Flat electrode and electrochemical reactor, in particular for anion exchange membrane (AEM) electrolysis

Abstract

A surface electrode (1) for an electrochemical reactor (25), in particular for anion exchange membrane (AEM) electrolysis, has a continuous metallic body (4) bounded by two parallel main surfaces (2, 3). Gas passages (8) passing through the metallic body (4) between the main surfaces (2, 3) are bounded by internal surfaces (9) of the metallic body (4), which are formed by spatially selective melting of a metal powder adjacent to the gas passages (8).

Description

TECHNICAL AREA OF INVENTION

[0001] The invention relates to a surface electrode for an electrochemical reactor, in particular for anion exchange membrane (AEM) electrolysis, and to an electrochemical reactor, also in particular for anion exchange membrane (AEM) electrolysis, with such a surface electrode. More precisely, the invention relates to a surface electrode with the features of the preamble of independent claim 1.

[0002] The efficiency of chemical reactors depends on the surface electrodes used. This is particularly true for anion exchange membrane (AEM) electrolysis. While cost-effective materials can generally be used for the surface electrodes in an AEM reactor, which combines alkaline electrolysis (AEL) with proton exchange membrane (PEM) electrolysis, the oxygen evolution reaction (OER) proceeds slowly without the use of noble metals in the electrodes. However, efficient AEM electrolysis without the use of noble metals is of great interest, for example, for the large-scale production of so-called green hydrogen. STATE OF THE ART

[0003] Conventional surface electrodes for electrochemical reactors have a continuous metallic body that can be inserted into the layer structure of, for example, an AEM electrolyzer with a central anion exchange membrane.

[0004] From DE 102 54 379 A1, a device for extracting oxygen from water is known, comprising a proton exchange membrane and surface electrodes arranged on both sides of the proton exchange membrane. The surface electrodes are based on expanded titanium metal, i.e., initially perforated and then stretched titanium sheets, which are subsequently flattened and may additionally be electrolytically platinized.

[0005] From DE 10 2020 203 833 A1, a fuel cell device, a method for manufacturing a fuel cell device, and an interconnector for a fuel cell device are known. The term interconnector refers to what is described in this description as a bipolar plate. The fuel cell device has an electrode that is arranged directly on the interconnector. The interconnector forms flow channels with a supply opening facing the electrode for supplying the electrode with a process gas. The supply opening has a cross-sectional area of ​​at most 500 µm. Specifically, the interconnector can also have a porous distribution layer facing the electrode. The interconnector is manufactured using an additive powder metallurgy process. Specifically, this can be selective laser sintering, selective laser melting, or selective electron beam melting.In a further process step, the electrode is applied directly to the interconnect using an additive manufacturing process. Manufacturing such an interconnect with a directly applied electrode is complex.

[0006] From DE 10 2006 054 347 A1, an electrode for the electrochemical processing of a workpiece is known, comprising at least one purge channel for the flow and exit of an electrolyte in at least one working area of ​​the electrode. The electrode is designed as a cathodically polarized tool electrode and has a geometry in the working area that corresponds to the geometry to be removed on the workpiece. The electrode is manufactured layer by layer by means of laser sintering, laser microsintering, laser melting, or electron beam melting. This manufacturing process allows for a small electrode structure. Furthermore, no machining of the purge channels is required, resulting in greater design freedom in the design of the purge channel geometry. The wall thickness of the electrode can range from 0.05 mm to 5.0 mm.Specifically, the electrode is intended for use in the production of sealing slots in the manufacture of low-pressure turbine blades and in the production of engine components made of nickel- or titanium-based alloys, in particular for the production of blade profiles. TASK OF INVENTION

[0007] The invention is based on the objective of demonstrating a surface electrode and an electrochemical reactor, in particular for anion exchange membrane (AEM) electrolysis, which, despite the use of cost-effective materials, exhibit high performance also with regard to the oxygen evolution reaction in anion exchange membrane (AEM) electrolysis. SOLUTION

