Gas diffusion electrode, membrane-electrode assembly and electrolytic device

Abstract

The invention relates to a gas diffusion electrode (4, 5) for a membrane-electrode assembly (1) for use in a fuel cell or in an electrolytic device, comprising a composite of a plurality of layered expanded metal layers (6, 7, 8), wherein: an outer expanded metal layer (6) located at one end of the composite rests, via its surface remote from the composite, against the membrane (2) of the membrane-electrode assembly (1); the surface of this outer expanded metal layer (6) that is remote from the composite is provided with an electrically conductive coating; the coating is made of iridium and / or an iridium-containing compound; exclusively the surface of this outer expanded metal layer (6) that is remote from the composite is coated with iridium and / or an iridium-containing compound; and a surface, which is remote from the composite, of a second outer expanded metal layer (8) located at the other end of the composite is coated with platinum and / or a platinum-containing compound.

Description

[0001] Gas diffusion electrode, membrane electrode assembly and

[0002] Electrolysis device

[0003] The invention relates to a gas diffusion electrode, also called gas diffusion layer (GDE), for a membrane electrode assembly (MEA) for use in a fuel cell, in particular a hydrogen-oxygen fuel cell, or a

[0004] Electrolysis device, comprising a composite of a plurality of expanded metal layers arranged in layers, wherein an outer expanded metal layer arranged at one end of the composite serves to be pressed with its surface facing away from the composite against the

[0005] Membrane of the membrane-electrode assembly, wherein the surface of this outer expanded metal layer facing away from the composite is provided with an electrically conductive

[0006] coating, wherein the coating is formed from iridium and / or an iridium-containing compound. Furthermore, the invention relates to a membrane

[0007] Electrode arrangement with two gas diffusion electrodes according to the invention and a

[0008] Electrolysis device with a membrane electrode arrangement according to the invention.

[0009] Gas diffusion electrodes are known from the state of the art. They are used in electrochemical processes, for example in

[0010] Fuel cells or in electrolysis devices designed as membrane electrolyzers.

[0011] DE 127 339 A1 discloses a gas diffusion electrode consisting of an electrically conductive catalyst support and an electrical connection. The catalyst support serves to accommodate the catalyst material. The catalyst support can be a fabric, fleece, foam, or felt made of electrically conductive material, an expanded metal plate, or a metal plate with a plurality of openings, to which the catalyst material is applied. To form a dimensionally stable gas diffusion electrode, the catalyst support is mechanically and electrically bonded by sintering to a gas-permeable metallic base plate, particularly made of nickel or its alloys.The advantage of this design is that, despite the open structure of the catalyst support for receiving the catalyst material, a comparatively dimensionally stable gas diffusion electrode is provided, which is achieved by the comparatively rigid substructure of the base plate, which takes on the function of an abutment when the catalyst material is pressed in.

[0012] DE 10 2004 023 161 A1 discloses an electrolysis cell which, in order to provide an electrode with a large specific surface area, proposes to form the cathodes and / or anodes as multi-layer expanded metal electrodes consisting of at least two expanded metal layers contacted with each other and with an edge electrode via internal resistance paths. The expanded metal layers each rest on base plates and are arranged in a

[0013] Cell trough or in several clamped electrode frames. To further increase the specific electrode surface,

[0014] Expanded metal layers preferably arranged with porous intermediate layers.

[0015] DE 197 29 429 C1 discloses an electrolysis device comprising a number of membrane electrolysis cells, each of which comprises a membrane provided with a contact layer on both sides. To ensure that the electrolysis device is suitable for comparatively high hydrogen production rates while maintaining a compact design and thus offers particularly flexible use, a contact plate is arranged at each contact layer. Each contact plate has a channel system for transporting water and / or gas on its surface facing the associated contact layer.

[0016] EP 2 985 096 B1 discloses a gas diffusion electrode comprising a plurality of expanded metal layers. The expanded metal layers can be arranged at right angles to each other with respect to their longitudinal extent.

[0017] DE 10 2018 105 115 A1 discloses an electrode for an electrochemical cell, in particular for an electrolyzer, comprising a support element with an active layer containing at least one catalyst. This active layer defines a contact surface for contact with an ion exchange membrane. It is provided that the active layer contains Pt, Ir, Ru, or oxides of these elements and compounds to form a proton exchange membrane electrolyzer.

