WO2024033553A1

WO2024033553A1 - System for dissociating molecules of a liquid medium by means of electrolysis

Info

Publication number: WO2024033553A1
Application number: PCT/ES2023/070493
Authority: WO
Inventors: José María BENLLOCH BAVIERA
Original assignee: Universitat Politècnica De València; Consejo Superior De Investigaciones Científicas (Csic)
Priority date: 2022-08-11
Filing date: 2023-07-31
Publication date: 2024-02-15
Also published as: ES2961789A1

Abstract

The invention relates to a system for dissociating molecules of a liquid medium by means of electrolysis, which includes a first conductive structure (11) and a second conductive structure (12) that act as electrodes (10). In operation, a voltage difference is applied between the first conductive structure (11) and the second conductive structure (12), generating an electric field. A third concentrating structure (13) defines a channel for the electric field to or from an exterior surface (10a) of each electrode (10), and comprises portions (13a, 33a) exposed to the liquid medium and which are associated with edges (11a, 12a, 5a) of the conductive structures (11, 12) that increase the concentration of the electric field, such that the voltage difference threshold needed to dissociate the molecules of the liquid medium into less complex gas molecules is lowered. A fourth separating structure (14) is also included.

Description

DESCRIPTION

SYSTEM TO DISSOCIATE MOLECULES FROM A LIQUID MEDIUM BY ELECTROLYSIS

FIELD OF THE INVENTION

The present invention belongs to the field of systems for dissociating molecules from a liquid medium. In particular, the invention is applicable to the production of hydrogen through electrolysis, dissociating water or other liquid with hydrogen atoms, at ambient temperature and pressure or under other temperature and pressure conditions. It is also related to electrolyzers.

BACKGROUND OF THE INVENTION

Through dissociation, the molecules of a medium are separated into simpler chemical components, such as smaller molecules or atoms. When the dissociation is carried out using electricity, it is called electrolysis.

In particular, if the molecules to be dissociated are water, we speak of electro-hydrolysis. Specifically, electro-hydrolysis to produce green hydrogen is of great interest since it constitutes a source of clean energy. The hydrogen obtained can be used as fuel without CO2 emissions.

In electro-hydrolysis, the hydrogen atoms present in the molecules of a liquid medium (electrolyte) are separated, usually alkaline water (for example, distilled water to which potassium hydroxide has been added) by applying a external electric field.

To carry out electro-hydrolysis, electrodes formed by conductive wires or meshes of conductive wires are normally used, both for the positive electrode, generally the anode, and for the negative electrode or generally, the cathode. Between the cathode and the anode is the electrolyte. By establishing a potential difference between both electrodes, an electric field is produced between them. Near the electrodes the electric field increases exponentially with a maximum on the surface of said electrodes. The electric field in the vicinity of the electrodes can be sufficiently high (eV vapors in the case of water) which favors the separation of the liquid molecules into dissociated components (hydrogen and oxygen in the case of water). When alkaline water is used, this method is called Alkaline Water Electrolysis (AWE).

It is desirable to make the electrolysis process more sustainable. One way considers using energy sources with low CO2 emissions, for example, renewables. Another way is to reduce the necessary energy, which involves reducing the potential difference between the electrodes.

The smaller the diameter of a conducting wire, the greater the electric field in its vicinity. Therefore, one way to require less energy is to use a smaller electrode, since it increases the ability to dissociate molecules. However, there is a drawback to this approach. A very small size for the electrodes generally implies less mechanical robustness. In practice, this means that miniaturized electrodes cannot withstand a high electric field.

BRIEF DESCRIPTION OF THE INVENTION

In light of the problems of the state of the art set forth in the previous section, an object of the present invention relates, mainly, to a system for dissociating molecules of a liquid medium into components using electrolysis. The applications are diverse, although the production of hydrogen for energy generation can be highlighted. However, there may be other applications that benefit from the advantages of the present invention. Among them, it is worth mentioning the deposition of atoms in layers or the chemical synthesis of molecules, both for the chemical industry. Also in the electrochemical reduction of CO2 into methanol.

