Elementary cell for electrolysis of a gas-producing electrolytic solution

Abstract

Elementary cell for electrolysis, the elementary anode having a channel for bubbles of a first gas, the elementary cathode having a channel for bubbles of a second gas, wherein the elementary anode and / or the elementary cathode extend locally into the elementary main channel near the mouth, along a downstream portion of the mouth in an average direction of the elementary main channel.

Description

Description Title: Elementary cell for the electrolysis of an electrolytic solution producing gases Technical field

[0001] The present disclosure relates to an elementary cell for the electrolysis of an electrolytic solution producing gases. Prior art

[0002] An electrolytic solution consists of an electrolyte and a solvent. The difficulty in collecting one of the gases produced by electrolysis of an electrolytic solution with good purity and efficiency lies in the existence of both interactions between the gas bubbles and between the gas bubbles and the walls of the electrolyzer. These interactions lead to the gas bubbles moving away from the walls of the electrolyzer, where they are produced. The consequence is the mixing of the bubbles of different gases, thus reducing the purity of the gases produced.

[0003] Electrolysis techniques are known which allow a purity / yield compromise, in which techniques provide: - to increase the distance between the anode and the cathode or to provide a physical separator, so as to maximize the separation of the bubbles of different gases generated by the electrolysis, and therefore increase the purity of the electrolysis product, and - to reduce the distance between the anode and the cathode, so as to minimize the electrical resistance of the electrolytic solution.

[0004] Several techniques are described below.

[0005] A known technique is the use of membranes separating electrodes, in order to maximize the purity of the electrolysis product by avoiding a mixture of bubbles of different gases produced by electrolysis. Such a technique has the disadvantage of consuming membranes due to wear.

[0006] An alternative technique is to dispense with the membrane and provide porous electrodes. Such electrodes consist of a solid foam or a random porous media, or mesh, to increase the surface area to volume ratio. The latter option has the disadvantage of trapping gas bubbles in the structure, thus reducing efficiency.

[0007] Another technique consists of imposing by pumping a flow of the electrolytic solution between the anode and the cathode.

[0008] Such a technique is described in WO2022106874A1 and in the following article: “A membrane-less electrolyzer with porous walls for high throughput and pure hydrogen production. Pooria Hadikhani et al. (Sustainable Energy Fuels, 2021, 5, 2419).

[0009] This technique has an additional energy cost compared to the electrical energy required for electrolysis alone, because the energy for pumping the electrolytic solution must also be provided. Summary

[0010] This disclosure improves the situation.

[0011] The present disclosure provides an optimized electrode topology that has a geometry that allows for capturing the produced gas bubbles while minimizing mixing of the different gases compared to the prior art.

[0012] The present disclosure relates to an elementary cell for the electrolysis of an electrolytic solution producing gases, comprising a massive elementary cathode and a massive elementary anode separated by an elementary main conduit intended to be filled with the electrolytic solution, said elementary main conduit being defined between an elementary anode wall and an elementary cathode wall.

[0013] The elementary anode has a recess forming a bubble conduit for a first gas. The elementary main conduit has an inlet mouth for said bubble conduit for the first gas. Said bubble conduit for the first gas is intended, in use, to fluidically connect the elementary main conduit to an outlet for the first gas, so that the first gas escapes from the elementary main conduit of the elementary cell via the bubble conduit for the first gas.

[0014] The elementary cathode has a recess forming a bubble conduit for a second gas. The elementary main conduit has an inlet mouth for said bubble conduit for the second gas. Said bubble conduit for the second gas is intended, in use, to fluidically connect the elementary main conduit to an outlet for the second gas, so that the second gas escapes from the elementary main conduit of the elementary cell via the bubble conduit for the second gas.

[0015] The elementary anode and / or the elementary cathode locally overflows into the elementary main conduit, at the mouth, on a downstream portion of the mouth in an average direction of the elementary main conduit.

[0016] The local overflow, also called "overflow", of the elementary anode and / or the elementary cathode makes it possible to capture the gas bubbles that one wishes to collect on their trajectory, and to redirect them in the vicinity of said elementary anode and / or elementary cathode towards the respective gas bubble conduit. Thus, by capturing said gas bubbles sufficiently upstream on their trajectory, one avoids their moving away from the walls and therefore their mixing with the bubbles of the other gas produced, and possibly coalescence with the bubbles of the other gas produced.

[0017] Thus, the elementary cell described above makes it possible to separate gas bubbles with good purity, for example at least 80%.

[0018] The elementary cell as described does not require pumping of the electrolytic solution to impose a directional flow on it, nor the use of a membrane, although these techniques can be used additionally to further increase the efficiency.

[0019] In one embodiment, the elementary cell does not comprise a membrane.

[0020] The optimized topology thus defined takes into account the dynamics of the bubbles formed during electrolysis, modeled by Stokesian dynamics, in order to optimize the purity / yield couple.

[0021] In embodiments, said average direction of the elementary main conduit is defined as the average of the half-distances between the two walls, that of the elementary anode and that of the elementary cathode, over the length of the main conduit.

[0022] In embodiments, said downstream portion is defined relative to a direction of flow of the gas bubbles in the average direction of the elementary main conduit.

[0023] The flow of gas bubbles in the elementary main conduit is at least produced by a difference in density between the electrolytic solution and the gas bubbles, the system being subject to volume forces. For example, the volume force is a gravitational force. For example, the direction of flow of gas bubbles is directed along an upward vertical in the case where the electrolytic solution is subject to Earth's gravity.

[0024] The elementary cell of the present disclosure comprises at least one gas bubble conduit per elementary electrode, but any number of conduits can be envisaged, including a different number between the elementary anode or the elementary cathode.

[0025] When referring to an "electrode," we are referring to either the anode or the cathode.

[0026] A "massive elementary electrode" means an electrode that is not porous.

