Highly conductive corrosion resistant oxide coating for water electrolysis bipolar plates and methods of making the same

Abstract

The application provides a high-conductivity corrosion-resistant oxide coating for water electrolysis metal bipolar plates and a preparation method thereof, and belongs to the technical field of coatings. The coating comprises a primer layer and an oxidation layer arranged on the surface of a substrate in sequence. The primer layer is composed of Ti and other metal elements for doping, and has a thickness of 50-100 nm, and is used for strengthening the bonding force between the oxidation layer and the substrate. The oxidation layer is composed of Ti, O and doped metal elements, has a thickness of 200-500 nm, and has an oxygen element content of 15%-40%. The doped metal elements are corrosion-resistant metal elements with a valence higher than that of Ti, and the proportion is 3%-10%. The application solves the contradiction between corrosion resistance and conductivity of the pure oxide coating by coupling design of oxygen content and high-valence element doping, and improves the corrosion resistance by using the passivation characteristics of the oxide, and optimizes the electronic structure to enhance the conductivity.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and in particular to a highly conductive and corrosion-resistant oxide coating for metal bipolar plates in water electrolysis and its preparation method, especially suitable for proton exchange membrane water electrolyzer (PEMWE) bipolar plates. Background Technology

[0002] Proton exchange membrane electrolyzers (PEMWEs) achieve large-scale production of green hydrogen through water electrolysis, realizing efficient energy conversion. Bipolar plates, as the core component of the fuel cell stack, undertake crucial functions such as electron conduction, mass transport, thermal management, and mechanical support. Compared to traditional graphite and composite bipolar plates, metal bipolar plates exhibit superior electrical, thermal, and mechanical properties. Their excellent formability ensures the feasibility of large-scale production, making them highly favored in high-power fuel cell stacks. However, under the harsh operating conditions of the electrolyzer—strong acidity (pH=0~3), high temperature and humidity (T=70~90 ℃), and high potential (1.6~2.2 V)—the weakly conductive oxides formed on the metal surface can cause a sharp decline in conductivity. To ensure fuel cell stack efficiency and safe service life, constructing a high-performance corrosion-resistant conductive coating on the metal substrate surface has become an essential choice for inhibiting plate corrosion.

[0003] Given the strong acidity and high potential operating characteristics of PEMWE, recent studies have shown that usable coating systems mainly include noble metal coatings, metal nitrides, oxide coatings, and their composite coatings. However, the high cost of noble metals limits their large-scale commercial application, while metal nitrides exhibit poor corrosion resistance at high potentials. Although oxide coatings show excellent corrosion resistance in acidic environments, their intrinsic low conductivity severely restricts their application prospects. Currently, the preparation of highly conductive oxides faces bottlenecks such as complex processes and insufficient stability. Therefore, there is an urgent need to develop novel oxide coatings that combine high corrosion resistance, excellent conductivity, low cost, and simplified processes for application on the surface of water electrolyzer electrode plates.

[0004] Typical coating schemes in the prior art are as follows: Patent application CN202111536819.6 discloses a composite coating for a water electrolysis metal bipolar plate and its preparation method. The structure consists of a self-healing layer and a corrosion-resistant layer (alternating at least once) alternately arranged outwards from the surface of a metal substrate, with a conductive layer as the outermost layer. The self-healing layer is made of titanium, zirconium, niobium, chromium, tantalum, or a multi-element alloy; the dense corrosion-resistant layer is a transition metal oxide layer; and the conductive layer is a transition metal nitride layer. This technology requires operation in three reaction gas environments, making the process relatively complex. More importantly, the titanium nitride conductive layer has limited corrosion resistance, leading to rapid attenuation of conductivity after corrosion; in the example, the constant potential polarization current at 1.8 V reached 2.2 μA / c. m2 This indicates that the high-potential durability of the coating is questionable.

[0005] Patent application number CN202310609178.5 discloses TinO 2n-1 The coating preparation method and PEM hydrogen production electrode plate include the following steps: the substrate surface is polished and then cleaned with ethanol, acetone, and deionized water; oxalic acid solution is etched at a constant temperature for a specific duration, followed by cleaning with excess deionized water and anhydrous ethanol; TiO2 is dispersed in an isopropanol aqueous solution and loaded onto the electrode plate using an equal-volume impregnation method; high-temperature sintering is performed using polyethylene oxide as a binder; finally, high-temperature reduction is carried out in a flowing hydrogen atmosphere, followed by cooling and purging with an inert atmosphere to obtain a sub-titanium oxide layer. This technology prepares a uniform and dense TiO2 coating through oxidation, and then synthesizes different sub-titanium oxides by controlling process parameters through hydrogen reduction, significantly reducing contact resistance. However, the process involves hydrogen reduction and high-temperature treatment, making it complex and posing safety risks.

