elementary cell for the electrolysis of an electrolytic solution producing gases

Abstract

Elementary cell for electrolysis, the elementary anode having a bubble conduit of a first gas, the elementary cathode having a bubble conduit of a second gas, wherein the elementary anode and / or the elementary cathode locally extends into the elementary main conduit, at the mouth, on a downstream portion of the mouth in a mean direction of the elementary main conduit. Abstract figure: Figure 1

Description

Title of the invention: 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. Previous technique

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

[0003] Electrolysis techniques allowing a purity / yield compromise are known, in which techniques include: - to increase the distance between the anode and the cathode or to provide a physical separator, so as to maximize the separation of the different gas bubbles generated by electrolysis, and thus increase the purity of the electrolysis product, and - to decrease 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 involves using membranes to separate electrodes in order to maximize the purity of the electrolysis product by preventing the mixing of different gas bubbles produced by electrolysis. This technique has the disadvantage of consuming membranes due to wear.

[0006] An alternative technique involves dispensing with the membrane and using porous electrodes. Such electrodes are made of a solid foam or a random porous medium, or even a mesh, in order to increase the surface area to volume ratio. This latter option has the disadvantage of trapping gas bubbles in the structure, thus reducing efficiency.

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

[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 presents an additional energy cost compared to the electrical energy required for electrolysis alone, because the energy for pumping the electrolytic solution must also be supplied. Summary

[0010] This disclosure improves the situation.

[0011] The present disclosure provides an optimized electrode topology that has a geometry that allows the gas bubbles produced to be captured while minimizing the mixing of 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 for said bubble conduit of the first gas. In operation, said bubble conduit of the first gas is intended to fluidly connect the elementary main conduit to an outlet of the first gas, so that the first gas escapes from the elementary main conduit of the elementary cell via the bubble conduit of the first gas.

[0014] The elementary cathode has a recess forming a bubble duct for a second gas. The elementary main duct has an inlet for said bubble duct of the second gas. In operation, said bubble duct of the second gas is intended to fluidly connect the elementary main duct to an outlet of the second gas, so that the second gas escapes from the elementary main duct of the cell via the bubble duct of the second gas.

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

[0016] The local overflow, also called "overflow," of the elementary anode and / or elementary cathode allows the gas bubbles to be captured along their trajectory and redirected in the vicinity of said elementary anode and / or elementary cathode toward the respective gas bubble conduit. Thus, by capturing these gas bubbles sufficiently upstream along their trajectory, their movement away from the walls is prevented, thus avoiding their mixing with the bubbles of the other gas produced, and potentially their coalescence with the bubbles of the other gas produced.

[0017] Thus, the elementary cell described above makes it possible to separate the 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, nor the use of a membrane, although these techniques can be used additionally to further increase the yield.

[0019] In one embodiment, the elementary cell does not have 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 ratio.

[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 with respect to a flow direction of gas bubbles in the average direction of the elementary main conduit.

[0023] The flow of gas bubbles in the elementary main conduit is produced at least by a difference in density between the electrolytic solution and the gas bubbles, the system being subjected to volumetric forces. For example, the volumetric force is a gravitational force. For example, the direction of flow of the gas bubbles is directed vertically upwards in the case where the electrolytic solution is subjected 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 may be envisaged, including a different number between the elementary anode or the elementary cathode.

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

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

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

[0028] The features described 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 exhibit symmetry along the axis defined by the average direction of the elementary main conduit.

[0030] In some embodiments, at least one of the inlet openings 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 duct.

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

[0033] Thus, the respective average exhaust direction is defined in a direction not perpendicular to the average direction of the elementary main conduit.

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

[0035] The bubble ducts may have a curved shape, or a linear shape, or even a linear and / or curved shape segment by segment, each segment having a different angle with the average direction of the elementary main duct. For example, some segments may be parallel to the average direction of the elementary main duct.

[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 fitting 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 average direction of the elementary main conduit, preferably in the upstream-downstream direction of the average 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 anode and the elementary cathode, or may be different.

[0039] In some embodiments, an internal wall of the gas bubble conduit in 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 average direction of the elementary main conduit.

[0040] In some 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 ducts by a physical mechanism called the "Coanda effect", also known as 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 internal wall of the elementary conduit forms an elementary anode tip and / or elementary cathode tip extending into the elementary main conduit.

