Catalytically coated membrane, electrochemical cell, and apparatus and method for coating a proton-permeable membrane
A catalytically coated membrane with controlled crack distribution and coating variations addresses uneven reaction intensities in electrochemical cells, enhancing performance and efficiency by ensuring uniformity and effective water management.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- SCHAEFFLER TECHNOLOGIES AG & CO KG
- Filing Date
- 2025-09-12
- Publication Date
- 2026-06-18
AI Technical Summary
Existing electrochemical cells, particularly fuel cells, face challenges in achieving uniform reaction conditions and efficient utilization of power due to varying reaction intensities within the system, leading to potential overheating and material damage.
A catalytically coated membrane with intentionally introduced cracks statistically distributed in one direction and unevenly distributed in another, combined with controlled variations in coating properties and drying parameters, to enhance uniformity and efficiency.
The solution ensures more uniform reaction conditions, enhances power output, and improves water management, thereby optimizing the performance and longevity of the electrochemical cell.
Smart Images
Figure DE2025100872_18062026_PF_FP_ABST
Abstract
Description
[0001] Catalytically coated membrane, electrochemical cell, as well as device and method for coating a proton-permeable membrane
[0002] The invention relates to a catalytically coated membrane suitable for use in an electrochemical cell, in particular a fuel cell. The invention further relates to an electrochemical cell, in particular a fuel cell. In addition, the invention relates to a method and a device for coating a proton-permeable membrane.
[0003] A method for producing a catalytically coated membrane is described, for example, in WO 2022 / 170717 A1. This manufacturing process involves, among other things, applying a grid with a defined mesh size to a surface to be coated. The device produced by the method according to WO 2022 / 170717 A1 is intended, among other things, to be suitable for water-gas separation.
[0004] Methods for producing microporous gas diffusion layers for electrochemical cells, in particular fuel cells, are disclosed in documents CN 116364947 A and CN 111164667 A. In both cases, gradients of certain properties are to be established within the gas diffusion layers.
[0005] The publication Kumano, Naomi et al.: Controlling cracking formation in fuel cell catalyst layers, Journal of Power Sources 419 (2019), pages 219–228, URL: https: / / doi.org / 10.1016 / j.jpowsour.2019.02.058, discusses various effects of cracks in catalytically active membrane coatings. A positive effect of cracks in catalyst layers on cell performance is explicitly highlighted. One method for generating these layers is the stretching of a membrane electrode assembly (MEA), which includes the catalytically active layer. In the publication Babu KP, Venkatesh et al.: Optimization of graded catalyst layer to enhance uniformity of current density and performance of high temperature-polymer electrolyte membrane fuel cell, Hydrogen Energy Publications LLC, 2021, URL: https: / / doi.Org / 10.1016 / j.ijhydene.2021.11.In section 006, two types of gradients are considered: Firstly, a catalytically active layer can exhibit a gradient in the thickness direction of the coating, that is, normal to the plane in which the coated surface lies. Secondly, the possibility of varying the loading of a layer in the flow direction of a reactant is mentioned.
[0006] Further information on catalytically coated membranes for electrochemical cells can be found in the following publications:
[0007] Kundu, S. et al.: Morphological features (defects) in fuel cell membrane electrode assemblies, Journal of Power Sources 157 (2006), pages 650 - 656, URL: https: / / doi.Org / 10.1016 / j.jpowsour.2005.12.027
[0008] Thiele, Simon et al.: New Advances in Grades PEMFC Catalyst Layers, The Electrochemical Society, Inc., Volume MA2023-02, URL: https: / / doi.org / 10.1149 / MA2023- 02381820mtgabs
[0009] Swider-Lyons, Karen et al.: Cathode Catalyst Layer Design with Graded Porous Structure for Proton Exchange Membrane Fuel Cells, The Electrochemical Society, Inc., Volume MA2019-02, URL: https: / / doi.org / 10.1149 / MA2019-02 / 32 / 1423
[0010] The invention is based on the objective of further developing catalytically coated membranes intended for use in electrochemical cells, in particular fuel cells, compared to the prior art, taking into account manufacturing aspects as well as the operating behavior within the electrochemical cell. This objective is achieved according to the invention by a catalytically coated membrane with the features of claim 1. The membrane is suitable for use in an electrochemical cell according to claim 4 and can be produced in the process specified in claim 5. An apparatus according to claim 9 is suitable for carrying out the process.
