Conductive and corrosion-resistant composite coating

Abstract

The present invention provides a substrate with a coating comprising, in order: a) a substrate; b) a primer layer comprising a first transition metal or an oxide thereof; c) one or more corrosion resistant layers, each layer comprising a first sub-layer, a second sub-layer and a third sub-layer, the sub-layers comprising the first transition metal and a second transition metal, where the ratio of the first transition metal and the second transition metal varies between the sub-layers; d) a conductive layer comprising the second transition metal, or a nitride thereof and / or an oxide thereof. The invention also describes a method for producing such a substrate with a coating. The coated substrate has good electrical conductivity and corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present invention relates to a coating that is electrically conductive and also has corrosion resistance, and methods of making and using such a coating. The coating is believed to be particularly suitable for use in electrolyser components, in particular bipolar plates, current collectors and porous transport layers. BACKGROUND

[0002] With increasing awareness of the impact of climate change, there is an increasing interest in alternative “non-fossil” energy sources such as hydrogen.

[0003] Proton exchange membrane (PEM) electrolyser technology has the advantages of compact structure, fast response, high current density and strong adaptability. Therefore, PEM water electrolysis for hydrogen production is an important technical route for future hydrogen production.

[0004] Bipolar plates, current collectors and porous transport layers (PTLs) are important components of PEM electrolyser. The environment on the anode side of a PEM electrolyser is relatively harsh (including high temperature of about 60°C to 80°C, strongly acidic environment of about pH 2, high voltage of about 1.4V to 2V and presence of oxygen). Therefore, the surface of untreated bipolar plates and porous transport layers is prone to oxidation, leading to an increase in contact resistance. This affects the overall operating efficiency of the PEM electrolyser.

[0005] Currently, to address this issue, noble metal materials such as platinum, gold or iridium oxide are coated on the surface of metal bipolar plates and porous transport layers to improve their electrical conductivity and corrosion resistance. However, noble metal coatings are relatively expensive, which limits the development of PEM electrolyser. Therefore, research and development of non-noble metal coatings with high electrical conductivity and high corrosion resistance is an important way to reduce costs and improve the service life of electrolyser.

[0006] CN114214658A describes a coating deposited by a magnetron sputtering deposition method, where the electrical conductivity test results show that the initial contact resistance of the coating is greater than 3.5 mΩ•cm 2 at 1.5 MPa.

[0007] CN114990605A describes a coating comprising transition metal nitride and oxide. The electrical conductivity and corrosion resistance of various coatings are compared, where the initial contact resistance is greater than 3 mΩ•cm 2 at 1.5 MPa.

[0008] CN115710713A describes a coating comprising doped metal oxide. The deposition of this coating is carried out by high temperature (400°C to 1000°C) PVD combined with evaporation, which is relatively complex and has a high cost of product manufacture.

[0009] CN113584441A describes a metal bipolar plate coating and a method for its preparation. The coating described therein comprises an underlayer, an oxidation resistant layer and a noble metal doped layer deposited sequentially on a substrate.

[0010] CN109735869B describes a corrosion resistant conductive alloy film layer and a method for its preparation, wherein the alloy film layer is co-deposited from Ti and Nb.

[0011] As mentioned above, some prior art coatings prepared by magnetron sputtering method generally have a large initial contact resistance and poor electrical conductivity. Other prior art coatings require high temperature deposition processes, which are complex and have high energy consumption for industrial applications. Furthermore, while noble metal coatings can be used, these coatings are expensive.

[0012] Therefore, there is a need for alternative coatings for electrolytic cells that exhibit good corrosion resistance, preferably more economical than currently available solutions. SUMMARY

[0013] The present invention provides a composite coating having high electrical conductivity and high corrosion resistance, which can be applied to electrolytic cell components to reduce the operating cost and increase the service life of a proton exchange membrane (PEM) water electrolyzer.

[0014] Accordingly, the present invention provides a coated substrate comprising, in order:

[0015] a) a substrate;

[0016] b) a seed layer, the seed layer comprising a first transition metal or an oxide thereof;

[0017] c) one or more corrosion resistant layers, each layer comprising a first sublayer, a second sublayer and a third sublayer, the sublayers comprising a first transition metal and a second transition metal, wherein the ratio of the first transition metal and the second transition metal varies between sublayers;

[0018] d) a conductive layer, the conductive layer comprising a second transition metal, or a nitride and / or an oxide thereof.

[0019] As shown in the following examples, the coating of the present invention has excellent electrical conductivity and corrosion resistance.

[0020] The present invention avoids the use of noble metals, thereby reducing production costs. Furthermore, the coating can be applied using a low temperature deposition process, for example a magnetron sputtering method.

[0021] The coating can be applied on bipolar plates, porous transport layers (PTLs), and current collectors of water electrolysis devices.

[0022] The present application also provides a method of making a substrate with a coating (e.g., a substrate with a coating as described herein), the method comprising depositing, in order, on a substrate:

[0023] a) a primer layer, the primer layer comprising a first transition metal or an oxide thereof;

[0024] b) one or more corrosion resistant layers, each layer comprising a first sublayer, a second sublayer, and a third sublayer, the sublayers comprising a first transition metal and a second transition metal, wherein the ratio of the first transition metal and the second transition metal varies between sublayers; and

[0025] c) a conductive layer, the conductive layer comprising a second transition metal, or a nitride and / or an oxide thereof. DETAILED DESCRIPTION

[0026] As described above, the coating imparts good corrosion resistance and electrical conductivity to the substrate with a coating. Accordingly, the coating can be used in a variety of applications. However, one particular application in which the coating can be used is in components for electrolyzers, particularly proton exchange membrane (PEM) electrolyzers.

[0027] Various components of a PEM electrolyzer are exposed to harsh conditions, such as high-potential environments and acidic environments, during use, which can lead to corrosion. Examples of such components include bipolar plates, current collectors, porous transport layers (PTLs), and gradient Ti meshes. These components are typically formed of titanium.

[0028] The substrate can also be formed of other materials that are typically used to manufacture bipolar plates (or other PEM electrolyzer components). The substrate is also typically a material that is susceptible to corrosion. For example, the substrate can be a metallic substrate. When the substrate is a metal, the substrate can be formed of a single metal or of an alloy (e.g., an alloy of iron, titanium, or aluminum). Preferably, the substrate is a titanium substrate, as titanium is a common material used for electrolyzers. The substrate can also be a steel substrate, preferably stainless steel, such as a SUS304 or 316L stainless steel substrate, which is commonly used to manufacture bipolar plates for PEM electrolyzers. SUS301 and SUS303 stainless steel can also be suitable for use as a substrate.

[0029] The dimensions of the metallic substrate will of course depend on the use of the substrate. For bipolar plates used in electrolytic cells, the thickness of the substrate (i.e. excluding the coating) is typically a few millimetres, for example 2 mm or less, 1.5 mm or less, for example preferably about 1 mm. The bipolar plates can have flow field channels on the surface, or can be flat metal plates with profiled insert parts (e.g. Ti mesh providing the channel structure).

[0030] As mentioned above, the coating comprises in order from the substrate: a primer layer, one or more corrosion resistant layers (each layer having a plurality of sub-layers), and a conductive layer.

[0031] Herein, the term "transition metal" refers to an element whose atom has an incompletely filled d sub-shell, according to the current IUPAC definition of the term, or to an element which forms one or more stable ions with an incompletely filled d sub-shell. In some embodiments, the transition metal is a first- or second-row transition metal.

[0032] The primer layer comprises one or more transition metal elements. For example, the primer layer can comprise one or more elements selected from Sc, Ti, Zr, Nb, W, Ta, V, Hf, Cr and Mo. The primer layer can also comprise alloys and / or oxides of these transition metals. Typically, the primer layer comprises one or more metals selected from Ti, Ta, Nb, Zr, W and oxides thereof. Preferred materials for the primer layer are selected from Ti, Nb and oxides thereof. Thus, the primer layer can consist of Ti or Nb or a combination thereof only. Alternatively, the primer layer can consist of an oxide of Ti, Nb or a combination thereof, thus comprising Ti, Nb and O. In many of the examples described herein, the primer layer is a titanium niobium oxide layer comprising Ti, Nb and O.

[0033] When present, the percentage of oxygen atoms in the primer layer can be in the range 1% to 20%, for example 5% to 15%. When the primer layer comprises Ti, Nb and O, the atomic percentages are typically as follows: the percentage of Ti atoms in the primer layer is typically in the range 20% to 70%, for example 30% to 60%, and / or the percentage of Nb atoms in the primer layer is typically in the range 15% to 65%, for example 25% to 55%.

[0034] When there is no oxygen in the primer layer and the primer layer comprises Ti and Nb, the percentage of Ti atoms in the primer layer is typically in the range 30% to 80%, for example 40% to 70%, and / or the percentage of Nb atoms in the primer layer is typically in the range 20% to 70%, for example 30% to 60%.