[0018] EP 3 670 703 A1 relates to a gas diffusion body comprising at least one base layer having through-openings, which base layer is made of electrically conductive expanded metal, of electrically conductive fabric or grid or of an electrically conductive, with

[0019] made of a metal plate provided with through holes, whereby the

[0020] Gas diffusion body has at least one additional layer which is applied as a powdery material using a thermal spraying process, wherein the powdery

[0021] Material consists at least largely of particles of electrically conductive material, in particular to a proportion of at least 70 wt.%, preferably to a proportion of at least 90 wt.%.

[0022] Although fuel cells and electrolysis devices, as well as gas diffusion electrodes used therein, are known in many different forms, there is still room for improvement.

[0023] It is therefore the object of the invention to propose a novel gas diffusion electrode which is improved in terms of efficiency and durability.

[0024] To achieve this object, the invention proposes a

[0025] Gas diffusion electrode of the type mentioned at the outset, which is characterized in that only the surface of this outer expanded metal layer facing away from the composite is coated with iridium and / or an iridium-containing compound and in that a surface of a second outer expanded metal layer arranged at the other end of the composite, facing away from the composite, is coated with platinum and / or a platinum-containing compound.

[0026] The coating according to the invention of the outer expanded metal layer, which is intended to be applied to the membrane of an MEA, has various advantages. In particular, it can catalyze the chemical reaction taking place at the electrode, provide corrosion protection for the material of the expanded metal layers, and / or improve the electrical conductivity of the expanded metal layer. In this way, the efficiency and durability of the electrode according to the invention can be improved.

[0027] The gas diffusion electrode according to the invention comprises a composite of a plurality of expanded metal layers arranged in layers. "Expanded metal" refers to a metal sheet formed with openings in its surface, wherein the openings, also called meshes, are created by offset cuts without material loss while simultaneously stretching the metal sheet. Several layers of expanded metal form the gas diffusion electrode according to the invention, with adjacent expanded metal layers being welded together. This results in a dimensionally stable composite of a plurality of expanded metal layers. Depending on the intended use of the gas diffusion electrode, four, five, six, or even more expanded metal layers can be provided. According to the invention, the coating is formed from iridium and / or an iridium-containing compound, in particular iridium oxide.It has been found that iridium and its compounds, in particular iridium oxide, with respect to the metals used in electrolysis in an electrolysis device, in particular the.

[0028] Water electrolysis, is particularly advantageous and provides catalytic, anti-corrosive and conductivity-related improvements.

[0029] However, iridium is a relatively rare element, and its

[0030] The invention therefore provides that only the surface of the outer

[0031] Expanded metal layer with iridium and / or an iridium-containing compound, in particular

[0032] Iridium oxide, coated. With regard to the composite according to the invention,

[0033] Expanded metal layers have shown that a coating of the intended

[0034] The surface of the corresponding expanded metal layer adjacent to the membrane, coated with iridium or an iridium-containing compound, is sufficient to realize the associated advantages. At the same time, the electrode according to the invention can be manufactured in a resource-efficient manner.

[0035] According to the invention, it is further provided that a second outer expanded metal layer arranged at the other end of the composite with respect to the membrane-side first outer expanded metal layer of the composite is coated with platinum and / or a platinum-containing compound, specifically the surface of the second outer expanded metal layer facing away from the composite. To further improve the corrosion and / or conductivity-related properties, it is advantageous to coat the surface facing away from the composite

[0036] To coat the surface of the second outer expanded metal layer, which is also called the spring layer, with platinum and / or a platinum-containing compound.

[0037] In particular, however, if the membrane-side surface of the first outer

[0038] If the first expanded metal layer is coated with iridium or an iridium compound, it is advantageous if the surface of the second outer expanded metal layer facing away from the composite is coated with platinum and / or a platinum-containing compound as a comparatively readily available metal. In this context, it is also advantageous that platinum has a higher modulus of elasticity than iridium and is therefore less brittle. This is particularly advantageous because the platinum-coated expanded metal layer serves as a spring layer for the composite. Therefore, it has proven to be an overall additional improvement if not both outer surfaces of the composite are coated with iridium or an iridium compound, but only the membrane-side

[0039] outer surface, whereas the other outer surface is coated with platinum or a platinum compound.

[0040] The above-described advantage is particularly effective when - as will be explained in more detail below - the individual expanded metal layers have differently sized mesh sizes, whereby the mesh size in

[0041] In this case, a composite of expanded metal layers that are as close to each other as possible, including a tight fit of the

[0042] Compound on the associated membrane is advantageous, the membrane facing away

[0043] To make the expanded metal layer comparatively elastic.

