Water electrolysis reactor (SOEC) or fuel cell (SOFC) with an increased rate of water vapour use or fuel use, respectively

Abstract

The invention relates to arranging a new seal within a porous substrate which forms the contact element of each hydrogen circulating electrode, such as the cathode for an SOEC reactor and the anode for an SOFC fuel cell, and in the periphery of the electrode beyond the ducts for supplying and recovering gases, in order to force the gases to circulate into the only useful zone of the cell which corresponds to the electrochemically active surface of the electrode. Thus, all of the gases supplied can be converted.

Claims

1. A device, comprising: an individual solid oxide electrolysis cell comprising a cathode, an anode and an electrolyte inserted between the cathode and the anode, a first and a second electrical and fluid interconnector, each consisting of a component made of electron-conducting and gastight material, the first and second interconnectors being arranged on either side of the individual cell; the first interconnector being pierced with a steam supplying conduit for supplying steam, which opens at a periphery of one side of the cathode, and with a hydrogen recovery conduit for recovering hydrogen produced, which opens at a periphery of the cell on a side of the cathode opposite the side on which the steam supplying conduit opens, so as to distribute the steam supplied and the hydrogen produced, in a first compartment; the second interconnector being pierced with an oxygen recovery conduit for recovering oxygen produced, which opens at a periphery of the cell on a side of the anode so as to distribute the oxygen produced to the oxygen recovery conduit in a second compartment; a first electrical contact element, different from the interconnectors, which is in mechanical contact on the one hand with the first interconnector and on the other hand with the cathode; the first electrical contact element being a porous substrate; a first seal arranged at a periphery of the individual cell and bearing both against the first interconnector and against the second interconnector; a second seal arranged at a periphery of the anode of the individual cell and bearing both against the second interconnector and against the electrolyte; and a third seal, inserted in the porous substrate of the first contact element and bearing against the first interconnector and the cathode by being arranged at a periphery of the steam supplying conduit and hydrogen recovery conduit, respectively, thus delimiting the first compartment for distributing the steam supplied and the hydrogen produced.

2. The device of claim 1, wherein the second interconnector being is pierced with a draining gas suppling conduit for supplying draining gas on the cell on a side of the anode opposite the side on which the oxygen recovery conduit opens, so as to distribute respectively the draining gas supplied and the oxygen produced, from the draining gas supplying conduit to the oxygen recovery conduit.

3. The device of claim 1, further comprising a second electrical contact element, which is in mechanical contact on the one hand with the anode and on the other hand with the second interconnector.

4. The device of claim 1, wherein the third seal additionally is arranged substantially in a vertical line with the second seal, the first contact element being considered to be above the electrolyte.

5. The device of claim 1, wherein the third seal at the periphery of the conduits is a bead based on glass and/or glass-ceramic inserted into the porous substrate of the first contact element.

6. The device of claim 1, wherein the third seal at the periphery of the conduits consists of a bead based on a solder inserted into the porous substrate of the first contact element.

7. The device of claim 1, wherein the third seal at the periphery of the conduits has the same height as that of the porous substrate of the first contact element.

8. The device of claim 1, wherein the porous substrate of the first contact element is a metal screen.

9. The device of claim 1, wherein the porous substrate of the first electrical contact element has a surface area identical to that of the electrode with which it is in contact.

10. An HTE electrolysis or co-electrolysis reactor, comprising a stack of a plurality of devices of claim 1.

11. A system, comprising the HTE electrolysis or co-electrolysis reactor of claim 10, wherein the HTE electrolysis or co-electrolysis reactor is operable reversibly as a fuel cell.

12. A device, comprising: an individual solid oxide electrochemical cell formed of an anode, a cathode and an electrolyte inserted between the cathode and the anode, a first and a second electrical and fluid interconnector, each consisting of a component made of electronconducting and gastight material, the first and second interconnectors being arranged on either side of the individual cell; the first interconnector being pierced with a fuel supplying conduit for supplying fuel, which opens at a periphery of one side of the anode, and with a water recovery conduit for recovering water produced, which opens at a periphery of the cell on a side of the anode opposite the side on which the fuel supplying conduit opens, so as to distribute the fuel supplied and the water produced, respectively, in a first compartment; the second interconnector being pierced with an air or oxygen supplying conduit for supplying air or oxygen, which opens at a periphery of the cell on one side of the cathode and with an air or oxygen recovery conduit for recovering surplus air or oxygen, which opens at a periphery of the cell on a side of the cathode opposite the side on which the air or oxygen supplying conduit opens, so as to distribute the air or oxygen to the air or oxygen recovery conduit in a second compartment; a first electrical contact element, different from the interconnectors, which is in mechanical contact on the one hand with the first interconnector and on the other hand with the anode; the first electrical contact element being a porous substrate; a first seal arranged at the periphery of the individual cell and bearing both against the first interconnector and against the second interconnector; a second seal arranged at the periphery of the cathode of the individual cell and bearing both against the second interconnector and against the electrolyte; a third seal, inserted into the porous substrate of the first contact element and bearing against the first interconnector and the anode by being arranged at a periphery of the fuel supplying conduit and the water recovery conduit, respectively, thus delimiting the first compartment for distributing the fuel supplied and the water produced.