[0006] Patent application CN202211469765.0 discloses a composite coating, a bipolar plate, and a water electrolysis device. The composite coating, applied to the surface of the bipolar plate, comprises: a base layer covering the substrate (containing a first non-noble metal); and a reinforcement layer (containing doped oxides AB, where A is a second non-noble metal oxide, B is at least one dopant component, and A and B are connected by chemical bonds) over the base layer. While this patent optimizes conductivity through doping, it fails to alter the essential properties of metal oxide semiconductors. Its technical solution neglects the decisive influence of precise oxygen content control on conductivity. Summary of the Invention

[0007] In view of this, in order to solve the technical problems of complex oxide coating processes, imprecise oxygen content control, and inability to balance corrosion resistance and conductivity in existing technologies, this invention uses a coupling design of oxygen content and high-valence element doping to improve corrosion resistance by utilizing the passivation properties of oxides, while simultaneously optimizing the electronic structure to enhance conductivity. This resolves the contradiction between corrosion resistance and conductivity in pure oxide coatings, and provides a low-cost, high-corrosion-resistant and conductive oxide coating for water electrolysis metal bipolar plates and its preparation method.

[0008] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a highly conductive and corrosion-resistant oxide coating for a water electrolysis metal bipolar plate, characterized in that it comprises an underlayer and an oxide layer sequentially disposed on the surface of a substrate. The substrate layer comprises Ti and other metal elements used for doping, with a thickness of 50-100 nm, and is used to strengthen the bonding force between the oxide layer and the substrate. The oxide layer contains Ti, O, and doped metal elements, with a thickness of 200-500 nm and an oxygen content of 15%-40%. The doped metal elements are selected from corrosion-resistant metal elements with a higher +4 valence state than Ti, and the proportion is 3%-10%.

[0009] Secondly, the present invention provides a method for preparing the above-mentioned highly conductive and corrosion-resistant oxide coating for water electrolysis metal bipolar plates, comprising the following steps: Step (1), Sputter cleaning: Ar gas is introduced into a vacuum environment to sputter clean the substrate surface; Step (2), Deposition of the underlayer: Using an alloy target, the underlayer is deposited in an Ar atmosphere; Step (3), Deposit oxide layer: Deposit oxide layer by controlling oxygen content through oxygen atmosphere or oxide target material.

[0010] This invention develops a simple, easy-to-operate, low-cost, and scalable method for preparing highly conductive oxide coatings. It eliminates the reliance on multi-step synthesis, high-temperature treatment, multi-layer deposition, and noble metal components found in existing technologies, providing a direct preparation route that allows pure oxide coatings to be used alone. This invention achieves precise control of the oxygen content in the coating, achieving an optimal balance between conductivity and corrosion resistance. It avoids conductivity degradation due to over-oxidation or corrosion resistance defects caused by under-oxidation, meeting the stringent requirements of water electrolyzers for both corrosion resistance and conductivity. Compared to existing technologies, it offers the following advantages: The coating design advantages lie in its precise balance between corrosion resistance and conductivity achieved through oxidation control and elemental doping coupling. On one hand, by precisely controlling the oxygen content (15%-40%), the passivation properties of the oxide are utilized to enhance the coating's corrosion resistance, avoiding insufficient corrosion resistance due to under-oxidation or conductivity degradation caused by over-oxidation. On the other hand, corrosion-resistant metal elements with higher valence states than Ti (such as Ta, Nb, Zr, etc.) are selected as dopants (Me) to enhance the coating's corrosion resistance while optimizing the oxide's electronic structure and improving conductivity. This solves the problem of existing pure oxide coatings struggling to balance corrosion resistance and conductivity.

[0011] Advantages of the preparation method: The preparation method is simple and easy to operate, requiring no complex processes or special conditions. The coating preparation method adopted in this invention (including oxygen deposition atmosphere, co-deposition of oxide and metal targets, etc.) is simple to operate, requiring only 1-2 types of targets. The oxygen content adjustment is only related to the oxygen flow rate or the oxide target power, making control convenient. The required equipment conditions are not demanding, eliminating the need for complex multi-step synthesis, high-temperature treatment, or multi-layer structure deposition as in existing technologies. Furthermore, it does not rely on precious metals or complex composite processes, reducing the difficulty and cost of preparation. Attached Figure Description

[0012] Figure 1 A schematic diagram of a coating structure and composition provided by the present invention. Detailed Implementation

[0013] This invention provides a highly conductive and corrosion-resistant oxide coating for a water electrolysis metal bipolar plate, comprising an underlayer and an oxide layer sequentially disposed on the surface of a substrate. For example... Figure 1 As shown, the bottom layer is the base, and above the base are deposited the underlayer and the oxide layer.

