BE1031984B1 - Interlayer for an electrolytic cell, electrolytic cell and electrolyzer stack - Google Patents

Abstract

The present invention relates to the technical field of electrolysis and more particularly to the design of an electrolytic cell. Particular aspects of the invention relate to an interlayer intended to be used in an electrolytic cell, to an electrolytic cell and to an electrolyzer stack. An interlayer (12) intended to be used in an electrolytic cell (10) and defining a space (125) between a bipolar plate (11) and a membrane (14), has a generally rectangular shape and comprises openings for supplying (121) electrolyte and for extracting (1221, 1222) electrolyte/gas mixture communicating with the space (125). According to the invention, at least one of the supply (121) or extraction (1221, 1222) openings opens into the space (125) via a flared section (123) on the surface of the insert (12).

Description

1 BE2023/5760

Interlayer for an electrolytic cell, electrolytic cell and electrolyzer stack

[0001] Description

[0002] The present invention relates to the technical field of electrolysis and more particularly to the design of an electrolytic cell. Particular aspects of the invention relate to an interlayer intended to be used in an electrolytic cell, to an electrolytic cell and to an electrolyzer stack.

[0003] Indication of prior art

[0004] The need to reduce greenhouse gas production and use renewable energy is now well known. Dihydrogen is an alternative to hydrocarbons because it is an easily storable energy vector, unlike electricity, and its oxidation releases very significant energy (285 kJ/mole).

[0005] Several ways of producing gaseous dihydrogen are known; the most advantageous consists of electrolyzing the water molecule because it is a high-yield reaction which does not directly produce CO) unlike the massively used processes of reforming methane, coal and hydrocarbons.

[0006] Three main types of electrolysers are known for the electrolysis of water: - alkaline electrolysers (AWE), which are characterised by the use of a liquid electrolyte which allows the transfer of hydroxyl ions (OH7) from the cathode to the anode, - high temperature electrolysers, the electrolyte of which is a ceramic; and - membrane electrolysers (PEM), the electrolyte of which is a proton-conducting ion exchange membrane.

[0007] The present invention relates more particularly to a membrane electrolyser.

[0008] A membrane electrolysis device generally comprises a stack of electrolytic cells within which the water electrolysis reaction is carried out. The electrolytic cells are electrically assembled in series and fluidically in parallel. Referring to Figures 1 to 3, an electrolytic cell 10 comprises, in order, a bipolar plate 11, a space 125 surrounded by an intermediate frame (or simply interlayer) 12, a first electrode 131, in this case a cathode, a membrane 14, a second electrode 132, namely an anode, a second space 125 surrounded by an intermediate frame 12 and a second bipolar plate 11. The space (sometimes also called electrode chamber) surrounded by the interlayer 12 is intended for the circulation of the electrolyte and the electrolysis gases and allows, thanks to the circulation of the electrolytic fluid, the arrival of the reactants (water and hydroxide ions) at the surface of the electrodes 131 and 132. The interlayer 12 is generally metallic and provides a low resistivity path for the electric current between each bipolar plate 11 and the electrode 131 or 132 attached to it. The electrodes 131, 132 are generally made of doped metal, for example nickel, but other conductive metals can also be used. The membrane 14 (also called a diaphragm or porous separator) provides electrical insulation between the two electrodes 131, 132 as well as the transport of protons or hydroxide ions from one electrode to the other while being impervious to electrolysis gases. The bipolar plates 11 (also called a current collector) have the function of supplying the current and evacuating the gases from the electrolytic cell 10. The materials of the bipolar plates 11 must therefore have a sufficient level of electrical conductivity and good chemical inertia with respect to the fluids present in the electrolytic cell 10 (electrolyte, acid, gas). The most common bipolar plates 11 are made of graphite, conductive composite material or metal (for example stainless steel). The bipolar plates 11 are generally provided with grooves or reliefs - promoting the evacuation of gases. The electrolyte (alkaline water solution) from a supply pipe 15 is introduced into the space 125 through a supply opening 121 in the spacer 12, the resulting electrolyte/gas mixture is extracted from the space 125 through a second extraction opening 1221 or 1222 made in the spacer 12. When it is the space 125 arranged between the bipolar plate 11 and the cathode 131, the electrolyte/gas mixture extracted through the extraction opening 1221 is essentially composed of gaseous dihydrogen, Hy, and the mixture is evacuated into the extraction pipe 161.