13. The device of claim 12, further comprising a second electrical contact element, which is in mechanical contact on the one hand with the cathode and on the other hand with the second interconnector.

14. A fuel cell, comprising a stack of a plurality of devices of claim 12.

15. A system, comprising the fuel cell of claim 14, wherein the fuel cell is operable reversibly as an HTE electrolysis or co-electrolysis reactor.

16. The device of claim 12, wherein the third seal additionally is arranged substantially in a vertical line with the second seal, the first contact element being considered to be above the electrolyte.

17. The device of claim 12, wherein the third seal at the periphery of the conduits is a bead based on glass and/or glass-ceramic inserted into the porous substrate of the first contact element.

18. The device of claim 12, wherein the third seal at the periphery of the conduits consists of a bead based on a solder inserted into the porous substrate of the first contact element.

19. The device of claim 12, wherein the third seal at the periphery of the conduits has the same height as that of the porous substrate of the first contact element.

20. The device of claim 12, wherein the porous substrate of the first contact element is a metal screen.

21. The device of claim 12, wherein the porous substrate of the first electrical contact element has a surface area identical to that of the electrode with which it is in contact.

22. An HTE electrolysis or co-electrolysis reactor, comprising a stack of a plurality of devices of claim 12.

Description

DETAILED DESCRIPTION

(1) Other advantages and features of the invention will become more clearly apparent on reading the detailed description of examples of implementation of the invention, given by way of nonlimiting illustration 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 electrolyzer (HTE) of SOEC type comprising interconnectors according to the prior art,

(4) FIGS. 3A and 3B are respectively longitudinal cross-sectional and top schematic views of anindividual unit of an HTE electrolyzer or of a fuel cell of SOFC type according to the prior art showing the configuration of the seals, electrical contacts and distribution of gases within the stack,

(5) FIGS. 4A and 4B repeat FIGS. 3A and 3B and show the circulation of the steam and of the hydrogen produced, according to the prior art,

(6) FIG. 5 is a view identical to FIG. 3A and shows the flexural stresses to which the cell is subjected,

(7) FIGS. 6A and 6B are respectively longitudinal cross-sectional and top schematic views of an individual unit of an HTE electrolyzer or of a fuel cell of SOFC type according to the prior art showing the configuration of the seals, electrical contacts and distribution of gases within the stack, these figures further showing the circulation of the steam and of the hydrogen produced, according to the prior art,

(8) FIG. 7 is a view identical to FIG. 6A and shows the absence of flexion for the cell when the seal in accordance with the invention is of suitable height and has a suitable position,

(9) FIG. 8 is a view identical to FIG. 6A and shows the displacements F of the cell when the seal in accordance with the invention is not positioned as in FIG. 7,

(10) FIG. 9 is a view identical to FIG. 6A and shows the stresses to which the cell is subjected when the seal in accordance with the invention does not have the height as in FIG. 7,

(11) FIG. 10 is a photographic reproduction, in top view, of an individual unit of an electrolyzer according to the invention showing the positioning of the seal in accordance with the invention,

(12) FIG. 11 shows curves representative of the polarization (change in voltage as a function of the current applied) of a stack of known cathode-supported electrolysis cells (CSC) having a surface area equal to 100 cm.sup.2, at a temperature of 800° C., under steam H.sub.2O at the inlet, respectively with a configuration according to the prior art and a configuration according to the invention;

(13) FIG. 12 shows curves representative of the change in voltage, during the polarization, as a function of the rate of steam use of a stack of known cathode-supported electrolysis cells (CSC) having a surface area equal to 100 cm.sup.2, at a temperature of 800° C., under steam H.sub.2O at the inlet, respectively with a configuration according to the prior art and a configuration according to the invention;

(14) FIG. 13 shows a curve representative of the change in voltage, during the polarization, as a function of the rate of steam use of a single known cathode-supported electrolysis cell (CSC) having a surface area equal to 100 cm.sup.2, at a temperature of 800° C., under steam H.sub.2O at the inlet, with a configuration according to the invention.

(15) It is specified here that, in FIGS. 1 to 2, the symbols and arrows of supply of, on the one hand, steam H.sub.2O, of distribution and recovery of dihydrogen H.sub.2 and of oxygen O.sub.2 and of the current and, on the other hand, of distribution and recovery 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 electrolysis reactor according to the prior art and of an electrolysis reactor according to the invention.

