Multifunctional bipolar plate, electrolytic cell and electrolyser comprising same

Abstract

The invention relates to a bipolar plate (14) for an electrolytic cell (10), comprising a central web (141) and a ring (142) surrounding the central web (141). The ring (142) is made of a synthetic material and the central web (141) is made of metal and has an outer periphery embedded in the ring (142). The invention also relates to an electrolytic cell and an electrolyser stack comprising such bipolar plates.

Description

[0001] MULTIFUNCTION BIPOLAR PLATE, ELECTROLYTIC CELL AND ELECTROLYSER COMPRISING IT

[0002] The invention relates to the field of electrolysis and more particularly the production of hydrogen.

[0003] BACKGROUND OF THE INVENTION

[0004] The overall architecture of an electrolyzer stack (generally referred to as an "electrolyzer stack") is usually made up of a block of electrolytic cells and sealing gaskets, said electrolytic cells being pressed between bottom plates (making it possible to delimit the set of electrolytic cells and to ensure the clamping of said electrolytic cells between them and their sealing) and distribution plates interposed between each bottom plate and the block of electrolytic cells to allow the power supply and electrical distribution of the electrolytic cells. The electrolytic cells are stacked in series from an electrical point of view and in parallel from a fluidic point of view.

[0005] Each electrolytic cell has the purpose of promoting the electrolysis of an electrolytic solution (alkaline water, pure water, unpurified water, salt, aqueous chloride solution, aqueous bromide solution, aqueous hydrochloric acid solution, etc.). For example, the functionality of an electrolyzer cell is to promote the reaction of production of dihydrogen (H2) and dioxygen (02) gas resulting from the dissociation of water after injecting a direct electric current into an alkaline solution, generally comprising potassium hydroxide (KOH) or sodium hydroxide (NaOH).

[0006] Each electrolytic cell, considered as a mainly metallic and conductive part (but some parts of which may be non-metallic), is generally composed of two bipolar plates, framing two interlayers (better known under the English term "flow field material"), themselves framing two electrodes generally in the form of plates or grids or metallic fabrics. In the case of an alkaline electrolyzer cell, said electrodes are generally made of nickel. The two electrodes (a cathode and an anode) are separated by a membrane (also called a diaphragm or porous separator in the case of the alkaline electrolyzer cell), which ensures electrical insulation between the two electrodes, the separation of gases as well as ionic conduction within the electrolytic cell.

[0007] An electrolytic cell of the prior art is shown in exploded perspective in Figure 1. The electrolytic cell, bearing the general reference 10, comprises two bipolar plates 14 which, when assembled, define between them an internal volume (or chamber) in which there is a central membrane 11 framed by two electrodes 12a and 12b (an anode and a cathode, respectively) which are themselves framed by two spacers 16 (or "flow field material" in English). Furthermore, the electrolytic cell 10 also comprises a sealing gasket 13 compressed between the two bipolar plates 14 of the electrolytic cell 10 to ensure the sealing of the internal volume of the electrolytic cell 10.

[0008] Each spacer 16 has two functionalities: i) providing a low resistivity metallic path between each bipolar plate 14 and the associated electrode 12a, 12b (the spacer 16 being pressed between said bipolar plate 14 and said electrode 12a, 12b) and ii) allowing suitable circulation of the electrolytic solution for cooling the electrolyzer stack and transporting the generated gases.

[0009] The name bipolar plate 14 comes from the fact that, as the electrolytic cells 10 are all placed side by side in an electrolyzer stack, a bipolar plate 14 N will have a potential: higher compared to the bipolar plate 14 N+l downstream, so that the bipolar plate 14 N will act as anode within an electrolytic cell 10 defined by the bipolar plates 14 N and 14 N+l; lower compared to the bipolar plate 14 Nl upstream, so that the bipolar plate 14 N will act as cathode within an electrolytic cell 10 defined by the bipolar plates 14 Nl and 14 N.

[0010] In most cases, each intercalary plate comprises a central veil surrounded by a ring providing a mechanical reinforcement function, and a fluid supply and evacuation function.

[0011] To be able to withstand the working environment (electrolytic solution containing potassium or sodium hydroxide, and therefore basic; temperature of 80 to 100 °C; presence of oxygen at a pressure of 30 to 40 bars), the bipolar plates 14 are made of carbon steel coated with nickel. The bipolar plate 14 is heavy and the application of the nickel coating to the entire bipolar plate 14 is time-consuming and resource-consuming.

[0012] Bipolar plates 14 are also known, each comprising two rings of synthetic material pinching a metal veil between them. It is necessary to provide a seal 13 between the two rings. This structure is certainly lighter but increases the number of parts: this therefore increases the risk of leakage and the handling required to constitute each electrolytic cell 10.

