Gas diffusion layer, electrochemical cell with the gas diffusion layer and method for producing the gas diffusion layer

Abstract

The gas diffusion layer (1) according to the invention for an electrochemical cell (10), comprising a substrate (2) through which a gas can be transported, a coating (6) applied directly to the substrate (2), an adhesion promoter layer (3) applied directly to the substrate (2), comprising chromium with a content of at least 90% by mass and having a thickness in the range of 0.01 µm to 1 µm, and a contact layer (4) which is an outer surface of the gas diffusion layer (1) and is electrically conductively connected to the adhesion promoter layer (3), comprising carbon with a content of at least 90% by mass and having a thickness in the range of 0.05 µm to 500 µm.

Description

[0001] The invention relates to a gas diffusion layer for an electrochemical cell and the electrochemical cell with the gas diffusion layer.

[0002] An electrochemical cell can be, for example, a component of an electrolyzer or a fuel cell. The electrochemical cell can have an anode-side gas diffusion layer and / or a cathode-side gas diffusion layer. During operation, hydrogen, oxygen, and water can be arranged in the gas diffusion layers. The anode-side gas diffusion layer is electrically connected to an anode and can also be electrically connected to a bipolar plate. The cathode-side gas diffusion layer is electrically connected to a cathode and can also be electrically connected to the bipolar plate. Contact resistances occur at the interfaces between the gas diffusion layers and other cell components, leading to electrical losses and thus a reduction in the cell's efficiency.To reduce contact resistance, the surfaces of the components can be coated with a precious metal, such as gold, iridium, or platinum. However, this is disadvantageously expensive.

[0003] The object of the invention is therefore to provide a gas diffusion layer, an electrochemical cell with the gas diffusion layer and a method for producing the gas diffusion layer, with which contact resistances can be reduced cost-effectively.

[0004] The gas diffusion layer according to the invention for an electrochemical cell comprises a substrate through which a gas can be transported and a coating that is applied directly to the substrate. The coating includes a contact layer. The contact layer is an outer surface of the gas diffusion layer, is electrically conductively connected to the substrate, contains carbon with a content of at least 90% by mass, and has a thickness in the range of 0.05 µm to 500 µm.

[0005] Because the contact layer is the outer surface, it makes contact with other components of an electrochemical cell, thus establishing electrically conductive connections. The carbon in the contact layer has good electrical conductivity, resulting in low contact resistance and high efficiency for the electrochemical cell. Carbon is inexpensive, especially compared to precious metals, which also makes the gas diffusion layer cost-effective.

[0006] The coating preferably comprises an adhesion promoter layer that is applied directly to the substrate, contains chromium and / or iron with a proportion of at least 90 wt% and has a thickness in the range of 0.01 µm to 0.5 µm, in particular 50 nm to 200 nm.

[0007] The contact layer is preferably applied directly to the adhesion promoter layer. This results in a simple and particularly cost-effective coating structure.

[0008] Alternatively, it is preferred that the coating comprises an intermediate layer applied directly to the adhesion promoter layer and containing a metal nitride, a metal carbide, a metal carbonitride, a semimetal carbide, a semimetal carbonitride, and / or a semimetal nitride with a proportion of at least 90 wt%, in particular at least 95 wt% or at least 99 wt%, wherein the contact layer is applied directly to the intermediate layer. Providing the intermediate layer reduces the probability of delamination of the contact layer and also prevents hydrogen from entering the adhesion promoter layer during cell operation. It is preferred that the intermediate layer comprises chromium nitride, CrC, CrCN, FeC, FeN, Fe-doped CN, and / or Fe-Cr-N, or consists, except for unavoidable impurities, of chromium nitride, CrC, CrCN, FeC, FeN, Fe-doped CN, and / or Fe-Cr-N.The intermediate layer preferably has a thickness in the range of 0.1 µm to 1 µm or 0.1 µm to 0.5 µm.

[0009] It is preferred that the contact layer is free of hydrogen. This results in particularly strong adhesion of the contact layer. Alternatively, it is preferred that the contact layer contains hydrogen. This allows for particularly good stability and a particularly low electrical resistance of the contact layer.

[0010] The contact layer preferably contains carbon at a proportion of at least 95% or at least 99% by weight. It is preferred that the contact layer consists of carbon and, optionally, hydrogen, except for unavoidable impurities. Alternatively, it is preferred that the contact layer is doped with chromium, chromium carbide, silicon, tungsten, nitrogen, fluorine, hydrogen, and / or silicon carbide. Doping can increase the hardness and durability of the contact layer. Doping can be achieved, for example, by vaporizing a first source containing the carbon and a second source, separate from the first and containing the dopant, in a coating process.The contact layer can consist of carbon, chromium, chromium carbide, silicon, tungsten, nitrogen, fluorine, hydrogen and / or silicon carbide, and optionally hydrogen, except for unavoidable impurities.