The proposed system manages to minimize the energy required to obtain dissociated molecules (eg hydrogen) by concentrating the electric field in the vicinity of the electrodes, reducing the voltage that must be applied between them. To do this, the system for dissociating molecules by electrolysis includes two conductive structures that act as electrodes, each with a region exposed to the liquid medium (electrolyte). The conductive structures define two chambers (for anode and cathode). If a voltage difference is applied between the conductive structures, an electric field is generated and the system minimizes the value necessary to cause the dissociation of the liquid medium. It is achieved thanks to a concentrating structure associated with the conductive structures that allows the formation of regions that extraordinarily concentrate the electric field to produce dissociation.

In one family of embodiments, the concentrator structure itself is used to perform various additional functions. One, which acts as a separating structure and separates both electrically and physically the conductive structures (electrodes) from each other. Two, it prevents bubbles of dissociated gaseous molecules, produced in the liquid medium by one of the conductive structures, from passing towards the other conductive structure. Three, it allows the passage of the liquid medium from one side to the other of the concentrator structure. On each side the concentrator structure is attached to a conductive structure. The assembly has small enough holes to prevent (or at least minimize) the exchange of bubbles from one side to the other of the concentrator structure (between the anode chamber and the cathode chamber) and, at the same time, allow some liquid exchange . The holes themselves also help to concentrate the electric field and produce an increase in a marginal region of the conductive structure exposed to the liquid medium. This increase is greater when a portion of the concentrating structure narrows part of the orifice. This marginal region includes the edge of the hole in the conductive structure where a high value for the electric field is reached. Various geometries can be defined (single wedge, double wedge, etc.) for the portion of the hole profile in the section corresponding to the concentrator structure. Also for the contour of the hole.

In this family of embodiments, the electrodes that constitute the conductive structures can be made as a mesh of wires. At the nodes of the mesh there may be a larger connecting element. They may also be extremely thin sheets, for example between 10 nanometers and 100 microns, preferably between 10 nanometers and 10 microns, more preferably between 10 nanometers and 1 micron. The advantage of sheets over meshes is their greater robustness. In both cases, the electrodes are extremely close to each other.

In another family of embodiments of the proposed system, the separating structure and the concentrating structure are differentiated. The electrodes are further apart in this case. The concentrator structure is composed of two electrically insulating substructures, immersed in the liquid medium. Each substructure integrates its corresponding conductive structure (electrode). Substructures include portions of material that form a series of cavities or valleys inside which a conductive element is housed. The valleys are separated from each other by ridges. This conductive element is part of the conductive structure that functions as an electrode (for example, a grid of conductive wires). The conductive element may be partially exposed to the liquid medium and partially embedded in the substructure for greater robustness. With this design, the field lines are also concentrated in the region of the cavity where said conductive element is located.

Aspects of both families can be combined. For example, valleys and crests can be designed with geometric shapes that help better concentrate the electric field in the vicinity of the conducting element. For example, modifying the profile for the channel for the field. Each channel is bounded by a valley separated by adjacent ridges and can have different shapes. For example, single wedge, double wedge or simply rectangular.

DESCRIPTION OF THE DRAWINGS

The characteristics and advantages will be fully understood from the detailed description of the invention, as well as from the embodiment examples referred to the attached figures, which are described in the following paragraphs.

FIG. 1A schematically shows an electrode formed by a conductive wire with its associated electric field lines. FIG. 1B shows a graph of the electric field intensity as a function of the distance to the center of the electrode.

FIG. 2 is a comparative graph of the current density per unit area for an embodiment according to the state of the art and according to the present invention.

FIG. 3A schematically shows a front view of a first embodiment of the present invention. FIG. 3B schematically shows a side section of a first embodiment of the present invention.

FIG. 4 schematically shows a side section of a second embodiment of the present invention.

FIG. 5A schematically shows a side section of a third embodiment of the present invention. FIG. 5B schematically shows a variation of the third embodiment with an insulating structure with an inner conductive sheet at an intermediate voltage.

FIG. 6A schematically shows a front view of a fourth embodiment of the present invention. FIG. 6B shows a rear perspective view. FIG. 7A schematically shows a section of a fifth embodiment of the present invention. FIG. 7B shows an enlargement of a part of the fifth embodiment.

