Device for electrochemical compression comprising a porous transport layer

Abstract

The invention relates to a device (1) and a method for electrochemically compressing and / or purifying hydrogen, the device (1) comprising a first half-cell (2), a second half-cell (3), and a membrane (5) separating the first half-cell (2) and the second half-cell (3), wherein the membrane (5) comprises a semipermeable first membrane layer (10) adjacent to the first half-cell (2) and a porous transport layer (11) for transporting water by capillary action, wherein the porous transport layer (11) is fluidically coupled to a water reservoir (14) by means of a transport structure (12) such that the first membrane layer (10) can be humidified with water from the water reservoir (14).

Description

[0001] DEVICE FOR ELECTROCHEMICAL COMPRESSION WITH POROUS TRANSPORT LAYER

[0002] The invention relates to a device and a method for the electrochemical compression and / or purification of hydrogen.

[0003] Prior art devices for the electrochemical compression of hydrogen have at least two electrodes separated by an electrolyte-filled membrane, each electrode being housed in a half-cell, with charge exchange taking place across the membrane. To avoid negatively impacting the process reliability and service life of an electrochemical compression device, the membrane must be kept moist with water to prevent damage from drying out and to ensure the effectiveness of the compression or purification process. Therefore, prior art methods for operating such a device have always required either a large quantity of water to be introduced into the half-cells, or...In particular, the hydrogen gas to be introduced into the half-cell of a pair of half-cells that has a higher pressure than the other half-cell can be introduced, for example, by flooding the half-cell with water into the half-cell with the lower pressure, or by using a conveying device for the targeted conveyance of water into the half-cell with the lower pressure, which for example comprises a pump, directly at or into the membrane, or by humidifying the hydrogen gas to be introduced. Operating the conveying device, for example the pump, or even actively humidifying the hydrogen gas intended for compression or purification requires additional equipment and energy. The object of the present invention was to overcome the disadvantages of the prior art and to provide a device and a method by which safe and efficient compression of hydrogen is possible.

[0004] This problem is solved by a device and a method according to the claims.

[0005] The device according to the invention for the electrochemical compression and / or purification of hydrogen comprises a first half-cell, a second half-cell and a membrane separating the first half-cell and the second half-cell, wherein a first electrode is arranged in the first half-cell and a second electrode is arranged in the second half-cell, wherein the first electrode, the membrane and the second electrode form a membrane-electrode unit (MEU), wherein the first half-cell, the second half-cell and the MUU form a first electrochemical cell, and wherein the membrane comprises a first semipermeable membrane layer closest to the first half-cell and a porous transport layer for transporting water by means of capillary action, wherein the porous transport layer is fluidically coupled to a water reservoir by means of a transport structure, so that the first membrane layer can be moistened with water from the water reservoir.

[0006] It can be provided that the porous transport layer itself forms the transport structure. For example, the water reservoir can be located in a sub-region of the second half-cell. During operation of the device, water can be present in this sub-region of the second half-cell. With a suitable spatial arrangement of the device, the porous transport layer can absorb water from the water reservoir through its capillary action and thus wet the first membrane layer. In particular, it can be provided that the transport structure is formed as part of the porous transport layer, with the transport structure extending exclusively over a region of the first membrane layer that, during operation of the device, is positioned in the area of ​​the water reservoir, ensuring that the transport structure is completely wetted with water.This prevents hydrogen from the second half-cell, which has a higher pressure than the first half-cell, from entering the transport structure to a predominant extent instead of water.

[0007] In particular, the invention includes an embodiment in which the membrane consists exclusively of the first semipermeable membrane layer and the porous transport layer.

