A pre-coat slurry and pre-coat titanium-based material, and method of making and plate therefrom

Abstract

The application provides a kind of precoating slurry and precoating titanium-based material and its preparation method and polar plate, belong to fuel cell technical field. With the total mass of the precoating slurry being 100%, the precoating slurry includes the following components: 0.6-5% conductive carbon black, 0.2-2.5% carbon nanotube, 0.3-3% dispersant, 0.1-3% binder, 0-1% surfactant, and 90-98% solvent. The precoating slurry of the embodiment of the application can effectively improve the conductivity and conductive durability of the subsequently formed precoating titanium-based material, and improve the operating efficiency of the fuel cell. Moreover, the precoating slurry of the embodiment of the application does not have special requirements for the carbon content on the surface of the titanium-based material, and does not need to perform a carbon concentration reduction treatment process during the subsequent preparation of the precoating titanium-based material, which is convenient for industrialization.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to a pre-coated slurry and a pre-coated titanium-based material, their preparation method, and electrode plates. Background Technology

[0002] Fuel cells contain plates (single plates and biplates). The function of the plates is to provide gas flow channels, prevent cross-contamination of different gases within the gas chamber, and establish a current path between the series-connected anode and cathode. Based on the material, plates are classified as graphite plates and metal plates. Graphite plates have poor processing performance, airtightness, and mechanical properties, and their large thickness results in low power density in the fuel cell stack, hindering fuel cell vehicle applications and large-scale mass production. Metal plates, on the other hand, have attracted significant attention due to their excellent electrical and thermal conductivity, fewer manufacturing steps, the ability to produce ultra-thin plates to increase stack power density, and the ability to be mass-produced using stamping methods, thus significantly reducing mass production costs.

[0003] Materials used for metal electrode plates include stainless steel, pure titanium, or titanium alloys. During use, the contact resistance between the metal electrode plate and the membrane electrode assembly (MEA) is relatively high. Because the electrode plate is exposed to high voltage, high humidity, and high oxidizing environments for extended periods, a non-conductive oxide film easily forms on the surface of the metal material, increasing the contact resistance between the electrode plate and the MEA, resulting in poor conductivity durability, increased polarization losses due to ohmic resistance, decreased fuel cell operating efficiency, and even premature failure of the entire fuel cell stack. Therefore, to improve the conductivity and conductivity durability of the metal electrode plates, a highly conductive and corrosion-resistant coating needs to be applied to the surface of the metal electrode plates for protection.

[0004] Metal electrode coatings mainly fall into two categories: the first is carbon-based coatings, such as graphite-like coatings; the second is metal-based coatings, such as noble metal coatings, metal carbide or nitride coatings, and metal oxide coatings. From a process perspective, there are currently four main different process routes: electroplating, electroless plating (e.g., hot-dip plating, paint spraying, spraying), CVD (chemical vapor deposition), and PVD (physical vapor deposition).

[0005] The most common manufacturing process for metal electrodes is to flatten and cut metal coils into sheets, then stamp each sheet to form a monopolar plate. Two monopolar plates (anode and cathode) are then welded together to form a bipolar plate. Finally, a conductive and corrosion-resistant coating is applied to the surface of the bipolar plate. This pre-forming, post-coating production method is called "post-coating" technology. It is an intermittent production process because the coating process requires mounting and removing individual bipolar plates, making automation difficult and resulting in low production efficiency.

[0006] To improve the production efficiency and reduce the cost of metal bipolar plates, pre-coated metal substrates have received widespread attention in recent years. Patent CN 110129727A discloses a method for preparing pre-coated metal strips for fuel cell metal bipolar plates. This method uses a PVD coating machine to prepare a conductive and corrosion-resistant coating on stainless steel strips. Because this metal strip has a conductive and corrosion-resistant coating, it can be directly assembled into fuel cell stacks after stamping and welding to form bipolar plates without further coating treatment. This production method of coating first and then forming is called "pre-coating" technology. This pre-coating technology can achieve continuous "roll-to-roll" coating production, which can significantly reduce coating production costs and accelerate the commercialization and industrialization of the fuel cell industry. However, this patent uses a PVD coating machine for coating preparation. PVD coating machines are expensive and have low production efficiency, resulting in high coating costs and hindering large-scale promotion.

[0007] Patent application CN 106463739 A discloses a method for manufacturing a pre-coated pure titanium or titanium alloy substrate, comprising: a coating step S2 of coating carbon black onto the surface of a substrate with a carbon concentration of less than 10 atomic% at a depth of 10 nm from the outermost surface; and a heat treatment step S3 of heat-treating the substrate after coating step S2 at an oxygen partial pressure of less than 25 Pa. Preferably, prior to coating step S2, a treatment step S1 is included to treat the surface of the substrate to reduce the carbon concentration of less than 10 atomic% at a depth of 10 nm from the outermost surface, wherein the treatment in the carbon concentration reduction step is an acid pickling treatment of the substrate in an acidic aqueous solution containing hydrofluoric acid. This patent does not employ the expensive PVD process and enables continuous "roll-to-roll" coating processing of electrode substrates, significantly increasing coating capacity and reducing coating costs, thus attracting widespread attention.

[0008] In patent application CN 106463739 A, paragraph

[0046] states that "Carbon is usually detected on the surface of the substrate 2 due to the adsorption of organic matter or the like in the atmosphere. In this invention, the portion of the surface layer of the substrate 2 from which the adsorbed organic matter or the like is removed (the dirt layer) is defined as the 'outer surface,' and the carbon concentration at a depth of 10 nm from this outer surface is specified as 10 atomic percent or less. A carbon concentration at this position exceeding 10 atomic percent indicates that during the rolling or other processes of manufacturing the substrate 2, the processing oil, organic matter or the like present in the atmosphere may penetrate and contaminate the surface of the substrate 2, or they may react with titanium to form titanium carbides. If the surface of the substrate 2 is contaminated by processing oil, organic matter or the like, or titanium carbides are formed, then during the heat treatment process S3 described later, it is difficult for carbon black to bond to the surface of the substrate 2. Therefore, it is difficult to form the mixed layer 3, and as a result, high conductivity and conductivity durability may not be obtained."