Numerical references used in the drawings:

I Electric field line.

5 Conductive element.

5a Edge of the conductive element.

8 Hole.

10 Electrode.

10a Exposed surface of the electrode (to the liquid medium).

I I First conductive sheet.

11a Edge of the hole of the first conductive sheet.

12 Second conductive sheet.

12a Edge of the hole of the second conductive sheet.

13 Insulating sheet.

13th Portion.

131 Inner conductive sheet (of the concentrator structure).

132 Layer of insulating material (of the concentrator structure).

14 Fourth separating structure.

21 First conductive mesh.

21a Edge of the first conductive mesh.

22 Second conductive mesh.

2nd Edge of the second conductive mesh.

33 Insulating substructure.

33rd Valleys.

33b Crests. DETAILED DESCRIPTION OF THE INVENTION

Below is a detailed description of the invention referring to different preferred or advantageous embodiments based on Figures 1 to 7. Said detailed description is provided for illustrative and non-limiting purposes with respect to the scope of the claimed invention.

Various designs of structures are presented that concentrate the electric field lines in the vicinity of the electrodes in a region exposed to the liquid medium that is to be dissociated.

In FIG. 1A shows a section of an electrode 10 formed by a conductive wire, and the associated electric field lines 1, to which a potential difference has been applied with another electrode (not shown). It can be seen that the density of electric field lines 1 is greater when approaching the electrode 10. The maximum occurs on the exposed surface 10a.

FIG. 1B is a graph of the electric field intensity as a function of the distance to the center of the electrode for the previous case. The distance to the electrode surface is represented on the x-axis. The intensity of the electric field is represented on the y-axis. It is clearly seen how the value for the intensity of the electric field increases exponentially in the vicinity of the electrode surface x=a.

As will be seen in the following embodiments, an insulating structure, suitably arranged in the vicinity of regions of a conductive structure, makes it possible to create a region for each electrode that favors dissociation. A further increase in the concentration of the electric field occurs. This region functions as a channel to route and concentrate the electric field.

FIG. 2 is a comparative graph of the current density per unit area for an electro-hydrolysis process according to the state of the art in dotted line and according to an embodiment of the present invention in solid line. On the x-axis, the measured voltage is represented in Volts (V). On the y-axis, the electric current density per unit area or surface current density is represented, measured in Amperes per square centimeter (A/cm ² ). The units shown are not precise and only serve to illustrate favorable behavior. It is clear from the comparison between curves that the proposed system manages to produce hydrogen by dissociating the water molecule through the application of lower value voltages. This result can be extended to other chemical electrolysis reactions, changing water for another liquid composed of other molecules, and choosing the appropriate electrolyte for said reaction. From these liquid molecules, the atomic elements that compose them or simpler molecules would be obtained.

FIG. 3A and FIG. 3B are both a schematic representation of a front view and a side section of one embodiment of the system. For clarity, the liquid medium with the molecules to be dissociated is not shown. The system includes an insulating sheet 13 that is externally joined on one side with a first conductive sheet 11 and on the other opposite side with a second conductive sheet 12. This three-layer structure has multiple holes 8. One of such holes is shown in the side section of FIG. 3B (hidden in the front view of FIG. 3A). The conductive sheets 11, 12 form the electrodes (anodes on one side and cathodes on the opposite side). The holes 8 are through and communicate one side (anode chamber) with the other (cathode chamber) allowing the passage of molecules to be dissociated in a liquid state, but preventing the passage of gas bubbles with molecules produced in the dissociation.

By applying a potential difference between the two electrodes (first conductive sheet 11, and second conductive sheet 12), the electric field lines 1 are concentrated around the holes 8 as shown in FIG. 3B. Due to the narrowing of the passage channel, an increase in the concentration of the electric field occurs in the center of the hole 8 and, therefore, near the edge 11a of the conductive sheet 11, 12 which is exposed to the liquid medium and in its vicinity. .