[0008] In any case, the inventive design of the device ensures that, on the one hand, process-related flooding of the second half-cell with water is prevented, and on the other hand, the membrane or the first membrane layer is protected from drying out by humidification via the porous transport layer. This improves the operational reliability of the device, increases efficiency through continuous humidification of the membrane, and consequently also extends the service life of the device. Additionally, this protects the first half-cell from drying out. Furthermore, it can be advantageous for the membrane to comprise a second membrane layer, with the porous transport layer arranged between the first semipermeable membrane layer and the second membrane layer. It is also possible for the second membrane layer to be designed as a semipermeable membrane layer.The porous transport layer is thus embedded between the two preferably semipermeable membrane layers, with a fluidic coupling of the porous transport layer with the transport structure.

[0009] Furthermore, the device may include a third half-cell with a third electrode and a fourth half-cell with a fourth electrode, wherein the third half-cell and the fourth half-cell are separated by a further membrane with a porous transport layer, wherein the porous transport layer of the further membrane is fluidically coupled to the transport structure, and wherein the further membrane is in particular identical in construction to the membrane between the first half-cell and the second half-cell.The third and fourth half-cells, each with corresponding electrodes and an intermediate membrane, form a second electrochemical cell. The second half-cell of the first electrochemical cell and the third half-cell of the second electrochemical cell are fluidically coupled, allowing hydrogen to be transported from the second half-cell to the third half-cell. Due to the process, each half-cell of a pair of half-cells has a higher pressure and therefore a higher accumulation of water. Furthermore, in an electrochemical compression device, it is advantageous to arrange several cells in series to achieve the desired pressure level of the product gas.The present measure thus advantageously provides water via the transport structure in the porous transport layers, preventing flooding of individual half-cells and ensuring the moistening of each membrane. Two adjacent cells can be separated, in particular, by a bipolar plate, while fluidic coupling is also provided between the half-cells of the second cell that are closest to the bipolar plate.

[0010] Furthermore, the transport structure can be designed as a fluid channel. This simple measure allows water to be supplied from any water reservoir. Additionally, a multi-cell device comprising more than two half-cells can be constructed in such a way that each porous transport layer can be easily supplied with water. In particular, the fluid channel can be made of or filled with porous material. The fluid channel itself can then exhibit capillary action, so that a higher pressure level in each half-cell promotes water transport in conjunction with the capillary effect of the porous material. Thus, even in a multi-cell configuration with more than two half-cells, the device can be designed without a pump.

[0011] An advantageous embodiment also includes a transport structure with at least one opening through the second membrane layer, wherein a water collection area is formed as a water reservoir in the second half-cell, or alternatively, water reservoirs are formed in both the second and fourth half-cells. Water can be absorbed by the porous transport layer through such an opening. It is also possible that the opening is filled with porous material. In any case, it is also advantageous to design such an opening below a water level in the water reservoir, thus ensuring that water can be absorbed by the porous transport structure at any time during operation of the device.

[0012] According to a further development, it is possible for at least one breakthrough to be filled with a diffusion-permeable or capillary-effect-enabling porous foam, or with hollow fibers made of polyethersulfone (PESU). Furthermore, it can be advantageous for the porous transport layer to be made of polyethersulfone (PESU), in particular comprising hollow fibers made of PESU. Alternative materials to polyethersulfone for porous capillaries in electrolysis applications include polysulfone, polyimide, mesoporous silicon dioxide, and mesoporous carbon. Polysulfone materials, especially when mixed with polyimides, offer novel macro- and mesoporous structures with adjustable pore sizes, making them suitable as a porous transport layer or filling material for the transport structure.Furthermore, mesoporous silicon dioxide (MCM-41) and mesoporous carbon (CMK-3) have proven to be effective adsorbents with pronounced pore characteristics, advantageous for the removal of specific compounds such as dibenzothiophene and its sulfone derivatives. This demonstrates their versatility in adsorption and filtration processes and makes them suitable for use as a porous transport layer or filler material for the transport structure. The combination of high surface area, tunable pore sizes, and chemical stability makes these materials promising alternatives to PESU for use in porous capillaries. Additionally, the semipermeable membrane layer can be configured as a proton exchange membrane (PEM) or an anion exchange membrane (AEM), with the membrane being formed as a single-piece membrane by bonding, welding, or laminating the individual layers.Furthermore, it may be provided that the electrodes are made of a material that is permeable to water diffusion, in particular porous metal foam.