[0009] It is evident that the manufacturing method for fuel cell spacer materials disclosed in patent application CN 106463739 A only allows the use of titanium-based materials with a carbon concentration of less than 10 atomic percent at a depth of 10 nm from the outermost surface. When the carbon concentration at this location exceeds 10 atomic percent, it is essential to first reduce the carbon concentration to below 10 atomic percent through treatments such as acid washing before proceeding with subsequent processes. However, in reality, the residual carbon content on the surface of titanium-based materials can typically reach 10 atomic percent or more, even exceeding 30%. This means that acid washing and other treatments are generally required to reduce the carbon content on the surface of the titanium-based material before subsequent processes can proceed.

[0010] Patent application CN 106463739A discloses a specific pickling process using a mixed aqueous solution of hydrofluoric acid and nitric acid to pickle titanium-based materials. However, for ultra-thin titanium-based materials with a thickness of approximately 0.1 mm, the pickling process is extremely difficult. Because titanium-based materials are thin and have low strength, excessive tension and prolonged pickling time can lead to fracture, making the process difficult to implement. Currently, there is no equipment in China for mass pickling of titanium-based materials with a thickness of approximately 0.1 mm, making the pickling process practically impossible. Furthermore, pickling also increases the surface roughness of titanium-based materials, reducing their corrosion resistance. In addition, pickling requires the use of hazardous chemicals such as hydrofluoric acid and generates a large amount of waste liquid, which is detrimental to environmental protection. Summary of the Invention

[0011] This invention is based on the inventor's discovery and understanding of the following facts and problems: If the requirement for carbon concentration on the surface of titanium-based materials can be reduced, the carbon concentration reduction process (i.e., acid washing) can be omitted, and a pre-coating can be directly prepared on the surface of titanium-based materials, then the preparation method of titanium-based material plates can be more practical and conducive to industrial promotion.

[0012] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a pre-coating slurry, a pre-coated titanium-based material, a method for preparing the same, and an electrode plate. The pre-coating slurry does not have specific requirements for the carbon concentration on the surface of the titanium-based material, thus eliminating the need for a carbon concentration reduction process. Furthermore, the prepared pre-coated titanium-based material exhibits excellent resistance to high-potential corrosion and high electrical durability.

[0013] The pre-coating slurry for titanium-based materials in this embodiment of the invention comprises the following components, based on 100% of the total mass of the pre-coating slurry: 0.6-5% conductive carbon black, 0.2-2.5% carbon nanotubes, 0.3-3% dispersant, 0.1-3% binder, 0-1% surfactant, and 90-98% solvent.

[0014] The advantages and technical effects of the pre-coating slurry in this invention are as follows:

[0015] (1) The pre-coating slurry of the present invention contains both conductive carbon black and carbon nanotubes, which can form a dot-and-line conductive network to enhance the conductivity of the pre-coated titanium-based material.

[0016] (2) Compared with conductive carbon black, carbon nanotubes have a smaller diameter and a larger specific surface area. The carbon nanotubes dispersed in the pre-coated slurry will fill the gaps between the conductive carbon black, thus enabling more effective direct contact with the areas of the titanium-based material surface that are not covered with carbon layer. During subsequent heat treatment, it is easier for reaction diffusion to occur, forming a metallurgical bond between carbon and titanium, enhancing the bonding strength of the bonding site. During the operation of the fuel cell, the carbon at the bonding site is not easy to peel off from the substrate, making it difficult for the contact resistance between the pre-coated layer and the membrane electrode to rise. This significantly improves the conductivity and durability of the pre-coated titanium-based material. Moreover, the pre-coated titanium-based material has excellent resistance to high potential corrosion.

[0017] (3) The pre-coating slurry of the present invention does not have special requirements for the carbon content on the surface of the titanium-based material. In the subsequent preparation of the pre-coated titanium-based material, there is no need to carry out a carbon concentration reduction process, which is convenient for industrial promotion.

[0018] In some embodiments, the mass ratio of the conductive carbon black to the carbon nanotubes is 2:(0.5-2).

[0019] In some embodiments, the conductive carbon black has an average particle size of 150–250 nm; and / or the carbon nanotubes have an average diameter of 7–11 nm and an average length of 4–20 μm.

[0020] In some embodiments, the solvent may be at least one of methanol, ethanol, isopropanol, toluene, cyclohexanone, formaldehyde solution, acetaldehyde solution, ketone, ether, and water.

[0021] This invention also provides a method for preparing a pre-coating slurry for titanium-based materials, comprising the following steps: mixing the components according to a specified content to obtain the pre-coating slurry.

[0022] The advantages and technical effects of the pre-coating slurry preparation method of this invention are as follows:

[0023] The preparation method of the pre-coating slurry in this embodiment of the invention is simple to operate and easy to promote industrially.

[0024] Furthermore, embodiments of the present invention also provide a method for preparing a pre-coated titanium-based material, comprising the following steps:

[0025] S1. Apply the pre-coating slurry of the present invention to the surface of the titanium-based material;

[0026] S2. Heat-treat the titanium-based material treated in step S1 under vacuum conditions.

[0027] The advantages and technical effects of the preparation method of the pre-coated titanium-based material in this invention are as follows:

[0028] The method for preparing the pre-coated titanium-based material in this embodiment of the invention does not have any particular limitation on the carbon content of the surface of the titanium-based material used, and it is applicable to all types of materials without the need for prior carbon content reduction treatment. This method is highly practical and can be industrially promoted.