[0035] Atomic content can be measured by an energy dispersive spectrometer (EDS) of an electron microscope. Other quantitative measurement methods include electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS).

[0036] The underlayer is typically 10 nm or more in thickness, for example 20 nm or more, preferably 50 nm or more or 80 nm or more. The underlayer is typically 3000 nm or less in thickness, for example 1500 nm or less, preferably 1000 nm or less or 800 nm or less. Thus, the underlayer can be from 10 nm to 3000 nm in thickness, for example from 20 nm to 1000 nm, for example from 20 nm to 800 nm.

[0037] The underlayer can be used to promote adhesion of the substrate and the corrosion resistant layer. Thus, the underlayer can be directly adjacent to the substrate and / or directly adjacent to the corrosion resistant layer (or to the lowermost corrosion resistant layer when there are multiple corrosion resistant layers).

[0038] The underlayer can also impart some corrosion resistance to the overall coating, and thus deposition of the underlayer should ensure as much coverage of the substrate as possible. The underlayer is preferably deposited as a high density. Thus, various physical or chemical vapour deposition techniques can be used to deposit the underlayer.

[0039] The coating also includes a conductive layer. The conductive layer is typically the uppermost layer of the coating to provide a coated substrate with a conductive surface, enabling it to perform its function, for example in a PEM electrolyser.

[0040] The conductive layer includes one or more transition metal elements. For example, the conductive layer can include one or more elements selected from Sc, Ti, Zr, Nb, W, Ta, V, Hf, Cr and Mo. The conductive layer can also include alloys, nitrides and / or oxides, and / or oxynitrides of these transition metals. Typically, the conductive layer includes one or more metals selected from Ti, Ta, Nb, Zr, W and their nitrides and / or oxides and / or oxynitrides. Preferred materials for the conductive layer are selected from Ti, Nb and their nitrides and / or oxides and / or oxynitrides. Thus, the conductive layer can consist of Ti, Nb, nitrides, oxides and oxynitrides of Ti and / or Nb. The conductive layer can include a mixture of Ti, Nb, N and O. In many examples described herein, the conductive layer is a layer including Ti, Nb, N and O.

[0041] The atomic percentage of the first transition metal in the conductive layer is between 30% and 60%, preferably between 35% and 55%, for example between 40% and 50%.

[0042] The atomic percentage of the second transition metal in the conductive layer is between 1 and 35%, preferably between 5 and 30%, for example between 10 and 25%.

[0043] The nitrogen content of the conductive layer can be between 1 and 60%, preferably for example between 5 and 50%, most preferably between 10 and 40%.

[0044] The oxygen content of the conductive layer can be between 1 and 40%, for example 5 and 35%, most preferably between 10 and 30%.

[0045] While pure nitride films can have a higher conductivity, their surface can be more susceptible to passivation, resulting in a decrease in conductivity. The addition of oxygen atoms to the conductive layer can serve to increase the corrosion resistance of the conductive layer while maintaining the conductivity.

[0046] The thickness of the conductive layer is typically 50 nm or more, for example 80 nm or more, preferably 100 nm or more or 200 nm or more. The thickness of the conductive layer is typically 3000 nm or less, for example 2500 nm or less, preferably 2000 nm or less or 1500 nm or less. Thus, the thickness of the conductive layer can be between 50 nm and 3000 nm, for example between 100 nm and 2000 nm, for example between 200 nm and 1500 nm.

[0047] The conductive layer is typically directly adjacent to the corrosion resistant layer (or the uppermost corrosion resistant layer when multiple corrosion resistant layers are present).

[0048] The coating of the present application comprises one or more corrosion resistant layers, wherein each layer comprises a first sublayer, a second sublayer and a third sublayer. Each sublayer comprises a first transition metal which is also present in the underlayer and a second transition metal which is also present in the conductive layer.

[0049] The first transition metal and the second transition metal are preferably different from each other. However, this of course does not exclude the second transition metal (and the first transition metal) being present in the underlayer and / or the first transition metal (and the second transition metal) being present in the conductive layer. What is important is that there is a first common transition metal between the underlayer and the corrosion resistant layer and a common second (different) transition metal between the corrosion resistant layer and the conductive layer.

[0050] As noted above, the first and second transition metals, which are also present in the corrosion resistant layer, are preferably titanium and niobium. However, the corrosion resistant layer can include other transition metals, including Sc, Zr, W, Ta, V, Hf, Cr, Mo, and / or nitrides and carbides thereof. Preferred additional transition metals that can be present in the corrosion resistant layer are Ta, Zr, and W, including nitrides and carbides thereof. Typically, the corrosion resistant layer includes one or more metals selected from Ti, Zr, Nb, W, and nitrides and / or oxides thereof. Preferred materials for the corrosion resistant layer are selected from Ti, Nb, and nitrides and / or carbides thereof.

[0051] As described herein, the ratio of the first transition metal to the second transition metal varies between sub-layers. Typically, the ratio of the first transition metal to the second transition metal increases from the first (i.e., the bottom-most) sub-layer to the second sub-layer, and then further increases from the second sub-layer to the third (top-most) sub-layer.

[0052] The variation in the ratio of the first transition metal to the second transition metal can occur step-wise across the sub-layers. In other words, the ratio of the first transition metal and the second transition metal is constant within each sub-layer, but the ratio changes between adjacent sub-layers. Figure 3 The variation in the ratio of the first transition metal to the second transition metal can occur step-wise across the sub-layers. In other words, the ratio of the first transition metal and the second transition metal is constant within each sub-layer, but the ratio changes between adjacent sub-layers. Figure 3 In the example shown, the first transition metal is Ti and the second transition metal is Nb. The Ti sputtering power is shown to increase in a step-wise fashion from alloy sub-layer 1 to alloy sub-layer 3, indicating an increase in Ti content from alloy sub-layer 1 to alloy sub-layer 3. At the same time, the Nb sputtering power decreases step-wise from alloy sub-layer 1 to alloy sub-layer 3, indicating a decrease in Nb content from alloy sub-layer 1 to alloy sub-layer 3. Thus, the Ti:Nb ratio varies in a step-wise manner between sub-layers.

[0053] Alternatively, the ratio of the first transition metal to the second transition metal can vary across the thickness of each sublayer, or it can vary between sublayers. In other words, the ratio of the first transition metal to the second transition metal at the bottom of a sublayer can be different than the ratio of the first transition metal to the second transition metal at the top of the sublayer. For example, the amount of the first transition metal in a sublayer can progressively increase or decrease across the thickness of the sublayer, while the amount of the second transition metal in the sublayer progressesively decreases or increases. As noted above, the ratio of the first transition metal to the second transition metal can also vary between different sublayers. In this arrangement, the ratio of the first transition metal to the second transition metal is a gradual transition across the thickness of each sublayer.

[0054] Figure 4 The power of the two sputter transition metal targets during deposition of the corrosion resistant layer with a step-wise transition across the sublayers is shown as a function of time. In this example, the first transition metal is Ti and the second transition metal is Nb. The Ti sputter power is shown as increasing progressively across the sublayers 1-4, indicating that the Ti content increases progressively across the sublayers 1-4. At the same time, the Nb sputter power is shown as decreasing progressively across the sublayers 1-4, indicating that the Nb content decreases progressively across the sublayers 1-4. Figure 4 In this example, the first transition metal is Ti and the second transition metal is Nb. The Ti sputter power is shown as increasing progressively across the sublayers 1 and 3, indicating that the Ti content increases progressively across the sublayers 1 and 3. At the same time, the Nb sputter power is shown as decreasing progressively across the sublayers 1 and 3, indicating that the Nb content decreases progressively across the sublayers 1 and 3. This is in contrast to the example shown in FIG. 2, where the Ti sputter power is shown as decreasing progressively across the sublayers 1 and 3, indicating that the Ti content decreases progressively across the sublayers 1 and 3. Figure 3 Very similar to the example shown in FIG. 2, Figure 4 The overall change in the Ti:Nb ratio across the sublayers is shown.

[0055] As shown in FIG. 1, the ratio of the first transition metal to the second transition metal can vary across the thickness of each sublayer, or it can vary between sublayers. In other words, the ratio of the first transition metal to the second transition metal at the bottom of a sublayer can be different than the ratio of the first transition metal to the second transition metal at the top of the sublayer. For example, the amount of the first transition metal in a sublayer can progressively increase or decrease across the thickness of the sublayer, while the amount of the second transition metal in the sublayer progressesively decreases or increases. As noted above, the ratio of the first transition metal to the second transition metal can also vary between different sublayers. In this arrangement, the ratio of the first transition metal to the second transition metal is a gradual transition across the thickness of each sublayer. Figure 3 and Figure 4 By using variable power deposition of the first transition metal (e.g., Ti) and the second transition metal (e.g., Nb) at high, medium, and low power across the sublayers of the corrosion resistant layer, the major elements of the alloy in each sublayer of the corrosion resistant layer can be finely tuned and controlled. This helps to better define the properties of each sublayer within the corrosion resistant layer and ensures that the corrosion resistant layer as a whole exhibits the properties of the first transition metal and the second transition metal.