[0013] The invention also relates to a method for operating a first electrochemical cell for the electrochemical compression of hydrogen with a membrane comprising a first semipermeable membrane layer and a porous transport layer located closest to a first half-cell of the electrochemical cell, wherein the first electrochemical cell comprises, in addition to the first half-cell, a second half-cell separated from the first half-cell by means of the membrane, wherein water from a water reservoir is absorbed by the porous transport layer by means of a transport structure fluidically coupled to the porous transport layer through a capillary effect of the porous transport layer and the first semipermeable membrane layer is moistened with absorbed water.This again results in the advantageous effects that the second half-cell can be protected from flooding by the removal of water, provided that the water reservoir is formed in the second half-cell or at least fluidically coupled to it, and that the first membrane layer can be moistened with this very water removed or absorbed by the transport structure.

[0014] In one particular configuration, absorbed water can be transported into the first half-cell via a further transport structure that fluidically couples the porous transport layer and the first half-cell, through the capillary effect of the porous transport layer. This moistens not only the first membrane layer but also the first half-cell.

[0015] According to an advantageous further development, it can be provided that water from a sub-area of ​​the second half-cell is directly absorbed by the porous transport layer via capillary action, serving as a water reservoir, with the transport structure being formed by the porous transport layer itself. Specifically, it can be provided that the transport structure is designed such that, at least during operation of the system, it is completely covered or wetted with water from the water reservoir in order to prevent or inhibit the penetration of hydrogen into the transport structure as far as possible.

[0016] In particular, it can be advantageous if water from a sub-area of ​​the second half-cell is absorbed as a water reservoir by the porous transport layer through the capillary effect of the same via a fluid channel that fluidically couples the porous transport layer and the water reservoir, or via a breakthrough that breaks through a second membrane layer, with the transport structure being formed by the breakthrough.

[0017] Furthermore, it can be provided that the uptake of water from the water reservoir by means of the porous transport layer and the moistening of the first semipermeable membrane layer is driven exclusively by the capillary effect of the porous transport layer and / or by a pressure difference between the first half-cell and the second half-cell in the direction of the first semipermeable membrane layer, wherein the porous transport layer is made of polyethersulfone PESU, wherein the porous transport layer in particular comprises hollow fibers made of PESU.

[0018] To better understand the invention, it is explained in more detail with reference to the following figures.

[0019] They each show, in a highly simplified, schematic representation:

[0020] Fig. 1 shows a cross-section through a possible first embodiment of the device for electrochemical compression;

[0021] Fig. 2 shows a cross-section through a possible second embodiment of the device for electrochemical compression.