[0029] In addition, this embodiment of the invention also provides a pre-coated titanium-based material, which is obtained by the preparation method of the pre-coated titanium-based material of this embodiment of the invention.

[0030] The advantages and technical effects of the pre-coated titanium-based material in this invention are as follows:

[0031] The pre-coated titanium-based material of this invention can effectively contact the area of ​​the titanium-based material surface that is not covered by a carbon layer, thereby enhancing the bonding strength of the bonding site. During the operation of the fuel cell, the carbon at the bonding site is not easily peeled off from the substrate, making it less likely for the contact resistance between the pre-coated material and the membrane electrode to increase, thus significantly improving the conductivity and durability of the pre-coated titanium-based material.

[0032] Furthermore, this embodiment of the invention also provides an electrode plate made of a pre-coated titanium-based material.

[0033] The electrode plates of this invention have excellent conductivity and conductivity durability, which is beneficial for the fuel cell to maintain high operating efficiency during long-term operation. Attached Figure Description

[0034] Figure 1 This is a surface optical morphology image of the substrate used in Example 1;

[0035] Figure 2 yes Figure 1 Raman spectra of the dark and light regions;

[0036] Figure 3 This is a schematic diagram of the distribution of the pre-coated slurry on the titanium-based material according to an embodiment of the present invention;

[0037] Figure 4 This is a schematic diagram of the contact resistance testing method;

[0038] Figure 5 The contact resistance of the pre-coated titanium-based materials prepared in Application Example 1 and Comparative Example 2 changes with a constant potential polarization time of 0.84V.

[0039] Figure 6The change in contact resistance of the pre-coated titanium-based materials prepared in Application Example 1 and Comparative Example 2 with a constant potential polarization time of 1.2V is shown.

[0040] Explanation of reference numerals in the attached figures:

[0041] 1-Titanium-based material; 2-Conductive carbon black; 3-Carbon nanotubes. Detailed Implementation

[0042] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0043] This invention provides a pre-coating slurry for titanium-based materials, comprising the following components based on 100% of the total mass of the pre-coating slurry: 0.6-5% conductive carbon black, 0.2-2.5% carbon nanotubes, 0.3-3% dispersant, 0.1-3% binder, 0-1% surfactant, and 90-98% solvent.

[0044] Typical morphology of pure titanium surface as follows Figure 1 As shown, there are many irregularly shaped black areas against a light-colored background. For example... Figure 2 The micro Raman analysis shown indicates that, corresponding to Figure 1 The Raman spectrum of the black region ① in the middle contains a carbon peak, while the corresponding peak is... Figure 1 The Raman spectrum in the light-colored region ② does not show any Raman peaks. This indicates that carbon on the titanium surface is usually distributed in island-like patterns, with diameters ranging from 1 to 100 μm, and is referred to as "carbon islands". Similarly, "carbon islands" also exist on the surface of titanium alloys.

[0045] The "carbon islands" on the surface of titanium-based materials reduce the direct contact between the conductive carbon black in the pre-coating slurry and the titanium-based material. During subsequent heat treatment, these "carbon islands" form diffusion barriers, hindering the diffusion reaction and bonding between titanium atoms within the titanium-based material and the conductive carbon black in the pre-coating. The conductive carbon black struggles to bond to the surfaces of the "carbon islands" and the substrate, making it difficult to form a mixed layer. This weakens the direct bond between the titanium-based material and the conductive carbon black particles. If this material is used to fabricate fuel cell plates, these weakly bonded areas will peel off. Patent application CN 106463739A aims to reduce the carbon content on the surface of the titanium-based material using acid pickling, thereby enabling the pre-coating formed in subsequent coating processes to bond tightly with the titanium-based material. When the carbon concentration at a depth of 10 nm from the outermost surface is above 10 atomic%, meaning the carbon content on the surface of the titanium-based material is too high and the area of ​​exposed titanium on the surface of the titanium-based material is too small, there will be a large number of weak bonding sites. During the operation of the fuel cell, the carbon at the weak bonding sites will peel off from the substrate, leading to an increase in the contact resistance of the pre-coating and membrane electrode, which may result in the electrode plate not achieving high conductivity and conductivity durability.

[0046] In addition to conductive carbon black 2, the pre-coating slurry of this embodiment also contains carbon nanotubes 3. Figure 3 The illustration shows the distribution of conductive carbon black 2 and carbon nanotubes 3 when the pre-coating slurry of this embodiment of the invention is applied to a titanium-based material 1. Due to their size characteristics (one-dimensional material), carbon nanotubes can form a network structure in the slurry, effectively connecting more conductive carbon black particles and enhancing conductivity. Moreover, compared to conductive carbon black, carbon nanotubes have a smaller diameter and a larger specific surface area. The dispersed carbon nanotubes in the pre-coating slurry fill the gaps between the conductive carbon black particles, thus enabling more effective direct contact with areas of the titanium-based material surface not covered by a carbon layer. This strengthens the bonding strength at the bonding sites during subsequent heat treatment. During fuel cell operation, the carbon at the bonding sites is less likely to peel off from the substrate, preventing a rise in the contact resistance between the pre-coating and the membrane electrode assembly, thereby significantly improving the conductivity and durability of the pre-coated titanium-based material. Therefore, the pre-coating slurry of this embodiment of the invention does not have special requirements regarding the surface carbon content of the titanium-based material. Even if the carbon content on the surface of the titanium-based material is greater than 10 atomic%, or even greater than 30 atomic%, the pre-coating slurry of this embodiment can still achieve high conductivity and conductivity durability in the pre-coated titanium-based material.