In FIG. 3B it can be seen that a channel is formed that passes through said hole 8 and that concentrates, as it passes through the interior, the electric field. When this channel is modified and made additionally narrower with a portion 13a (in the form of a projection) of the insulating sheet 13 extending in a direction transverse to the direction of the electric field, it is possible to additionally concentrate the electric field that must pass through the hole 8 and with it, on the edges 11a of each hole 8 of the conductive sheet 11. In this way, the electrolysis reaction is favored.

The profile shown by FIG. 3B is called double wedge. That is, the diameter of the hole 8 progressively decreases from the faces of the insulating sheet 13 (each face next to one of the conductive sheets 11, 12) to an interior plane. For example, up to a plane that divides the insulating sheet 13 into two halves of equal thickness. That is to say, It would be spindle shaped. However, other shapes would be possible for the inner channel portion of hole 8 (surrounded by insulator) as will be shown below. Some shapes have advantages in particular configurations.

In FIG. 4 illustrates another geometry, called simple wedge, for a portion 13a of the channel formed internally by the hole 8, which would have a conical shape. As in the previous embodiment, the system has a conductive sheet 11, 12 that is joined with a different face of the insulating sheet 13. With the simple portion 13a the diameter of the hole 8 progressively decreases from one of the faces of the insulating sheet 13. to the other opposite side.

In FIG. 5A illustrates another geometry, called cylindrical, where the interior channel defined by hole 8 is cylindrical. A rectangular portion of the insulating sheet 13 is observed that extends in the interior channel in the section through which the insulating sheet 13 crosses. It is observed that it narrows with respect to the conductive sheets 11,12 located on the outside. The portion of the insulating sheet 13 reduces the free space for the passage of the electric field through the hole 8 and thereby increases the electric field at the edge 11a of the hole 8 in the conductive sheet 11, and similarly at the edge 12a of the hole 8 in the conductive sheet 12.

In FIG. 5B illustrates the same geometry as FIG. 5A but using a different insulating structure. Instead of a uniform insulating sheet, a sandwich structure is used, where an inner conductive sheet 131 is covered with a layer 132 of insulating material on each side, which prevents the inner conductive sheet 131 from being in contact with the conductive sheets 11, 12. Thus each element 11, 12, 131 can be at a different voltage. In particular, it is shown that the voltage V1 is applied to the first conductive sheet 11, the voltage V2 is applied to the second conductive sheet 12 and the voltage V3 is applied to the inner conductive sheet 131. It is true that V1>V2>V3.

In FIGS. 6A and FIG. 6B illustrates a schematic representation of another embodiment quite similar to that shown in FIG. 3A. In this embodiment, instead of a conductive sheet, a mesh 21 with multiple annular conductors 7 and threads 9 between them is used. As can be seen, the meshes 21,22 cover much less surface area of the insulating sheet 13 than a sheet. Analogously to the previous embodiment, there is an inner portion (not shown) of the insulating sheet 13 that narrows the passage through the hole 8 and concentrates the electric field on the edge 21a of the hole 8 of the annular conductor 7 of the conductive mesh 21. In FIG. 6B shows the other side, corresponding to the hidden face of FIG. 6A, with the other conductive mesh 22. Each hole 8 is surrounded on both sides of the insulating sheet 13 by an annular conductor 7, one corresponding to the conductive mesh 21, another with the conductive mesh 22 on the other side. There is also an edge 22a defined by the hole 8 that coincides with the inner diameter of the annular conductors 7 present in the conductive mesh 22.

Regarding the geometries mentioned above in FIGS. 3A, 4 and 5 for the insulating portion responsible for reducing the channel and concentrating the electric field, indicate that they are equally applicable to this embodiment with a mesh instead of a sheet. Below are some characteristic properties of each geometry.

A double wedge has the advantage of concentrating the field lines even more and is easier to manufacture by chemical attack techniques. A simple wedge close to the electrode that produces the dissociated molecule of interest (e.g., hydrogen) has the advantage that it makes it less likely that recombination of the dissociated molecule will occur in the molecule to be dissociated (e.g., water).

Any additional portion of insulator allowing the electric field to be concentrated in the vicinity of the electrodes with the holes would be applicable. Other geometries could be used to reduce the passage channel to a different degree (e.g. 25%, 35%, 50%, 75%, 90%, etc. with respect to the contour of the hole in the conductor).