[0027] “Fluidic connection” means a direct or indirect connection for the first gas or the second gas, and / or the electrolytic solution.

[0028] The features set out in the following paragraphs may, optionally, be implemented independently of each other or in combination with each other.

[0029] In embodiments, the elementary cell does not have symmetry along the axis defined by the average direction of the elementary main conduit.

[0030] In embodiments, at least one of the inlet mouths has a funnel shape. In other words, the width of the bubble conduit decreases from a wider junction with the elementary main conduit in the direction of the corresponding gas outlet.

[0031] Thanks to this funnel shape, it is possible to avoid mixing between the bubbles of the first gas and the bubbles of the second gas, by guiding the bubbles towards the corresponding gas bubble conduit.

[0032] In embodiments, the bubble conduits each have a respective average exhaust direction inclined relative to the average direction of the elementary main conduit. The average exhaust direction is oriented in the upstream-downstream direction of movement of the gas bubbles escaping from the elementary main conduit in the direction of the corresponding gas outlet.

[0033] Thus, the respective average exhaust direction is defined in a direction non-perpendicular to the average direction of the elementary main duct.

[0034] In one embodiment, the respective average exhaust direction and the average direction of the downstream elementary main duct form a respective first acute angle, the average direction of the elementary main duct being oriented in the direction upstream-downstream direction of movement of the gas bubbles, and the average exhaust direction being oriented in the upstream-downstream direction of movement of the gas bubbles, said first acute angle being for example between 30° and 60°, for example between 40° and 50°. The respective angle may be the same for the anode and the elementary cathode, or may be different.

[0035] Bubble conduits may have a curved shape, a linear shape, or a linear and / or curved shape per segment, each segment having a different angle with the average direction of the elementary main conduit. For example, some segments may be parallel to the average direction of the elementary main conduit.

[0036] In one embodiment, the inclination of a segment of the bubble line at the mouth is less than the inclination of a segment of the bubble line at a connection to said outlet of the first or second gas.

[0037] In embodiments, an internal wall of the gas bubble conduit of the downstream portion of the inlet mouth forms a second acute angle with the mean direction of the elementary main conduit, preferably in the upstream-downstream direction of the mean direction of the elementary main conduit.

[0038] In embodiments, said second acute angle is preferably between 40° and 60°, for example between 45° and 55°. Said respective second acute angle may be the same for the elementary anode and cathode, or may be different.

[0039] In embodiments, an internal wall of the gas bubble conduit of the downstream portion of the mouth forms a third acute angle with a local wall internal to the elementary main conduit of said elementary anode and / or elementary cathode, said local wall being located downstream of the mouth in the mean direction of the elementary main conduit.

[0040] In embodiments, said local wall internal to the elementary main conduit is not parallel to said mean direction. For example, said local wall internal to the elementary main conduit of said elementary anode and / or elementary cathode forms a fourth acute angle with said mean direction of the elementary main conduit, said local wall being located downstream of the mouth in the mean direction of the elementary main conduit.

[0041] Thanks to the fourth acute angle thus formed, the gas bubbles are at least redirected towards the walls or redirected towards the gas bubble conduits by a physical mechanism called the "Coanda effect", also called the "teapot effect".

[0042] In embodiments, a junction between said internal wall of the gas bubble conduit of the downstream portion of the mouth and said local wall internal to the elementary conduit forms an elementary anode and / or elementary cathode tip projecting into the elementary main conduit.

[0043] In embodiments, the acute angle has an angle between 30° and 40°.

[0044] There are many ways to promote the movement of gas bubbles in the elementary main conduit. For example, a flow of the electrolytic solution can be imposed in the elementary main conduit of the elementary cell, for example by pumping. In this case, the general flow direction of the gas bubbles and the flow direction of the electrolytic solution are substantially parallel, because the movement of the electrolytic solution can carry the gas bubbles. In this case too, it is the shape of the electrodes that promotes the separation of the bubbles of the two gases, while the flow of the electrolytic solution simply promotes the routing of said gas bubbles.

[0045] Alternatively or cumulatively, in one embodiment, the elementary cell is intended, in use, to be subjected to a gravitational force, and arranged so that the average direction of the elementary main conduit forming an inter-electrode axis is substantially placed parallel to the gravitational force.

[0046] Alternatively or cumulatively, the electrolytic solution of the elementary cell can be subjected to another accelerating force, for example centrifugal force.

[0047] Thanks to these characteristics, the bubbles are directed by Archimedes' thrust. For example, the elementary cell is arranged vertically on Earth, the interelectrode axis being substantially parallel to the Earth's force of attraction. In this embodiment, the bubble conduits form the branches of a general vertical "Y" shape, not necessarily symmetrical. For example, the two branches take root at a respective different distance from the foot of the "Y".

[0048] The optimized topology of the elementary cell of the present disclosure allows the electrolysis of many different electrolytic solutions generating two produced in the form of gas. For example, a possible electrolysis is a chlorine-soda electrolysis.

[0049] In embodiments, the electrolytic solution comprises water (of formula H2O), the first gas is oxygen (of formula O2), and the second gas is hydrogen (of formula H2).

[0050] In embodiments, the electrolyte solution is an aqueous solution containing an electrolyte, for example H2SO4, KCl or KOH, at a concentration of between 0.1 and 2 M. The pH of this electrolyte solution may be between 0 (strongly acidic) and 14 (strongly alkaline).

[0051] Thanks to the topological characteristics of the elementary cell, it is possible to guarantee a purity of at least 92% of the collected dihydrogen. Such an embodiment allows the production of green hydrogen by electrolysis of water, for example without the use of a membrane, with the aim of reducing the environmental impact of fossil fuels.

[0052] According to embodiments, the anode and cathode mouths can be opposite each other or offset, all solutions being possible.

