Titanium felt with composite coating, preparation method and application of titanium felt and membrane electrode

Abstract

The invention relates to the technical field of metal surface treatment, in particular to a titanium felt with a composite coating, a preparation method and application of the titanium felt and a membrane electrode. The titanium felt comprises a titanium felt substrate, a metal fluoride layer covering the fiber surface of the titanium felt substrate, and an iridium oxide layer covering the metal fluoride layer and forming a compact and continuous composite coating together with the metal fluoride layer. The preparation method of the titanium felt adopts a pulse laser deposition technology, and the metal fluoride layer and the iridium oxide layer are sequentially deposited. The titanium felt has the beneficial effects that through the three-layer composite structure design of the titanium felt base body, the metal fluoride layer and the iridium oxide layer, the original porosity of the titanium felt is kept, and meanwhile uniform and controllable deposition of a nanoscale coating is achieved. The composite coating titanium felt is used as a reusable gas transmission layer electrode, the iridium load of a membrane electrode can be remarkably reduced, and the cost is greatly reduced while the electrolysis performance is ensured.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, specifically to a titanium felt with a composite coating, a method for preparing the titanium felt and its application, and a membrane electrode. Background Technology

[0002] With the rapid development of electrochemical energy technology and electrocatalysis industry, the market demand for high-performance electrode materials is increasing. Among many electrode substrates, titanium felt, due to its unique three-dimensional network through-pore structure, possesses high specific surface area, excellent porosity, and outstanding gas diffusion performance, making it a versatile material that can be widely used in various electrochemical environments such as electrolytic synthesis, environmental treatment, and energy conversion.

[0003] Applying functional coatings to the surface of titanium felt is a common technique to enhance its performance. Since most electrochemical environments involve high temperatures and strong oxidizing conditions, the metals that can be used for titanium felt coatings are mainly noble metals such as platinum and iridium, and their oxides. Among them, iridium oxide (IrO2) coatings / layers have become one of the most representative surface functionalization methods due to their excellent electrocatalytic activity, high chemical stability, and superior electrical conductivity, playing an irreplaceable role in many industrial fields such as hydrogen production through water electrolysis, chlor-alkali industry, metal electrowinning, wastewater treatment, and cathodic protection.

[0004] Taking the specific application of proton exchange membrane electrolysis for hydrogen production as an example, this technology places particularly stringent requirements on electrode performance. In this scenario, the titanium felt serves as the gas transport layer inside the electrolyzer, and its performance directly affects the overall energy efficiency of the electrolyzer. The low oxygen evolution potential characteristic of iridium oxide catalysts under high current conditions is of great significance for reducing the energy consumption of the entire system. Depositing an iridium oxide coating on the gas transport layer in contact with the anodic catalyst layer of the membrane electrode not only improves the catalytic efficiency of the reaction interface but also enhances the chemical stability of the gas transport layer itself.

[0005] However, the implementation of this technical route faces severe challenges. Iridium is an extremely rare element on Earth, with a content of only 0.0004 ppm in the Earth's crust, making it one of the least abundant elements in the crust. Global iridium production in 2024 was only 8-9 tons, far lower than the 3,600 tons of gold produced annually. This extreme scarcity makes it a "strategic metal" in high-end manufacturing. Considering that titanium felt can be used as a reusable component in industrial applications, achieving a uniform and firm deposition of an iridium oxide layer on the surface of titanium felt has significant technical and economic value.

[0006] For titanium felt, its pore structure directly determines gas transport efficiency. Since the pore size of titanium felt is primarily on the micrometer scale, traditional coating methods struggle to meet coating uniformity requirements without significantly sacrificing porosity. Therefore, developing a process for preparing iridium oxide nanolayers / through-pore titanium felt that can reduce precious metal loading, offer reusability, and improve the overall performance of the electrolyzer has become a common technological need in the green hydrogen industry and even the broader electrochemical industry.

[0007] In the prior art, various surface engineering techniques have been explored for constructing noble metal coatings on titanium substrates. For example: The scientific paper "Nano-thickness Platinum coating on porous Titanium via displacement induced autocatalytic electroless plating" (DOI: 10.1021 / jacs.5c11154) reports a method for achieving nanoscale thick platinum coatings on porous titanium through displacement-induced autocatalytic electroless plating, which is suitable for fuel cell electrodes and aims to reduce the interfacial resistance between the membrane electrode and the gas transport layer.

[0008] The paper "Advanced Fabrication of Ultrathin Ruthenium Films Using Synergistic Atomic Layer Deposition and Etching" (DOI: 10.1002 / smtd.202402166) uses a combination of atomic layer deposition and atomic layer etching techniques to prepare ultrathin, smooth ruthenium films, achieving nanoscale surface roughness control.

[0009] The paper "Surface and Interface Engineering of Noble Metal Heterostructures for Superior ORR Performance: Unlocking Ultralow Loading and Maximum Catalyst Utilization" (DOI: 10.1002 / smll.202506018) reviews strategies for optimizing electronic structure, improving interfacial charge transfer efficiency, and reducing reaction energy barriers by constructing noble metal catalyst heterostructures on the surface of the gas transport layer.