(16) It is also specified that, throughout the application, the terms “above”, “below”, “in a vertical line with”, “vertical”, “lower”, “upper”, “bottom”, “top”, “below” and “above” should be understood with reference to an SOEC electrolysis reactor or an SOFC fuel 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.

(17) It is also specified that all the electrolyzers described are of solid oxide type (SOEC, acronym of “solid oxide electrolysis cell”) operating at high temperature. Thus, all the constituents (anode/electrolyte/cathode) of an electrolysis cell are ceramics. The high operating temperature of an electrolyzer (electrolysis reactor) is typically between 600° C. and 1000° C.

(18) Typically, the characteristics of an individual SOEC electrolysis cell suitable for the invention, of the cathode-supported (CSC) type, may be those indicated as follows in table 1 below.

(19) TABLE-US-00001 TABLE 1 Electrolysis cell Unit Value Cathode 2 Material from which it is made Ni-YSZ 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 made LSM 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 made YSZ Thickness μm Resistivity Ω m 0.42

(20) All of the FIGS. 1 to 5 have already been commented on in the preamble. They are therefore not described below.

(21) FIGS. 6A and 6B show an individual unit of an HTE electrolyzer according to the invention.

(22) This unit firstly repeats all of the components, with their relative arrangements, of the unit according to FIGS. 4A and 4B according to the prior art.

(23) The contact element 8 is here a nickel screen of the same surface area as the cathode 2.

(24) According to the invention, a third seal 10 is provided in addition to the first seal 6 and second seal 7. This third seal 10 is inserted in the nickel screen 8, bears against the top interconnector 5.1 and the cathode 2 by being arranged at the periphery of the conduits for supplying steam 52, and for recovering the hydrogen produced 54, respectively.

(25) The arrangement of the third seal 10 according to the invention thus delimiting the compartment 50 for distributing the steam supplied and the hydrogen produced which is restricted relative to the one from the prior art. Specifically, as shown by the arrows on the figures in FIGS. 4A and 4B, the steam is distributed uniformly and solely over the entire surface of the cathode 2. Thus, unlike the prior art, the steam is not distributed into non-active zones in the free space between the first seal 6 and the periphery of the cell, such as the zones Z1 from FIGS. 4A and 4B.

(26) In order to produce the seal 10 according to the invention, a continuous bead of a glass-ceramic in the pasty state is deposited at ambient temperature on the surface of the nickel screen 8. Next, by passing beyond its glass transition temperature, between 850 and 1000° C., the paste melts and fills the meshes of the nickel screen 8 by conforming to the shape thereof. At the operating temperature of the electrolyzer, typically between 600 and 850° C., the glass-ceramic third seal 10 is crystallized.

(27) The seal is deposited using a syringe and a deposition robot. The syringe pressure and the size of the needle are adjustable which makes it possible to obtain a deposited amount over a given time. The speed of advance of the arm of the robot is itself also adjustable. These parameters make it possible to meter the amount of glass/glass-ceramic deposited.

(28) The temperature increase and decrease rates of the seal are preferably less than 5° C. min.

(29) FIG. 7 illustrates the judicious positioning of the seal 10, the height of which is additionally well calibrated. As is seen, the third seal 10 is arranged in line with, i.e. in a vertical line with, the seal 7 under the electrolyte 3 at the periphery of the anode 4, and its height is substantially the same as that of the nickel screen 8. With these parameters, it may be seen that under clamping stresses represented in the form of arrows P, the stresses are uniformly distributed on either side of the cell which is not therefore subjected to tensile mechanical stresses that are detrimental thereto. Thus, only compressive stresses are applied uniformly on either side of the cell, these stresses being easily withstood by the cell.

(30) FIG. 8 illustrates a configuration according to which the third seal 10 according to the invention is not positioned in an optimal manner. In this configuration, during the clamping, flexural displacements symbolized by the arrows F are applied to the cell. These flexural displacements give rise to detrimental tensions within the latter.

(31) FIG. 9 illustrates a configuration according to which the seal 10 according to the invention has not been deposited with a suitable amount of glass-ceramic, which ultimately results in too high a height of the seal 10. It may be seen that in this configuration the clamping stresses P are not transmitted in full, or even are not transmitted at all to the nickel screen 8. Therefore, the mechanical contact between the top interconnector 5.1, the nickel screen 8 in the cathode 2 is not optimal, or even non-existent owing to an unoccupied zone Z2. Another risk is the overflowing of the glass-ceramic into the gas inlet and outlet channels.

