Separator element having a coating containing nanostructures - Patents.com

Abstract

A separator element (300) for an electrochemical cell (100, 200), the separator element (300) comprising a conductive substrate (310) and a coating (320) deposited on the conductive substrate, the coating comprising a first portion and a second portion, the first portion comprising a base layer (321) extending along a surface of the conductive substrate (310), and the second portion comprising a plurality of nanostructures (322) extending from the surface of the conductive substrate (310).

Description

[Technical field]

[0001] The present disclosure relates to electrochemical cells, such as fuel cells and electrolyzers, and in particular to separator elements suitable for such cells. [Background technology]

[0002] In modern energy systems, electrochemical cells, such as batteries, fuel cells, and electrolyzers, are becoming more and more widely used. Electrolysis of water to form hydrogen gas is a promising technology to replace the production of hydrogen gas from fossil fuels. It is also useful for energy storage, for example if surplus electrical energy from intermittent energy sources, such as solar and wind power, can be used to power the electrolysis process. Meanwhile, fuel cells are used to convert chemical energy to electrical energy, for example for use in vehicles. Fuel cells are generally more efficient than internal combustion engines, and some fuel cells can use sustainably produced hydrogen gas as fuel.

[0003] In existing electrochemical cells, high contact resistance between different cell components can lead to reduced efficiency. This problem can be exacerbated by the formation of non-conductive surface layers on some components under the influence of the cell's chemical environment. In addition, corrosion of components such as bipolar or separator plates can itself reduce efficiency and shorten cell life.

[0004] WO 2021 / 014144 discloses a carbon-based coating for separator elements intended to improve corrosion resistance.

[0005] WO 2019 / 186047 discloses a separator element for an electrochemical cell having reduced contact resistance.

[0006] There remains a need for separator elements that exhibit lower contact resistance and better corrosion resistance. Summary of the Invention [Problem to be solved by the invention]

[0007] It is an object of the present disclosure to provide, among other things, an improved separator element for electrochemical cells that reduces contact resistance with adjacent components and enhances corrosion resistance. [Means for solving the problem]

[0008] This object is achieved, at least in part, by a separator element for an electrochemical cell, the separator element including a conductive substrate and a coating disposed on the conductive substrate, the coating including a first portion and a second portion, the first portion including a base layer extending along a surface of the conductive substrate, and the second portion including a plurality of nanostructures extending from a surface of the conductive substrate. Effect of the Invention

[0009] The base layer contained within the first portion of the coating advantageously covers the surface of the conductive substrate, shielding it from the chemical environment of the electrochemical cell and reducing the risk of corrosion, while the nanostructures contained within the second portion of the coating provide multiple contact points between the separator element and adjacent cell components, thereby reducing the contact resistance between the separator element and adjacent cell components, such as gas diffusion layers.

[0010] Specifically, if the adjacent component has an uneven or porous surface, including ridges, bumps, pits, and / or grooves, the actual contact area between the separator element without the coating and the adjacent component may be very small, since only the ridges and bumps contact the separator element surface. If the separator element has a coating that includes a plurality of nanostructures extending from the separator element surface, these nanostructures contact additional portions of the surface of the adjacent component, thereby increasing the contact area. This reduces the contact resistance between the separator element and the adjacent component.

[0011] According to an embodiment, the base layer may include a carbon material. Many carbon materials are known to have good electrical and thermal conductivity, which is advantageous because they make them suitable for use as separator element coatings and, in particular, for reducing contact resistance. Some carbon materials are also known to be chemically stable under conditions found in electrochemical cells, in particular, proton exchange membrane (PEM) fuel cells and cathode sides of PEM electrolyzers. For example, the base layer may include any of graphene, graphite, and amorphous carbon.

[0012] The nanostructures may include carbon nanostructures. For example, the carbon nanostructures may include at least one carbon nanowall and / or any of carbon nanotubes, carbon nanowires, and carbon nanofibers. In addition to the aforementioned advantages of carbon materials in general, the properties of these carbon nanostructures, such as density and shape, can be adjusted by changing the conditions under which the nanostructures are fabricated. Carbon nanowalls, nanofibers, and nanowires are also mechanically rigid, making it easier to maintain a preferred orientation of the nanostructures relative to the surface of the conductive substrate.

[0013] An additional advantage of carbon nanowalls, also known as vertical graphene, is that they can be grown without the use of a growth catalyst. Specifically, a combination of a carbon-containing base layer and multiple carbon nanowalls can be grown in a single manufacturing step without a growth catalyst, which is efficient and reduces manufacturing costs.

[0014] The nanostructures in the plurality of carbon nanostructures extend parallel to one another along a direction perpendicular to the extending plane of the conductive substrate, and such a nearly uniform orientation of the nanostructures facilitates the formation of additional contact points with adjacent components, such as gas diffusion layers.

[0015] Optionally, the conductive substrate comprises a flow field device. The flow field comprises a plurality of flow channels separated by a plurality of flow channel supports. The flow channels are arranged to promote uniform distribution of gas and / or liquid throughout the conductive substrate. Advantageously, uniform distribution of gas and / or liquid throughout the flow field results in uniform distribution of reactants and products within the electrochemical cell, leading to more efficient utilization of the overall area of ​​the cell.

[0016] Due to the harsh chemical environment within the electrochemical cell, resulting for example from high or low pH and high electrical potential, materials forming the components of the electrochemical cell may be at risk of corrosion. Therefore, the separator element may be at least partially covered by a protective layer arranged to enhance corrosion resistance. The protective layer may for example comprise any of titanium, gold and platinum.

[0017] Also disclosed herein is an electrolytic cell comprising at least one separator element as described above. Advantageously, the coating contained within the separator element reduces the contact resistance between the separator element and adjacent components, such as gas diffusion layers, thereby increasing the efficiency of the electrolytic cell.

[0018] Also disclosed herein is a fuel cell comprising at least one separator element as described above. As with electrolysers, the efficiency of fuel cells is increased due to the reduced contact resistance between the separator element and adjacent components, such as the diffusion layers.

[0019] Objects are also achieved, at least in part, by a method of making a separator element including a conductive substrate and a coating disposed on the conductive substrate, the method including disposing the conductive substrate and depositing a first portion of the coating onto the conductive substrate, the first portion including a base layer extending along a surface of the conductive substrate, the method further including depositing a second portion of the coating onto the conductive substrate, the second portion including a plurality of nanostructures extending from a surface of the conductive substrate.

[0020] The base layer contained within the first portion of the coating advantageously protects the surface of the conductive substrate, shields the conductive substrate from the chemical environment of the electrochemical cell, and reduces the risk of corrosion, while the nanostructures contained within the second portion of the coating reduce the contact resistance between the separator element and adjacent cell components, such as gas diffusion layers, by providing multiple contact points between the separator element and adjacent cell components.