[0010] In addition, the paper "Impacts of PTL coating gaps on cell performance for PEMwater electrolyzer" (DOI: 10.1016 / j.apenergy.2023.122274) reports a scheme to deposit patterned platinum group metal coatings on the surface of porous transport layer of titanium anode in order to minimize the component cost of proton exchange membrane water electrolyzer.

[0011] In summary, coating the surface of titanium felt with precious metals (such as platinum, iridium, and their oxides) is an effective way to improve the overall stability of the electrolyzer. Using iridium oxide, which has catalytic activity for the oxygen evolution reaction, as the titanium felt coating not only improves the contact resistance between the titanium substrate and the membrane electrode, but also helps reduce the loading requirements of the membrane electrode itself on iridium-based catalysts. Since titanium felt is a reusable component in proton exchange membrane water electrolyzers, using through-hole titanium felt with an iridium-based coating is expected to reduce the overall amount of precious metals used in the system, thereby reducing the manufacturing cost of the electrolyzer and simultaneously improving its operating performance and service life.

[0012] From the perspective of deposition processes, there are various traditional methods for preparing iridium oxide coatings on titanium substrates, but all of them have certain limitations. The thermal decomposition method, as the most widely used method in industry, prepares coatings through the coating of iridium-containing compounds and subsequent high-temperature thermal decomposition. However, it suffers from problems such as cumbersome process flow, low utilization rate of iridium raw materials, poor coating uniformity, and easy oxidation of the titanium substrate at high temperatures.

[0013] In the published invention patent CN117364133A, an integrated electrode fabrication method based on a porous transport layer with a through-hole structure is provided. This method involves placing a titanium felt with through-holes in an iridium-containing solution (iridium source concentration 0.05–0.5 M / L), reacting it at 80–200°C for 30 minutes to 4 hours, and then calcining it in a muffle furnace at 350–600°C for 30 minutes to 4 hours after cooling. While the sol-gel method can obtain a relatively uniform iridium oxide coating, it still faces the following technical challenges that affect its application on titanium felt with through-holes: 1. The raw materials are expensive and the process is complex. The utilization rate of precious metal iridium salt is low, and the synthesis by-products may cause environmental pollution.

[0014] 2. During the drying and heat treatment process, the coating is prone to cracking, resulting in insufficient coating density and high surface roughness, which in turn increases the surface roughness of the titanium felt and the contact resistance with the membrane electrode.

[0015] 3. The uniformity of coating thickness deposited on the complex surface of titanium felt with through holes by this method is difficult to guarantee, and additional surface smoothing treatment is often required for the coated titanium felt.

[0016] 4. The impregnation-sintering process can easily cause iridium oxide to clog the pores of titanium felt, reducing its effective porosity.

[0017] 5. The high-temperature sintering process involved in the sol-gel method is prone to causing oxidation on the surface of titanium felt, forming a titanium oxide layer, which often results in insufficient adhesion between the prepared iridium oxide coating and the substrate.

[0018] To address the aforementioned technical pain points, the present invention aims to solve the following key technical challenges: 1. Existing methods for preparing iridium oxide coatings are insufficient to form uniform, dense, and strongly adherent coatings within the three-dimensional network structure of titanium felt substrates. In particular, solid-phase and liquid-phase decomposition / deposition methods tend to result in excessive deposition of the coating on the outer surface of the titanium felt, while insufficient coverage of the internal pores leads to localized pore blockage. Liquid-phase electrodeposition methods, due to uneven current distribution, are difficult to obtain coatings with good consistency in complex microporous structures.

[0019] 2. The bonding force between the iridium oxide coating prepared by traditional methods and the titanium felt substrate is insufficient. Under the strong oxidizing environment of the electrolysis process and the physical erosion caused by gas evolution, the coating is prone to peeling off, which greatly shortens the service life of the electrode.

[0020] 3. High-temperature processing can easily lead to excessive oxidation of the titanium felt substrate surface, forming a titanium oxide layer with poor conductivity, which significantly reduces the conductivity of the electrode. This problem is particularly prominent in titanium felt with a large specific surface area.

[0021] 4. Existing technologies make it difficult to precisely control the stoichiometry and microstructure of iridium oxide coatings on complex three-dimensional substrates such as titanium felt, thus affecting the final electrocatalytic activity and long-term stability of the coating.

[0022] 5. Low utilization rate of expensive iridium resources. In traditional methods such as solid-phase pyrolysis and liquid-phase deposition, a large amount of precious iridium fails to form an effective catalytic layer, resulting in resource waste, increased costs, and excessively high costs for subsequent waste recycling. Summary of the Invention

[0023] The purpose of this invention is to provide a titanium felt with a composite coating. The composite coating of the titanium felt has a dense structure, uniform crystal phase, and a strong bond between the deposited layer and the titanium felt. It also has excellent electrical conductivity, catalytic activity and structural stability, without sacrificing its original high porosity characteristics.

[0024] Another objective of this invention is to provide a method for preparing the above-mentioned titanium felt with a composite coating. This method uses pulsed laser deposition technology to deposit a composite coating on the surface of the titanium felt, thereby achieving controllable deposition of a nanometer-precision coating on a three-dimensional porous structure.

