Electrically conductive component, method of coating at least one electrically conductive component and apparatus for coating at least one electrically conductive component

Abstract

The present invention relates to an electrically conductive component, such as a bipolar plate, a half plate, an electrode and a gasket, the electrically conductive component comprising: a metal component; an adhesion layer optionally formed on the metal component; and a carbon coating formed on the adhesion layer, if provided, or on the metal component; wherein the carbon coating comprises an amorphous, at least substantially hydrogen free DLC layer and at least one nanocrystalline graphite component embedded in said amorphous, at least substantially hydrogen free DLC layer; wherein the at least one nanocrystalline graphite component comprises two or more stacked layers; and wherein the nanocrystalline graphite component is aligned perpendicular to and / or at least substantially perpendicular to an axis A defined by an interface between the carbon coating and the metal component or an interface between the carbon coating and the adhesion layer, if provided.

Description

[0001] Electrically conductive component, method of coating at least one electrically conductive component and apparatus for coating at least one electrically conductive component

[0002] The present invention relates to an electrically conductive component, such as a bipolar plate, a half plate, an electrode and a gasket, the electrically conductive component comprising: a metal component; an adhesion layer optionally formed on the metal component; and a carbon coating formed on the adhesion layer, if provided, or on the metal component; wherein the carbon coating comprises an amorphous, at least substantially hydrogen free DLC layer and at least one nanocrystalline graphite component embedded in said amorphous, at least substantially hydrogen free DLC layer; wherein the at least one nanocrystalline graphite component comprises two or more stacked layers; and wherein the at least one nanocrystalline graphite component is aligned perpendicular to and / or at least substantially perpendicular to an axis A defined by an interface between the carbon coating and the metal component or an interface between the carbon coating and the adhesion layer, if provided. The invention further relates to a method of coating at least one electrically conductive component, and to an apparatus for coating at least one electrically conductive component.

[0003] The electrical industry, in particular the automotive industry, is seeking for low cost, highly efficient and high-volume solutions for developing and manufacturing of electrical devices, such as fuel cell stacks or batteries. One of the main components in a fuel cell stack are the bipolar plates (BPP). One of the main components in batteries are the electrodes. Low cost steel can be relatively easily formed mechanically into electrodes, or so-called half plates with good quality flow fields (note, two welded half plates make a bipolar plate, BPP). However, a highly electrically conductive and protective coating on the steel is required to provide a long fuel cell lifetime due to the aggressive operating environment under low pH value and voltage level. For this reason, it is an object of the present invention to provide an electrically conductive component with improved electrical properties, e.g. for a fuel cell stack or a battery. It is a further object of the present invention to provide an electrically conductive component with improved mechanical properties. It is a further object of the present invention to provide an electrically conductive component with improved anti-corrosive properties. It is a further object of the present invention to provide an electrically conductive component with a reduced contact resistance. It is a further object of the present invention to provide a method of fabricating such an electrically conductive component, and an apparatus for carrying out said method. In particular, wherein the method can be carried out in a short time period to produce large volumes of said component.

[0004] This problem is solved by the present invention by providing an electrically conductive component according to claim 1 .

[0005] Such an electrically conductive component, such as a bipolar plate, a half plate, an electrode, a gasket etc., comprises: a metal component; an adhesion layer optionally formed on the metal component; and a carbon coating formed on the adhesion layer, if provided, or on the metal component; wherein the carbon coating comprises an amorphous, at least substantially hydrogen free DLC layer and at least one nanocrystalline graphite component embedded in said amorphous, at least substantially hydrogen free DLC layer; wherein the at least one nanocrystalline graphite component comprises two or more stacked layers; and wherein the at least one nanocrystalline graphite component is aligned perpendicular to and / or at least substantially perpendicular to an axis A defined by an interface between the carbon coating and the metal component or an interface between the carbon coating and the adhesion layer, if provided.

[0006] The electrically conductive component as described herein is a component, e.g., of a fuel cell stack or a battery, that is characterized by a reduced contact resistance (CR), such as interface contact resistance (ICR) or electrical contact resistance (ECR). The electrically conductive component has an improved electrical conductivity, and thus may serve as any component required to effectively conduct an electrical current from and / or to a power source. Furthermore, the herein described electrically conductive component has an improved mechanical stability and corrosion resistance, in particular against a chemical environment surrounding the electrically conductive component during operating. The electrically conductive component is therefore associated with enhanced electrical properties throughout an elongated lifetime, in particular due to the versatile nature of the herein described carbon coating. Non-limiting examples of the electrically conductive component are a bipolar plate; a half plate; an electrode, such as an electrode for a Lithium (Li)-ion battery; a gasket; or a porous transport layer (PTL), such as PTL for proton exchange membrane water electrolyzer (PEMWE).

[0007] The herein described “metal component” may be a component comprising or consisting of a metallic material being at least electrically conductive. Said metallic material may comprise or consist of stainless steel (SS), titanium (Ti), nickel (Ni), magnesium (Mg), niobium (Nb) and / or aluminum (Al), preferably aluminum, stainless steel (SS) or titanium (Ti), more preferably stainless steel (SS). Said metal component may be an alloy comprising at least one of the aforementioned metallic materials as main ingredient. As described herein, the main ingredient forms at least 50% by mass of the total mass of the alloy, preferably at least 60%, 70%, 80% or 90%. For example, the metal component may be a Ti-alloy, such as Ti-AI6-V4. In case the metal component comprises or consists of Ti, the deposition of an adhesion layer may not be necessary due to the outstanding corrosion resistance of Ti, thereby making the manufacture of such components simpler. The metal component may further comprise or consist of aluminum because of its general low cost and low weight.

[0008] The herein described “adhesion layer” is optional. When used, it may be selected from any layer capable of providing improved adhesion between the carbon layer and the metal component. In addition, the adhesion layer preferably improves the corrosion resistance of the metal component. This may, for example, be necessary in case the metal component comprises or consists of a corrosive metal, such as iron. As described above, the use of a metal component comprising or consisting of titanium may render the deposition of an adhesion layer moot from a corrosion protection point of view. Moreover, the adhesion layer may decrease the diffusion of ions from the electrically conductive component into an environment surrounding the electrically conductive component which diffusion could lead to a poisoning of a system comprising the electrically conductive component, e.g., the system being a battery, a fuel cell, or a flow battery. Nonlimiting examples of the material forming the adhesion layer are group IV elements (Ti, Zr and / or Hf), group V elements (V, Nb and / or Ta), and / or group VI elements (Cr, Mo and / or W). The material forming the adhesion layer may be a ceramic material, such as titanium nitride (TiN) or zirconium nitride (ZrN). The adhesion layer may be an adhesion multilayer, i.e. , consisting of at least two stacked adhesion layers as described above, e.g., adhesion multilayer consisting of one layer of TiN and one layer of Ti, wherein TiN is layered on top of Ti or vice versa.

[0009] The herein described “carbon coating” (herein, also referred to as carbon layer) is essential for the electrically conductive component of the present invention. When no adhesion layer is used, the carbon coating may be applied / deposited in the form of a layer, i.e., coated, directly on a surface of the metal component. When an adhesion layer is used, the carbon coating may be applied / deposited in the form of a layer, i.e., coated, on a surface of the adhesion layer that is already deposited on a surface of the metal component. In other words, when an adhesion layer is used, the adhesion layer is arranged between the metal component and the carbon coating. The carbon coating is preferably a continuous carbon coating, i.e., continuous carbon layer.

[0010] The “carbon coating” described herein comprises an amorphous, at least substantially hydrogen free DLC layer and at least one nanocrystalline graphite component embedded (also referred to as “integrated”, “incorporated” or “included”) in said amorphous, at least substantially hydrogen free DLC layer. The use of the carbon coating ensures both, electrical properties of e.g. an active side of a bipolar plate, and mechanical stability and durability of the electrically conductive component. In this connection it should be noted that the carbon coating further provides for corrosion reduction and reduced contact resistance.

[0011] As used herein, the term “at least substantially hydrogen free DLC layer” preferably refers to a DLC layer containing less than 1 at% hydrogen, based on 100 at% of the at least substantially hydrogen free DLC layer, e.g., less than 0.8 at% hydrogen or less than 0.5 at% hydrogen. The term “DLC” means “diamond-like carbon” and is well-known to the skilled person.

[0012] As used herein, the “at least substantially hydrogen free DLC layer” is amorphous. Said amorphous, at least substantially hydrogen free DLC layer preferably comprises a-C layer and / or a ta-C layer. The terms “a-C layer” and “ta-C layer” are well-known to the person skilled in the art. The amorphous, at least substantially hydrogen free DLC layer may be formed from a single amorphous, at least substantially hydrogen free DLC layer. Alternatively, the amorphous, at least substantially hydrogen free DLC layer may be formed from two or more amorphous, at least substantially hydrogen free DLC layers. In the latter case, the layers are arranged on top of the other, i.e. , in a stacked manner. The at least two DLC layers may be at least substantially the same (i.e., varying slightly) or different in their absolute values of the herein described characteristics in comparison to one another. For example, the amorphous, at least substantially hydrogen free DLC layer may be formed from an a-C layer (first DLC layer) and a ta-C layer (second DLC layer) arranged on top of the a-C layer, i.e., the two DLC layers are different from one another, e.g. in their predominant C-C bond types (hybridization types, sp2and / or sp3). In a further example, the amorphous, at least substantially hydrogen free DLC layer may comprise two a-C layers, i.e., the two stacked DLC layers being the same. The latter terminology may be useful in the case that only one of the two a-C layers is embedded with nanocrystalline graphite components.

