Method for modifying titanium-based porous transport layer using supercritical fluid technology

Abstract

The present invention relates to a method for modifying a titanium-based porous transmission layer using supercritical fluid technology, and belongs to the field of electrochemical technology. The present invention uses supercritical fluid technology to modify titanium fibers, which can achieve uniform and dense deposition of precious metals on the substrate, thereby obtaining a high-quality precious metal coating on the surface of the titanium fiber, improving the corrosion resistance of the titanium fiber, reducing the oxygen content of the titanium fiber felt, and improving the conductivity of the titanium fiber felt; at the same time, the precious metal layer plated on the surface of the titanium fiber has catalytic activity, which can reduce the overall electrolytic cell catalyst loading. Compared with the coating obtained by other methods, the coating obtained by the present invention has a more uniform thickness, stronger bonding force, and is not easy to fall off. The prepared titanium fiber felt has a lower resistivity and is more resistant to oxidation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electrochemistry, and relates to a method for modifying a titanium-based porous transport layer by using supercritical fluid technology. BACKGROUND

[0002] A PEM electrolyzer is mainly composed of end plates, bipolar plates, diffusion layers, catalyst layers, proton exchange membranes and gaskets. The anode porous transport layer is mainly in the form of titanium mesh, sintered titanium particle plate, titanium fiber sintered felt and the like. At present, the titanium fiber sintered felt, referred to as titanium felt, is mostly used in the PEM electrolysis water market at home and abroad. The main processing technology includes titanium fiber drawing, pressing and sintering and surface treatment. Most of the fibers used in the titanium fiber felt are prepared by cutting or drawing method. After the titanium fiber felt is prepared, titanium oxide is easily generated in the working process of the electrolysis cell, which increases the resistance of the electrolysis cell and reduces the performance of the electrolysis cell. Therefore, the current titanium-based porous transport layer is mostly further provided with a protective plating layer on the surface thereof by chemical plating or electroplating after the titanium fiber felt is sintered into shape. However, the titanium fiber felt is easily oxidized in the sintering process. If the treatment is not proper in the chemical plating or electroplating process, the bonding force of the plating layer is poor and the plating layer is easily peeled off.

[0003] The supercritical fluid refers to a special state fluid formed when the temperature and pressure thereof are both above the critical point. The supercritical fluid has the advantages of low viscosity, controllable density, large diffusion coefficient, zero surface tension, good flowability and permeability and excellent transfer characteristics. Therefore, the physical properties of the supercritical fluid, such as density, viscosity, dielectric constant and diffusion coefficient, are sensitive to the changes of pressure and temperature. The supercritical fluid deposition generally refers to a high-purity thin film deposition process realized by a chemical reaction route in a supercritical carbon dioxide environment on the surface of a substrate by using a soluble organometallic compound.

[0004] In this process, hydrogen and metal precursors are first diffused and adsorbed to the surface of the substrate, then react on the surface to generate pure metal and hydride ligand, and then the hydride ligand is desorbed from the surface of the substrate and dissolved in the supercritical carbon dioxide solution, and finally the pure metal thin film is left on the surface of the substrate. Compared with ordinary electrochemical deposition, the supercritical fluid deposition process has the characteristics of low surface tension and viscosity and high diffusion coefficient, and the prepared deposition layer has excellent performance. In the modification of fibers, the supercritical fluid deposition process has the characteristics of normal temperature, non-toxicity, environmental protection, safety and convenience in use and high product quality. SUMMARY

[0005] The present application provides a method for modifying a titanium-based porous transport layer by using supercritical fluid technology. Compared with the plating layer obtained by other methods, the plating layer obtained by the method has more uniform thickness, stronger bonding force and is not easy to peel off. The resistivity of the prepared titanium fiber felt is lower and more resistant to oxidation.

[0006] The object of the present application can be achieved by the following technical solutions.