[0022] It should be noted by way of introduction that in the differently described embodiments, identical parts are provided with the same reference numerals or component designations, whereby the disclosures contained in the entire description can be applied analogously to identical parts with the same reference numerals or component designations. Furthermore, the positional designations chosen in the description, such as top, bottom, side, etc., refer to the figure directly described and illustrated, and these positional designations are to be applied analogously to the new position if the position is changed. Figure 1 shows a cross-section of a first possible embodiment of the device 1 in a highly simplified, schematic representation.The device 1 is primarily suitable for the electrochemical compression of hydrogen and can also be used for purification, i.e., increasing the purity of the hydrogen, or for the simultaneous compression and purification of hydrogen. The device 1 comprises a first half-cell 2 and a second half-cell 3. The first half-cell 2 and the second half-cell 3 are separated by a membrane 5. An electrode is formed in each of the half-cells 2 and 3. A first electrode 6 is formed in the first half-cell 2 and a second electrode 7 is formed in the second half-cell 3. The device 1 can further comprise a third half-cell 4 with a third electrode 8 and a fourth half-cell 18 with a fourth electrode 19, wherein the third half-cell 4 and the fourth half-cell 18 can be separated by a further membrane 9.Membrane 5, together with the surrounding electrodes 6 and 7, forms an assembly that can be called a membrane electrode assembly (MEA). Similarly, the fourth half-cell 18 and the third half-cell 4 can be separated from each other by means of the additional membrane 9, whereby the fourth electrode 19 and the third electrode 8, together with the additional membrane 9, form a membrane electrode assembly (MEA), or at least an assembly of these components can be designated as such. Thus, the first half-cell 2, the second half-cell 3, and the associated MEA form a first electrochemical cell 17. Furthermore, the third half-cell 4, the fourth half-cell 18, and their associated MEA form a second electrochemical cell 20. In principle, it can be provided that all membranes, i.e., both membrane 5 and the additional membrane 9, can be structurally identical to each other. In this sense, a membrane can also be understood as a diaphragm.In any case, both membrane 5 and the further membrane 9 can each be an anion exchange membrane (AEM) or a proton exchange membrane (PEM). The possible first embodiment of the device 1 shown in Fig. 1 is not limited to the number of half-cells or cells shown. Rather, it is advantageous for a device 1 to comprise a plurality of half-cells arranged in series and each separated by a membrane. Cells arranged in series can be separated by bipolar plates in a cell stack. Thus, a bipolar plate can be formed between two half-cells of two cells. In any case, it can be ensured that two half-cells closest to a given bipolar plate, or indeed two nearest half-cells of two cells, are fluidically coupled.Thus, hydrogen can be transported from a half-cell of a first electrochemical cell 17 to a nearest half-cell of a second electrochemical cell 20, enabling multi-stage electrochemical compression.

[0023] The membrane 5 comprises a semipermeable first membrane layer 10 located closest to the first half-cell 2 and a porous transport layer 11. The first membrane layer 10 is preferably an anion exchange membrane or a proton exchange membrane made of Nafion or SPEEK. The porous transport layer 11 is suitable for transporting water by capillary action and is preferably made of hollow fibers or with a foam-like but rigid structure for this purpose, and in particular of polyethersulfone (PESU).

[0024] The device 1 can further comprise a second membrane layer 13, such that the porous transport layer 11 is sandwiched between the first membrane layer 10 and the second membrane layer 13. The second membrane layer 13 can be made of the same material as the first membrane layer 10 and have the same electrochemical properties.

[0025] The device 1 further comprises a transport structure 12, wherein, in the present possible first embodiment of the device 1, the transport structure 12 can be formed by a fluid channel, the fluid channel or, respectively, the transport structure 12 being fluidically coupled to the porous transport layer 11 and to a water reservoir 14. The water reservoir 14 can preferably be formed in a partial region 15 of the second half-cell 3. Alternatively, or optionally additionally, the water reservoir 14 can be formed within the fluid channel, i.e., within the transport structure 12, or by these components themselves. Thus, water can be absorbed from the water reservoir 14 by the porous transport layer 11 via the transport structure 12 by capillary action and made available in the porous transport layer 11 for moistening the first membrane layer 10.Likewise, a further water reservoir can be formed in the fourth half-cell 18, whereby it can be provided that each water reservoir of an electrochemical cell 17 or 20 is fluidically coupled to the transport structure 12.

[0026] This basic principle is applicable to each additional pair of half-cells or to each additional electrochemical cell of the device 1. Thus, another water reservoir in a further sub-area of ​​the fourth half-cell 18 can be fluidically coupled to a porous transport layer of the additional membrane 9 via the transport structure 12, thereby humidifying a first membrane layer of the additional membrane 9 by means of the porous transport layer of the additional membrane 9. The driving force, in addition to the capillary effect, for the active humidification of the respective first membrane layer 10 of a membrane 5 or, respectively, of another membrane 9, is the pressure difference between two adjacent half-cells. The device 1 is designed for the electrochemical compression of hydrogen, such that a lower pressure prevails in the first half-cell 2 than in the second half-cell 3. This pressure gradient continues with each additional cell in series.