[0021] According to an embodiment, depositing the first portion of the coating may advantageously include growing the base layer using chemical vapor deposition. The advantage of growing the base layer using chemical vapor deposition is that the structure and thickness of the base layer may be controlled to achieve a desired result, such as a high coverage of the substrate surface or a desired thickness of the base layer.

[0022] Growing the base layer using chemical vapor deposition may include adjusting growth parameters to achieve a desired layer thickness, such as substrate temperature, plasma power, partial pressure of precursor gases, and total pressure in the growth chamber. Adjusting growth parameters is advantageous because it is a direct means of controlling the base layer thickness.

[0023] According to an embodiment, depositing the second portion of the coating may include growing a plurality of nanostructures on the base layer using chemical vapor deposition. Growing a plurality of nanostructures using chemical vapor deposition allows control of parameters such as the type of nanostructure, the number of nanostructures per unit area of ​​substrate, and the size and shape of the nanostructures. In particular, growing a plurality of nanostructures using chemical vapor deposition may include adjusting growth parameters to achieve desired nanostructure morphological properties. The growth parameters may be, for example, substrate temperature, plasma power, partial pressure of precursor gas, and total pressure in the growth chamber. This means that the nanostructures may be tailored to achieve a greater reduction in contact resistance between the separator element and the adjacent component. This is advantageous.

[0024] Growing multiple nanostructures using chemical vapor deposition may include growing multiple nanostructures of different types, such as nanowalls, nanotubes, nanowires, and nanofibers. An advantage of having multiple nanostructures of different types is that the combination of different types of nanostructures provides more possibilities to tailor the overall structure to achieve a desired result, such as covering a certain percentage of a substrate surface or producing a nanostructure with a desired height or mechanical stiffness. Growing multiple nanostructures of different types may include adjusting growth parameters to grow the different nanostructure types.

[0025] Certain advantages can be achieved by growing a base layer comprising a carbon material, such as graphene, graphite, or amorphous carbon, and a carbon nanowall, also known as vertical graphene. Such a combination of a carbon base layer and a carbon nanowall can be grown without the use of a growth catalyst, thereby reducing manufacturing costs.

[0026] The method may include depositing a growth catalyst layer on the conductive substrate and growing the base layer and / or the plurality of nanostructures on top of the growth catalyst layer. To grow some types of nanostructures, the use of a growth catalyst may be required to facilitate the chemical reactions involved in the growth of the nanostructures. The use of a growth catalyst layer allows for the inclusion of these types of nanostructures in the film, which is advantageous.

[0027] The methods disclosed herein are associated with the same advantages as those discussed above with respect to the different devices.

[0028] Broadly speaking, all terms used in the claims should be interpreted according to their ordinary meaning in the art, unless expressly defined otherwise herein. Any reference to "a / an / the element, apparatus, component, means, step, etc." should be openly interpreted as meaning at least one instance of that element, apparatus, component, means, step, etc., unless expressly specified otherwise. The steps of any method disclosed herein need not be performed in the exact order disclosed, unless expressly specified otherwise. Further features and advantages of the present invention will become apparent upon consideration of the appended claims and the following description. As will be apparent to one skilled in the art, different features of the present invention may be combined to form different embodiments than those described below without departing from the scope of the present invention.

[0029] The present disclosure will now be described in detail with reference to the accompanying drawings. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a schematic diagram showing a fuel cell. [Diagram 2] FIG. 2 is a schematic diagram showing an electrolytic cell. [Diagram 3] FIG. 3 is a schematic diagram showing a separator element. [Figure 4]4A and B are schematic diagrams showing separator element arrangements. [Diagram 5] FIG. 5 is a cross-sectional view that illustrates a schematic diagram of a carbon nanowall. [Figure 6] 6A and B are schematic diagrams showing the flow field device. [Figure 7] FIG. 7 is a scanning electron microscope (SEM) image showing the carbon nanostructures. [Figure 8] FIG. 8 is a flow chart illustrating the method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Aspects of the present disclosure are described in detail below with reference to the accompanying drawings. However, the various devices and methods disclosed herein may be embodied in many different forms and should not be construed as being limited to the aspects shown herein. Like reference numerals in the drawings refer to like elements throughout the drawings.

[0032] The terminology used herein is for the purpose of describing the disclosed embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly dictates otherwise.

[0033] The following description focuses on two types of electrochemical cells: fuel cells and electrolyzers. Specifically, the following description addresses fuel cells and electrolyzers, respectively, that include a proton exchange membrane and that use hydrogen gas as a fuel or produce hydrogen gas from water. However, as will be apparent to one of ordinary skill in the art, the devices and methods described herein can also be used with other types of electrochemical cells, batteries, or supercapacitors.

[0034] The present disclosure may also be applied to types of fuel cells and electrolysers other than those detailed here, such as fuel cells that use methanol as fuel, or electrolysers that use alkaline electrolytes, in particular fuel cells and electrolysers in which another type of solid electrolyte, such as an anion exchange membrane, is used instead of a proton exchange membrane.

[0035] In a fuel cell, chemical energy from a fuel is converted into electrical energy through reduction and oxidation reactions. A fuel cell contains two electrodes and an electrolyte that allows ions to move between the electrodes. The electrodes are also electrically connected to an electrical load, where the generated electrical energy is used.

[0036] Fuel cell electrolytes must be good ionic conductors, i.e. capable of transporting ions, and at the same time poor electronic conductors, i.e. inhibiting the transport of electrons. Fuel cell electrolytes can be liquids, e.g. solutions of alkali salts or molten carbonate compounds, or solids, e.g. polymeric membranes or metal oxides. Examples of polymeric membrane materials are sulfonated tetrafluoroethylene, also known as Nafion, and polymers based on polysulfone or polyphenol oxide. Ionically conducting metal oxides can be, e.g., doped barium zirconate, doped barium cerate, doped lanthanum gallate, or stabilized zirconia. Different electrolytes may be suitable to conduct different types of ions. For example, membranes based on sulfonated tetrafluoroethylene, e.g. Nafion, can conduct hydrogen ions, i.e. protons, and are therefore known as proton exchange membranes or PEMs. Numerous metal oxides are suitable to conduct oxygen ions.

[0037] Preferably, the electrolyte should also inhibit the transport of fuel from one electrode through the electrolyte to the other electrode. If the electrolyte membrane is made of a material that is too fuel permeable, another material may be added to the membrane to inhibit fuel transport. As an example, in a methanol fuel cell that includes a Nafion membrane, ruthenium may be added to one side of the membrane.