[0013] Preferably, the herein described carbon coating comprises or consists of at least one amorphous, at least substantially hydrogen free DLC layer embedded with at least one nanocrystalline graphite component. In a preferred embodiment, the carbon coating comprises or consists of two or more amorphous, at least substantially hydrogen free DLC layers, wherein each one of the amorphous, at least substantially hydrogen free DLC layer is embedded with at least one nanocrystalline graphite component.

[0014] The herein described “nanocrystalline graphite component” (also referred to as “nanocrystalline graphite cluster” or “multi-layered graphite cluster”) comprises two or more stacked layers of a carbon-based plane. The nanocrystalline graphite components are uniformly distributed throughout the amorphous, at least substantially hydrogen free DLC layer. The nanocrystalline graphite components may be considered as spatially isolated from one another, while simultaneously being electrically connected to one another, e.g., via the surrounding amorphous, at least substantially hydrogen free DLC layer. The stacked layers may or may not have the same length in a nanocrystalline graphite component.

[0015] Notably, the nanocrystalline graphite component forms a single crystal and is not aggregated with a further nanocrystalline graphite component (e.g., not aggregated into a spherical, or any other shape). The nanocrystalline graphite component is a monocrystalline graphite (also referred to as “single crystal structure”). Microscopically and macroscopically, “monocrystalline graphite” has an orderly and highly oriented graphite crystal structure (graphite cluster) in which carbon-based planes (e.g., graphene) are stacked.

[0016] Each stacked layer is a planar layer of carbon atoms, i.e. , carbon-based plane. In a single layer, carbon atoms may be arranged in a hexagonal or honeycomb-like lattice. The stacked layer is preferably a graphene layer, or at least partially a graphene layer.

[0017] The nanocrystalline graphite component is aligned perpendicular to and / or at least substantially perpendicular to an axis A, wherein the axis A is defined by an interface between the carbon coating and the metal component or an interface between the carbon coating and the adhesion layer, if provided. In other words, each stacked layer forming a nanocrystalline graphite component is aligned perpendicular to and / or at least substantially perpendicular to the axis A. In a preferred embodiment, a total amount of the nanocrystalline graphite components embedded in the amorphous, at least substantially hydrogen free DLC layer is aligned perpendicular to and / or at least substantially perpendicular to the axis A. The axis A (see Fig. 1 ) may alternatively be understood to be defined by a surface of the carbon coating opposite to i) the interface between the carbon coating and the metal component, or ii) the interface between the carbon coating and the adhesion layer, if provided. The nanocrystalline graphite components show a high degree of order with regard to the axis A. The orientation of the nanocrystalline graphite components with regard to the axis A is therefore not random. Said orientation may be determined by any suitable technique known to the skilled person, for example by means of TEM analysis (transmission electron microscopy analysis). This highly ordered orientation of the nanocrystalline graphite components with regard to the axis A further enhances the electrical conductivity of the electrically conductive component described herein. In the herein described electrically conductive component, an electrical current applied thereto can flow to the direction perpendicular to the interface (interface between the carbon coating and the metal component, or interface between the carbon coating and the adhesion layer, if provided), which is a parallel or an at least substantially parallel direction to the carbon-based plane, e.g., graphene plane, in the nanocrystalline graphite components. In contrast thereto e.g., in highly oriented pyrolytic graphite (HOPG), an electrical conductivity in parallel to the graphene plane (2e6 S / m) is 4000 times higher than an electrical conductivity perpendicular to the graphene plane (5e2 S / m).

[0018] The present invention further concerns a method of coating at least one electrically conductive component, in particular at least one electrically conductive component in accordance with the present disclosure, such as a bipolar plate, half plate, an electrode, gasket etc., the method comprising the steps of:

[0019] - providing an uncoated metal component;

[0020] - etching the uncoated metal component; - optionally depositing an adhesion layer on the etched uncoated metal component by means of one of a physical vapor deposition process, an arc physical vapor deposition process, an arc ion plating process, a sputtering process, an EBPVD (electron-beam physical vapor deposition) process, or a Hipims process; and

[0021] - depositing a carbon coating on the adhesion layer if provided or directly on the etched uncoated metal component; wherein the carbon coating is deposited with a layer thickness selected in the range of from 5 to 300 nm at a bias voltage of -20 to -400 V by means of at least one of a physical vapor deposition (PVD) process, such as an arc PVD, a sputtering process, an arc ion plating process, an EBPVD (electronbeam physical vapor deposition) process, and / or a Hipims process.

[0022] By means of such a process, electrically conductive components, in particular, components comprising the herein described carbon coating, can be coated in a comparatively short period of time permitting the production of large volumes. Moreover, comparatively low-cost electrically conductive components can be created by way of such coating processes.

[0023] The carbon coating process may be performed using an inline coating process or a batch process.

[0024] A common method to deposit carbon is sputtering (also referred to as sputter deposition), especially using an unbalanced magnetron (UBM) sputtering setup. These are well-known methods for inline or batch coating as sputtering provides good uniformity, controllability and long target life time which is mostly required for industrial production (for example glass coating machines, PVD lines for display glass coating, and roll-to-roll coating machines).

[0025] Furthermore, UBM provides clean and smooth coatings without any droplets from the target material. On the other hand, arc PVD and arc ion plating, respectively, is a very fast deposition technology but more difficult to implement for robust industrial processing due to the fact that the arc PVD as used in this case is a point source rather than a linear source. Machine complexity and design efforts are also higher in order to deliver a reliable, controllable and uniform industrial process. However, the final solution provides much higher productivity and hence lower cost of ownership for the user compared to the implementation of more conventional UBM technology.

[0026] The step of etching may be a plasma etching process and / or a metal ion etching process. The etching process is typically used in order to remove an oxide layer present on the metal substrate. The oxide layer usually leads to less electrical conductivity and less adhesion of the carbon coating. Hence, its removal is desired in order to increase the electrical conductivity of an electrically conductive component and also the adhesion of the carbon coating to an electrically conductive component.

[0027] The present invention further relates to an apparatus for coating at least one electrically conductive component, such as one or more bipolar plates, one or more half plates, one or more electrodes, one or more gaskets etc., in particular at least one electrically conductive component in accordance with the present disclosure, said apparatus being configured to carry out a method in accordance with the present disclosure, the apparatus being an inline coating system, comprising:

[0028] - a plurality of vacuum chambers arranged in a series one after another;

[0029] - one or more cathodes arranged in at least some of the plurality of vacuum chambers; and

[0030] - one or more fixtures respectively configured to receive a plurality of the uncoated metal components, with the first outer surface and the second outer surface to be coated each facing a cathode, the cathodes being a cathode for at least one of a physical vapor deposition (PVD) process, such as an arc PVD, a sputtering process, an arc ion plating process, an EBPVD (electron-beam physical vapor deposition) process, and / or a Hipims process; wherein said one or more fixtures are arranged to be moved linearly within the respective vacuum chamber and from vacuum chamber to vacuum chamber, wherein each vacuum chamber is configured to carry out a process, preferably a stationary process, with the process being selected from the group of members comprising: heating, evacuating, etching, cooling, depositing an adhesion layer, carbon coating, removing and / or combinations of the foregoing, and wherein the cathodes in the vacuum chamber configured to carry out the carbon coating process are arranged substantially parallel to one another.

[0031] In such an apparatus, the metal component to be carbon coated is arranged between the cathodes. For example, the metal component may be sandwiched between two cathodes arranged opposite to one another, i.e. , the two cathodes being arranged parallel to one another.

[0032] The cathodes are therefore arranged without a pitch along the longitudinal axis of the inline coating system. Such an arrangement was found to provide for a particularly beneficial type of an electrically conductive component.

[0033] The cathode may provide a linear carbon source (e.g., in sputtering process) or may provide point carbon sources (e.g., a cathode bank for point arc sources).

[0034] In a preferred embodiment, the carbon coating is deposited using two or more cathodes, wherein each cathode is equipped with carbon. That way, the thickness of the carbon coating may be increased. For example, a surface of an optionally adhesion layered metal component may be carbon coated using three successively arranged cathodes. Said surface of the optionally adhesion layered metal component may then have a three-times thicker carbon coating thickness than an optionally adhesion layered metal component’s surface being carbon coating by using only one cathode. Of course, if desired, the same arrangement of one, two or more cathodes may additionally be used for a second surface of the optionally adhesion layered metal component.

[0035] By means of such an apparatus the electrically conductive components discussed in the foregoing can be coated with a durable coating. Moreover, such coatings can be produced at high volumes in the inline PVD coating system at attractive costs per part.

[0036] Furthermore, if an Arc-PVD process is used in the inline system, the speed of coating can be increased in comparison to sputtering, thereby reducing equipment complexity and costs for the automotive industry, building industry, aviation industry, stationary applications, heavy duty transportation, marine applications, fork lift trucks etc.

[0037] In the following, preferred embodiments of the present invention are described:

[0038] In a preferred embodiment, a total amount of the at least one nanocrystalline graphite component is embedded in the amorphous, at least substantially hydrogen free DLC layer.