[0056] Generally, the embodiments of the present application involving a step-wise transition across the sublayers, as well as the embodiments of the present application involving a gradual transition across the sublayers, both include a central (i.e., second) sublayer that contains a constant ratio of the first transition metal to the second transition metal.

[0057] In one embodiment, the ratio of the first transition metal to the second transition metal varies across the thickness of the first and third sublayers, but remains constant across the entire second sublayer. Figure 4The variation of sputtering power of the two transition metal targets over time is shown during deposition of the corrosion resistant layer with gradual transition on sub-layers.

[0058] The ratio of the first transition metal and the second transition metal within the sub-layers can be controlled by varying the power of the magnetron sputtering target. By forming different sub-layers (using variable power deposition), the properties of the corrosion resistant layer are transitioned from being more electrically conductive to being more corrosion resistant. This simultaneously achieves both corrosion resistance and high electrical conductivity.

[0059] The above describes how each corrosion resistant layer comprises 3 sub-layers. However, it will be appreciated that there can be more sub-layers. For example, each corrosion resistant layer can comprise 4, 5, 6 or more sub-layers. Regardless of the number of sub-layers, there is a variation in the ratio of the first transition metal and the second transition metal between the sub-layers, preferably increasing / decreasing as described above from the lower layers to the upper layers (or vice versa).

[0060] Configuring each corrosion resistant layer to comprise 3, 4, 5, 6 or more sub-layers allows for a gradual or stepped transition in the primary alloying component from the second transition metal to the first transition metal. This allows each corrosion resistant layer to have the properties of both transition metals, thereby ensuring the coating of the present application has good corrosion resistance and high electrical conductivity.

[0061] Typically, in the coating of the present application, the hardness of the corrosion resistant layers increases from the first (bottom) sub-layer to the third (top) sub-layer. This is achieved by transitioning the primary alloying component from a lower hardness transition metal (e.g. Nb) to a higher hardness transition metal (e.g. Ti). The first (bottom) sub-layer of the corrosion resistant layer which is directly connected to the base layer preferably comprises a lower hardness alloy typically formed from Ti and Nb, with the primary alloying component preferably being Nb. The third (top) sub-layer which is directly connected to the conductive layer preferably comprises a harder alloy typically formed from Ti and Nb, with the primary alloying component preferably being Ti.

[0062] The ratio of the first transition metal (e.g. Ti) in the third (top) sub-layer is preferably greater than the ratio of the first transition metal in the first (bottom) sub-layer. This results in the third (top) sub-layer having an increased hardness (relative to the first sub-layer) and improves the adhesion of the third (bottom) sub-layer to the conductive layer. Likewise, the ratio of the second transition metal (e.g. Nb) in the first (bottom) sub-layer is preferably greater than the ratio of the second transition metal in the third (top) sub-layer. This results in the first (bottom) sub-layer having a reduced hardness (relative to the third sub-layer) and improves the adhesion of the first (bottom) sub-layer to the base layer.

[0063] The overall coating hardness is typically in the range of 100 HV to 1000 HV, preferably 200 HV to 500 HV, most preferably 300 HV to 400 HV. Hardness values (HV) are measured according to ASTM E2546 nanoindentation standard.

[0064] The ratio of the first (e.g. Ti) transition metal to the second (e.g. Nb) transition metal in sublayer 1 can be between 0.2:1 to 0.9:1, preferably between 0.3:1 to 0.8:1.

[0065] The ratio of the first (e.g. Ti) transition metal to the second (e.g. Nb) transition metal in sublayer 2 can be between 0.5:1 to 1.8:1, preferably between 0.6:1 to 1.3:1.

[0066] The ratio of the first (e.g. Ti) transition metal to the second (e.g. Nb) transition metal in sublayer 3 can be between 0.9:1 to 5:1, preferably between 1:1 to 4:1.

[0067] The coating can comprise two or more corrosion resistant layers (e.g. Figure 2 as shown), wherein each corrosion resistant layer comprises three sublayers as described above. The use of multiple corrosion resistant layers can help to avoid the formation of columnar structures within the coating, which can be caused by the thickness of a single layer film and affect the susceptibility of the coating to corrosion.

[0068] In thicker single layer coatings, columnar structures tend to form more easily and become more pronounced. By dividing each corrosion resistant layer into different sublayers in the coating of the present application, the likelihood of columnar structure formation can be reduced and any columnar structures that do form are smaller and able to extend through a lower proportion of the corrosion resistant layer. This reduces the development of void networks formed by columnar structures, thereby improving the corrosion resistance of the coating.

[0069] It will be appreciated that in certain embodiments of the present application comprising two or more corrosion resistant layers, an interface is formed between the top (third) sublayer of the first corrosion resistant layer and the bottom (first) sublayer of the second corrosion resistant layer.

[0070] As mentioned above, in each corrosion resistant layer, the first transition metal (typically Ti) content in each sub-layer increases from the first (bottom) sub-layer to the third (top) sub-layer. Therefore, the interface between adjacent corrosion resistant layers preferably involves a transition between the third (top) sub-layer of the first corrosion resistant layer (having a higher proportion of the first transition metal (e.g. Ti) which has a higher hardness and corrosion resistance) and the adjacent first (bottom) sub-layer in the adjacent second corrosion resistant layer (having a lower proportion of the first transition metal but a higher proportion of the second transition metal (e.g. Nb) which has a higher hardness and lower corrosion resistance but higher electrical conductivity). This interface between corrosion resistant layers in the present application helps to reduce the interfacial contact resistance, thereby enhancing the electrical conductivity of the coating according to the present application.

[0071] Preferably, the proportion of the second transition metal (typically Nb) in the first (bottom) sub-layer of the first corrosion resistant layer is lower than the proportion of the second transition metal (typically Nb) in the first (bottom) sub-layer of the second corrosion resistant layer. Preferably, the overall proportion of Nb is higher in the second corrosion resistant layer relative to the first corrosion resistant layer. This results in the second corrosion resistant layer having a higher electrical conductivity than the first corrosion resistant layer. In particular embodiments of the present application comprising two or more corrosion resistant layers, preferably the proportion or content of Nb increases in subsequent corrosion resistant layers from the first (bottom) corrosion resistant layer to the top corrosion resistant layer.

[0072] The thickness of each sub-layer within the corrosion resistant layer is typically greater than 10 nm, for example greater than 20 nm. The maximum thickness of each sub-layer is typically up to 1500 nm, preferably up to 1000 nm, for example up to 500 nm or up to 250 nm. Thus, the thickness of each sub-layer can be from 10 nm to 1000 nm, for example from 20 nm to 500 nm, preferably from 20 nm to 250 nm.

[0073] In some embodiments, each sub-layer within the corrosion resistant layer will have the same thickness. In other embodiments, the thickness of the second sub-layer is less than the thickness of the first sub-layer and / or the thickness of the third sub-layer is less than the thickness of the second sub-layer.

[0074] The deposition rate of different transition metals will vary even if the sputtering power is the same. The duration for sputtering each sub-layer can be the same or different depending on the deposition rate of the metal used and the preferred thickness of each sub-layer. When sputtering each sub-layer with the same duration, the thickness of sub-layer 1 to sub-layer 3 can increase or decrease depending on the combination of transition metals and the nature of their deposition rates.

[0075] For example, at the same sputtering power, the deposition rate of Ti is lower than the deposition rate of Nb. Therefore, when the same sputtering duration is employed for each sub-layer, the thickness of the sub-layer decreases from sub-layer 1 to sub-layer 3 as the sputtering power of Nb is decreased.

[0076] The total thickness of the corrosion resistant layer is typically greater than 50 nm, preferably greater than 100 nm. The maximum thickness of the corrosion resistant layer can be up to 3000 nm, for example up to 2000 nm. Thus, the total thickness of the corrosion resistant layer can be in the range of 60 nm to 3000 nm, preferably in the range of 100 nm to 2000 nm. In this context, the term total thickness refers to the thickness of all corrosion resistant layers when multiple corrosion resistant layers are present.

[0077] The electrical conductivity of a substrate with a coating depends not only on the material present in the conductive layer, but also on the material of the underlying layers and the interfacial resistance between the different layers. It is more meaningful to measure the electrical conductivity of the entire composite coating (together with the substrate) than to measure the electrical conductivity of the conductive layer. The electrical conductivity of a substrate with a coating is measured by the interfacial contact resistance (ICR).

[0078] A standard method to measure the ICR of a hydrogen fuel cell bipolar plate is available from the US Department of Energy (DOE) and is adopted herein for measuring the ICR of an electrolyzer assembly, such as a bipolar plate. A similar method is also described in Wang H. et al . J. Power Sources , 2003, 115, 2, 243-251 。

[0079] In these methods, the sample is sandwiched between two sheets of conductive carbon paper, two copper plates are placed on the outside of the carbon paper, and a compaction force is applied through the two copper plates. An electrical current is provided through the two copper plates, and the voltage drop is measured while the compaction force is gradually increased. The ICR of the carbon paper / sample interface can be calculated from the total electrical resistance (sum of the four interfacial components, including the two carbon paper / copper plate interfaces and the two carbon paper / sample interfaces) and the carbon paper / copper plate interfacial contact resistance.

