Members coated with a carbon-based layer

Abstract

The present invention relates to a member comprising a metal substrate and a layer of amorphous carbon-based material having sp2 hybrid bonds and sp3 hybrid bonds, The aforementioned layer is: - The first content of sp3 hybrid bonds on the substrate side, and - The second content of sp3 hybrid bonds on the outer surface side of the layer, The first content is greater than the second content. The present invention relates to a component characterized in that the average content of sp3 hybrid bonds within the layer is 5% to 65%, preferably 5% to 45%, and the content of sp3 hybrid bonds changes continuously within the layer.

Description

[Technical Field]

[0001] The present invention relates to the technical field of coatings for electrodes of fuel cells or electrolytic devices. [Background technology]

[0002] The present invention relates to electrochemical systems such as fuel cells and electrolysis devices, and more particularly to proton exchange membrane fuel cells (PEMFCs).

[0003] The operation of these electrochemical systems involves an acidic or basic environment, oxidation at the cathode, temperatures that can range from 60°C to 160°C, and optionally the presence of halides. This environment promotes corrosion of system elements such as electrodes, interconnects, or interconnect plates, also known as bipolar or monopolar plates.

[0004] In detail, bipolar plates are one of the critical components for the durability of these systems: they consist of metal sheets with a thickness of approximately 100 μm. They must be protected by a coating to maintain sufficient surface electrical conductivity, minimize electrical loss at the interface, and prevent corrosion of the metal sheets in the invasive medium of the battery.

[0005] The surface conductivity of a bipolar plate made of metallic material is generally obtained by depositing a carbon-based or gold-based functional layer on the outermost surface of the substrate, including in the corrosive medium. In the case of a carbon layer, pre-depositing the underlying layer on the substrate can improve the adhesion of the functional layer and ensure the mechanical strength of the laminate.

[0006] Generally, the adhesion between the layer and the substrate, and the mechanical strength of the functional layer, which is reflected by the absence of damage due to cracking or delamination, are important parameters.

[0007] In fact, the barrier function of this layer must not degrade over the operating period of the electrochemical system in order to protect the metal substrate from oxidation and prevent the release of even small amounts of metal cations from the substrate into the battery medium.

[0008] Localized and usually transient fluctuations in the state of an electromechanical system place greater stress on the functional layer, and defects within this functional layer, such as defects, cracks, holes, and gaps between columns, can cause rapid degradation of the substrate, particularly due to galvanic bonding with the functional layer.

[0009] Furthermore, if the battery membrane is made of a fluoropolymer, fluoride ions F - It may release fluoride ions F - In particular, pitting of the stainless steel substrate can accelerate corrosion, leading to rapid and catastrophic failure of the entire battery.

[0010] To protect batteries from such failures and to satisfy the objectives of mechanical strength and electrical conductivity mentioned above, it is known from conventional technology to deposit a functional layer, particularly a carbon-based functional layer.

[0011] Physical vapor deposition (PVD) of carbon has the characteristic of being able to produce a wide range of materials with greatly different properties, even when depositing only carbon; for example, by adjusting the ratio of sp2 hybrid atoms to sp3 hybrid atoms, it is possible to obtain materials with significantly different usage characteristics.

[0012] To improve the characteristics of the deposited layers, it is common to impart additional energy during deposition. It is also possible to introduce higher or lower proportions of hydrogen within the carbon layers.

[0013] By adding other elements to carbon, good performance has been obtained. Therefore, Document WO2011 / 077755 describes a bipolar plate for a fuel cell coated with a carbon-based functional layer doped with nitrogen at a content rate of 3 to 20 atomic % and doped with hydrogen at a content rate exceeding 0% and not exceeding 20 atomic %.

[0014] Document WO2007 / 136131 describes a conductive component provided with an amorphous carbon layer doped with silicon at a content rate of less than 1 atomic % and containing hydrogen at a maximum content rate of 30 atomic %.

[0015] Document WO2013 / 114836 describes an amorphous carbon layer containing hydrogen, nitrogen, and oxygen at maximum content rates of 30, 20, and 3 atomic %, respectively.

[0016] However, controlling the content rate of additional atoms complicates the method and makes the process more expensive.

[0017] Document Japanese Patent No. 6512577 describes a coating including two different layers of different types of amorphous carbon, and PCT applications PCT / FR2022 / 051631 and PCT / FR2022 / 051642 in the name of the applicant provide solutions that enable meeting the requirements of the U.S. Department of Energy (DOE). However, the durability of some coatings can be further improved, particularly at high potentials or high temperatures.

[0018] Finally, one of the problems is the contradiction that in order to perform deposition quickly, the layer should be as thin as possible, but the thinner the layer, the lower the durability and the faster it deteriorates.

[0019] Therefore, one object of the present invention is to overcome the above drawbacks.

Summary of the Invention

[0020] To this end, the present invention aims to provide a carbon coating with optimized essential properties in order to ensure high performance, for example, in electrodes for fuel cells.

[0021] Another object of the present invention is to provide a carbon coating having essential properties suitable for reversible systems (unitized regenerative fuel cells, i.e., URFCs) that operate at a higher potential than PEMFCs, or a carbon coating suitable for components of high-temperature fuel cells (HT PEMFCs) that operate in the range of 120°C to 200°C.

[0022] This invention also relates to efficient and inexpensive components suitable for specific applications of fuel cells.

[0023] The present invention also relates to a deposition method that makes it possible to obtain such a carbon film.