When it comes to the space 125 arranged between the anode 132 and the bipolar plate 11, the electrolyte/gas mixture extracted through the extraction opening 1222 is essentially composed of gaseous dioxygen, O7, and the mixture is discharged into the extraction pipe 162. The extraction pipes 161 and 162 conduct the electrolyte/gas mixture to separate degassing devices (not shown) for recovering the dihydrogen and the dioxygen respectively. In the space 125, either the electrodes 131, 132 are against the bipolar plate 11, or a metal net, preferably made of nickel, is placed between the bipolar plate 11 and the electrodes 131, 132.

[0009] The electrolyser stack therefore comprises a stack of such electrolytic cells 10, the bipolar plate 11 terminating the first electrolytic cell 10 constitutes the start of the following electrolytic cell 10. Thus, the bipolar plate 11 of the first electrolytic cell 10 (upstream of the following one) has a higher potential than that of the bipolar plate 11 of the second electrolytic cell 10 (downstream of the preceding one) and consequently, its surface in contact with the space 125 adjoining the cathode 131 plays the role of anode 132. Conversely, the surface of the bipolar plate 11 in contact with the space 125 adjoining the anode 132 plays the role of cathode 131.

[0010] Two bottom plates (not shown) are provided at the ends of the electrolytic cell 10 and ensure the clamping of the electrolytic cells 10 between them and their sealing.

[0011] The present invention is based on the observation of several problems linked to this design of the electrolytic cells 10. A first problem is that the feed openings 121, and extraction openings 1221, 1222 made in the interlayer 12 for the feed of electrolyte and the extraction of electrolyte/gas mixture from the space 125 cannot be arranged symmetrically with respect to the space 125. The openings must imperatively be distant from the membrane 14 and are therefore arranged close to the bipolar plate 11 adjoining the space 125. If such a configuration is not adopted, under the effect of the pressures to which the membrane 14 is subjected, the latter 14, which is very flexible, deforms to the point of penetrating the feed openings 121 or extraction openings 1221, 1222 with the consequence that the feed or extraction flow rate can be reduced and that the sealing of the membrane 14 can be compromised and that the two spaces 125 on either side of the membrane 14 communicate. This latter consequence poses unacceptable problems for the safety of personnel and the installation.

[0012] This is why the feed 121 and extraction 1221, 1222 openings must be arranged close to the bipolar plate 11 adjoining the space 125. From the point of view of water electrolysis, this configuration is far from ideal because the main reactions (decomposition of water on the anode 132 side with formation of oxygen and formation of hydrogen on the cathode 131 side) take place at the membrane 14/electrode 131, 132 interface. The electrolyte introduced into the feed pipe 15 close to the bipolar plate 11 enters the space 125 through the feed opening 121 in order to cross the space 125 before arriving at the membrane 14/electrode 131, 132 interface. Similarly, the gas produced must cross the space 125 from the membrane 14/electrode 131, 132 interface to be extracted through the extraction opening 1221 or 1222. In addition, the gas produced tends to accumulate at the membrane 14 in the form of bubbles and the circulation of the electrolyte can only weakly entrain these bubbles. These gas bubbles have an electrically insulating character and this results in a loss of conductivity of the installation.

[0013] Another problem that arises is related to the size of the electrolyte supply openings 121 and extraction openings 1221, 1222 of the electrolyte/gas mixture. For technical reasons, it is ensured that the passage section of the supply openings 121 and extraction openings 1221, 1222 are smaller than the passage sections of the electrolyte supply pipes 15 or extraction pipes 161, 162 of the electrolyte/gas mixture into which they open respectively. These differences in passage sections cause a pressure difference between the space 125 and the supply openings 121 and extraction openings 1222, 1221 which, in turn, allows the circulation of the electrolyte from the supply pipe 15 to the space 125, then to the extraction pipes 161 or 162. Unfortunately, this pressure difference is unfavorable in terms of circulation of the electrolyte and gases within the space 125 of the electrolytic cell 10.