One of the difficulties of systems that carry out electrolysis is recombination. In particular, when it comes to hydrolysis, recombination involves a mixture of oxygen and hydrogen gas bubbles. Through the previous embodiments, the oxygen and hydrogen gas bubbles are separated by the design of the concentrating structure of the field lines. As an additional function, the concentrator structure is also a separator and allows the passage of bubbles to be reduced; the holes are small in size and limit or prevent the passage of bubbles. Thus, it is important to establish an adequate size of the holes so that the exchange of molecules of the liquid medium (water, in the case of electro-hydrolysis) is allowed but the exchange of dissociated gas molecules (molecular hydrogen, H2) is prevented.

One of the advantages of using conductive sheets is that the energy required to produce electrolysis is lower since, on the one hand, there is a concentration of the field lines near the hole, and, on the other hand, the distance between The electrodes can be much smaller because they are more robust. In this way, the field can be higher than for conductive meshes.

Mention that different techniques can be used to manufacture the different embodiments. In particular, the manufacturing process of the insulating sheet can be very varied. For example, starting from an insulating sheet, such as mylar or kapton, a thin layer of copper or another low-cost conductor is deposited, in which a perforation is subsequently made by chemical attack to make the holes. To obtain a regular mesh of holes, for example, a template with holes would be used through which the substance that carries out the chemical attack for the drilling would pass, but which is not affected by said substance.

In FIG. 7A schematically represents a horizontal section of a different embodiment where the concentrator structure is divided into two insulating substructures 33. Each insulating substructure 33 incorporates its corresponding electrode. For clarity, the liquid medium whose molecules are to be dissociated is not shown. The vertical direction (perpendicular to the plane of the figure) coincides with the direction of the Earth's gravity. This embodiment allows the use of a separator structure 14 that may be conventional. The separator structure 14 prevents bubbles of dissociated gaseous molecules from passing through it and allows the exchange of liquid.

Each insulating substructure 33 forms valleys 33a and ridges 33b to concentrate the electric field lines near the electrodes. The electrodes are formed with a conductive structure 31, 32 (dotted boxes) composed of a thread 9 (although it can also be a ribbon, the thread can form a three-dimensional grid) that connects a series of larger integrated conductive elements 5 in the insulating substructure 33.

Each valley 33a forms a cavity where the conductive element 5 is housed, partially surrounded by insulating material. In the valley 33a, lines 1 of the electric field are concentrated towards the conductive element 5. At the edge 5a of said conductive element 5 exposed to the liquid medium y, a greater increase in the electric field is achieved, which favors molecular dissociation.

In an analogous embodiment, instead of using electrical insulating material for the entire concentrator structure, a conductive material subjected to a lower potential than the electrodes could be used. In this case, the electrode should be separated from the conductive material that concentrates the field lines by means of an insulator (eg completely covered by an insulating layer, eg similar to FIG. 5B) or by a distance.

The electrodes can be deposited in the valley part by different methods, for example, chemical vapor deposition, sputtering, etc.

In all embodiments, the insulating material can be any insulating material, which can be arranged in thin but robust sheets, such as kapton, mylar or even a very thin sheet of aluminum, operating at very low voltages, for example, between 0.5 V and 1V, or between 1V and 2 V. The material of the electrodes can also be very diverse, such as copper or any low-cost but robust conductive compound. The shape of the holes and valleys is preferably circular but could also be hexagonal or any other polygonal shape.

For illustrative purposes, some measurements and ranges are offered for various elements described here.

The thickness of the insulating sheet is generally between 1 micron and 100 microns. It can also be up to tens of nanometers, for example 90, 50 or 30 nanometers.

The entrance or exit diameter of the holes can be between 1 micron and 50 microns.