[0014] The substrate layer, consisting of Ti and other doping metal elements Me, has a thickness of 50-100 nm and is used to strengthen the adhesion between the oxide layer and the substrate. The doping metal element Me is preferably at least one of Ta, Nb, and Zr. x Me y The alloy is preferably composed of 97%-90% x and 3%-10% y.

[0015] The oxide layer comprises Ti, O, and a doped metal element Me (preferably at least one of Ta, Nb, and Zr), with a thickness of 200-500 nm and an oxygen content of 15%-40%. The doped metal element is selected from corrosion-resistant metals with a higher valence state than Ti, and its proportion is 3%-10%. Further, in this invention, the oxide layer has an oxygen content of 24%-37% and a doped metal element proportion of 3%-5%. The alloy underlayer has a thickness of 60 nm, and the oxide layer has a thickness of 220-430 nm.

[0016] In this invention, the phase composition of the oxide layer is: Ti, Ti metal oxides, and doped metal oxides. The Ti metal oxides include fully oxidized Ti oxides and partially oxidized Ti oxides. For example, the fully oxidized Ti oxide is TiO2; the partially oxidized Ti oxide is Ti... n O 2n-1 Oxides doped with metallic elements, such as TiTaO, etc.; the retained metallic components are used for conductivity. For example... Figure 1 As shown, the oxide layer contains Ti, TiO2, and Ti n O 2n-1 TiMe x O y (Ti oxides are doped with 3%-10% Me).

[0017] In the highly conductive and corrosion-resistant oxide coating for water electrolysis metal bipolar plates provided by this invention, the oxygen content is controlled at 15%-40%. While introducing an appropriate amount of oxide, some metal is retained; the oxide serves for corrosion resistance, and the metal serves for conductivity. The doping metal is selected from corrosion-resistant metal elements with a higher valence state than Ti (+4), at a ratio of 3%-10%. High-valence metal doping can reduce the Ti content in TiO2. 4+Oxidation state alters the electronic structure of oxides and promotes the formation of suboxides, thereby improving the conductivity of oxide coatings. Furthermore, elements such as Ta, Nb, and Zr inherently possess excellent corrosion resistance, but are limited by high cost. Introducing them through small-scale doping not only controls cost but also improves corrosion resistance. In summary, this coating design couples oxidation control and elemental doping, achieving excellent corrosion resistance and conductivity at a low cost and with a simple preparation method.

[0018] The present invention also provides a method for preparing the above-mentioned highly conductive and corrosion-resistant oxide coating for water electrolysis metal bipolar plates, characterized by comprising the following steps: Step (1), Sputter cleaning: Ar gas is introduced into a vacuum environment to sputter clean the substrate surface; Step (2), Deposition of the underlayer: Using an alloy target, the underlayer is deposited in an Ar atmosphere; Step (3), Deposit oxide layer: Deposit oxide layer by controlling oxygen content through oxygen atmosphere or oxide target material.

[0019] By way of example, the present invention provides the following specific preparation steps that can be implemented: (1) Use TA1 as the substrate with a thickness of 0.1 mm. Clean the surface before coating to remove dust, oil and other contaminants. (2) Place the clean substrate into the stage, and create a vacuum of less than 5 × 10⁻⁶ inside the cavity. -3 After Pa and the temperature rises to 250°C, Ar gas is introduced at a flow rate of 500 sccm. (3) The surface of the substrate is sputtered cleaned with a bias voltage of 900V and a surface cleaning time of 40 min. (4) Deposit TiMe as the underlayer (Me is preferably at least one of Ta, Nb, and Zr), Ar gas flow rate 80 sccm, alloy target (TiTa, TiNb, TiTaNb, etc.) power set to 4 kW-6 kW, bias voltage set to 400 V, deposition time 5-20 min; (5) Deposition of TiMe x O y The oxide layer (Me is preferably at least one of Ta, Nb, and Zr) can be oxidized using an oxygen atmosphere and an oxide target. Oxygen atmosphere method: An argon-oxygen mixed atmosphere is used as the reaction gas, with a total Ar+O2 gas flow rate of 80 sccm and an O2 gas flow rate of 3%-10%, achieved by adjusting the ratio of 5% or 20% argon-oxygen mixed gas to pure argon. The alloy target power is set to 4 kW-6 kW, the bias voltage is set to 800 V, and the deposition time is 40-60 min. Oxide target method: Ar gas flow rate of 80 sccm, alloy target power set to 4 kW-6 kW, TiO2...x The oxide current was set to 2A-6A, the bias voltage was set to 800V, and the deposition time was 30-60 min.