[0039] In another preferred embodiment, the metal component has a first side and a second side, the first side and the second side facing different directions, preferably opposite directions; the adhesion layer is optionally formed on at least one of the first side and the second side of the metal component; the carbon coating is formed on the first side and the second side of the metal component and / or of the adhesion layer if provided. In other words, the metal component may be coated on two (2) or more sides (i.e. , surfaces) thereof. It is preferred that the two (2) sides face opposite directions, e.g., in case the electrically conductive component is a bipolar plate. It is also possible that all surfaces of a metal component are coated as described herein, e.g., in case the electrically conductive component is an electrode.

[0040] In another preferred embodiment, the carbon coating on the first side of the metal component, and the carbon coating on the second side of the metal component are similar or different to one another, the first side and / or the second side of the metal component being optionally adhesion layered. For example, the carbon coating on the first side of the metal component and the carbon coating on the second side of the metal component may be similar or different to one another with regard to a thickness of the carbon coating; the composition of the amorphous, at least substantially hydrogen free DLC layer (e.g., kind and number of DLC layers, hybridization ratio of sp2to sp3); the degree of embedding with nanocrystalline graphite components; the orientation of the nanocrystalline graphite components along the axis A; etc.

[0041] In a preferred embodiment, the amorphous, at least substantially hydrogen free DLC layer comprises one or more ta-C layers, and / or one or more a-C layer.

[0042] In another preferred embodiment, a proportion of the sp2to sp3content of the amorphous, at least substantially hydrogen free DLC layer lies in the range of 30 - 80% sp2to 70 - 20% sp3. A ratio of the sp2to sp3content in the amorphous, at least substantially hydrogen free DLC layer may lie in a range of from 30% sp21 70% sp3to 80% sp2120% sp3. In a more preferred embodiment, the sp2content of the amorphous, at least substantially hydrogen free DLC layer is higher than 40% sp2, more preferably higher than 60%, based on 100% of the amorphous, at least substantially hydrogen free DLC layer. These are beneficial characteristics of the amorphous, at least substantially hydrogen free DLC layer. The content of sp2and sp3of the amorphous, at least substantially hydrogen free DLC layer may be determined by any suitable technique known to the skilled person, for example by means of X-ray Photoelectron Spectroscopy (XPS).

[0043] In another preferred embodiment, the amorphous, at least substantially hydrogen free DLC layer is a DLC layer containing less than 1 at% hydrogen based on 100 at% of the amorphous, at least substantially hydrogen free DLC layer. The hydrogen content of the amorphous, at least substantially hydrogen free DLC layer may be determined by any suitable technique known to the skilled person, for example by means of Secondary-Ion Mass Spectrometry (SIMS).

[0044] In another preferred embodiment, the at least one nanocrystalline graphite component comprises two (2), three (3), four (4), five (5), ten (10), fifteen (15) or more stacked layers. That is, each one of the at least one nanocrystalline graphite component may be formed from two (2), three (3), four (4), five (5), ten (10), fifteen (15) or more stacked layers. In a more preferred embodiment, the at least one nanocrystalline graphite component comprises three (3) or more stacked layers. Notably, in the same DLC layer, a nanocrystalline graphite component may have the same and / or different number of stacked layers. For example, a DLC layer may comprise an amount X of nanocrystalline graphite components having three (3) stacked layers, and further an amount Y of nanocrystalline graphite components having five (5) stacked layers, wherein X < Y. The number of stacked layers of the nanocrystalline graphite component preferably lies in the range of from 2 to 100, and more preferably of from 2 to 80, from 2 to 60, from 2 to 50, from 2 to 30, from 2 to 20, from or 2 to 15, from 2 to 10 and / or from 2 to 5. The number of stacked layers of the nanocrystalline graphite components may be determined by any suitable technique known to the skilled person, for example by means of TEM analysis (transmission electron microscopy analysis). Nanocrystalline graphite components having a number of stacked layers as mentioned above can form a uniform distribution throughout the amorphous, at least substantially hydrogen free DLC and may therefore enhance the electrical conductivity of the electrically conductive component.

[0045] In another preferred embodiment, the at least one nanocrystalline graphite component has an aspect ratio of from 1 :1 to 1 :20. In a more preferred embodiment, the at least one nanocrystalline graphite component has an aspect ratio of 1 :5, 1 :1.1 or 1 :1. The aspect ratio is determined from a side view of the nanocrystalline graphite components, i.e. , view onto a total number of stacked layers forming a nanocrystalline graphite component. As used herein, the “aspect ratio” is defined as the ratio of the length (L) to the width (W) of the nanocrystalline graphite component, wherein length (L) > width (W). Given that length (L) > width (W), the length (L) of a nanocrystalline graphite component may be defined as a sum of the interlayer distances between the total number of stacked layers forming a nanocrystalline graphite component. For example, a nanocrystalline graphite component being formed from eight (8) stacked layers, each having an interlayer spacing of 0.32 nm to the adjacent layer, may have a length (L) of about 2.24 nm (7 x 0.32 nm). Given that length (L) > width (W), the width (W) of a nanocrystalline graphite component may be defined by the width of the stacked layer having the highest width in the nanocrystalline graphite component. The length (L), width (W), and the aspect ratio of the nanocrystalline graphite components may be determined by any suitable technique known to the skilled person, for example by means of TEM analysis (transmission electron microscopy analysis).

[0046] Nanocrystalline graphite components having an aspect ratio as mentioned above can form a uniform distribution throughout the amorphous, at least substantially hydrogen free DLC and therefore may enhance the electrical conductivity of the electrically conductive component.

[0047] In another preferred embodiment, the stacked layers of the nanocrystalline graphite component have an interlayer spacing of about 0.1 nm to about 2 nm, preferably of from about 0.2 nm to about 0.6 nm, and more preferably of about 0.3 nm (about meaning ± 0.05 nm). The interlayer spacing is the distance between two adjacent layers in a nanocrystalline graphite component. An interlayer spacing of about 0.3 nm corresponds to the lattice spacing of the graphite (0002) plane. The interlayer spacing may be measured by means of any suitable method known to the skilled person, e.g., by using TEM. Such spacings have been found to provide particularly beneficial nanocrystalline graphite components.

[0048] In another preferred embodiment, the nanocrystalline graphite component being aligned at least substantially perpendicular to the axis A is a nanocrystalline graphite component being inclined ± 30 degrees or less with regard to an axis P perpendicular to the axis A. In a more preferred embodiment, said inclination is ± 20 degrees or less, ± 15 degrees or less, ± 10 degrees or less, or ± 5 degrees or less. These inclination degrees prevent a random orientation of the nanocrystalline graphite component along the axis A. The nanocrystalline graphite components are perpendicular to the axis A, and / or at least substantially perpendicular to the axis A. The latter (substantially perpendicular) means that the nanocrystalline graphite component is inclined ± 70 degrees or more with regard to the axis A, i.e. , it is inclined ± 30 degrees or less with regard to the axis P perpendicular to the axis A (see Fig. 11 ). The carbon coating of the herein described invention may therefore have a series of nanocrystalline graphite components of which some part is aligned perpendicular to the axis A, of which some part is inclined ± 30 degrees with regard to the axis P, of which some part is inclined ± 15 degrees with regard to the axis P, and so on. This highly ordered orientation of the nanocrystalline graphite components with regard to the axis A further enhances the electrical conductivity of the electrically conductive component described herein.

[0049] In another preferred embodiment, based on the total amount (100 %) of the carbon coating, a ratio of an amount of the amorphous, at least substantially hydrogen free DLC layer to an amount of the at least one nanocrystalline graphite component lies in the range of from 20 % to 90 %. In a more preferred embodiment, it ranges from 40% to 80%, even more preferably from 30 % to 70 %. Such ratios have been found to provide particularly beneficial carbon coatings for the electrically conductive component with regard to improved electrical conductivity and reduced contact resistance.

[0050] In another preferred embodiment, the carbon coating has a thickness of from 5 to 300 nm. In a more preferred embodiment, said thickness lies in the range of from 15 to 150 nm. In an even more preferred embodiment, said thickness lies in the range of from 25 to 100 nm. Such carbon coatings have been found to be mechanically stable and also resistant to chemical environments, e.g., present in the fuel cell stack.

[0051] In another preferred embodiment, the electrically conductive component comprises the adhesion layer, wherein the adhesion layer comprises at least one material selected from the group of members consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, nickel, cobalt, magnesium, gadolinium, nitrogen, carbon, boron, aluminum, and combinations of the foregoing. In a more preferred embodiment, the adhesion layer comprises or consists of titanium. Such materials have been found to provide a particularly beneficial type of adhesion layer. In another preferred embodiment, the amorphous, at least substantially hydrogen free DLC layer has an Argon content of less than 5 at% Argon, based on 100 at% of the amorphous, at least substantially hydrogen free DLC layer. In a more preferred embodiment, the Argon content is less than 2 at% Argon, more preferably of less than 1 at% Argon. For example, a sputtered carbon coating may have an argon content of 2 at% Argon, based on 100 at% of the amorphous, at least substantially hydrogen free DLC layer. A carbon coating formed by an arc- PVD process may have an Argon content less than 2 at% Argon, based on 100 at% of the amorphous, at least substantially hydrogen free DLC layer. Carbon coatings comprising such an amorphous, at least substantially hydrogen free DLC layer may have an enhanced quality, for example due to an improved corrosion stability.