[0014] It would therefore be desirable to provide a solution for introducing the electrolyte and extracting the electrolyte/gas mixture from or into the space 125 so that the electrolyte can better interact with the electrode 131, 132 (elimination of gas bubbles generated on the surface of the electrode 131, 132, reduction of the path and convection time of the electrolyte in the space 125).

[0015] Statement of the invention

[0016] According to the invention, these problems are solved thanks to a particular shape of the frame of the interlayer. Thus, the invention relates according to a first of its aspects to an interlayer intended to be used in an alkaline electrolyzer cell, the interlayer having a generally parallelepiped shape, with two long sides defining a height of the interlayer, two short sides defining a width of the interlayer, the short sides and the long sides defining a plane of the interlayer and the direction perpendicular to the plane of the interlayer defining a thickness of the interlayer, the interlayer having a recess between its long sides and its short sides over its entire thickness, the recess of the interlayer defining a space, the interlayer having a generally rectangular or circular shape and comprising in the short sides openings for supplying electrolyte and for extracting electrolyte/gas mixture communicating with a space comprising certain specific constituents of the electrolyzer. At least one of the supply or extraction openings opens into the space through a flared section. According to the invention, the flared section extends along the thickness of the interlayer in a plane angularly offset by an angle alpha (α) less than 90° relative to the plane of the interlayer and in that it joins an edge on the short side adjacent to the space. The flared shape makes it possible to avoid or, at the very least, significantly reduce, the pressure difference between the space 125 and the supply 121 and extraction openings 1222, 1221. The angular offset thereof makes it possible to have the small base of the trapezoid-shaped flared section close to the bipolar plate from the point of view of the thickness of the interlayer. This is so that this small base joins a cylindrical portion of the supply and extraction openings. These cylindrical portions join the supply and extraction channels. Even more advantageously, the large base of the trapezoidal flared section is flush with the surface of the interlayer. In this way, the electrolyte can be injected tangentially to the electrode and to the electrode/membrane interface (thus continuously bringing fresh electrolyte into contact with the electrode) and/or the electrolyte/gas mixture can be extracted at the electrode/membrane interface (thus dislodging gas bubbles formed at the electrode), all without risking sealing problems for the electrolyser or the electrolytic cell.

[0017] Advantageously, the angle alpha (a) is between 10 and 40°. Advantageously, the flared section has a trapezoidal shape and opens into the space at the electrode/membrane interface.

[0018] According to a preferred embodiment, the opening having a trapezoidal shape also has a cylindrical part (in the geometric sense of the term). Thus, it is easy to connect this opening to the pre-existing electrolyte supply and electrolyte/gas mixture extraction pipes.

[0019] Advantageously, the supply and extraction openings do not open opposite each other in space. For example, they can be offset by a distance of maximum 3 cm, preferably maximum 10 mm.

[0020] Preferably, both the supply and extraction openings open into the space through a flared section. Thus the maximum technical effect can be achieved.

[0021] According to an advantageous embodiment, the cylindrical section of the feed opening has a passage section smaller than the passage section of the extraction opening.

[0022] According to another of its aspects, the invention relates to an electrolytic cell comprising two bipolar plates, two electrodes, a membrane and two interlayers, at least one of the two interlayers being as defined above and the interlayer being arranged so that at least one of the electrolyte supply and electrolyte/gas mixture extraction openings communicating with the space is arranged against the membrane.

[0023] Such an electrolytic cell no longer has the drawbacks observed with the electrolytic cells of the prior art.

[0024] According to a third aspect, the invention relates to an electrolyser stack containing a plurality of electrolytic cells as defined above as well as two bottom plates, an electrolyte supply pipe and electrolyte/gas mixture extraction pipes.

[0025] Advantageously, at least one of the openings, preferably two of them, has a passage section close to, preferably identical to, the passage section of the extraction pipes.