[0043] In some 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, since the movement of the electrolytic solution can carry away the gas bubbles. In this case as well, 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 facilitates the transport 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 may be subjected to another accelerating force, for example the centrifugal force.

[0047] Thanks to these characteristics, the bubbles are oriented by Archimedes' principle. For example, the elementary cell is arranged vertically on Earth, with the interelectrode axis being substantially parallel to the Earth's gravitational force. In this mode In practice, the bubble tubes form branches in a general vertical "Y" shape, not necessarily symmetrical. For example, the two branches may originate at different distances from the base of the "Y".

[0048] The optimized topology of the elementary cell of the present disclosure allows for the electrolysis of many different electrolytic solutions, generating two products in gaseous form. For example, a possible electrolysis is a chlor-sodium hydroxide electrolysis.

[0049] In some embodiments, 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).

[0050] In some embodiments, the electrolytic solution is an aqueous solution containing an electrolyte, for example H2SO4, KC1 or KOH, at a concentration between 0.1 and 2 M. The pH of this electrolytic solution can be between 0 (strongly acidic) and 14 (strongly alkaline).

[0051] Thanks to the topology 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 water electrolysis, 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 duct of the first gas and a wall of the elementary main duct, and a second junction, defined between a wall of a downstream portion of the mouth of the bubble duct of the second gas and a wall of the elementary main duct, are separated by a length between % and ¾ of the length of the elementary main duct, preferably between % and U2, for example a length selected from the list consisting of: [1 / 4, 1 / 3, U2, 2 / 3, ¾] of the length of the elementary main duct.

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

[0055] In some 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 part of at least one of the inlets and / or on part of the walls of the elementary main conduit, for example near at least one inlet.

[0056] In particular, the incomplete portion is defined at least on the surface where it occurs the electrolysis reaction. 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 sites for the nucleation of gas bubbles.

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

[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 one portion of the wall of the gas bubble duct and / or at least one portion of the wall of the elementary main duct.

[0062] Thanks to this feature, it is possible to provide an elementary cell in which the gas bubbles formed 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 has a micro-texture on at least a portion of the wall of the elementary main conduit, in order to allow movement of 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 gas bubbles.

[0065] In some 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 an electrolysis cell of an electrolytic solution comprising a plurality of elementary cells as defined above, identical or not, in which the elementary cells are connected, such that the elementary main conduit of one elementary cell is fluidly connected to the elementary main conduit of the next elementary cell.

[0067] For example, in said electrolysis cell, the elementary anodes are The individual cells are electrically connected to each other, and the individual cathodes are electrically connected to each other. For example, the individual anodes form the anode of the system, and the individual cathodes form the cathode of the system. Conversely, it is also possible to have the individual cells held at different potentials.

[0068] Similarly, it is possible that the topological shapes of the elementary cells may be identical or different. In one example, the elementary cells are identical and repeated linearly, such that the bubble ducts of the first gas are parallel to each other, and 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 ducts of different elementary electrodes can vary from zero to the length of an elementary main duct. Thus, in some embodiments, the inlet mouths are opposite each other for the anode and the cathode. Alternatively, in other embodiments, the bubble ducts of the first gas and the bubble ducts of the second gas are alternated along the elementary main duct. Thanks to this feature, 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 ducts are alternated at equal distances from each other in the case where the bubble size is the same for both gases.For example, the inlet ports of the gas bubble ducts are alternated at 1 / 3 of the length of a basic main duct.

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

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

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

[0073] - or to the bubble ducts of the second gas.

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

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

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

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

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

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

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

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

[0082] [Fig.7] Fig.7 represents a stack of photolithography masks used to the fabrication of a simplified laboratory test of the electrolysis cell of [Fig.9], and an enlarged view of a detail of the mask stacking. Fig. 8

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

[0084] [Fig.9] [Fig.9] is a photograph of the electrolysis cell taken by photo lithography on a glass disc from the stack of masks of [Fig.7], and a photograph with a binocular loupe of a detail of one of the elementary electrodes of the electrolysis cell; Fig. 10

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

[0086] [Fig. 11] The [Fig. 11] represents a cross-sectional view of a detail of an electrode of the electrolysis cell of the [Fig. 10]. Fig. 12