[0052] In another preferred embodiment, the amorphous, at least substantially hydrogen free DLC layer has an iron content of less than 5 at%, based on 100 at% of the amorphous, at least substantially hydrogen free DLC layer. In a more preferred embodiment, the iron content is less than 1 at%, even more preferably less than 0,1 at%. Carbon coatings comprising such an amorphous, at least substantially hydrogen free DLC layer may have an enhanced quality for the herein described applications.

[0053] In another preferred embodiment, the electrically conductive component has a contact resistance (CR) of 0.01 0 cm2or less measured at a contact pressure of 1 MPa. In a more preferred embodiment, the contact resistance is 0.008 0 cm2or less, 0.005 0 cm2or less, or 0.003 0 cm2or less measured at a contact pressure of 1 MPa. The lower limit may be 0.001 0 cm2or more measured at a contact pressure of 1 MPa. Depending on the use of the electrically conductive component, the CR may be ICR (interface contact resistance, e.g., in a fuel cell) or ECR (electrical contact resistance, e.g., in a battery). An electrically conductive component having such a contact resistance has been found to have particularly beneficial electrical properties. Herein, all of the preferred embodiments and features described above or in the claims for the electrically conductive component itself apply mutatis mutandis to the method of coating at least one electrically conductive component.

[0054] According to a further aspect, the present invention relates to a method of coating at least one electrically conductive component, in particular at least one electrically conductive component in accordance with the present disclosure, such as a bipolar plate, half plate, an electrode, gasket etc.

[0055] In a preferred embodiment, the uncoated metal component has a first side (i.e., first surface) and a second side (i.e., second surface), the first side and the second side facing different directions, for example, opposite directions; the first side and the second side of the uncoated metal component are etched; at least one of the first side and the second side of the etched uncoated metal component is optionally deposited with an adhesion layer; and the first side and the second side being adhesion layered if provided and / or being etched are deposited with a carbon coating. In other words, the uncoated metal component may be coated on two (2) or more sides (i.e., surfaces) thereof. It is preferred that two (2) sides facing opposite directions are coated, e.g., in case the electrically conductive component is a bipolar plate. It is also possible that all surfaces of a metal component are coated as described herein, e.g., in case the electrically conductive component is an electrode.

[0056] In another preferred embodiment, during the step of carbon coating, the metal component and the adhesion layer, if provided, are subjected to a continuous (i.e., stable) heating. The heating essentially arises from the evaporation of the carbon at the cathode during the carbon coating step so that ions are formed and transferred to the metal component and the adhesion layer, if provided, thereby resulting in heating of the metal component and the adhesion layer, if provided. In other words, during the step of carbon coating, the metal component and the adhesion layer, if provided, have a continuous (i.e., stable) temperature gradient resulting from said heating. The term “continuous temperature gradient” as used herein is to be understood as a homogenous temperature profile of the entire optionally adhesion layered metal component during the carbon coating step. As used herein, during the step of carbon coating on both sides of the metal component, the heating and the resulting temperature gradient may be instable or noncontinuous in case the metal component and the adhesion layer, if provided, are subjected to successive carbon coating steps on each side, i.e. , carbon coating on first side and then carbon coating on second side of the metal component and the adhesion layer, if provided.

[0057] In another preferred embodiment, the step of etching comprises a plasma etching process, preferably an argon plasma etching process, carried out for a period ranging between 0.1 and 60 minutes, in particular 0.5 to 5 min, with a bias voltage lying in the range of from -50 to -1200 V, preferably of from -150 to -350 V. The plasma etching process may be necessary in case one should desire to reduce or avoid an oxide layer on the metal component’s surface. The plasma etching process as described above can reduce about 20 nm (at least 10 nm) of the metal component’s surface potentially comprising the oxide layer. Etching away of the oxide layer can decrease the ICR but also degrade an adhesion of the adhesion layer, if provided. In a more preferred embodiment, said plasma etching process is an argon plasma etching process and the bias voltage being between -150 to -350 V.

[0058] In another preferred embodiment, the step of etching comprises a metal ion etching process carried out for a period ranging between 0.1 and 60 minutes, in particular 0.5 to 5 min, with a bias voltage lying in the range of from -50 to -1200 V, preferably of from -600 V to -1200 V. The metal ion etching process may be necessary in case one should desire to reduce or avoid an oxide layer on the metal component’s surface. The metal ion etching process as described above can reduce about 20 nm (at least 10 nm) of the metal component’s surface potentially comprising the oxide layer. Etching away of the oxide layer can decrease the ICR and increase an adhesion of the adhesion layer, if provided. In another preferred embodiment, the bias voltage during the step of etching (e.g., plasma etching process or metal ion etching process) comprises d.c., unipolar and / or bipolar.

[0059] In another preferred embodiment, the method further comprises the step of depositing the adhesion layer, and wherein said step comprises depositing an adhesion layer having a thickness in the range of from 25 to 500 nm at a bias voltage lying in the range of from -0 V to -350V. In a more preferred embodiment, the adhesion layer has a thickness in the range of from 30 to 300 nm, even more preferably from 40 to 200 nm, from 50 to 150 nm, and further preferably from 50 to 100 nm. For example, in case the adhesion layer comprises titanium generally having high anti-corrosive properties, it may be sufficient to select a smaller thickness, e.g., of 100 nm (± 5 nm). This may simultaneously be cost-effective.

[0060] In another preferred embodiment, the method further comprises the step of depositing the adhesion layer, and wherein the adhesion layer is deposited using an arc-PVD process. In a more preferred embodiment, in such a case, the bias voltage lies in the range of from -20V to -400 V.

[0061] In another preferred embodiment, the method further comprises the step of depositing the adhesion layer, and wherein adhesion layer is deposited using a sputtering and / or HIPIMS process. In a more preferred embodiment, in such a case, the bias voltage lies in the range of from -20 V to -350 V.

[0062] In another preferred embodiment, the method further comprises the step of depositing the adhesion layer, and wherein the adhesion layer comprises at least one of Ti, Cr, V, Ta, Ni, Co, Nb, Mg, B, Gd, Zr, TiN, CrN, NbN, ZrN, and combinations thereof. In a more preferred embodiment, the adhesion layer comprises Ti and / or Cr due to their high anti-corrosive properties.

[0063] In another preferred embodiment, the carbon coating comprises an amorphous, at least substantially hydrogen free DLC layer and at least one nanocrystalline graphite component embedded in said amorphous, at least substantially hydrogen free DLC layer.

[0064] In another preferred embodiment, the amorphous, at least substantially hydrogen free DLC layer comprises either a top layer having a dopant present therein, or includes a dopant throughout the amorphous, at least substantially hydrogen free DLC layer. It has been found that the use of a dopant provides for a highly beneficial carbon coating with regard to its electrical properties, anti-corrosive properties, mechanical stability, in particular at higher voltages.

[0065] In another preferred embodiment, the dopant is selected from the group of members consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, nitrogen, boron, silicon, and combinations of the foregoing. In a more preferred embodiment, the dopant is boron and / or silicon. Using e.g., boron as dopant may increase thermal resistance and electrical conductivity while decreasing internal stress of the electrically conductive component described herein.

[0066] In another preferred embodiment, a percentage of the dopant is 0.2 to 10 at%, based on 100 at% of the amorphous, at least substantially hydrogen free DLC layer or of the top layer thereof comprising the dopant. In a more preferred embodiment, a percentage of the dopant is 0.5 to 6 at%, based on 100 at% of the amorphous, at least substantially hydrogen free DLC layer or of the top layer thereof comprising the dopant. In an even more preferred embodiment, a percentage of the dopant is 2 to 4 at%.

[0067] In another preferred embodiment, the method is conducted in a vacuum chamber, such as of an inline coating system or a batch coating system, and a temperature of said vacuum chamber is regulated to a temperature in the range of from 23 °C to 400 °C, in particular of 23 °C to 250 °C, during the step of depositing a carbon coating. In this way, particularly hard and durable layer structures can be formed. Also, the growth of nanocrystalline, graphite components as described herein may be further enhanced. In another preferred embodiment, the carbon coating is deposited with a layer thickness lying in the range of from 5 to 300 nm. In an even more preferred embodiment, the carbon coating is deposited with a layer thickness lying in the range of from 15 to 150 nm, 25 to 100 nm, or 40 to 80 nm. Such carbon coatings have been found to be mechanically stable and also resistant to the chemical environments present in the operating system, e.g., battery or fuel cell stack.

[0068] In another preferred embodiment, the carbon coating is deposited at a bias voltage lying in the range of from -20 V to -400 V. Such carbon coatings have been found to be mechanically stable and also resistant to the chemical environments present in the operating system, e.g., battery or fuel cell stack.

[0069] In another preferred embodiment, the carbon coating is deposited using the arc physical vapor deposition process or the arc ion plating process, and wherein an arc cathode current preferably lies in the range of from 40 to 150 A, more preferably of from 50 to 80 A. These ranges are typically used on round point sources with a target diameter of 102 mm. Using a higher current than described above may result in overheating, and thus reduce the herein described effects of the electrically conductive component.