[0047] In the pre-coating slurry of this invention, the content of conductive carbon black is 0.6% to 5%, for example, 0.6%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc., and the content of carbon nanotubes is 0.2% to 2.5%, for example, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, etc. The content of conductive carbon black and carbon nanotubes within the above ranges helps to improve the conductivity and conductivity durability of the pre-coated titanium-based material. When the content of conductive carbon black is less than 0.6%, and / or the content of carbon nanotubes is less than 0.2%, the conductivity and conductivity durability of the pre-coated titanium-based material are significantly reduced. When the content of conductive carbon black is higher than 5%, and / or the content of carbon nanotubes is higher than 2.5%, although the thickness of the pre-coating increases, the contact area between the pre-coating and the region of the titanium-based material surface not covered by the carbon layer does not increase further. Therefore, the conductivity and durability of the pre-coated titanium-based material do not improve further; instead, production costs increase. Preferably, the content of the conductive carbon black is 1.5–2.5%, and the content of the carbon nanotubes is 0.5–1.5%.

[0048] In some embodiments, the mass ratio of the conductive carbon black to the carbon nanotubes is 2:(0.5-2), for example, 2:0.5, 2:0.8, 2:1, 2:1.2, 2:1.4, 2:1.6, 2:1.8, 2:2, etc. When the mass ratio of conductive carbon black to carbon nanotubes is within the above range, it is more beneficial to improve the conductivity and conductivity durability of the pre-coated titanium-based material. When the mass ratio of conductive carbon black to carbon nanotubes is too small, it is not conducive to improving the conductivity durability of the pre-coated titanium-based material. When the mass ratio of conductive carbon black to carbon nanotubes is too large, it is not conducive to improving the initial conductivity of the pre-coated titanium-based material. Preferably, the mass ratio of the conductive carbon black to the carbon nanotubes is 2:(0.5-1.5).

[0049] In some embodiments, the average particle size of the conductive carbon black is 150–250 nm, such as 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, etc. An average particle size of conductive carbon black within this range is beneficial for improving the conductivity and conductivity durability of the pre-coated titanium-based material. When the average particle size of the conductive carbon black is too low, it is detrimental to improving the initial conductivity. When the average particle size of the conductive carbon black is too high, it is detrimental to improving conductivity durability. Preferably, the average particle size of the conductive carbon black is 180–220 nm.

[0050] In some embodiments, the average diameter of the carbon nanotubes is 7–11 nm, such as 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, etc., and the average length is 4–20 μm, such as 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, etc. When the size of the carbon nanotubes is within the above range, it is beneficial to improve the conductivity and conductivity durability of the pre-coated titanium-based material. When the average diameter of the carbon nanotubes is too small, it is not conducive to improving conductivity durability. When the average diameter of the carbon nanotubes is too large, it is not conducive to improving initial conductivity. When the average length of the carbon nanotubes is too small, it is not conducive to improving conductivity. When the average length of the carbon nanotubes is too large, it is not conducive to the preparation and coating of the slurry.

[0051] It is important to know that the average particle size of conductive carbon black, the average diameter of carbon nanotubes, and the average length can be determined using TEM or SEM methods.

[0052] In the pre-coating slurry of this invention, the content of the dispersant is 0.3% to 3%, for example, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, etc. Within this range, the dispersant content allows for more uniform dispersion of conductive carbon black and carbon nanotubes, preventing their agglomeration. This improves the direct contact between the conductive carbon black and carbon nanotubes and the areas of the titanium-based material surface not covered with a carbon layer. During subsequent heat treatment, this enhances the bonding strength at the bonding sites. During fuel cell operation, the carbon at the bonding sites is less likely to peel off from the substrate, making it less likely for the contact resistance of the pre-coating and the membrane electrode to increase, thereby improving the conductivity and durability of the pre-coated titanium-based material. When the dispersant content is below 0.3%, the above effects are not easily achieved. When the dispersant content is above 3%, the above effects are not further improved and are actually detrimental to cost reduction and efficiency improvement. Preferably, the content of the dispersant is 0.8% to 1.5%.

[0053] The pre-coating slurry of this invention does not have a particular limitation on the type of dispersant, as long as it can ensure that the conductive carbon black and carbon nanotubes are uniformly dispersed in the slurry system, preventing sedimentation and not affecting subsequent coating processes. For example, the dispersant can be at least one of sodium carboxymethyl cellulose, sodium alginate, sodium silicate, and silica sol.

[0054] In the pre-coating slurry of this invention, the binder content is 0.1% to 3%, for example, 0.1%, 0.3%, 0.5%, 1.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, etc. When the binder content is within the above range, the pre-coating slurry can be effectively bonded to the titanium-based material after being applied. Subsequently, after heat treatment to ashing the slurry, conductive carbon black and carbon nanotubes form titanium carbides with the titanium-based material, tightly bonding to the surface of the titanium-based material, forming a strong metallurgical bond. When the binder content is below 0.1%, the above effects are not easily achieved. When the binder content is above 3%, it is not conducive to cost reduction and efficiency improvement. Preferably, the binder content is 0.8% to 1.5%.

[0055] The pre-coating slurry of this invention does not particularly limit the type of adhesive, as long as it can bond to the titanium-based material after being applied. For example, the adhesive can be at least one of the following: waterborne polyacrylic acid modified resin, polyvinyl alcohol, styrene-butadiene latex, carboxylated styrene-butadiene latex, phenolic resin, anionic emulsion resin copolymerized with styrene and acrylic acid, vinyl acetate and acrylate copolymer emulsion, vinyl acetate and ethylene copolymer, and acrylonitrile multi-component copolymer.

[0056] In the pre-coating slurry of this invention, the surfactant content is 0-1%, for example, 0, 0.2%, 0.4%, 0.6%, 0.8%, 1%, etc. A surfactant content within this range can improve the uniformity of the pre-coating slurry coating on the titanium substrate. When the surfactant content is higher than 1%, it is not conducive to cost reduction and efficiency improvement.

[0057] The pre-coating slurry of this invention does not particularly limit the type of surfactant. For example, the surfactant may be polyether-modified silicone oil and / or fluorocarbon surfactant.