[0008] The object of the invention is achieved by a surface electrode with the features of independent claim 1, an electrochemical reactor with such a surface electrode and with the further features of claim 11. Dependent claims 2 to 10 relate to preferred embodiments of the surface electrode according to the invention; and dependent claims 12 to 15 relate to preferred embodiments of the reactor according to the invention. DESCRIPTION OF THE INVENTION

[0009] A surface electrode according to the invention for an electrochemical reactor, in particular an electrochemical reactor designed for anion exchange membrane (AEM) electrolysis, comprises a separately handleable, continuous metallic body bounded by two parallel main surfaces. Gas passages run through the metallic body between the main surfaces. The gas passages are bounded by inner surfaces of the metallic body formed by the spatially selective melting of a metal powder adjacent to the gas passages. Typically, the entire metallic body is additively manufactured by the spatially selective melting of the metal powder.By spatially selectively melting the metal powder in a vacuum or under a protective gas atmosphere, the inner surface can be formed with a large surface area of ​​high quality, which, for example, leads to an increased oxygen evolution reaction in AEM electrolysis even without the use of precious metals.

[0010] Typically, the internal surfaces of a metallic body that bound the gas passages exhibit a surface area increased by a factor of at least 100, and particularly by a factor of 200 to 500, compared to smooth surfaces (i.e., surfaces traversed via the shortest path between the main surfaces). This very large surface area of ​​the internal surfaces can be achieved using a metal powder with a mean particle size between 20 µm and 100 µm, if the powder is melted locally (i.e., spatially selectively adjacent to the gas passages) with the aim of forming internal surfaces of the gas passages with a particularly large surface area. The particle sizes of the metal powder can be concentrated around its mean particle size. In general, the particle sizes of the metal powder can range from 0 µm to 200 µm.

[0011] The surface electrode, and consequently the metal powder, typically consists largely of nickel and / or titanium. The metal powder can consist of at least 40% nickel and / or at least 40% titanium. Preferably, the metal powder consists of at least 75%, more preferably at least 90%, and most preferably at least 95% by weight of nickel and / or titanium. Ferritic components in the metal powder should never exceed 5% by weight. Preferably, they do not exceed 1% by weight of the metal powder. Even more preferably, apart from unavoidable impurities, no ferritic components are present in the surface electrode or, consequently, in the metal powder.

[0012] Specifically, the internal surfaces of the metallic body that define the gas passages can be formed by laser sintering of the metal powder in a powder bed adjacent to the gas passages. This laser sintering can be a so-called micro-laser sintering process. Despite being called sintering, laser sintering results in a spatially selective melting of the metal powder. Alternatively, electron beam sintering could be used to form the internal surfaces. Laser or electron beam sintering in the powder bed readily produces the desired large surface area of ​​the internal surfaces of the metallic body that define the gas passages.This large surface area corresponds to a surface roughness that is often undesirable in the additive manufacturing of shaped bodies by laser or electron beam sintering in a powder bed, especially when forming fine structures, but which is an advantage in the surface electrode according to the invention.

[0013] At least one of the outer surfaces of the metallic body of the surface electrode, extending along the main surfaces, can be formed by sawing or eroding a continuous shape formed by selectively melting the metal powder layer by layer in a direction normal to the main surfaces. Preferably, each surface electrode is separated from this continuous shape by electrical discharge machining (EDM). This results in highly defined outer surfaces of the metallic body. Alternatively, one of the outer surfaces of the metallic body extending along the main surfaces can also be formed by selectively melting the metal powder adjacent to the respective main surface.

[0014] In the surface electrode according to the invention, the free volume of the gas passages typically accounts for between 50% and 80% of the space between the main surfaces of the metallic body. In other words, the metallic body fills only a maximum of half, and sometimes only one-fifth, of the space between its main surfaces.