[0025] Another object of the present invention is to provide the application of the above-mentioned titanium felt with composite coating as a gas transport layer electrode in a proton exchange membrane water electrolyzer.

[0026] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a titanium felt with a composite coating, comprising: Titanium felt matrix; A metal fluoride layer covering the surface of the titanium felt matrix fibers, the thickness of the metal fluoride layer being 0.1~10 nanometers; and, An iridium oxide layer covers the metal fluoride layer and together with the metal fluoride layer forms a dense and continuous composite coating.

[0027] Preferably, the metal fluoride layer is selected from one or more of alkaline earth metal fluorides, rare earth metal fluorides, and lithium fluoride; the iridium oxide layer is iridium oxide with a rutile phase structure.

[0028] Preferably, the thickness of the iridium oxide layer is not less than 80 nanometers.

[0029] Secondly, the present invention provides the use of the titanium felt with the composite coating as a gas transport layer electrode, wherein the titanium felt has a through-hole structure.

[0030] Thirdly, the present invention provides a membrane electrode, comprising: Gas transport layer on the cathode side; Cathode catalyst layer; Proton exchange membrane; Anode catalyst layer; and, The titanium felt with a composite coating on the surface as described above has a through-hole structure and is disposed outside the anode catalyst layer, with the iridium oxide catalyst layer facing the anode catalyst layer.

[0031] Fourthly, the present invention provides a method for preparing a titanium felt with a composite coating, wherein the method employs pulsed laser deposition technology to sequentially deposit the metal fluoride layer and the iridium oxide layer.

[0032] Preferably, the laser used in pulsed laser deposition is an excimer laser with the following laser parameters: wavelength of 190~360 nm, pulse width of 5~50 ns, pulse repetition frequency of 1~100 Hz, and single pulse energy of 100~200 mJ.

[0033] Preferably, the process conditions for depositing the metal fluoride layer include: a vacuum degree of 5 × 10⁻⁶ m² / 40⁻¹² ... -6 ~ 5×10 -5Pa; the titanium felt substrate temperature is 50~250℃; the deposition rate is less than 0.2 nm / min; the process conditions for depositing the iridium oxide layer include: the vacuum chamber is filled with oxygen with a purity of more than 99.999%, the oxygen partial pressure is 10~100 Pa; the titanium felt substrate temperature is 300~550℃; the deposition rate is less than 0.5 nm / min.

[0034] Preferably, the method further includes a surface pretreatment process for the titanium felt substrate before pulsed laser deposition, the surface pretreatment process including deburring, pickling, deionized water cleaning and drying steps performed sequentially.

[0035] Preferably, the acid used in the pickling treatment is an oxalic acid solution with a concentration of 2% to 12%; the pickling temperature is 40 to 80°C, and the treatment time is 5 to 60 minutes; the deionized water rinsing needs to be carried out until the conductivity of the rinsing water is less than 10 microsiemens per centimeter (μS / cm); the drying step is to use nitrogen gas to dry.

[0036] Compared with the prior art, the present invention has the following significant advantages: 1. Composite structure coating This invention employs a three-layer composite structure: a titanium felt substrate, a metal fluoride layer, and an iridium oxide layer. The 0.1–10 nm metal fluoride layer acts as a crucial passivation layer, effectively preventing the formation of high-resistivity titanium oxide on the titanium substrate surface during high-temperature processing and significantly enhancing the adhesion between the outer iridium oxide layer and the titanium felt, thus solving the problem of easy peeling of traditional coatings. The outer iridium oxide layer provides excellent catalytic activity and chemical stability for the oxygen evolution reaction. Together, these two layers constitute a dense and continuous functional composite coating, achieving a synergistic effect of enhanced adhesion, prevention of substrate oxidation, and improved catalytic activity.

[0037] 2. Achieve precise and controllable conformal deposition Pulsed laser deposition technology is used to bombard the target material with high-energy laser pulses to generate highly directional plasma plumes, which can achieve uniform and conformal deposition of nanoscale thickness coatings inside complex three-dimensional through-hole mesh structures.

[0038] This process perfectly solves the problems caused by traditional methods (such as thermal decomposition and sol-gel methods), such as pore blockage, uneven coating, and large differences in the coverage of inner and outer surfaces.

[0039] By precisely controlling laser parameters (wavelength, energy, frequency) and deposition environment (vacuum, temperature, oxygen partial pressure), it is possible to achieve precise control over coating thickness, stoichiometry (oxidation state), and crystal structure (such as rutile phase), resulting in good process repeatability and high utilization of the precious metal iridium.

[0040] 3. Can maintain the advantages of the matrix structure As shown in the attached figures and test data, after processing with the process of the present invention, the original structure of the titanium felt substrate (such as the through-hole structure in the embodiment) is completely preserved, and its porosity and pore size distribution remain almost unchanged (for example, the porosity only slightly decreases from 37% to 35%). This means that while the present invention imparts high catalytic activity to the surface of the titanium felt, it does not sacrifice the high permeability and gas transport capacity necessary for it to function as a gas transport layer.

[0041] By avoiding adverse oxidation of the titanium substrate and forming a dense conductive coating, the product has low and stable interfacial contact resistance, which helps to reduce the energy consumption of the electrolytic cell.