[0058] In the pre-coating slurry of this invention, the solvent content is 90-98%, for example, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, etc. A solvent content within this range allows for the acquisition of a pre-coating slurry with suitable viscosity. When the solvent content is below 90%, the viscosity of the pre-coating slurry is too high, which is not conducive to subsequent uniform coating. When the solvent content is above 98%, the solid content of the pre-coating slurry is too low, making it difficult for conductive carbon black and carbon nanotubes to fully cover the surface of the titanium-based material, thus reducing the conductivity and conductive durability of the pre-coated titanium-based material. Preferably, the solvent content is 93-96%.

[0059] The pre-coating slurry of this invention does not particularly limit the type of solvent, as long as it can uniformly disperse the conductive carbon black and carbon nanotubes. For example, the solvent can be at least one selected from methanol, ethanol, isopropanol, toluene, cyclohexanone, formaldehyde solution, acetaldehyde solution, ketones, ethers, and water. Using water as the solvent results in low process equipment costs. Preferably, the solvent is water.

[0060] In addition, this embodiment of the invention also provides a method for preparing a pre-coating slurry for titanium-based materials, comprising the following steps: mixing the components according to a specified content to obtain the pre-coating slurry.

[0061] The preparation method of the pre-coating slurry in this embodiment of the invention is simple to operate and easy to promote industrially.

[0062] Preferably, the dispersant and the solvent are first mixed and then dispersed; then a surfactant is added and dispersed again; next, the conductive carbon black and the carbon nanotubes are added and dispersed; finally, the binder is added and dispersed to obtain the pre-coating slurry. This order of addition facilitates uniform dispersion of the pre-coating slurry and improves the uniformity of subsequent coating.

[0063] Furthermore, embodiments of the present invention also provide a method for preparing a pre-coated titanium-based material, comprising the following steps:

[0064] S1. Apply the pre-coating slurry of the present invention to the surface of the titanium-based material;

[0065] S2. Heat-treat the titanium-based material treated in step S1 under vacuum conditions.

[0066] The method for preparing the pre-coated titanium-based material in this invention does not have a particular limitation on the carbon content of the surface of the titanium-based material used; it is applicable to all types without the need for prior carbon content reduction treatment. This method is highly practical and can be industrially promoted. However, it is understood that the titanium-based material in step S1 is preferably a substrate with a carbon concentration of less than 30% carbon black at a depth of 10 nm from the outermost surface, which is more conducive to improving the conductivity and durability of the pre-coated titanium-based material. It should be noted that the carbon concentration on the surface of the titanium-based material is evaluated by the carbon concentration at a depth of 10 nm from the outermost surface, and is determined by depth-direction compositional analysis using XPS. It should also be noted that organic matter and other substances present in the atmosphere will usually be adsorbed on the surface of the substrate. In this invention, the surface portion (dirt layer) of the substrate with adsorbed organic matter and other substances in the XPS depth analysis results is removed, and the remaining substrate is regarded as the "outermost surface".

[0067] In some embodiments, the coating amount of the pre-coating slurry in step S1 is 0.2–0.6 mg / cm³. 2For example, 0.2 mg / cm 2 0.3 mg / cm 2 0.4 mg / cm 2 0.5 mg / cm 2 0.6 mg / cm 2 When the coating amount is within the above range, the coating slurry can completely cover the surface of the titanium-based material, improving the conductivity and conductivity durability of the pre-coated titanium-based material. If the coating amount is too low, the above effects are not conducive to performance. If the coating amount is too high, it is not conducive to cost reduction and efficiency improvement.

[0068] In some embodiments, the oxygen partial pressure under the vacuum condition in step S2 is 2 × 10⁻⁶. -4 ~2Pa (vacuum degree 10) -3 ~10 Pa), for example, the partial pressure of oxygen is 2 × 10. -4 Pa, 2×10 -3 Pa, 2×10 -2 The vacuum conditions, such as Pa, 0.2 Pa, and 2 Pa, are designed to facilitate the metallurgical bonding of carbon black and carbon nanotubes with titanium-based materials, thereby improving the conductivity of the pre-coated titanium-based materials. However, excessively low oxygen partial pressures lead to high manufacturing costs for vacuum equipment. Conversely, excessively high oxygen partial pressures may cause carbon black and carbon nanotubes to react with oxygen to form carbon dioxide, hindering the metallurgical bonding between these materials and the titanium-based materials, and consequently negatively impacting the conductivity of the pre-coated titanium-based materials.

[0069] In some embodiments, the heat treatment temperature in step S2 is 600–850°C, such as 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, etc., and the heat treatment time is 5–35 min, such as 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, etc. Through heat treatment, the conductive carbon black and carbon nanotubes in the pre-coating slurry react and diffuse with the titanium-based material, forming a strong metallurgical bond between carbon and titanium. During fuel cell operation, the pre-coating is less likely to peel off from the titanium-based material, improving the conductivity, durability, and resistance to high-potential corrosion of the pre-coated titanium-based material. When the heat treatment temperature is too low, the conductive carbon black and carbon nanotubes in the pre-coating slurry are less likely to react and diffuse with the titanium-based material, forming a strong metallurgical bond between carbon and titanium. When the heat treatment temperature is too high, it can cause a phase transition in the titanium-based material, reducing its mechanical properties and hindering cost reduction and efficiency improvement. It is understandable that the higher the heat treatment temperature, the shorter the heat treatment time required. In other words, the heat treatment time can be adaptively adjusted according to the heat treatment temperature.

[0070] In some embodiments, the method for preparing the pre-coated titanium-based material further includes: step S3. Brush cleaning and / or ultrasonic cleaning of the pre-coated titanium-based material. This step is to remove excess conductive carbon black and carbon nanotubes, thereby facilitating the subsequent stamping and forming of the pre-coated titanium-based material.