(32) On the contrary, in the case of too low a deposited amount of glass-ceramic, the nickel screen 8 may not be completely leaktight, which would have the consequence of reintroducing at least some of the steam into the zones Z1 as in the prior art.

(33) FIG. 10 shows a concrete embodiment of a third seal 10 made of glass within and at the periphery of a nickel screen 8 intended to constitute a contact element between interconnector and cathode. The composition and the use of this glass seal 10 are as described in patent FR3014246 B1.

(34) The inventors experimentally validated the effectiveness of a seal according to the invention.

(35) They thus carried out comparative tests between a high-temperature electrolyzer according to the prior art and an electrolyzer according to the invention with exactly the same components arranged identically, the electrolyzer according to the invention being further provided with a glass seal 10 inserted in a nickel screen 8.

(36) Each of the electrolyzers tested comprises a stack of 25 individual units with, for each cell, an active surface area of 100 cm.sup.2.

(37) The flow rates of steam sent to the inlet of electrolyzers are 10.8 Nml/min and per cm.sup.2 of active surface area of the stack. Added to this steam is a hydrogen flow rate of 1.2 Nml/min/cm.sup.2, also sent to the inlet.

(38) The electrolyzers were tested at an operating temperature of 800° C. The two electrolyzers have excellent leaktightness and 100% of the gases sent to the inlet are recovered at the outlet.

(39) FIG. 11 presents polarization curves respectively of the electrolyzer according to the prior art and according to the invention, which are subjected to an increasing current. The total voltage of the stack is then measured. From these polarization curves, it is possible to calculate the equivalent electrical resistance referred to as ASR (acronym for “area specific resistance”).

(40) It emerges from this FIG. 11 that the ASR values are identical for the two electrolyzers, with a value of 0.34 Ohm.Math.cm.sup.2, which shows that, in both cases, the electrical contacts are good. In other words, the seal 10 according to the invention does not disrupt the quality of the electrical contacts or the performance of the electrolyzer.

(41) An electrolyzer consumes the steam sent and converts it into hydrogen. When a polarization curve is produced, the current increases continuously which consumes more and more steam. The rate of use of the steam sent therefore increases during the polarization. When the residual steam in the active zones decreases, then the voltage within the electrolyzer increases greatly. This great increase in the voltage over the polarization curve is a marker indicating that most of the steam present in the active zones has been consumed. This great increase in voltage is referred to as “concentration overvoltage”. For the commercial electrochemical cells of the prior art, if the concentration overvoltages appear for values of less than 90% of the rate of steam use, it may be considered that a portion of the steam is not distributed in the active zones of the electrolyzer and that it is lost for the application.

(42) FIG. 12 presents the rate of steam use over the polarization curve as a function of the measured voltage, this being for an electrolyzer according to the prior art and the one according to the invention which were considered in the previous test.

(43) It emerges from this FIG. 12 that the electrolyzer according to the prior art has a good performance up to a rate of use of 45%. Then concentration overvoltages are visible since the voltage increases rapidly.

(44) The electrolyzer according to the invention itself operates up to rates of use of at least 65% without the appearance of a concentration overvoltage. This tends to prove that the seal 10 according to the invention makes it possible to substantially improve the distribution of the gases within the stack. In this test, the rates of use greater than 65% were not tested. However, the increase of at least 20% in the maximum rate of use is already indicative of a marked improvement in the performance.

(45) An additional test was carried out on another electrolyzer according to the invention with a single individual unit therefore provided with a single electrolysis cell having an active surface area of 100 cm.sup.2.

(46) The flow rates injected at the cell inlet are here 10.8 Nml/min/cm.sup.2 of active surface area for the steam to which a hydrogen flow rate of 1.2 Nml/min/cm.sup.2 is added. The test is also carried out at a temperature of 800° C.

(47) It is observed that this single-unit electrolyzer is perfectly leaktight and 100% of the gases sent are recovered at the outlet.

(48) FIG. 13 presents the change in voltage at the terminals of the electrolyzer over a polarization curve and is plotted as a function of the rate of use.

(49) It emerges from this FIG. 13 that the rate of use increases during the test and the concentration overvoltages appear for values of the order of 95% of rate of steam use. This proves that all of the steam sent is used.

(50) Following the tests carried out, it is therefore possible to conclude that the additional seal 10 according to the invention makes it possible to distribute the steam in an optimal manner in the active zones of the cells and that therefore, unlike the configurations according to the prior art, no amount of steam is sent into non-active zones of the electrolyzer, such as the zones Z1 from FIGS. 4A and 4B according to the prior art.

(51) 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.

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

(53) In particular, if the material inserted in the nickel screen 8 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 that seals the screen over its periphery, before or after its my placement within the stack.

(54) Instead of a nickel screen, use may be made of other contact elements containing a porous substrate and that are electron conductors.