[0042] 4. Improve the utilization efficiency of the precious metal iridium. The composite coated titanium felt prepared according to this invention is used as the anode gas transport layer in a PEM electrolyzer. Its iridium oxide layer can directly participate in the catalytic reaction, thus allowing for a significant reduction in the iridium loading in the membrane electrode catalytic layer. Experiments show that using the titanium felt of this invention, the anode iridium loading is only 0.35 mg / cm³. 2 In this case, its electrolytic performance is superior to that using ordinary titanium felt and its iridium loading is as high as 0.5 mg / cm³. 2 The traditional approach has achieved the goal of reducing iridium and increasing efficiency.

[0043] Because the coating bondes firmly to the substrate and has stable performance, this titanium felt can be reused as a gas transport layer component, further reducing the cost of using precious metals in the electrolyzer throughout its entire life cycle, which is of great significance for promoting the commercial development of the green hydrogen industry. Attached Figure Description

[0044] The above features and advantages of the present invention will become clearer and more readily understood from the following description of exemplary embodiments thereof in conjunction with the accompanying drawings.

[0045] Figure 1 : Schematic diagram of the titanium felt structure fabricated in Example 1; Figure 2 Schematic diagram of the cross-section of the membrane electrode assembly; Figure 3 Microscopic photograph of a typical commercially available titanium felt with a straight-through hole structure; Figure 4 Microscopic image of a titanium felt with a through-hole structure after iridium oxide layer deposition; Figure 5 Polarization test curves of a commercially available through-hole titanium felt assembled electrolytic cell Figure 6 Polarization test curves of an electrolytic cell assembled with iridium-plated through-hole titanium felt; Figure 7 Pump test data before and after deposition of iridium oxide layer on commercial through-hole titanium felt. Detailed Implementation

[0046] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] In the specific embodiments described in this invention, unless otherwise specified, the term 'room temperature' refers to an ambient temperature of 15 °C to 30 °C.

[0048] Example 1: (1) Matrix selection and pretreatment Substrate selection: Commercially available through-hole titanium felt made of high-purity titanium was used as the substrate. The titanium felt with the through-hole structure is made of high-purity titanium.

[0049] Those skilled in the art should note that the method for preparing titanium felt with a composite coating provided by this invention can be applied to various types of titanium felt, such as commercially available titanium wire type titanium felt, through-hole type titanium felt, etc. The commercially available through-hole type titanium felt used in Examples 1 and 2 is only for illustrative purposes and is not intended to limit the structure and preparation method of the titanium felt with a composite coating provided by this invention to this type.

[0050] Preprocessing: Deburring treatment: The titanium felt with a straight hole structure is deburred, and the surface color of the titanium felt changes from the original silver-gray to a bright silver. This step is to improve the smoothness of the titanium felt surface, which helps to improve the adhesion of subsequent coatings.

[0051] Pickling treatment: The titanium felt with straight holes, after surface deburring, undergoes pickling treatment. The pickling process can expose the clean substrate on the surface of the titanium felt by removing metal impurities introduced during metal processing, such as metal oxides. The specific operation is as follows: prepare a 10wt% oxalic acid solution, heat it to 60℃, and immerse the titanium felt in it for 30 minutes.

[0052] Deionized water cleaning: After acid washing, rinse the titanium felt repeatedly with deionized water until the conductivity of the outflowing water is less than 10 μS / cm. Only then can it be considered that there is no cleaning acid residue on the surface of the through-hole titanium felt.

[0053] Drying: Use nitrogen to dry the material. The pretreatment step is complete, and the material can be used as a matrix material for subsequent deposition.

[0054] (2) PLD deposition of metal fluoride layer The pretreated titanium felt was placed in the vacuum chamber of the PLD equipment, with the target-substrate distance set to 50 mm. The vacuum was then evacuated to 9 × 10⁻⁶ mm. -6 Pa was used to heat the titanium felt substrate to 120°C. A krypton fluoride (KrF) excimer laser was used with the following parameters: wavelength 248 nm, pulse width 25 ns, repetition rate 10 Hz, single pulse energy 100 mJ, and laser spot size 2 × 3 mm. 2 A magnesium fluoride (MgF2) target was bombarded, and the deposition rate was controlled at approximately 0.05 nm / min. After 10 minutes of deposition, a magnesium fluoride layer with a thickness of approximately 0.5 nm was obtained.

[0055] The pulsed laser deposition (PLD) process used involves bombarding a target with a high-energy laser pulse to generate a plasma plume containing atoms, ions, and agglomerates, which is then deposited onto the substrate surface to form a film. Specifically, the high-energy laser pulse instantly vaporizes the target, forming a high-temperature, high-speed plasma plume containing magnesium and fluorine atoms and ions. This plume is directed towards the substrate along the normal direction of the target. The titanium felt substrate to be deposited is positioned at the forefront of this sputtering direction. The plasma containing metal elements and fluorides migrates, diffuses, and reassembles on the surface of the titanium felt substrate with sufficient energy, nucleating and growing to form a continuous and dense metal fluoride passivation layer.