[0038] Fuel cells using ion exchange membranes, such as Nafion, are often called proton exchange membrane fuel cells or PEMFCs because the membranes conduct protons. In a PEMFC, a hydrogen-containing fuel, such as hydrogen gas, is introduced at a first electrode, the anode, while an oxygen-containing gas is introduced at a second electrode, the cathode. At the anode, hydrogen is split into protons and electrons with the assistance of an electrocatalyst. This is called the hydrogen oxidation reaction. The protons cross the ion exchange membrane to reach the cathode, while the electrons cross the electrical connection between the anode and the cathode, where the generated electrical energy can be utilized. At the cathode, the protons and electrons react with oxygen via the oxygen reduction reaction to form water. This reaction is assisted by an electrocatalyst.

[0039] A catalyst is a material or compound that facilitates a chemical reaction, for example by reducing the amount of energy required for the reaction. Electrocatalysts are catalysts used in electrochemical reactions, such as the hydrogen oxidation and oxygen reduction reactions, that take place in fuel cells. Fuel cell electrocatalysts often contain precious metals, such as platinum, ruthenium, or palladium.

[0040] For PEMFCs, and other fuel cells using solid ion conductors, the anode and cathode catalysts are often arranged as electrocatalyst layers on the opposing surfaces of the ion exchange membrane. For PEMFCs in particular, the electrocatalyst layer often comprises an electrocatalyst material such as platinum in the form of nanoparticles, i.e. particles having diameters significantly below 1 micrometer, mainly between 1 and 100 nm. The electrocatalyst layer typically also comprises a catalyst binder or catalyst support, which often comprises carbon nanomaterials, e.g. carbon nanoparticles or nanotubes, or carbon black. The electrocatalyst layer may comprise an ion-conducting polymer arranged to facilitate the transport of hydrogen ions to the ion exchange membrane, and a hydrophobic material, e.g. polytetrafluoroethylene. According to an embodiment, the catalyst layer may be 5 to 50 nm thick. According to another embodiment, the thickness of the catalyst layer may depend on the type of catalyst used.

[0041] An ion exchange membrane having an anode electrode catalyst layer and a cathode electrode catalyst layer disposed on opposing surfaces thereof is sometimes called a membrane electrode assembly.

[0042] For a fuel cell to operate, ions and electrons must be able to travel from the anode electrocatalyst through the ion exchange membrane and the electrical load, respectively, and reach the cathode electrocatalyst. In addition, reactant gases, such as hydrogen and oxygen gases, must be able to reach the electrocatalyst layers, while product water vapor must be continuously removed from the cell. In most PEMFCs, this is accomplished by placing an electrically conductive porous material in the layer next to each electrocatalyst layer, and also placing an electrically conductive separator element next to the porous layer.

[0043] The porous material layer may be referred to as, for example, a porous transport layer (PTL), a mass transport layer, a gas diffusion layer (GDL), or simply a diffusion layer. Some of these terms, such as gas diffusion layer, are commonly used in the context of fuel cells, whereas some terms, such as porous transport layer, are more commonly used in the context of electrolyzers. However, they all refer to a porous material layer that serves the function of simultaneously allowing both electron transport and product and reactant transport to and from an active layer, such as an electrocatalyst layer. Thus, the different terms mentioned above will be used interchangeably in this disclosure, both in the context of fuel cells and in the context of electrolyzers.

[0044] An electrically conductive material, element, or component is considered herein to be a material, element, or component that has a high electrical conductivity. High electrical conductivity is defined as electrical conductivity typically associated with metallic or semiconducting materials, or electrical conductivity greater than 100 Sm -1 It is also possible for the conductivity to be ultra high.

[0045] FIG. 1 shows a fuel cell 100 including an ion exchange membrane 130, a first electrode catalyst layer 111, and a second electrode catalyst layer 121. The first and second electrode catalyst layers 111, 121 are disposed adjacent to the ion exchange membrane on either side of the ion exchange membrane. A first GDL 112 and a second GDL 122 are disposed adjacent to the first electrode catalyst layer 111 and the second electrode catalyst layer 121, respectively, on the side of the electrode catalyst layers opposite the ion exchange membrane 130. A first separator element 113 and a second separator element 123 are disposed adjacent to the first GDL 112 and the second GDL 122, respectively, on the side opposite the electrode catalyst layers 111, 121, respectively. Each separator element is electrically connected to a load 140.

[0046] The GDLs 112, 122 are positioned to allow reactants and products, such as hydrogen gas, oxygen gas, and water, to be transported through the pores of the GDLs while still maintaining electrical contact between the electrocatalyst layers and the separator element. The GDLs often comprise a porous, conductive material, such as metal foam, porous carbon, or carbon paper. The GDLs may also provide structural support for the electrocatalyst layers 111, 121 and the ion exchange membrane 130.

[0047] The separator elements 113, 123 often comprise a metallic material, such as steel, titanium, and / or other electrically conductive materials, such as carbon composites. The separator elements 113, 123 are connected to an electrical load and also separate the fuel cell from its surroundings. If the fuel cells form part of a fuel cell stack, the separator element may form part of the cathode side of one fuel cell and part of the anode side of an adjacent fuel cell, in which case the separator element may be called a bipolar plate. Other possible terms used to denote the separator element are separator plate, separator element, or flow plate.

[0048] As mentioned above, the present disclosure also relates to electrolyzers. Water electrolyzers, on the other hand, use electrical energy to split water into oxygen gas and hydrogen gas. Electrolyzers may generally include similar components as those described above for fuel cells. Specifically, electrolyzers include an ion-conducting electrolyte and two electrodes. One of these electrodes is a cathode and the other is an anode. The cathode and anode are electrically connected to a power source. Proton exchange membranes, such as Nafion, can be used as electrolytes in electrolyzers and fuel cells, as can the other polymer membranes and solid oxide ion conductors described above. Liquid electrolytes, including alkaline solutions, may also be used.

[0049] In an electrolytic cell containing a proton conducting electrolyte, such as PEM, water is introduced at the anode side where it is split into oxygen and hydrogen, known as the oxygen evolution reaction. The oxygen forms oxygen gas, while the hydrogen is subsequently split into protons which traverse the ion exchange membrane to the cathode, and electrons which travel to the cathode through a power source. At the cathode, the protons and electrons form hydrogen gas via the hydrogen evolution reaction.

[0050] The electrocatalysts used in electrolysers may be different from those used in fuel cells. In electrolysers using PEM electrolytes, the anode side electrocatalyst often contains iridium oxide, while the cathode side electrocatalyst generally contains platinum or other platinum group metals. In electrolysers using anion exchange membrane AEM electrolytes, both electrocatalysts may instead contain materials such as nickel or cobalt.