[0013] SUBJECT OF THE INVENTION

[0014] An aim of the invention is to propose a simpler electrolyser cell which advantageously has improved efficiency.

[0015] SUMMARY OF THE INVENTION

[0016] For this purpose, according to the invention, a bipolar plate for an electrolytic cell is provided, comprising a central web and a ring surrounding the central web. The ring is made of synthetic material and the central web is made of metal and has an external periphery embedded in the ring.

[0017] Thus, the bipolar plate is monolithic even though it comprises two different materials, including a synthetic material that is lighter than steel but can be chosen to be able to withstand the operating environment. Assembly is therefore easier and the electrolyser stack has a reduced weight.

[0018] According to two particular alternative or combined embodiments:

[0019] - the bipolar plate comprises a metal spacer connected to the central web by at least one weld and, preferably, the bipolar plate also comprises a metal anode connected to the spacer by at least one weld;

[0020] - the bipolar plate comprises a metal anode connected to the central veil by at least one weld.

[0021] This is particularly advantageous because it has been found that, in known electrolyser cells, the contact resistances on the anode side are an order of magnitude higher than the contact resistances on the cathode side due to the oxidation caused by the release of oxygen. Welding the anode to the central web with or without the interposition of an interlayer makes it possible to have a lower electrical resistance and therefore to improve the performance of the electrolyser cell.

[0022] The invention also relates to an electrolytic cell and an electrolyzer stack comprising such bipolar plates.

[0023] Other characteristics and advantages of the invention will emerge from reading the following description of particular and non-limiting embodiments of the invention.

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Reference will be made to the accompanying drawings, among which: Figure 1 is an exploded schematic view of an electrolytic cell of an electrolyzer stack according to the prior art,

[0026] Figure 2 is a view of an electrolyzer stack according to the invention,

[0027] Figure 3 is a cross-sectional view of a bipolar plate of an electrolytic cell according to a first particular embodiment of the invention;

[0028] Figure 4 is a cross-sectional view of a bipolar plate of an electrolytic cell according to a second particular embodiment of the invention.

[0029] DETAILED DESCRIPTION OF THE INVENTION

[0030] With reference to Figure 2, the invention relates to an electrolyzer stack comprising a stack of elements extending longitudinally in a general direction A.

[0031] The different elements are mainly formed by electrolytic cells which will be described below.

[0032] The electrolyzer stack 1 comprises a block 2 of electrolytic cells 10 which comprises at least two electrolytic cells 10 which are mounted adjacent to each other in the general direction A. Within the block 2, the electrolytic cells 10 are mounted in parallel from a fluidic point of view and in series from an electrical point of view.

[0033] At both ends (in the general direction A) of the block 2 of the electrolyser stack 1 are arranged two end or bottom plates 3 and .

[0034] These bottom plates 3 and 4 form supports between which the electrolytic cells are compressed so that the electrolyser stack 1 is sealed and so that a good quality electrical contact is created inside the electrolytic cells.

[0035] In addition, the bottom plates 3 and 4 make it possible to support the forces generated by the internal pressure in block 2 as well as the external forces in block 2 necessary to ensure the compression of block 2.

[0036] The bottom plates 3 and 4 can play the role of electrical conductor and current distributor.

[0037] Nevertheless, the electrolyser stack 1 preferably comprises a first distribution plate 5 associated with the first bottom plate 3 and a second distribution plate 6 associated with the second bottom plate 4. It is then the distribution plates 5 and 6 which will here play the role of electrical conductors and current distributors.

[0038] The first distribution plate 5 (associated with the positive terminal) is arranged upstream of the block 2 and the second distribution plate 6 (associated with the negative terminal) is arranged downstream of said block 2. The notions "upstream" and "downstream" are understood according to the conventional direction of circulation of the current through the block 2.

[0039] A first of the two distribution plates, 5, is connected to the positive terminal of the electrolyser cell 1. Then, a portion of the main internal face of the first bottom plate 3 (main face facing the block 2 and in particular the distribution plate 5) is covered with a pellet made of electrically insulating material. Said portion is for example arranged in the centre of said main internal face.

[0040] The second of the two distribution plates, 6, is connected to the negative terminal of the electrolyser cell 1. The second bottom plate 4 will be at the same potential and also serves as a gateway for the supply of an electrolytic solution and the exhaust of this same solution charged with the gases formed during electrolysis in the block 2.

[0041] Thus, holes are provided in said second bottom plate 4. Said holes often have a different section between the two main faces of the second bottom plate 4. For example, the external main face (the one facing the outside of the block 2) has at least one or two holes (for example cylindrical in shape) for supplying electrolytic solution and two holes for discharging electrolytic reaction products in addition to the heated electrolytic solution. At least three or four holes are drilled on the internal main face (opposite the external main face) of said second bottom plate 4 for the same purpose, and for example oblong holes to improve the distribution or collection of fluids. For example, the holes in the external main face are equipped with suitable flanges for connecting the inlet and return pipes for the electrolytic solution.