[0080] The ICR value of a substrate with a coating measured at 1.4 MPa before being subjected to the corrosion test conditions is typically in the range of 1 mW-cm 2 to 3 mW-cm 2 .

[0081] The total thickness of the coating (including the primer layer, the corrosion resistant layer, and the conductive layer) is typically 10 pm or less, for example 8 pm or less or 5 pm or less. The total thickness of the coating can be in the range of 180 nm to 9000 nm, preferably in the range of 600 nm to 5000 nm, more preferably in the range of 800 nm to 5000 nm.

[0082] The total thickness of the coating is typically measured using a stylus profilometer. The deposition rate of different materials at different power conditions can be used to calculate the duration required to deposit a thin layer of the required thickness. The thickness of each sub-layer is typically measured using a scanning electron microscope. This technique captures a cross-sectional image of the substrate with the coating, so that the thickness of each layer can be determined.

[0083] The following provides specific embodiments of the present invention:

[0084] A. A substrate having a coating comprising, in order:

[0085] a) a substrate;

[0086] b) a primer layer comprising a first transition metal or an oxide thereof;

[0087] c) one or more corrosion resistant layers, each layer comprising a first sub-layer, a second sub-layer and a third sub-layer, wherein the content of the first transition metal increases from the first sub-layer to the third sub-layer and the content of a second transition metal decreases from the first sub-layer to the third sub-layer; and

[0088] d) a conductive layer comprising a second transition metal, or a nitride and / or an oxide thereof.

[0089] B. A substrate having a coating comprising, in order:

[0090] a) a substrate;

[0091] b) a primer layer comprising Ti, Nb or an oxide thereof;

[0092] c) one or more corrosion resistant layers, each layer comprising a first sub-layer, a second sub-layer and a third sub-layer, wherein the content of Ti increases from the first sub-layer to the third sub-layer and the content of Nb decreases from the first sub-layer to the third sub-layer; and

[0093] d) a conductive layer comprising Ti, Nb, or a nitride and / or an oxide thereof (preferably a nitride and an oxide of Ti or Nb).

[0094] The primer layer, corrosion resistant layers and conductive layer can each be deposited by conventional techniques used in thin film deposition. For example, the layers can be deposited by ion implantation, sputtering, multi-arc ion plating or atomic layer deposition. Preferably, the layers are deposited by magnetron sputtering (including high power pulsed magnetron sputtering as this helps to make the coating dense).

[0095] As mentioned above, the coating can be used on a component part of a proton exchange membrane electrolyser. Thus, there is also provided a substrate having a coating as defined herein, wherein the substrate can be a component part of a water electrolyser, for example a PEM electrolyser. The component part can be selected from the group consisting of an electrolyser assembly, a bipolar plate, a current collector and a porous transport layer. The present application also provides an electrolyser comprising one or more components plated with a coating as described herein.

[0096] The present application also provides a method of making a substrate having a coating (for example a substrate having a coating as defined herein), the method comprising depositing, in order, on a substrate:

[0097] a) a primer layer, the primer layer comprising a first transition metal or an oxide thereof;

[0098] b) one or more corrosion resistant layers, each layer comprising a first sub-layer, a second sub-layer and a third sub-layer, the sub-layers comprising the first transition metal and a second transition metal, wherein the ratio of the first transition metal and the second transition metal varies between sub-layers;

[0099] c) a conductive layer, the conductive layer comprising a second transition metal, or a nitride thereof and / or an oxide thereof.

[0100] The substrate, primer layer, corrosion resistant layers and conductive layer can have the features and properties described above in relation to the substrate having a coating itself.

[0101] The method can further comprise a pre-treatment step prior to depositing the primer layer onto the substrate. The pre-treatment step can comprise removing any impurities (for example oxides or oils) from the surface of the substrate and / or etching the surface of the substrate. Etching can be performed using an ion beam source.

[0102] The pre-treatment and / or deposition is typically performed in a vacuum environment in a coating chamber at a gas pressure of 1 Pa or less, for example 0.7 Pa or less, 0.5 Pa or less or 0.3 Pa or less. The gas pressure is maintained by argon gas. The coating chamber can be heated to a temperature of 50 °C or more but less than 200 °C.

[0103] In the pre-treatment cleaning step, the substrate is typically applied with a bias voltage of -50 V to -900 V and an ion cleaning time of 0.1 hours to 1 hour can be used to remove oxides from the surface of the substrate.

[0104] When depositing the corrosion resistant layers, the metal targets can be sputtered in the presence of argon gas at different powers, wherein the power of one metal target is gradually increased and the power of the other metal target is gradually decreased. By adjusting the power of the different metal targets, the first sub-layer, second sub-layer and third sub-layer can be deposited. As mentioned above, the deposition of the sub-layers can be repeated to form a coating having a plurality of corrosion resistant layers. BRIEF DESCRIPTION OF DRAWINGS

[0105] Figure 1 Schematically showing the structure of a substrate with a coating according to one embodiment of the present application, comprising a substrate (1); a primer layer (2); a corrosion resistant layer (3) having a first sublayer (3-1), a second sublayer (3-2) and a third sublayer (3-3); and a conductive layer (4).

[0106] Figure 2 Schematically showing the structure of a substrate with a coating according to another embodiment of the present application, comprising a substrate (1); a primer layer (2); two corrosion resistant layers (3), each layer having a first sublayer (3-1), a second sublayer (3-2) and a third sublayer (3-3); and a conductive layer (4).

[0107] Figure 3 Showing the variation of the power of Ti and Nb sputter targets over time during deposition of a corrosion resistant layer in a coating of the present application, wherein the ratio of the first transition metal and the second transition metal varies stepwise over the sublayers.

[0108] Figure 4 Showing the variation of the power of Ti and Nb sputter targets over time during deposition of a corrosion resistant layer in a coating of the present application, wherein the ratio of the first transition metal and the second transition metal varies gradually over the thickness of the first and third sublayer.

[0109] Example

[0110] The present application will now be illustrated by the following examples. All examples below, including the comparative examples, use a TA1 titanium sheet substrate. TA1 is an industrial pure titanium alloy.

[0111] Example 1

[0112] Step 1: Mount the pre-cleaned pure titanium substrate (TA1) onto a plating fixture (also known as a substrate holder).

[0113] Step 2: Load the plating fixture pre-mounted with the substrate into the plating chamber and pump the chamber down to the desired vacuum level. The temperature of the heater is set to 135 °C and this temperature is maintained throughout the plating process.

[0114] Step 3: Pump the chamber down to 0.03 Pa. Once the temperature has reached 135 °C, maintain the gas pressure at 0.1 Pa by introducing argon gas. Apply a bias voltage of -700 V to the substrate and perform an ion clean for 0.5 hours to remove the oxide layer from the surface of the substrate.

[0115] Step 4: After the ion clean is complete, maintain the vacuum and introduce argon and oxygen gas to maintain the gas pressure at 0.5 Pa and the temperature at 135 °C. Sputter a Ti metal target and a Nb metal target to form a dense primer layer with a thickness of 200 nm on the surface of the Ti substrate.

[0116] Step 5: Sputtering of Ti and Nb targets under argon gas with variable power sputtering, where the power of the Ti target is gradually increased and the power of the Nb target is gradually decreased (see Figure 2). The alloy sublayer 1, the alloy sublayer 2 and the alloy sublayer 3 are deposited and the three sublayers are deposited twice (i.e. three layers are deposited in repetition). The thickness of the first alloy sublayer, the second alloy sublayer and the third alloy sublayer is 120 nm, 80 nm and 50 nm, respectively. The deposition is performed at a pressure of 0.4 Pa and a temperature of 135 °C. The film thickness of the corrosion resistant layer is 500 nm. Figure 4

[0117] Step 6: Finally, Ti and Nb targets are sputtered under argon, nitrogen and oxygen gas at a pressure of about 0.7 Pa and a deposition temperature of 135 °C. The thickness of the conductive layer is 500 nm, wherein the proportion of nitrogen atoms is 30% and the proportion of oxygen atoms is 20%.

[0118] The total thickness of the non-noble metal composite coating obtained is 1200 nm.

[0119] The interfacial contact resistance (ICR) of the substrate with the coating is measured as described before. Three readings are taken at a compressive force of 1.4 MPa, the average is calculated and recorded.