[0051] In electrolytic cells containing solid electrolytes, such as PEMs and AEMs, the anode and cathode electrocatalysts are often disposed in electrocatalyst layers on opposite sides of the electrolyte membrane to form a membrane electrode assembly, as described above for fuel cells. One or both electrocatalysts may be in the form of nanoparticles. In addition to the electrocatalyst itself, the electrocatalyst layer may include a catalyst support, such as carbon black, carbon nanotubes, or metal foam. The electrocatalyst layer may include an ion-conducting polymer and a hydrophobic material, such as Teflon.

[0052] The requirements for ion transport through the electrolyte, mass transport of reactants and products to and from the electrocatalysts, and good electrical contact between elements within the cell are similar in electrolyzers to those in fuel cells. Thus, electrolyzers often also include a porous diffusion layer disposed adjacent to each electrocatalyst layer, and a separator element disposed adjacent to each diffusion layer. The diffusion layers may comprise porous carbon materials, often including titanium, metal foams, or metal meshes. The separator elements may comprise, for example, metallic materials, such as steel or titanium, or conductive carbon composites.

[0053] 2 shows an electrolytic cell 200 including an ion exchange membrane 230, a first electrode catalyst layer 211 and a second electrode catalyst layer 221. The first and second electrode catalyst layers are disposed adjacent to the ion exchange membrane 230 on either side of the ion exchange membrane. A first porous transport layer 212 and a second porous transport layer 222 are disposed adjacent to the first and second electrode catalyst layers on the side of the electrode catalyst layers opposite the ion exchange membrane 230. A first separator element 213 and a second separator element 223 are disposed adjacent to the first porous transport layer 212 and the second porous transport layer 222 on the side opposite the respective electrode catalyst layers. Both separator elements are electrically connected to a power source 240.

[0054] In both fuel cells and electrolyzers, it is important to minimize the electrical contact resistance between the separator elements and the gas diffusion / porous transport layers, and to prevent corrosion of the components to maintain efficient operation. However, higher contact resistance can occur between a separator element and an adjacent gas diffusion layer, for example as a result of poor physical contact between the two components. This problem can be exacerbated by the formation of non-conductive compounds, such as metal oxides, on the surface of the separator elements.

[0055] To reduce problems associated with contact resistance and corrosion, a coating can be applied to the surface of the separator element. Figure 3 shows a separator element 300 for an electrochemical cell, in which the separator element 300 includes a conductive substrate 310 and a coating 320 applied to the conductive substrate. The coating includes a first portion and a second portion. The first portion includes a base layer 321 that extends along the surface of the conductive substrate 310. The second portion includes a plurality of nanostructures 322 that extend from the surface of the conductive substrate 310.

[0056] Typically, the conductive substrate 310 is a planar element or plate comprising a metal element, such as stainless steel or titanium. A planar element is elongated in two dimensions and relatively thin in a third dimension. The two dimensions in which such an element extends define a plane of extension of the element.

[0057] Each planar element generally comprises two broad boundary surfaces. These boundary surfaces are mostly parallel to the extension plane and are typically the broadest boundary surfaces of the element. These boundary surfaces may be referred to as the first and second sides of the planar element. In the case of an electrochemical cell, at least one side of the conductive substrate faces a gas diffusion layer or GDL. The GDL may also be a planar element. In this case, the first side of the conductive substrate 310 may be said to face the first side of the GDL.

[0058] The GDL generally comprises a porous material, such as carbon paper, carbon felt, or a porous metal material. The surface of the GDL will therefore be uneven, and may include, for example, pits, bumps, ridges, and grooves. When the GDL is pressed against the separator element, only the bumps and ridges may come into contact with the surface of the separator element. This means that the actual surface area of ​​contact between the separator element and the GDL is relatively small compared to the total surface area of ​​the separator element, resulting in a higher contact resistance. It should be noted that the conductive substrate 310 may also have an uneven surface, which may contribute to the above problem.

[0059] The coating 320 applied to the conductive substrate 310 is positioned to alleviate this problem. A first portion of the coating, including a base layer 321, covers a majority of the side of the conductive substrate 310 that faces the GDL. For example, the base layer 321 may cover more than 90% of the surface. Preferably, the base layer 321 may cover more than 100% of the surface.

[0060] It should be noted that if separator element 300 is a bipolar plate separating two adjacent electrochemical cells, there may be a first GDL facing a first side of conductive substrate 310 and a second GDL facing a second side of conductive substrate 310. In this case, coating 320 may cover both the first and second sides of conductive substrate 310 since both the first and second sides face gas diffusion layers.

[0061] The second portion of the coating includes a plurality of nanostructures 322. The nanostructures included within the plurality of nanostructures 322 may be arranged to increase the proportion of the substrate that is covered by the coating 320. As an example, if the substrate 321 covers 90% of the surface, some of the nanostructures within the plurality of nanostructures 322 may cover the remaining 10%. For efficient corrosion protection, it is advantageous for the coating 320 to cover as large a proportion of the surface of the conductive substrate 310 as possible.

[0062] A nanostructure is a structure having a size substantially smaller than 1 micrometer, preferably 1-100 nm, in at least one dimension. The plurality of nanostructures 322 may include generally planar nanostructures. These nanostructures have one dimension, shown here as thickness, that is substantially smaller than two other dimensions, shown here as length and height. "Substantially smaller" may mean, for example, that the thickness is less than 20% of the length or height. Such nanostructures may be referred to as nanowalls or nanosheets.

[0063] That a nanostructure is generally planar should not be taken to mean that it is completely flat, but can also mean that the nanostructure is, for example, concave, convex, uneven, or undulating, so long as it extends along two dimensions and is significantly smaller along a third dimension.

[0064] With respect to the surface of the conductive substrate 310, the length of a planar nanostructure is considered here to be the dimension extending along the surface of the conductive substrate 310, whereas the height is the dimension extending away from the surface of the conductive substrate 310.

[0065] The plurality of nanostructures 322 may include elongated nanostructures in which one dimension, shown here as height, is substantially greater than the other two dimensions. As an example, consider a generally cylindrical nanostructure characterized by a height and a diameter. A nanostructure is considered elongated if the height is significantly greater than the diameter, for example, if the height is greater than twice the diameter. Similar reasoning may be applied to nanostructures that are substantially conical, frustoconical, rectangular, or of any shape.

[0066] Elongated nanostructures can be, for example, straight, helical, branched, wavy, or tapered. Optionally, elongated nanostructures can be classified as nanowires, nanohorns, nanotubes, nanowalls, crystalline nanostructures, or amorphous nanostructures.