[0087] [Fig. 12] The [Fig. 12] represents a cross-sectional view of a detail of an electrode of an alternative to the topology of the electrolysis cell of the [Fig. 10]; Fig. 13

[0088] [Fig. 13] The [Fig. 13] represents a mask of different test topologies of micro-textured electrodes that can be adapted to the principle diagram of the electrolysis cell beyond [Fig.10].; Fig. 14

[0089] [Fig. 14] The [Fig. 14] represents technical characteristics selected to carry out the tests in particular of the mask of the [Fig. 13]. Description of the implementation methods

[0090] Reference is now made to [Fig.1]. [Fig.1] represents a cross-section of an elementary cell 1 for the electrolysis of an electrolytic solution producing gases.

[0091] The elementary cell 1 comprises a massive elementary anode 2 and a massive elementary cathode 3 separated by an elementary main conduit 4 intended to be filled with the electrolytic solution.

[0092] 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 an average direction 12 oriented in a flow direction defined as an average flow direction of the gas bubbles produced by electrolysis.

[0093] 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 an opening 8 forming the inlet of the conduit 7. The opening 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.

[0094] The conduit 7 is intended for the transport of bubbles of a first gas from electrolysis, the bubbles being captured from the elementary main conduit 4 and guided out of the elementary cell 1. The conduit 7 is intended, in use, to fluidly connect the elementary main conduit 4 to an outlet of the first gas.

[0095] 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 an opening 10 forming the inlet of the conduit 9. The opening 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.

[0096] The conduit 9 is intended for the transport of bubbles of a second gas from the electrolysis, the bubbles being captured from the elementary main conduit 4 and guided out of the elementary cell 1. The conduit 9 is intended, in use, to fluidly connect the elementary main conduit 4 to an outlet of the second gas.

[0097] In [Fig. 1], the elementary cell 1 is shown in cross-section, in the plane of the average direction 12. The elementary cell 1 is in fact three-dimensional. The elementary anode 2 and the elementary cathode 3 have a defined thickness in the direction perpendicular to the plane of section, and an invariant topology in said perpendicular direction.

[0098] The elementary anode 2 is therefore formed of two distinct massive 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 schematically shown in the figure.

[0099] Similarly, the elementary cathode 3 is therefore formed of two distinct massive blocks, an upstream block 31 and a downstream block 32 which are electrically connected to each other by an electrical connection 33.

[0100] The schematic representation does not in any way limit the choice of technology, form and arrangement of electrical connections 23 and 33.

[0101] 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.

[0102] The acute angle 26 has the function of capturing the bubbles of the second gas on their trajectory and guiding them in the conduit 9, in order to limit the mixing between the bubbles of the first gas and those of the second gas.

[0103] 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.

[0104] The acute angle 28 has the function of capturing the bubbles of the first gas on their trajectory and guiding them in the conduit 7, in order to limit the mixing between the bubbles of the first gas and those of the second gas.

[0105] As can be seen in [Fig.1], the two upstream 61 and downstream 62 portions of the wall 6 of the main elementary conduit 4 delimiting the elementary cathode 3 are perfectly aligned on either side of the mouth 10. This feature is possible but not preferred.

[0106] On the other hand, the two upstream portions 51 and downstream portions 52 of the wall 5 of the pipe main ment 4 delimiting the elementary anode 2 are not aligned on either side of the mouth 8.

[0107] This non-alignment, or non-parallelism, results in the formation of a local overhang 56 of the wall 52 at 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 conduit 4.

[0108] Furthermore, the downstream portion 52 forms an acute angle 99 with the axis 12 of the main pipe 4e, thus forming a point 11 in the cutting plane. The function of this point 11 is to push the bubbles back onto the wall 52 by the Coanda effect.

[0109] In other words, the tip of the point 11 forming the junction between the downstream portion 52 and the wall 13 extends in the width of the elementary main conduit 4 beyond a local part of the portion 51 near the mouth 8.

[0110] 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 back towards the walls, thanks in particular to the Coanda effect by the acute angle 99 formed with the axis 12 of the pipe 4.

[0111] The elementary cell 1 further comprises two insulating and corrosion-resistant planes (not shown) sandwiching the assembly formed by the elementary anode 2 and the elementary cathode 3 in said perpendicular direction.