[0042] Furthermore, the electrolyzer cell 1 is here supplied with direct current. For example, the first distribution plate 5 has a potential of several hundred volts while the second distribution plate 6 has a potential of 0 volts (the electrolyzer cell 1 typically comprises between 10 and 400, preferably between 100 and 350, electrolytic cells 10 having a cell voltage of the order of 2 volts and preferably less than 1.85 volts at the nominal point at the start of life). The supply and evacuations of electrolytic solution are carried out at the level of the second distribution plate 6 and the second bottom plate 4, the second distribution plate 6 having a potential of 0 Volts which avoids any current leakage (the potential of the second distribution plate 6 being that of the earth).

[0043] Inside the electrolyser stack 1, the current passes through the electrolytic solution through a membrane 11 which will be introduced below. Within the block 2 there are seals (which will be described below): these seals are chosen from a material having a much greater electrical resistance than that of the electrolytic solution.

[0044] The pile of 1electrolyser 1 comprises an end seal (not visible in the figures) arranged between the first distribution plate 5 and the first bottom plate 3. However, the first bottom plate 3 is grounded so that the potential difference at said end seal reaches the same value as the voltage applied between the positive and negative terminals of the electrolyser cell 1, for example, substantially 700 Volts. As a result, the first bottom plate 3 is electrically insulated from the block 2. For example, the electrolyser cell 1 comprises a layer (not visible in the figures) of electrically insulating material, layer arranged between the first bottom plate 3 and the first distribution plate 5. The layer is for example an added disc or a deposit made on the first bottom plate 3 and / or the first distribution plate 5.

[0045] The electrolyzer stack 1 comprises means for fixing the different electrolytic cells 10 together by common clamping. For example, the fixing means comprise a plurality of tie rods 7. Each tie rod 7 extends rectilinearly in the stack of the electrolyzer stack 1. Each tie rod 7 thus extends longitudinally in the electrolyzer stack 1 parallel to the general direction A. Each tie rod 7 is shaped as a rod. The tie rods 7 therefore all extend parallel to each other. The tie rods 7 are positioned on the periphery of the different electrolytic cells 10. Preferably, the tie rods 7 are distributed all around the block 2 and preferably at a regular interval.

[0046] The tie rods 7 extend through the bottom plates 3 and 4 of the electrolyser stack 1, through specific holes in said bottom plates 3 and 4, and thus each have two ends external to the block 2.

[0047] Preferably, the tie rods 7 are partially covered with a sleeve made of electrically insulating material. This makes it possible to avoid short circuits between the electrolytic cells 10 in the event of contact or projection. For example, the sleeve extends over the entire section of the tie rod 7 arranged between the two base plates 3 and 4.

[0048] Preferably, the ends of the tie rods 7 are threaded. For example, the threads at the ends are rolled threads. The rolled threads will have the advantage of making the machining of the tie rods 7 easier, particularly if the tie rods 7 are of a significant length, for example several meters in length.

[0049] The fixing means also comprise nuts 8 screwed onto the ends of the tie rods 7. The nuts 8 make it possible to constrain the two bottom plates 3 and 4 together, and therefore the different electrolytic cells 10 together, which ensures good sealing of the electrolyser stack 1 of electrolytic cells 10.

[0050] Preferably, the fixing means also comprise means for prestressing the two bottom plates 3 and 4 between them and therefore the different electrolytic cells 10 between them. Said prestressing means also make it possible to absorb the deformations and / or variations in thickness of the elements constituting the electrolyser stack 1, due to thermal expansion or to variations in external and internal mechanical stresses in the electrolyser stack 1 (such as for example the internal pressure in the electrolyser stack 1). The prestressing means are received on the ends of the tie rods 7 so as to be arranged, for a given end, between the closest bottom plate (3 or 4) and the nuts 8 arranged on the same end. For example, the fixing means comprise spring washers 9 such as Belleville washers. The spring washers 9 are received on the ends of the tie rods 7.The spring washers 9 are more precisely here arranged on each tie rod 7, at the level of the external part of said tie rod 7, when the latter has passed through the nearest bottom plate (3 or 4). The fixing means thus allow the electrolyser stack 1 to cope in particular with thermal expansions and / or variations in mechanical stresses external and internal to the electrolyser stack 1 (such as for example the internal pressure to the electrolyser stack 1). Nevertheless, the prestressing means are optional. In the present case, all the electrolytic cells 10 of the electrolyser stack 1 are identical to each other so that the following description of an electrolytic cell 10 in relation to FIGS. 3 and 4 is also applicable to the description of the other electrolytic cells 10.

