Method of processing a gas diffusion layer

Abstract

The invention relates to a method of processing a gas diffusion layer (2b) for use in an electrochemical cell, comprising the steps of: - providing a substrate (10) consisting of an already used gas diffusion layer (2a) having two opposite contact surfaces (4, 6), - defining a total thickness (dg) for the processed gas diffusion layer (2b), and - applying an additional ply (8) at least to one of the contact surfaces (4) such that the processed gas diffusion layer (2b) reaches the defined total thickness (dg). The proposed method compensates for the settling effect in the used gas diffusion layer (2a), which results in reusability of the gas diffusion layer (2b).

Description

[0001] 2024PF00759 Foreign version

[0002] 1

[0003] Description

[0004] Method for preparing a gas diffusion layer

[0005] The invention relates to a method for preparing a gas diffusion layer for use in an electrochemical cell. The invention further relates to a prepared gas diffusion layer and the use of such a prepared gas diffusion layer in an electrochemical cell.

[0006] The so-called PEM electrolysis (PEM stands for "polymer electrolyte membrane" or "proton exchange membrane") is gaining increasing potential for industrial applications due to its high potential for producing cost-effective green hydrogen, as well as for use as a storage medium or component in energy storage systems. In the context of climate change, hydrogen and / or the possibility of producing hydrogen from renewable energy sources via PEM or water electrolysis has long since emerged as a key factor for the energy sector and related industries. Even though most hydrogen is still produced today through steam reforming of methane, aggressive investments, regulations, and subsidies will undoubtedly lead to a trend toward renewable hydrogen production in the foreseeable future.

[0007] Hydrogen is already used in countless industrial and technical applications. The potential to produce H2 in large quantities in a climate-neutral way and / or to store or transport it "carbon-free" via hydrogen carriers such as ammonia opens up entirely new avenues for various industrial sectors, such as transportation, chemicals, and steel, to supply entire sectors with green energy or operate them in a climate-friendly manner. Furthermore, hydrogen is already showing promise as a fuel or fuel additive. 2024PF00759 Foreign version

[0008] 2. tivisch is highly interesting because of its potential to produce no or fewer emissions.

[0009] A particularly promising method for producing hydrogen (H2) is the electrolysis of water, especially using renewable electrical energy. Hydrogen can serve as an energy storage medium, for example, by being used as a fuel to stabilize the electrical energy supply, particularly from renewable sources such as wind power, photovoltaics, or similar technologies. Hydrogen can also be used in other processes that require a fuel or a reducing agent. The hydrogen produced by electrolysis can thus be used industrially, or electrical energy can be generated from the hydrogen electrochemically using fuel cells.

[0010] The separation of water into its chemical components, hydrogen (H₂) and oxygen (O₂), can therefore be carried out using suitable electrolysis cells. A particularly important form is the aforementioned PEM electrolysis, which—compared to alkaline electrolysis approaches—proves to be more load-dynamic and better suited for coupling fluctuating power sources, especially due to its less complex peripherals. In particular, high current densities and power outputs can be achieved via PEM electrolysis even under higher load gradients, while the high quality or purity of the hydrogen product is advantageously maintained even under partial or overload operation.

[0011] In PEM electrolyzers, several cells are connected in series and operated as a stack. Each cell contains various components. For example, the proton exchange membrane (PEM) technology uses metallic bipolar plates (BPP), metallic or carbon-based (cathode only) porous transport layers (PTL) – also known as gas diffusion layers (GDL) – catalyst layers (GL), and membranes (PEM). Typically, the anodic and cathodic catalyst layers are combined with the PEM to form a catalyst-coated membrane (CCM). Additional components such as gaskets and frames are also used.The gas diffusion layers are specifically designed to enable the necessary mass, electrical current, and heat transfer during the intended operation of the electrolysis cell. These layers are typically made of titanium or stainless steel. They are sometimes further coated with materials such as platinum (Pt), iridium (Ir), titanium nitride (TiN), or similar substances. On the cathode side, the gas diffusion layers can also be carbon-based. The gas diffusion layer provides the necessary electrical conductivity to couple the bipolar plates and the catalyst layers. This allows the desired electrochemical reaction to occur within the catalyst layers.

[0012] During the clamping and operation of a stack, the components settle, meaning they become thinner over time. Gas diffusion layers, in particular, settle due to their porous nature. This settling can range from a few millimeters to several hundred millimeters. For example, if a new gas diffusion layer is initially 5.00 mm thick, it might only be 4.70 mm thick after operation. Its material properties (strength, electrical conductivity, etc.) are not affected by operation; that is, the material itself could be reused if it weren't for the reduction in thickness (the settling effect).

[0013] This settling effect poses a problem when reusing the gas diffusion layers if the old stack is defective and a new stack needs to be built. (See 2024PF00759 Foreign Version)

[0014] 4. If the other components are new or within specification and not yet installed, the used and installed gas diffusion layer is too thin and the required contact pressure, which is essential for proper operation, is not achieved.