[0011] The carbon is preferably present in an amorphous form. This advantageously results in good electrical conductivity in all directions. Furthermore, it allows for good hardness and thus improved durability.

[0012] The thickness of the contact layer is preferably in the range of 0.05 µm to 100 µm or from 0.05 µm to 5 µm.

[0013] The adhesion promoter layer preferably contains chromium and / or iron with a proportion of at least 95 wt% or at least 99 wt%.

[0014] The substrate preferably comprises or consists of stainless steel. The stainless steel can, for example, be CrNiMo steel and, in particular, CrNiMo 1.4401, CrNiMo 1.4571 and / or CrNiMo 1.4404.

[0015] It is preferred that the substrate be porous to allow the fluid to be transported through it. The substrate can, for example, comprise expanded metal, metal fibers (especially sintered and / or woven), particles (especially sintered), metal threads, perforated sheet metal, wire mesh, knitted wire, wire fabric, metal foam, and / or steel wool (especially processed into a nonwoven fabric).

[0016] The electrochemical cell according to the invention comprises a gas diffusion layer. The electrochemical cell preferably comprises a bipolar plate, a cathode, and an anode, and the gas diffusion layer electrically connects the bipolar plate to the cathode or to the anode. It is preferred that the contact layer contacts the bipolar plate and / or the cathode, or that the contact layer contacts the bipolar plate and / or the anode.

[0017] The inventive method for producing a gas diffusion layer comprises the following steps: c) applying the contact layer directly or indirectly to the substrate. It is preferred that the method comprises the following step: a) applying the adhesion promoter layer directly or indirectly to the substrate. This results in the contact layer being applied indirectly to the substrate in step c). The method may further comprise the following step: b) applying the intermediate layer to the adhesion promoter layer, in particular directly to the adhesion promoter layer. This results in the contact layer being applied indirectly to the adhesion promoter layer in step c).

[0018] It is preferred that in step c) the contact layer is applied by means of a spraying process, a coating process, a dipping process, a physical vapor deposition (PVD) process, a chemical vapor deposition (CVD) process and / or a conversion process.

[0019] In the spraying, application, and immersion processes, a suspension containing carbon and a liquid can be used. The solvent is then removed, for example, by applying heat.

[0020] The conversion process can, for example, involve plasma carburizing or plasma nitrocarburizing. These processes have the advantage of preventing surface oxidation, which would otherwise lead to an increase in contact resistance. Furthermore, these processes have the advantage of increasing the hardness of the gas diffusion layer through the introduction of carbon.

[0021] The physical vapor deposition process can involve cathode sputtering (magnetron sputtering), particularly reactive cathode sputtering, or arc evaporation, particularly reactive arc evaporation. Targets can include, for example, chromium, a chromium-containing alloy, iron, an iron-containing alloy, carbon, silicon, a silicon-containing alloy, tungsten, and / or a tungsten-containing alloy. Reactive gases can include, for example, ethyne, hexamethyldisiloxane (HDMSO), tetramethylsilane (TMS), or nitrogen.

[0022] The chemical vapor deposition process can, for example, be a plasma-enhanced vapor deposition (PACVD) process. Targets such as chromium, iron, carbon, silicon, and / or tungsten can be used. Reactive gases such as ethyne, hexamethyldisiloxane (HDMSO), tetramethylsilane (TMS), or nitrogen can be used.

[0023] The invention will be explained in more detail below with reference to the accompanying schematic drawings. These show: Fig. 1 a section through a first embodiment of the gas diffusion layer according to the invention, Fig. 2 a section through a second embodiment of the gas diffusion layer and Fig. 3 a section through an electrochemical cell according to the invention.

[0024] How it looks Fig. 1 and Fig. As can be seen in Figure 2, a gas diffusion layer 1 for an electrochemical cell 10 comprises a substrate 2 and a coating 6. A fluid can be transported through the substrate 2. The coating 6 is applied directly to the substrate 2. The coating 6 may include an adhesion promoter layer 3, which is applied directly to the substrate 2, and a contact layer 4, which is an outer surface of the gas diffusion layer 1 and is electrically conductively connected to the substrate 2. The adhesion promoter layer 3 contains chromium and / or iron with a content of at least 90% by mass, in particular at least 95% by mass or at least 99% by mass, and has a thickness in the range of 0.01 µm to 0.5 µm or from 50 nm to 200 nm.The contact layer contains carbon with a content of at least 90 wt%, in particular at least 95 wt% or at least 99 wt%, and has a thickness in the range of 0.05 µm to 500 µm, in particular from 0.05 µm to 100 µm or from 0.05 µm to 5 µm. The contact layer 4 can be configured to contact a surface of a component of the electrochemical cell 10 that is different from the gas diffusion layer 1, thus establishing an electrically conductive connection with the component that is different from the gas diffusion layer 1.