[0056] To enhance the adhesion between the iridium oxide deposition layer and the surface of the through-hole titanium felt, the cleaned through-hole titanium felt needs to undergo PLD deposition of a 0.1–10 nm thick metal fluoride layer in a vacuum environment. A metal fluoride layer must first be deposited as a surface passivation layer. Too thin a metal fluoride coating will not meet the adhesion requirements of the subsequent iridium oxide deposition layer, while too thick a metal fluoride deposition layer will increase the interfacial resistance.

[0057] (3) PLD deposition of iridium oxide layer After the deposition of metal fluoride is completed, to prevent the metal fluoride in the vacuum chamber from contaminating subsequent deposits, the vacuum chamber is continuously evacuated until the vacuum level in the vacuum chamber is <2×10⁻⁶. -6 After maintaining the pressure at 20 Pa for more than 30 minutes, high-purity oxygen with a purity >99.999% was then introduced to stabilize the oxygen partial pressure at 20 Pa.

[0058] The titanium felt substrate temperature was raised to 350℃. The KrF laser was restarted, and the parameters were adjusted to: repetition frequency 20 Hz, single pulse energy 120 mJ. The iridium oxide deposition rate was controlled at approximately 0.2 nm / min, and deposition was carried out for 500 minutes to obtain an iridium oxide layer with a thickness of approximately 100 nm.

[0059] The laser beam from an excimer laser bombards a high-purity iridium metal target, forming a plasma plume containing iridium metal elements. Simultaneously, some oxygen molecules are excited and dissociated under the bombardment of the high-energy laser beam and the plasma environment, forming oxygen-containing active groups (such as oxygen atoms and oxygen ions). The surface of the titanium felt substrate, already coated with a metal fluoride passivation layer, is positioned at the forefront of this composite sputtering direction. The plasma / active groups of iridium metal elements and oxygen elements interact on the heated titanium felt substrate surface, migrating, reacting, and reassembling, ultimately epitaxially growing a dense iridium oxide layer with a rutile phase structure.

[0060] When depositing iridium oxide using a PLD, the titanium felt needs to be heated to a high temperature. The heating temperature range for the titanium felt substrate is 300~550℃. The temperature of the titanium felt substrate directly affects the density of the iridium metal oxide deposition layer, and the temperature should be adjusted appropriately according to the oxygen partial pressure. In this embodiment, the temperature is raised to 350℃.

[0061] After the metal fluoride layer is deposited, the vacuum chamber atmosphere during the redeposition of iridium oxide is a low-vacuum environment containing some high-purity oxygen (purity > 99.999%). After replenishing with high-purity oxygen, the deposition of the metal oxide begins when the oxygen partial pressure is in the range of 10–100 Pa; in this embodiment, the oxygen partial pressure is 20 Pa. The oxygen partial pressure directly affects the oxidation state of iridium metal. During PLD deposition of the iridium oxide layer, high-purity oxygen needs to be added to the vacuum chamber. The low concentration of oxygen reacts with the plasma-state iridium metal at high temperatures, providing oxygen for the deposition of the iridium oxide layer. The purity of the oxygen used should be > 99.999%, and the vacuum level in the vacuum chamber will decrease to 10–100 Pa.

[0062] See Figure 1-2 As shown in the figure, the labels are: 10- Titanium felt matrix 20- Metal fluoride layer 30-Iridium oxide layer 31- The side of the titanium felt substrate with an iridium oxide coating 40- Through pores on the titanium felt substrate 50 - Platinum-carbon catalyst layer on the cathode side of the electrolytic cell 60- Proton exchange membrane 70- Iridium-based catalyst layer on the anode side of the electrolyzer 80- Carbon Paper Titanium felt prepared in Example 1 See Figure 1 As shown, the titanium felt structure fabricated in Example 1 includes: Titanium felt substrate 10; A metal fluoride layer 20 is applied to the surface of the fibers of the titanium felt substrate 10, the thickness of which is 0.5 nanometers; and an iridium oxide layer 30 is applied to the metal fluoride layer 20 and together with the metal fluoride layer 20 forms a dense and continuous composite coating.

[0063] The titanium felt structure assembled film electrode in Example 1 See Figure 2 As shown, the structure of the titanium felt structure fabricated in Example 1 after assembling the membrane electrode includes: Platinum-carbon catalyst layer 50 on the cathode side of the electrolytic cell; Carbon paper 80, gas transport layer on the cathode side; Proton exchange membrane 60; The iridium-based catalyst layer 70 on the anode side of the electrolyzer; and, The titanium felt with a composite coating as described above is disposed outside the anode catalyst layer, and the iridium oxide catalyst layer (the side 31 of the titanium felt substrate with the iridium oxide coating) faces the anode catalyst layer 70.

[0064] The results of the characterization of the titanium felt structure and the performance tests of the electrolytic cell are as follows: Figure 3 These are microscope images of a typical commercially available titanium felt with a straight-through hole structure. Figure 4 Microscopic image of a titanium felt with through-hole structure after iridium oxide layer deposition. (Comparison) Figure 3 , Figure 4 As can be seen from the photographs, the microporous structure is almost unaffected before and after deposition.