[0053] In one embodiment, a first junction, defined between a wall of a downstream portion of the mouth of the bubble conduit of the first gas and a wall of the elementary main conduit, and a second junction, defined between a wall of a downstream portion of the mouth of the bubble conduit of the second gas and a wall of the elementary main conduit, are separated by a length of between and 3 A of the length of the elementary main conduit, preferably between and 1 / 2, for example a length selected from the list consisting of: [1 / 4, 1 / 3, 1 / 2, 2 / 3, 3 A] of the length of the elementary main conduit.

[0054] In one embodiment, said selected length depends on the ratio between an average size of the bubbles of the first gas and an average size of the bubbles of the second gas.

[0055] In embodiments, the elementary anode and / or the elementary cathode comprises metal on an incomplete portion of the elementary anode and / or the elementary cathode. For example, the incomplete portion is present on at least a portion of at least one of the mouths and / or on a portion of the walls of the elementary main conduit, for example near the at least one mouth.

[0056] In particular, the incomplete portion is defined at least on the surface where the electrolysis reaction occurs. For example, the incomplete portion is defined on walls in contact with the electrolytic solution, for example on walls of said electrode tip.

[0057] Thanks to these characteristics, it is possible to provide such an elementary cell while minimizing the costs related to the volume of metal required, instead of having the entire electrode made of metal.

[0058] For example, the incomplete portion corresponds to a non-continuous deposition of metal, so as to form controlled defects, or holes in the metal layer, in order to define gas bubble nucleation sites.

[0059] With these features, it is possible to locate gas bubble nucleation sites along the path of gas bubble conduits, so as to maximize the proportion of gas bubbles captured by the gas bubble conduits.

[0060] For example, the metal can be selected from the following list of metals, including alloys: either precious metals (e.g. platinum (Pt), palladium (Pd), rhodium (Rh), etc.) or semi-precious metals, such as titanium (Ti), or transition metals (e.g. nickel (Ni), cobalt (Co), iron (Fe) etc.). Zinc oxide (ZnO) can also be chosen.

[0061] In embodiments, the elementary anode and / or the elementary cathode comprises an aerophobic material on at least a wall portion of the gas bubble conduit and / or at least a wall portion of the elementary main conduit.

[0062] Thanks to this feature, it is possible to provide an elementary cell in which the formed gas bubbles are prevented from wetting said portion of the wall of the gas bubble conduit.

[0063] In embodiments, said elementary anode wall and / or said elementary cathode wall comprises a micro-texture on at least a portion of the wall of the elementary main conduit, in order to allow movement of the gas bubbles by taking advantage of the different surface tensions of the solid-liquid-gas system.

[0064] In one embodiment, the micro-texture consists of grooves and / or ribs for guiding the gas bubbles.

[0065] In embodiments, the elementary anode and the elementary cathode are fabricated by photolithography on a metallized substrate. For example, the substrate is a silicon wafer, or glass.

[0066] The present disclosure further relates to a cell for electrolysis of an electrolytic solution comprising a plurality of elementary cells as defined above, identical or not, in which the elementary cells are connected, so that the elementary main conduit of an elementary cell is fluidically connected to the elementary main conduit of the following elementary cell.

[0067] For example, in said electrolysis cell, the elementary anodes are electrically connected to each other and the elementary cathodes are electrically connected to each other. For example, the elementary anodes form the anode of the assembly, and the elementary cathodes form the cathode of the assembly. Conversely, it is also possible to provide for the elementary cells to be brought to different potentials.

[0068] Similarly, it is possible for the topological shapes of the elementary cells to be identical or different. In one example, the elementary cells are identical and linearly repeated, so that the bubble ducts of the first gas are parallel to each other, the bubble ducts of the second gas are parallel to each other.

[0069] The distance between the inlet mouths of the two successive elementary gas bubble conduits of different elementary electrodes can vary between zero and the length of an elementary main conduit. Thus, in embodiments, the inlet mouths are opposite each other for the anode and the cathode. Alternatively, in embodiments, the bubble conduits of the first gas and the bubble conduits of the second gas are alternated along the elementary main conduit. Thanks to this characteristic, the separation of the gas bubbles produced by each of the two electrodes is maximized, so as to maximize the purity of the electrolysis products. For example, the inlet mouths of the gas bubble conduits are alternated at equal distances from each other in the case where the dimension of the bubbles is the same for the two gases.For example, the inlet mouths of the gas bubble conduits are alternated at 1 / 3 the length of an elementary main conduit.

[0070] The present disclosure further relates to a use of the electrolysis cell as described without using a membrane and / or without using pumping.

[0071] The present disclosure further relates to a device for electrolysis comprising an electrolysis cell as defined above, comprising a gas reservoir, in which the gas reservoir is fluidically connected:

[0072] - either to the bubble lines of the first gas,

[0073] - either to the bubble pipes of the second gas.

[0074] In one embodiment, there are two gas reservoirs fluidly connected to the first gas bubble lines and the second gas bubble lines, respectively. Brief description of the drawings

[0075] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which: Fig. 1

[0076] [Fig. 1] Figure 1 is a schematic plan view of the topology of an elementary cell for electrolysis of an electrolytic solution producing gases according to one embodiment; Fig.2

[0077] [Fig. 2] Figure 2 is a schematic plan view of an exemplary topology of an electrolysis cell comprising a plurality of elementary cells of linearly repeated pattern; Fig.3

[0078] [Fig. 3] Figure 3 is a schematic plan view of the topology of one of the elementary electrodes of an elementary electrolysis cell according to one embodiment; Fig.4

[0079] [Fig. 4] Figure 4 is a schematic view of the topology of a variant of the elementary electrode of Figure 3; Fig.5

[0080] [Fig. 5] Figure 5 is a schematic perspective view of a slice of an elementary cell according to one embodiment; Fig. 6

[0081] [Fig. 6] Figure 6 represents a schematic perspective view of an electrolysis cell composed of a linear stack of five elementary cells each having the topology according to the slice represented in Figure 5; Fig. 7