[0026] Very advantageously, the supply and extraction pipes can be arranged in the spacer. Thus, assembly of the stack is extremely rapid.

[0027] Advantageously, the spacer extends in height beyond the other elements of the electrolytic cell (the bipolar plates, the electrodes and the membrane). In this case, it is possible to advantageously place a seal between two consecutive spacers as defined above.

The gasket can be made of any material that ensures the sealing of the stack and withstands the operating conditions of the electrolytic cell, preferably elastomer and even more preferably EPDM (ethylene-propylene-diene monomer) rubber. The gasket has a generally rectangular or cylindrical shape corresponding to the periphery of the spacer. The interior of the gasket is cut in the same way as the spacer. Thus, in the case where the flared section of a feed or extraction opening is flush with the surface of the spacer, the gasket also has a cutout with a corresponding trapezoidal flared section. In such a configuration, three gaskets are present for three parts, namely the first electrode, the membrane and the second electrode. In addition, the electrode straddles the space and its gasket.

This configuration ensures perfect positioning and rigid maintenance of the assembly of the two electrodes and the membrane and thus solves the problems of loss of sealing, clogging of the supply and extraction openings.

[0028] The performance of the electrolyser stack is significantly improved.

[0029] Brief description of the figures

[0030] The invention will now be described by means of figures which have no other purpose than to illustrate the present invention. These figures schematically represent:

[0031] Fig. 1, an electrolytic cell of the prior art

[0032] Fig. 2, a prior art interlayer

[0033] Fig. 3, a stack of electrolytic cells of the prior art

[0034] Fig. 4, an interlayer according to the invention

[0035] Fig. 5, a sectional view of the insert of Fig. 4 along a plane perpendicular to the plane of the insert of Fig. 4 and taken in its middle.

[0036] Fig. 6 a sectional view of an interlayer according to another embodiment of the invention in the same orientation as that of the interlayer of Fig. 5

[0037] Detail of an embodiment

[0038] Figures 4 and 5 show a section of an interlayer 12 according to an embodiment of the invention. It shows an interlayer 12 intended to be used in an electrolytic cell 10 and defining a space 125 between a bipolar plate 11 and a membrane 14. This space 125 is intended to contain the cathode 131 and the anode 132 as well as all the reactive species involved in the electrolysis reaction, namely the electrolyte solution, the ions and the gases produced by the electrolysis. The interlayer 12 has a generally rectangular or circular shape and comprises an electrolyte supply opening 121 and an electrolyte/gas mixture extraction opening 1221 or 1222 inclined along the thickness of the interlayer 12 and communicating with the space 125. In this case, the interlayer 12 has been (arbitrarily) shown arranged on the side of the cathode 131 where the dihydrogen is produced by electrolysis. Thus the extraction opening 1221 of the electrolyte/gas mixture communicates with the extraction pipe 161 of the electrolyte/dihydrogen mixture (not shown in these figures). Of course, the interlayer 12 present on the other side of the electrode 131/membrane 14 assembly has a similar configuration. As can be seen, at least one of the supply openings 121 or extraction openings 1221, 1222 (in this case, both) opens into the space 125 via a flared section 123 of trapezoidal shape.

[0039] Figure 5 shows a sectional view of the same insert 12 presented in Figure 4 along a plane perpendicular to the plane of insert 12 in Figure 4 and taken in its middle.