[0120] In order to be able to accelerate the tests, the following corrosion environment is used: constant potential of 2 V vs. Standard Hydrogen Electrode (SHE) for potentiostatic voltammetry; 0.5 M H2SO4 is used to prepare 5 ppm F - in an acidic environment with a pH of 2; the temperature is 80 °C. These conditions are more severe than the actual operating conditions of a PEM electrolyser. The test procedure is as follows:

[0121] 1) The substrate with the coating is placed in a three-electrode system for electrochemical testing (the substrate with the coating is the working electrode) and an electrolyte with a pH of 2 containing 0.5 M H2SO4 + 5 ppm F - is added;

[0122] 2) The wires of the electrochemical workstation are connected to the three electrodes of the electrolysis system, i.e. the working electrode, the counter electrode and the reference electrode, and the voltage is set to 2 V vs. SHE;

[0123] 3) Before starting the potentiostatic polarization test and recording the corrosion current data, the electrolyte is heated until the temperature reaches 80 °C;

[0124] 4) A durability test of 10 hours is performed.

[0125] ​The interfacial contact resistance (ICR) after potentiostatic polarization was tested again under a compaction force of 1.4 MPa, and the average of three readings was calculated and recorded.

[0126] All the examples and comparative examples listed in the present invention have adopted the above-mentioned test procedure.

[0127] Test results of Example 1

[0128] (1) Contact resistance: The initial ICR between the titanium plate and the carbon paper was 1.7 mW-cm 2 under 1.4 MPa. After the long-term durability test (2 V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 6.33 mW-cm 2 .

[0129] (2) Potentiostatic polarization curve: In 0.5 M H2SO4+5 ppm F - solution, after the long-term durability test (2 V vs. SHE, 10 hours), the corrosion current density of the potentiostatic (2 V vs. SHE) test was 3.34 pA / cm 2 .

[0130] Example 2

[0131] Steps 1 to 3 are as described in Example 1, with the only difference being that in Step 3, the bias voltage is set to -500 V.

[0132] Step 4: After the ion cleaning is completed, the vacuum is maintained, and argon gas is introduced to maintain a pressure of 0.5 Pa. The temperature is set to 135 °C, the Nb target is sputtered, and a dense primer layer of 80 nm is formed on the surface of the Ti substrate.

[0133] Steps 5 and 6 are as described in Example 1.

[0134] The total thickness of the obtained non-noble metal composite coating 2 is 1080 nm.

[0135] Test results of Example 2

[0136] (1) Contact resistance: The initial ICR between the titanium plate and the carbon paper was 1.36 mW-cm 2 under 1.4 MPa. After the long-term durability test (2 V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 14.28 mW-cm 2 .

[0137] (2) Potentiostatic polarization curve: In 0.5 M H2SO4+5 ppm F -In solution, after long-term durability test (2V vs. SHE, 10 hours), the corrosion current density of the constant potential (2V vs. SHE) test was 4.74 μA / cm 2 .

[0138] Example 3

[0139] Steps 1 to 4 are as described in Example 1.

[0140] Step 5: Introduce argon gas, and sputter the metal targets of Ti, Zr, Nb and W with variable power, in which the power of the Ti target and the Zr target gradually increases, and the power of the Nb target and the W target gradually decreases. Deposition of alloy sublayer 1, alloy sublayer 2 and alloy sublayer 3 respectively, and deposition of three sublayers twice (repeat variable power cycle), in which the thickness of the alloy sublayer is 200 nm, 120 nm, 80 nm, the deposition gas pressure is 0.4 Pa, and the deposition temperature is 135°C, to form a dense corrosion-resistant layer with a thickness of 800 nm.

[0141] Step 6 is as described in Example 1.

[0142] The total thickness of the obtained non-noble metal composite coating 3 is 1500 nm.

[0143] Test results of Example 3

[0144] (1) Contact resistance: The initial ICR between the titanium plate and the carbon paper is 1.76 mΩ•cm 2 After long-term durability test (2V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper is 15.34 mΩ•cm 2 .

[0145] (2) Constant potential polarization curve: In 0.5M H2SO4+5ppm F - After long-term durability test (2V vs. SHE, 10 hours), the corrosion current density of the constant potential (2V vs. SHE) test is 4.66 μA / cm 2 .

[0146] Example 4

[0147] Steps 1 to 3 are as described in Example 1.

[0148] Step 4: After ion cleaning, the chamber is pumped to the deposition gas pressure, and argon and oxygen are introduced to maintain the gas pressure at 0.5 Pa. The temperature is maintained at 135°C, and the Nb target is sputtered to form a dense primer layer with a thickness of 20 nm on the surface of the Ti substrate.

[0149] Step 5: Introduce argon gas, sputter the Ti metal target and Nb metal target with variable power sputtering, where the power of the Ti target is gradually increased and the power of the Nb target is gradually decreased. Alloy sublayer 1, alloy sublayer 2 and alloy sublayer 3 are deposited respectively, and the three sublayers are deposited twice, where the thickness of the alloy sublayers is 24 nm, 16 nm and 10 nm respectively. The deposition pressure is 0.4 Pa, the deposition temperature is 135 °C, and a dense corrosion-resistant layer with a thickness of 100 nm is formed.

[0150] Step 6: Finally, sputter the Ti target using argon and nitrogen at a deposition pressure of about 0.7 Pa and a deposition temperature of 135 °C. A conductive layer with a thickness of 100 nm is formed.

[0151] A non-noble metal composite coating 4 with a total thickness of 220 nm is obtained.

[0152] Test results of Example 4

[0153] (1) Contact resistance: The initial ICR between the titanium plate and the carbon paper is 1.05 mΩ•cm 2 at 1.4 MPa. After long-term durability testing (2 V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper is 794.15 mΩ•cm 2 .

[0154] (2) Potentiostatic polarization curve: In a 0.5 M H2SO4+5 ppm F - solution, after long-term durability testing (2 V vs. SHE, 10 hours), the corrosion current density of the potentiostatic (2 V vs. SHE) test is 1.53 μA / cm 2 .

[0155] Example 5

[0156] Steps 1 to 3 are as described in Example 1.

[0157] Step 4: After ion cleaning, the chamber is pumped to a deposition pressure, argon gas is introduced at a pressure of 0.5 Pa, the temperature is maintained at 135 °C, and the Ti metal target and the Nb metal target are sputtered to form a dense primer layer with a thickness of 200 nm on the surface of the Ti substrate.

[0158] Steps 5 and 6 are as described in Example 1.

[0159] A non-noble metal composite coating 5 with a total thickness of 1200 nm is obtained.

[0160] Test results of Example 5

[0161] (1) Contact resistance: The initial ICR between the titanium plate and the carbon paper is 1.45 mΩ•cm2 After long-term durability test (2V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 15.29 mΩ•cm 2 .

[0162] (2) Potentiostatic polarization curve: in 0.5M H2SO4+5ppm F - After long-term durability test (2V vs. SHE, 10 hours), the corrosion current density tested at constant potential (2V vs. SHE) was 4.13 μA / cm 2 .

[0163] Example 6

[0164] Steps 1 to 5 were as described in Example 1.

[0165] Step 6: Argon, nitrogen and oxygen were introduced to sputter Ti, Nb, Zr, W targets. The deposition pressure was about 0.7 Pa, the deposition temperature was 135°C, and the thickness of the conductive layer was 500 nm, with a nitrogen atom ratio of 20% and an oxygen atom ratio of 5%.

[0166] A non-noble metal composite coating 6 with a total thickness of 1200 nm was obtained.

[0167] Test results of Example 6

[0168] (1) Contact resistance: the initial ICR between the titanium plate and the carbon paper was 1.6 mΩ•cm at 1.4 MPa 2 After long-term durability test (2V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 10.31 mΩ•cm 2 .

[0169] (2) Potentiostatic polarization curve: in 0.5M H2SO4+5ppm F - After long-term durability test (2V vs. SHE, 10 hours), the corrosion current density tested at constant potential (2V vs. SHE) was 4.52 μA / cm 2 .

[0170] Example 7

[0171] Steps 1 to 3 were as described in Example 1.

[0172] Step 4: After ion cleaning, the chamber was evacuated to a deposition pressure, argon and oxygen were introduced to maintain the pressure at 0.5 Pa, the temperature was maintained at 135°C, Ti and Nb targets were sputtered, and a dense primer layer with a thickness of 250 nm was formed on the surface of the Ti substrate.

[0173] Step 5: Introduce argon and nitrogen, and sputter the Ti metal target and the Nb metal target using variable power sputtering, wherein the power of the Ti target is gradually increased and the power of the Nb target is gradually decreased. Deposition of alloy sublayer 1, alloy sublayer 2 and alloy sublayer 3, respectively, and deposition of the three sublayers twice, wherein the thickness of the alloy sublayers is 100 nm, 60 nm and 40 nm, respectively. The deposition pressure is 0.7 Pa, and the deposition temperature is 135 °C. A corrosion-resistant layer with a thickness of 400 nm is formed.

[0174] Step 6 is as described in Example 1.

[0175] A non-noble metal composite coating 7 with a total thickness of 1150 nm is obtained.

[0176] Test results of Example 7

[0177] (1) Contact resistance: The initial ICR between the titanium plate and the carbon paper is 2.15 mΩ•cm 2 at 1.4 MPa. After long-term durability testing (2 V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper is 65.14 mΩ•cm 2 .