[0020] The technical solution of the present invention will be clearly and thoroughly described below with reference to specific embodiments and accompanying drawings.

[0021] Example 1 TA1 was used as the substrate with a thickness of 0.1 mm. The surface was cleaned before coating to remove dust, oil, etc.

[0022] Place the cleaned substrate into the stage, and create a vacuum of less than 5 × 10⁻⁶ within the cavity. -3 After Pa and the temperature rises to 250 °C, Ar gas is introduced at a flow rate of 500 sccm.

[0023] The substrate surface was sputter-cleaned with a bias voltage of 900V for 40 minutes.

[0024] TiTaO-TiO x Using a TiTa alloy (Ta ~6%), a power of 6 kW, a bias voltage of 400 V, and a deposition time of 10 min, an alloy underlayer with a thickness of 60 nm was prepared.

[0025] Ar flow rate 80 sccm, using TiO x Using a target material (x≈0.65) as the oxygen source, a current of 6 A was applied, maintaining a TiTa alloy target power of 6 kW for a deposition time of 50 min. A TiTaO oxide layer with a thickness of 430 nm was prepared, with a composition of 60% Ti-3% Ta-37% O. The coating was subjected to constant potential polarization testing at 2 V, 80 °C, and 0.5 M H₂SO₄ for 24 h, and the stable corrosion current density was as low as 0.24 μA / cm². 2 The initial interfacial contact resistance (ICR) of the coating at 140 N is 2.98 mΩ. cm 2 It achieves excellent corrosion resistance and electrical conductivity.

[0026] Example 2 TA1 was used as the substrate with a thickness of 0.1 mm. The surface was cleaned before coating to remove dust, oil, etc.

[0027] Place the cleaned substrate into the stage, and create a vacuum of less than 5 × 10⁻⁶ within the cavity. -3 After Pa and the temperature rises to 250 °C, Ar gas is introduced at a flow rate of 500 sccm.

[0028] The substrate surface was sputter-cleaned with a bias voltage of 900V for 40 minutes.

[0029] TiTaO-O2 was used to prepare an alloy underlayer with a thickness of 60 nm using a TiTa alloy (Ta ~ 6%), a power of 6 kW, a bias voltage of 400 V, and a deposition time of 10 min.

[0030] O2 + Ar was introduced as the reaction atmosphere. The gas flow rates for coatings with different O2 ratios are shown in Table 1. Maintaining a TiTa alloy target power of 6 kW and a deposition time of 50 min, a TiTaO oxide layer with a thickness of 220 nm was prepared. The elemental content, interfacial contact resistance, and corrosion current density of coatings with different O2 ratios are shown in Table 2. Under conditions of 3%-10% O2, the oxygen content varied between 15%-40%, with the 5% O2 coating exhibiting the best performance. The composition ratio was 71% Ti-5% Ta-24% O. This coating underwent a constant potential polarization test at 2 V, 80 ℃, and 0.5 M H2SO4 for 24 h, and the stable corrosion current density was as low as 0.12 μA / cm². 2 The initial ICR and the ICR after polarization testing of the coating were 2.25 and 4.9 mΩ, respectively. cm 2 It achieves excellent corrosion resistance and electrical conductivity, and significantly mitigates the rapid decay of the coating's conductivity during high-potential polarization.

[0031] Table 1 Gas flow rates of TiTaO-O2 coatings with different O2 ratios

[0032] Example 3 TA1 was used as the substrate with a thickness of 0.1 mm. The surface was cleaned before coating to remove dust, oil, etc.

[0033] Place the cleaned substrate into the stage, and create a vacuum of less than 5 × 10⁻⁶ within the cavity. -3 After Pa and the temperature rises to 250 °C, Ar gas is introduced at a flow rate of 500 sccm.

[0034] The substrate surface was sputter-cleaned with a bias voltage of 900V for 40 minutes.

[0035] TiTa was used, employing a TiTa alloy (Ta ~6%), with a power output of 6 kW, a bias voltage of 400 V, an Ar flow rate of 80 sccm, and a deposition time of 60 min. The alloy coating, without introduced oxides, exhibited an ICR as high as 115.32 mΩ due to natural oxidation in air. cm 2.

[0036] Example 4 TA1 was used as the substrate with a thickness of 0.1 mm. The surface was cleaned before coating to remove dust, oil, etc.

