead forming a gas distribution barrier separating the first gas flow sector comprising the first and third zones from the second gas flow sector comprising the second and fourth zones, the first gas flow sector and the second gas flow sector being adjoined by the gas distribution barrier, forming an area substantially equal to that of each cell; the first to fourth zones being dimensioned, and the gas circulation barrier being arranged, such that a length of the first gas flow sector in a direction perpendicular to a direction of gas flow increases or decreases between the first and third zones and a length of the second gas flow sector in a direction perpendicular to a direction of gas flow also increases or decreases between the second and fourth zones; and the first and second zones of each of the plurality of electrical and fluid interconnectors are supplied such that a gas circulation to each cathode in the first flow sector is in counterflow to a gas circulation in the second flow sector.

2. The method of claim 1, wherein the first gas flow sector and the second gas flow sector are of trapezoidal form.

3. The method of claim 2, comprising in-situ methanation, wherein supply is carried out via a largest base of the first gas flow sector and of the second gas flow sector of trapezoidal form delimited respectively by the first and the third zone, in order to minimize an in-situ methanation reaction compared to a co-electrolysis reaction of steam H.sub.2O and carbon dioxide CO.sub.2 within the stack of individual electrolysis cells.

4. The method of claim 2, wherein supply is carried out via the smallest base of the first and second trapezoidal sectors delimited respectively by the first and the third zone, in order to maximize the in situ methanation reaction compared to the co-electrolysis reaction within the stack.

5. The method of claim 2, comprising in-situ methanation, wherein a length ratio between small and large bases of the first gas flow sector and of the second gas flow sector of trapezoidal form is determined beforehand in order to promote or not promote an in-situ methanation reaction compared to a co-electrolysis reaction of steam H.sub.2O and carbon dioxide CO.sub.2 within the stack of individual electrolysis cells.

6. The method of claim 1, wherein a fifth zone of each electrical and fluid interconnector is supplied with draining gas, and it is distributed to the anode of each individual electrolysis cell, then the oxygen O.sub.2 produced and the draining gas are recovered in a sixth zone of each interconnector, so as to have a same supply of draining gas and a same recovery of oxygen produced for the first gas flow sector and the second gas flow sector.

7. The method of claim 1, comprising in-situ methanation, wherein the co-electrolysis is carried out at least in part with steam H.sub.2O produced by in-situ methanation.

Description

DETAILED DESCRIPTION

(1) Other advantages and features of the invention will become more clearly apparent on reading the detailed nonlimiting and illustrative description of exemplary embodiments of the invention given with reference to the following figures, in which:

(2) FIG. 1 is a schematic view showing the operating principle of a high-temperature water electrolyzer,

(3) FIG. 2 is a schematic exploded view of a part of a high-temperature steam co-electrolyzer comprising interconnectors according to the state of the art,

(4) FIG. 3 is a schematic sectional view of a co-electrolysis reactor implementing the method for high-temperature co-electrolysis according to one mode of the invention,

(5) FIG. 4 is a schematic top view of a co-electrolysis reactor implementing the method for high-temperature co-electrolysis according to one mode of the invention,

(6) FIG. 5 is a schematic top view of a co-electrolysis reactor implementing the method for high-temperature co-electrolysis according to another mode of the invention which is alternative to that of FIG. 4,

(7) FIG. 6A is an exploded view from beneath of a part of a co-electrolysis reactor according to the invention with interconnectors and an electrical contact and gas distribution element enabling independent supply and circulation for cathode gases (H.sub.2O, CO.sub.2, H.sub.2, CO, CH.sub.4) in counterflow from one gas flow sector of trapezoidal form to another which is adjoining, the sum of the areas of which is equal to that of a co-electrolysis cell,

(8) FIG. 6B is an exploded top view of the part of the reactor shown in FIG. 6A, the supply/recovery of the draining gas and of the oxygen produced being common to the two trapezoidal gas flow sectors,

(9) FIG. 7 is an exploded view of an interconnector of a co-electrolysis reactor according to one embodiment of the invention, which enables independent supply and circulation of cathode gases (H.sub.2O, CO.sub.2, H.sub.2, CO, CH.sub.4) from one gas flow sector of trapezoidal form to another which is adjoining, the sum of the areas of which is equal to that of a co-electrolysis cell.