[0051] With reference to Figure 3 and according to the first embodiment, such an electrolytic cell 10 comprises a central membrane 11 which is framed by two electrodes 12a and 12b (an anode and a cathode, respectively) which are themselves framed by two spacers 16a, 16b (or "flow field material" in English) which are themselves framed by two bipolar plates 14. Furthermore, the electrolytic cell 10 also comprises a seal 13 (the existence of which has already been mentioned above) which is compressed between the two bipolar plates 14 of the electrolytic cell 10.

[0052] The membrane 11, the interlayer 16b associated with the anode 12a and the cathode 12b being known from the prior art, they will not be detailed here.

[0053] The two bipolar plates 14 of an electrolytic cell 10 being identical to each other, the following description of one of the bipolar plates 14 is also applicable to the other of the bipolar plates 14 of the same electrolytic cell 10.

[0054] Each bipolar plate 14 comprises a central web 141 and a ring 142 surrounding the central web 141. The ring 142 is made of synthetic material and the central web 141 is made of metal and has an external periphery embedded in the ring 142. The central web 141 of the bipolar plate 14 is made of a material capable of withstanding the corrosive environment prevailing inside the electrolytic cell 10 and for example nickel-based. The central web 141 is here made of nickel or carbon steel coated externally with a layer of nickel or even stainless steel coated externally with a layer of nickel. The central web 141 has a thickness of 2 mm for example (the thickness is also fixed by the diameter or the main dimension in the plane perpendicular to the axis A). The ring 142 is made of a material allowing the ring 142 to provide a mechanical reinforcement function, an electrical conduction function and a fluid supply and evacuation function.The ring 142 may also include structural reinforcements judiciously placed so as to increase its capacity to absorb forces while minimizing its mass. The basic material of the ring 142 is any thermoplastic material resistant to strongly basic environments and to temperature such as for example PEEK or PPS. The material of the ring 142 may be reinforced with fibers such as glass, carbon or aramid fibers. The ring 142 has for example a small square, rectangular, polygonal, oval, circular or other section. For example, the ring 142 is sized to meet the standard applicable to pressure vessels and for example the PED 2014 / 68 / EU standard.

[0055] The central web 141 is provided with the spacer 16a which is made of metal and which is connected to the central web 141 by at least one weld. Said spacer 16a is itself provided with the anode 12a which is made of metal and which is connected to the spacer 16a by at least one weld. The weld may be continuous or discontinuous, around the perimeter or comprise weld points or lines distributed over the entire surface of the spacer 16a so as to uniform the current distribution over the entire anode 12a. In this case, the spacer 16a and the anode 12a have, like the central veil 141, an external periphery embedded in the ring 142. The anode 12a can be a plate pierced with holes, a net, a grid, a plate of expanded metal, metal wool, etc. allowing the flow of the electrolyte and the evacuation of gas bubbles.

[0056] The interlayer 16a is for example an expanded metal plate, metal wool, corrugated sheet, metal foam, etc. allowing the flow of the electrolyte and the evacuation of gas bubbles.

[0057] On the side opposite the spacer 16a and the anode 12a, the central veil 141 is free.

[0058] Thus, the bipolar plate 14 is shaped so as to have two main faces: a first main face facing the inside of the electrolytic cell 10 considered and a second main face facing the outside of the electrolytic cell 10 considered and the bipolar plates 14 are asymmetrical (along a plane of symmetry passing through the center of the bipolar plate 14 considered). Consequently, within the same electrolytic cell 10, the first face of the bipolar plate 14 (the one on which the interlayer 16a and the anode 12a are fixed) is opposite a second face (the one which is free) of another bipolar plate 14 identical to that which is being described. Within block 2, all the bipolar plates 14 are oriented in the same way.

[0059] Subsequently, a plane is defined in which each main face of the bipolar plate 14 extends and the axis normal to said plane.

[0060] When the bipolar plate 14 is in place in the electrolytic cell 10 which is itself in place in the electrolyser stack 1, the axis normal to said plane is here merged with the general direction A.

[0061] The thickness of the bipolar plate 14 (along the normal axis) is less important than its other dimensions. The bipolar plate 14 is shaped so as to have a cross-section (in the plane) having any geometric shape (square, rectangular, disc, etc.). The bipolar plate 14 here has a disc cross-section.

