Interlayer for an electrolytic cell, electrolytic cell and electrolyser stack

Abstract

The present invention relates to electrolysis, in particular to an interlayer (12) intended for use in an electrolytic cell (10), which has a general parallelepiped shape and a cavity between its sides through the entire thickness thereof. This cavity defines a space (125), wherein the short sides of the interlayer comprise an electrolyte supply opening (121) and electrolyte / gas mixture discharge openings (1221, 1222), the openings being inclined and in communication with the space (125). The openings are formed in the interlayer (12) substantially across the entire width of the space (125) along the thickness of the interlayer (12) and thereby connect the electrode (131, 132) / membrane (14) interface on the one side to the supply channel (15) or the discharge channels (161, 162) on the other side, and have an inclination of less than 90° with respect to the plane of the interlayer (12).

Description

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 for use 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 a very high energy content (285 kJ / mol).

[0005] There are several known ways to produce gaseous dihydrogen; the most advantageous is to electrolyze the water molecule because it is a high-yield reaction that does not directly produce CO2, unlike the widely used processes of reforming methane, coal and hydrocarbons.

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

[0007] The present invention relates more particularly to an alkaline membrane electrolyzer.

[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, in this case an anode, a second space 125 surrounded by an intermediate frame 12 and a second bipolar plate 11.The space (sometimes also called the 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, 132). The spacer 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. Thus, the electrodes 131, 132 are installed in the space 125 so that two configurations (not shown) are possible: either the electrodes 131, 132 are against the bipolar plate 11, or the electrodes 131, 132 are electrically connected to the bipolar plate 11 by a metal net, the latter preferably being made of nickel. The membrane 14 (also called diaphragm or porous separator) ensures the electrical insulation between the two electrodes 131, 132 as well as the transport of protons from one electrode to the other while being impervious to electrolysis gases. The bipolar plates 11 (also called 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) coming from a supply pipe 15 is introduced into the space 125 through a supply opening 121 in the interlayer 12, the resulting electrolyte / gas mixture is extracted from the space 125 through a second extraction opening 1221 or 1222 made in the interlayer 12.When it is the space 125 arranged between the bipolar plate 11 and the cathode 131, the electrolyte / gas mixture extracted by the extraction opening 1221 is essentially composed of gaseous dihydrogen, H2, and the mixture is discharged into the extraction pipe 161. When it is the space 125 arranged between the anode 132 and the bipolar plate 11, the electrolyte / gas mixture extracted by the extraction opening 1222 is essentially composed of gaseous dioxygen, O2, 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.

[0009] The electrolyser stack therefore comprises a stack of such electrolytic cells 10, the bipolar plate 11 terminating a 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 stack and ensure the electrolytic cells are clamped together and sealed.

[0011] The present invention is based on the observation of a problem related to this design of electrolytic cells. In the current electrolyzer design, the feed 121 and extraction 1221, 1222 openings are located close to the bipolar plate 11 relative to the thickness of the interlayer 12. If such a configuration is not adopted and if these openings 121, 1221 and 1222 were arranged at the electrode / solution interface, the very flexible membrane 14 would deform to the point of penetrating the feed 121 or extraction 1221, 1222 openings under the effect of the pressures to which the installation is subjected. The direct consequence is that the sealing of the membrane 14 may be compromised and the two spaces 125 on either side of the membrane 14 enter into communication. This latter consequence poses unacceptable problems for the safety of personnel and the installation.This is why the feed 121 and extraction 1221, 1222 openings must be arranged close to the bipolar plate 11 adjoining the space 125. As far as the electrolysis of water is concerned, 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 electrode-solution interface where the electrochemical reactions take place. Likewise, the produced gas must pass through the space 125 to be extracted through the extraction opening 1221 or 1222.Furthermore, 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. 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 at the electrode 131, 132 / solution interface so that the electrolyte can better interact with the electrode 131, 132 (elimination of the 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).

[0012] It would therefore be desirable to propose a new configuration that would overcome these problems.

[0013] Statement of the invention

[0014] According to the invention, these problems are solved by means of 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 electrolytic 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 short sides of the interlayer comprising electrolyte supply and electrolyte / gas mixture extraction openings communicating with the space. According to the invention, the electrolyte supply openings of the space and the electrolyte / gas mixture extraction openings from the space are inclined and formed in the short sides of the interlayer substantially over the entire width of the space. In other words, this supply opening is inclined along the thickness of the interlayer to join the electrode / membrane interface on the one hand and the supply and / or extraction channel on the other hand, without risking sealing problems for the electrolyzer or the electrolytic cell.This helps to increase the performance of the electrolyser.