[0082] [Fig. 7] Figure 7 shows a stack of photolithography masks used in the fabrication of a simplified laboratory test of the electrolysis cell of Figure 9, and an enlarged view of a detail of the stack of masks. Fig. 8

[0083] [Fig. 8] Figure 8 is a non-scale sectional diagram of the main pipe of the system of Figure 9. Fig. 9

[0084] [Fig. 9] Figure 9 is a photograph of the electrolysis cell produced by photolithography on a glass wafer from the stack of masks in Figure 7, and a photograph with a binocular magnifying glass of a detail of one of the elementary electrodes of the electrolysis cell; Fig. 10

[0085] [Fig. 10] Figure 10 represents a schematic perspective view of an electrolysis cell whose electrodes have a topology according to a variant; Fig. 11

[0086] [Fig. 1 1] Figure 1 1 shows a sectional view of a detail of an electrode of the electrolysis cell of Figure 10. Fig. 12 [Fig. 12] Figure 12 shows a sectional view of a detail of an electrode of an alternative to the topology of the electrolysis cell of Figure 10; Fig. 13

[0087] [Fig.13] Figure 13 represents a mask of different test topologies of micro-textured electrodes that can be adapted to the schematic diagram of the electrolysis cell of Figure 10.; Fig. 14

[0088] [Fig.14] Figure 14 represents selected technical characteristics for carrying out the tests, in particular of the mask in Figure 13. Description of the embodiments

[0089] Reference is now made to Figure 1. Figure 1 represents a section of an elementary cell 1 for the electrolysis of an electrolytic solution producing gases.

[0090] The elementary cell 1 comprises a massive elementary anode 2 and a massive elementary cathode 3 separated by a main elementary conduit 4 intended to be filled with the electrolytic solution.

[0091] The elementary main conduit 4 is defined between a wall 5 of the elementary anode 2 and a wall 6 of the elementary cathode 3, along a mean direction 12 oriented in a flow direction defined as a mean direction of flow of the gas bubbles produced by the electrolysis.

[0092] The elementary anode 2 has a recess forming a conduit 7 defined between two conduit walls 13 and 18. The elementary main conduit 4 has a mouth 8 forming the inlet of the conduit 7. The mouth 8 forms a discontinuity in the wall 5 between an upstream portion 51 of the wall 5 and a downstream portion 52 of the wall 5.

[0093] The pipe 7 is intended for transporting bubbles of a first gas resulting from the electrolysis, the bubbles being captured from the main elementary pipe 4 and guided out of the elementary cell 1. The pipe 7 is intended, in use, to fluidically connect the main elementary pipe 4 to an outlet of the first gas.

[0094] Similarly, the elementary cathode 3 has a recess forming a conduit 9 defined between two conduit walls 20 and 24. The elementary main conduit 4 has a mouth 10 forming the inlet of the conduit 9. The mouth 10 forms a discontinuity in the wall 6 between an upstream portion 61 of the wall 6 and a downstream portion 62 of the wall 6.

[0095] The pipe 9 is intended for transporting bubbles of a second gas resulting from the electrolysis, the bubbles being captured from the main elementary pipe 4 and guided out of the elementary cell 1. The pipe 9 is intended, in use, to fluidically connect the main elementary pipe 4 to an outlet of the second gas.

[0096] In Figure 1, the elementary cell 1 is shown in section, in the plane of the mean direction 12. The elementary cell 1 is in reality three-dimensional. The elementary anode 2 and the elementary cathode 3 have a thickness defined in the direction perpendicular to the section plane, and an invariant topology in said perpendicular direction.

[0097] The elementary anode 2 is therefore formed of two distinct solid blocks, an upstream block 21 and a downstream block 22, the upstream-downstream direction being defined in the average direction 12, which are electrically connected to each other by an electrical connection 23 as shown diagrammatically in the figure.

[0098] Similarly, the elementary cathode 3 is therefore formed of two separate solid blocks, an upstream block 31 and a downstream block 32 which are electrically connected to each other by an electrical connection 33.

[0099] The schematic representation does not in any way limit the choice of technology, shape and arrangement of electrical connections 23 and 33.

[0100] For the elementary cathode 3, the upstream block 31 has an obtuse angle 25 between the wall 61 and the wall 20, while the downstream block 32 has an acute angle 26 between the wall 24 and the wall 62.

[0101] The acute angle 26 has the function of capturing the bubbles of the second gas on their trajectory and guiding them into the pipe 9, in order to limit the mixing between the bubbles of the first gas and those of the second gas.

[0102] Similarly, for the elementary anode 2, the upstream block 21 has an obtuse angle 27 between the wall 18 and the wall 51, while the downstream block 22 has an acute angle 28 between the wall 52 and the wall 13.

[0103] The acute angle 28 has the function of capturing the bubbles of the first gas on their trajectory and guiding them into the pipe 7, in order to limit the mixing between the bubbles of the first gas and those of the second gas.

[0104] As can be seen in Figure 1, the two upstream 61 and downstream 62 portions of the wall 6 of the main elementary pipe 4 delimiting the elementary cathode 3 are perfectly aligned on either side of the mouth 10. This characteristic is possible but not preferred.

[0105] On the other hand, the two upstream 51 and downstream 52 portions of the wall 5 of the main elementary pipe 4 delimiting the elementary anode 2 are not aligned on either side of the mouth 8.

[0106] This non-alignment, or non-parallelism, results in the formation of a local overhang 56 of the wall 52 at the level of the mouth 8. This local overhang 56 has the function of directing the upstream bubbles towards the mouth 8 in order to extract them from the main pipe 4.

[0107] Furthermore, the downstream portion 52 forms an acute angle 99 with the axis 12 of the main pipe 4 e, thus forming a point 11 in the section plane. The function of this point 11 is to push the bubbles back onto the wall 52 by the Coanda effect.