[0062] The ring 142 of the bipolar plate 14 is further provided, here on a face located on the side of the first face of the bipolar plate 14, with a seal 13 which is integral with the ring 142 and the ring 142 has, opposite the seal 13 and therefore on the side of the second face, a textured face. For example, the textured face has grooves, ridges, asperities, a rough appearance, etc. Preferably, the seal 13 is shaped so as to have a square or rectangular cross-section (along a transverse section plane). The seal 13 is therefore called a "flat seal". In the present case, the seal 13 is annular and covers the entire face of the ring 142 intended to be applied against the ring 142 of the second bipolar plate 14 forming the electrolytic cell 10. The seal 13 is made of homopolymer material or copolymer material and for example of thermoplastic material.For example, the seal 13 is made of a material of the polytetrafluoroethylene or polytetrafluoroethylene type (commonly abbreviated PTFE or better known under the trade name Teflon - registered trademark) or FKM (better known under the trade name Viton - registered trademark). Preferably, the material is made of, or based on, or of the type, polytetrafluoroethylene or polytetrafluoroethylene with at least one filler added. For example, the filler is fiberglass. For example, said material is reinforced polytetrafluoroethylene. For example, reinforced polytetrafluoroethylene is glass fiber reinforced polytetrafluoroethylene or reinforced polytetrafluoroethylene is carbon fiber reinforced polytetrafluoroethylene.

[0063] The properties of the seal 13 described are defined below: good behavior of the material and preservation of its good mechanical properties at the operating temperature of the electrolytic cell 10 which is nevertheless high (typically of the order of 90 to 95 degrees Celsius) and this over the long term; resistance to the corrosive environment inside the electrolytic cell 10 and this over the long term; good sealing properties; good electrical insulation properties (given by good electrical resistance) and this even at the operating temperature and in contact with the electrolyte solution; little creep allows a good longevity of the stack of electrolytic cells 10; slight creep behavior all the same in order to best match the geometrical particularities of the seating zone 21 of the seal 13; uniformity of the thickness (along the axis normal to the plane).The bipolar plate 14 is here manufactured by bi-injection molding of thermoplastic materials. In a mold in the shape of the bipolar plate 14, the central web 141 is placed to which the spacer 16a and the anode 12a have been fixed and the following is injected:

[0064] - in a first part of the mold in the shape of the ring 142, the thermoplastic material constituting the ring 142;

[0065] - in a second part of the mold in the shape of the seal 13, the thermoplastic material constituting the seal 13.

[0066] The external peripheries of the central veil 141, of the insert 16a and of the anode 12a extending in projection into the first part of the mold, they are embedded in the ring 142 (“insert molding”).

[0067] The adhesion of the seal 13 to the ring 142 is here the result of the bi-injection. Alternatively, the seal 13 could be attached to the ring 142 by another means such as gluing or fitting together complementary shapes belonging to the ring 142 and the seal 13.

[0068] To form an electrolytic cell 10, two bipolar plates 14 are pressed against each other so that the bipolar plates 14 delimit between them an internal volume whose peripheral sealing is ensured by the sealing gasket 13 clamped between the rings 142 of the two bipolar plates 14.

[0069] This internal volume is divided in two by the diaphragm 11 on a first side of which are the spacer 16a and the anode 12a welded to the first face of the central web 141 of a first of the two bipolar plates 14; and on a second side of which are the cathode 12b and the spacer 16b which are placed opposite the second face of the central web 141 of a second of the two bipolar plates 14.

[0070] The cathode 12b can be a plate pierced with holes, a net, a grid, an expanded metal plate, metal wool, etc. allowing the flow of the electrolyte and the evacuation of gas bubbles.

[0071] The interlayer 16b is for example an expanded metal plate, metal wool, corrugated sheet, metal foam, etc. allowing the flow of the electrolyte and the evacuation of gas bubbles.

[0072] The central veil 141 plays the role of current collector and will transmit it to the spacers 16a, 16b which are on either side of it.

[0073] Furthermore, the bipolar plate 14 comprises conduits which pass through it from one side to the other and which are dedicated to the supply of electrolytic solution to the internal volume of the electrolytic cell 10 and to the escape of the electrolysis products from the internal volume of the electrolytic cell 10. More precisely, the ring 142 is provided with fluid conduits 15 extending in an axial direction of the bipolar plate 14, that is to say parallel to the direction A, and with radial conduits 151, 152 each opening respectively on one side of the central web 141. For example, the bipolar plate 14 comprises between three and six conduits. The conduits are for example associated two by two, the pairs of two conduits being distributed homogeneously over the circumference of the bipolar plate 14.In this case, the bipolar plate 14 comprises a pair of conduits for the electrolyte supply, a first conduit for discharging a first electrolysis product (a two-phase mixture of electrolyte and oxygen gas), a second conduit for discharging a second electrolysis product (a two-phase mixture of electrolyte and hydrogen gas). The conduits may have a circular, oblong, etc. cross-section or another shape. For example, at least one of the conduits 15 has an oblong cross-section. The conduits may be made in whole or in part during molding (for example using a slide mold) or may be machined subsequently. It is noted that the sealing gasket 13 is pierced with a plurality of holes. This ensures the supply of block 2 and the evacuation of fluids from block 2. The holes made in the sealing gasket 13 correspond here to the conduits 15 of the bipolar plate 14.