[0070] In another preferred embodiment, the carbon coating is deposited using the HIPIMS process, and wherein the target density is 70 Watt / cm2or more. In a more preferred embodiment, the target density is 100 Watt / cm2or more, 150 Watt / cm2or more, or 200 Watt / cm2or more. For example, the power intensity in an HIPIMS process may be 220 W / cm2(12.5 x 99.1 cm the target size) using pulse peak may be 272 kW during ta-C with 12 kW power on a carbon target.

[0071] In a preferred embodiment, the carbon coating is deposited within a time interval lying in the range of from 0.1 to 15 min. In a more preferred embodiment, said time interval lies in the range of from 0.5 to 5 min. Such a method may enable the production of large volumes of electrically conductive components within in a short time period. The invention will now be described in further detail and by way of example only with reference to the accompanying drawings and figures as well as by various examples of the electrically conductive component and method of the invention. In the drawings there are shown:

[0072] Fig. 1 a schematic sectional view of an electrically conductive component of the present invention;

[0073] Fig. 2 a schematic sectional view of a further electrically conductive component of the present invention;

[0074] Fig. 3 a schematic sectional view of a further electrically conductive component of the present invention;

[0075] Fig. 4 a schematic sectional view of a further electrically conductive component of the present invention;

[0076] Fig. 5 a schematic sectional view of a further electrically conductive component of the present invention;

[0077] Fig. 6 a schematic sectional view of a further electrically conductive component of the present invention;

[0078] Fig. 7 high-magnification bright-field TEM image of a sectional view of an electrically conductive component of the present invention;

[0079] Fig. 8 high-magnification bright-field TEM image of a sectional view of a reference component (State of the Art);

[0080] Fig. 9 enlarged view on the reference component in Fig. 8 (State of the Art);

[0081] Fig. 10 a schematic sectional view of a carbon coating of the present invention;

[0082] Fig. 11 enlarged view on a nanocrystalline graphite component in Fig 10;

[0083] Fig. 12 high-magnification bright-field TEM image of a sectional view of a carbon coating presented in Fig. 7;

[0084] Fig. 13 high-magnification bright-field TEM image of a sectional view of the electrically conductive component (bottom images), and FFT images thereof (top images and middle images) presented in Fig. 7;

[0085] Fig. 13a visualization of inclination degree and interlayer distance from data obtained in Fig. 13; Fig. 14 high-magnification bright-field TEM image of a sectional view of the reference component (bottom images), and FFT images thereof (top images and middle images) presented in Fig. 8 (State of the Art);

[0086] Fig. 14a visualization of inclination degree and interlayer distance from data obtained in Fig. 14 (State of the Art);

[0087] Fig. 15 comparison of the reference carbon coating (left) shown in Fig. 8 and the carbon coating shown in Fig. 7 (right);

[0088] Fig. 16 superimposed Raman spectra of the reference carbon coating 24 shown in Fig. 8 and the carbon coating 16 shown in Fig. 7 (x axis: counts in a.u.; y-axis: wavelength in nm);

[0089] Fig. 17 high-magnification bright-field TEM image of a sectional view of an electrically conductive component of the present invention (top image), and FFT images thereof (bottom images) obtained from a batch coating process;

[0090] Fig. 18 high-magnification bright-field TEM image of a sectional view of a reference component (top images), and FFT images thereof (bottom images) obtained from a batch coating process (State of the art);

[0091] Fig. 19 inline coating apparatus of the present invention; and

[0092] Fig. 20 inline coating apparatus in accordance with the state of the art.

[0093] In the following, the same reference numerals will be used for parts having the same or equivalent function. Any statements made having regard to the direction of a component are made relative to the position shown in the drawing and can naturally vary in the actual position of application.

[0094] Fig. 1 shows a schematic sectional view of an electrically conductive component 10. The electrically conductive component 10 is formed from two parts: a metal component 12 and a carbon coating 16. The carbon coating 16 is deposited on one side of the metal component 12, in particular covering an entire surface of said side. The carbon coating 16 comprises a single amorphous, at least substantially hydrogen free DLC layer embedded with nanocrystalline graphite components (not shown). In this embodiment, the metal component 12 may be or may comprise titanium. Fig. 2 shows a schematic sectional view of a further electrically conductive component 10’. The electrically conductive component 10 is formed from three parts: a metal component 12, an adhesion layer 14 and a carbon coating 16. The metal component 12, the adhesion layer 14, and the carbon coating 16 are arranged in a stacked manner, wherein the adhesion layer 14 is in-between. Similar to Fig. 1 , only one side of the metal component is coated. The adhesion layer 14 preferably covers an entire surface of said side. And the carbon coating 16 preferably covers an entire surface of a side of the adhesion layer 14 opposite to the metal component 12. The carbon coating 16 comprises a single amorphous, at least substantially hydrogen free DLC layer embedded with nanocrystalline graphite components (not shown). In this embodiment, the metal component 12 may be or may comprise titanium and / or stainless steel.

[0095] Fig. 3 shows a schematic sectional view of a further electrically conductive component 10a. This component 10a is almost similar to the component 10 in Fig. 1 with the difference that the carbon coating 16 of the component 10a comprises two different types of an amorphous, at least substantially hydrogen free DLC layer 18a, 18b. For example, the DLC layer 18a is an a-c DLC layer, and the DLC layer 18b is a ta-c DLC layer. Notably, at least one of the DLC layers 18a, 18b is embedded with nanocrystalline graphite components (not shown). Preferably, both 18a and 18b are embedded with nanocrystalline graphite components (not shown). It is also possible that both DLC layers 18a, 18b are a-c DLC layers or ta-c DLC layers, however, wherein each one contains a different amount of nanocrystalline graphite components (not shown).

[0096] It is also possible that the carbon coating 16 in Fig. 3 may be formed from three (3) or more amorphous, at least substantially hydrogen free DLC layers (18a, 18b, 18c etc.; not shown). In such a case, at least one of said DLC layer is embedded with nanocrystalline graphite components (not shown). Preferably, each one of the DLC layer is embedded with nanocrystalline graphite components (not shown). Fig. 4 shows a schematic sectional view of a further electrically conductive component 10b. This component 10b is almost similar to the component 10’ in Fig. 2 with the difference that the carbon coating 16 of the component 10a comprises two different types of an amorphous, at least substantially hydrogen free DLC layer 18a, 18b. For example, the DLC layer 18a is an a-c DLC layer, and the DLC layer 18b is a ta-c DLC layer. Notably, at least one of the DLC layers 18a, 18b is embedded with nanocrystalline graphite components (not shown). Preferably, both 18a and 18b are embedded with nanocrystalline graphite components (not shown). It is also possible that both DLC layers 18a, 18b are a-c DLC layers or ta-c DLC layers, however, wherein each one contains an amount of nanocrystalline graphite components (not shown).

[0097] It is also possible that the carbon coating 16 in Fig. 4 may be formed from three (3) or more amorphous, at least substantially hydrogen free DLC layers (18a, 18b, 18c etc.; not shown). In such a case, at least one of said DLC layer is embedded with nanocrystalline graphite components (not shown). Preferably, each one of the DLC layer is embedded with nanocrystalline graphite components (not shown).

[0098] Fig. 5 shows a schematic sectional view of a further electrically conductive component 10”. The arrangement and composition of the component 10” is almost similar to the component 10 shown in Fig. 1 with the difference that component 10” is coated on two sides (i.e., surfaces) of the metal component facing opposite directions. The component 10” may therefore be a symmetric electrically conductive component. The carbon coatings 16, 16’ in component 10” have the same thickness. However, depending on the use of the component 10”, the carbon coatings 16, 16’ in such a component 10” may be different. For example, both coatings 16, 16’ may be different in their thickness, hardness, and / or composition (not shown). Both coatings 16, 16’ may alternatively have the same thickness, hardness, and / or composition. Such a component 10” may be used in a fuel cell stack, in particular as a bipolar plate (not shown).

[0099] Notably, the electrically conductive component 10” shown in Fig. 5 may contain a carbon coating 16 comprised of two different types of an amorphous, at least substantially hydrogen free DLC layer 18a, 18b - similar to the component 10a in Fig. 3. At least some parts of the description of Fig. 3 therefore may apply to component 10”.

[0100] Fig. 6 shows a schematic sectional view of a further electrically conductive component 10”’. The arrangement and composition of the component 10”’ is almost similar to the component 10’ shown in Fig. 2 with the difference that component 10’” is coated on two sides of the metal component facing opposite directions. The component 10’” may therefore be a symmetric electrically conductive component. The description regarding Fig. 3 may apply to the component 10’”. As shown in Fig. 4, the adhesion layers 14, 14’ in component 10’” have the same thickness. However, depending on the use of the component 10”, the adhesion layers 14, 14’ in such a component 10’” may be different. For example, both adhesion layers 14, 14’ may be different in their thickness, and / or composition. Both adhesion layers 14, 14’ may alternatively have the same or different thickness, and / or composition. Such a component 10’” may be used in a fuel cell stack, in particular as a bipolar plate (not shown).

[0101] Notably, the electrically conductive component 10’” shown in Fig. 6 may contain a carbon coating 16 comprised of two different types of an amorphous, at least substantially hydrogen free DLC layer 18a, 18b - similar to the component 10b in Fig. 4. At least some parts of the description of Fig. 4 therefore may apply to component 10’”.