[0024] To achieve this objective, a member comprising a metal substrate and a layer of amorphous carbon-based material having sp2 hybrid atoms and sp3 hybrid atoms, wherein the layer is: - The first content of sp3 hybrid atoms on the substrate side, and - A component was developed having a second content of sp3 hybrid atoms on the outer surface of the layer, where this second content is lower than the first content.

[0025] According to the present invention, the average content of sp3 hybrid bonds within the layer is 5% to 65%, preferably 5% to 45%, and the content of sp3 hybrid bonds changes continuously within the layer. There is a gradient in content from the substrate towards the outer surface. Conversely, the content of sp2 hybrid atoms shows the opposite gradient within the layer (the sum of sp2 and sp3 content is 100%).

[0026] Thus, the carbon-based material layer possesses optimal essential properties for ensuring high performance in electrodes. The high content of sp3 hybrid atoms provides the advantage of excellent resistance to oxidation and degradation inherent in the sp3 form of carbon on the substrate side. On the other hand, the high content of sp2 bonds on the outer surface avoids the disadvantage of high resistivity characteristic of the sp3 form of carbon.

[0027] Therefore, the component according to the present invention has low interfacial contact resistance and good surface conductivity thanks to the sp2 form of carbon, while also having an excellent service life thanks to the resistance of the sp3 form.

[0028] Because the content of sp3 hybridized atoms within the layer changes continuously, there are no discontinuities or interfaces in the distribution of internal stress and Young's modulus within the carbon layer. These can lead to preferential degradation, such as delamination or interlaminar delamination.

[0029] Therefore, the cohesion (adhesion) of the carbon layer is improved, contributing to the durability of the component, particularly through increased resistance to temporary phenomena.

[0030] In specific cases of use within fuel cells, the component forms part of a monopolar or bipolar plate for the fuel cell. In this case, the component satisfies the requirements of the DOE.

[0031] The average content of sp3 hybrid atoms is measured by Raman spectroscopy at multiple laser excitation wavelengths (325 nm, 442 nm, 488 nm, 633 nm). The laser output is limited to prevent the material from changing upon irradiation. The intensity spectrum as a function of the Raman shift is adjusted using two Gaussian distributions, one representing the G peak (stretching mode) and the other the D peak (vibrational mode) of the carbon bond. Plotting the position of the G peak (Raman shift) against the wavelength yields a straight line, the slope of which represents the dispersion of the G peak (unit: cm). -1The dispersion is ( / nm). This dispersion is proportional to the sp3 content of the analyzed material. For reference, a chart is shown in the paper "Structure of diamondlike carbon films deposited by femtosecond and nanosecond pulsed laser ablation" by Sikora et al. (Journal of Applied Physics, 108, 113516, 2010).

[0032] The local content of sp3 hybrid atoms can be determined based on the local density of the material constituting layer (C). This density is measured cross-sectionally using electron energy loss spectroscopy (EELS) with a transmission electron microscope (TEM), and is spatially resolved and evaluated by restricting the electron beam size to a portion of the nanometer. A proportional relationship exists between the layer density and the sp3 hybrid atom content (see, for example, the paper "Diamond-Like Amorphous Carbon" by J. Robertson (Materials Science and Engineering, R 37(2002) 129-281, Figure 32)).

[0033] Independent of or in combination with the fundamental features of the present invention, carbon can be injected into the layer-receiving material, i.e., the substrate material or the underlying layer material. This carbon injection is performed during layer deposition and advantageously contributes to improving the adhesion of the layer to the support. Surprisingly, the applicant has found that carbon injection in the early stages of deposition brings excellent properties to the component with respect to the above requirements.

[0034] In other words, it is quite conceivable to provide a component comprising a metal substrate and a layer of amorphous carbon-based material having sp2 and sp3 hybrid atoms. This layer is - The first content of sp3 hybrid atoms on the substrate side, - The layer has a second content of sp3 hybrid atoms on the outer surface, and this second content is lower than the first content. Here, carbon is injected into the material that receives the layer (whether it is the base material or the underlying layer material), and this carbon injection is obtained during the deposition of the layer. In this case, the average content of sp3 / sp2 hybridization within the layer is not particularly considered.

[0035] In a preferred embodiment, the component comprises a single layer of carbon-based material. The method for manufacturing the component comprises a single carbon deposition step. This is therefore simplified and reduces the cost of the component. More preferably, the component comprises a single layer of material consisting solely of carbon.

[0036] To promote the conductivity of the component, the average content of sp3 hybrid bonds is limited. Therefore, the average content of sp3 hybrid bonds in the layer is 10% to 45%. Preferably, the average content of sp3 hybrid bonds in the layer is 10% to 30%. In some embodiments, the material forms a thin layer commonly referred to as "aC". Preferably, the sp3 hybrid bond content is uniform within the layer and not localized by crystalline clusters having a high sp3 hybrid bond content. Such clusters form a carbon layer with a non-uniform sp3 hybrid bond content.

[0037] To reduce the manufacturing cost of the components, the carbon-based material does not contain metal dopants. Furthermore, dopants form carbides within the carbon layer, and these localized carbides constitute preferential defect and corrosion areas. When depositing with dopants, metal droplets may also form, which also constitute preferential corrosion areas. These disadvantages are avoided.

[0038] In particular, the highest performance in terms of durability at high potentials was obtained with a layer of carbon-based material that does not contain nitrogen or hydrogen.

[0039] "Hydrogen and nitrogen-free" and "dopant-free" mean that these elements are not intentionally added to the sedimentary layer, and that they can only be present in amounts insufficient to impart the characteristic properties of the sedimentary layer. Preferably, these elements are present only in trace amounts.