[0071] Furthermore, to further improve the durability of the coating, the pre-coated titanium-based material treated in step S3 can be heat-treated in an atmospheric atmosphere to form a titanium oxide layer on the titanium surface, thus improving durability. The heat treatment temperature is 200–500℃, and the time is 0.5–8 min. Excessive temperature can cause the combustion of carbon black and carbon nanotubes, leading to reduced conductivity. Conversely, excessively low temperatures are not conducive to the formation of titanium oxide, resulting in poor conductivity and durability. Higher heat treatment temperatures in an atmospheric atmosphere require shorter heat treatment times, which is beneficial for improving production efficiency.

[0072] In addition, this embodiment of the invention also provides a pre-coated titanium-based material, which is obtained by the preparation method of the pre-coated titanium-based material of this embodiment of the invention.

[0073] The pre-coated titanium-based material of this invention can effectively contact areas on the surface of the titanium-based material that are not covered by a carbon layer. During subsequent heat treatment, it is easier for reaction diffusion to occur, forming a metallurgical bond between carbon and titanium, which enhances the bonding strength at the bonding site. During fuel cell operation, the carbon at the bonding site is not easily peeled off from the substrate, making it less likely for the contact resistance between the pre-coated material and the membrane electrode to increase. This significantly improves the conductivity and durability of the pre-coated titanium-based material.

[0074] Furthermore, this embodiment of the invention also provides an electrode plate made of a pre-coated titanium-based material.

[0075] The electrode plates of this invention have excellent conductivity and conductivity durability, which is beneficial for the fuel cell to maintain high operating efficiency during long-term operation.

[0076] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0077] Example 1

[0078] A pre-coating slurry for titanium-based materials, comprising, by weight 100%, the following components: 2% conductive carbon black, 0.5% carbon nanotubes, 1% dispersant, 1% binder, 1% surfactant, and the balance being solvent.

[0079] The preparation method of the pre-coating slurry described above includes the following steps:

[0080] (1) Add 1% sodium carboxymethyl cellulose (dispersant) and deionized water to a disperser, control the disperser temperature at 25℃ and the speed at 2000 rpm, and disperse for 1 hour;

[0081] (2) Add 1% of SiC polyether modified silicone oil (surfactant) to the disperser, keep the disperser temperature at 25℃ and the speed at 1000 rpm, and disperse for 1 hour;

[0082] (3) Select conductive carbon black with an average particle size of 200 nm and a purity of ≥99.9%. Select carbon nanotubes with an average tube diameter of 9 nm, an average length of 10 μm, and a purity of ≥99.9%. Then add 0.5% carbon nanotubes and disperse for 1 h, then add 2% conductive carbon black and disperse for 1 h to obtain a black slurry;

[0083] (4) Add 1% of water-based acrylonitrile copolymer (binder) to the obtained black slurry and disperse for 1 hour to obtain a black liquid phase mixture with a viscosity of 200 mPa·S, which is the pre-coating slurry.

[0084] Application Example 1

[0085] A method for preparing a pre-coated titanium-based material includes the following steps:

[0086] (1) Substrate

[0087] Titanium material No. 1 with a thickness of 0.1 mm was used, and a 240×300 mm titanium material was cut out as the substrate. The carbon concentration at a depth of 10 nm from the outermost surface of the substrate was determined to be 22 atoms by XPS analysis.

[0088] (2) Coating

[0089] The pre-coating slurry from Example 1 was sprayed onto the substrate at a coating weight of 0.4 mg / cm². 2 .

[0090] (3) Heat treatment

[0091] The substrate obtained from the coating process was heat-treated for 10 minutes at 700°C in a vacuum environment with an oxygen partial pressure of 0.1 Pa.

[0092] (4) The heat-treated substrate is ultrasonically cleaned for 10 minutes to remove excess conductive carbon black and carbon nanotubes. Then, it is heat-treated at 400°C for 4 minutes in an atmospheric atmosphere to form a titanium oxide layer on the titanium surface and improve its durability.

[0093] Application Example 2

[0094] The preparation method of the pre-coated titanium-based material in this application embodiment is the same as that in application embodiment 1. The difference is that in step (3), the substrate obtained by the coating process is heat-treated at a temperature of 600°C for 30 minutes.

[0095] Application Example 3

[0096] The preparation method of the pre-coated titanium-based material in this application embodiment is the same as that in application embodiment 1. The difference is that in step (3), the substrate obtained by the coating process is heat-treated for 5 minutes in a vacuum environment with an oxygen partial pressure of 0.02 Pa and a temperature of 800°C.

[0097] Application Example 4

[0098] The preparation method of the pre-coated titanium-based material in this application embodiment is the same as that in application embodiment 1. The difference is that step (1) uses titanium material No. 2, and the carbon concentration at a depth of 10 nm from the outermost surface of the substrate is determined to be 7 atoms by XPS analysis.

[0099] Example 2

[0100] A pre-coating slurry for titanium-based materials, comprising, by weight 100%, the following components: 2% conductive carbon black, 1% carbon nanotubes, 1% dispersant, 1% binder, 1% surfactant, and the balance being solvent.

[0101] Application Example 5

[0102] The preparation method of the pre-coated titanium-based material in this application embodiment is the same as that in application embodiment 1, except that the pre-coating slurry used is the pre-coating slurry of embodiment 2.

[0103] Example 3

[0104] A pre-coating slurry for titanium-based materials, comprising, by weight 100%, the following components: 2% conductive carbon black, 1.5% carbon nanotubes, 1% dispersant, 1% binder, 1% surfactant, with the balance being solvent.

[0105] Application Example 6

[0106] The preparation method of the pre-coated titanium-based material in this application embodiment is the same as that in application embodiment 1, except that the pre-coating slurry used is the pre-coating slurry of embodiment 3.