To facilitate understanding of the invention, Figure 5 also shows the bipolar plate 11 and the cathode 131 which, with the spacer 12, define the space 125. This space 125 is supplied by a supply opening 121 which communicates with the electrolyte supply pipe 15 which is not shown in this figure. Similarly, the electrolyte and the electrolyte gas produced (in this case dihydrogen (approach is similar with regard to dioxygen)) are extracted from the electrolytic cell 10 through the extraction opening 1221. Both the feed 121 and extraction 1221 openings have a flared portion 123. The upper part of the figure shows an embodiment in which the flared portion 123 is flush with the surface of the interlayer 12 and therefore allows the extraction of the electrolyte/dihydrogen mixture tangentially to the electrode 131, which greatly improves the efficiency of the elimination of gas bubbles on the surface of the latter 131. The lower part shows a flared portion 123 which is slightly set back from the surface of the interlayer 12. Although this configuration allows the electrolyte to circulate in the space 125 in a very favorable manner, since the jet of electrolyte opening into the space 125 is directed towards the surface of the electrode 131, this configuration is less preferred than that where the flared part 123 is flush with the surface of the interlayer 12. Of course, it is understood that the two configurations can be identical or different (flush on both sides, flush on the supply side and not on the extraction side and vice versa, no flush at all). The preferred configuration is that in which there are two flared portions 123 and each of them is flush with the surface of the interlayer 12 on the side of the electrode 131. It is also seen that the flared portion 123 extends along the thickness of the interlayer 12 joining the electrode 131/membrane 14 interface in a plane angularly offset by an angle alpha (a) less than 90° relative to the plane of the interlayer 12 along the thickness of the interlayer 12 joining the electrode 131/membrane 14 interface, in this case, the angle alpha is approximately 35°.

[0040] It can also be seen in Figures 4 and 5 that the feed 121 and extraction 1221 openings have, in addition to the flared section 123, a cylindrical section opening into the flared part 123. It can also be seen in these figures that the two feed 121 and extraction 1221 openings do not open into the space 125 opposite each other. — Advantageously, the offset between the mouths of the openings 121 and 1221 is less than 3 cm and preferably less than 10 mm. In this case, the offset is 4 mm. Thus, the flow of electrolyte in the space 125 is made more homogeneous.

[0041] Figure 6 shows a preferred embodiment of the invention. It can be seen in this figure that the spacer 12 extends in height beyond the other elements of the electrolytic cell 10, namely the bipolar plates 11, the electrodes 131, 132 and the membrane 14. The electrolyte supply pipe 15 has been arranged and the extraction pipes 161 and 162 for the electrolyte/gas mixture are arranged in the spacer 12. This greatly facilitates assembly. The supply 121 and extraction 1221 openings extend respectively from the supply 15 and extraction 161 pipes to the space 125. After a short cylindrical section starting from the supply 15 and extraction 161 pipes, the supply 121 and extraction 1221 openings each have a flared section 123 extending to the space 125.

[0042] It can also be seen that at least one of the supply openings 121 or extraction opening 1221 (in this case, both) has a passage section close to the passage section of the extraction pipe 161. The two supply openings 121 and extraction opening 1221 have a passage section identical to the passage section of the extraction pipe 161.

[0043] A seal 17 is present on the side of the spacer 12 and is arranged between this spacer 12 and the consecutive spacer 12 (not shown) of the electrolytic cell 10. Two particular configurations of the spacer 12 are shown. The upper part shows the spacer 12 partially overhanging the seal 17 while the lower part shows a seal 17 extending substantially over the entire height of the spacer 12.

[0044] The interior of the seal 17 is cut in the same way as that of the spacer 12 (it has approximately the shape of the spacer in FIG. 3). Thus, in the case where the flared section 123 of a supply opening 121 or extraction opening 1221 is flush with the surface of the spacer 12, the seal 17 also has a cutout having a corresponding flared section. The assembly of the two electrodes 131, 132 and the membrane 14 is thus arranged inside the cutout of the seal 17. This configuration ensures perfect positioning and rigid holding of the assembly of the two electrodes 131, 132 and the membrane 14.

[0045] List of drawing references: 10 Electrolytic cell 11 Bipolar plate 12 Interlayer 121 Electrolyte supply opening 1221 Dihydrogen electrolyte mixture extraction opening 1222 Dioxygen electrolyte mixture extraction opening 123 Flared section of the opening 125 Space 131 Electrode (cathode) 132 Electrode (anode) 14 Membrane 15 Electrolyte supply pipe 161 Electrolyte/dihydrogen mixture extraction pipe

162 Electrolyte/oxygen mixture extraction pipe 17 Joint a Angle of inclination of the flared part relative to the plane of the spacer

Claims (16)