[0065] Figure 5 Polarization test curves for a commercially available through-hole titanium felt assembled electrolytic cell / iridium-plated through-hole titanium felt assembled electrolytic cell were generated. The electrolytic cell was tested at a temperature of 65℃ and a flow rate of 40 ml / min. For the membrane electrode A assembled with commercially available through-hole titanium felt, the platinum / iridium metal loadings at the anode and cathode were 0.2 mg / cm³, respectively. 2 (0.5 mg / cm) 2 ); The membrane electrode B, assembled with commercially available through-hole titanium felt, has platinum / iridium metal loadings at the anode and cathode of 0.2 mg / cm³, respectively. 2 ), (0.35mg / cm 2 ); The membrane electrode assembled with iridium-plated through-hole titanium felt has platinum / iridium metal loadings at its anode and cathode of 0.2 mg / cm³, respectively. 2 ), (0.35mg / cm 2 ).

[0066] The membrane electrode assembly of the electrolyzer is carried out according to Figure 2Assemble in the order shown, and activate in the electrolytic cell for more than a week. The activation process for the three membrane electrodes is completely identical and all are standard testing procedures.

[0067] Figure 2 As shown, the titanium felt with deposited iridium oxide is assembled in the electrolytic cell in the same way as the existing process, only requiring that the side with the iridium oxide coating be aligned with the anode catalyst layer. Figure 5 Data shows that, under the same test conditions, comparing data from groups A and B of commercial titanium felt, increasing the iridium-based catalyst loading on the anode side can further reduce the polarization voltage, meaning that the electrolyzer has higher voltage efficiency at the same current density. Comparing data from group B of commercial titanium felt with iridium-plated through-hole titanium felt, when the membrane electrode has the same noble metal loading, iridium plating on the titanium felt can further reduce the polarization voltage, meaning that the electrolyzer has higher voltage efficiency at the same current density.

[0068] Figure 6 Pump test data before and after deposition of iridium oxide layer on commercially available through-hole titanium felt are used to compare the porosity changes before and after the titanium felt is attached with the deposited layer.

[0069] Table 1 shows the comparison results of the pore size distribution of titanium felt before and after iridium oxide deposition using the mercury indentation method.

[0070] Figure 6 The data in Table 1 show that the actual pore size distribution and values ​​of the through-hole titanium felt remain basically unchanged before and after iridium plating. The porosity is maintained at around 37%, which is the same as the original data of the purchased commercial titanium felt.

[0071]

[0072] It is well known in the art that in gas diffusion electrodes, the thickness of the catalyst layer (such as an iridium oxide layer) directly affects its catalytic active area, electron conduction pathway, and mass transfer resistance of reactants / products, thus affecting the overall performance of the electrode. An excessively thin catalyst layer may result in insufficient active sites, while an excessively thick catalyst layer may clog the channels of the porous matrix, reducing porosity and mass transfer efficiency. Therefore, for specific application scenarios (such as required current density, electrolyte environment, etc.), there exists an optimized range for catalyst layer thickness.

[0073] One of the key advantages of this invention lies in the pulsed laser deposition (PLD) process employed. This technology generates highly directional plasma plumes using high-energy laser pulses, enabling the deposition of highly uniform and shape-preserving nanoscale coatings on the complex three-dimensional fiber network surface of titanium felt. Unlike traditional wet chemical methods (such as sol-gel and electrodeposition), which are prone to problems such as uneven coating, pore blockage, or insufficient internal coverage, the PLD process ensures uniform coverage of the iridium oxide layer on the surface of the titanium felt fibers, with excellent consistency in thickness at the microscale.

[0074] Based on this characteristic of the PLD process, the relationship between the thickness of the iridium oxide layer and the macroscopic porosity of the final titanium felt composite becomes highly predictable. Because the coating adheres uniformly to the surface of each fiber, there is no aberration at pore junctions or fiber intersections. Therefore, for a given initial porosity and fiber diameter, those skilled in the art can predictably estimate the retained porosity of the titanium felt at the target coating thickness using simple geometric models (e.g., considering the fibers as uniformly coated cylinders) and material volume calculations. This avoids the extensive repetitive trial-and-error experiments required in traditional processes to determine the appropriate thickness.

[0075] Therefore, although the embodiments of this application preferably demonstrate the excellent performance achieved by an iridium oxide layer with a thickness of about 100 nm (such as high catalytic activity and high porosity), those skilled in the art, based on the above-mentioned common knowledge and the uniformity advantage of the PLD process disclosed in this invention, can extend the thickness of the iridium oxide layer to the desired extent, such as 200 nm, without creative effort through conventional calculations and limited experiments. At the same time, they can ensure that the porosity meets the requirements through calculations to achieve the best balance between catalytic activity, structural stability and gas transport performance. This also falls within the protection scope of this invention.

[0076] Example 2 Matrix selection and pretreatment Same as Example 1.

[0077] (2) PLD deposition of metal fluoride layer The titanium felt material was placed in the vacuum chamber of the PLD equipment, with a vacuum level of 5×10⁻⁶. -5 Pa, the titanium felt was heated to 100℃; a pulsed laser, specifically a xenon chloride (XeCl) excimer laser, was used with the following parameters: wavelength 308 nm, pulse width 20 ns, repetition rate 10 Hz, and single pulse energy 100 mJ. The laser beam was used to bombard the lithium fluoride target, controlling the lithium fluoride deposition rate at 0.01 nm / min and the deposition time at 20 min, to complete the deposition of a 0.2 nm thick lithium fluoride layer.