[0015] The invention is based on the objective of processing a gas diffusion layer that has been used up in an electrochemical cell in such a way that it can be reused in a PEM electrolyzer.

[0016] The problem is solved according to the invention by a method for preparing a gas diffusion layer for use in an electrochemical cell, comprising the steps:

[0017] - Providing a substrate consisting of a previously used gas diffusion layer which has two opposing contact surfaces,

[0018] - Specification of a total thickness for the processed gas diffusion layer, and

[0019] - Applying an additional layer to at least one of the contact surfaces so that the prepared gas diffusion layer reaches the specified total thickness.

[0020] The proposed method compensates for the settling effect of the previously used gas diffusion layer, thus enabling its reuse. The overall thickness is selected such that the required contact pressure can be adjusted when reusing the reconditioned gas diffusion layer. This can lead to cost reductions, particularly by increasing component availability, especially when the reconditioned gas diffusion layers of the replaced stack are made of materials with limited availability, such as titanium.

[0021] Preferably, an original thickness of the gas diffusion layer before its use is used, and a thickness is set as the total thickness which corresponds to the original thickness 2024PF00759 Foreign version

[0022] 5 corresponds. The total thickness is adjusted to the thickness of a new gas diffusion layer to ensure the required contact pressure.

[0023] A porous layer is preferably used as the additional layer, in particular an expanded metal mesh, a metallic fleece, a wire mesh, a perforated sheet, a knitted wire, a wire fabric, or a combination thereof. The additional layer can be single-part or multi-part, meaning that several additional layers can be applied on top of each other on the same contact surface. Furthermore, the additional layer can be compressible, meaning that its thickness can be flexibly adjusted or it can exhibit spring properties.

[0024] According to a first preferred embodiment, the additional layer is loosely placed on the substrate. This allows for a particularly simple construction of the prepared gas diffusion layer.

[0025] According to an alternative preferred embodiment, the additional layer is bonded to the substrate in a materially bonded manner, in particular by welding or sintering. The welded joint can be formed by either full-surface welding or local welding. A materially bonded connection of the two components of the processed gas diffusion layer enables particularly high stability.

[0026] Since the settling effect is not always uniform, different thicknesses result in used gas diffusion layers (substrates). To compensate for these during the reprocessing process, the current thickness of the used gas diffusion layer is preferably measured, and the thickness of the additional layer is selected based on this current thickness so that the specified total thickness of the reprocessed gas diffusion layer is achieved. The additional layer is always tailored to the respective substrate without requiring further steps to adjust the substrate thickness. 2024PF00759 Foreign version

[0027] 6

[0028] Carbon-based gas diffusion layers also settle significantly and could be reused with an additional layer. However, the additional layer cannot be applied in a way that creates a strong bond, at least not without considerable effort.

[0029] Alternatively, reprocessed gas diffusion layers can always be restored to the same overall thickness by first calendering the used gas diffusion layer to a predetermined minimum thickness before applying the additional layer. Calendering is a mechanical process in which materials are passed through a series of rollers to smooth, compact, and uniformly increase their thickness. This process is often used in the production of various materials to improve their surface properties or prepare them for further processing. The previously used gas diffusion layers, which serve as substrates, are always brought to the same minimum thickness, ensuring that the thickness of the additional layers also remains constant. For example, if...By setting the minimum thickness to 4.70mm, all used gas diffusion layers can be calendered to 4.70mm and additional layers of 0.30mm are added to achieve the desired total thickness of 5.00mm when the processed gas diffusion layers are assembled.

[0030] Advantageously, before applying the additional layer, any oxide layer that has formed during operation is removed from the used gas diffusion layer. This intermediate step before applying the additional layer is necessary to remove the oxide layer formed during operation and to ensure low contact resistance of the gas diffusion layer. The oxide layer can be removed, for example, by pickling, cleaning, etc.

[0031] The problem is further solved according to the invention by a processed gas diffusion layer with a predetermined Ge- 2024PF00759 Foreign version

[0032] 7 velvet-thick comprising a substrate consisting of a previously used gas diffusion layer having two opposing contact surfaces, and comprising an additional layer applied to at least one of the contact surfaces.

[0033] The problem is also solved according to the invention by using such a processed gas diffusion layer in an electrochemical cell for a PEM electrolyzer.

[0034] The advantages and preferred designs already mentioned in connection with the processing methods can be applied analogously to the gas diffusion layer and its use in an electrochemical cell.

[0035] An embodiment of the invention is explained in more detail with reference to a drawing. Here, schematic and highly simplified representations are shown:

[0036] FIG 1 a new gas diffusion layer, FIG 2 a used gas diffusion layer, and FIG 3 a refurbished gas diffusion layer.

[0037] In the figures, the same reference symbols have the same meaning.