(10) FIG. 7A is a view of a detail of FIG. 7,

(11) FIG. 7B is a perspective view of a detail of FIG. 7,

(12) FIGS. 8A and 8B are front views respectively of either side of an interconnector of a co-electrolysis reactor according to the invention, more specifically showing the arrangement of the sealing beads including the barrier delimiting the trapezoidal gas flow sectors in accordance with the invention, and also the path of the gases, the circulation of the oxygen produced occurring in a single compartment over the whole area of the anode;

(13) FIGS. 9A and 9B correspond respectively to FIGS. 8A and 8B, more specifically showing the arrangement of the weld seams of the three flat metal sheets forming an interconnector according to the invention,

(14) FIGS. 10A and 10B are front views respectively of either side of an interconnector of a co-electrolysis reactor according to the invention, more specifically showing the arrangement of the sealing beads including the barrier delimiting the trapezoidal gas flow sectors in accordance with the invention, and also the path of the gases with the circulation of the oxygen produced occurring in two distinct trapezoidal gas flow sectors.

(15) It is specified here that, in all of FIGS. 1 to 10B, the symbols and arrows of supply firstly of steam H.sub.2O and of carbon dioxide CO.sub.2, of distribution and recovery of the products of the co-electrolysis with, where appropriate, the in situ methanation reaction, and of oxygen O.sub.2 and of the current are shown for the purposes of clarity and precision, to illustrate the operation of a steam and CO.sub.2 co-electrolysis reactor according to the state of the art and of a steam co-electrolysis reactor according to the invention.

(16) It is also specified that, throughout the application, the terms “above”, “below”, “vertically in line with”, “vertical”, “lower”, “upper”, “bottom”, “top”, “below” and “above” should be understood with reference to an SOEC electrolysis reactor or an SOFC cell in the vertical configuration in operation, that is to say with the planes of interconnectors and electrochemical cells being horizontal, the O.sub.2 electrode below the H.sub.2 electrode. It is finally specified that all the electrolyzers described are of solid oxide type (SOEC, acronym for Solid Oxide Electrolysis Cell) operating at high temperature. The high operating temperature of an electrolyzer (electrolysis reactor) is typically between 600° C. and 950° C.

(17) Typically, the characteristics of an individual SOEC electrolysis cell suitable for the invention, of the cathode (H.sub.2 electrode)-supported type (CSC), may be those indicated as follows in table 2 below.

(18) TABLE-US-00002 TABLE 2 Electrolysis cell Unit Value Cathode 2 Material from which it is Ni-YSZ made Thickness μm 315 Thermal conductivity W m.sup.−1 K.sup.−1 13.1 Electrical conductivity Ω.sup.−1 m.sup.−1 10.sup.5  Porosity 0.37 Permeability m.sup.2 10.sup.−13 Tortuosity 4 Current density A .Math. m.sup.−2 5300 Anode 4 Material from which it is LSM made Thickness μm 20 Thermal conductivity W m.sup.−1 K.sup.−1 9.6 Electrical conductivity Ω.sup.−1 m.sup.−1 1 × 10.sup.4 Porosity 0.37 Permeability m.sup.2 10.sup.−13 Tortuosity 4 Current density A .Math. m.sup.−2 2000 Electrolyte 3 Material from which it is YSZ made Thickness μm 90 μm in support electrolyte and 5 μm in support electrode Resistivity Ωm 0.42

(19) Typically, the area of a cell is of the order of 100 cm.sup.2.

(20) FIGS. 1 and 2 have already been described in detail in the preamble. They are therefore not described hereafter.

(21) By convention, and in order to facilitate the reading of the circulations of the gases in the different figures, the following symbols are used: EH2(1): denotes the inlet of the gases circulating through the stack of the mixture of steam and of carbon dioxide supplying a trapezoidal gas flow sector T1 of the co-electrolysis cells C1, C2 . . . ; SH2(1): denotes the outlet of the gases circulating through the stack and containing the products of the co-electrolysis reaction and, where appropriate, of in situ methanation, recovered at the outlet of a trapezoidal gas flow sector T1 of the co-electrolysis cells C1, C2; EH2(2): denotes the inlet of the gases circulating through the stack of the mixture of steam and of carbon dioxide supplying a trapezoidal gas flow sector T2 of the co-electrolysis cells C1, C2 . . . ; S12(2): denotes the outlet of the gases circulating through the stack and containing the products of the co-electrolysis reaction and, where appropriate, of in situ methanation, recovered at the outlet of a trapezoidal gas flow sector T2 of the co-electrolysis cells C1, C2; E(O.sub.2): denotes the inlet of the oxidizing gas circulating through the stack and supplying all the co-electrolysis cells C1, C2; S(O.sub.2): denotes the outlet of the oxidizing gas circulating through the stack and containing the oxygen produced at the co-electrolysis cells C1, C2.