[0108] In other words, the end of the tip 11 forming the junction between the downstream portion 52 and the wall 13 extends across the width of the elementary main conduit 4 beyond a local part of the portion 51 near the mouth 8.

[0109] This tip 11 therefore has the two functions described: the first, to capture the bubbles of the first gas on their trajectory by the overflow, and the second, to push the bubbles towards the walls, thanks in particular to the Coanda effect by the acute angle 99 formed with the axis 12 of the pipe 4.

[0110] The elementary cell 1 further comprises two planes (not shown) which are insulating and resistant to corrosion from electrolysis, sandwiching the assembly formed by the elementary anode 2 and the elementary cathode 3 in said perpendicular direction.

[0111] Thus, the elementary cell 1 can be placed in a container containing the electrolytic solution.

[0112] Thanks to the particular topology of the elementary cell 1, the purity and efficiency of electrolysis are increased.

[0113] Subsequently, identical or similar elements will be identified by the same reference numbers in order to simplify reading, including in different embodiments.

[0114] Figure 2 represents in section a cell 14 comprising a plurality of elementary cells 1 whose topological pattern of elementary cell 1 was obtained by optimized methods of topological simulation taking into account the formation and the displacement of the bubbles 16 of O2 and the bubbles 17 of H2 during the electrolysis of water, when the cell 14 is placed so that the average direction 12 is vertical to the Earth. To simplify reading, bubbles 16 are represented by empty circles, and bubbles 17 by solid circles. Bubbles 16 and 17 correspond to a snapshot of the numerical simulation carried out, on which their movement can be followed.

[0115] The topological pattern is linearly repeated in the average direction 12. Thus, the portion 51 and the portion 52 of two adjacent patterns form a single wall of a block 22 of anode 2. Thus, the portion 61 and the portion 62 of two adjacent patterns form a single wall of a block 32 of cathode 3.

[0116] As can be seen, in this embodiment, each elementary cell 1 has a tip 11 of elementary anode 2 and a tip 15 of elementary cathode 3, each locally projecting into the main elementary conduit 4.

[0117] The bubbles 16 are formed by electrolysis at the nucleation sites of the elementary anode 2. The nucleation sites are present in particular on the portion 51 near the mouth 8.

[0118] The bubbles 16 are submillimetric at their formation. The shape of the topology of the cell 14 makes it possible to extract the bubbles 16 as quickly as possible after their formation, so as to avoid in particular coalescence during which the bubbles 16 merge.

[0119] The bubbles 16 thus formed are subject to their own dynamics in the gravity field. In other words, they move mainly vertically in the mean direction 12, and are therefore captured by the tip 11 so as to guide them into the pipe 7.

[0120] Cleverly, the topological shape of the tip 11 and the wall 5 of the elementary anode 2 make it possible to limit the distance of the bubbles 16 from the wall 5 by the Coanda effect. Thanks to this characteristic, the bubbles 16 do not mix with the bubbles 17.

[0121] Thus, the purity of the collected H2 gas is greater than 98%.

[0122] This description applies, mutatis mutandis, to the formation and movement of bubbles 17 on the elementary cathode 3.

[0123] Reference is now made to Figures 3 and 4 showing two variants of elementary anodes 2 for an electrolysis cell 14.

[0124] In Figure 3, the elementary anode 2 has a non-truncated tip 11, while the elementary anode 2 of Figure 4 has a truncated tip 11. The tips 11 of the topologies optimized within the framework of the present disclosure may be truncated or not truncated, depending on the optimization sought, such as for example optimization for a particular electrolysis.

[0125] In addition, the topology of Figures 3 and 4 shows a linear pipe shape 7 per segment. The segment 71 of the pipe 7 which is closest to the mouth 8 has a slope forming an angle 29 with the mean direction 12. The following segment 72 of the pipe 7 has an angle 30 with the mean direction 12. The angle 30 is smaller than the angle 29, so that the slope of the segment 72 approaches the mean direction 12. This topology is favorable, in particular, in the case where the electrolysis cell 14 is arranged so that the mean direction 12 is vertical in the gravitational field. Thus, the bubbles 16 can escape vertically by Archimedes' thrust, limiting the risks of sticking to the wall 13.

[0126] In Figure 3, a final segment 73 of the pipe 7 is shown forming an outlet for the first gas. This segment has a funnel shape, so that the pipe 7 widens towards its outlet. Thus, the escape of the bubbles of the first gas is facilitated.

[0127] The description made with reference to figures 3 and 4 can be applied, mutatis mutandis, to topologies of elementary cathodes 3.

[0128] Reference is now made to Figure 5. Figure 5 represents in perspective a slice of elementary cell 1 in its thickness.

[0129] As shown, the pattern of elementary cell 1 has a vertical length of 10 mm, a width of 5 mm, and the thickness of the represented slice is 100 pm.

[0130] As shown, the mouths 8 and 10 have a funnel shape, or a truncated cone shape in a plane including the mean direction 12, so as to more easily capture the gas bubbles from the elementary main conduit 4 to the gas bubble conduits 7 and 9.

[0131] Figure 6 represents an electrolysis cell 14 comprising five elementary cells 1 repeated linearly in the vertical direction. The electrolysis cell 14 is oriented according to the acceleration of gravity g representing the Earth's gravity, the axis of which is parallel with the vertical of the orientation represented by the reference in Cartesian coordinates.

[0132] The slice shown in Figure 5 appears framed in dotted lines. As shown, the thickness of the electrolysis cell 14 comprises a large number of slices.

[0133] As shown, block 21 of an elementary cell 1 and block 22 of the next elementary cell in the vertical direction actually form a single anode block. This description applies, mutatis mutandis, to blocks 31 and 32 of the cathode.

[0134] Although five elementary cells 1 are shown making up the electrolysis cell 14, such an electrolysis cell may comprise a different number of elementary cells 1.