[0074] Locations can be provided in the mold for one or more micro-sensors (pressure, temperature, etc.) which will thus be directly associated with the ring 142 either to open into one or other or more of the conduits, or into the internal volume.

[0075] It is noted that the role of the central web 141 is not actually to withstand high pressure forces unlike the ring 142: in fact, the forces are equal on both faces of the central web 141. The central web 141 thus has the main role of serving as a support for the components stacked within the electrolytic cell 10, namely the spacers 16, the electrodes 12a and 12b and the membrane 11. It should also be noted that within the electrolyser stack 1, all the bipolar plates 14 are separated two by two by a seal 13 and that each bipolar plate 14 plays the role of cathode for an electrolytic cell 10 and anode for another electrolytic cell 10 immediately adjacent.

[0076] The main functionalities of the seal 13 are as follows: i) ensuring the sealing of each electrolytic cell 10 with respect to the exterior of the electrolyzer stack 1, ii) ensuring the sealing of the channels carrying a gas which is generated within the block 2 with respect to those carrying another gas generated within the block 2, iii) ensuring the sealing of the chambers which are the seats of the electrolysis reactions where the two aforementioned gases are generated to isolate them from each other but also ensuring the sealing towards the channels mentioned just before, iv) acting as an electrical insulation layer between two adjacent bipolar plates 14 and v) defining the thickness to which the electrolytic cells 10 are compressed in the Z direction.

[0077] The seal 13 is shaped to have a diameter (of its cross-section) as constant as possible over all its internal and external circumferences and / or a thickness (along the normal axis) as constant as possible over its entire circumference (but also from one seal 13 to another). This makes it possible to improve the efficiency of the electrolytic cells 10 of the electrolyser stack 1. In particular, this makes it possible to have faces of the seal 13 as parallel as possible to each other and to the main faces of the facing bipolar plates 14. This makes it possible to further improve the sealing of the assembly.

[0078] The tolerance on the dimensions of the seal 13 will depend on the application for which it is intended (for example the tolerance is + / -0.1 millimeter in thickness). Thus, when the seal 13 is in the rest state, it has a conventional annular shape and a substantially single initial thickness.

[0079] When the seal 13 is compressed between two bipolar plates 14, the part of the electrolytic cell 10 located at the rings 142 of the two bipolar plates 14 and the seal 13 makes it possible to prevent the electrolyte solution or gases from escaping from the electrolyser stack 1, in other words it is dedicated to ensuring the sealing of the electrolytic cell 10 with respect to the external environment. For example, it ensures a seal greater than or equal to 10 -3milligrams per meter per second - mg / (m*s) when the tightness is measured using helium gas - and preferably a tightness greater than or equal to 10 -4 mg / (m*s) . The free face of the ring 142 applied against the seal 13 being textured as seen, the seal 13 can, by deforming, fill the hollows of said face and thus reinforce the sealing of the electrolytic cell 10. Indeed, this texture constitutes an additional obstacle to the gases and other substances present, to find the path towards the outside of the electrolyzer stack 1. This presence of texture also plays a role which promotes the friction between the electrolytic cells 10 and therefore the self-maintenance of the plurality of electrolysis cells 10 stacked to form the block 2. This advantage is reinforced when the block 2 is horizontal in operation.

[0080] For example, the compression of the seal 13 is such that the seal 13 reaches a maximum thickness (along the Z axis) of 94% and preferably 78% and, more preferably, 75% of its starting thickness (when it is in its resting state flat on a flat surface without external stress). The starting thickness is for example equal to or greater than 3.0 millimeters. Preferably, this starting thickness does not exceed 3.5 millimeters. Alternatively, a thinner seal can be used.

[0081] It is therefore noted that the membrane 11 and the seal 13 are then compressed between the rings 142 of the two bipolar plates 14: the seal 13 is thus superimposed on the membrane 11 on this part of the electrolytic cell 10. This ensures very good sealing around the membrane 11 on its perimeter and in the direction of the fluid supply and evacuation conduits.

[0082] According to one option, the end seal arranged between the first distribution plate 5 and the first bottom plate 3 is made of the same material as that of said seal 13 of an electrolytic cell 10 which has just been described. The end seal is for example identical to said seal 13. Said end seal is optionally made of homopolymer material or copolymer material and for example of thermoplastic material.

[0083] According to one option, the layer of electrically insulating material between the first base plate 3 and the first distribution plate 5 is made of the same material as that of said end seal arranged between the first distribution plate 5 and the first base plate 3. According to one option, the layer of electrically insulating material between the first base plate 3 and the first distribution plate 5 is made of the same material as that of said seal 13. Said layer is optionally made of homopolymer material or copolymer material and for example of thermoplastic material.