(22) The inventors were able to analyze that it was possible to envisage directly producing methane within a co-electrolysis reactor itself, depending on typical conditions of temperature and pressure.

(23) Armed with this observation, the inventors also highlighted that, despite the numerous developments in the architectures of solid oxide cell stack reactors, and more particularly the interconnectors, it is not possible to promote or not promote, as desired, the catalytic reactions within the existing reactors independently of the electrochemical operation, due to the fact that the catalytic and electrochemical areas are the same and correspond to the area of the cermet.

(24) Thus, in order to overcome this difficulty, they conceived of defining a reactor with a catalytic section of the cathode which varies with the composition of the gases along the distribution. They then conceived of dividing the active area of the cathode into two adjoining trapezoidal gas flow sectors, the sum of the areas of which corresponds to the total area of an electrochemical cell, and in which the circulation of the gases in one of the gas flow sectors is in counterflow to the other.

(25) Thus, for the same electrochemical area of the cell (the sum of the two trapezoids), the catalytic methanation reaction may be promoted or not promoted by the change in the rate of the gases within these gas flow sectors, and also by the catalytic section passed through by a given mixture of gas along the path of the cell. The prior determination of the form of the trapezoids, especially the length ratio of the bases thereof, makes it possible to control this ratio between methanation reaction and electrochemical co-electrolysis reaction.

(26) The method of co-electrolysis of steam H.sub.2O and of carbon dioxide CO.sub.2 and, where appropriate, of in situ methanation, according to the invention is carried out in a reactor 1 comprising a stack of individual electrolysis cells C1, C2 . . . of solid oxide type, of rectangular or square surface.

(27) Each cell C1, C2 . . . is formed of a cathode 2.1, 2.2 . . . comprising material(s) catalyzing the methanation reaction, of an anode 4.1, 4.2 . . . and of an electrolyte 3.1, 3.2 . . . inserted between the cathode and the anode.

(28) The stack also comprises a plurality of electrical and fluid interconnectors 5 each arranged between two adjacent individual cells C1, C2 with one face thereof in electrical contact with the anode 4.1 of one C1 of the two individual cells and the other face thereof in electrical contact with the cathode 2.2 of the other C2 of the two individual cells, and a plurality of electrical contact and gas distribution elements 9, each arranged between a cathode and an interconnector.

(29) In accordance with the invention, each electrical contact and as distribution element 9 integrates a sealing bead 10 as schematically illustrated in FIGS. 4 and 5. Preferably in order to produce these beads, a glass or glass-ceramic bead is deposited on each of the nickel screens, which penetrates both the nickel screen and the porous cathode, and a leaktight separation is thus produced between the two adjoining gas flow sectors T1, T2 of the the cathode compartments.

(30) In addition, as illustrated in FIGS. 3 to 5, a first zone (inlet EH2(1) on the left of FIG. 3 and at the top of FIG. 4) and a second zone (inlet EH2(2) on the right of FIG. 3 and at the bottom of FIG. 4) of each interconnector 5, is independently supplied with a mixture of steam H.sub.2O and of carbon dioxide CO.sub.2 and it is distributed to the cathode 2.1, 2.2 of each individual cell C1, C2 . . . then the synthesis gas produced (mixture of carbon monoxide CO and hydrogen H.sub.2) and where appropriate the additional mixture of methane CH.sub.4 and of steam H.sub.2O produced by methanation are recovered in a third zone (outlet SH2(1) at the bottom of FIG. 4) and a fourth zone (outlet SH2(2) at the top of FIG. 4) of each interconnector in fluid communication respectively with the first zone and the second zone, the sealing bead 10 forming a gas distribution barrier 10 separating the first trapezoidal gas flow sector (T1) comprising the first and third zones from a second trapezoidal gas flow sector (T2) comprising the second and fourth zones, the first and second gas flow sectors being adjoined by the barrier, forming an area substantially equal to that of each cell; the first to fourth zones being dimensioned, and the gas circulation barrier being arranged, such that the flow section of the gases increases or decreases between the first and third zones within the gas flow sector (T1) and the flow section of the gases also increases or decreases between the second and fourth zones within the second gas flow sector (T2).