[0067] The nanostructures in the plurality of nanostructures 322 can be considered to extend in a direction away from the surface of the conductive substrate 310. This extension is along what is shown here as the height dimension of the nanostructure. By the nanostructures extending from the surface of the conductive substrate, it is taken to mean that the extension forms an angle with the extension plane of the conductive substrate, and that this angle is at least 30 degrees, and preferably greater than 45 degrees. Optionally, the angle can be about 90 degrees.

[0068] By extending from the surface of the conductive substrate, the plurality of nanostructures 322 increases the number of points at which the GDL can make physical contact with the separator element 300. This increases the total surface area of ​​contact of the separator element with the GDL. This reduces the contact resistance between the two components.

[0069] In this manner, the nanostructures increase the mechanical contact between separator element 300 and the GDL. Increased mechanical contact improves electrical contact and, if the nanostructures comprise a conductive material, reduces contact resistance. In this case, the physical contact between the nanostructures and the GDL also establishes electrical contact.

[0070] 4A and 4B show a separator element device 400 including a separator element 300 and a porous gas diffusion layer 410 including a textured surface. The separator element 300 and the gas diffusion layer are disposed adjacent to one another. FIG. 4A shows a separator element 300 including a conductive substrate 310 without a coating. The conductive substrate 310 contacts the gas diffusion layer 410 at only a few points 411 due to the textured surface of the gas diffusion layer 410. FIG. 4B shows a separator element 300 including a conductive substrate 310 with a base layer 321 and a plurality of nanostructures 322. The nanostructures increase the number of points 411 at which the gas diffusion layer 410 and the separator element are in contact.

[0071] According to some embodiments, the extension directions of different nanostructures included in the plurality of nanostructures may have different angles with respect to the extension plane of the conductive substrate, so that the different nanostructures extend in different directions from the surface. According to other embodiments, and referring to FIG. 3, the nanostructures included in the plurality of nanostructures extend parallel to one another along a direction perpendicular to the extension plane of the conductive substrate 310.

[0072] To increase the number of contact points between the GDL and the separator element, it is advantageous to have the nanostructures oriented in a uniform direction. This should not be taken to mean that the nanostructures are perfectly straight or perfectly perpendicular to the extension plane of the conductive substrate 310. The nanostructures may generally extend along a direction perpendicular to the extension plane. This can be taken to mean that they may have a slight inclination with respect to the vertical vector of the extension plane, or may bend back and forth to form a spiral or wave shape. In this context, a slight inclination can mean that the angle between the extension direction of the nanostructures and the extension plane is greater than 60 degrees, and preferably greater than 80 degrees.

[0073] The base layer 321 is preferably arranged to shield the conductive substrate from the chemical environment of the cell, thereby enhancing its corrosion resistance whilst maintaining good electrical conductivity. The base layer 321 thus preferably comprises a material having high electrical conductivity and good chemical stability under the conditions of the electrochemical cell. The base layer may comprise a metal, for example titanium, platinum or gold, or a compound such as titanium nitride. Preferably, the base layer 321 comprises a carbon material.

[0074] Due to their good electrical conductivity and chemical stability, carbon materials are frequently used in electrochemical cells. Specifically, carbon materials are used in both the anode and cathode sides in fuel cells and in the cathode side in electrolyzers. According to an embodiment, the base layer 321 includes any of graphene, graphite, and amorphous carbon. The base layer 321 may include graphene foam or graphite foam.

[0075] The nanostructures included within the plurality of nanostructures 322 comprise any of a conductive material, such as a metal, a metal alloy, a semiconductor, and a conductive metal oxide. In particular, the plurality of nanostructures 322 may comprise a plurality of carbon nanostructures. Similar to the carbon materials discussed above, carbon nanostructures also have high electrical conductivity and good chemical stability. Additionally, the shape and structure of the carbon nanostructures can be altered by adjusting the conditions under which the nanostructures are grown to obtain, for example, a desired density or shape of the nanostructures, a desired size of the nanostructures, or a desired number of nanostructures per surface area.

[0076] The shape and structure of the elongated carbon nanostructures can also be modified by adjusting the conditions under which the nanostructures are grown, for example to obtain a desired density or shape of the nanostructures, a desired size of the nanostructures, or a desired number of nanostructures per surface area. Carbon nanostructures also have the advantage, based on their chemical stability, that non-conductive compounds are less likely to form on the surface, which is advantageous for maintaining a low electrical contact resistance. This is particularly advantageous compared to metallic materials, such as steel or titanium, which can form non-conductive metal oxides on the surface.

[0077] The plurality of carbon nanostructures 322 may include at least one carbon nanowall. A carbon nanowall, also known as a carbon nanosheet or vertical graphene, includes at least one graphene layer that protrudes at an angle from the surface on which the nanostructure is grown. The angle may be greater than 80 degrees, i.e., the vertical graphene may protrude from the surface on which it is grown along a direction close to perpendicular to the extending plane.

[0078] Graphene has high electrical and thermal conductivity, which makes it suitable for forming part of the coating 320 of the separator element 300. Vertical graphene in particular provides a large surface area with as many contact points as possible between the graphene and the GDL, which is advantageous for reducing contact resistance.

[0079] If the base layer 321 comprises a carbon material, such as amorphous carbon, graphene, or graphite, the vertical graphene nanostructure may be formed integrally with the base layer by growing both the base layer and the vertical graphene on the conductive substrate. The graphene sheets in the vertical graphene and the carbon contained in the base layer 321 will then bond at the base of the vertical graphene. This allows the coating 320 to entirely cover the surface of the conductive substrate with a reduced number of holes or gaps. This is shown diagrammatically in FIG. 5, which shows the structure of two carbon nanowalls in cross section. The carbon nanowall 510 is shown extending upward from the base layer and bonded to the base layer.

[0080] In addition, the growth of the carbon base layer 321 and the plurality of nanostructures 322 comprising vertical graphene on the conductive substrate can be achieved without the use of special catalysts. Figure 7 is an SEM image showing carbon nanowalls or vertical graphene grown on a substrate.

[0081] Referring again to FIG. 3, the plurality of carbon nanostructures may include any of carbon nanotubes, carbon nanowires, and carbon nanofibers. The advantage of carbon nanofibers and nanowires is that they are stiffer and more rigid, which makes them less likely to be deformed when the fuel cell is assembled by methods such as pressing the components together, and more likely to remain in the intended orientation relative to the conductive substrate 310. Carbon nanotubes, carbon nanowires, and carbon nanofibers may be included in the plurality of carbon nanostructures separately, in combination, and / or in combination with vertical graphene, as an example. Advantageously, carbon nanotubes, carbon nanofibers, and carbon nanowires may also be grown on a conductive substrate along with a carbon-containing base layer and vertical graphene nanostructures. When the multiple carbon nanostructures include a combination of several types of carbon nanostructures, such as carbon nanofibers and vertical graphene, the properties of the different nanostructures can be used, for example, to maximize the surface area of ​​the conductive substrate 310 that is covered by the coating 320 or to increase the proportion of the surface of the conductive substrate 310 that is covered by the coating 320.