[0011] The membrane intended for use in an electrochemical cell, particularly a fuel cell, is provided with a catalytically active coating. This coating features intentionally introduced cracks which are statistically uniformly distributed across the membrane surface in a first direction and statistically unevenly distributed in a direction orthogonal to this first direction. The first direction is referred to below as the longitudinal direction, and the second direction as the transverse direction.
[0012] The invention is based on the consideration that reaction conditions can vary within the volume of an electrochemical system. This can lead, among other things, to undesirable uneven heat generation within the electrochemical system. To avoid overheating and / or material damage, the power output of the electrochemical system can be limited according to those volume regions where the intensity of the electrochemical reactions is highest. This inevitably results in the potential conductivity of the electrochemical cells not being fully utilized in other volume regions.To address this shortcoming, various approaches are being explored to adjust the flow conditions in the electrochemical system, particularly through flow-guiding elements which may also have static functions, in such a way as to ensure the most uniform reaction conditions possible throughout the entire electrochemical system.
[0013] The patent application deliberately departs from such approaches and instead proposes varying the properties of a catalytically active layer in the plane in which the layer is spread, in a manner that is easily controllable from a manufacturing perspective. With regard to flow-conducting elements of the electrochemical system, the patent application is not subject to any design limitations. Various parameters regarding the dimensions and properties of the catalytically active coating applied to the membrane can be suitably selected, depending on the nature of the overall electrochemical system. For example, the coating has a thickness of at least 5 pm and not more than 20 pm, and the coating thickness can be uniform across the entire surface of the membrane.
[0014] The mean width of the cracks formed in the catalytically active coating, which varies in a defined direction (i.e., transversely across the membrane), can, for example, range from 5 pm to 50 pm. A crack density of two to three cracks per cm² is possible. Simultaneously, the porosity of the coating acting as a catalyst layer is, for example, in the range of 60% to 70%.
[0015] An electrochemical cell comprising a catalytically coated membrane according to claim 1 can form a cell stack, in particular a fuel cell stack or electrolysis cell stack, with a plurality of similarly constructed electrochemical cells.
[0016] The patent application process for coating a proton-permeable membrane comprises the following steps:
[0017] - Provision of a proton-permeable base material of a membrane on a coil,
[0018] - Unwinding the strip-shaped base material from the coil,
[0019] - uniform coating of the base material across its width with a catalytically active material, in particular a platinum-containing material,
[0020] - continuous drying of the ribbon-shaped material in a dryer such that the drying takes place with a gradient in the transverse direction of the ribbon-shaped material, so that a pattern of cracks is created in the coating, i.e. in the catalytically active material, which varies in the transverse direction of the ribbon-shaped material.
[0021] The drying parameters depend primarily on the composition of the membrane and the catalytically active material. For example, drying takes place at a temperature of no more than 100°C. During drying, a temperature can be set that changes continuously in exactly one direction across the ribbon-like material. Process variants are also possible in which a volume flow of hot air, changing in the transverse direction of the ribbon-like material, is used for drying purposes.
[0022] The patented device for coating a proton-permeable membrane comprises an application device designed for the continuous application of a catalytically active coating onto a ribbon-shaped base material. The coating device further comprises a dryer downstream of the application device, which is designed to dry the coating on the ribbon-shaped base material unevenly in the transverse direction of the ribbon-shaped base material.
[0023] The dryer may in particular be a hot air dryer which has several slot nozzles extending longitudinally along the base material and parallel to each other, which can be operated with different drying parameters.
[0024] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows, in some cases roughly simplified:
[0025] Fig. 1 shows a section of an electrochemical cell with a catalytically coated membrane,
[0026] Fig. 2 shows a schematic side view of a production plant for manufacturing the membrane used in the arrangement according to Fig. 1, Fig. 3 shows a partial top view of the production plant according to Fig. 2,
[0027] Fig. 4 - 6 different surface areas of a proton-permeable, catalytically coated membrane produced with the manufacturing system according to Fig. 2,
[0028] Figs. 7-9 show sections corresponding to figures 4 to 6 of the surface sections of another membrane for an electrochemical cell produced with the manufacturing plant according to Fig. 2.
[0029] A manufacturing plant, designated as 10, is designed for the production of a catalytically coated membrane 1, which is intended for use in an electrochemical cell 8, namely a fuel cell. Regarding the function of the membrane 1 in a fuel cell 8, reference is made to the prior art cited above.