[0178] (2) Potentiostatic polarization curve: In a 0.5 M H2SO4+5 ppm F - solution, after long-term durability testing (2 V vs. SHE, 10 hours), the corrosion current density of the potentiostatic (2 V vs. SHE) test is 2.96 μA / cm 2 .

[0179] Example 8

[0180] Steps 1 to 3 are as described in Example 1.

[0181] Step 4: After ion cleaning, the chamber is evacuated to the deposition pressure, argon and oxygen are introduced to maintain the pressure at 0.5 Pa, the temperature is maintained at 135 °C, and the Ti metal target and the Nb metal target are sputtered to form a dense primer layer with a thickness of 250 nm on the surface of the Ti substrate.

[0182] Step 5: Introduce argon and acetylene gas, and sputter the Ti metal target and the Nb metal target 3 times using variable power sputtering, wherein the power of the Ti target is gradually increased and the power of the Nb target is gradually decreased. Deposition of alloy sublayer 1, alloy sublayer 2 and alloy sublayer 3, respectively, and deposition of the three sublayers twice, wherein the thickness of the alloy sublayers is 160 nm, 110 nm and 55 nm, respectively. The deposition pressure is 0.5 Pa, and the deposition temperature is 135 °C. A corrosion-resistant layer with a thickness of 650 nm is formed.

[0183] Step 6 is the same as described in Example 1.

[0184] A non-noble metal composite coating 8 having a total thickness of 1400 nm was obtained.

[0185] Test results for Example 8

[0186] (1) Contact resistance: The initial ICR between the titanium plate and the carbon paper was 1.36 mW-cm at 1.4 MPa 2 . After the long-term durability test (2 V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 20.05 mW-cm 2 .

[0187] (2) Potentiostatic polarization curve: In 0.5 M H2SO4+ 5 ppm F - solution, after the long-term durability test (2 V vs. SHE, 10 hours), the corrosion current density tested at a constant potential (2 V vs. SHE) was 5.32 pA / cm 2 .

[0188] Example 9

[0189] Steps 1 to 3 were as described in Example 1.

[0190] Step 4: After the ion cleaning was completed, the chamber was evacuated to a deposition pressure, argon was introduced, the chamber pressure was maintained at 0.5 Pa, the temperature was maintained at 135 °C, a Ti metal target was sputtered, and a Ti dense primer layer having a thickness of 200 nm was formed on the surface of the Ti substrate.

[0191] Steps 5 and 6 were as described in Example 1.

[0192] A non-noble metal composite coating 9 having a total thickness of 1200 nm was obtained.

[0193] Test results for Example 9

[0194] (1) Contact resistance: The initial ICR between the titanium plate and the carbon paper was 1.4 mW-cm at 1.4 MPa 2 . After the long-term durability test (2 V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 9.2 mW-cm 2 .

[0195] (2) Potentiostatic polarization curve: In 0.5 M H2SO4+ 5 ppm F - solution, after the long-term durability test (2 V vs. SHE, 10 hours), the corrosion current density tested at a constant potential (2 V vs. SHE) was 3.65 pA / cm 2 .

[0196] Example 10

[0197] Steps 1 to 4 were as described in Example 1.

[0198] Step 5: After the ion cleaning, the chamber was pumped down to the deposition pressure, argon and oxygen were introduced to maintain the pressure at 0.5 Pa, and the temperature was maintained at 135°C. The Ti metal target and the Nb metal target were sputtered to form a dense primer layer with a thickness of 100 nm on the surface of the Ti substrate. Figure 4 Step 6: After the ion cleaning, the chamber was pumped down to the deposition pressure, argon and oxygen were introduced to maintain the pressure at 0.5 Pa, and the temperature was maintained at 135°C. The Ti metal target and the Nb metal target were sputtered to form a dense primer layer with a thickness of 100 nm on the surface of the Ti substrate.

[0199] Step 6 was as described in Example 1.

[0200] A non-noble metal composite coating 10 with a total thickness of 1700 nm was obtained.

[0201] Test results of Example 10

[0202] (1) Contact resistance: The initial ICR between the titanium plate and the carbon paper was 2 mΩ•cm 2 at 1.4 MPa. After the long-term durability test (2 V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 20.1 mΩ•cm 2 .

[0203] (2) Potentiostatic polarization curve: In a 0.5 M H2SO4+5 ppm F - solution, after the long-term durability test (2 V vs. SHE, 10 hours), the corrosion current density of the potentiostatic (2 V vs. SHE) test was 4.14 μA / cm 2 .

[0204] Example 11

[0205] Steps 1 to 3 were as described in Example 1.

[0206] Step 4: After the ion cleaning, the chamber was pumped down to the deposition pressure, argon and oxygen were introduced to maintain the pressure at 0.5 Pa, and the temperature was maintained at 135°C. The Ti metal target and the Nb metal target were sputtered to form a dense primer layer with a thickness of 100 nm on the surface of the Ti substrate.

[0207] Step 5: After the ion cleaning, the chamber was pumped down to the deposition pressure, argon and oxygen were introduced to maintain the pressure at 0.5 Pa, and the temperature was maintained at 135°C. The Ti metal target and the Nb metal target were sputtered to form a dense primer layer with a thickness of 100 nm on the surface of the Ti substrate. Figure 4). The alloy sublayer 1, the alloy sublayer 2 and the alloy sublayer 3 were deposited respectively, and the three sublayers were deposited twice, wherein the thickness of the alloy sublayer was 60 nm, 40 nm, 25 nm respectively. The deposition pressure was 0.4 Pa, the deposition temperature was 135 °C, and the film thickness of the corrosion-resistant layer was 250 nm.

[0208] Step 6: Argon, nitrogen and oxygen were introduced to sputter the Ti target and the Nb target. The deposition pressure was about 0.7 Pa, the deposition temperature was 135 °C, and the thickness of the conductive layer was 250 nm, wherein the proportion of nitrogen atoms was 30%, and the proportion of oxygen atoms was 20%.

[0209] A non-noble metal composite coating 11 with a total thickness of 600 nm was obtained.

[0210] Test results of Example 11

[0211] (1) Contact resistance: The initial ICR between the titanium plate and the carbon paper was 3.95 mΩ•cm 2 at 1.4 MPa. 2 .

[0212] (2) Potentiostatic polarization curve: In 0.5 M H2SO4+5 ppm F - solution, the corrosion current density of the potentiostatic (2 V vs. SHE) test was 2.09 μA / cm 2 after the long-term durability test (2 V vs. SHE, 10 hours).

[0213] Example 12

[0214] Steps 1 to 3 were as described in Example 1.

[0215] Step 4: After the ion cleaning was completed, the chamber was pumped to the deposition pressure, argon and oxygen were introduced to maintain the pressure at 0.5 Pa, the temperature was maintained at 135 °C, the Ti metal target and the Nb metal target were sputtered, and a dense primer layer with a thickness of 130 nm was formed on the surface of the Ti substrate.

[0216] Step 5: Argon was introduced, and the Ti metal target and the Nb metal target were sputtered using variable power sputtering, wherein the power of the Ti target was gradually increased, and the power of the Nb target was gradually decreased (see Figure 4 ). The alloy sublayer 1, the alloy sublayer 2 and the alloy sublayer 3 were deposited respectively, and the three sublayers were deposited twice, wherein the thickness of the alloy sublayer was 80 nm, 50 nm, 40 nm respectively. The deposition pressure was 0.4 Pa, the deposition temperature was 135 °C, and the film thickness of the corrosion-resistant layer was 340 nm.

[0217] Step 6: Introduce argon, nitrogen and oxygen to sputter the Ti and Nb targets. The deposition pressure is about 0.7 Pa, the deposition temperature is 135 °C, and the thickness of the conductive layer is 330 nm, with a nitrogen atom ratio of 25% and an oxygen atom ratio of 20%.

[0218] A non-noble metal composite coating 12 with a total thickness of 800 nm is obtained.

[0219] Test results of Example 12

[0220] (1) Contact resistance: The initial ICR between the titanium plate and the carbon paper is 1.25 mW-cm 2 at 1.4 MPa. After long-term durability testing (2 V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper is 52.75 mW-cm 2 .

[0221] (2) Potentiostatic polarization curve: In a 0.5 M H2SO4+5 ppm F - solution, after long-term durability testing (2 V vs. SHE, 10 hours), the corrosion current density of the potentiostatic (2 V vs. SHE) test is 3.47 pA / cm 2 .

[0222] Example 13

[0223] Steps 1 to 4 are as described in Example 1.

[0224] Step 5: Introduce argon, and use variable power sputtering to sputter the Ti and Nb metal targets 3 times, with the power of the Ti target gradually increasing and the power of the Nb target gradually decreasing (see Figure 4 ). Deposition of alloy sublayer 1, alloy sublayer 2 and alloy sublayer 3 is carried out respectively and repeated six times for each sublayer, with the thickness of the alloy sublayers being 120 nm, 80 nm and 50 nm respectively. The deposition pressure is 0.4 Pa, the deposition temperature is 135 °C, and the thickness of the corrosion-resistant layer is 1500 nm.