[0040] Advantageously, the layer has a thickness of 20 nm or more, preferably 20 nm to 250 nm, more preferably 50 nm to 150 nm, and even more preferably 60 nm to 100 nm.

[0041] To improve the adhesion of the layer to the component and protect the substrate from potential oxidation, the component includes an underlayer positioned between the substrate and the layer of carbon-based material, and in contact with the layer.

[0042] Advantageously, the underlying material is selected from chromium, titanium, zirconium, tantalum, niobium, or alloys thereof, and their nitrides and carbides, or the underlying material is a ceramic. Preferably, the underlying material is an electrically conductive material that becomes passivated when subjected to oxidation. Titanium is a preferred material.

[0043] To have a favorable balance between the deposition time of the metal underlayer and the resulting improvement in adhesion, its thickness is 5 nm to 100 nm, preferably 20 nm to 40 nm, for example, 50 nm.

[0044] In specific embodiments suitable for the fuel cell field, the substrate includes stainless steel, titanium, titanium alloys, or nickel-based alloys, chromium-based alloys, and iron-based alloys. Preferably, it is Inconel®.

[0045] Preferably, the substrate is a plate having a thickness of 10 μm to 1000 μm.

[0046] Preferably, such a component constitutes part of a monopolar or bipolar plate for a fuel cell. This component has technical characteristics that ensure sufficient durability and performance to meet the requirements in the fuel cell field.

[0047] The present invention also relates to a method for vacuum deposition of a layer of amorphous carbon-based material onto a substrate. The method is as follows: The parameters that affect the ratio of sp2 or sp3 hybrid bonds in carbon are: - The first content of sp3 hybrid bonds on the substrate side, and - The second content of sp3 hybridization on the outer surface of the layer, and this second content changes continuously during the deposition of the layer so that it is lower than the first content, and The average content of sp3 hybrid bonds within the layer is 5% to 65%, preferably 5% to 45%, and The content of sp3 hybridization is noteworthy because it changes continuously within the layer.

[0048] "Continuously changing" means that the parameter does not exhibit discontinuities between depositions, for example, between the deposition of consecutive individual layers, each having a different sp3 hybridization content. Nevertheless, the parameter may exhibit strictly increasing or decreasing changes, or changes that are not strictly increasing or decreasing (e.g., oscillations). [Brief explanation of the drawing]

[0049] [Figure 1] Figure 1 is a cross-sectional view of the member according to the present invention.

[0050] [Figure 2] Figure 2 is a graph showing the variation in the content of sp3 hybridized carbon atoms within the layer of carbon-based material in such a component.

[0051] [Figure 3] Figure 3 is a graph showing the variation in the content of another component according to the present invention.

[0052] [Figure 4] Figure 4 is a graph showing the variation in the content of another component according to the present invention.

[0053] [Figure 5] Figure 5 is a graph showing the variation in the content of another component according to the present invention.

[0054] [Figure 6] Figure 6 is a graph showing the variation in the content of another component according to the present invention.

[0055] [Figure 7] Figure 7 is a graph showing the corrosion current density during the test.

[0056] [Figure 8] Figure 8 is a graph showing the corrosion current density during another test.

[0057] [Figure 9] Figure 9 is a graph showing the corrosion current density during another test. [Modes for carrying out the invention]

[0058] Several types of techniques exist in the field of vacuum deposition, each with its own advantages and disadvantages. In the context of processing components (P), and especially monopolar or bipolar plates for fuel cells, the applicant sought to optimize known deposition methods.

[0059] The applicant conducted a series of tests and analyses aimed at obtaining a coating of carbon-based material that forms a layer (C) on a substrate (S), which has particularly good properties of mechanical strength, corrosion resistance, adhesion, and electrical conductivity.

[0060] Preferably, deposition is carried out by a cathode arc. In this embodiment, the equipment used to carry out one embodiment of the method comprises a pumping device, a plasma source, an arc spray source, and a secondary vacuum enclosure equipped with a substrate holder on which a substrate or a plurality of substrates (S) to be processed is attached.

[0061] The pump device creates a secondary vacuum in the chamber, i.e., 10 -7 mbar (millibar) ~ 5 × 10 -5 This makes it possible to obtain pressures on the order of mbar. A pumping device, or another separate device, can introduce a gas into the vacuum chamber. The gas is intended to be ionized and is preferably argon.

[0062] The arc spray source is conventional and supplied continuously. Alternatively, the supply may be pulsed. The discharge against the graphite target generates carbon ions. The arc supply may be ignited intermittently (e.g., 60 seconds on and 10 seconds off).

[0063] The substrate support is polarized, that is, a negative voltage or potential difference is applied to its terminals, which generates a flow of carbon ions in the direction of the substrate support. This acceleration of ions occurs in the vicinity of the substrate (S). This is because the electric field generated by the polarization of the component (P) spreads only over a short distance of a few millimeters.

[0064] When a substrate (S) is polarized in a plasma, the polarization voltage is applied between the substrate (S) and the equipment's ground. A potential difference is established between the substrate (S) and the plasma. Ions are accelerated within this potential drop region, extending approximately 0.5 to 2 mm above the surface of the substrate (S).

[0065] Various tests are performed within the facility by changing parameters such as the thickness of the layer (C), the presence or absence of an underlayer (SC) between the substrate (S) and the layer (C), the polarization voltage (its value, its application in continuous or pulsed mode, and the duty cycle in the case of pulsed voltage), and the power supply ignition current (current value, or intermittent duty cycle).