[0112] Thus, the elementary cell 1 can be placed in a container containing the electrolytic solution.

[0113] Thanks to the particular topology of the elementary cell 1, the purity and yield of an electrolysis are increased.

[0114] Subsequently, identical or similar elements will be identified by the same reference numbers in order to simplify reading, including in different embodiments.

[0115] Figure 2 shows a cross-section of a cell 14 comprising a plurality of elementary cells 1, the topological pattern of which was obtained by optimized topological simulation methods taking into account the formation and movement of O2 bubbles 16 and H2 bubbles 17 during the electrolysis of water, when the cell 14 is positioned so that the average direction 12 is vertical to the Earth. For ease of reading, the bubbles 16 are represented by open circles, and the bubbles 17 by filled circles. The bubbles 16 and 17 correspond to a snapshot of the numerical simulation performed, on which their movement can be followed.

[0116] The topological pattern is repeated linearly in the average direction 12. Thus, the portion 51 and the portion 52 of two adjacent patterns form a single wall of an anode block 22 2. Thus, the portion 61 and the portion 62 of two adjacent patterns form a single wall of a cathode block 32 3.

[0117] As can be seen, in this embodiment, each elementary cell 1 has an elementary anode tip 11 2 and an elementary cathode tip 15 3, each locally overflowing into the elementary main conduit 4.

[0118] 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.

[0119] The bubbles 16 are submillimeter in size when they form. The shape of the topology of the cell 14 allows the bubbles 16 to be extracted as quickly as possible after their formation, so as to avoid in particular coalescence during which the bubbles 16 merge.

[0120] The bubbles 16 thus formed are subject to their own dynamics in the gravitational field. In other words, they move mainly vertically in the average direction 12, and are therefore captured by the tip 11 so as to guide them in the conduit 7.

[0121] Cleverly, the topological shape of the tip 11 and the wall 5 of the elementary anode 2 limits the separation of the bubbles 16 from the wall 5 by the Coanda effect. Thanks to this feature, the bubbles 16 do not mix with the bubbles 17.

[0122] Thus, the purity of the collected H2 gas is greater than 98%.

[0123] This description applies, mutatis mutandis, to the formation and movement of bubbles 17 on the elementary cathode 3.

[0124] Reference is now made to figures 3 and 4 representing two variants of elementary anodes 2 for an electrolysis cell 14.

[0125] In [Fig. 3], the elementary anode 2 has an untruncated tip 11, while the elementary anode 2 in [Fig. 4] has a truncated tip 11. The tips 11 of the topologies optimized within the scope of this disclosure may be truncated or untruncated, depending on the optimization sought, such as, for example, optimization for a particular electrolysis.

[0126] Furthermore, the topology of Figures 3 and 4 shows a linear conduit shape 7 segment by segment. Segment 71 of the conduit 7, which is closest to the opening 8, has a slope forming an angle 29° with the mean direction 12. The next segment 72 of the conduit 7 has an angle 30° with the mean direction 12. Angle 30° is smaller than angle 29°, so that the slope of segment 72 approaches the mean direction 12. This topology is particularly advantageous when the electrolysis cell 14 is positioned so that the mean direction 12 is vertical in the gravitational field. Thus, the bubbles 16 can escape vertically due to buoyancy, limiting the risk of sticking to the wall 13.

[0127] In [Fig. 3], a final segment 73 of the conduit 7 is shown, forming an outlet for the first gas. This segment has a funnel shape, so that the conduit 7 flares out towards its outlet. Thus, the escape of the bubbles from the first gas is ease.

[0128] The description given with reference to figures 3 and 4 can be applied, mutatis mutandis, to elementary cathode topologies 3.

[0129] Reference is now made to [Fig.5]. [Fig.5] represents in perspective a slice of elementary cell 1 in its thickness.

[0130] As shown, the pattern of the elementary cell 1 has a vertical length of 10 mm, a width of 5 mm, and the thickness of the slice shown is 100 pm.

[0131] As shown, the mouths 8 and 10 have a funnel shape, or a truncated cone shape in a plane including the average direction 12, so as to more easily capture gas bubbles from the elementary main conduit 4 to the gas bubble conduits 7 and 9.