[0082] The shape and structure of the carbon nanostructures can also be altered by adjusting the conditions under which the nanostructures are grown to obtain, for example, a desired density or shape of the nanostructures, a desired size of the nanostructures, or a desired number of nanostructures per surface area.

[0083] Separator elements used in electrochemical cells often include a flow field device. The flow field device is used to promote uniform distribution of reactants throughout the separator element and to facilitate removal of reaction products. Uniform or uniform distribution is taken herein to mean that the concentration of reactants is similar throughout the flow field device. Thus, the flow field device is positioned to promote uniform distribution of reactants if this contributes to making the concentration of reactants more uniform across the separator element surface as compared to a separator element without a flow field device.

[0084] A schematic diagram of one example of a flow field device is shown in Figures 6A and B. The flow field device 600 includes a number of grooves known as channels 610 that are separated by ridges known as ribs or channel supports 620. Gases and liquids can flow along the channels 610 and thus spread throughout the separator element. As one example, the flow field device may be formed by scoring into the conductive substrate 310 of the separator element to form the channels 610. As another example, the flow field device may be formed by depositing material on a surface of the separator element 310 to form the channel supports 620.

[0085] When the separator element is a planar element, the flow field devices are generally arranged on said first and second sides, i.e. on the surfaces of the element that are parallel to the extension plane of the element. In the separator element devices described herein, the flow fields may be arranged on the surface of the separator element that faces the GDL. When the separator element is a bipolar plate used in a stack of electrochemical cells, two flow field devices may be arranged on opposite sides of the separator element.

[0086] 6A and 6B is known as a linear parallel flow field device because the arrangement of ribs promotes parallel flow of gas and / or liquid through adjacent flow channels. Other flow field device designs may be used, such as serpentine, interdigitated, or pin-type flow field devices.

[0087] Thus, the conductive substrate 310 may include a flow field device 600. The flow field device includes a plurality of flow channels 610 separated by a plurality of flow channel supports 620. The flow channels are arranged to promote uniform or even distribution of gas / liquid throughout the flow field device, i.e., the flow channels are arranged to contribute to making the concentrations of gas and liquid more uniform throughout the flow field device.

[0088] The chemical environment in an electrochemical cell may cause corrosion and / or degradation of some materials. Although carbon materials are generally sufficiently chemically stable to be used in fuel cells and on the cathode side in electrolyzers, they may require additional surface treatment for use, for example, on the anode side in electrolyzers. Other materials used in separator elements, such as stainless steel, may also require additional treatment to withstand the environment in an electrochemical cell. Thus, the separator elements may be at least partially covered by a protective layer disposed thereon to enhance corrosion resistance. The protective layer may include titanium, gold, and platinum, or combinations thereof. The protective coating may include titanium nitride, a ceramic material, or a metal oxide, such as aluminum oxide, cerium oxide, and zirconium oxide. The protective coating may include a carbon-based material. The protective coating may cover at least a portion of the coating 320. The protective coating may cover a surface of the conductive substrate 310 that is not covered by the coating 320, such as the opposite side or edges of the conductive substrate 310.

[0089] Also disclosed herein is an electrolyzer 100 including at least one separator element 300 as described above, as well as a fuel cell 200 including at least one separator element 300 as described above.

[0090] 8 illustrates a method of fabricating a separator element 300, the separator element including a conductive substrate 310 and a coating 320 disposed on the conductive substrate. The method includes positioning (S1) the conductive substrate 310 and depositing (S2) a first portion of the coating 320 onto the conductive substrate 310. The first portion of the coating 320 includes a base layer 321 that extends along a surface of the conductive substrate. The method also includes depositing (S3) a second portion of the coating 320 onto the conductive substrate 310, the second portion including a plurality of nanostructures 322 extending from the surface of the conductive substrate.

[0091] The conductive substrate may comprise a material such as stainless steel or titanium. The first and second portions of the coating may comprise a material such as a metal, a metal alloy, a semiconductor, and a conductive metal oxide. The first and second portions of the coating may comprise a carbon material.

[0092] The base layer 321 may be deposited using methods such as evaporation, plating, sputtering, molecular beam epitaxy, pulsed laser deposition, spin coating, spray coating, or other suitable methods. The deposition method may be selected depending on the materials to be included in the base layer 321.

[0093] A plurality of nanostructures 322 may be generated through lithographic methods, such as colloidal or nanosphere lithography, focused ion beam machining, and laser machining. Nanostructures including carbon or organic compounds may be generated using methods such as electrospinning or chlorination of carbides or metal organic compounds, such as titanium carbide and ferrocene. The generated nanostructures may then be deposited onto the conductive substrate 310 or base layer 321.

[0094] Preferably, chemical vapor deposition (CVD) techniques can be used to deposit the first and / or second portions of the coating. In general, CVD processes involve exposing a substrate to precursor gases. The precursor gases are then reacted on the surface of the substrate to produce the desired structure. The formation of the structure may be aided by factors such as the substrate temperature, the pressure in the growth chamber, the presence of other gases, such as inert carrier gases or reducing gases, and the presence of a growth catalyst.

[0095] Examples of CVD methods include rapid thermal CVD, hot filament CVD, laser CVD, combustion CVD, and plasma-assisted CVD. Plasma-assisted CVD or PECVD further includes methods such as capacitively coupled plasma PECVD, inductively coupled plasma PECVD, radio frequency plasma PECVD, DC plasma CVD, and microwave plasma PECVD.

[0096] According to an embodiment, depositing the first portion of the coating (S2) may include growing (S21) the base layer 321 using chemical vapor deposition. Optionally, the base layer 321 may be deposited using hot filament CVD or rapid thermal CVD.

[0097] The base layer 321 may be deposited using PECVD. According to one embodiment, the base layer 321 may be deposited using a low plasma power, for example, a plasma power of 5-50 w. According to another embodiment, the plasma power may be adjusted to provide a base layer with desired properties, for example, high density or a desired structure.

[0098] The growth of the base layer 321 using CVD is controlled by several growth parameters, such as temperature, pressure, and which gases are used as precursor gases, reducing gases, and inert carrier gases, as well as the relative concentrations of the precursor gases, reducing gases, and inert carrier gases. In the case of PECVD, the plasma power and the type of plasma, such as RF plasma or DC plasma, are also growth parameters. These growth parameters affect the properties of the base layer 321, such as thickness and structure. Thus, growing the base layer 321 using chemical vapor deposition involves adjusting one or several of these growth parameters to achieve a desired layer thickness.