[0027] Figure 2 shows a cross-section through another, and optionally independent, embodiment of the device 1, whereby the same reference numerals and component designations are used for identical parts as in the preceding Figure 1. To avoid unnecessary repetition, reference is made to the detailed description in the preceding Figure 1.

[0028] In the possible second embodiment of the device 1, it can be provided that the transport structure 12 is formed by a breakthrough 16, wherein the breakthrough 16 breaks through the second membrane layer 13, so that water from the water reservoir 14 can be supplied via the porous transport layer 11 to moisten the first membrane layer 10.

[0029] Another embodiment is also conceivable in which no second membrane layer 13 is provided. In this embodiment, the membrane can consist exclusively of the semipermeable first membrane layer 10 and the porous transport layer 11. The porous transport layer 11 functions, at least partially or in certain areas of the second half-cell 3, as a transport structure 12, so that water from the water reservoir 14 is absorbed by the porous transport layer 11 via its capillary effect and made available for moistening the first membrane layer 10 by distributing the absorbed water within the porous transport layer 11 via capillary action.

[0030] The exemplary embodiments show possible embodiment variants, whereby it should be noted at this point that the invention is not limited to the specifically illustrated embodiment variants, but rather various combinations of the individual embodiment variants are also possible and this possibility of variation lies within the skill of the person skilled in this technical field due to the teaching on technical action by the present invention.

[0031] The scope of protection is defined by the claims. However, the description and drawings must be consulted for the interpretation of the claims. Individual features or combinations of features from the different embodiments shown and described can, in themselves, represent independent inventive solutions. The problem underlying these independent inventive solutions can be found in the description.

[0032] All references to value ranges in this description are to be understood as encompassing any and all sub-ranges thereof, e.g., the reference 1 to 10 is to be understood as including all sub-ranges, starting from the lower limit 1 and the upper limit 10, i.e., all sub-ranges begin with a lower limit of 1 or greater and end with an upper limit of 10 or less, e.g., 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

[0033] Finally, for the sake of clarity, it should be noted that, for a better understanding of the structure, some elements have been shown not to scale and / or enlarged and / or reduced in size.

[0034] Reference numeral list

[0035] device

[0036] First half-cell

[0037] Second half-cell

[0038] Third half-cell

[0039] membrane

[0040] First electrode

[0041] Second electrode

[0042] Third electrode

[0043] Other membrane

[0044] First membrane layer

[0045] Transport layer

[0046] Transport structure

[0047] Membrane layer

[0048] water reservoir

[0049] sub-area

[0050] breakthrough

[0051] First electrochemical cell

[0052] Fourth half-cell

[0053] Fourth electrode

[0054] Second electrochemical cell

Claims

P a t e n t a n s p r ü c h e 1. Device (1) for the electrochemical compression and / or purification of hydrogen comprising a first half-cell (2), a second half-cell (3) and a membrane (5) separating the first half-cell (2) and the second half-cell (3), wherein a first electrode (6) is arranged in the first half-cell (2) and a second electrode (7) is arranged in the second half-cell (3), wherein the first electrode (6), the membrane (5) and the second electrode (7) form a membrane electrode assembly (MEA), wherein the first half-cell (2), the second half-cell (3) and the MEA form a first electrochemical cell (17), and wherein the membrane (5) comprises a semipermeable first membrane layer (10) closest to the first half-cell (2) and a porous transport layer (11) for transporting water by means of capillary action, characterized in that the porous transport layer (11) is connected to a water reservoir (14) by means of a transport structure (12). fluidically coupled,so that the first membrane layer (10) can be moistened with water from the water reservoir (14).

2. Device (1) according to claim 1, characterized in that the membrane (5) comprises a second membrane layer (13), wherein the porous transport layer (11) is arranged between the semipermeable first membrane layer (10) and the second membrane layer (13).