[0132] Figure 6 represents an electrolysis cell 14 comprising five elementary cells 1 repeated linearly in the vertical direction. The electrolysis cell 14 is oriented along the gravitational acceleration g representing Earth's gravity, whose axis is parallel with the vertical of the orientation represented by the coordinate system in Cartesian coordinates.

[0133] The slice shown in [Fig. 5] is outlined in dotted lines. As shown, the thickness of the electrolysis cell 14 comprises a large number of slices.

[0134] 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.

[0135] Although five elementary cells 1 are shown to compose the electrolysis cell 14, such an electrolysis cell may comprise a different number of elementary cells 1.

[0136] A material resistant to corrosion of the electrolytic solution, for example glass, plexiglass, or polydimethylsiloxane (PDMS) can be deposited on both sides of the thickness of the electrolysis cell.

[0137] Alternatively or cumulatively, the electrolysis cell can be immersed in a beaker containing the electrolytic solution.

[0138] Blocks 21, 22, 31, and 32 may, regardless of the embodiment described with reference to the figures above, be made of solid or non-solid materials. For example, the blocks may be hollow to save material. The blocks serve as supports to define the walls.

[0139] 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.

[0140] Said walls are at least partially covered with a conductive coating of electricity, such as for example a metal or a metal alloy. Thus, it is possible to limit the manufacturing costs associated with the use of metal.

[0141] The metal is for example platinum (Pt).

[0142] Molecular complexes incorporating metallic cations or metallic anions can also be deposited on the coating to improve the catalytic effect.

[0143] To improve the adhesion of the metal deposit to the substrate, an additional bonding layer may be provided. For example, the bonding layer for platinum (Pt) may be titanium (Ti) or chromium (Cr).

[0144] The internal material of the blocks can be glass, polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE) Teflon, optical adhesive, such as for example that of the trade name "Norland optical additive NOA", or polyethylene (PE).

[0145] In the laboratory, PDMS can be used as the internal material for the blocks, but another material should preferably be chosen for industrialization because PDMS cannot withstand acidic or alkaline conditions over time.

[0146] In particular, PTFE resistant to acidic and basic solutions, or polyethylene which has both good resistance and ease of shaping, will be preferred in order to allow industrial manufacturing of said blocks to be less expensive and simpler.

[0147] Reference is now made to Figures 7 to 9 describing a simplified laboratory test system for the design and fabrication of the electrolysis cell 14 of [Fig. 6]. The orientation of Figures 7 to 9 is shown in the XYZ plane. For example, for these figures, the Z-axis may be considered to represent the Earth's vertical. The fabrication of the electrolysis cell 14 can essentially be carried out by photolithography from a substrate 60 placed horizontally, but the electrolysis cell 14, once formed, can advantageously be placed in operation so that the average direction 12 is at the Earth's vertical.

[0148] Figure 7 shows, in the XY plane, a stack of 40 photolithography masks used in the manufacture of the laboratory test. Also shown is an enlarged view 70 of a detail of the mask stack at the mouthpiece 8.

[0149] Fig. 8 represents a cross-section along the cutting plane 75, of the simplified electrolysis cell 14 as provided by the stacking of masks 40 of Fig. 7, and whose photograph is shown in Fig. 9.

[0150] The simplified electrolysis cell 14 is produced by photolithography on the substrate 60. A photograph taken with a binocular microscope corresponding to a part of the detail 41 is further shown in [Fig.9].

[0151] The stack of masks 40 is intended to form on the glass (SiO2) substrate 60 of diameter 44 equal to 2” a thin layer 43 of platinum (Pt) of thickness 100 nm to form the electrodes.

[0152] The thickness of the simplified electrolysis cell 14 can 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 [Fig.5] (corresponding to the relative direction Z on [Fig.9]).

[0153] The thin layer 43 covers the substrate 60 in two parts, left and right, separated by the main conduit 4 of the simplified electrolysis cell 14.

[0154] The stacking 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.

[0155] 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 slightly overflows the walls of the blocks.

[0156] As shown with reference to [Fig.8], a PDMS cover 76 is provided on blocks 22 and 23, so as to define between the substrate 60, the cover 76 and the respective walls of blocks 22 and 23, the main conduit 4.