[0030] The membrane 1 has a proton-permeable base material 2 and a coating 3, i.e., a catalytic layer, located thereon. The completed electrochemical cell 8 also contains, among other things, a gas diffusion layer 4. An electrochemical system, only partially sketched in Fig. 1, is stacked and comprises a plurality of electrochemical cells 8. Bipolar plates, which separate the individual electrochemical cells 8 from one another, are not shown.
[0031] As illustrated in Fig. 2, the base material 2, in the form of a coil 9, is provided as the starting material for the production of the catalytically coated membrane 1. The base material 2, unwound from the coil 9, is guided, among other things, by a deflecting roller 12 and reaches an application device 11, which applies the coating 3, here in its still-dry state. The coating process is continuous, and the coating material can be in the form of an ink. The direction in which the ribbon-like material, unwound from the inlet coil 9, is conveyed is designated LR. QR denotes the transverse direction of the membrane 1, which is in the form of a ribbon. After passing the application device 11, the membrane 1 reaches a dryer 13.The dryer 13, in this case a hot air dryer, comprises a plurality of slot nozzles 15 extending longitudinally LR and arranged parallel to one another. Various drying parameters are adjustable. For example, the drying temperature can be up to 100°C, particularly in the range between 50°C and 100°C. Similarly, the relative humidity, particularly in the range of 60% to 80%, and the air volume flow rate can be adjusted. As will be explained in more detail below with reference to Figures 4 to 9, these settings can be made differently within the hot air dryer 13. In any case, after passing through the hot air dryer 13, the membrane 1, coated 3, is wound onto an outlet coil 14.
[0032] Regarding the composition of the coating 3, reference is again made to Fig. 1. The coating contains cracks, generally designated 7, which increase the surface area of the coating 3. Furthermore, the components of the coating 3 include carbon 5 and platinum as a catalyst 6. An ionomer, that is, a binder in which the components 5 and 6 of the coating 3, which are present in particle form, are dispersed, is designated 16.
[0033] Within the electrochemical cell 8, in which the membrane 1 is used, substances whose conversion is enabled or promoted by the catalytic layer 3 flow primarily in the transverse direction QR. The reaction conditions are not uniform in the flow direction of the substances in question, i.e., in the transverse direction QR, with respect to the orientation of the initially ribbon-shaped, later suitably cut membrane 1. This is taken into account by selectively varying the properties of the coating 3 in the transverse direction QR during the manufacturing process—more precisely, during the drying process. The width of the initially ribbon-shaped membrane 1, measured in the transverse direction QR, corresponds at least approximately to the extent of a bipolar plate of the stacked electrochemical system, i.e., the fuel cell system, measured in the transverse direction QR.To vary the properties of membrane 1, which is to be installed in cell 8 in a later step, the adjacent slot nozzles 15, staggered in the transverse direction QR, are adjusted to different settings. Various possible variations are shown in the microscope images in Figures 4 to 6 and Figures 7 to 9. The scale is identical in all images.
[0034] Figures 4 to 6, arranged one above the other, refer to set drying temperatures of 25°C, 30°C, and 35°C. The mass flow rates are, as noted in Figures 4 to 6, 1.2 g / (m³). 2 s), 1.6 g / (m²) 2 s) and 2.5 g / (m²) 2s). As Figures 4 to 6 clearly show, increasing drying temperatures lead to more pronounced cracks 7. This relationship is exploited by treating sections of the membrane 1, in which the desired electrochemical reactions would proceed with below-average intensity compared to other sections (assuming a uniform membrane 1), for example due to lower reactant exposure, in such a way (here: with an increased drying temperature) that the specific surface area of the catalytic layer is increased. In other words: Below-average reactivity within the electrochemical cell 8 is compensated for by the increased generation of cracks 7.
[0035] The performance of the catalytic layer 3 is also enhanced by a drainage effect. Here, the cracks 7 facilitate the removal of water in liquid form, which is generated in the electrochemical cell 8. This removal of water improves the access of the reactants to the catalytic centers provided by the coating 3.