[0015] The free cross-sections of the gas passages can have identical square basic shapes. The basic shape of the metallic body is then that of a two-dimensional grid whose bars run in the same main grid plane. If the gas passages are then arranged along the main surfaces in a square grid, the basic shape of the metallic body is that of a square grid. Free cross-sections of the gas passages can have diameters between 0.2 mm and 4 mm. Preferably, these diameters are between 0.3 mm and 1 mm.

[0016] The thickness of the metallic body, i.e., the distance between the main surfaces of the metallic body, is typically between 0.2 mm and 4 mm, and preferably between 0.4 mm and 0.7 mm. The thickness of the metallic body is therefore at least approximately equal to the diameter of the free cross-sections of the gas passages. These dimensions of the metallic body and the formation of the inner surfaces of its gas passages by spatially selective melting make it particularly easy to achieve the desired large surface area of ​​these inner surfaces, because a sharp demarcation of the melted areas of a metal powder is only possible with considerable effort, if at all, in such fine structures. This is a disadvantage in conventional additive manufacturing by laser or electron beam sintering in a laser bed. It is an advantage in the production of the surface electrode according to the invention.

[0017] Along its main surfaces, the metallic body can have a usable area ranging from a few square centimeters to several hundred square centimeters, for example, between 3 cm² and 400 cm². Preferably, the usable area is between 10 cm² and 200 cm². The outer dimensions of the metallic body and its usable area are preferably rounded, and even more preferably circular. Electrochemical reactors with a rounded cross-section, for example, offer advantages in terms of sealing at their outer circumference.

[0018] For such a seal, a gasket made of an elastomeric plastic can be injection-molded onto the metallic body, circumferencing around a central usable surface of the electrode along the main surfaces and sealing some of the gas passages gas-tight. Preferably, this gasket extends circumferentially around the central usable surface and perpendicular to the main surfaces, over both main surfaces.

[0019] An electrochemical reactor according to the invention, in particular for AEM electrolysis, has an anion exchange membrane, a bipolar plate on at least one side of the anion exchange membrane and a surface electrode according to the invention between the anion exchange membrane and the bipolar plate.

[0020] In a preferred embodiment of the reactor according to the invention, the bipolar plate has knobs facing the surface electrode, which support the surface electrode at one of its main surfaces. Specifically, the knobs can have a diameter between 0.8 mm and 5 mm and / or a length of 0.3 mm to 4 mm, wherein the scaling of the knobs normal to the main surfaces of the surface electrodes can be between 0.25:1 and 2:1. Preferably, the diameter of the knobs is larger than their length, so that the scaling of the knobs is less than 1:1 and is approximately 0.4:1 to 0.8:1.If the sum of the end faces of the nubs of the bipolar plate facing the surface electrode is between 5% and 40% of the surface area of ​​the surface electrode, the spaces between the nubs of the bipolar plate running parallel to the main surfaces of the surface electrode are large enough to ensure a good supply of working gas or liquid and sufficient removal of reaction products, even if no forced flow channels are formed.

[0021] In the reactor according to the invention, an edge of the anion exchange membrane can be embedded in a circumferential seal, and the anion exchange membrane can be arranged in an insulating frame in a sealing manner with the circumferential seal. The surface electrode can be arranged on the anion exchange membrane within the insulating frame. Alternatively, a circumferential seal can be injection-molded onto the metallic body of the surface electrode, which is arranged between the insulating frame and a circumferential sealing edge of the bipolar plate. In the layered structure of the reactor, an additional diffusion layer can be arranged between the ion exchange membrane and the surface electrode.

[0022] The ion exchange membrane of the reactor according to the invention can be a proton exchange membrane (PEM). Preferably, it is an anion exchange membrane (AEM).

[0023] Advantageous further developments of the invention result from the patent claims, the description and the drawings.

[0024] The advantages of features and combinations of features mentioned in the description are merely exemplary and can have an effect alternatively or cumulatively, without the advantages necessarily having to be achieved by embodiments according to the invention.