[0066] The component (P) is covered with a functional layer (C) made of carbon-based material, which is intended to protect the substrate (S) from oxidation in order to ensure the service life of the component (P), and is also configured to have low interfacial contact resistance in order to ensure the performance of the battery or electrolysis device containing the component (P).

[0067] The service life of layer (C) is evaluated by subjecting it to an electrochemical corrosion test.

[0068] Under normal battery operating conditions, the cathode potential is less than 0.9V compared to a standard hydrogen electrode (NHE) (denoted as 0.9V / NHE). However, under accidental or transient conditions, the electrode may be exposed to a higher potential, i.e., up to 1.6V / NHE.

[0069] This is especially true when the battery is started or stopped. In this case, if an H2 / air or H2 / O2 front is present on the plate, a reverse current phenomenon can occur: the powered portion of the battery discharges to the unpowered portion, generating a locally very high potential (electrolysis condition).

[0070] These transient phenomena may persist longer if the battery is not sufficiently drained after shutdown (presence of residual water) and if the ambient temperature is very low: ice formed from residual water can clog distribution channels, delaying compartment filling and homogenization.

[0071] Therefore, interconnection plates (wiring boards) must be able to withstand very high potentials for periods of several hours relative to the battery's lifespan. This is even more important for batteries used in heavy vehicles.

[0072] Therefore, the electrochemical tests conducted by the applicant are more stringent than those required by the DOE and are performed in an acidic solution with a pH of 3, a temperature of 80°C, and a fluoride ion concentration of 0.1 ppm. This test medium is defined by the DOE in the United States to simulate the operating environment of a PEMFC. In the context of this test, the potential is set to +1.6 V / NHE on the working electrode to which the material under test is attached. This potential used is higher than the value recommended by the DOE (0.8 V / NHE) to make the test more stringent and to select only the best deposits that can withstand accidental conditions. By adding air bubbling, it is possible to simulate the cathode compartment of the fuel cell. The test is performed over a period of 20 hours.

[0073] Corrosion current is an indicator of the degradation rate of a component (P) containing a substrate (S) coated with a layer (C) of material. In fact, the higher the corrosion current, the more the component (P) is being oxidized, meaning that the layer (C) of material is not adequately performing its protective function. Specifically, after 20 hours at a potential of 1.6V / NHE, the corrosion current density was 2000 nA / cm². 2 If it is less than that, it is considered acceptable.

[0074] The surface conductivity of a coating is evaluated by measuring its interfacial contact resistance, or "ICR". A coating with good surface conductivity has a low ICR, for example, 10 mΩ·cm. 2 It has less than .

[0075] ICR is measured on a laminate composed of a copper block - carbon sheet (GDL: Gas Diffusion Layer) - deposit - nickel paint - copper block. For this laminate, a current of 100 mA per 1 cm 2 of surface area is applied, and then the resistance of the assembly is calculated from the measured voltage.

[0076] This laminate represents the contact between the coated bipolar plate and the gas diffusion layer (C). For this, a pressure of 138 N / cm 2 is applied by a lever - arm system with weights, and this pressure represents the pressure applied during the assembly of the electrochemical cell.

[0077] The obtained resistance R total is the sum of the following terms: · Resistance of the Cu - Cu system · 1 × Contact resistance R of the copper - carbon interface Cu / C · 1 × Resistance RC of the carbon felt · Contact resistance R between the deposit and carbon C / deposit · Linear resistance R of the deposit deposit · Resistance R of the 316L steel plate 316L · 1 × Contact resistance R of the nickel - copper interface Ni / Cu

[0078] [Equation 1] R total =R offset +R Cu / C +R C / deposit +R deposit +R Ni / Cu (1)

[0079] ICR is determined using the following equation.

[0080] [Equation 2] R C / deposit +R deposit =RCI = R total - R offset - R Cu / C-R Ni / Cu (2)

[0081] It is important to confirm the ICR after the more stringent corrosion tests described above. In fact, a substrate (S) coated with a metal underlayer (SC) followed by a carbon layer (C) may exhibit good corrosion resistance, but such corrosion resistance may be explained by the passivation of the underlayer (SC) material when the carbon layer (C) degrades. However, this passivated material does not have sufficient surface conductivity. Therefore, a bipolar plate functionalized with such deposition may protect the fuel cell from accidental degradation, but it will mean that the performance of the fuel cell will be reduced. Thus, these two parameters must be considered cumulatively.

[0082] The passivated lower layer ensures that the stainless steel of the substrate (S) does not release metal cations into the electrochemical system.

[0083] Another evaluation criterion is the visual appearance of layer (C), which must not be macroscopically damaged, worn, or peeled at the end of the test.

[0084] A series of tests were conducted within the facility. The component under test (P) was a test specimen with a base material (S) made of 316L stainless steel, intended to be coated on both sides to simulate the coating of a bipolar plate.

[0085] The substrate (S) is placed on a jig and subjected to cleaning and blowing treatment to remove any contaminants and dust present on its surface. It is then introduced into the vacuum deposition apparatus.

[0086] Activate the pump device and increase the pressure inside the chamber to 5 × 10⁻¹⁰ -6 The temperature is reduced to less than mbar, and the chamber (10) is heated to remove moisture adsorbed on the wall surface.

[0087] The surface of the substrate (S) to be coated is heated and then struck with argon ions. This is done to remove moisture adsorbed on these surfaces and to pickle the oxide layer (C) present on the surface.