3. Device (1) according to claim 1 or 2, characterized in that the device (1) comprises a third half-cell (4) with a third electrode (8) and a fourth half-cell (18) with a fourth electrode (19), wherein the third half-cell (4) and the fourth half-cell (18) are separated by a further membrane (9) with a porous transport layer (11), wherein the third half-cell (4) and the fourth half-cell (18) with corresponding electrodes (8) and (19) and with the further membrane (9) form a second electrochemical cell (20), wherein the second half-cell (3) and the third half-cell (4) are fluidically coupled, and wherein the porous transport layer (11) of the further membrane (9) is fluidically coupled to the transport structure (12).

4. Device (1) according to claim 3, characterized in that the transport structure (12) is a fluid channel.

5. Device (1) according to one of claims 2 or 3, characterized in that the transport structure (12) is formed by at least one opening (16) through the second membrane layer (13), wherein a collection area for water is formed as a water reservoir (14) in the second half-cell (3) or respectively in the second half-cell (3) and in the fourth half-cell (18) respectively as a water reservoir (14).

6. Device (1) according to claim 5, characterized in that the at least one opening (16) is filled with a diffusion-permeable or a porous foam enabling a capillary effect or with hollow fibers made of polyethersulfone PESU or materials with similar technical properties.

7. Device (1) according to one of the preceding claims, characterized in that the porous transport layer (11) is made of polyethersulfone PESU, wherein the porous transport layer (11) in particular comprises hollow fibers made of PESU.

8. Device (1) according to one of the preceding claims, characterized in that the semipermeable first membrane layer (10) is designed as a proton exchange membrane (PEM) or as an anion exchange membrane (AEM), wherein the membrane (5) is formed as a one-piece membrane (5) by bonding, welding or laminating the individual layers.

9. Device (1) according to one of the preceding claims, characterized in that the electrodes (6, 7 or 8) are made of a material that is permeable to water diffusion, in particular of porous metal foam.

10. Method for operating a first electrochemical cell (17) for the electrochemical compression of hydrogen with a membrane (5) comprising a semipermeable first membrane layer (10) and a porous transport layer (11) nearest to a first half-cell (2) of the electrochemical cell, wherein the first electrochemical cell (17) additionally comprises a second half-cell (3) separated from the first half-cell (2) by means of the membrane (5), characterized in that water from a water reservoir (14) is absorbed by the porous transport layer (11) by means of a transport structure (12) fluidically coupled to the porous transport layer (11) through the capillary effect of the porous transport layer (11) and the semipermeable first membrane layer (10) is moistened with absorbed water.

11. Method according to claim 10, characterized in that absorbed water is introduced into the first half-cell (2) by means of a transport structure (12) fluidically coupling the porous transport layer (11) and the first half-cell (2) through the capillary effect of the porous transport layer (11).

12. Method according to one of claims 10 or 11, characterized in that water from a partial area (15) of the second half-cell (3) is directly absorbed by the porous transport layer (11) as a water reservoir (14) by the same through capillary action, wherein the transport structure (12) is formed by the porous transport layer (11) itself.

13. Method according to one of claims 10 or 11, characterized in that water from a partial region (15) of the second half-cell (3) is taken up by the porous transport layer (11) as a water reservoir (14) by the capillary effect of the same via a fluid channel which fluidically couples the porous transport layer (11) and the water reservoir (14) or via a breakthrough (16) which breaks through a second membrane layer (13), wherein the transport structure (12) is formed by the breakthrough (16).

14. Method according to any one of claims 10 to 13, characterized in that the uptake of water from the water reservoir (14) by means of the porous transport layer (11) and the moistening of the semipermeable first membrane layer (10) is driven exclusively by the capillary effect of the porous transport layer (11) and / or by a pressure difference between the first half-cell (2) and the second half-cell (3) in the direction of the semipermeable first membrane layer (10), wherein the porous transport layer (11) is made of Polyethersulfone PESU is formed, wherein the porous transport layer (11) in particular Includes hollow fibers made of PESU.

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