[0084] According to one option, the end seal arranged between the second distribution plate 6 and the second bottom plate 4 is made of the same material as that of said seal 13 of an electrolytic cell 10 which has just been described. Said end seal is for example identical to said seal 13. Said end seal is optionally made of homopolymer material or copolymer material and for example of thermoplastic material.

[0085] According to one option, the pellet arranged on the internal face of the first distribution plate 5 is a layer of material directly applied to the first distribution plate 5 or is formed by deposition of powder, such as a fluoropolymer and in particular ethylene-chlorotrifluoroethylene such as that produced under the brand name HALAR by the company SOLVAY.

[0086] The electrolytic cell 10 thus described has very good sealing due to the specific compression of the sealing gasket 13 between the bipolar plates 14.

[0087] It is also noted that the electrolytic cell 10 is made watertight thanks to a single seal 13. The use of a single seal 13 made of thermoplastic material also makes it possible to improve the watertightness of the electrolyser cell 1. In fact, the seal 13 is made of a hard material resistant to the strong mechanical compressions to which the electrolyser cell 1 is subjected and is more resistant, even over a long period, to the corrosive environment prevailing inside the electrolyser cell 1. Alternatively, it is nevertheless possible to use a more conventional elastomer seal 13.

[0088] A method of assembling the electrolyzer stack 1 will now be described.

[0089] According to a first step, a bipolar plate 14 with the anode 12a oriented opposite the distribution plate 5, a diaphragm 11, a cathode 12b, an interlayer 16b, a bipolar plate 14 with the anode 12a oriented opposite the distribution plate 5 and so on are stacked successively on a first base plate 3 and a first distribution plate 5 to form adjoining electrolytic cells 10.

[0090] In a second step, the last electrolytic cell 10 is covered by the second distribution plate 6, itself covered by the second bottom plate 4, thus delimiting the electrolyser stack 1.

[0091] In a third step, the newly assembled electrolyser stack 1 is compressed using the tie rods 7, nuts 8 and spring washers 9.

[0092] Such an assembly with thick distribution plates 5 and 6 and thin, flat bipolar plates 14 allows homogeneity of the current in all the electrolytic cells 10 of the electrolyzer stack 1 while the voltage is different at the terminals of each electrolytic cell 10 and the current is only connected to one or more points at the periphery of each distribution plate 5 and 6.

[0093] Furthermore, the bipolar plates 14 are parallel to each other within the block 2 thanks to their particular shape and the good tightening of each sealing joint 13. This further improves the homogeneity of the current in all the electrolytic cells 10.

[0094] The assembly process must ideally allow each sealing joint 13 in particular: to deform according to the geometry imposed by the bipolar plates 14 enclosing it, to bring its material into a range of elastic behavior (centered on an operating point of the electrolyzer cell 1), to reach the desired tightening value combining both the desired seals and the electrical contacts between the different components making it possible to achieve the envisaged energy performances.

[0095] The nominal operating point of the electrolyser stack 1 is for example 85 degrees Celsius under 3 Megapascals.

[0096] According to the second embodiment of the bipolar plates 14, shown in FIG. 4, the central web 141 comprises projecting reliefs 141' and the bipolar plate 14 comprises a metal anode 12a connected to the reliefs 141' by welds.

[0097] As previously, the ring 142 is made of synthetic material and the central web 141 is made of metal and has an external periphery embedded in the ring 142. The central web 141 of the bipolar plate 14 is made of a material capable of withstanding the corrosive environment prevailing inside the electrolytic cell 10 and for example nickel-based. The central web 141 is here made of nickel or carbon steel coated externally with a layer of nickel. The central web 141 has a thickness of 2 mm for example. The ring 142 is made of a material allowing the ring 142 to provide a mechanical reinforcement function, and a fluid supply and evacuation function. The basic material of the ring 142 is any thermoplastic material resistant to strongly basic environments and to temperature such as for example PEEK or PPS. The material of the ring 142 may be reinforced with fibers such as glass, carbon, or aramid fibers.The ring 142 has, for example, a small square, rectangular, polygonal, oval, circular or other cross-section. For example, the ring 142 is sized to meet the standard applicable to pressure vessels and, for example, the PED 2014 / 68 / EU standard.

[0098] The central web 141 is provided with the anode 12a which is made of metal and which is connected to the central web 141 by at least one weld. The weld may be continuous or discontinuous, around the perimeter or comprise weld points or lines distributed over the entire surface of the anode 12a so as to uniform the current distribution over the entire anode 12a. In this case, the welds are distributed and the anode 12a has, like the central web 141, an external perimeter embedded in the ring 142.