[0107] Example 4

[0108] A pre-coating slurry for titanium-based materials, comprising, by weight 100%, the following components: 2% conductive carbon black, 2% carbon nanotubes, 1% dispersant, 1% binder, 1% surfactant, and the balance being solvent.

[0109] Application Example 7

[0110] The preparation method of the pre-coated titanium-based material in this application embodiment is the same as that in application embodiment 1, except that the pre-coating slurry used is the pre-coating slurry of embodiment 4.

[0111] Example 5

[0112] A pre-coating slurry for titanium-based materials, comprising, by weight 100%, the following components: 1% conductive carbon black, 2% carbon nanotubes, 1% dispersant, 1% binder, 1% surfactant, and the balance being solvent.

[0113] Application Example 8

[0114] The preparation method of the pre-coated titanium-based material in this application embodiment is the same as that in application embodiment 1, except that the pre-coating slurry used is the pre-coating slurry of embodiment 5.

[0115] Example 6

[0116] A pre-coating slurry for titanium-based materials is the same as in Example 1, except that the average particle size of the conductive carbon black is 150 nm.

[0117] Application Example 9

[0118] The preparation method of the pre-coated titanium-based material in this application embodiment is the same as that in application embodiment 1, except that the pre-coating slurry used is the pre-coating slurry of embodiment 6.

[0119] Example 7

[0120] A pre-coating slurry for titanium-based materials is the same as in Example 1, except that the average particle size of the conductive carbon black is 250 nm.

[0121] Application Example 10

[0122] The preparation method of the pre-coated titanium-based material in this application embodiment is the same as that in application embodiment 1, except that the pre-coating slurry used is the pre-coating slurry of embodiment 7.

[0123] Example 8

[0124] A pre-coating slurry for titanium-based materials is the same as in Example 1, except that the average diameter of the carbon nanotubes is 7 nm and the average length is 4 μm.

[0125] Application Example 11

[0126] The preparation method of the pre-coated titanium-based material in this application embodiment is the same as that in application embodiment 1, except that the pre-coating slurry used is the pre-coating slurry of embodiment 8.

[0127] Example 9

[0128] A pre-coating slurry for titanium-based materials is the same as in Example 1, except that the average diameter of the carbon nanotubes is 11 nm and the average length is 20 μm.

[0129] Application Example 12

[0130] The preparation method of the pre-coated titanium-based material in this application embodiment is the same as that in application embodiment 1, except that the pre-coating slurry used is the pre-coating slurry of embodiment 9.

[0131] Comparative Example 1

[0132] A pre-coating slurry for titanium-based materials, comprising, by weight 100%, the following components: 2.5% carbon nanotubes, 1% dispersant, 1% binder, 1% surfactant, and the balance being solvent.

[0133] Application Comparative Example 1

[0134] The preparation method of the pre-coated titanium-based material in this comparative example is the same as that in application example 1, except that the pre-coating slurry used is the same as that in comparative example 1.

[0135] Comparative Example 2

[0136] A pre-coating slurry for titanium-based materials, comprising, by weight 100%, the following components: 2.5% conductive carbon black, 1% dispersant, 1% binder, 1% surfactant, and the balance being solvent.

[0137] Application Comparative Example 2

[0138] The preparation method of the pre-coated titanium-based material in this application comparison example is the same as that in application example 1, except that the pre-coating slurry used is the pre-coating slurry of comparison example 2.

[0139] Application Comparative Example 3

[0140] The preparation method of the pre-coated titanium-based material in this application comparison example is the same as that in application example 1. The difference is that the pre-coating slurry used is the pre-coating slurry of comparison example 2, and the substrate obtained by the coating process in step (3) is heat-treated at a temperature of 600°C for 30 minutes.

[0141] Application Comparative Example 4

[0142] The preparation method of the pre-coated titanium-based material in this application comparison example is the same as that in application example 1. The difference is that the pre-coating slurry used is the pre-coating slurry of comparison example 2, and in step (3), the substrate obtained by the coating process is heat-treated for 5 minutes in a vacuum environment with an oxygen partial pressure of 0.02 Pa and a temperature of 800°C.

[0143] Performance testing

[0144] Initial contact resistance and subsequent contact resistance tests were performed on the pre-coated titanium-based materials prepared in Application Examples 1-8 and Comparative Examples 1-2. The contact resistance testing methods are as follows: Figure 4 It should be noted that the durability corrosion test was conducted in a sulfuric acid solution at 80℃ and pH=3, with an external voltage of 0.84V vs. SHE for 240 hours under constant potential polarization. The test results for initial contact resistance and contact resistance after the durability corrosion test are shown in Table 1. The initial contact resistance was less than 5 mΩ·cm. 2 A passing grade indicates compliance, while a failing grade indicates failure. The failure criterion for durability testing is that, after the durability test, the sample's contact resistance is greater than 10 mΩ·cm. 2 .

[0145] Table 1. Parameters and performance test results of substrate surface carbon content, pre-coating slurry composition, and preparation method of pre-coated titanium-based material.

[0146]

[0147] As can be seen from Table 1, regardless of whether the carbon concentration is 7 atomic% or 22 atomic% at a depth of 10 nm, the pre-coating slurry of the present invention can achieve high conductivity and high durability. However, if the pre-coating slurry of Comparative Example 1 or Comparative Example 2 is used, although high conductivity can be achieved in the initial state, the durability is poor.