[0015] From US-A1-2022 / 307487, a hydrogen electrochemical compressor and a support member for a solid-phase electrochemical cell are disclosed, which comprises, in a flow field member, flow field grooves through which an anode gas (e.g., hydrogen gas) can flow in a predetermined direction, and a plurality of through-holes, one end of which opens into the flow field grooves, and the other ends of which are in communication with ventilation holes of an anode current conductor. At least a portion of the through-holes (e.g., discharge through-holes or supply through-holes) are inclined at an acute angle relative to an upstream side of the flow field grooves (e.g., discharge flow field grooves).The inclination of the through holes allows their outlet to be positioned further downstream or their inlet further upstream in the grooves of the flow field and thus ensures better drainage of the condensation water.

[0016] Also disclosed from US-A1-2023 / 110742 is a metal-supported solid oxide fuel cell (SOFC) that improves power generation efficiency by allowing a gas to smoothly flow into or out of through-holes. The plate-shaped metal support has a plurality of through-holes penetrating from a front surface on which an electrode layer is disposed to a rear surface, and the metal support has inclined through-holes, which have a central axis inclined relative to the thickness direction. This configuration enables better gas supply and discharge, while reducing production costs and facilitating the manufacture of SOFCs.

[0017] Advantageously, the openings for supplying the chamber with electrolyte and for extracting the electrolyte / gas mixture from the chamber extend in a plane angularly offset by an angle alpha (a) less than 90° relative to the plane of the interlayer and extend along the thickness of the interlayer joining the electrode / membrane interface of a part and the supply and / or extraction channel on the other hand. Advantageously, the angle alpha (a) is between 10 and 40°. This oblique arrangement of the openings for supplying the chamber with electrolyte and for extracting the electrolyte / gas mixture from the chamber is particularly suitable for an electrolyzer stack composed of several electrolytic cells in which pipes for supplying the chamber (containing the electrodes) with electrolyte and for extracting the electrolyte / gas mixture supply several electrolytic cells.In this way, the electrolyte can be injected tangentially to the electrode or towards the electrode (thus continuously bringing fresh electrolyte into contact with the electrode) in order to bring the electrolyte directly to the electrode / membrane interface (where the electrolyte and water undergo an electrochemical reaction) and to evacuate the gas from the electrode / membrane interface (where it is produced), all without risking sealing problems for the electrolyser or the electrolytic cell.

[0018] When one or more feed and extraction opening(s) are formed in the interlayer over the entire width of the chamber and this or these feed and extraction opening(s) extend(s) along the thickness of the interlayer joining the electrode / membrane interface in a plane angularly offset by an angle alpha (a) less than 90° relative to the plane of the interlayer, the electrolyte from the electrolyte feed pipe of the electrolyzer stack is directly injected into the electrode chambers specifically at the electrode / membrane interface. Similarly, the electrolyte / gas mixture extracted from the electrolyzer stack by the extraction pipe is extracted from the electrode chambers at the electrode / membrane interface.This configuration allows in particular particularly significant convection movements at the electrode / solution interface and therefore a particularly efficient extraction of the gas bubbles produced there. Also, a portion of the interlayer surface always appears which is full above the flared sections of the extraction holes. This configuration ensures the perfect positioning and rigid maintenance of the assembly of the two electrodes and the membrane and thus resolves the problems of loss of sealing, of clogging by the membrane of the supply and extraction openings.

[0019] Brief description of the figures

[0020] 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:

[0021] Fig. 1, a prior art electrolytic cell

[0022] Fig. 2, a prior art interlayer

[0023] Fig. 3, a stack of electrolytic cells of the prior art

[0024] Fig. 4, an interlayer according to the invention

[0025] 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 at its midpoint.

[0026] Figures 4 and 5 show a section of an interlayer 12 according to one embodiment of the invention. There is shown an interlayer 12 intended to be used in an electrolytic cell 10. The interlayer 12 has a generally parallelepiped shape, in this case rectangular, with two long sides 123, 124 defining a height of the interlayer 12, two short sides 126, 127 defining a width of the interlayer 12, the short sides 126, 127 and the long sides 123, 124 defining a plane of the interlayer 12 and the direction perpendicular to the plane of the interlayer 12 defining a thickness of the interlayer, the interlayer 12 having a recess between its long sides 123, 124 and its short sides 126, 127 over its entire thickness, the recess of the interlayer thus defines a space 125. During assembly of the cell, this space will be found between a plate bipolar 11 and a membrane 14.This space 125 is intended to contain all the reactive species involved in the electrolysis reaction, namely the electrolyte solution, the ions and the gases produced by the electrolysis. Thus, the electrodes 131, 132 are installed at the limit of the space 125 so that two configurations (not shown) are possible: either the electrodes 131, 132 are against the bipolar plate 11, or the electrodes 131, 132 are electrically connected to the bipolar plate 11 by a metal net, the latter preferably being made of nickel. The short sides 126, 127 of the insert 12 comprise an electrolyte supply opening 121 and an electrolyte / gas mixture extraction opening 1221 or 1222 inclined in the thickness of the insert 12 and communicating with the space 125. In this case, the insert 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 or 1222 of the electrolyte / gas mixture also communicates with the extraction pipe 161 of the electrolyte / dihydrogen mixture. Of course, the insert 12 present on the other side of the electrode 131 / membrane 14 assembly has a similar configuration. As can be seen shown, at least one of the supply openings 121 or extraction openings 1221, 1222 (in this case, both) is formed in at least one of the (in this case in both) short sides 126, 127 of the insert 12 substantially over the entire width of the space 125.