[0044] Furthermore, the coating according to the invention of the membrane-side surface of the first outer expanded metal layer with iridium or an iridium compound and the

[0045] The surface of the second outer expanded metal layer facing away from the composite would be coated with platinum or a platinum compound, leaving all other expanded metal layers of the composite completely uncoated. This is particularly important because the composite consists of

[0046] Expanded metal layers in the uncoated state exhibit an unfavorable ohmic resistance with regard to conductivity, which impedes electron transport. However, it has been shown that the ohmic resistance in an MEA reaches its maximum value at the interface between the outer expanded metal layer and the membrane, while it decreases with increasing distance from the membrane. A corresponding coating in precisely this boundary region has already resulted in a significant reduction of the ohmic

[0047] resistance and a consequent increase in conductivity. This ensures that the advantages associated with the coating in question regarding catalysis, corrosion protection and, in particular, conductivity are sufficiently

[0048] dimensions, but particularly resource-efficient

[0049] According to a preferred feature of the invention, it is provided that the composite has at least partially uncoated expanded metal layers, wherein to form the

[0050] The composite comprises coated and at least partially uncoated expanded metal layers that are welded and pressed together. The expanded metal layers, preferably joined by welding, advantageously form a smooth, flat, and stable support for the proton-conducting membrane of the membrane-electrode assembly. In the final assembled state of the membrane-electrode assembly, this membrane is located between two gas diffusion electrodes. One of the two gas diffusion electrodes, in the case of water electrolysis, for example, is made of titanium (oxygen side) and the other gas diffusion electrode is made of stainless steel (hydrogen side).

[0051] Adjacent expanded metal layers are preferably joined to one another in a planar manner at the contact points of their mutually facing flat sides by means of resistance pulse welding. Due to the lattice design of the expanded metal layers, "planar" in the sense of the invention does not mean across the entire surface. However, in the sense of a planar design, a connection is made at the contact points between two adjacent expanded metal layers, which, due to the lattice design of the expanded metal layers, regularly extend over the entire mutually facing flat sides of the expanded metal layers. In this respect, not just a point-like connection is achieved, but rather one that is planar in that countless contact points are formed in a regular configuration over the entire surface of the mutually contacting flat sides of adjacent expanded metal layers.This advantageously provides a very dimensionally stable composite of expanded metal layers.

[0052] Due to the manufacturing process, the individual expanded metal layers have a plastic height that is greater than the thickness of the metal sheets chosen as the starting material. This plastic height gives the expanded metal certain spring properties, which are advantageously retained when the expanded metal layers are joined using resistance pulse welding. The expanded metal layers, welded together to form a composite, thus possess defined spring properties that can be calculated and reproduced based on the spring characteristics of the individual expanded metal layers.It is therefore advantageously possible, due to the structural design according to the invention, to specifically influence the subsequent contact force between the gas diffusion electrode on the one hand and the membrane adjoining it on the other, with the aim of ensuring that the membrane permanently and securely contacts the associated gas diffusion electrode(s) over the entire surface. Compared to the sintering known from the prior art, joining by means of resistance pulse welding also has the advantage that expanded metal layer composites with a defined thickness, i.e. a small tolerance, can be produced, for example a tolerance of + / - 0.5 mm, preferably + / - 0.3 mm, even more preferably + / - 0.05 mm. Such a small tolerance is particularly useful in the.

[0053] Connecting several membrane electrode arrangements to form a complete cell is advantageous because the negative effects on membrane contact

[0054] Settling phenomena are minimized.

[0055] According to a further feature of the invention, it is provided that some of the

[0056] Each expanded metal layer has meshes with different mesh sizes.

[0057] A specific mesh size is provided for each expanded metal layer. This mesh size can vary from layer to layer. This design is particularly advantageous in two respects. The mesh size, which is desirable in the intended

[0058] This supports the turbulent fluid flow to be achieved in this application. Furthermore, an uneven distribution of the fluids between the individual

[0059] Contact points forming expanded metal layers, which ensures the dimensional stability of the later

[0060] network additionally promotes.

[0061] According to a further feature of the invention, the mesh of the expanded metal layer adjacent to the membrane of the membrane-electrode assembly has the smallest mesh size. Accordingly, the expanded metal layer that comes into contact with the membrane of the membrane-electrode assembly during its intended use has the finest possible expanded metal. This advantageously provides the membrane with a surface that is as smooth as possible, yet porous.