[0157] Similarly, as shown with reference to [Fig. 7], a PDMS reservoir 45 is provided, which is to be preformed, also by photolithography, and then placed on the substrate 60 around the electrolysis cell 14. The mask of the reservoir 45 is U-shaped in the XY plane. The walls of the reservoir 45 are to be positioned at a distance from the electrolysis cell 14 so as to define, between the anode 2 and the reservoir 45, an exhaust channel 46 for the first gas into which the conduits 7 open. Likewise, an exhaust channel 47 for the second gas is defined between the reservoir 45 and the cathode 3, with the conduits 9 opening into the channel 47.

[0158] As shown in the enlarged view 70 and [Fig. 8], it can be observed that, unlike the electrolysis cell 14 in [Fig. 6], the internal material 42 of blocks such as block 22 is not covered on its walls 74 with the electrically conductive coating. This is intended to simplify the fabrication of the test, which is constrained by laboratory conditions. However, ideally, the electrically conductive material covers the walls in order to increase the efficiency of the electrodes, as described previously in embodiments.

[0159] Fig. 10 represents a schematic perspective view of an electrolysis cell 48 according to a variant, used for the electrolysis of water.

[0160] The electrolysis cell 48 is oriented so that the average inter-electrode direction 12 is oriented in the opposite direction to the acceleration of gravity g representing terrestrial gravity, and whose axis is parallel with the vertical of the orientation represented by the Cartesian coordinate frame of the [Fig. 10].

[0161] In this variant, the cathode 49 and the anode 50 each have a shape The general design consists of a vertical rectangular parallelepiped, each with two substantially flat and parallel surfaces, SI and S2. Specifically, the cathode and anode are each formed by cleaving a silicon wafer serving as a substrate and having a metallized coating. Another variant could also be created using non-planar wafers.

[0162] An inter-electrode space 151 is defined between the SI surface of the anode 50 and the SI surface of the cathode 49. We will subsequently refer to the internal surface SI and the external surface S2, the terms "internal" and "external" referring to the inside of the inter-electrode space 151, and to the outside of the electrolysis cell formed by the two electrodes.

[0163] The cathode 49 and the anode 50 are each micro-perforated in the thickness e of the electrode to define fluidic connections between the surface SI and the surface S2. Each fluidic connection has a frustoconical shape with a wider base on the surface SI, so as to capture the respective H2 and O2 gas bubbles formed on the electrodes.

[0164] The SI and S2 surfaces are further micro-textured so as to guide the H2 and O2 gas bubbles formed by electrolysis. These micro-textures include, in particular, vertical ribs on the internal SI and external S2 walls.

[0165] In particular, a rib 152 opening into a micro-perforation 53 is shown on the surface S1 of the cathode 49, in the vertical direction. On the surface S2 of the cathode 49, a rib 54 originating in the micro-perforation 53 is shown. Thus, a bubble of H2 gas is guided by the rib 152 from the inside to the rib 54 on the outside along a generally vertical trajectory.

[0166] The assembly formed by the micro-perforation 53 and the rib 54 constitutes a gas bubble conduit from the inside to the outside.

[0167] The micro-perforation 53 is separated from the base of another rib 55 originating higher on the surface SL. 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 inner wall of the rib 52.

[0168] Thanks to this overhang 56, the H2 gas bubble guided by the rib 152 is captured instead of moving away from the wall SI and mixing with the O2 gas bubbles.

[0169] Several gas bubble channels are thus formed on each of the electrodes according to the same logic.

[0170] Fig. 11 shows a cross-sectional view of the micro-perforation 53 in the thickness e of the cathode 49. As described above, the overhang 56 is observed, extending further inwards than the surface of the rib 152. However, this overhang 56 has an obtuse angle 81 in the plane of section, in contrast to the modes of rea- lisations described with reference to figures 1 to 9.

[0171] A bubble of H2 is described at three successive locations 57, 58, and 59, in order, along its path from the inside to the outside. As shown in [Fig. 11], in order to take advantage of the frustoconical shape of the micro-perforation 53, which is larger on the S1 surface than on the S2 surface, the cathode material 49 on the inner surface of the micro-perforation is more aerophilic than hydrophilic. For example, the material is Teflon.