[0135] A material resistant to corrosion of the electrolytic solution, for example glass, plexiglass, or polydimethylsiloxane (PDMS) can be deposited on either side of the thickness of the electrolysis cell.

[0136] Alternatively or cumulatively, the electrolysis cell can be immersed in a beaker containing the electrolytic solution.

[0137] The blocks 21, 22, 31 and 32 may, whatever the embodiment described with reference to the figures above, be composed massively or not. For example, the blocks may be hollow to save material. The blocks serve as support to define the walls.

[0138] The internal material of said blocks may be different from the coating of the walls 5, 6, 13, 18, 20 and 24. For example, the internal material may be non-conductive.

[0139] Said walls are at least partially covered with an electrically conductive coating, such as for example a metal or a metal alloy. Thus, it is possible to limit the manufacturing costs linked to the use of metal.

[0140] The metal is for example platinum (Pt).

[0141] In addition, molecular complexes incorporating metal cations or metal anions can be deposited on the coating in order to improve the catalysis effect.

[0142] To improve the adhesion of the metal deposit to the substrate, it is possible to additionally provide a bonding layer. For example, the bonding layer for platinum (Pt) can be titanium (Ti) or chromium (Cr).

[0143] The internal material of the blocks can be glass, polyetheretherketone (PEEK), Teflon polytetrafluoroethylene (PTFE), optical glue, such as that of the trademark “Norland optical additive NOA”, or polyethylene (PE).

[0144] In the laboratory, PDMS can be used as an internal material for the blocks, but another material should preferably be chosen for industrialization because PDMS will not be able to withstand acidic or alkaline conditions over time.

[0145] In particular, PTFE resistant to acid and basic solutions, or polyethylene which has both good resistance and ease of shaping, will be preferred, in order to allow industrial production of said blocks to be less expensive and simpler.

[0146] Reference is now made to Figures 7 to 9 describing a system called simplified laboratory test for designing and manufacturing the electrolysis cell 14 of Figure 6. The orientation of Figures 7 to 9 is represented in the XYZ plane. For example, for these figures, the Z axis can be considered to represent the Earth vertical. The manufacture of the electrolysis cell 14 can substantially be carried out by photolithography from a substrate 60 placed horizontally, but the electrolysis cell 14 once formed can advantageously be placed in use so that the average direction 12 is at the Earth vertical.

[0147] Figure 7 represents, in the XY plane, a stack of photolithography masks 40 used for the manufacture of the laboratory test. Also shown is an enlarged view 70 of a detail of the stack of masks at the mouth 8.

[0148] Figure 8 represents a cross-section along the cutting plane 75, of the simplified electrolysis cell 14 as provided by the stack of masks 40 of Figure 7, and the photograph of which is shown in Figure 9.

[0149] The simplified electrolysis cell 14 is produced by photolithography on the substrate 60. A photograph taken with a binocular corresponding to a part of the detail 41 is also shown in FIG. 9.

[0150] The stack of masks 40 provides for forming on the substrate 60 made of glass (SiO2) with a diameter 44 equal to 2” a thin layer 43 of platinum (Pt) with a thickness of 100 nm to form the electrodes.

[0151] The thickness of the simplified electrolysis cell 14 may be that of an elementary cell 1 such as that described previously with reference to FIG. 5, for example 100 microns thick in the relative direction Y shown with reference to Figure 5 (corresponding to the relative direction Z in Figure 9).

[0152] The thin layer 43 covers the substrate 60 on two parts, left and right, separated by the main conduit 4 of the simplified electrolysis cell 14.

[0153] The stack of masks 40 further provides for forming on the thin layer 43 of platinum (Pt) the blocks of the electrolysis cell 14 in the internal material 42 of the blocks, here PDMS.

[0154] At the level of the electrolysis cell 14, the mask of the thin layer 43 is of similar shape but of slightly larger surface area than the mask of the internal material 42 of the blocks 22 and 32, so that the thin layer 43 protrudes slightly from the walls of the blocks.

[0155] As shown with reference to Figure 8, a PDMS cover 76 is provided on the blocks 22 and 23, so as to define between the substrate 60, the cover 76 and the respective walls of the blocks 22 and 23, the main conduit 4.

[0156] Similarly, shown with reference to Figure 7, a PDMS reservoir 45 is provided, which must be preformed, also by photolithography, then placed on the substrate 60 around the electrolysis cell 14. The mask of the reservoir 45 provides a U shape in the XY plane. The walls of the reservoir 45 must be placed at a distance from the electrolysis cell 14, so as to define between the anode 2 and the reservoir 45 a channel 46 for exhausting the first gas into which the pipes 7 open. In an identical manner, a channel 47 for exhausting the second gas is defined between the reservoir 45 and the cathode 3, the pipes 9 opening into the channel 47.

[0157] As shown in the enlarged view 70 and FIG. 8, it is observed that, unlike the electrolysis cell 14 of FIG. 6, the internal material 42 of the blocks such as the block 22 is not covered on its walls 74 with the electrically conductive coating. This is intended to simplify the manufacture of the test, constrained by the laboratory conditions. However, ideally, the electrically conductive material covers the walls in order to increase the efficiency of the electrodes, as previously described in embodiments.

[0158] Figure 10 represents a schematic perspective view of an electrolysis cell 48 according to a variant, used for the electrolysis of water.

[0159] The electrolysis cell 48 is oriented so that the average inter-electrode direction 12 is oriented in the direction different from the acceleration of gravity g representing Earth's gravity, and whose axis is parallel with the vertical of the orientation represented by the Cartesian coordinate system in figure 10.

[0160] In this variant, the cathode 49 and the anode 50 each have the general shape of a vertical rectangular parallelepiped, each having two surfaces S1 and S2 that are substantially flat and parallel to each other. In particular, the cathode and the anode each come from a cleavage of a silicon wafer serving as a substrate and having a metallized coating. Another variant could also be produced with non-flat wafers.