[0027] Figure 5 shows a sectional view of the same insert 12 shown in Figure 4 along a plane perpendicular to the plane of the insert 12 of Figure 4 and taken in its middle. To facilitate understanding of the invention, Figure 5 also shows the bipolar plate 11 and the membrane 14 which, with the insert 12, define the space 125. This space 125 is supplied by a supply opening 121 which communicates with the electrolyte supply pipe 15. Similarly, the electrolyte and the electrolyte gas produced (in this case dihydrogen (the approach is similar with regard to dioxygen)) are extracted from the electrolytic cell 10 through the extraction opening 1221 which communicates with the extraction pipe 161 of the electrolyte / dihydrogen mixture. The two feed openings 121 and extraction openings 1221 are formed in the spacer 12 substantially across the entire width of room 125.

[0028] The upper and lower parts of the figure show an embodiment in which the two feed 121 and extraction 1221 openings extend into the thickness of the insert and connect an edge of the short side adjacent to the space (125) in a plane angularly offset by an angle alpha (a) less than 90° relative to the plane of the insert 12, in this case, the angle alpha is approximately 35°.

[0029] List of drawing references: 10 Electrolytic cell 11 Bipolar plate 12 Intercalary 121 Electrolyte supply opening 1221 Dihydrogen electrolyte mixture extraction opening 1222 Oxygen electrolyte mixture extraction opening 123 Long side of the interlayer 124 Long side of the interlayer 125 Space 126 Short side of the interlayer 127 Short side of the interlayer 131 Electrode (cathode) 132 Electrode (anode) 14 Membrane 15 Electrolyte supply line 161 Electrolyte / dihydrogen mixture extraction pipe 162 Electrolyte / oxygen mixture extraction pipe a Angle of inclination of the flared part relative to the plane of the spacer

Claims

Claims 1. An interlayer (12) for use in an electrolytic cell (10), the interlayer (12) having a generally parallelepiped shape, with two long sides (123,124) defining a height of the interlayer, two short sides (126,127) defining a width of the interlayer, the short sides (126,127) and the long sides (123,124) 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 (123,124) and its short sides (126,127) over its entire thickness, the recess of the interlayer defining a space (125), the short sides (126,127) of the interlayer (12) comprising feed openings (121) in electrolyte and extraction (1221, 1222) in electrolyte / gas mixture communicating with the space (125), characterized in that the supply openings (121) in electrolyte of the space (125) and extraction (1221,1222) of the electrolyte / gas mixture of the space (125) are inclined and formed in the short sides (126,127) of the interlayer (12) substantially over the entire width of the space (125)., 2. Interlayer (12) according to the preceding claim in which at least one of the electrolyte supply openings (121) and electrolyte / gas mixture extraction openings (1221, 1222) communicating with the space (125) extends in the thickness of the interlayer (12) and connects an edge of the short side (126, 127) adjacent to the space (125) in a plane angularly offset by an angle alpha (a) less than 90° relative to the plane of the interlayer (12).

3. Interlayer (12) according to claim 2 wherein the two openings for supplying (121) electrolyte and extracting (1221, 1222) electrolyte / gas mixture communicating with the space (125) extend along the thickness of the interlayer (12) joining the electrode (131, 132) / membrane (14) interface in a plane angularly offset by an angle alpha (a) less than 90° relative to the plane of the interlayer (12).

4. Interlayer (12) according to one of claims 2 or 3 in which the angle alpha (a) is between 10 and 40°.

5. 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 claims 2 to 4, the interlayer being arranged so that at least one of the openings for supplying (121) electrolyte and extracting (1221, 1222) electrolyte / gas mixture communicating with the space (125) being arranged against the membrane (14).

6. Electrolyzer stack containing a plurality of electrolytic cells (10) as defined in claim 5, two bottom plates, an electrolyte supply pipe (15) and extraction pipes (161, 162) for electrolyte / gas mixture.

7. Electrolyzer stack according to claim 6 wherein 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.

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