[0038] FIG 1 shows a gas diffusion layer 2, which is part of an electrochemical cell (not shown in detail here). The electrochemical cell is intended to form a stack with other identically constructed cells, which is installed in a PEM electrolyzer during operation (also not shown here). The gas diffusion layer 2 is made of titanium or stainless steel and is porous. The gas diffusion layer 2 has two opposing contact surfaces 4, 6, between which there is an initial thickness di. The initial thickness di is, for example, 5.00 mm. 2024PF00759 Foreign version

[0039] During operation of the PEM electrolyzer, the components, including the gas diffusion layer 2, become worn over time and gradually thinner. This is illustrated in Fig. 2, which shows that the thickness d2 of a used gas diffusion layer 2a is di-x. The difference x between the original thickness di and the current thickness d2 is 0.30 mm in the illustrated embodiment. However, the material properties of the gas diffusion layer 2a, such as strength, electrical conductivity, etc., are not affected by its use.

[0040] To reuse the already used and thinned gas diffusion layer 2a in a new stack during servicing, it serves as a substrate 10, as shown in FIG. 3. An additional layer 8 is applied to the contact surface 4 of this substrate. FIG. 3 shows the case where an additional layer 8 is applied to only one side; however, it is also possible to supplement both contact surfaces 6 and 4 of the substrate 10 with an additional layer 8 each. The additional layer 8 is made of, for example, titanium or stainless steel (and can also be coated with Pt, Ir, TiN, etc.) and has similar properties to the substrate 10. Additional layers 8 made of titanium alloys are also possible. The additional layer 8 is particularly porous. The additional layer 8 can be loosely placed on the substrate 10 or bonded to it, for example, by sintering or welding.Before applying the additional layer 8, it may be necessary to remove an oxidation layer that has formed during operation from the contact side 4 of the substrate 10.

[0041] To determine the total thickness d g To adjust the restored gas diffusion layer 2b to the original thickness di of the gas diffusion layer 2 before its use, for example, a current thickness d2 of the substrate 10 is determined. If the current thickness d2 is known, the difference x between the original thickness di and the current thickness d2 can be calculated. Once the difference x is also known, 2024PF00759 Foreign version

[0042] 9, the thickness of the additional layer 8 is set to x. For example, if d g If di = 5.00mm and d2 = 4.70mm, then x = 0.30mm.

[0043] Alternatively, the substrate 10 can first be calendered to a predetermined minimum thickness d2, which is e.g. 4.70mm.

[0044] For a majority of used gas diffusion layers 2a, all are calendered to 4.70 mm. Subsequently, an additional layer of x = 0.3 mm is applied to each used gas diffusion layer 2a, which is now used as substrate 10, and, if necessary, firmly bonded to it.

[0045] The proposed method compensates for the settling effect in the used gas diffusion layer 2a, thus making it possible to reuse the gas diffusion layer 2b.

Claims

2024PF00759 Foreign version 10 Patent claims 1. Method for preparing a gas diffusion layer (2b) for use in an electrochemical cell, comprising the steps: - Providing a substrate (10) consisting of a previously used gas diffusion layer (2a) which has two opposing contact surfaces (4, 6), - Specification of a total thickness (d g ) for the prepared gas diffusion layer (2b) , and - Applying an additional layer (8) to at least one of the contact surfaces (4) , so that the prepared gas diffusion layer (2b) has the specified total thickness (d g ) reached.

2. The method of claim 1, wherein an initial thickness (di) of the gas diffusion layer (2) prior to its use is taken into account and is considered as the total thickness (d). g ) a thickness is set which corresponds to the original thickness (di).

3. Method according to one of the preceding claims, wherein a porous layer is used as the additional layer (8).

4. Method according to one of the preceding claims, wherein the additional layer (8) is loosely placed on the substrate (10).

5. Method according to one of the preceding claims, wherein the additional layer (8) is materially bonded to the substrate (10), in particular by welding or sintering.

6. A method according to any one of claims 1 to 3, wherein a current thickness (d2) of the used gas diffusion layer (2a) is measured and a thickness (x) of the additional layer (8) is selected as a function of the current thickness (d2) such that the predetermined total thickness (d) g ) the processed gas diffusion layer (2b) is reached.

7. Method according to one of the preceding claims, wherein the used gas diffusion layer (2a) is first applied to a 2024PF00759 Foreign version 11 specified minimum thickness (d2) is calendered before the additional layer (8) is applied.

8. Method according to one of the preceding claims, wherein, prior to the application of the additional layer (8), an oxidation layer formed during operation is removed from the used gas diffusion layer (2a).

9. Prepared gas diffusion layer (2b) with a predetermined total thickness (d g ) comprising a substrate (8) consisting of a previously used gas diffusion layer (2a) having two opposing contact surfaces (4, 6), and comprising an additional layer (8) applied to at least one of the contact surfaces (4, 6).

10. Use of a processed gas diffusion layer (2b) according to claim 9 in an electrochemical cell for a PEM electrolyzer.

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