[0161] An inter-electrode space 151 is defined between the surface S1 of the anode 50 and the surface S1 of the cathode 49. We will subsequently speak of internal surface S1 and external surface S2, the terms “internal” and “external” referring to the interior of the inter-electrode space 151, and to the exterior of the electrolysis cell formed by the two electrodes.

[0162] The cathode 49 and the anode 50 are each micro-perforated in the thickness e of the electrode to define fluid connections between the surface S1 and the surface S2. Each fluid connection has a wider base frustoconical shape on the surface S1, so as to capture the respective gas bubbles of H2 and O2 formed on the electrodes.

[0163] The surfaces S1 and S2 are further micro-textured to guide the H2 and O2 gas bubbles formed by electrolysis. These micro-textures include, in particular, vertical ribs on the internal S1 and external S2 walls.

[0164] In particular, there is shown on the surface S1 of the cathode 49, in the vertical direction, a rib 152 opening into a micro-perforation 53. On the surface S2 of the cathode 49, there is shown a rib 54 originating in the micro-perforation 53. Thus, a gas bubble of H2 is guided by the rib 152 from the inside to the rib 54 on the outside along a generally vertical trajectory.

[0165] The assembly formed by the micro-perforation 53 and the rib 54 constitutes a gas bubble conduit from the inside to the outside.

[0166] The micro-perforation 53 is separated from the base of another rib 55 originating higher on the surface S1. Thus, the upper edge of the micro-perforation 53 forms with the base of the rib 55 an overhang 56 which extends inwards compared to the internal wall of the rib 52.

[0167] Thanks to this overhang 56, the H2 gas bubble guided by the rib 152 is captured instead of moving away from the wall S1 and mixing with the O2 gas bubbles.

[0168] Several gas bubble conduits are thus formed on each of the electrodes according to the same logic.

[0169] Figure 11 shows a sectional view of the micro-perforation 53 in the thickness e of the cathode 49. As described above, the overhang 56 is observed to extend further inwards than the surface of the rib 152. However, this overhang 56 has an obtuse angle θ1 in the sectional plane, in contrast to the embodiments described with reference to Figures 1 to 9.

[0170] A bubble of H2 is described at three successive locations 57, 58 and 59, in order, of its path from the inside to the outside. As shown in Figure 11, in order to take advantage of the frustoconical shape of the micro-perforation 53 being wider on the surface S1 than on the surface S2, the material of the cathode 49 on the inner surface of the micro-perforation is more aerophilic than hydrophilic. For example, the material is Teflon.

[0171] Conversely, as shown in Figure 12, the truncated micro-perforation 153 is oriented in the opposite direction to that of the micro-perforation 53. This is advantageous when the material of the cathode 49 on the internal surface of the micro-perforation is more hydrophilic than aerophilic. For example, the material is glass, on which a partial metal deposit is made to form the electrodes. In this embodiment, and due to the choice of the orientation of the truncated shape, we find the pointed shape with an acute angle 80 in the cutting plane.

[0172] Although the micro-perforations 53 and 153 shown with reference to figures 10 to 12 are of truncated cone shape, that is to say of circular base, other forms of micro-perforations can be envisaged, such as for example truncated cone shapes of oval base or of any base, truncated pyramid shapes, of polygonal base or not, or even cylindrical shapes of any base, including polygonal, oval or circular base.

[0173] Figure 13, for example, represents a screenshot of a digital mask of tests of different electrode topologies intended to be micro-textured on a silicon wafer.

[0174] Advantageously, to simplify the micro-perforation in the wafer, the shape of the micro-perforation 60 is a truncated tetrahedron passing through the crystalline wafer, also called in English “silicon wafer”, forming an entry pore E on the surface S1 and an exit pore S on the exit surface S2. The micro-perforations 60 in the figure are represented by squares.

[0175] As shown, several 63 electrode patterns are tested. In the screenshot, nine of them appear, from the first pattern M1 to the ninth pattern M9, starting from the top left to the bottom right. Each pattern has a grid of 5 columns and 5 rows.

[0176] In particular, when they exist, the lines 64 present above the microperforations 60 correspond to ribs on the surface S2, and the lines 65 present below the micro-perforations 60 correspond to ribs on the surface S1. The ribs are then interconnected via the micro-perforation 60.

[0177] As can be seen in the figure, patterns M3, M4 and M5 each have micro-perforations 60 and ribs on surface S1, but no ribs on surface S2, in order to avoid the step of micro-texturing surface S2.

[0178] Patterns M4, M5 and M6 each have a single micro-perforation per column, on the middle row. Thanks to this feature, the movement of gas bubbles is less polluted by bubbles coming from the other micro-perforations.

[0179] Patterns M1, M2 and M3 have 60 micro-perforations arranged in a staggered pattern in the grid.

[0180] Several numbers and widths of micro-perforation ribs were tested depending on the patterns.

[0181] Figure 14 represents a table summarizing tests according to patterns M1 to M6 as described above.

[0182] Column C1 describes the width of the micro-perforation at the entrance E and at the exit S. Column C2 describes the depth p of the ribs and their width w. Column C3 describes the number N of micro-texturing ribs per micro-perforation, and the inter-rib spacing s. Column C4 describes the presence P or absence A of ribs (microtexturing) on ​​each of the surfaces S1 and S2. Column C5 specifies whether the pattern has a staggered arrangement Q of the micro-perforations, or an arrangement C which has only one micro-perforation per column.

[0183] Due to these advantageous features described in the above embodiments, it is possible to separate gas bubbles without external forcing or use of membrane, which constitutes an original alternative, allowing a less polluting, less expensive and more robust system.

[0184] The electrode shapes were generated by topological optimization using an electrolysis simulator. This electrolysis simulator is based on an original bubble dynamics meta-model, including in particular the production, and therefore the nucleation of bubbles by electrolysis. In particular, the current density - gas produced relationship, the detachment of bubbles from the walls and the bubble dynamics were taken into account.