(31) All the first to fourth zones of the interconnectors 5 are situated individually vertically in line respectively with the first to fourth zones of the other interconnectors 5 of the stack.

(32) In addition, as can be seen in FIGS. 4 and 5, the first and second zones of each interconnector are supplied such that the circulation to each cathode in the first trapezoidal gas flow sector T1 is in counterflow to the circulation in the second trapezoidal gas flow sector T2.

(33) In the configuration according to FIG. 4, the mixture of steam and carbon dioxide is supplied via the largest base of the trapezoidal gas flow sectors T1 and T2, in order to minimize the in situ methanation reaction compared to the co-electrolysis reaction within the stack, the catalytic area decreasing along the path of the gases produced for the same electrochemical area.

(34) In the configuration according to FIG. 5, the mixture of steam and carbon dioxide is supplied via the smallest base of the trapezoidal gas flow sectors T1 and T2, in order to maximize the methanation reaction compared to the co-electrolysis reaction within the stack, the catalytic area increasing along the path of the gases produced for the same electrochemical area.

(35) The interconnectors 5 may also be produced to arrange the different zones for supply and recovery of the draining gas and of the oxygen produced such that their circulation at the cells C1 is in co-current to the circulation at the cells C2, or in counter-current thereto.

(36) FIGS. 6A and 6B show a schematic representation of a part of a high-temperature solid oxide co-electrolyzer (SOEC) according to the invention.

(37) This co-electrolysis reactor comprises a stack of individual electrolysis cells of SOEC type (C1, C2), each formed of a cathode 2.1, 2.2, of an anode 4.1, 4.2, and of an electrolyte 3.1, 3.2, inserted between the cathode and the anode.

(38) A fluid and electrical interconnector 5 is arranged between two adjacent individual cells C1, C2, with one face thereof in electrical contact with the anode of one of the two individual cells and the other face thereof in electrical contact with the cathode of the other of the two individual cells.

(39) As shown in FIGS. 6A and 6B, insulation and leaktightness frames 11 are also provided, making it possible to provide electrical insulation between two adjacent interconnectors 5. Each frame 11 is pierced with ports O, suitable for accommodating rods for fixing the stack, and also seals 12 provided to produce leaktightness around the ports for supplying the gases in co-electrolysis, H.sub.2O, CO.sub.2, air, and for recovering the gases produced, H.sub.2, CO, O.sub.2 with air, and also around the cell.

(40) The same electrical current passes through all the electrolysis cells C1 and C2.

(41) In the reactor according to the invention, all the cathode compartments 50 of the cells C1, C2 of the same trapezoidal gas flow sector T1 or T2, in which the supply mixture of steam H.sub.2O and of CO.sub.2 and the hydrogen produced H.sub.2 with optional syngas circulate, communicate with one another. On the other hand, the circulation of the gases within each cathode compartment 50 of the trapezoidal gas flow sector T1 is independent of that of the as flow sector T2.

(42) The co-electrolysis reaction produces oxygen which is collected by all the anode compartments 51 which communicate with one another.

(43) According to the invention, each electrical contact and gas distribution element 9 integrating a sealing bead 10 forms a gas distribution barrier between on the one hand a first 61, 71, 81 and a third 63, 73, 83 interconnector zone 5 and on the other hand a second 62, 72, 82 and a fourth 64, 74, 84 interconnector zone.

(44) The first to fourth interconnector zones 5 are dimensioned, and the gas circulation barrier 10 is arranged, such that the distribution of the gases between the first 61, 71, 81 and the third 63, 73, 83 zone is carried out in a first gas flow sector T1 of trapezoidal form. The distribution of the gases between the second 62, 72, 82 and the fourth zone 64, 74, 84 is carried out in a second as flow sector T2 of trapezoidal form.

(45) As can be seen in FIG. 6B, the two trapezoidal gas flow sectors T1 and T2 are adjoined by the barrier 10, forming an area substantially equal to the rectangular or square area of each cell.

(46) In addition, as shown in FIGS. 8A and 8B, a seal 12 ensures leaktightness at the periphery of the cathode compartment 50. The barrier 10 also adjoins this seal 12.