Claims 1. Interlayer (12) intended to be used in an electrolytic cell (10), the interlayer (12) having a generally parallelepiped shape, with two long sides defining a height of the interlayer, two short sides defining a width of the interlayer, the short sides and the long sides defining a plane of the interlayer and the direction perpendicular to the plane of the interlayer defining a thickness of the interlayer, the interlayer having a recess between its long sides and its short sides over its entire thickness, the recess of the interlayer defining a space (125), the interlayer (12) having a generally rectangular shape and comprising in the short sides openings for supplying (121) electrolyte and extraction (1221, 1222) of electrolyte/gas mixture communicating with the space (125), at least one of the supply openings (121) or extraction (1221, 1222) opening into the space (125) by a flared section (123), characterized in that the flared section (123) extends along the thickness of the interlayer (12) in a plane angularly offset by an angle alpha (a) less than 90° relative to the plane of the interlayer (12) and in that it joins an edge on the short side adjacent to the space (125). 2. Interlayer (12) according to claim 1, in which the flared section (123) has a trapezoidal shape. 3. Insert (12) according to one of the preceding claims, in which at least one of the feed (121) or extraction (1221, 1222) openings also has a cylindrical section opening into the trapezoid-shaped flared portion (123) at the small base of the trapezoid, so that this cylindrical portion is inclined along the thickness of the insert (12) and connects at one of its ends the trapezoid-shaped flared section (123) via the cylindrical section and at the other, the feed (121) or extraction (1221, 1222) channel. 4. Interlayer (12) according to one of the preceding claims in which the two supply (121) and extraction (1221, 1222) openings open into the space (125) via a flared section (123). 5. Interlayer (12) according to claim 3 in which the supply (121) and extraction (1221, 1222) openings do not open opposite each other into the space (125). 6. Interlayer (12) according to the preceding claim in which the supply (121) and extraction (1221, 1222) openings are offset by a distance of maximum 3 cm, preferably maximum 10 mm. 7. Interlayer (12) according to any one of claims 3 to 5 in which the cylindrical section of the feed opening (121) has a passage section smaller than the passage section of the extraction opening (1221, 1222). 8. Interlayer (12) according to any one of the preceding claims in which angle alpha (x) is between 10 and 40°. 9. Electrolytic cell (10) comprising two bipolar plates (11), two electrodes (131, 132), a membrane (14) and two interlayers (12), at least one of the two interlayers (12) being as defined in any one of the preceding claims, the interlayer being arranged so that at least one of the electrolyte supply openings (121) and the electrolyte/gas mixture extraction openings (1221, 1222) communicating with the space (125) is arranged against the membrane (14). 10. Electrolytic cell (10) according to claim 9 in which the spacers (12) extend beyond the other elements of the electrolytic cell (10) in height. 11. Electrolytic cell (10) according to one of claims 9 or 10 in which a seal (17) is present between the two spacers (12). 12. Electrolytic cell (10) according to one of claims 10 or 11 in which the seal (17) has a generally rectangular shape corresponding to a periphery of the insert (12), the interior of the seal (17) being cut in the same way as that of the insert (12) around the space (125) and in which the two electrodes (131, 132) and the membrane (14) are arranged inside the cutout of the seal (17). 13. Electrolyzer stack containing a plurality of electrolytic cells (10) as defined in one of claims 9 to 12, two bottom plates, an electrolyte supply pipe (15) and extraction pipes (161, 162) for electrolyte/gas mixture. 14. Electrolyzer stack according to the preceding claim in which at least one of the supply (121) and extraction (1221, 1222) openings has a passage section close to, preferably identical to, the passage section of the extraction pipes (161, 162). 15. Electrolyzer stack according to the preceding claim in which all the supply (121) and extraction (1221, 1222) openings have a passage section close to, preferably identical to, the passage section of the extraction pipes (161, 162). 16. Electrolyzer stack according to one of claims 13 to 15 in which the electrodes (131, 132) are housed in the space (125) either against a bipolar plate (11), or electrically connected to a bipolar plate (11) by a metal net between the electrode (131, 132) and the bipolar plate (11), said metal net preferably being made of nickel.