[0088] Subsequently, the flow rate of argon into the chamber is adjusted by a pumping device, and the argon pressure during the deposition process is approximately 2 × 10⁻⁶. -4 The concentration should be in mbar. Argon is used for ionization and is not intended to be incorporated into the carbon-based layer (C).

[0089] Reactive deposition of layer (C) is not intended: the pumping device does not introduce nitrogen or other additive elements such as dopants into the chamber; therefore, the internal space of the chamber, and consequently the deposited layer (C), does not contain nitrogen or other additive elements.

[0090] Layer (C) does not contain hydrogen, nitrogen, or other dopants such as tungsten. In the art, "does not contain" means that the content is zero, trace, or at least less than 1 atomic percent. In any case, it is intended that these elements are present in amounts low enough not to impart any properties to the deposited layer (C). None of these elements are intentionally added during deposition.

[0091] However, despite the heating performed, a small amount of adsorbed water still remains in the chamber: in fact, approximately 10% of the heating performed -5 At a vacuum pressure of mbar, unless the chamber has significant leaks, virtually only residual water vapor exists within the chamber. Therefore, it is impossible to avoid the presence of oxygen via the water in the chamber, and this component can be found in the deposits during its formation. Since graphite targets are generally porous, oxygen can also be present in carbon-based targets.

[0092] Unlike hydrogen, oxygen is not easily removed from layer (C) during its deposition, and its content depends on the ion bombardment conditions applied, which themselves are specific to the method used. Therefore, only oxygen can be present in layer (C), excluding, of course, atoms from the inert gas (argon) that may be present in small amounts.

[0093] A lower layer (SC) made of a metallic material may be optionally deposited on the substrate (S). For example, it can be deposited by cathode sputtering a target corresponding to a desired material (metal or ceramic, or optionally in a reactive atmosphere to change the composition of only the lower layer (SC)).

[0094] Next, a layer of carbon-based material is formed from a graphite target by arc deposition.

[0095] The first series of tests will be conducted with the following changes: - The value of the polarization voltage (whether continuous or pulsed); - Duty cycle of polarization voltage, if applicable; - Intermittent duty cycle for ignition (arc ignition) of a graphite target.

[0096] All test samples have a 50nm thick titanium underlayer (SC) and a 70nm thick carbon layer (C).

[0097] Next, component (P) was characterized to identify the differences between the obtained sediments.

[0098] After conducting the tests, the applicant found the following: Despite the preconception that "higher sp3 hybridization content leads to higher protection," as described in references such as WO2022 / 049245A1 and WO2021 / 28399A1, some sp3-rich (56% sp3) samples exhibited high corrosion currents and a significant increase in ICR after corrosion testing. Therefore, it is considered that a single criterion, such as the average sp3 content, is insufficient to distinguish between the resulting components (P).

[0099] Furthermore, components (P) with a moderate sp3 content exhibit very different properties: a sample containing an average of 20% sp3 bonds may be unsuitable, while a sample containing 45% is suitable.

[0100] Unexpectedly, the presence of oxygen within layer (C) is not a decisive criterion.

[0101] In the first embodiment, the sp3 bond content changes continuously within the layer (C) according to a gradient decreasing from the substrate (S) to the outer surface (SE). This characteristic explains why a sample with an average sp3 bond content of 45% is suitable, while samples with average content of 20% and 56% are not.

[0102] in fact: - At the start of deposition, the sp3 content is high (i.e., on the substrate (S) side); - During sedimentation, the sp3 content decreases continuously and gradually; - At the end of deposition, the sp3 content is lower (i.e., on the outer surface (SE) side of member (P)).

[0103] In another embodiment, the gradient decreases strictly from the substrate (S) to the outer surface (SE). The term “strictly decreases” means that the sp3 bond content never increases. However, the content can remain flat. In this embodiment, the first content (sp3%1h) is equal to the maximum sp3 content (sp3%max) within layer (C), and the second content (sp3%2b) is the minimum sp3 content (sp3%min).

[0104] In another embodiment, the sp3 bond content exhibits oscillations, and consequently increases across at least a portion of the layer in response to variations in the influencing parameters. In this embodiment, the first content (sp3%1h) is not the maximum sp3 content (sp3%max) within layer (C), and the second content (sp3%2b) is not the minimum content (sp3%min).

[0105] In either case, the overall content of sp3 bonds within layer (C) shows a decreasing trend. In fact, if the content of sp3 bonds on the outer surface is too high, the ICR becomes excessive, while if the content of sp2 bonds in the substrate is too high, corrosion resistance decreases.

[0106] Variations in the level of sp3 hybridization alter the properties of the layer (C). Carbon layers containing 10% to 35% sp3 bonds (the remainder being sp2) belong to the "aC" family of amorphous carbon layers, while carbon layers containing 60% to 85% sp3 bonds belong to the "ta-C" family of tetrahedral carbon layers. Within the "ta-C" family of tetrahedral carbon layers, it is known that carbon layers containing 65% sp3 bonds do not have the same properties (mechanical and electrical) as carbon layers containing 85% sp3 bonds.

[0107] Therefore, the sp3 bond content in a material imparts specific properties to that material, and variations in the sp3 bond content within layer (C) make it possible to obtain several properties of the material within that layer.