[0025] Regarding the disclosure content—not the scope of protection—of the original application documents and the patent, the following applies: Further features can be derived from the drawings—in particular, the geometries depicted and the relative dimensions of several components to one another, as well as their relative arrangement and functional connection. The combination of features from different embodiments of the invention or from features of different claims is also possible, deviating from the chosen cross-references of the claims, and is hereby encouraged. This also applies to features that are illustrated in separate drawings or mentioned in their description. These features can also be combined with features from different claims.Likewise, features listed in the patent claims may be omitted for further embodiments of the invention, but this does not apply to the independent patent claims of the granted patent.

[0026] The features mentioned in the claims and the description are to be understood, with regard to their number, as meaning that exactly that number or a greater number than the stated number is present, without the need for the explicit use of the adverb "at least". Thus, for example, if a metal powder is mentioned, this is to be understood as meaning that exactly one metal powder, two metal powders, or more metal powders are used. The features listed in the claims may be supplemented by further features or may be the only features that the subject matter of the respective claim possesses.

[0027] The reference numerals contained in the patent claims do not constitute a limitation of the scope of the subject matter protected by the patent claims. They merely serve the purpose of making the patent claims easier to understand. BRIEF DESCRIPTION OF THE FIGURES

[0028] The invention will now be further explained and described with reference to preferred embodiments shown in the figures. Fig. 1 is a top view of a surface electrode according to the invention. Fig. 2 is an enlarged microscopic image of an area of ​​the surface electrode according to Fig. 1 . Fig. 3 shows a shaped body produced by laser sintering, from which the surface electrode is made according to the Fig. 1 and 2 is separated out by erosion. Fig. 4 shows a stacking element for forming a reactor for AEM analysis with an anion exchange membrane and an electrode according to the Figs. 1 to 3 . Fig. 5A top view shows a bipolar plate as a further stacking element for forming the reactor. Fig. 6 shows the bipolar plate in a diagonal cross-section. Fig. 7 is an exploded view of the reactor and Fig. 8 shows a detail of the assembled reactor. FIGURE DESCRIPTION

[0029] The in Fig. 1 The surface electrode 1 shown in a top view is intended for an electrochemical reactor, in particular for anion exchange membrane (AEM) electrolysis, and has a continuous metallic body 4 bounded by two parallel main surfaces 2 and 3, of which only main surface 2 is visible here. The metallic body 4 has a lattice-like basic shape, which can be seen from the microscopic image according to Fig. 2This becomes clearer. The lattice-like basic shape is formed by lattice bars 5 and 6 running at right angles to each other in the same main lattice plane, at whose intersection points 7 the metallic body 4 is not thickened between its main surfaces 2 and 3. Gas passages 8 with rhombic free cross-sections, arranged in a square grid, remain between the lattice bars 5 and 6. The edge lengths of the rhombuses are ≥ 0.2 mm. The inner surfaces 9 of the metallic body 4, which bound the gas passages 8, have very large geometric surface areas 10, which are increased by a factor of ≥ 200 compared to virtual reference surfaces passing along the shortest path between the main surfaces 2 and 3. The inner surfaces 9 are recognizably formed by the spatially selective melting of a metal powder adjacent to the gas passages 8. Fig. 1shows that the surface electrode 1 has circular outer dimensions and that on the metallic body 4 a circumferential gas passage 8 extends along the main surfaces 2 and 3 around a central usable surface 11 of the surface electrode 1 and some of the gas passages 8 according to Fig. 2 The sealing gasket 12 is injection-molded from an elastomeric plastic 13. Fig. 1 It is not visible that the seal 12 extends around the central usable area 11, perpendicular to both main surfaces 2 and 3, over both main surfaces 2 and 3.