(47) FIG. 7 shows an exploded view of an interconnector 5 according to the invention, making it possible to provide the supply of steam H.sub.2O and CO.sub.2, the counterflow circulation in the two trapezoidal gas flow sectors of the mixture of steam, of CO.sub.2 and of the syngas produced at the cells C1, C2, and also the recovery of the oxygen O.sub.2 produced within the stack.

(48) The interconnector 5 consists of three flat metal sheets 6, 7, 8, elongated along two axes of symmetry (X, Y) orthogonal to one another, the flat metal sheets being laminated and assembled together by welding. A central metal sheet 7 is inserted between a first 6 and a second 8 end metal sheet.

(49) The second 8 end metal sheet is intended to come into mechanical contact with the plane of a cathode 2.1 of an individual electrolysis cell C1 and the central metal sheet 7 is intended to come into mechanical contact with the plane of an anode 4.1 of an adjacent individual electrolysis cell, each of the two adjacent individual electrolysis cells (C1, C2) of SOEC type being formed from a cathode 2.1, 2.2, from an anode 4.1, 4.2, and from an electrolyte 3.1, 3.2, inserted between the cathode and the anode.

(50) Each of the three flat metal sheets 6, 7, 8 comprises a central part 60, 70, 80.

(51) The first end metal sheet 6 comprises a pierced central part 60, while the second end metal sheet 8, and also the central metal sheet 7, comprises a non-pierced central part, respectively 80 and 70.

(52) Each metal sheet 6, 7, 8 is pierced, at the periphery of the central part thereof, with six ports 61, 62, 63, 64, 65, 66; 71, 72, 73, 74, 75, 76; 81, 82, 83, 84, 85, 86.

(53) The first 61, 71, 81 to fourth 64, 74, 84 ports of each metal sheet are elongated over a length corresponding to a portion of the length of the central part 60, 70, 80 along one of the axes X of the metal sheets, and are distributed pairwise on either side of said axis X.

(54) The fifth 65, 75, 85 port is elongated over a length corresponding substantially to the length of the central part 60, 70, 80 along the other of the axes Y.

(55) The sixth 66, 76, 86 port is elongated over a length corresponding substantially to the length of the central part 60, 70, 80 along the other of the axes Y.

(56) The first 6 end metal sheet also comprises a seventh 67 and an eighth 68 port arranged symmetrically on either side of the axis Y, inside its first to fourth ports 61 to 64, and are elongated over a length corresponding substantially to the length of the central part along the axis Y.

(57) The second 8 end metal sheet also comprises a seventh 87, eighth 88, ninth 89 and tenth 800 port inside, respectively, its first 81, second 82, third 83 and fourth 84 ports, each of these seventh to tenth ports being elongated over a length corresponding substantially respectively to the length of the first to fourth ports along the axis X.

(58) As can be seen in FIG. 7, the first 71 to sixth 76 ports of the central metal sheet are widened towards the interior relative, respectively, to the first 61, 81 to sixth 66, 86 ports of each end metal sheet 6, 8.

(59) The first 61, 71, 71 and second 62, 72, 82 ports of the three metal sheets 6, 7, 8 are of substantially identical dimensions to one another.

(60) The third 63, 73, 83 and fourth 64, 74, 84 ports of the three metal sheets 6, 7, 8 are of substantially identical dimensions to one another.

(61) The length of the first 61, 71, 71 and second 62, 72, 82 ports is greater than that of the third 63, 73, 83 and fourth 64, 74, 84 ports of the three metal sheets 6, 7, 8. The length ratio between that of the first and second ports and that of the third and fourth ports determines the geometrical form of the trapezoidal pas flow sectors T1, T2 and therefore determines the ratio that it will be possible to obtain between the in situ methanation reaction and the electrochemical co-electrolysis reaction.

(62) The seventh 87 and eighth 88 ports of the second end metal sheet 8 are of substantially identical dimensions to those of the first 81 and second 82 ports thereof.

(63) The ninth 89 and tenth 800 ports of the second end metal sheet 8 are of substantially identical dimensions, in the X direction, to those of the third 83 and fourth 84 ports thereof.