[0099] The anode 12a may be a plate pierced with holes, a net, a grid, an expanded metal plate, metal wool, etc., allowing the flow of the electrolyte and the evacuation of gas bubbles. As before, on the side opposite the anode 12a, the central veil 141 is free.

[0100] The bipolar plate 14 is, as previously, provided with a sealing gasket 13 and produced by molding.

[0101] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0102] The end seal(s) may be different from the sealing gaskets 13.

[0103] The electrolyzer stack 1 may be assembled differently from what has been described.

[0104] The electrolyzer stack 1 may be used horizontally, vertically, or in any other position. The electrolyzer stack 1 may be assembled horizontally, vertically, or in any other position. Preferably, the electrolyzer stack 1 will be assembled vertically and used horizontally.

[0105] It will be possible to have only one conduit associated with the supply of the electrolytic solution and a single conduit associated with the evacuation of each electrolysis product. However, it will be preferable to have two conduits associated with the supply of the electrolytic solution and / or two conduits associated with the evacuation of each electrolysis product for reasons of redundancy in the event that one of the conduits becomes blocked. In general, the electrical distribution plate may have only one conduit opening at each of its ends onto one of the respective main faces of the electrical distribution plate.

[0106] Similarly, it is preferable to have two grooves associated with each end of each conduit for redundancy reasons.

[0107] The different conduits may not be identical to each other.

[0108] The two distribution plates 5 and 6 each associated with one end of block 2 may be different and not identical to each other as mentioned above.

[0109] For example, the distribution plate 5, 6 may comprise at least one conduit opening at least at one of its ends into a recess in said distribution plate 5, 6. Optionally, the conduit will open at least at one of its ends at a position sufficiently close to the external periphery of one of the main faces to allow complete or almost complete emptying (emptying of a liquid and / or a gas) present in the space between the distribution plate 5, 6 in question and the facing bottom plate 3, 4. Optionally, this conduit may be arranged so as to open at a first end into the recess in the first main face of the distribution plate 5, 6 and to open at a second end into the recess in the second main face of said distribution plate 5, 6 so as to put the two recesses in communication.

[0110] The electrolyzer cell 1 may comprise three electrodes 12, namely two end cathodes 12b and a central anode 12a.

[0111] The spring washers 9 can be placed at both ends of the tie rod or at just one of these ends and / or be replaced by any elastic compression member.

[0112] The two embodiments may be mixed, for example, by providing reliefs on the veil of the first embodiment, the interlayer being crossed by the reliefs.

Claims

CLAIMS 1. Bipolar plate (14) for electrolytic cell (10), comprising a central web (141) and a ring (142) surrounding the central web (141), characterized in that the ring (142) is made of synthetic material and the central web (141) is made of metal and has an external periphery embedded in the ring (142) and in that a metal insert (16) or a metal anode (12a) is connected to the central web (141) by at least one weld.

2. Bipolar plate (14) according to claim 1, in which the spacer is connected to the web by at least one weld and the anode (12a) is connected to the spacer (16) by at least one weld.

3. Bipolar plate (14) according to claim 1, in which the central web (141) comprises projecting reliefs (141').

4. Bipolar plate (14) according to claim 4, in which the anode (12a) is connected to the reliefs (141') by welds.

5. Bipolar plate (14) according to any one of the preceding claims, wherein the ring (142) is provided with at least one fluid conduit (15, 151, 152).

6. Bipolar plate (14) according to any one of the preceding claims, in which a seal (13) is integral with the ring (142).

7. Electrolytic cell (10) comprising at least a first and a second bipolar plate (14) which are both in accordance with any one of the preceding claims, between which extend at least one diaphragm (11), an anode (12a) between the diaphragm (11) and the first bipolar plate (14), a cathode (12b) between the diaphragm (11) and the second bipolar plate (14) and a seal (13) between the rings (142) of the bipolar plates (14).

8. Electrolyzer stack comprising two end plates (3, 4) enclosing a stack of elements (2) comprising electrolytic cells (10), each electrolytic cell (10) being in accordance with the preceding claim and comprising at least one electrolyte supply conduit, a first conduit for discharging a first electrolysis product and a second conduit for discharging a second electrolysis product (15) communicating from one electrolytic cell (10) to the other (10) to form in the electrolyzer stack (1) along the latter (1) an electrolyte supply network, a first network for discharging the first electrolysis product and a second network for discharging the second electrolysis product.

9. Electrolyzer cell (1) according to the preceding claim, comprising a distribution plate (5, 6) extending between an end plate (3, 4) and the adjacent electrolytic cell (10).

10. Electrolyzer cell (1) according to one of claims 6 and 7, wherein the cell stack (2) is arranged vertically or horizontally.

Images