[0148] Therefore, the pre-coating slurry used in the embodiments of the present invention can significantly improve the high-potential durability of the pre-coating. Figure 5 The changes in contact resistance over time of the pre-coated titanium-based materials prepared in Application Example 1 and Comparative Example 2 under a 0.84V constant potential polarization test are shown. It can be seen that the contact resistance of the pre-coated titanium-based material prepared in Application Example 1 only increases to 3.1 mΩ·cm after 240 hours of 0.84V constant potential polarization. 2 The pre-coated titanium-based material prepared using Comparative Example 2 showed a contact resistance increase to 15.1 mΩ·cm after 240 hours of testing. 2 Exceeding the DOE specification by 10 mΩ·cm 2 It can be seen that the pre-coated titanium-based material prepared by Example 1 of the present invention is significantly better than that of Comparative Example 2 in terms of high potential resistance.

[0149] Figure 6 The changes in contact resistance over time of the pre-coated titanium-based materials prepared in Application Example 1 and Comparative Example 2 under a 1.2V constant potential polarization test are shown. It can be seen that the contact resistance of the pre-coated titanium-based material prepared in Application Example 1 only increases to 4.8 mΩ·cm after 18 hours of 1.2V constant potential polarization. 2 The pre-coated titanium-based material prepared using Comparative Example 2 showed a contact resistance increase to 46 mΩ·cm after 9 hours of testing. 2 It far exceeds the DOE specification of 10 mΩ·cm 2 It can be seen that the pre-coated titanium-based material prepared by Example 1 of the present invention is significantly better than that of Comparative Example 2 in terms of high potential resistance.

[0150] Furthermore, a comparison of Application Example 1 and Application Examples 9-12 in Table 1 shows that when the sizes of the conductive carbon black and carbon nanotubes are not within the preferred range (the average particle size of the conductive carbon black is 150-250 nm; the average diameter of the carbon nanotubes is 7-11 nm, and the average length is 4-20 μm), the initial conductivity and conductivity durability of the prepared pre-coated titanium-based material are worse than those of Application Example 1.

[0151] This demonstrates that adding appropriate carbon nanotubes to carbon black in Examples 1-9 significantly improves the durability of the pre-coated titanium-based materials. In Comparative Example 2, where only carbon black is used, the pre-coated titanium-based material exhibits a lower contact resistance, but after a durability corrosion test, its contact resistance exceeds 10 mΩ·cm. 2 One possible reason is that the initial carbon content on the surface of the titanium-based material is relatively high (22 atomic%), which hinders the bonding between carbon black particles and the titanium-based material during heat treatment, leading to reduced durability of the pre-coated titanium-based material. Adding a specified amount of carbon nanotubes to the carbon black allows them to fill the gaps between carbon black particles due to their small diameter, thus enabling better contact with the titanium-based material. Even if the carbon content on the titanium surface is >10 atomic%, resulting in "carbon islands" occupying a large portion of the titanium surface and less exposed surface area, the unique structure of carbon nanotubes (small diameter, long length) effectively fills the gaps between the "carbon islands." Furthermore, the length of carbon nanotubes can reach 4–20 μm. Even if one end of the carbon nanotube contacts a "carbon island," the other end may directly contact the exposed titanium surface. Although the bonding between the end in contact with the "carbon island" and the titanium-based material is weak after heat treatment, the other end of the carbon nanotube can still bond tightly to the titanium-based material. In addition, the linear structure of carbon nanotubes enables them to form a network structure between carbon black particles, which enhances the conductivity and density of the carbon layer and is beneficial to improving the durability of pre-coated titanium-based materials.

[0152] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0153] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A pre-coating slurry for titanium-based materials, characterized in that, The titanium-based material is not acid-washed, and the carbon content on the surface of the titanium-based material is greater than 10 atomic%. Based on the total mass of the pre-coating slurry as 100%, it includes the following components: 0.6-5% conductive carbon black, 0.2-2.5% carbon nanotubes, 0.3-3% dispersant, 0.1-3% binder, 0-1% surfactant, and 90-98% solvent; the mass ratio of the conductive carbon black to the carbon nanotubes is 2:(0.5-2); the average diameter of the carbon nanotubes is 7-9 nm, and the average length is 4-12 μm; the dispersant is at least one of sodium carboxymethyl cellulose, sodium alginate, sodium silicate, and silica sol.

2. The pre-coating slurry for titanium-based materials according to claim 1, characterized in that, The average particle size of the conductive carbon black is 150~250nm.

3. The pre-coating slurry for titanium-based materials according to claim 1 or 2, characterized in that, The solvent is at least one of methanol, ethanol, isopropanol, toluene, formaldehyde solution, acetaldehyde solution, ketone, ether, and water.

4. The method for preparing a pre-coating slurry for titanium-based materials according to any one of claims 1 to 3, characterized in that, Includes the following steps: The components are mixed in the specified amounts to obtain the pre-coated slurry.

5. A method for preparing a pre-coated titanium-based material, characterized in that, Includes the following steps: S1. Provide a titanium-based material, wherein the carbon content on the surface of the titanium-based material is greater than 10 atomic%; omitting the pickling treatment of the titanium-based material, the pre-coating slurry according to any one of claims 1 to 3 is directly coated on the surface of the titanium-based material; S2. The titanium-based material treated in step S1 is subjected to heat treatment under vacuum conditions to obtain the pre-coated titanium-based material.

6. The method for preparing the pre-coated titanium-based material according to claim 5, characterized in that, The coating amount of the pre-coating slurry in step S1 is 0.2~0.6 mg / cm³. 2 ; and / or, the oxygen partial pressure under the vacuum conditions described in step S2 is 2 × 10⁻⁶. -4 ~2Pa; and / or, the heat treatment temperature is 600~850℃, and the heat treatment time is 2~35min.

7. The method for preparing the pre-coated titanium-based material according to claim 5 or 6, characterized in that, It also includes: step S3. Brush cleaning and / or ultrasonic cleaning of the pre-coated titanium-based material to remove excess carbon material.

8. A pre-coated titanium-based material, characterized in that, Obtained by the preparation method described in any one of claims 5 to 7.

9. An electrode plate, characterized in that, Made from the pre-coated titanium-based material as described in claim 8.

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