(64) All the widened ports 71 to 76 of the central metal sheet 7 comprise, in their widened part, tongues of metal sheets spaced apart from one another, forming a comb, each of the slits defined between the edge of a widened slit and a tongue or between two consecutive tongues opening onto one of the inner ports 67, 68 or 87, 88, 89, 800, respectively of the first 6 or of the second 8 end metal sheet,

(65) The lamination and the assembly of the three metal sheets 6, 7, 8 with one another are carried out such that: the tongues of metal sheets form spacers between first 6 and second 8 end metal sheets, respectively between the fifth 65 and seventh 67 ports of the first end metal sheet 6, between the sixth 66 and eighth 68 ports of the first end metal sheet 6, between the first 81 and seventh 87 ports of the second end metal sheet 8, between the second 82 and eighth 88 ports of the second end metal sheet 8, between the third 83 and ninth 89 ports of the second end metal sheet, and between the fourth 84 and tenth 800 ports of the second end metal sheet 8, each of the first 71 to sixth 76 ports of the central metal sheet 7 is individually in fluid communication respectively with one of the corresponding first 61, 81 to sixth 66, 86 ports of the two other metal sheets 6, 8, the fifth 65 and seventh 67 ports of the first end metal sheet 6 are in fluid communication via slits of the fifth widened port 75 of the central metal sheet 7, while the sixth 66 and eighth 68 ports of the first end metal sheet are in fluid communication via slits of the sixth widened port 76 of the central metal sheet 7, the first 81 and seventh 87 ports of the second end metal sheet 8 are in fluid communication via slits of the first widened port 71 of the central metal sheet 7, while the second 82 and eighth 88 ports of the second end metal sheet 8 are in fluid communication via slits of the second widened port 72 of the central metal sheet 7, the third 83 and ninth 89 ports of the second end metal sheet are in fluid communication via slits of the third widened port 73 of the central metal sheet 7, and the fourth 84 and tenth 800 ports of the second end metal sheet 8 are in fluid communication via slits of the fourth widened port 74 of the central metal sheet 7.

(66) FIGS. 7A and 7B show in detail the production of the comb formed by the tongues of metal sheet 710 at the widened slit 71 of the central metal sheet and its arrangement between the two end metal sheets 6, 8 in order to enable the supply of a cell, here a mixture of steam H.sub.2O and of carbon dioxide CO.sub.2. Thus, the comb formed 710, 711 enables the mixture to pass from the supply manifold 61, 71, 81 to the distribution slit 87, by passing into the space between the two end metal sheets 6, 8. The thickness of the central metal sheet 7 at this comb 710, 711 provides it with a spacer function and thereby guarantees the height of the passage for the gas mixture into the space between the end metal sheets 6, 8. Such a passage of gases according to the invention via the inside of the interconnector 5a has the advantage of liberating a flat surface for producing seals. In addition, by virtue of these comb forms for the widened slits 71,72, on one side and 75 on the other, a homogeneous distribution of each gas (H.sub.2O, CO.sub.2, Air) is obtained over each trapezoidal gas flow sector of a co-electrolysis cell, and by virtue of these comb forms for widened slits on one side 73, 74 and 76 on the other, a recovery of the gases produced (H.sub.2, CO, O.sub.2).

(67) The operating method of a co-electrolysis reactor according to the invention, as has just been described, will now be described with reference to FIGS. 8A and 8B:

(68) The first ports 61, 71, 81 are supplied with a mixture of steam and of carbon dioxide CO.sub.2 of the interconnector 5 (see reference EH2(1)) and simultaneously but separately the second ports 62, 72, 82 of the same interconnector 5 are also supplied preferably with the same mixture and the same flow rate (see reference EH2(2)).

(69) The path within an interconnector 5 of the gas mixture injected, converting gradually into H.sub.2+CO, is schematically depicted in FIG. 8A. It can be seen that each trapezoidal gas flow sector T1 is passed through by the mixture in counterflow to that which passes through the adjoining trapezoidal gas flow sector T2. The barrier 10 within the electrical contact element 9 and the electrode 2.1, preferably a nickel screen, and the peripheral seal, preferably made of glass, enable perfect leaktightness between on the one hand the two gas flow sectors T1 and T2 and relative to the exterior of the stack on the other hand.

(70) In addition, the fifth 65, 75, 85 ports of the three metal sheets 6, 7, 8 of each interconnector 5 are supplied with a draining gas (reference E(O.sub.2)), such as air or pure oxygen.