[0225] Step 6 is the same as described in Example 1.

[0226] A non-noble metal composite coating 13 with a total thickness of 2200 nm is obtained.

[0227] Test results of Example 13

[0228] (1) Contact resistance: The initial ICR between the titanium plate and the carbon paper is 1.25 mW-cm 2 at 1.4 MPa. After long-term durability testing (2 V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper is 52.75 mW-cm2 .

[0229] (2) Potentially constant polarization curve: at 0.5 M H2SO4 + 5 ppm F - In solution, after a long-term durability test (2V vs. SHE, 10 hours), the corrosion current density under constant potential (2V vs. SHE) testing was 4.29 μA / cm². 2 .

[0230] Example 14

[0231] Steps 1 to 3 are as described in Example 1.

[0232] Step 4: After ion cleaning, the chamber is evacuated to the deposition pressure, and argon and oxygen are introduced to maintain the pressure at 0.5 Pa and the temperature at 135°C. Ti metal target and Nb metal target are sputtered to form a dense underlayer with a thickness of 500 nm on the surface of Ti substrate.

[0233] Step 5: Introduce argon gas and perform three sputtering operations on the Ti and Nb metal targets using variable power sputtering, with the power gradually increasing for the Ti target and gradually decreasing for the Nb target (see [link to relevant documentation]). Figure 4 Alloy sublayers 1, 2, and 3 were deposited separately, and each sublayer was deposited twice. The thicknesses of the alloy sublayers were 240 nm, 160 nm, and 100 nm, respectively. The deposition pressure was 0.4 Pa, the deposition temperature was 135°C, and the thickness of the corrosion-resistant layer was 1000 nm.

[0234] Step 6: Introduce argon, nitrogen, and oxygen to sputter the Ti and Nb targets. The deposition pressure is approximately 0.7 Pa, the deposition temperature is 135°C, and the conductive layer thickness is 1500 nm, with nitrogen atoms accounting for 30% and oxygen atoms accounting for 20%.

[0235] A non-precious metal composite coating with a total thickness of 3000 nm was obtained.14

[0236] Test results of Example 14

[0237] (1) Contact resistance: At 1.4 MPa, the initial ICR between the titanium plate and the carbon paper is 2.72 mΩ•cm. 2 After long-term durability testing (2V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 15.78 mΩ•cm. 2 .

[0238] (2) Potentially constant polarization curve: at 0.5 M H2SO4 + 5 ppm F -In solution, after a long-term durability test (2V vs. SHE, 10 hours), the corrosion current density under constant potential (2V vs. SHE) testing was 4.59 μA / cm². 2 .

[0239] Example 15

[0240] Steps 1 to 3 are as described in Example 1.

[0241] Step 4: After ion cleaning, the chamber is evacuated to the deposition pressure, and argon and oxygen are introduced to maintain the pressure at 0.5 Pa and the temperature at 135°C. Ti metal target and Nb metal target are sputtered to form a dense underlayer with a thickness of 800 nm on the surface of Ti substrate.

[0242] Step 5: Introduce argon gas and perform three sputtering operations on the Ti and Nb metal targets using variable power sputtering, with the power gradually increasing for the Ti target and gradually decreasing for the Nb target (see [link to relevant documentation]). Figure 4 Alloy sublayers 1, 2, and 3 were deposited separately, and each sublayer was deposited twice. The thicknesses of the alloy sublayers were 480 nm, 320 nm, and 200 nm, respectively. The deposition pressure was 0.4 Pa, the deposition temperature was 135°C, and the thickness of the corrosion-resistant layer was 2000 nm.

[0243] Step 6: Introduce argon, nitrogen, and oxygen to sputter the Ti and Nb targets. The deposition pressure is approximately 0.7 Pa, the deposition temperature is 135°C, and the conductive layer thickness is 2000 nm, with nitrogen atoms accounting for 30% and oxygen atoms accounting for 20%.

[0244] A non-precious metal composite coating with a total thickness of 4800 nm was obtained.15

[0245] Test results of Example 15

[0246] (1) Contact resistance: At 1.4 MPa, the initial ICR between the titanium plate and the carbon paper is 1.7 mΩ•cm. 2 After long-term durability testing (2V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 7.73 mΩ•cm. 2 .

[0247] (2) Potentially constant polarization curve: at 0.5 M H2SO4 + 5 ppm F - In solution, after a long-term durability test (2V vs. SHE, 10 hours), the corrosion current density under constant potential (2V vs. SHE) testing was 11.2 μA / cm. 2 .

[0248] Example 16

[0249] Steps 1 to 4 are as described in Example 1.

[0250] Step 5: In the presence of argon gas, such as Figure 3 As shown, Ti and Nb metal targets were sputtered using stepped variable power sputtering. The power of the Ti target was constant across all sublayers, with low power in sublayer 1, medium power in sublayer 2, and high power in sublayer 3. The power of the Nb target was constant across all sublayers, decreasing stepwise from sublayer 1 to sublayer 3. Three sublayers were deposited, with alloy sublayer thicknesses of 240 nm, 160 nm, and 100 nm. The deposition gas pressure was 0.4 Pa, the deposition temperature was 135°C, and the corrosion-resistant layer thickness was 500 nm.

[0251] Step 6 is as described in Example 1.

[0252] A non-precious metal composite coating with a total thickness of 1200 nm was obtained.16

[0253] Test results of Example 16

[0254] (1) Contact resistance: At 1.4 MPa, the initial ICR between the titanium plate and the carbon paper is 1.3 mΩ•cm. 2 After long-term durability testing (2V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 9.2 mΩ•cm. 2 .

[0255] (2) Potentially constant polarization curve: at 0.5 M H2SO4 + 5 ppm F - In solution, after a long-term durability test (2V vs. SHE, 10 hours), the corrosion current density under constant potential (2V vs. SHE) testing was 2.71 μA / cm². 2 .

[0256] Example 17

[0257] Steps 1 to 4 are as described in Example 1.

[0258] Step 5: In the presence of argon, Ti and Nb metal targets are sputtered using stepped variable power sputtering. The power of the Ti target is constant across all sublayers, with low power in sublayer 1, medium power in sublayer 2, and high power in sublayer 3. The power of the Nb target is constant across all sublayers, decreasing stepwise from sublayer 1 to sublayer 3. The first three sublayers are deposited, with alloy sublayer thicknesses of 120 nm, 80 nm, and 50 nm. These three sublayers are repeated to produce another set of three sublayers. The deposition pressure is 0.4 Pa, the deposition temperature is 135°C, and the corrosion-resistant layer thickness is 500 nm.

[0259] Step 6 is as described in Example 1.

[0260] A non-precious metal composite coating with a total thickness of 1200 nm was obtained.17

[0261] Test results of Example 17

[0262] (1) Contact resistance: At 1.4 MPa, the initial ICR between the titanium plate and the carbon paper is 1.75 mΩ•cm. 2 After long-term durability testing (2V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 9.3 mΩ•cm. 2 ;

[0263] (2) Potentially constant polarization curve: at 0.5 M H2SO4 + 5 ppm F - In solution, after a long-term durability test (2V vs. SHE, 10 hours), the corrosion current density under constant potential (2V vs. SHE) testing was 3.01 μA / cm². 2 ;

[0264] Comparative Example 1: Uncoated Ti board

[0265] (1) Contact resistance: At 1.4 MPa, the initial contact resistance between the titanium plate and the carbon paper is 16.4 mΩ•cm. 2 After a long-term durability test (2V vs. SHE, 10 hours), the contact resistance between the substrate and the carbon paper was 1197.8 mΩ•cm. 2 ;

[0266] (2) Potentially constant polarization curve: at 0.5 M H2SO4 + 5 ppm F - In solution, after a long-term durability test (2V vs. SHE, 10 hours), the corrosion current density under constant potential (2V vs. SHE) testing was 4.42 μA / cm². 2 .

[0267] Comparative Example 2: Ti plate coated with a 500nm platinum coating

[0268] (1) Contact resistance: At 1.4 MPa, the initial ICR between the titanium plate and the carbon paper is 1.25 mΩ•cm. 2 After long-term durability testing (2V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 3.85 mΩ•cm. 2 ;

[0269] (2) Potentially constant polarization curve: at 0.5 M H2SO4 + 5 ppm F - In solution, after long-term durability testing (2V vs. SHE, 10 hours), the corrosion current density under constant potential (2V vs. SHE) testing was 533 μA / cm. 2 .

[0270] Comparative Example 3

[0271] Steps 1 to 3 are as described in Example 1.

[0272] Step 4: After ion cleaning, the chamber is evacuated to the deposition pressure, the argon pressure is maintained at 0.5 Pa, the temperature is maintained at 135°C, and a Ti metal target is sputtered to form a 200 nm thick Ti dense underlayer on the surface of the Ti substrate.