[0030] Fig. 3Figure 1 shows a continuous shaped body 14 on a base plate 15. The shaped body 14 is formed by layer-by-layer local, i.e., spatially selective, melting of metal powder in a powder bed. Several surface electrodes 1 are removed from the shaped body 14 by electrical discharge machining (EDM), in particular by spark erosion, along the main surfaces 2 and 3. The distance between the parallel main surfaces 2 and 3 is typically between 0.4 mm and 0.7 mm. The powder bed in which the shaped body was formed by laser sintering has a composition predominantly of nickel and / or titanium and particle sizes below 200 µm, which allows the removal of the unmelted portions of the powder bed from the shaped body 14, at least after it has been divided into the individual surface electrodes 1 by EDM.

[0031] Fig. 4Figure 16 is a top view of a stacking element 16 for forming a stacked reactor for anion exchange membrane (AEM) electrolysis and accordingly includes an AEM 17. The AEM 17 is arranged within an insulating frame 18 and is gas-tightly connected to the insulating frame 18. Supply channels 19 and 20 are formed in the insulating frame 18. A surface electrode 1 is arranged on each side of the AEM 17. The surface electrodes 1 do not have a seal 12. They are arranged within the sealing frame 18.

[0032] The Fig. 5 and 6 show a bipolar plate 21 which is provided for the rear support of the surface electrodes 1 in order to attach them to the AEM 17 according to Fig. 4to press down. The bipolar plates 21 are made of an electrically conductive plastic 22. The bipolar plates 21 support the adjacent surface electrodes 1 via studs 23, between which free spaces 24 remain, which communicate with the channels 19 and 20 respectively, in order to discharge the gases developed at the surface electrodes 1 or to supply water to be electrolyzed.

[0033] Fig. 7 shows the stacking elements stacked in a reactor 25 for AEM electrolysis in the form of the stacking elements 16 according to Fig. 4 and the bipolar plates 21 according to the Fig. 5 and 6 as well as modified bipolar plates 26 with electrical connections 27 and stacking end plates 28. The stacking elements 16, 21, 26 and 28 of the reactor 25 are clamped against each other by clamping screws (not shown here) passing through holes 29, so that the reactor is sealed gas-tight in the radial direction.

[0034] The detail according to Fig. 8shows the sealed, stacked elements in the assembled reactor 25. REFERENCE MARK LIST

[0035] 1 Surface electrode 2 Main surface 3 Main surface 4 Metallic body 5 Grid rod 6 Grid rod 7 Intersection point 8 Gas passage 9 Inner surface 10 Surface 11 Usable area 12 Seal 13 Elastomeric plastic 14 Molded body 15 Base plate 16 Stacking element 17 Anion exchange membrane (AEM) 18 Insulating frame 19 Supply channel 20 Supply channel 21 Bipolar plate 22 Electrically conductive plastic 23 Nubs 24 Free space 25 Reactor 26 Bipolar plate with power connection 27 Power connection 28 Stacking end plate 29 Hole

Claims

1. Surface electrode (1) for an electrochemical reactor (25), in particular for anion exchange membrane (AEM) electrolysis, having a continuous metallic body (4) delimited by two parallel main surfaces (2, 3), wherein gas passages (8) passing through the metallic body (4) between the main surfaces (2, 3) are delimited by inner surfaces (9) of the metallic body (4), characterized in that the inner surfaces (9) of the metallic body (4) delimiting the gas passages (8) are formed by spatially selective melting of a metal powder adjacent to the gas passages (8).

2. Surface electrode (1) according to claim 1, where the inner surfaces (9) of the metallic body (4) delimiting the gas passages (8) have a surface area (10) which is enlarged by a factor of at least 100 and in particular by a factor of between 200 and 500 compared to comparison surfaces passing through the shortest path between the main surfaces (2, 3).

3. Surface electrode (1) according to claim 1 or 2, where the metal powder - has an average particle size between 20 µm and 100 µm and / or - particle sizes from 0 µm to 200 µm and / or - at least 40% by weight and preferably at least 75% by weight nickel and / or - at least 40% by weight and preferably at least 75% by weight titanium and / or - not more than 5% by weight and preferably not more than 1% by weight ferritic components.