[0062] According to a further feature, it is proposed in this context that the mesh size of the expanded metal layers decreases in the layer thickness direction to the expanded metal layer adjacent to the membrane of the membrane-electrode assembly. Accordingly, coarser expanded metals are used in the inner layers of the composite farthest from the membrane, with the mesh size decreasing towards the membrane, i.e., the coarser expanded metals are followed by finer expanded metals towards the membrane. The task of the coarser expanded metals is, on the one hand, to form a stable and flat surface, but on the other hand, to create a certain spring effect. This spring effect is created by selected expanded metal combinations and can be varied over a wide range. In this way, the spring characteristic of the subsequent expanded metal layer composite, i.e., the gas diffusion electrode, can be specifically influenced.The spring action emanating from the expanded metal layer composite is crucial for ensuring the secure contact of the membranes with the associated gas diffusion electrodes during subsequent use. Due to its design, the inventive design allows for very precise adjustment of this spring action, which is why the gas diffusion electrodes according to the invention are particularly suitable for high-pressure applications, for example, at pressures exceeding 30 bar, 40 bar, 50 bar, and more.

[0063] According to a further feature of the invention, a further expanded metal layer is provided, which is connected to the expanded metal layer opposite the expanded metal layer lying against the membrane of the membrane-electrode assembly. Accordingly, a further expanded metal layer is used, which in the final assembled state is formed opposite the expanded metal layer which, in the intended use, lies against the membrane of the membrane-electrode assembly. This further expanded metal layer can be formed from a particularly coarse expanded metal and preferably serves to provide a precisely defined spring force. In this context, it is further provided that the further expanded metal layer is spot-welded to its adjacent expanded metal layer, i.e., in contrast to the other expanded metal layers, it is not welded over the entire surface to its adjacent expanded metal layer.

[0064] This spot-welded design ensures that the spring properties provided by the additional expanded metal layer are also available in the subsequent expanded metal layer composite. However, surface welding would minimize the spring properties provided by the additional expanded metal layer.The objective of the additional expanded metal layer is therefore not to additionally stabilize the expanded metal layer composite, but rather to provide a type of bracing agent which, particularly in the case of high-pressure applications, ensures that the gas diffusion electrodes of the individual membrane-electrode arrangements combined to form a stack are permanently in full contact with their associated membranes, thus ensuring reliable use with a high degree of efficiency, along with advantageous current conduction due to the spot welds.

[0065] The invention further relates to a membrane electrode assembly of a fuel cell, in particular a hydrogen-oxygen fuel cell, or an electrolysis device, in particular an electrolysis device for the

[0066] Water electrolysis, comprising a membrane, a first gas diffusion electrode according to the

[0067] invention and a second gas diffusion electrode, both of which are located on opposite sides of the membrane. It is preferred that the

[0068] Membrane is equipped with a catalyst layer on both sides and the first

[0069] Gas diffusion electrode and the second gas diffusion electrode each under

[0070] The second gas diffusion electrode is preferably also provided with a catalyst layer according to the invention.

[0071] Gas diffusion electrode formed.

[0072] Furthermore, the invention relates to an electrolysis device, in particular for water electrolysis, with a membrane electrode arrangement according to the invention.

[0073] Further features and advantages of the invention will become apparent from the following description with reference to the figures. The figures show a purely schematic representation according to

[0074] Fig. 1 shows an exploded view of a membrane electrode assembly;

[0075] Fig. 2 shows an exploded view of a gas diffusion electrode;

[0076] Fig. 3 shows a detailed view of a section of an expanded metal layer;

[0077] Fig. 1 shows a purely schematic representation of a membrane electrode assembly 1 (also called membrane-electrode assembly, or MEA for short). In the illustrated embodiment, the membrane electrode assembly 1 has a membrane 2, which is equipped on both sides with a catalyst layer 3. These catalyst layers

[0078] 3, a first gas diffusion electrode 4 according to the invention and a second gas diffusion electrode 5 according to the invention are provided.

[0079] For example, gas diffusion electrode 4 forms the anode side and gas diffusion electrode 5 forms the cathode side.

[0080] According to the invention, the gas diffusion electrodes 4 and 5 are formed from individual layers of welded-together expanded metal layers 6, 7, 8, as is shown by way of example with reference to the gas diffusion electrode 4 in Fig. 2. As can be seen from Fig. 2, the gas diffusion electrode 4 in the shown

[0081] The embodiment comprises a total of six expanded metal layers, with expanded metal layers having mesh sizes of different sizes. There are two expanded metal layers 6 with relatively small mesh sizes, three expanded metal layers 7 with larger

[0082] mesh sizes and an expanded metal layer 8 with a comparatively coarse

[0083] The mesh size increases from coarse to fine in the direction of arrow 11, that is, with reference to the illustration in Fig. 1, in the direction of the

[0084] Gas diffusion electrode in the final assembled state adjacent membrane 2.