[0185] The electrodes as described in the above embodiments can be manufactured by conventional clean room techniques in a micrometric version, or by metal 3D printing, for example in titanium, and can then be coated with a standard electrocatalyst by electrodeposition or vacuum vaporization (for example platinum).

[0186] The electrodes are then placed in a corrosion-resistant tank and positioned face to face with each other.

[0187] For simplification purposes, some of the described embodiments were generated using models taking into account a two-dimensional simulation, and the electrodes having the simulated topological patterns were tested to be invariant in the thickness plane. As described in other embodiments, bubble dynamics can also be taken into account to generate 3D topological patterns, and thus establish a non-invariant three-dimensional electrode topology, a cutting plane of which has the overhang, with or without a tip.

[0188] The Cartesian coordinate systems used in the figures do not assume the orientation of this system relative to the terrestrial vertical parallel to the acceleration of gravity g representing the terrestrial gravity, unless gravity g is mentioned and described in the figures concerned.

[0189] Although the preferred embodiments of certain figures mention the orientation of the electrolysis cell so that the average direction 12 is vertical to the Earth, the electrolysis cell of each of the embodiments described could be used in a direction other than the vertical direction. For example, the average direction could be placed horizontal to the Earth, if for example pumping of the electrolytic solution is required. Indeed, the topological choices then also have the advantage of capturing, by the overflow, the gas bubbles on their trajectory.

Claims

Claims

1. Elementary cell (1) for the electrolysis of an electrolytic solution producing gases, comprising a solid elementary cathode (3, 49) and a solid elementary anode (2, 50) separated by an elementary main conduit (4, 51) intended to be filled with the electrolytic solution, said elementary main conduit (4, 51) being defined between a wall (5, S1) of the elementary anode and a wall (6, S1) of the elementary cathode, the elementary anode (2, 50) having a recess (53, 153) forming a conduit (7) for bubbles of a first gas, the elementary main conduit having an inlet mouth (8) for said conduit for bubbles of the first gas, said conduit for bubbles of the first gas being intended, in use, to fluidically connect the elementary main conduit (4, 51) to an outlet of the first gas, the elementary cathode (3, 49) having a recess (53, 153) forming a conduit (9) for bubbles of a second gas,the elementary main conduit having an inlet mouth (10) of said bubble conduit of the second gas, said bubble conduit of the second gas being intended, in use, to fluidically connect the elementary main conduit (4, 51) to an outlet of the second gas, in which the elementary anode (2, 50) and / or the elementary cathode (3, 49) locally overflows (11, 56) into the elementary main conduit (4), at the inlet mouth (8, 10), on a downstream portion of the inlet mouth in a mean direction (12) of the elementary main conduit.,

2. Elementary cell according to claim 1, in which at least one of the inlet openings (8, 10) has a funnel shape.

3. Elementary cell according to any one of claims 1 or 2, in which the bubble conduits (7, 9) each have a respective average exhaust direction inclined relative to the average direction (12) of the elementary main conduit.

4. Elementary cell according to any one of claims 1 to 3, in which an internal wall (13) of the gas bubble conduit of the downstream portion of the inlet mouth forms an acute angle with the mean direction (12) of the elementary main conduit.

5. Elementary cell according to one of claims 1 to 4, in which an internal wall (13) of the gas bubble conduit of the downstream portion of the mouth forms an acute angle (26, 28) with a local internal wall of the main elementary conduit (4) of said elementary anode and / or elementary cathode, said local wall being located downstream of the mouth (8, 10) in the mean direction (12) of the elementary main conduit (4).

6. Elementary cell according to claim 5, in which a junction between said internal wall (13) at the gas bubble conduit and said local wall internal to the main elementary conduit (4) forms a tip (11, 15) of elementary anode and / or elementary cathode projecting into the main elementary conduit (4).

7. Elementary cell according to one of claims 1 to 6, in which a local wall internal to the elementary main conduit (4) of said elementary anode and / or elementary cathode forms an acute angle with said mean direction (12) of the elementary main conduit (4), said local wall being located downstream of the mouth (8, 10) in the mean direction (12) of the elementary main conduit (4).

8. Elementary cell according to any one of claims 1 to 7, the elementary cell being intended, in use, to be subjected to a gravitational force, and arranged so that the average direction (12) of the elementary main conduit forming an inter-electrode axis (151) is substantially placed parallel to the gravitational force.

9. An elementary cell according to any one of claims 1 to 8, wherein the electrolytic solution comprises water (of formula H2O), the first gas is dioxygen (of formula O2), and the second gas is dihydrogen (of formula H2).

10. An elementary cell according to any one of claims 1 to 9, wherein the elementary anode and / or the elementary cathode comprises metal on an incomplete portion of the elementary anode and / or the elementary cathode, the incomplete portion comprising at least part of the vicinity of at least one of the openings (8, 10).

11. Elementary cell according to any one of claims 1 to 10, in which the elementary anode and / or the elementary cathode comprises an aerophobic material on at least a portion of the wall of the gas bubble conduit and / or at least a portion of the wall of the elementary main conduit.

12. Elementary cell according to any one of claims 1 to 11, in which said elementary anode wall and / or said elementary cathode wall has a micro-texture (52, 53, 55) on at least a portion of the wall of the elementary main conduit.

13. An elementary cell according to any one of claims 1 to 12, wherein the elementary anode and the elementary cathode are manufactured by photolithography on a substrate.

14. Electrolysis cell (14) comprising a plurality of elementary cells according to any one of claims 1 to 13, in which the elementary cells are connected, so that the elementary main conduit of an elementary cell is fluidically connected to the elementary main conduit of the following elementary cell.

15. A device for electrolysis comprising an electrolysis cell according to claim 14, comprising a gas reservoir, wherein the gas reservoir is fluidically connected either to the bubble lines of the first gas or to the bubble lines of the second gas.

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