[0025] Fig. Figure 1 shows a first embodiment of the gas diffusion layer 1, in which the contact layer 4 is applied directly to the adhesion promoter layer 3. A current can thus flow directly from the adhesion promoter layer 3 to the contact layer 4 and vice versa. According to the first embodiment, the coating 6 can consist of the adhesion promoter layer 3 and the contact layer 4.

[0026] Fig. Figure 2 shows a second embodiment of the gas diffusion layer 1, in which the coating 6 has an intermediate layer 5 that is applied directly to the adhesion promoter layer 3 and comprises a metal nitride and / or a semimetal nitride with a proportion of at least 90 wt%, in particular 95 wt% or at least 99 wt%, wherein the contact layer 4 is applied directly to the intermediate layer 5. In this embodiment, the contact layer 4 is applied indirectly to the adhesion promoter layer 3 via the intermediate layer 5. A current can thus flow from the adhesion promoter layer 3 via the intermediate layer 5 to the contact layer 4 and vice versa. It is conceivable that the intermediate layer 5 consists, apart from unavoidable impurities, of the metal nitride, a metal carbide, a metal carbonitride, a semimetal carbide, a semimetal carbonitride, and / or the semimetal nitride.In particular, the intermediate layer 5 can comprise chromium nitride, CrC, CrCN, FeC, FeN, Fe-doped CN and / or Fe-Cr-N, or consist of chromium nitride, CrC, CrCN, FeC, FeN, Fe-doped CN and / or Fe-Cr-N, except for unavoidable impurities. The intermediate layer 5 can, for example, have a thickness in the range of 0.1 µm to 1 µm or from 0.1 µm to 0.5 µm. According to the second embodiment, the coating 6 can consist of the adhesion promoter layer 3, the intermediate layer 5, and the contact layer 4.

[0027] Fig. 1 and Fig. Figure 2 shows that the substrate 2 can have a surface onto which the coating 6 is applied and which can have a normal. The contact layer 4, optionally the adhesion promoter layer 3, and optionally the intermediate layer 5 can be arranged next to each other in the direction of the normal. The thicknesses of the adhesion promoter layer 3, the contact layer 4, and optionally the intermediate layer 5 can be the extents of the respective layer in the direction of the normal.

[0028] The contact layer 4 can be hydrogen-free or hydrogen-containing. It is conceivable that the contact layer 4 consists, apart from unavoidable impurities, of carbon and optionally hydrogen. Alternatively, it is conceivable that the contact layer is doped and consists, apart from unavoidable impurities, of carbon, the dopant, and optionally hydrogen. The dopant can be chromium, chromium carbide, silicon, tungsten, nitrogen, fluorine, hydrogen, and / or silicon carbide. The carbon can, for example, be in an amorphous form. The thickness of the contact layer 4 can, for example, be in the range of 0.05 µm to 100 µm or from 0.05 µm to 5 µm.

[0029] The thickness of the adhesion promoter layer 3 can, for example, be in a range of 0.01 µm to 0.1 µm or from 50 nm to 200 nm.

[0030] Substrate 2 can be made of stainless steel and, in particular, consist entirely of stainless steel. Substrate 2 can be porous to allow the fluid to be transported through it. The stainless steel can, for example, be CrNiMo steel, and in particular CrNiMo 1.4401, CrNiMo 1.4571, and / or CrNiMo 1.4404. Substrate 2 can also be expanded metal, metal fibers (especially sintered and / or woven), particles (especially sintered), metal threads, perforated sheet metal, wire mesh, knitted wire, wire fabric, metal foam, and / or steel wool (especially processed into a nonwoven fabric), or consist entirely of expanded metal and / or steel wool.

[0031] Fig. Figure 3 shows an electrochemical cell 10 with the gas diffusion layer 1. The electrochemical cell 10 can comprise a bipolar plate 11, a proton exchange membrane 14, a cathode 12, and an anode 13. The cathode 12 and / or the anode 13 can be arranged as a respective catalytic layer on the proton exchange membrane 14 and / or on the substrate 2. The gas diffusion layer 1 can electrically connect the bipolar plate 11 to the cathode 12. A further gas diffusion layer 1, configured according to the invention, can be provided, which electrically connects the bipolar plate 11 to the anode 13. It is conceivable that several of the electrochemical cells 10 are connected in series, as shown in Figure 3. Fig. 10 is indicated.