[0037] Place the cleaned substrate into the stage, and create a vacuum of less than 5 × 10⁻⁶ within the cavity. -3 After Pa and the temperature rises to 250 °C, Ar gas is introduced at a flow rate of 500 sccm.

[0038] The substrate surface was sputter-cleaned with a bias voltage of 900V for 40 minutes.

[0039] TiO x Using a TiTa alloy (Ta ~6%), a power of 6 kW, a bias voltage of 400 V, and a deposition time of 10 min, an alloy underlayer with a thickness of 60 nm was prepared.

[0040] Ar flow rate 80 sccm, TiTa alloy target shut off, TiO x The target current was 6 A, the deposition time was 50 min, and the composition ratio was 35% Ti-0% Ta-65% O. The coating exhibited an ICR as high as 3.824 Ω. cm 2 The results are shown in Table 2: Table 2 Test Results

[0041] Note: Due to its poor conductivity, the corrosion resistance of Examples 3-4 is no longer a concern.

[0042] The above description is merely a preferred embodiment of the present invention. However, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention should be covered within the scope of protection of the present invention.

Claims

1. A highly conductive and corrosion-resistant oxide coating for a metal bipolar plate used in water electrolysis, characterized in that, This includes a base layer and an oxide layer sequentially applied to the surface of the substrate; The substrate layer comprises Ti and other metal elements used for doping, with a thickness of 50-100 nm, and is used to strengthen the bonding force between the oxide layer and the substrate. The oxide layer contains Ti, O, and doped metal elements, with a thickness of 200-500 nm and an oxygen content of 15%-40%. The doped metal elements are selected from corrosion-resistant metal elements with a higher +4 valence state than Ti, and the proportion is 3%-10%.

2. The highly conductive and corrosion-resistant oxide coating for a water electrolysis metal bipolar plate according to claim 1, characterized in that, The doped metal elements in the underlayer and oxide layer are at least one of Ta, Nb and Zr.

3. A highly conductive and corrosion-resistant oxide coating for a water electrolysis metal bipolar plate according to claim 1 or 2, characterized in that, The phase composition of the oxide layer is: Ti, Ti metal oxide and doped metal oxide.

4. The highly conductive and corrosion-resistant oxide coating for a water electrolysis metal bipolar plate according to claim 3, characterized in that, Ti metal oxides include Ti in its fully oxidized state and Ti in its partially oxidized state.

5. The highly conductive and corrosion-resistant oxide coating for a water electrolysis metal bipolar plate according to claim 1, characterized in that, The oxide layer contains 24%-37% oxygen and 3%-5% doped metal elements.

6. A highly conductive and corrosion-resistant oxide coating for a water electrolysis metal bipolar plate according to any one of claims 1-5, characterized in that, The thickness of the alloy underlayer is 60 nm, and the thickness of the oxide layer is 220-430 nm.

7. A method for preparing a highly conductive and corrosion-resistant oxide coating for a water electrolysis metal bipolar plate according to any one of claims 1-6, characterized in that, Includes the following steps: Step (1), Sputter cleaning: Ar gas is introduced into a vacuum environment to sputter clean the substrate surface; Step (2), Deposition of the underlayer: Using an alloy target, the underlayer is deposited in an Ar atmosphere; Step (3), Deposit oxide layer: Deposit oxide layer by controlling oxygen content through oxygen atmosphere or oxide target material.

8. The method for preparing a highly conductive and corrosion-resistant oxide coating for a water electrolysis metal bipolar plate according to claim 7, characterized in that, In step (3), the oxygen atmosphere is as follows: an argon-oxygen mixed atmosphere is used as the reaction gas, the total flow rate of Ar+O2 is 80 sccm, the flow rate of O2 gas is 3%-10%, which is achieved by adjusting the ratio of 5% or 20% argon-oxygen mixed gas and pure argon gas. The alloy target power is set to 4 kW-6 kW, the bias voltage is set to 800 V, and the deposition time is 40-60 min.

9. The method for preparing a highly conductive and corrosion-resistant oxide coating for a water electrolysis metal bipolar plate according to claim 7, characterized in that, In step (3), the oxide target material is set to an Ar gas flow rate of 80 sccm, the alloy target power is set to 4kW-6kW, and the TiO2 target power is set to 4kW-6kW. x The oxide current was set to 2A-6A, the bias voltage to 800V, and the deposition time to 30-60 min.

10. A method for preparing a highly conductive and corrosion-resistant oxide coating for a water electrolysis metal bipolar plate according to any one of claims 7-9, characterized in that, In step (2), the Ar gas flow rate is 80 sccm, the alloy target power is set to 4 kW-6 kW, the bias voltage is set to 400 V, and the deposition time is 5-20 min.

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