[0108] Referring to Figure 1, member (P) has the following within the carbon layer (C): - A first zone (e1) on the substrate (S) side that is rich in sp3 bonds, wherein the first composition (C1) of the layer (C) mainly exists within this first zone (e1); - A second zone (e2) on the outer (SE) side that is not very rich in sp3 bonds, and in which the second composition (C2) of layer (C) mainly exists; - The first zone (e1) and the second zone (e2) are separated by an intermediate zone which is considered negligible with respect to the present invention.

[0109] The first composition corresponds to an sp3 bond content greater than the first threshold (sp3%1b), or an sp3 bond content between the first threshold (sp3%1b) and the first content (sp3%1h).

[0110] The second composition corresponds to an sp3 bond content lower than the second threshold (sp3%2h), or an sp3 bond content between the second content (sp3%2b) and the second threshold (sp3%2h).

[0111] The first composition (C1) is defined, for example, by a first threshold (sp3%1b) of sp3 bond content of more than 80%, or more than 75%, or more than 70%, or more than 65%, or more than 60%, or more than 55%, or more than 50%, or more than 45%, or more than 40%, or more than 35%, or more than 30%, or more than 25%, or more than 20%, or more than 15%.

[0112] The second composition (C2) has a second threshold sp3 bond content (sp3%) that is lower than that of the first composition (C1), for example, less than 4%, or less than 5%, or less than 10%, or less than 15%, or less than 20%, or less than 25%, or less than 30%, or less than 35%, or less than 40%, or less than 45%, or less than 50%, or less than 55%, or less than 60%. 2h Defined by:

[0113] Depending on the values ​​used for the first and second compositions, each of the first zone (e1) and / or second zone (e2) is 1 nm to 30 nm, or 5 nm to 15 nm, or 7 nm to 10 nm.

[0114] The first zone (e1), which is rich in sp3 bonds, possesses good mechanical properties and resistance to oxidation.

[0115] The second zone (e2), which is less rich in sp3 bonds, has the advantage of having better electrical conductivity, and therefore implies a decrease in ICR.

[0116] Therefore, the combination of these two zones within the same layer (C) allows for the combination of the respective advantages of the sedimentary properties. Since the present invention provides enhanced resistance at high potential, it is possible to manufacture layers with thinner thicknesses than those of the prior art that have equivalent or even exceeding the requirements of the DOE.

[0117] In addition to shorter deposition times, the smaller film thickness also contributes to improved resistance to deformation. Specifically, when molding (for example, channel formation in a bipolar plate) is performed after layer (C) has been deposited on a flat member, the member (P) is less prone to defects such as cracks and delamination after molding due to the low film thickness of layer (C) and the presence of an SP3-rich layer near the interface (I) between layer (C) and the receiving material.

[0118] Furthermore, continuous variation in sp3 bond content improves layer durability. The lack of discontinuity: - Enables a good distribution of internal stress in the carbon layer (C), and therefore avoids flaking; - Allows for good cohesion of materials within layer (C), and therefore avoids the presence of preferred sites for corrosion attack.

[0119] Variations in sp3 bond content are obtained by changing parameters that affect the deposition process. For example, the influencing parameter may be the polarization voltage, whether continuous or pulsed: - It is possible to initiate the deposition of layer (C) using an appropriate polarization voltage so that the deposited carbon ions are deposited onto the material (P) with a large amount of energy, thereby promoting sp3 hybridization. - During deposition, the polarization voltage is gradually reduced, so that the ion collision energy also gradually decreases. The conditions for sp3 hybridization become increasingly unfavorable, and therefore, its content gradually decreases.

[0120] The influencing parameters are selected based on the deposition method being performed, and the criterion is the continuous variation in the amount of energy supplied during deposition. For example, in the case of high-power impulse magnetron sputtering (HiPIMS), the influencing parameters may be the amount of ions generated by the plasma source, which depends on the pulse parameters.

[0121] Alternatively, the influencing parameters could be the arc current applied to the cathode, or the ignition rate of the pulsed polarization. In the case of pulsed polarization voltage, it should be noted that, with respect to a given average value, a voltage inversely proportional to the ignition time is applied to the substrate holder. For example: For an average voltage of -100V and an ignition rate of 50%, the substrate holder (S) may be 0V for half the time and 200V for the other half (average 100V); For an average voltage of -100V and an ignition rate of 25%, the substrate holder (S) may be at 0V for three-quarters of the time and at 400V for the remaining quarter (average 100V).

[0122] Although the average voltage is the same, the significant difference in instantaneous voltage indicates a change in the energy supply to carbon ions during the deposition of layer (C).

[0123] By adapting to variations in the influencing parameters (whether linear or not), it is possible to obtain different gradient profiles.

[0124] Figures 2-4 show three different gradient profiles of sp3 content (sp3%) based on their location within the thickness (e) of layer (C). Based on the content variation profile, layer (C) will contain a first zone (e1) and a second zone (e2) of variable thickness. The first zone (e1) extends from the interface (I) between layer (C) and the material receiving it to a first depth (z1), and the second zone (e2) extends between the second depth (z2) and the outer surface (SE).

[0125] Figure 2 shows the first embodiment in which the sp3 bond content decreases regularly. As a result, the first zone (e1) and the second zone (e2) have equal thickness.

[0126] Figure 3 shows a second embodiment in which the sp3 bond content decreases irregularly, with a first flat area at the start of deposition and a second flat area at the end of deposition. These steps can be achieved by momentarily stopping the fluctuations of the influencing parameters. The first zone (e1) and the second zone (e2) have equal thickness because the two flat areas are of equivalent length, but their thickness is greater than that of the embodiment in Figure 2. In contrast, the thickness of the intermediate zone is thinner than that of the first embodiment.