4. Surface electrode (1) according to one of the preceding claims, where the inner surfaces (9) of the metallic body (4) delimiting the gas passages (8) are formed by laser sintering the metal powder in a powder bed adjacent to the gas passages (8).

5. Surface electrode (1) according to one of the preceding claims, whereat least one of the outer surfaces of the metallic body (4) extending along the main surfaces (2, 3) is formed by sawing or eroding a coherent shaped body (14) which is formed by locally and spatially selectively melting the metal powder layer by layer in the direction normal to the main surfaces (2, 3).

6. Surface electrode (1) according to claim 5, where the other of the outer surfaces of the metallic body (4) extending along the main surfaces (2, 3) is formed by spatially selective melting of the metal powder adjacent to the respective main surface.

7. Surface electrode (1) according to one of the preceding claims, where- a free volume of the gas passages (8) amounts to between 50 percent and 80 percent of an intermediate space between the main surfaces (2, 3) and / or - free cross sections of the gas passages (8) have identical square basic shapes and / or - the gas passages (8) are arranged in a square grid along the main surfaces (2, 3) and / or - free cross sections of the gas passages (8) have diameters between 0.2 mm and 4 mm and preferably between 0.3 mm and 1 mm.

8. Surface electrode (1) according to one of the preceding claims, where a distance between the main surfaces (2, 3) is between 0.2 mm and 4 mm and preferably between 0.4 mm and 0.7 mm.

9. Surface electrode (1) according to one of the preceding claims, where the metallic body (4) along the main surfaces (2, 3) - a useful surface (11) between 3 cm 2 and 400 cm 2 and preferably between 10 cm 2 and 200 cm 2and / or - has rounded and preferably circular external dimensions.

10. Surface electrode (1) according to one of the preceding claims, where a seal (12) made of an elastomeric plastic (13) is injection-molded onto the metallic body (4), said seal running along the main surfaces (2, 3) around a central useful surface (11) of the surface electrode (1) and closing some of the gas passages (8) in a gas-tight manner, said seal preferably projecting circumferentially around the central useful surface (11) over both main surfaces (2, 3).

11. Electrochemical reactor (25), in particular for anion exchange membrane (AEM) electrolysis, with - an anion exchange membrane (EAM) (17), - a bipolar plate (21) on at least one side of the anion exchange membrane (EAM) (17) and - with a surface electrode (1) according to one of the preceding claims between the anion exchange membrane (EAM) (17) and the bipolar plate (21).

12. Reactor (25) according to claim 11, where the bipolar plate (21) has knobs (23) facing the surface electrode (1).

13. Reactor (25) according to claim 12, where the knobs (23) - have a diameter between 0.8 mm and 5 mm and / or a length of 0.3 mm to 4 mm and / or - an extension normal to the main surfaces (2, 3) of the surface electrode (1) between 0.25: 1 and 2:

1.

14. Reactor (25) according to claim 12 or 13, where a sum of end surfaces of the knobs (23) of the bipolar plate facing the surface electrode (1) is between 5 and 40 percent of the surface of the surface electrode (1).

15. Reactor (25) according to one of claims 11 to 14, where- an edge of the anion exchange membrane (EAM) (17) is embedded in a circumferential seal and the anion exchange membrane (EAM) (17) is arranged with the circumferential seal in an insulating frame (18) in a sealing manner, - a circumferential seal (12) is injection-molded onto the metallic body (4) of the surface electrode (1), which seal is arranged between the insulating frame (18) and a circumferential sealing edge of the bipolar plate, or wherein the surface electrode (1) is also arranged in the insulating frame (18), and - wherein, optionally, a diffusion layer is arranged between the anion exchange membrane (EAM) (17) and the surface electrode (1).

Images