[0032] Fig.Figure 3 shows that the coating 6 of the gas diffusion layer 1 can contact the bipolar plate 11 and that a further coating 6 of the gas diffusion layer 1, configured according to the invention, can contact the cathode 12. Similarly, the coating 6 of the further gas diffusion layer 1 can contact the bipolar plate 11, and a further coating 6 of the further gas diffusion layer 1, configured according to the invention, can contact the anode 13.

[0033] Cell 10 can be part of an electrolyzer and / or a fuel cell. If cell 10 is part of an electrolyzer, water, in particular demineralized water, and the oxygen produced by electrolysis can be arranged in the gas diffusion layer 1 during operation of the electrolyzer. In the case that cell 10 is part of a fuel cell, hydrogen can be introduced into the gas diffusion layer 1 during operation of the fuel cell, and water produced by the reaction with oxygen can be arranged there.

Claims

[1] Gas diffusion layer for an electrochemical cell (10), comprising a substrate (2) through which a gas can be transported, a coating (6) which is applied directly to the substrate (2) and has a contact layer (4) which is an outer surface of the gas diffusion layer (1), is electrically conductively connected to the substrate (2), has carbon with a proportion of at least 90 wt% and has a thickness in the range of 0.05 µm to 500 µm. [2] Gas diffusion layer according to claim 1, wherein the coating (6) comprises an adhesion promoter layer (3) which is applied directly to the substrate (2), which comprises chromium and / or iron with a proportion of at least 90 wt% and has a thickness in the range of 0.01 µm to 0.5 µm, in particular 50 nm to 200 nm. [3] Gas diffusion layer according to claim 2, wherein the contact layer (4) is applied directly to the adhesion mediation layer (3). [4] Gas diffusion layer according to claim 2, wherein the coating (6) has an intermediate layer (5) which is applied directly to the adhesion promoter layer (3) and comprises a metal nitride, a metal carbide, a metal carbonitride, a semimetal carbide, a semimetal carbonitride and / or a semimetal nitride with a proportion of at least 90 wt%, wherein the contact layer (4) is applied directly to the intermediate layer (5). [5] Gas diffusion layer according to claim 4, wherein the intermediate layer (5) comprises chromium nitride, CrC, CrCN, FeC, FeN, Fe-doped CN and / or Fe-Cr-N or consists, except for unavoidable impurities, of the chromium nitride, the CrC, the CrCN, the FeC, the FeN, the Fe-doped CN and / or the Fe-Cr-N, in particular wherein the intermediate layer (5) has a thickness in the range of 0.01 µm to 1 µm or of 0.01 µm to 0.5 µm. [6] Gas diffusion layer according to any one of claims 1 to 5, wherein the contact layer (4) is doped with chromium, chromium carbide, silicon, tungsten, nitrogen, fluorine, hydrogen and / or silicon carbide. [7] Gas diffusion layer according to one of claims 1 to 6, wherein the carbon is in amorphous form. [8] Gas diffusion layer according to any one of claims 1 to 7, wherein the thickness of the contact layer (4) is in a range of 0.05 µm to 100 µm, in particular from 0.05 µm to 5 µm. [9] Gas diffusion layer according to any one of claims 1 to 8, wherein the substrate (2) comprises stainless steel. [10] Gas diffusion layer according to one of claims 1 to 9, wherein the substrate (2) is porous and in particular comprises expanded metal, metal fibers which are in particular sintered and / or woven, particles which are in particular sintered, metal threads, a perforated sheet, a wire mesh, a wire knitting, a wire fabric, a metal foam and / or steel wool which is in particular arranged as a nonwoven. [11] Electrochemical cell with a gas diffusion layer (1) according to any one of claims 1 to 10. [12] Electrochemical cell according to claim 11, wherein the electrochemical cell (10) comprises a bipolar plate (11), a cathode (12) and an anode (13) and the gas diffusion layer (1) electrically connects the bipolar plate (11) to the cathode (12) or to the anode (13). [13] Electrochemical cell according to claim 12, wherein the contact layer (4) contacts the bipolar plate (11) and / or the cathode (12) or wherein the contact layer (4) contacts the bipolar plate (11) and / or the anode (13). [14] Method for producing a gas diffusion layer (1) according to any one of claims 1 to 12, comprising the steps: c) applying the contact layer (4) directly or indirectly to the substrate (2). [15] Method according to claim 14, wherein in step c) the contact layer (4) is applied by means of a spraying process, a coating process, a dipping process, a physical vapor deposition process and / or a conversion process.

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