(71) The path of the air as draining gas injected and of the oxygen produced within an interconnector 5 is schematically illustrated in FIG. 8B.

(72) The hydrogen and the CO produced (reference SH2(1)) by the co-electrolysis of steam and of CO.sub.2 and also, where appropriate, the methane produced by the methanation reaction within the electrode 2.1 itself are thus recovered at gas flow sector T1 of the cells, in the third ports 63, 73, 83 of each interconnector 5.

(73) The hydrogen and the CO produced (reference SH2(2)) by the co-electrolysis of steam and of CO.sub.2 and also, where appropriate, the methane produced by the methanation reaction are also recovered at gas flow sector T2 of the cells, in the fourth ports 64, 74, 84 of each interconnector 5.

(74) Simultaneously, the oxygen O.sub.2 produced S(O.sub.2) is recovered in the sixth ports 66, 76, 86 of the three metal plates of each interconnector 5. The circulation of draining gas and the recovery of oxygen are therefore common to all the cells, independently of the separation thereof into two as flow sectors T1, T2, at the cathodes.

(75) FIGS. 10A and 10B show a variant of circulation of the gases on the anode 4 side, according to which the same separation into two adjoining trapezoidal gas flow sectors is carried out on the side of the oxygen electrode (anode 4). As can be seen, the trapezoidal gas flow sectors on the cathode 2 side are at 90° to those on the anode 4 side. Thus, the draining gas such as air supplies the zone 66.1, 76.1, 86.1 and independently the zone 65.2, 75.2, 85.2. In addition, the oxygen produced with, where appropriate, the draining gas, is recovered at zone 65.1, 75.1, 85.1 and independently zone 66.2, 76.2, 86.2. The circulation of the oxygen produced between the zone 66.1, 76.1, 86.1 and the zone 65.1, 75.1, 85.1 is also in counterflow between the zone 65.2, 75.2, 85.2 and the zone 66.2, 76.2, 86.2.

(76) This thus gives a cross-current circulation of the oxygen produced relative to the hydrogen produced, with additionally a circulation of the oxygen produced in two distinct trapezoidal gas flow sectors.

(77) The three flat metal sheets 6, 7, 8 constituting each interconnector 5 according to the invention are thin flat metal sheets, pierced and assembled with one another by welding. The thin metal sheets are preferably metal sheets less than 3 mm thick, typically with a thickness of the order of 0.2 mm. All the welds between metal sheets are produced upon manufacture and may advantageously be produced according to a transmission laser technique, which is possible due to the small thickness of the thin metal sheets, typically of the order of 0.2 mm.

(78) All the metal sheets are advantageously made of ferritic steel with approximately 20% chromium, preferably made of CROFER® 22APU or FT18TNb, AISI 441, or based on nickel of Inconel® 600 or Haynes® type in thicknesses typically of between 0.1 and 1 mm.

(79) Assembly by weld lines ls around the ports between flat metal sheets 6, 7, 8 guarantees good leaktightness during operation of the electrolyzer between the mixture of steam and of carbon dioxide CO.sub.2 conveyed to the interconnectors 5 and distributed, and also the gases recovered in a trapezoidal gas flow sector T1 and that of the adjoining gas flow sector T2, and with the draining gas conveyed E(O2) and the oxygen S(O2) recovered. The weld lines are illustrated in FIGS. 9A to 9B.

(80) As illustrated on all the FIGS. 7 to 10B, the three metal sheets 6, 7, 8 are pierced at their periphery by additional ports O suitable for accommodating fixing rods. These fixing rods make it possible to apply a retention force to the stack of the different components of the electrolysis reactor.

(81) The invention is not limited to the aforementioned examples; in particular, features of the illustrated examples may be combined in variants that have not been illustrated.

(82) Other variants and improvements may be envisaged within the context of the invention.

(83) In particular, if the material inserted into the nickel screen 8 and into the cathode 2 in order to produce the sealing bead 10 is a glass-ceramic in the examples described in detail above, it may be any material that opposes the passage of the gases and that may be readily shaped within a porous metallic substrate of a contact element. It may especially be a solder before or after being placed within the stack.

CITED REFERENCE

(84) [1]: Fabien Ocampo et al., “Methanation of carbon dioxide over nickel-based Ce0.72Zr0.28O2 mixed oxide catalysts prepared by sol-gel method”, Journal of Applied Catalysis A: General 369 (2009) 90-96.