[0099] According to another embodiment, depositing (S3) the second portion of the coating includes growing (S31) the plurality of nanostructures 322 on the base layer 321 using chemical vapor deposition. Preferably, the plurality of nanostructures 322 may be grown using PECVD.

[0100] Similar to growing the base layer 321, the properties of the resulting nanostructures grown by CVD depend on the growth parameters, such as temperature, pressure, and which gases are used as the precursor gas, reducing gas, and inert carrier gas, as well as the relative concentrations of the precursor gas, reducing gas, and inert carrier gas. In the case of PECVD, the plasma power and the type of plasma, such as RF plasma or DC plasma, are also growth parameters. Growing the nanostructures 322 using chemical vapor deposition (S31) may include adjusting one or several of these growth parameters to achieve desired nanostructure morphological properties.

[0101] The plurality of nanostructures may include only one type of nanostructure, e.g., only one type of nanostructure, e.g., nanowall, nanotube, nanowire, or nanofiber. The plurality of nanostructures may include different types of nanostructures, e.g., a combination of nanowall and nanofiber. Thus, growing the plurality of nanostructures 322 using chemical vapor deposition (S31) may include growing different types of nanostructures, e.g., nanowall, nanotube, nanowire, and nanofiber. Growing different types of nanostructures 322 may be achieved by adjusting growth parameters, e.g., temperature, pressure, or plasma power, to grow different nanostructure types. Other parameters that may be adjusted are which gases are used as precursor gas, reducing gas, and inert filler gas, as well as the relative concentrations of precursor gas, reducing gas, and inert carrier gas. The type of plasma, e.g., RF plasma or DC plasma, may also be changed to affect the growth results.

[0102] When different types of nanostructures are grown sequentially, this may be used to increase the percentage of the surface of the conductive substrate 310 that is covered by the nanostructures. As an example, if multiple nanowalls are grown first and multiple nanofibers are subsequently grown, the nanofibers may fill in the gaps between the nanowalls, thereby increasing the coverage.

[0103] The growth process may require the deposition of additional layers on the substrate, such as an auxiliary layer or a growth catalyst layer. The growth catalyst layer comprises a material that is catalytically active and promotes the chemical reactions involved in the formation of the grown nanostructures. For example, an auxiliary layer may be used to control the properties of the grown nanostructures, facilitate vertically oriented growth, or otherwise improve the growth process results. The catalyst layer or the auxiliary layer, or both, may comprise materials such as nickel, iron, platinum, palladium, nickel-silicide, cobalt, molybdenum, or gold. Thus, the method may include depositing a growth catalyst layer on the conductive substrate 310 and growing a base layer 321 and / or a plurality of nanostructures 322 on top of the growth catalyst layer.

[0104] The help layer or growth catalyst layer may be deposited using methods such as evaporation, plating, sputtering, molecular beam epitaxy, pulsed laser deposition, spin coating, spray coating, or any other suitable method. According to one embodiment, the growth catalyst layer may comprise a uniform layer of growth catalyst material. According to another embodiment, the growth catalyst layer may comprise a plurality of growth catalyst nanoparticles.

[0105] According to some embodiments, portions of the helplayer or catalyst layer may be removed after growth of the nanostructures, e.g., by etching. The removed portions of the helplayer or catalyst layer may be portions that extend between the grown nanostructures.

[0106] In some cases, the plurality of nanostructures 322 may include one type of nanostructures preferably grown with the aid of a growth catalyst and another type of nanostructures preferably grown without a growth catalyst. In this case, the type of nanostructures that require a growth catalyst may be grown first using a first set of growth parameters. The type of nanostructures that do not require a growth catalyst may then be grown using a second set of growth parameters.

[0107] According to some aspects, the method may include depositing a protective coating on the separator element. The protective coating is arranged to enhance corrosion resistance. The protective coating may include, for example, any of titanium, titanium nitride, gold, and platinum.

[0108] According to one embodiment, the base layer 321 may include a carbon material, such as graphene, graphite, diamond-like carbon, or amorphous carbon, while the plurality of nanostructures 322 may include carbon nanowalls or vertical graphene. The plurality of nanostructures 322 may include any of carbon nanofibers, carbon nanotubes, and carbon nanowires.

[0109] Advantageously, the film comprising the base layer 321 comprising a carbon material and the plurality of nanostructures 322 comprising vertical graphene may be grown using CVD in a single process step, optionally without the use of a growth catalyst, thereby reducing manufacturing costs compared to other films. Single process step is taken here to mean that rather than requiring the substrate to be removed from the growth chamber or handled between growing the base layer 321 and the plurality of nanostructures 322, the growth of both the base layer and the plurality of nanostructures may be achieved by adjusting the growth parameters of the CVD process.

[0110] Also described herein is a method of growing a carbon-containing base layer and a plurality of carbon nanowalls on a substrate, the method including providing a substrate, depositing a carbon base layer on the substrate using chemical vapor deposition (CVD), and growing a plurality of carbon nanowalls on the substrate using CVD.

[0111] The substrate may be a conductive substrate, as described above, including, for example, stainless steel or titanium, but may also be any other suitable substrate, optionally including materials such as silicon, glass, ceramics, or silicon carbide.

[0112] In general, CVD processes involve exposing a substrate to precursor gases. The precursor gases are then reacted on the surface of the substrate to produce the desired structure. The formation of the structure is aided by factors such as the substrate temperature, the pressure in the growth chamber, the presence of an inert carrier gas and / or a reducing gas, and the presence of a growth catalyst. To grow carbon structures, the precursor gas may be a hydrocarbon gas, such as acetylene or methylene, and the reducing gas may be hydrogen gas or ammonia. The carrier gas may be, for example, argon or nitrogen gas.

[0113] The carbon underlayer and the plurality of carbon nanowalls may be grown by a CVD method, such as rapid thermal CVD, hot filament CVD, laser CVD, or combustion CVD. Optionally, the carbon underlayer and the plurality of carbon nanowalls are grown by plasma-assisted CVD, PECVD. PECVD further includes methods such as capacitively coupled plasma PECVD, inductively coupled plasma PECVD, radio frequency plasma PECVD, DC plasma CVD, and microwave plasma PECVD.