[0036] The effect of an uneven distribution of cracks 7 across the surface of the coating 3 is also achieved by varying the heat transfer coefficient in the transverse direction QR, i.e., from slot nozzle 15 to slot nozzle 15, during drying. Figures 7 to 9 show staggered surface sections of the proton-permeable membrane 1 in the transverse direction QR, in which the heat transfer within the hot air dryer 13 is reduced to 35 W / (m²). 2 K), 50 W / (m 2 K) and 75 W / (m²) 2 K). The mass flow rates in these three cases, as can be seen in Figures 7 to 9, are 1.2 g / (m³).2 s), 1.7 g / (m²) 2 s) and 2.5 g / (m²) 2 s). Even with this approach, more intensive drying of the catalytic layer 3 leads both to an increase in crack density and to the formation of wider cracks 7.
[0037] In contrast to the exemplary embodiment in which the crack patterns shown in Figures 4 to 9 are produced by a convection drying process, the drying process can also be implemented using infrared radiation. In this case, for example, infrared emitters in the form of quartz emitters or an infrared laser are used. The slot nozzles 15 visible in Figure 3 are accordingly replaced by elongated infrared emitters or by fanned-out laser beams in the infrared range.
[0038] The thickness of the coating 3 is largely uniform in both the longitudinal direction LR and the transverse direction QR, and is, for example, 5 pm to 20 pm. The mean width of the cracks 7, which varies in the transverse direction QR, is on the order of 5 pm to 50 pm in the exemplary embodiment, with a crack density of approximately two to three cracks 7 per cm. The dried, catalytically active coating 3 exhibits a porosity of approximately 60% to 70%, expressed as the ratio between the pore volume and the total volume.
[0039] List of reference signs
[0040] 1 membrane
[0041] 2 base material, band-shaped material
[0042] 3. Coating, catalytic layer
[0043] 4 Gas diffusion layer
[0044] 5 Carbon
[0045] 6 Catalyst, platinum
[0046] 7 crack
[0047] 8 electrochemical cell, fuel cell
[0048] 9 Coil, input side
[0049] 10 production plant
[0050] 11. Ordering device
[0051] 12 Pulley
[0052] 13 dryers, hot air dryers
[0053] 14 Coil, output side
[0054] 15 slot nozzles
[0055] 16 Ionomer
[0056] LR longitudinal direction
[0057] QR transverse direction
Claims
Patent claims 1. Catalytically coated membrane (1) for an electrochemical cell (8), wherein a catalytically active coating (3) has cracks (7) which are statistically uniformly distributed on the membrane surface in a first direction (LR) and statistically unevenly distributed in an orthogonal direction (QR).
2. Membrane (1) according to claim 1 , characterized in that the coating (3) has a thickness of at least 5 pm and at most 20 pm.
3. Membrane (1) according to claim 1 or 2, characterized in that the mean width of the cracks (7) varying in a defined direction (QR) on the coating (3) is in the range of 5 pm to 50 pm.
4. Electrochemical cell (8) comprising a catalytically coated membrane (1) according to claim 1.
5. Method for coating a proton-permeable membrane (1) , comprising the following steps: - Provision of a base material (2) of a membrane (1) on a coil (9), - Unwinding the strip-shaped base material (2) from the coil (9), - uniform coating of the base material (2) across its width with a catalytically active material, - continuous drying of the ribbon material in a dryer (13) such that the drying takes place with a gradient in the transverse direction (QR) of the ribbon material, so that in the coating (3), i.e. in the catalytically active material, a pattern of cracks (7) is created which varies in the transverse direction (QR) of the ribbon material.
6. Method according to claim 5, characterized in that the drying takes place at a temperature of not more than 100°C.
7. Method according to claim 5 or 6, characterized in that during drying a temperature is set which changes continuously in exactly one direction in the transverse direction (QR) of the ribbon-shaped material.
8. Method according to claim 5 or 6, characterized in that during drying a volume flow of hot air is set which changes in the transverse direction (QR) of the ribbon-shaped material.
9. Device for coating a proton-permeable membrane (1) comprising an application device (11) which is designed for the continuous application of a catalytically active coating (3) onto a ribbon-shaped base material (2), and a dryer (13) downstream of the application device (11) which is designed to dry the coating (3) located on the ribbon-shaped base material (3) unevenly in the transverse direction (QR) of the ribbon-shaped base material (2).
10. Device according to claim 9, characterized in that the dryer (13) is designed as a hot air dryer and has several slot nozzles (15) extending in the longitudinal direction (LR) of the base material (2) and parallel to each other, which can be operated with different drying parameters.