The voltage ranges for different electrolysis reactions are indicated below:

Water (hydrolysis): Between 1.23 V and 1.8 V

Electrochemical reduction of CO2 in methanol: Between 1 V and 1.5 V

Claims

1. System for dissociating molecules from a liquid medium by electrolysis that comprises:

- a first conductive structure (11,21,31) with a plurality of edges (11a, 12a, 5a) exposed to the liquid medium on a first face;

- a second conductive structure (12,22,32) with a plurality of edges (11a, 12a, 5a) exposed to the liquid medium on a first face; where, in operation, both conductive structures (11,12) act as electrodes and there is a voltage difference between the first conductive structure (11,21) and the second conductive structure (12,22) that generates an electric field; characterized by comprising:

- a third concentrating structure (13,33) configured to concentrate the electric field, where the third concentrating structure (13,33) is coupled with both conductive structures (11,12) by a second face opposite the first face, where the third concentrating structure (13,33) comprises a plurality of portions (13a, 33a) exposed to the liquid medium and associated with the plurality of edges (11 a, 12a, 5a) of the conductive structures (11, 12) where the portions ( 13a, 33a, 33b) cause an increase in the concentration of the electric field at the edges (11 a, 12a, 5a), so that the voltage difference threshold necessary to dissociate the molecules of the liquid medium into dissociated gaseous molecules of less complexity;

- a fourth separator structure (14) configured to separate the first conductive structure (11,21) from the second conductive structure (12,22), to allow the exchange of molecules of the liquid medium, and to limit a mixture of gaseous dissociated molecules produced in each conductive structure (11,12,21,22).

2. System for dissociating molecules from a liquid medium by electrolysis according to claim 1, where the third concentrator structure (13,33) is made of insulating material.

3. System for dissociating molecules from a liquid medium by electrolysis according to claim 1, where the third concentrator structure (13,33) is made of material conductor (131) partially covered with a layer of insulating material (132), where, in operation, a voltage intermediate between the voltage value of the first structure is applied to the conductive material of the third concentrating structure (13,33). conductive structure (11) and the second conductive structure (12).

4. System for dissociating molecules from a liquid medium by electrolysis according to any one of claims 1 to 3,

- where the first structure is a first conductive sheet (11), the second structure is a second conductive sheet (12), where the third concentrating structure (13) is also the fourth separating structure; where the three structures (11,12,13) are joined and each comprise a plurality of through holes (8), where each hole (8) has an associated edge (11 a, 12a) in each conductive sheet (11 ,12).

5. System for dissociating molecules from a liquid medium by electrolysis according to any one of claims 1 to 3,

- where the first conductive structure is a first conductive mesh (21), where the second conductive structure is a second conductive mesh (22), where each conductive mesh (21, 22) comprises a plurality of annular conductors (7) and threads drivers (9);

- where the third concentrator structure (13) is also the fourth separator structure (14) and where the third concentrator structure is insulating and is linked to both conductive meshes (21,22); where the first conductive mesh (21), the second conductive mesh (22) and the third insulating sheet (13) comprise a plurality of holes (8) passing through the annular conductors (7), where each hole (8) has an associated edge (11a, 12a) on each annular conductor (7) of each conductive sheet (11,12).

6. System for dissociating molecules from a liquid medium by electrolysis according to claim 4 or 5, wherein a channel defined by the hole (8) in the insulating sheet (13) has a profile that is narrowed by a protruding portion (13a).

7. System for dissociating molecules from a liquid medium by electrolysis according to claim 6, wherein the profile of the channel defined by the hole (8) has the shape of a simple wedge, double wedge or rectangular.

8. System for dissociating molecules from a liquid medium by electrolysis according to any one of claims 1 to 3, wherein each conductive structure (31,32) comprises a plurality of conductive elements (5) and conductive wires (9); where the third concentrator structure (13) comprises two insulating substructures (33), each associated with a different electrode, where the portions (33a, 33b) are in each insulating substructure (33) forming a valley (33a) and a ridge ( 33b), where the valley (33a) houses a conductive element (5) at least evenly exposed to the liquid medium by an edge (5a).

9. System for dissociating molecules from a liquid medium by electrolysis according to claim 8, wherein the profile for a channel defined by the valley (33a) separated by two ridges (33b) has the shape of a simple wedge, double wedge or rectangular.

10. System for dissociating molecules from a liquid medium by electrolysis according to any one of claims 1 to 9, wherein the liquid medium to dissociate is water.

11. System for dissociating molecules from a liquid medium by electrolysis according to any one of claims 1 to 9, wherein the liquid medium for dissociation is methanol.