[0114] During the growth of the carbon base layer, the substrate temperature is preferably selected to allow the precursor gases to dissociate on the substrate. This facilitates the growth of the carbon base layer. The exact temperature required will depend on the specific CVD method used and the settings of other parameters such as pressure, plasma power, and type of plasma. According to one embodiment, the carbon base layer can be grown using thermal CVD at a substrate temperature of 500-1000°C. According to another embodiment, the carbon base layer can be grown using RF-CVD at a substrate temperature of about 600°C. According to a third embodiment, the carbon base layer can be grown using hot filament CVD at a substrate temperature close to 1000°C.

[0115] Advantageously, once the carbon base layer has been grown, the growth of the carbon nanowalls may be started by changing the growth conditions in the growth chamber. This may involve changing the CVD used, for example from thermal CVD to plasma-assisted CVD. This may involve changing the precursor gas, reducing gas, or inert filler gas, or adjusting the relative concentrations of the different gases. The temperature and pressure may be changed. In the case of PECVD, the plasma power may be adjusted. The type of plasma may be changed, for example from DC plasma to RF plasma, or vice versa.

[0116] According to one embodiment, initiating the growth of the carbon nanowalls may involve changing the precursor gas, for example from acetylene to methane. According to another embodiment, initiating the growth of the carbon nanowalls may involve switching the reducing gas to hydrogen instead of ammonia, or changing the inert filler gas to argon. According to a third embodiment, initiating the growth of the carbon nanowalls may involve setting the temperature above 700° C. or the pressure between 1-10 mbar.

[0117] An advantage of a coating comprising a carbon base layer and a plurality of carbon nanowalls is that both may be grown without the use of a growth catalyst. However, under some circumstances, disposing the substrate may still include depositing a growth catalyst layer or auxiliary layer. In particular, a growth catalyst may be used to grow other types of carbon nanostructures in addition to carbon nanowalls, such as carbon nanofibers or carbon nanotubes.

[0118] The growth catalyst layer comprises a material that is catalytically active and promotes the chemical reactions involved in the formation of the grown nanostructures. For example, an auxiliary layer may be used to control the properties of the grown nanostructures, facilitate vertically oriented growth, or otherwise improve the growth process results. The catalyst layer or auxiliary layer, or both, may comprise materials such as nickel, iron, platinum, palladium, nickel-silicide, cobalt, molybdenum, or gold.

[0119] The help layer or growth catalyst layer may be deposited using methods such as evaporation, plating, sputtering, molecular beam epitaxy, pulsed laser deposition, spin coating, spray coating, or any other suitable method. According to one embodiment, the growth catalyst layer may comprise a uniform layer of growth catalyst material. According to another embodiment, the growth catalyst layer may comprise a plurality of growth catalyst nanoparticles.

Claims

1. 1. A separator element (300) for an electrochemical cell (100, 200), the separator element (300) comprising a conductive substrate (310) and a coating (320) deposited on the conductive substrate, the coating comprising a first portion and a second portion, the first portion comprising a base layer (321) extending along a surface of the conductive substrate (310), and the second portion comprising a plurality of nanostructures (322) extending from the surface of the conductive substrate (310).

2. The separator element (300) of claim 1, wherein the base layer (321) comprises a carbon material.

3. The separator element (300) of claim 2, wherein the base layer (321) comprises one of graphene, graphite, and amorphous carbon.

4. The separator element (300) of any one of claims 1 to 3, wherein the plurality of nanostructures (322) comprises a plurality of carbon nanostructures.

5. The separator element (300) of claim 4, wherein the plurality of carbon nanostructures (322) comprises at least one carbon nanowall.

6. The separator element (300) of claim 4, wherein the plurality of carbon nanostructures (322) comprises any of carbon nanotubes, carbon nanowires, and carbon nanofibers.

7. 4. The separator element (300) of claim 1, wherein the nanostructures contained in the plurality of carbon nanostructures extend parallel to each other along a direction perpendicular to the extension plane of the conductive substrate (310).

8. 4. The separator element (300) of claim 1, wherein the conductive substrate (310) comprises a flow field device (600), the flow field device comprising a plurality of flow channels (610) separated by a plurality of flow channel supports (620), the flow channels being arranged to promote uniform distribution of gas and / or liquid throughout the conductive substrate.

9. The separator element (300) of any one of claims 1 to 3, wherein the separator element is at least partially covered by a protective layer arranged to enhance corrosion resistance.

10. The separator element (300) of claim 9, wherein the protective layer comprises one of titanium, gold, and platinum.

11. Electrolytic cell (200) comprising at least one separator element (300) according to any one of claims 1 to 3.

12. A fuel cell (100) comprising at least one separator element (300) according to any one of claims 1 to 3.

13. A method of manufacturing a separator element (300), said separator element (300) comprising a conductive substrate (310) and a coating (320) deposited on said conductive substrate, said method comprising: disposing the conductive substrate (310) (S1); depositing (S2) a first portion of the coating (320) onto the conductive substrate (310), wherein the first portion includes a base layer (321) extending along a surface of the conductive substrate; and depositing (S3) a second portion of the coating (320) onto the conductive substrate (310), wherein the second portion includes a plurality of nanostructures (322) extending from a surface of the conductive substrate; Contains, A method for manufacturing a separator element (300).

14. 14. The method of claim 13, wherein depositing (S2) the first portion of the coating comprises growing (S21) the base layer (321) using chemical vapor deposition.

15. 15. The method of claim 14, wherein growing the base layer (321) using chemical vapor deposition includes adjusting growth parameters to achieve a desired layer thickness.

16. 16. The method of claim 15, wherein the growth parameter is one of a substrate temperature, a plasma power, a partial pressure of a precursor gas, and a total pressure in a growth chamber.

17. 17. The method of any one of claims 13 to 16, wherein depositing (S3) the second portion of the coating comprises growing (S31) a plurality of nanostructures (322) on the base layer (321) using chemical vapor deposition.

18. 20. The method of claim 17, wherein growing (S31) the plurality of nanostructures (322) using chemical vapor deposition includes adjusting growth parameters to achieve desired nanostructure morphological characteristics.

19. 20. The method of claim 18, wherein the growth parameter is one of a substrate temperature, a plasma power, a partial pressure of a precursor gas, and a total pressure in a growth chamber.

20. 20. The method of claim 17, wherein growing (S31) a plurality of nanostructures (322) using chemical vapor deposition includes growing a plurality of different types of nanostructures, such as nanowalls, nanotubes, nanowires, and nanofibers.

21. 21. The method of claim 20, wherein growing a plurality of nanostructures (322) of different types comprises adjusting growth parameters to grow the different nanostructure types.

22. 17. The method of any one of claims 13 to 16, comprising depositing a growth catalyst layer on the conductive substrate (310) and growing the base layer (321) and / or the plurality of nanostructures (322) on top of the growth catalyst layer.

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