[0007] The method for modifying titanium-based porous transport layer by using supercritical fluid technology comprises the following steps in sequence:

[0008] S11, the precursor of noble metal is put into the supercritical device, the titanium fiber is placed at the bottom of the device, the sealed container is connected with carbon dioxide gas, the gas flow is 220-520 mL / min, the supercritical device is heated to 200-400 DEG C according to the program under the condition that the carbon dioxide gas flows, the pressure is increased to 15-18 MPa, the precursor of noble metal and carbon dioxide in the device reach the supercritical fluid state, the whole heating process is kept magnetic stirring, the stirring speed is 100-200 r / min, the deposition is more uniform, the deposition time is 20-30 min, after the deposition is completed, the pressure is released to 5 MPa, the hydrogen gas is connected at the speed of 500-700 mL / min, the temperature of the pressure relief process is 300 DEG C, the time is 2h, after the pressure relief is completed, the titanium fiber modified by the coating is obtained;

[0009] S12, the titanium fiber modified by the coating and the water-soluble vinylon fiber are mixed in the mass ratio (8-9) :(1-2) and are put into the deionized water for ultrasonic treatment for 3h to be uniformly dispersed, then the sheet is formed by the sheet former, and the titanium fiber felt with uniform thickness is formed, the quantitative of the titanium fiber felt is 50-400 g / m 2 ;

[0010] S13, the titanium fiber felt in step S12 is laminated and pressed, then is put into the vacuum sintering furnace at 1000 DEG C and is sintered for 4h, the impurities and part of the adhesive components in the production process are removed, the holding time is 2h, finally the roller is pressed to be flat, and the prepared titanium fiber felt has the thickness of 0.2-0.8 mm.

[0011] As a preferred technical scheme of the application, in step S11, the precursor of noble metal is one or more of ruthenium chloride trihydrate, [bis (2, 2, 6, 6-tetramethyl-3, 5-heptanedioic acid) (1, 5-cyclohexadiene) ruthenium], and iridium acetylacetone.

[0012] As a preferred technical scheme of the application, in step S11, the diameter of the titanium fiber is 18-50 μm.

[0013] As a preferred technical scheme of the application, in step S12, wherein the diameter of the water-soluble vinylon fiber is 7-20 μm.

[0014] The method for modifying titanium-based porous transport layer by using supercritical fluid technology comprises the following steps in sequence:

[0015] S51, titanium fibers and water-soluble vinylon fibers are mixed in a mass ratio of 8:2, and are placed in deionized water for ultrasonic dispersion for 3h until evenly dispersed, and then are formed into a sheet by a sheet former to form a titanium fiber felt with a uniform thickness, and the obtained titanium fiber felt has a basis weight of 50-500g / m 2 ;

[0016] S52, the titanium fiber felt obtained in S51 is laminated and pressed, and then is sintered in a 1000℃ vacuum sintering furnace for 4h, and is kept for 2h, and finally is rolled flat, and the prepared titanium fiber felt has a thickness of 0.23-0.90mm;

[0017] S53, the titanium fiber felt in S52 is first cleaned with a methanol solution, and then is immersed in an oxalic acid solution with a mass fraction of 15-20% for 20min, and is repeatedly washed with deionized water until the surface of the titanium fiber felt is neutral, and is dried to obtain a titanium fiber felt substrate to be deposited;

[0018] S54, a precursor of a noble metal is placed in a supercritical device, the titanium fiber felt substrate to be deposited is placed at the bottom of the device, carbon dioxide gas with a flow rate of 220-600mL / min is introduced, the device is heated to 200℃, and is pressurized to 16-18MPa, the noble metal precursor and the carbon dioxide in the device are brought to a critical fluid state, the stirring speed is 100-180r / min, the deposition time is 20-30min, the device is depressurized to 5MPa, hydrogen gas with a flow rate of 500mL / min is introduced at 300℃ for 2h, and a titanium fiber felt with a ruthenium coating is obtained, and the titanium fiber felt has a thickness of 0.25-0.93mm.

[0019] As a preferred technical solution of the present application, in step S51, the diameter of the titanium fibers is 18-50μm, and the diameter of the water-soluble vinylon fibers is 15-20μm.

[0020] As a preferred technical solution of the present application, in step S54, the precursor of the noble metal is one or more of ruthenium chloride trihydrate, [bis(2,2,6,6-tetramethyl-3,5-heptanedioate)(1,5-cyclooctadiene)ruthenium], and acetylacetone iridium.