[0127] Figure 4 shows a third embodiment in which the sp3 bond content decreases irregularly and the first flat area is present only at the start of deposition. As a result, the first zone (e1) is thicker than the second zone (e2).

[0128] Figure 5 shows a fourth embodiment in which the intermediate zone constitutes the main proportion of layer (C), as the first zone (e1) and the second zone (e2) are thin, for example, 1 nm to 15 nm or 5 nm to 10 nm in thickness.

[0129] Figure 6 shows a fifth embodiment in which the content is varied so as not to decrease strictly: fluctuations in the influencing parameters result in oscillations in the sp3 bond content. Nevertheless, the second sp3 bond content (sp3%2b) is strictly lower than the first sp3 bond content (sp3%1h), and as a result, layer (C) has a first zone (e1) and a second zone (e2). Based on the downward trend of the sp3 bond content and the amplitude of the oscillation, it is possible to obtain intermediate zones that constitute the main proportion of layer (C). The first zone (e1) and the second zone (e2) may be thin, about a few nanometers, for example, 1 nm to 20 nm, or 5 nm to 10 nm.

[0130] The intermediate zone is a zone that provides a transition between the first zone (e1) and the second zone (e2). This preferably includes a limited average sp3 bond content in order to maintain a low overall resistivity of the layer. For example, the average sp3 bond content in the intermediate layer is less than 40%, preferably less than 25%. Nevertheless, the first sp3 bond content (sp3%1h) is preferably at least 30% to 40% in order to protect the substrate from oxidation.

[0131] The second sp3 bond content (sp3%2b) is preferably at most 5% to 25% in order to ensure good surface conductivity of the member (P).

[0132] Therefore, by adjusting the thickness of the first zone (e1) relative to the thickness of the second zone (e2), it is possible to prioritize one composition over the other.

[0133] The primary sp3 bond content (sp3%1h) is within the range of 30% to 85%, or 35% to 80%, or 40% to 75%, or 45% to 60%, or 50% to 65%, or any of these combined values.

[0134] The second sp3 bond content (sp3%2b) is selected to be less than the first sp3 bond content (sp3%1h), and is within the range of 3% to 70%, or 15% to 65%, or 20% to 60%, or 25% to 55%, or 50% to 45%, or 35% to 45%, or any of these values ​​combined.

[0135] The ratio of the second content (sp3%2b) to the first content (sp3%1h) is within the range of 0.05 to 1 (excluding 1), 0.2 to 0.9, 0.3 to 0.8, 0.4 to 0.7, 0.5 to 0.6, or any of these values ​​obtained by combining them.

[0136] The average sp3 bond content of the layer, i.e., the average content over the entire thickness of the layer, is in the range of 5% to 65%, or 10% to 60%, or 15% to 55%, or 20% to 50%, or 25% to 40%, or 30% to 35%, for example, 9%, or 15%, or 19%, or 22%, or 45%, or 56%, or any range obtained by combining these values.

[0137] Based on the selection of the first concentration (sp3%1h) and the second concentration (sp3%2b): - A layer of aC-type amorphous carbon having a primary sp3 content of less than approximately 40% (C); - A layer of ta-C type amorphous carbon with a secondary sp3 content of over 60% (C); - A layer of carbon having the following (C) *The first zone (e1) is rich in sp3 bonds and has a first content of over 40% (sp3%1h); and *It is possible to obtain a second zone (e2) rich in sp2 bonds with a second content (sp3%2b) of less than approximately 40%.

[0138] In certain embodiments implemented independently of or in combination with the fundamental properties of the present invention, the ion energy is sufficiently high, and carbon is implanted into the material at the interface (I) between the layer (C) and the supporting material receiving it (whether it be a substrate (S) or a sublayer (SC)).

[0139] The injection occurs over a thickness of approximately 1 nm to 3 nm, for example, 1.5 nm to 2 nm or 2.5 nm.

[0140] These carbon injections allow for the adhesion of layer (C) to be promoted.

[0141] In this embodiment, according to the present invention, it is possible to easily manufacture a member (P) having a layer (C) that has good electrical and electrochemical properties and excellent adhesion to the member (P). This is because the adjustment of the energy level is configured to suit both the injection of carbon into the member (P) and the deposition of carbon in sp3 bond form.

[0142] The performance of component (P) corresponding to the present invention was compared with the performance of a conventional device.

[0143] In this embodiment, the component (P) consists of a 316L substrate (S), a 50 nm thick titanium underlayer (SC), and a 70 nm thick carbon layer (C) deposited by a cathode arc. Within this component, the sp3 hybrid bond content decreases in the direction from the substrate (S) towards the outer surface (SE).

[0144] The carbon layer (C) contains neither dopants nor nitrogenous elements to avoid the presence of preferential corrosion sites. In contrast, the presence of oxygen within layer (C) is not a definitive criterion.

[0145] Comparative example: - Comparative Example 1 (EC1): A component consisting of a 316L substrate (S), a 50 nm thick titanium underlayer (SC), and a 70 nm thick carbon layer, not according to the present invention; - Comparative Example 2 (EC2): 316L substrate without coating; - Comparative Example 3 (EC3): Titanium substrate without coating, That is the case.

[0146] A corrosion test was conducted at a potential of +1.6V / NHE.

[0147] Referring to Figure 6, the current density of member (P) according to the present invention decreases rapidly, reaching 200 nA / cm² at the end of the test. 2 This value is less than , equivalent to that of a bare titanium substrate (EC3). Unlike Comparative Example 1 (EC1), where the carbon layer (C) was consumed, the coating was still present. At the end of this more rigorous test, the ICR of component (P) was low, which is not the case for bare titanium.