[0102] Fig. 7 shows a high-magnification bright-f ield TEM image of a sectional view of an electrically conductive component 10’”. Said component 10’” is formed from a metal component 12 (not shown), two adhesion layers 14 (shown), 14’ (not shown) facing opposite directions, and two carbon coatings 16 (shown), 16’ (not shown) facing opposite directions, as schematically shown in Fig. 6. The carbon coating 16 shows a uniform, homogenous structure (i.e., composition) in the nanometer range. This indicates that the nanocrystalline graphite components 20 are embedded throughout the amorphous, at least substantially hydrogen free DLC layer 18 of the carbon coating 16. The electrically conductive component in Fig. 7 has been found to have good electrical and mechanical properties, and low contact resistance values, i.e. , 0.002 0 cm2or less.

[0103] Notably, in the production of the electrically conductive component 10”’ shown in Fig. 7, the temperature profile of the adhesion layered metal component was homogenous during the carbon coating step on both sides.

[0104] For the production of the electrically conductive component 10”’ shown in Fig. 7, an inline coating apparatus was used, wherein the arc cathodes were facing each other (i.e., arranged parallel to each other), for example as shown in Fig. 19. The metal component 12 was etched by using an argon plasma etching process carried out for a period ranging of 3 min, with a bipolar bias voltage lying in the range of from -150 to -350 V. The etching process was performed by subsequently etching the first side and the second side of the metal component 12. No quality loss of the electrically conductive component 10’” was observed when performing the etching process simultaneously on both sides of the metal component 12 (not shown). The adhesion layers 14, 14’ were then deposited by using a sputtering process at a bias voltage lying in the range of from -20 V to -350 V. The thickness of the adhesion layer 14 is approximately 100 nm. The deposition of the adhesion layers 14, 14’ was performed simultaneously on the first side and the second side of the metal component 12. No quality loss of the electrically conductive component 10’” was observed when performing the adhesion layering process subsequently on both sides of the metal component 12 (not shown). The carbon coatings 16, 16’ were deposited by using an arc PVD process at a bias voltage of from -20V to -400 V in an, wherein both sides of the adhesion layered metal component (14, 14’) were simultaneously subjected to a step of carbon coating.

[0105] Fig. 8 shows a high-magnification bright-f ield TEM image of a sectional view of a reference component 22. Said reference component 22 is formed from a metal component 12 (not shown), two adhesion layers 14 (shown), 14’ (not shown) facing opposite directions, and two reference carbon coatings 24 (shown), 24’ (not shown) facing opposite directions, as schematically shown in Fig. 6 (however including reference carbon coatings). The reference carbon coating 24 shows non-uniform, non-homogeneous structure (i.e. , composition) in the nanometer range, as compared to the carbon coating 16 in Fig. 7. Instead, the reference carbon coating 24 comprises two separate layers, an amorphous carbon layer 26 and graphite crystal layer 28. The amorphous carbon layer 26 is visibly darker than the graphite crystal layer 28, and may therefore be differentiated by means of a boundary 30; see also enlarged view of Fig. 8 in Fig. 9. This stacked (i.e., not embedded) arrangement of the amorphous carbon layer 26 and the graphite crystal layer 28 is also evidence by means of Fast Fourier Transform (FFT) imaging, as described further below.

[0106] The reference component in Fig. 8 has been found to have poor electrical and mechanical properties, and high contact resistance values as compared to the coating shown in Fig. 7, i.e., the reference component in Fig. 8 having a contact resistance value of » 0.005 0 cm2

[0107] Notably, in the production of the reference component 22 shown in Fig. 8 and Fig. 9, the temperature profile of the adhesion layered metal component was not homogenous during the carbon coating step.

[0108] Fig. 10 shows a schematic sectional view of a carbon coating 16. The carbon coating 16 comprises an amorphous, at least substantially hydrogen free DLC layer 18, wherein nanocrystalline graphite components 20 are embedded therein. A portion of the total nanocrystalline graphite components 20 is aligned perpendicular to the axis A, as shown for components 20a. In addition (shown) or alternatively (not shown) thereto, a portion of the total nanocrystalline graphite components 20 is inclined with regard to an axis P perpendicular to the axis A, as shown for component 20b having an inclination degree of +15 degrees, and component 20c having an inclination degree of -15 degrees. Of course, the carbon coating may comprise nanocrystalline graphite components having other inclination degrees selected in the range of ± 30 degrees or less (not shown). Each nanocrystalline component shown in Fig. 10 is formed from five (5) stacked layers.

[0109] Fig. 11 shows an enlarged view on an inclined nanocrystalline graphite component 20b in Fig 10. The inclination degree 32 of each nanocrystalline graphite component may be determined with regard to the axis P perpendicular to axis A, as shown therein. Of course, the inclination degree of a nanocrystalline graphite component 20a is 0 degrees as it is perpendicular to the axis A. Furthermore, Fig. 11 shows an interlayer distance 34 between two stacked layers of the nanocrystalline graphite component 20b. The interlayer distance (i.e. , spacing) 34 is preferably 0.3 nm which corresponds to the lattice spacing of the graphite (0002) plane.

[0110] Fig. 12 shows a high-magnification bright-field TEM image of a sectional view of the carbon coating 16 presented in Fig. 7. The TEM image shows a plurality of island-like components in the form of stacked lines, i.e., a series of localized dashed lines. Each one of these components are assigned to a nanocrystalline graphite component 20. Three of these components 20a, 20b, 20c are highlighted in Fig. 12 for the sake of a better visualization. As can be seen, the components 20a, 20b, 20c are formed from four (4) stacked layers. The nanocrystalline graphite component 20a is aligned perpendicular to the axis A. The nanocrystalline graphite components 20b, 20c are inclined with regard to the axis P perpendicular to the axis A. As shown, the inclination degree is ±15 degrees.

[0111] Fig. 13 shows a high-magnification bright-field TEM image of a sectional view of an electrically conductive component (bottom images), and FFT images thereof (top images and middle images) presented in Fig. 7. The electrically conductive component was carbon coated on two opposite sides using an inline coating process, as already outlined above with regard to Fig. 7. The left-hand images show a TEM image and two FFT images of the carbon coating 16 on the first side of the metal component 12. The right-hand images show a TEM image and two FFT images of the carbon coating 16’ on the second side of the metal component 12. The Fast Fourier Transform (FFT) images of both sides show that an upper portion (large, dashed rectangular) and a lower portion (small, continuous rectangular) of the carbon coatings 16, 16’ comprise an amorphous, at least substantially hydrogen free DLC layer embedded with nanocrystalline graphite components. Said embedding is therefore shown in a uniform manner throughout the DLC layer. Moreover, the increased signals in the FFT images at the left and right from the center point indicate a periodicity of C lattice planes perpendicular to the surface (spacing is 0.32 ± 0.02 nm). The arc-shaped appearance of the FFT spots is related to a variation in orientation of the C lattice planes.

[0112] Fig. 13a shows a visualization of inclination degree and interlayer distance from data obtained in Fig. 13. The entire amorphous, at least substantially hydrogen free DLC layer (i.e. , top portion / layer and bottom portion / layer) is embedded with highly ordered nanocrystalline graphite components.

[0113] Fig. 14 shows a high-magnification bright-field TEM image of a sectional view of the reference component (bottom images), and FFT images thereof (top images and middle images) presented in Fig. 8. The electrically conductive component was carbon coated on two opposite sides using an inline coating process, as already outlined above with regard to Fig. 8. The left-hand images show a TEM image and two FFT images of the reference carbon coating 24 on the first side of the metal component 12. The right-hand images show a TEM image and two FFT images of the carbon coating 24’ on the second side of the metal component 12. The Fast Fourier Transform (FFT) images of both sides show that an upper portion (dashed rectangular) is composed differently than a lower portion (continuous rectangular) of the carbon coatings 24, 24’. As compared to Fig. 13, the FFT images of the upper portion of the C layer show concentrated spots and are not arc-shaped which indicates no variation in orientation of the C lattice planes. The lower part of the C layer shows less pronounced spots in the FFT images, indicating an amorphous nature of the layer. To sum up, the obtained FFT images show that the reference component 22 is composed of a lower amorphous carbon layer 26 and an upper graphite crystal layer 28, i.e., a stacked arrangement of layers 26 and 28. The graphite crystals in the layer 28 are therefore not embedded in the amorphous carbon layer 26. Fig. 14a shows a visualization of inclination degree and interlayer distance from data obtained in Fig. 14. Only the upper portions (i.e. , layer) of the reference carbon layer show the presence of graphite crystals. The lower portion (i.e., layer) of the reference carbon layer show the presence of an amorphous carbon layer only.

[0114] Fig. 15 shows a comparison of a reference carbon coating 24 (left) and a carbon coating 16 of the present invention (right). The TEM images show an enlarged view on the amorphous carbon layer 26 of the reference component 22 shown in and described for Fig. 8, and an electrically conductive component 10 shown in and described for Fig. 7. The left-hand image shows an entirely amorphous structure in the amorphous carbon layer 26 of the reference component 22. In contrast thereto, the right-hand image shows a series of nanocrystalline graphite components 20 with an interlayer distance 34 and embedded in an amorphous, at least substantially hydrogen free DLC layer 18. Some of the nanocrystalline graphite components 20 are traced for visual purposes. In contrast to the amorphous carbon layer 24, the amorphous, at least substantially hydrogen free DLC layer 18 of an electrically conductive component 10 contains nanocrystalline graphite components 20 throughout said DLC layer. An aspect ratio of the components 20 varies, as shown. In one example, the aspect ratio of a component 20 is 1 :1.1 . On top of the right-hand image, two stacked layers of a nanocrystalline component (not shown) are traced. The interlayer distance of the two stacked layers is 0.32 nm.