[0085] With reference to the illustration in Figure 2, the surface of the right outermost expanded metal layer 6 facing away from the composite is fully coated with iridium. In the present example, the left outer expanded metal layer 8 is coated with platinum on both sides, at least in some areas. The inner expanded metal layers 7, 6 can be coated with platinum in some areas and / or be uncoated. Overall, this allows the conductivity of the expanded metal composite of the electrode 4, 5 to be improved by reducing the ohmic resistance. In particular, the iridium coating also has

[0086] Advantages in terms of catalysis and corrosion resistance.

[0087] Fig. 3 shows a section of the expanded metal layer 8 in a detailed view. As can be seen from the illustration, the expanded metal layer 8 has a plurality of diamond-shaped meshes 9, each of which has the mesh width W. This results in the longitudinal orientation 10 of the expanded metal layer 8 in the direction of the

[0088] Mesh size determining mesh width W.

[0089] Preferably, it is provided that the individual expanded metal layers of the

[0090] Gas diffusion electrodes 4 and 5 are welded together at contact points on their facing flat sides. This creates a contact connection between adjacent expanded metal layers that can be described as a surface-to-surface connection. The further

[0091] Expanded metal layer 8 is not connected to the composite formed from expanded metal layers 6 and 7 over the entire surface, but only at points, which is achieved by spot welding.

[0092] Reference symbol

[0093] 1 Membrane electrode assembly

[0094] 2 membrane

[0095] 3 Catalyst layer 4 Gas diffusion electrode

[0096] 5 Gas diffusion electrode

[0097] 6 expanded metal

[0098] 7 expanded metal layer 8 expanded metal layer

[0099] 9 stitches

[0100] 10 Longitudinal alignment

[0101] 11 Arrow W Mesh size

Claims

Patent claims 1. Gas diffusion electrode for a membrane electrode assembly for use in a Fuel cell or an electrolysis device, comprising a composite of a A plurality of expanded metal layers (6, 7, 8) arranged in layers, wherein an outer expanded metal layer (6) arranged at one end of the composite serves to bear against the membrane (2) of the membrane-electrode arrangement (1) with its surface facing away from the composite, wherein the surface of this outer expanded metal layer (6) facing away from the composite is provided with an electrically conductive coating, wherein the coating is formed from iridium and / or an iridium-containing compound, characterized in that only the surface of this outer expanded metal layer (6) facing away from the composite is coated with iridium and / or an iridium-containing compound and that a surface facing away from the composite of a second outer expanded metal layer (8) arranged at the other end of the composite is coated with platinum and / or a platinum-containing compound.

2. Gas diffusion electrode according to claim 1, characterized in that the composite comprises at least partially uncoated expanded metal layers (6, 7, 8), wherein coated and at least partially uncoated Expanded metal layers (6, 7, 8) are welded and pressed together.

3. Gas diffusion electrode according to claim 1 or 2, characterized in that some of the expanded metal layers (6, 7, 8) each have meshes with different mesh sizes (W).

4. Gas diffusion electrode according to claim 3, characterized in that the meshes of the membrane (2) of the membrane-electrode arrangement (1) adjacent Expanded metal layer (6) has the smallest mesh size (W).

5. Gas diffusion electrode according to claim 3 or 4, characterized in that the Mesh width (W) of the mesh of the expanded metal layers (6, 7, 8) in Layer thickness direction (11) to the membrane (2) of the membrane electrode Arrangement (1 ) adjacent expanded metal layer (6) decreases 6. Gas diffusion electrode according to one of the preceding claims, characterized in that a further expanded metal layer is provided which is connected to the layer of expanded metal lying on the membrane (2) of the membrane-electrode arrangement (1). Expanded metal layer (6) opposite expanded metal layer (8).

7. Membrane electrode assembly of a fuel cell, in particular a Hydrogen-oxygen fuel cell, or an electrolysis device, in particular an electrolysis device for water electrolysis, with a Membrane (2), a first and second gas diffusion electrode (4, 5) according to one of the preceding claims 1 to 6, both of which are respectively located on opposite sides of the membrane (2).

8. Membrane electrode assembly according to claim 7, characterized in that the Membrane (2) is equipped on both sides with a catalyst layer (3) and the first The first gas diffusion electrode (4) and the second gas diffusion electrode (5) each bear against the membrane (2) with a catalyst layer (3) interposed therebetween.

9. An electrolysis device, in particular for water electrolysis, comprising a membrane-electrode arrangement (1) according to one of claims 7 or 8.

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