[0172] Conversely, as shown in [Fig. 12], the frustoconical 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, onto which a partial metallic deposit is made to form the electrodes. In this embodiment, and due to the choice of the orientation of the frustoconical shape, the acute angle 80 is obtained in the plane of section.

[0173] Although the micro-perforations 53 and 153 shown with reference to Figures 10 to 12 are of truncated conical shape, i.e. of circular base, other forms of micro-perforations can be envisaged, such as for example truncated conical shapes of oval base or of any base, truncated pyramid shapes, of polygonal base or not, or even cylindrical shapes of any base, including of polygonal, oval or circular base.

[0174] Fig. 13 represents, for example, a screenshot of a digital test mask of different electrode topologies intended to be micro-textured on a silicon wafer.

[0175] Advantageously, to simplify the micro-perforation in the wafer, the shape of the micro-perforation 60 is a truncated tetrahedron traversing the crystalline wafer, also called in English "silicon wafer", forming an entrance pore E on the surface SI and an exit pore S on the exit surface S2. The micro-perforations 60 in the figure are represented by squares.

[0176] As shown, several electrode patterns 63 are tested. In the screenshot, nine patterns are visible, 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.

[0177] In particular, when they exist, the features 64 present above the micro-perforations 60 correspond to ribs on the surface S2, and the features 65 present below the micro-perforations 60 correspond to ribs on the surface SL. The ribs are then interconnected via the micro-perforation 60.

[0178] As can be seen in the figure, motifs M3, M4 and M5 each have micro-perforations 60 and ribs on the SI surface, but no ribs on the surface S2, in order to avoid the micro-texturing step of surface S2.

[0179] Motifs 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 contaminated by bubbles from other micro-perforations.

[0180] Motifs M1, M2 and M3 have 60 micro-perforations arranged in a staggered pattern in the grid.

[0181] Several numbers and widths of ribs per micro-perforation were tested according to the patterns.

[0182] Fig. 14 represents a table summarizing tests according to patterns M1 to M6 as described above.

[0183] Column C1 describes the width of the micro-perforation at the inlet E and outlet 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 (micro-texturing) on ​​each of the surfaces S1 and S2. Column C5 specifies whether the pattern has a staggered arrangement Q of micro-perforations, or an arrangement C which has only one micro-perforation per column.

[0184] Thanks to these advantageous characteristics described in the embodiments above, it is possible to separate the gas bubbles without external forcing or the use of a membrane, which constitutes an original alternative, allowing a less polluting, less expensive and more robust system.

[0185] 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. Specifically, the relationship between current density and produced gas, the detachment of bubbles from the walls, and bubble dynamics were taken into account.

[0186] The electrodes as described in the above embodiments can be manufactured by conventional cleanroom techniques in a micrometric version, or by metallic 3D printing, for example in titanium, and can then be coated with a standard electrocatalyst by electrodeposition or vacuum vaporization (for example platinum).

[0187] The electrodes are then placed in a corrosion-resistant tank and positioned face to face with respect to each other.

[0188] For the sake of simplification, some of the described embodiments were generated using models that incorporate two-dimensional simulation, and the electrodes exhibiting the simulated topological patterns were tested as invariant in the thickness plane. As described in other embodiments, the dynamics Bubbles can also be taken into account to generate 3D topological patterns, and thus establish a non-invariant three-dimensional electrode topology, of which a cutting plane shows the overhang, with or without a tip.

[0189] The Cartesian coordinate frames used in the figures do not presume the orientation of this frame with respect to the terrestrial vertical parallel to the acceleration of gravity g representing terrestrial gravity, unless the gravity g is mentioned and described on the figures concerned.

[0190] Although the preferred embodiments shown in some figures mention the orientation of the electrolysis cell such that the average direction 12 is vertical to the ground, the electrolysis cell in each of the described embodiments could be used in a direction other than vertical. For example, the average direction could be placed horizontally to the ground, if, for instance, pumping of the electrolytic solution is required. Indeed, the topological choices then also have the advantage of capturing, via the overflow, the gas bubbles along 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 an elementary anode wall (5, 11) and an elementary cathode wall (6, 11), 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) of 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) to the gas bubble conduit of the downstream portion of the mouth form an acute angle (26, 28) with a local wall internal to the elementary main 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 H2 0), 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 one of the elements. less 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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