[0115] Fig. 16 shows superimposed Raman spectra of the reference carbon coating 24 shown in Fig. 8 and the carbon coating 16 shown in Fig. 7. In Fig. 16, an ID / IG ratio of D peak (deconvoluted gaussian peak around 1400 cm’1) and G peak (deconvoluted gaussian peak around 1590 cm’1) is higher in the spectrum of carbon coating 16 (namely being 1 .9) than in the spectrum of reference carbon coating 24 (namely being 1 .8). A higher ID / IG ratio is associated with a higher sp2content, therefore indicating nanocrystalline graphite components. The ID / IG ratios in Fig. 16 fit to the TEM images shown in Fig. 7 and Fig. 8, respectively. Fig. 17 shows a high-magnification bright-field TEM image of a sectional view of an electrically conductive component of the present invention (top image), and FFT images thereof (bottom images) obtained from a batch coating process. In contrast to the electrically conductive component in Figs. 7, 12, 13, 13a, and 15 right, the electrically conductive component (sample B) analyzed in Fig. 17 was produced using a batch coating process. The top image shows a carbon coating of Sample B comprising a first (bottom (interface)) layer of an amorphous, at least substantially hydrogen free DLC layer embedded with highly ordered nanocrystalline graphite components, and a second (top (surface)) layer of an amorphous, at least substantially hydrogen free DLC layer embedded with highly ordered nanocrystalline graphite components.

[0116] For the production of the electrically conductive component shown in Fig. 17, a batch coating apparatus was used. The metal component was etched by using an argon plasma etching process carried out for a period ranging of 3 min, with a bipolar bias voltage lying in the range of from -0 to -350 V. The etching process was performed by subsequently etching the first side and the second side of the metal component. The adhesion layers were then deposited by using a sputtering process at a bias voltage lying in the range of from -20 V to -350 V. The thickness of the adhesion layer is approximately 100 to 120 nm. The deposition of the adhesion layers was performed subsequently on the first side and the second side of the metal component. The carbon coatings were deposited by using an arc PVD process at a bias voltage of from -20 V to -400 V, wherein each side of the adhesion layered metal component was subsequently subjected to carbon coating. No quality loss of the electrically conductive component was observed when performing the etching process, the adhesion layer deposition or the carbon coating simultaneously on both sides of the metal component 12.

[0117] The electrically conductive component in Fig. 17 has been found to have good electrical and mechanical properties, and low contact resistance values, i.e. , 0.001 0 cm2or less. Fig. 18 shows a high-magnification bright-field TEM image of a sectional view of a reference component (top image), and FFT images thereof (bottom images) obtained from a batch coating process (state of the art). In contrast to the reference component in Figs. 8, 9, 14, 14a, and left-hand side image of Fig. 15, the reference component (Sample C) analyzed in Fig. 18 was produced using a batch coating process. The FFT images show only an amorphous coating with no orientation.

[0118] The ID / IG ratio of D peak (deconvoluted gaussian peak around 1400 cm-1) and G peak (deconvoluted gaussian peak around 1590 cm-1) in a Raman spectrum (not shown) taken from a sample of reference carbon coating shown in Fig.18 is 1 .2, i.e. , ID / IG = 1 .2. Such a low value of the ID / IG ratio indicates that no nanocrystalline graphite component is present in entire carbon layer.

[0119] The reference component in Fig. 18 has been found to have poor electrical and mechanical properties, and high contact resistance values, i.e., » 0.005 0 cm2

[0120] Fig. 19 shows an inline coating apparatus 36 of the present invention. The process takes place in inert gas atmosphere, e.g., Argon atmosphere. Each one of the chambers 38, 40, 42 and 44 are vacuum chambers. After the metal component 12 (not shown) is inserted into the loading chamber 38 of the apparatus 36, the metal component 12 is subjected to an etching step in chamber 40. Etching is shown to take place on two opposite sides of the metal component 12. Thereafter, the two etched sides of the metal component are adhesion layered in the next chamber 42. Deposition of the adhesion layers 14, 14’ may be carried out on both sides simultaneously or subsequently. Then, the metal component 12 comprising the adhesion layers 14, 14’ is carbon coated in a carbon coating chamber 44. The chamber 44 preferably has a temperature in the range of from 23 °C to 400 °C during the step of depositing a carbon coating. As shown, the carbon coating sources (herein: arc cathodes) are arranged parallel to one another, i.e., without a pitch. This enables a simultaneous carbon coating on both sides of the metal component, thereby ensuring a stable temperature gradient during carbon coating. Such an apparatus provides for an electrically conductive component of the present invention.

[0121] Fig. 20 shows an inline coating apparatus 46 in accordance with the state of the art. The apparatus 46 is almost similar to the one described for Fig. 19 with the difference that the carbon coating chamber has two arc cathodes shifted from one another, i.e. , not parallel to one another. The arc cathodes therefore carbon coat the two sides of the metal component 12 in a subsequent manner. Such a method cannot provide for a stable temperature gradient during carbon coating. The resulting carbon coated components therefore have poor electrical and mechanical properties, as well as high contact resistance.

[0122] List of reference numerals:

[0123] A axis A

[0124] P axis P

[0125] 10, 10’, 10”, 10’” electrically conductive component

[0126] 10a, 10a’ electrically conductive component

[0127] 12 metal component

[0128] 14, 14’ adhesion layer

[0129] 16, 16’ carbon coating

[0130] 18, 18a, 18b amorphous, at least substantially hydrogen free DLC layer

[0131] 20, 20a, 20b, 20c nanocrystalline graphite components

[0132] 22 reference component

[0133] 24, 24’ reference carbon coating

[0134] 26 amorphous carbon layer

[0135] 28 graphite crystal layer

[0136] 30 boundary

[0137] 32 inclination degree

[0138] 34 interlayer distance

[0139] 36 inline coating apparatus

[0140] 38 loading chamber (vacuum chamber)

[0141] 40 etching chamber (vacuum chamber)

[0142] 42 chamber for depositing of an adhesion layer

[0143] (vacuum chamber)

[0144] 44 carbon coating chamber (vacuum chamber)

[0145] 46 inline coating apparatus (state of the art)

[0146] 48 carbon coating chamber (vacuum chamber; state of the art)

Claims

Claims1 . An electrically conductive component, such as a bipolar plate, a half plate, an electrode and a gasket, the electrically conductive component comprising: a metal component; an adhesion layer optionally formed on the metal component; and a carbon coating formed on the adhesion layer, if provided, or on the metal component; wherein the carbon coating comprises an amorphous, at least substantially hydrogen free DLC layer and least one nanocrystalline graphite component embedded in said amorphous, at least substantially hydrogen free DLC layer; wherein the least one nanocrystalline graphite component comprises two or more stacked layers; and wherein the least one nanocrystalline graphite component is aligned perpendicular to and / or at least substantially perpendicular to an axis A defined by an interface between the carbon coating and the metal component or an interface between the carbon coating and the adhesion layer, if provided.

2. The electrically conductive component in accordance with claim 1 , wherein the metal component has a first side and a second side, the first side and the second side facing different directions, preferably opposite directions; the adhesion layer is optionally formed on at least one of the first side and / or the second side of the metal component; the carbon coating is formed on the first side and the second side of the metal component, the first side and / or the second side of the metal component being optionally adhesion layered.

3. The electrically conductive component in accordance with claim 2, wherein the carbon coating on the first side of the metal component, and the carbon coating on the second side of the metal component are similar or different to one another, the first side and / or the second side of the metal component being optionally adhesion layered.

4. The electrically conductive component in accordance with any one of claims 1 to 3, wherein the amorphous, at least substantially hydrogen free DLC layer comprises one or more ta-C layers, and / or one or more a-C layer.

5. The electrically conductive component in accordance with any one of claims 1 to 4, wherein a proportion of the sp2to sp3content of the amorphous, at least substantially hydrogen free DLC layer lies in the range of 30 to 80% sp2to 70 to 20% sp3, in particular wherein the sp2content is higher than 40 % sp2and especially higher than 60%, based on 100% of the amorphous, at least substantially hydrogen free DLC layer.

6. The electrically conductive component in accordance with any one of claims 1 to 5, wherein the amorphous, at least substantially hydrogen free DLC layer is a DLC layer containing less than 1 at% hydrogen based on 100 at% of the amorphous, at least substantially hydrogen free DLC layer.

7. The electrically conductive component in accordance with any one of claims 1 to 6, wherein the at least one nanocrystalline graphite component comprises two (2), three (3), four (4), five (5), ten (10), fifteen (15) or more stacked layers, preferably three (3) or more stacked layers.

8. The electrically conductive component in accordance with any one of claims 1 to 7, wherein the at least one nanocrystalline graphite component has an aspect ratio of from 1 :1 to 1 :20, preferably 1 :5, 1 :1.1 or 1 : 1 .