[0148] Therefore, the component (P) according to the present invention has both very good conductivity (low ICR) and very good resistance to oxidation (low corrosion current, no consumption of layer (C)).

[0149] Other corrosion tests were performed at a potential of +1.6V / NHE.

[0150] Referring to Figure 7, the corrosion resistance of member (P) according to the present invention was compared with that of Comparative Example 1 (EC1).

[0151] The sp3 content characteristics according to the present invention affect the high-potential resistance of layer (C): - The layer (C) of component (P) is not consumed, and the corrosion current density is very low; - Comparative Example 1 (EC1) has a low final corrosion current, but the carbon layer (C) is consumed entirely, and the metal sublayer (SC) is exposed on the surface (corresponding to the observation of a larger corrosion current between 0 and 6 hours).

[0152] Referring to Figure 9, another corrosion resistance test was conducted this time at a potential of 1.2 V / NHE and a temperature of 90°C for 10 hours.

[0153] At the end of this other, more rigorous test, component (P) according to the present invention was found to be comparable to comparative example (EC1) (100 mΩ·cm). 2 Superior corrosion resistance (approximately 10 mΩ·cm) 2 It has been observed again that it possesses only this characteristic.

[0154] Those skilled in the art will understand that by adjusting the deposition parameters, particularly the influencing parameters, the ratio of sp3 hybrid atoms to sp2 hybrid atoms can be continuously varied, thereby satisfying the requirements of the present invention.

[0155] It should be noted that the present invention has the advantage of providing greater durability to the component (P) compared to conventional solutions in proton exchange membrane fuel cells, particularly at high temperatures and high potentials (under conditions more severe than the standard conditions set by the U.S. Department of Energy (DOE)).

[0156] Furthermore, the component (P) can be molded into a shape different from that of the embodiments described without departing from the scope of the present invention. The scope of the present invention is defined by the claims.

[0157] In some embodiments, the member (P) has a laminate of multiple underlayers (SC) disposed between a base material (S) and an outer layer (C) of a carbon-based material.

[0158] The carbon layer (C) is described as the outer layer because it is a layer intended to come into contact with the electrochemical medium of the battery, and it needs to protect the component (P) from corrosion and promote electrical conductivity. This term does not preclude the presence of additional thin carbon layers, such as aC-type or aC:H-type, deposited on top of the carbon layer (C).

[0159] The sp3 bond content within layer (C) may have a profile other than that exemplified.

[0160] Furthermore, the technical characteristics of various embodiments and the above-described variations can be combined, either entirely or partially. Therefore, component (P) can be adapted in terms of cost, functionality, and performance.

Claims

1. A member (P) comprising a metal substrate (S) and a layer (C) of amorphous carbon material having sp2 hybrid bonds and sp3 hybrid bonds, The aforementioned layer (C) is: - The first content of sp3 hybrid bonds on the substrate (S) side (sp3%1h), and - The outer surface (SE) side of the layer (C) has a second content (sp3%2b) of sp3 hybrid bonds, - The first content (sp3%1h) is greater than the second content (sp3%2b), The average content of sp3 hybrid bonds within layer (C) is 5% to 65%, preferably 5% to 45%, and the content of sp3 hybrid bonds changes continuously within layer (C). Component (P).

2. The member (P) is characterized by comprising a single layer (C) of a carbon-based material. The member (P) according to claim 1.

3. The carbon-based material includes amorphous carbon "a-C", The member (P) according to claim 1 or claim 2.

4. The carbon-based material is characterized by not containing a dopant. The member (P) according to any one of claims 1 to 3.

5. The carbon-based material is characterized by not containing nitrogen and hydrogen, and more preferably not containing oxygen. The member (P) according to any one of claims 1 to 4.

6. The carbon-based material is characterized by having an average content of sp3 hybrid bonds of 10% to 45%, preferably 10% to 30%. The member (P) according to any one of claims 1 to 5.

7. The layer (C) is characterized by having a thickness of 20 nm to 250 nm, preferably 50 nm to 150 nm. The member (P) according to any one of claims 1 to 6.

8. The member (P) is characterized by comprising a lower layer (SC) which is disposed between the base material (S) and the carbon-based material layer (C) and is in contact with the layer (C), The member (P) according to any one of claims 1 to 7.

9. The material of the lower layer (SC) is selected from chromium, titanium, zirconium, tantalum, niobium, or alloys thereof, and nitrides, nitrocarbides, and carbides thereof, or the material of the lower layer (SC) is a ceramic. The member (P) according to claim 8.

10. The material receiving the aforementioned layer (C) is characterized in that carbon is injected into it. The member (P) according to any one of claims 1 to 9.

11. A method for vacuum deposition of a layer (C) of amorphous carbon-based material onto a substrate (S), The parameters that affect the ratio of sp2 or sp3 hybrid bonds in carbon are: - The first content of sp3 hybrid bonds on the substrate (S) side (sp3%1h), and - The second content (sp3%2b) of sp3 hybrid bonds on the outer surface (SE) side of the layer (C), wherein this second content is lower than the first content (sp3%1h), The layer (C) changes continuously during deposition so that it has the following characteristics: The average content of sp3 hybrid bonds in the layer (C) is 5% to 65%, preferably 5% to 45%, and The content of sp3 hybrid bonds is characterized by continuously changing within the layer (C). Vacuum deposition method.

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