[0078] (3) PLD deposition of iridium oxide layer After the deposition of the metal fluoride layer is completed, the laser is temporarily shut down, and the metal fluoride target is replaced with an iridium target, maintaining the ambient vacuum level at less than 2 × 10⁻⁶. -6After at least 30 minutes under Pa pressure, high-purity oxygen (at least 99.999%) is added to the vacuum environment, reducing the vacuum level to 60 Pa. The titanium felt is heated to 350°C, and the xenon chloride (XeCl) excimer laser is restarted with the following parameters: wavelength 308 nm, pulse width 20 ns, repetition frequency adjusted to 5 Hz, and single pulse energy 140 mJ. The laser beam is then used to bombard the iridium target, controlling the deposition rate of the iridium oxide layer to 0.4 nm / min and the deposition time to 200 minutes, thus completing the deposition of an iridium oxide layer with a thickness of 80 nm.

[0079] Example 3 Matrix selection and pretreatment Same as Example 1.

[0080] (2) PLD deposition of metal fluoride layer Vacuum degree is 2×10 -5 Pa, titanium felt substrate temperature 200℃. A KrF excimer laser with a repetition rate of 20 Hz and a single pulse energy of 150 mJ was used to bombard the calcium fluoride (CaF2) target at a deposition rate of approximately 0.15 nm / min for 33 minutes, resulting in a calcium fluoride layer with a thickness of approximately 5 nm.

[0081] (3) PLD deposition of iridium oxide layer After replacing the iridium target, evacuate to a vacuum level below 2×10⁻⁶. -6 The pressure was maintained at 50 Pa for 30 minutes. High-purity oxygen was introduced to achieve an oxygen partial pressure of 50 Pa, and the titanium felt substrate temperature was 400 °C. A KrF laser was used with a repetition rate of 15 Hz and a single pulse energy of 180 mJ. The deposition rate was approximately 0.3 nm / min, and the deposition time was 333 minutes, resulting in an iridium oxide layer with a thickness of approximately 100 nm.

[0082] Example 4 (1) Matrix selection and pretreatment Same as Example 1.

[0083] (2) PLD deposition of metal fluoride layer Vacuum degree is 1×10 -5 Pa, titanium felt substrate temperature 80℃. A XeCl excimer laser was used to bombard the lanthanum fluoride (LaF3) target. The deposition rate was approximately 0.08 nm / min, and deposition time was 125 minutes, yielding a lanthanum fluoride layer with a thickness of approximately 10 nm.

[0084] (3) PLD deposition of iridium oxide layer After replacing the iridium target, evacuate to a vacuum level below 2×10⁻⁶. -6The pressure was maintained at 80 Pa for 30 minutes. High-purity oxygen was introduced to achieve an oxygen partial pressure of 80 Pa, and the titanium felt substrate temperature was 500 °C. A XeCl laser was used with a repetition rate of 25 Hz and a single pulse energy of 160 mJ. The deposition rate was approximately 0.45 nm / min, and the deposition time was 222 minutes, resulting in an iridium oxide layer with a thickness of approximately 100 nm.

[0085] Example 5 (1) Matrix selection and pretreatment Same as Example 1.

[0086] (2) PLD deposition of metal fluoride layer Vacuum degree is 8×10 -6 Pa, titanium felt substrate temperature 150℃. A KrF excimer laser was used to bombard the cerium fluoride (CeF3) target. The deposition rate was approximately 0.1 nm / min, and deposition time was 50 minutes, yielding a cerium fluoride layer with a thickness of approximately 5 nm.

[0087] (3) PLD deposition of iridium oxide layer After replacing the iridium target, evacuate to a vacuum level below 2×10⁻⁶. -6 The pressure was maintained at 30 Pa for 30 minutes. High-purity oxygen was introduced to bring the oxygen partial pressure to 30 Pa, and the titanium felt substrate temperature was 300 °C. A KrF laser was used with a repetition rate of 30 Hz and a single pulse energy of 110 mJ. The deposition rate was approximately 0.25 nm / min, and deposition time was 400 minutes, resulting in an iridium oxide layer with a thickness of approximately 100 nm.

[0088] Comparative Example 1: (1) Matrix selection and pretreatment Same as Example 1.

[0089] (2) PLD deposition of metal fluoride layer Omit this step (3) PLD deposition of iridium oxide layer Same as in Example 1, i.e., iridium oxide is directly PLD deposited on the treated substrate.

[0090] Table 2 shows the coating adhesion tested using the cross-cut adhesion test. The coating adhesion of Example 1, Comparative Example 1, and a certain brand of through-hole titanium oxide felt coated with traditional sol-gel process was tested.

[0091] Test method: Using a cutting tool, the coating is cut through to the substrate in a right-angled grid pattern. Since titanium felt is a planar porous metal material, the cut surface is transferred using tape. The cutting method is six horizontal and six vertical. The result is evaluated by the area of ​​coating peeling off. The cutting spacing is 2 mm.