9. The electrically conductive component in accordance with any one of claims 1 to 8, wherein the stacked layers of the nanocrystalline graphitecomponent have an interlayer spacing of 0.1 nm to 2 nm, preferably of from 0.2 nm to 0.6 nm, and more preferably of 0.3 nm.

10. The electrically conductive component in accordance with any one of claims 1 to 9, wherein the nanocrystalline graphite component being aligned at least substantially perpendicular to the axis A is a nanocrystalline graphite component being inclined ± 30 degrees or less with regard to an axis P perpendicular to the axis A, preferably ± 20 degrees or less, ± 15 degrees or less, ± 10 degrees or less, or ± 5 degrees or less.11 . The electrically conductive component in accordance with any one of claims 1 to 10, wherein, based on the total amount (100%) of the carbon coating, a ratio of an amount of the amorphous, at least substantially hydrogen free DLC layer to an amount of the at least one nanocrystalline graphite component lies in the range of from 20% to 90%, preferably in the range of from 30% to 70%, or 40% to 80%.

12. The electrically conductive component in accordance with any one of claims 1 to 11 , wherein the carbon coating has a thickness of from 5 to 300 nm, preferably of 15 to 150 nm, and more preferably of from 25 to 100 nm.

13. The electrically conductive component in accordance with any one of claims 1 to 12, further comprising the adhesion layer, wherein the adhesion layer comprises at least one material selected from the group of members consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, nickel, cobalt, magnesium, gadolinium, nitrogen, carbon, boron, aluminum, and combinations of the foregoing and preferably comprising titanium.

14. The electrically conductive component in accordance with any one of claims 1 to 13, wherein the amorphous, at least substantially hydrogen free DLC layer has an Argon content of less than 5 at% Argon, preferably of less than2 at% Argon, more preferably of less than 1 at%, based on 100 at% of the amorphous, at least substantially hydrogen free DLC layer.

15. The electrically conductive component in accordance with any one of claims 1 to 14, wherein the amorphous, at least substantially hydrogen free DLC layer has an iron content of less than 5 at%, preferably of less than 1 at%, based on 100 at% of the amorphous, at least substantially hydrogen free DLC layer.

16. The electrically conductive component in accordance with any one of claims 1 to 15, the electrically conductive component has a contact resistance (CR) of 0.01 0 cm2or less measured at a contact pressure of 1 MPa, preferably of 0.003 0 cm2or less.

17. A method of coating least one electrically conductive component, in particular in accordance with at least one of the claims 1 to 16, such as a bipolar plate, half plate, an electrode, gasket etc., the method comprising the steps of:- providing an uncoated metal component;- etching the uncoated metal component;- optionally depositing an adhesion layer on the etched uncoated metal component by means of one of a physical vapor deposition process, an arc physical vapor deposition process, an arc ion plating process, a sputtering process, an EBPVD process, or a Hipims process; and- depositing a carbon coating on the adhesion layer if provided or directly on the etched uncoated metal component; wherein the carbon coating is deposited with a layer thickness selected in the range of from 5 to 300 nm at a bias voltage of -20 to -400 V by means of at least one of a physical vapor deposition (PVD) process, such as an arc PVD, a sputtering process, an arc ion plating process, an EBPVD (electron-beam physical vapor deposition) process, and / or a Hipims process.

18. The method in accordance with claim 17, wherein the uncoated metal component has a first side and a second side, the first side and the second side facing different directions, for example, opposite directions; the first side and the second side of the uncoated metal component are etched; at least one of the first side and the second side of the etched uncoated metal component is optionally deposited with an adhesion layer; and the first side and the second side being adhesion layered if provided and / or being etched are deposited with a carbon coating.

19. The method of claim 18, wherein the carbon coating is deposited simultaneously on the first side and the second side being adhesion layered if provided and / or being etched.

20. The method in accordance with any one of claims 17 to 19, wherein during the step of carbon coating, the metal component and the adhesion layer, if provided, are subjected to a continuous heating.21 . The method in accordance with any one of claims 17 to 20, wherein the step of etching comprises a plasma etching process, preferably an argon plasma etching process, carried out for a period ranging between 0.1 and 60 minutes, in particular 0.5 to 5 min, with a bias voltage lying in the range of from -50 to -1200 V, preferably of from -150 to -350 V.

22. The method in accordance with any one of claims 17 to 20, wherein the step of etching comprises a metal ion etching process carried out for a period ranging between 0.1 and 60 minutes, in particular 0.5 to 5 min, with a bias voltage lying in the range of from -50 to -1200 V, preferably of from -600 V to -1200 V.

23. The method in accordance with claim 21 or 22, wherein the bias voltage during the step of etching comprises d.c., unipolar and / or bipolar.

24. The method in accordance with any one of claims 17 to 23, further comprising the step of depositing the adhesion layer, and wherein said step comprises depositing an adhesion layer having a thickness in the range of from 25 to 500 nm at a bias voltage lying in the range of from -0 V to -350 V.

25. The method in accordance with any one of claims 17 to 24, further comprising the step of depositing the adhesion layer, and wherein the adhesion layer is deposited using an arc-PVD process, preferably at a bias voltage lying in the range of from -20 V to -400 V.

26. The method in accordance with any one of claims 17 to 25, further comprising the step of depositing the adhesion layer, and wherein the adhesion layer is deposited using a sputtering and / or HIPIMS process, preferably at a bias voltage lying in the range of from -20 V to -350 V.

27. The method in accordance with any one of claims 17 to 26, further comprising the step of depositing the adhesion layer, and wherein the adhesion layer comprises at least one of Ti, Cr, V, Ta, Ni, Co, Nb, Mg, B, Gd, Zr, TiN, CrN, NbN, ZrN, and combinations thereof.

28. The method in accordance with any one of claims 17 to 27, wherein the carbon coating comprises an amorphous, at least substantially hydrogen free DLC layer and at least one nanocrystalline graphite component embedded in said amorphous, at least substantially hydrogen free DLC layer.

29. The method in accordance with claim 28, wherein the amorphous, at least substantially hydrogen free DLC layer comprises either a top layer having a dopant present therein, or includes a dopant throughout the amorphous, at least substantially hydrogen free DLC layer.

30. The method in accordance with claim 29, wherein the dopant is selected from the group of members consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, nitrogen, boron, silicon, and combinations of the foregoing.31 . The method in accordance with claim 29 or claim 30, wherein a percentage of the dopant is 0.2 to 10 at%, in particular 0.5 to 6 at% or 2 to 4 at%, based on 100 at% of the amorphous, at least substantially hydrogen free DLC layer or of the top layer thereof comprising the dopant.

32. The method in accordance with any one of the claims 17 to 31 , wherein said method is conducted in a vacuum chamber, such as of an inline coating system or a batch coating system, and a temperature of said vacuum chamber is regulated to a temperature in the range of from 23 °C to 400 °C, in particular of 23 °C to 250 °C, during the step of depositing a carbon coating.

33. The method in accordance with any one of claims 17 to 32, wherein the carbon coating is deposited with a layer thickness lying in the range of from 5 to 300 nm, preferably of from 15 to 150 nm, and more preferably of from 25 to 100 nm.

34. The method in accordance with any one of claims 17 to 33, wherein the carbon coating is deposited at a bias voltage lying in the range of from -20V to -400V.

35. The method in accordance with any one of claims 17 to 34, wherein the carbon coating is deposited using the arc physical vapor deposition process or the arc ion plated process, and wherein an arc cathode current preferably lies in the range of from 40 to 150 A, more preferably of from 50 to 80 A.

36. The method in accordance with any one of claims 17 to 35, wherein the carbon coating is deposited using the HIP IMS process, and wherein the target density is 70 Watt / cm2or more.

37. The method in accordance with any one of claims 17 to 36, wherein the carbon coating is deposited using a sputtering process.

38. The method in accordance with any one of claims 17 to 36, wherein the carbon coating is deposited using an EBPVD process.

39. The method in accordance with any one of claims 17 to 38, wherein the carbon coating is deposited within a time interval lying in the range of from 0.1 to 15 min, preferably from 0.5 to 5 min.

40. An apparatus for coating at least one electrically conductive component, such as one or more bipolar plates one or more half plates, one or more electrodes, one or more gaskets etc., in particular in accordance with at least one of the claims 1 to 16, said apparatus being configured to carry out a method in accordance with one of the claims 17 to 39, the apparatus being an inline coating system, comprising:- a plurality of vacuum chambers arranged in a series one after another;- one or more cathodes arranged in at least some of the plurality of vacuum chambers; and- one or more fixtures respectively configured to receive a plurality of the uncoated metal components, with the first outer surface and the second outer surface to be coated each facing a cathode, the cathodes being a cathode for at least one of a physical vapor deposition (PVD) process, such as an arc PVD, a sputtering process, an arc ion plating process, an EBPVD (electron-beam physical vapor deposition) process, and / or a Hipims process; wherein said one or more fixtures are arranged to be moved linearly within the respective vacuum chamber and from vacuum chamber to vacuum chamber, wherein each vacuum chamber is configured to carry out aprocess, preferably a stationary process, with the process being selected from the group of members comprising: heating, evacuating, etching, cooling, depositing an adhesion layer, carbon coating, removing and / or combinations of the foregoing, and wherein the cathodes in the vacuum chamber configured to carry out the carbon coating process are arranged substantially parallel to one another.

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