[0273] Step 5: Introduce argon gas and sputter the Ti and Nb metal targets at a constant power. The deposition pressure is 0.4 Pa, the deposition temperature is 135°C, and the alloy layer thickness is 500 nm.

[0274] Step 6 is as described in Example 1.

[0275] The total thickness of the comparative coating 3 is 1200 nm.

[0276] Compare the test results of Example 3

[0277] (1) Contact resistance: At 1.4 MPa, the initial ICR between the titanium plate and the carbon paper is 3.98 mΩ•cm. 2 After long-term durability testing (2V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 320.82 mΩ•cm. 2 .

[0278] (2) Potentially constant polarization curve: at 0.5 M H2SO4 + 5 ppm F - In solution, after a long-term durability test (2V vs. SHE, 10 hours), the corrosion current density under constant potential (2V vs. SHE) testing was 3.67 μA / cm. 2 .

[0279] Comparative Example 4

[0280] Steps 1 to 3 are as described in Example 1.

[0281] Step 4: After ion cleaning, the chamber is evacuated to the deposition pressure, and argon and oxygen are introduced to maintain the pressure at 0.5 Pa and the temperature at 135°C. Ti metal target is sputtered, and a dense underlayer with a thickness of 200 nm is formed on the surface of the Ti substrate.

[0282] Step 5: Introduce argon gas and sputter Ti and Nb metal targets at constant power. The deposition pressure is 0.4 Pa, the deposition temperature is 135°C, and the alloy layer thickness is 500 nm.

[0283] Step 6 is as described in Example 1.

[0284] The total thickness of the comparative coating 4 is 1200 nm.

[0285] Compare the test results of Example 4

[0286] (1) Contact resistance: At 1.4 MPa, the initial ICR between the titanium plate and the carbon paper is 2.8 mΩ•cm. 2 After long-term durability testing (2V vs. SHE, 10 hours), the ICR between the substrate and the carbon paper was 70.13 mΩ•cm. 2 ;

[0287] (2) Potentially constant polarization curve: at 0.5 M H2SO4 + 5 ppm F - In solution, after a long-term durability test (2V vs. SHE, 10 hours), the corrosion current density under constant potential (2V vs. SHE) testing was 3.9 μA / cm. 2 .

[0288] Comparative Example 5

[0289] (1) Contact resistance: At 1.4 MPa, the initial contact resistance between the titanium plate coated with a 400 nm monolayer Ti coating and the carbon paper is 8.53 mΩ•cm. 2 After long-term durability testing in a solution at pH 2 (2V vs. SHE, 80°C, 3 hours), the contact resistance between the titanium plate with a single-layer Ti coating and the carbon paper was 153.37 mΩ•cm. 2 ;

[0290] (2) Potentially constant polarization curve: at 0.5 M H2SO4 + 5 ppm F -In solution, after long-term durability testing (2V vs. SHE, 80℃, 3 hours), the corrosion current density under constant potential (2V vs. SHE) testing was 3.67 μA / cm. 2 .

[0291] Comparative Example 6

[0292] (1) Contact resistance: At 1.4 MPa, the initial contact resistance between the titanium plate coated with a 400 nm monolayer Nb coating and the carbon paper is 1.78 mΩ•cm. 2 After long-term durability testing in a solution at pH 2 (2V vs. SHE, 80°C, 3 hours), the contact resistance between the titanium plate with a single Nb coating and the carbon paper was 100.44 mΩ•cm. 2 ;

[0293] (2) Potentially constant polarization curve: at 0.5 M H2SO4 + 5 ppm F - In solution, after long-term durability testing (2V vs. SHE, 80℃, 3 hours), the corrosion current density under constant potential (2V vs. SHE) testing was 9.54 μA / cm. 2 .

[0294] The test results of the example are as follows:

[0295]

[0296] As can be seen from the table above, the initial interfacial contact resistance (ICR) of most of the currently developed composite coatings at 1.4 MPa is less than 2 mΩ•cm. 2 This is comparable to the conductivity of the platinum coating in Comparative Example 2, but the corrosion current density is much lower than that of the platinum coating, indicating that the composite coating has better corrosion resistance.

[0297] After a 10-hour corrosion durability test, the ICR value typically increases. It can be seen that, using the composite coating of the present invention, the polarized ICR value is significantly lower than that of the uncoated Ti plate (Comparative Example 1).

[0298] Comparative Examples 3 and 4 have a single-layer alloy structure as an intermediate layer. Compared with a composite coating of the same total thickness (with multiple intermediate sub-layers deposited by power variation) (see Examples 1, 5, 6, and 9), Examples 1, 5, 6, and 9 have lower initial ICR and polarized ICR values, indicating the advantage of having multiple alternating sub-layers as intermediate layers.

[0299] The difference between Comparative Example 3 and Comparative Example 4 lies in the underlayer. In Comparative Example 3, the underlayer was Ti, while in Comparative Example 4, the underlayer contained both Ti and O. Comparative Example 4 exhibited lower contact resistance both before and after the polarization test, indicating that the presence of oxygen in the underlayer improved the overall performance of the composite coating. The same trend was observed in Examples 1 and 5, where the presence of oxygen in the underlayer helped reduce ICR after the corrosion durability test and improve the conductivity of the coated components under operating conditions.

[0300] In summary, the coating of the present invention uses non-precious metal materials, which has significant advantages in terms of performance and cost, and can play an important role in promoting the use of water electrolyzers.

[0301] Comparative Examples 5 and 6 show that, compared to the substrate coated with a single layer of Nb, the substrate coated with a single layer of Ti exhibits a lower corrosion current density and therefore better corrosion resistance. Because Nb has better conductivity than Ti, the initial ICR value and the polarized ICR value of the substrate coated with a single layer of Nb (Comparative Example 6) are lower than those of the substrate coated with a single layer of Ti (Comparative Example 5).

Claims

1. A substrate having a coating, comprising, in sequence: a) Substrate; b) Applying a base layer, wherein the base layer comprises Ti or an oxide thereof; c) One or more corrosion-resistant layers comprising Ti, Nb, or oxides thereof, each layer comprising a first sublayer, a second sublayer, and a third sublayer, wherein the content of Ti increases from the first sublayer to the third sublayer, and the content of Nb decreases from the first sublayer to the third sublayer. d) A conductive layer comprising Nb, or its nitrides and / or its oxides.

2. The coated substrate according to claim 1, wherein the ratio of Ti and Nb in each sublayer of the one or more corrosion-resistant layers is constant over its thickness.

3. The coated substrate according to claim 1, wherein the ratio of Ti and Nb in at least the first and third sublayers of the one or more corrosion-resistant layers varies with their thickness.

4. The coated substrate according to any one of claims 1 to 3, wherein the substrate is a titanium substrate.

5. The substrate with a coating according to any one of claims 1 to 3, wherein the underlayer comprises Ti and / or Nb or oxides thereof.

6. The substrate with a coating according to any one of claims 1 to 3, wherein the thickness of the underlayer is 20 nm to 1000 nm.

7. The substrate with a coating according to any one of claims 1 to 3, wherein the thickness of each sublayer in the corrosion-resistant layer is from 20 nm to 500 nm.

8. A coated substrate according to any one of claims 1 to 3, comprising two or more corrosion-resistant layers, each layer comprising a first sublayer, a second sublayer and a third sublayer as defined in any one of claims 1 to 3.

9. A substrate with a coating according to any one of claims 1 to 3, wherein the conductive layer comprises Ti and / or Nb or their oxides and / or their nitrides.

10. The substrate with a coating according to any one of claims 1 to 3, wherein the total thickness of the coating is from 180 nm to 9000 nm.

11. The coated substrate according to claim 1, comprising, in sequence: a) Substrate; b) Applying an underlayer, wherein the underlayer comprises Ti, Nb, or oxides thereof; c) One or more corrosion-resistant layers, each layer comprising a first sublayer, a second sublayer, and a third sublayer, wherein the content of Ti increases from the first sublayer to the third sublayer, and the content of Nb decreases from the first sublayer to the third sublayer; and d) A conductive layer comprising Ti, Nb, or their nitrides and / or their oxides and / or their oxynitrides.

12. The coated substrate according to any one of claims 1 to 3 and claim 11, wherein the substrate is selected from electrolytic cell assemblies, bipolar plates, current collectors, and porous transport layers.

13. A method for preparing a substrate having a coating according to any one of claims 1 to 12, the method comprising sequentially depositing on the substrate: a) A base layer, wherein the base layer comprises a first transition metal or an oxide thereof; b) One or more corrosion-resistant layers, each layer comprising a first sublayer, a second sublayer, and a third sublayer, wherein each sublayer contains a first transition metal and a second transition metal, wherein the ratio of the first transition metal to the second transition metal varies between the sublayers; and c) A conductive layer comprising the second transition metal, or its nitride and / or its oxide.

14. An electrolytic cell comprising a coated substrate according to any one of claims 1 to 12.

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