[0092]

[0093] Table Explanation: Due to the ease with which an oxide layer forms on the titanium substrate in traditional processing environments, and the existence of thermal stress caused by the difference in thermal expansion coefficients between iridium and titanium, the coating adhesion test rating of the traditional sol-gel method group is 4B. This is mainly because during the sintering process of the coating deposited on the titanium felt, the formation of a titanium oxide layer on the surface of the titanium felt cannot be avoided, resulting in a lack of strong bonding between the iridium-based coating and the titanium felt. In the control group without metal fluorides in Comparative Example 1, under high temperature conditions, oxygen can directly react with the titanium felt during the PLD deposition process. The resulting deposited layer is a titanium-iridium bimetallic oxide layer on the side closest to the surface of the titanium felt, resulting in a lack of strong bonding between the iridium-based coating and the titanium felt. In Example 1, a metal fluoride layer is added between the iridium-based deposition layer and the titanium felt, which can effectively protect the surface of the titanium felt and form a stronger bonding layer during the subsequent iridium-based coating deposition process. This is mainly because the metal fluorides selected in this invention are basically hexagonal or tetragonal crystal systems, so the metal fluoride layer and the iridium-based deposition layer (tetragonal crystal system) have a higher degree of bonding.

[0094] This was verified in the coating adhesion test of three sets of control experiments. The adhesion test results of the three sets of Example 1, the metal fluoride-free control group of Example 1, and the iridium oxide titanium felt with a certain brand of through hole were 5B, 4B, and 4B, respectively. The foregoing embodiments have provided a detailed description of the inventive intent and implementation of the present invention. However, those skilled in the art will understand that the above embodiments are merely preferred embodiments of the present invention. Due to space limitations, not all embodiments can be listed here. Any implementation that embodies the technical solution of the claims of the present invention is within the protection scope of the present invention.

[0095] It should be noted that the above content is a further detailed description of the present invention in conjunction with specific embodiments, and it should not be considered that the specific embodiments of the present invention are limited to this. Under the guidance of the above embodiments, those skilled in the art can make various improvements and modifications based on the above embodiments, and these improvements or modifications fall within the protection scope of the present invention.

Claims

1. A titanium felt with a composite coating, characterized in that, include: Titanium felt matrix; A metal fluoride layer covering the surface of the titanium felt matrix fibers, the thickness of the metal fluoride layer being 0.1~10 nanometers; and, An iridium oxide layer covers the metal fluoride layer and together with the metal fluoride layer forms a dense and continuous composite coating.

2. The titanium felt with a composite coating as described in claim 1, characterized in that: The metal fluoride layer is selected from one or more of alkaline earth metal fluorides, rare earth metal fluorides, and lithium fluoride; the iridium oxide layer is iridium oxide with a rutile phase structure.

3. The titanium felt with a composite coating as described in claim 1, characterized in that: The thickness of the iridium oxide layer is not less than 80 nanometers.

4. Use of the titanium felt with composite coating as a gas transport layer electrode according to any one of claims 1 to 3, wherein the titanium felt has a through-hole structure.

5. A membrane electrode, characterized in that, include: Gas transport layer on the cathode side; Cathode catalyst layer; Proton exchange membrane; Anode catalyst layer; as well as, The titanium felt with a composite coating on its surface as described in any one of claims 1 to 3, wherein the titanium felt has a through-hole structure disposed outside the anode catalyst layer, and the iridium oxide catalyst layer faces the anode catalyst layer.

6. A method for preparing a titanium felt with a composite coating, characterized in that, The method employs pulsed laser deposition technology to sequentially deposit the metal fluoride layer and the iridium oxide layer.

7. The method for preparing a titanium felt with a composite coating as described in claim 6, characterized in that, The laser used in pulsed laser deposition is an excimer laser with the following laser parameters: wavelength 190~360 nm, pulse width 5~50 ns, pulse repetition frequency 1~100 Hz, and single pulse energy 100~200 mJ.

8. The method for preparing a titanium felt with a composite coating as described in claim 7, characterized in that: The process conditions for depositing the metal fluoride layer include: a cavity vacuum of 5 × 10⁻⁶. -6 ~ 5×10 -5 Pa; titanium felt substrate temperature: 50~250℃; deposition rate: less than 0.2 nm / min; The process conditions for depositing the iridium oxide layer include: the vacuum chamber is filled with oxygen with a purity of 99.999% or higher, the oxygen partial pressure is 10~100 Pa; the temperature of the titanium felt substrate is 300~550℃; and the deposition rate is less than 0.5 nm / min.

9. A method for preparing a titanium felt with a composite coating as described in any one of claims 6-8, characterized in that: The method further includes a surface pretreatment process for the titanium felt substrate before pulsed laser deposition. The surface pretreatment process includes deburring, pickling, deionized water cleaning and drying steps performed sequentially.

10. The method for preparing a titanium felt with a composite coating as described in claim 9, characterized in that: The acid used in the pickling process is an oxalic acid solution with a concentration of 2% to 12%; the pickling temperature is 40 to 80°C, and the processing time is 5 to 60 minutes; the deionized water rinsing is carried out until the conductivity of the rinsing water is less than 10 microsiemens per centimeter (μS / cm); the drying step is to use nitrogen gas to dry the water.

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