[0021] The present application has the following beneficial effects:

[0022] (1) In the present application, noble metal thin film is prepared on titanium fiber by catalytic reduction of hydrogen gas under the setting temperature, pressure and reaction time, with noble metal compound as precursor and supercritical carbon dioxide as solvent. Compared with traditional heat treatment method, supercritical fluid technology needs lower temperature, which helps to reduce energy consumption and the risk of substrate deformation. At the same time, supercritical fluid does not produce harmful substances during operation, reducing environmental pollution. During the deposition process, due to the different sensitivity of the used precursor to the pressure increase speed, the pressure increase speed is adjusted by adjusting the gas flow of carbon dioxide. In the present application, the gas flow of carbon dioxide is controlled at 220 mL / min when using ruthenium compound. In order to avoid the defects of the plated metal thin film structure caused by too fast temperature rising speed, affecting the quality of the deposited layer, the temperature is controlled at 200℃. After the deposition is completed, hydrogen gas is introduced, which is to reduce metal oxide to obtain pure metal thin film, including the reduction of titanium fiber and the reduction of plated metal.

[0023] (2) In the present application, whether the titanium fiber plated by supercritical fluid technology is sintered first or sintered first and then treated by supercritical fluid, the electrochemical performance of the prepared titanium-based porous transport layer is better, which shows that the advantage of using supercritical fluid technology to obtain noble metal plating is more obvious. Because there is no binding force between the titanium fibers in the wet-formed titanium fiber felt, the titanium fibers are interlaced and overlapped to form a felt, and the felt strength is poor, therefore a small amount of water-soluble vinylon fiber is added to improve the felt strength. The residue of the added water-soluble vinylon fiber can be removed by the vacuum sintering process in the subsequent step, ensuring the purity of the noble metal plating.

[0024] (3) Using supercritical fluid technology to modify titanium fiber can realize uniform and dense deposition of metal on the substrate, so as to obtain high-quality noble metal plating on the surface of titanium fiber, improve the corrosion resistance of titanium fiber, and then lay the modified titanium fiber into a net, then press and flatten, and finally sinter to prepare titanium fiber felt, which can prevent titanium from being oxidized during sintering, reduce the oxygen content of titanium fiber felt, and improve the conductivity of titanium fiber felt. At the same time, the noble metal layer plated on the surface of titanium fiber has catalytic activity, which can reduce the loading of the overall electrolytic cell catalyst. Compared with other methods, the plating layer deposited on the surface of titanium fiber by supercritical fluid technology has more uniform thickness and stronger adhesion, and is not easy to fall off. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to facilitate the understanding of those skilled in the art, the present application will be further described below with reference to the accompanying drawings.

[0026] Figure 1 The resistivity curve of the anode gas transport layer prepared in the examples and comparative examples;

[0027] Figure 2Polarization curves of the electrolytic cells assembled after the anode gas transport layer prepared for the examples and comparative examples. DETAILED DESCRIPTION

[0028] To further illustrate the technical means and effects taken by the present application to achieve the predetermined inventive purposes, the specific embodiments, structures, features and effects according to the present application are described in detail below in combination with the drawings and preferred embodiments.

[0029] Example 1

[0030] S1, 30 mg of ruthenium chloride trihydrate and 20 mg of iridium acetylacetonate were respectively weighed into a supercritical device, titanium fibers with a diameter of 20 μm were placed at the bottom of the device, carbon dioxide gas was introduced at a flow rate of 220 mL / min, the device was heated to 200 ℃, and the pressure was increased to 15 MPa, so that the noble metal precursors and carbon dioxide in the device reached the critical fluid state, the stirring speed was 100 r / min, and the deposition time was 20 min; the device was depressurized to 5 MPa at 300 ℃, hydrogen gas was introduced at a flow rate of 500 mL / min for 2 h, and a titanium fiber coated with a layer was obtained.

[0031] S2, the modified titanium fibers and water-soluble vinylon fibers with a diameter of 15 μm were mixed in a mass ratio of 8:2 and ultrasonically dispersed in deionized water for 3 h until uniformly dispersed, then sheeted by a sheeting machine to form a titanium fiber felt with uniform thickness, and the obtained titanium fiber felt had a basis weight of 100 g / m 2 ;

[0032] S3, 4 layers of the titanium fiber felt prepared in S2 were placed in order and pressed, then placed in a 1000 ℃ vacuum sintering furnace for sintering for 4 h, and finally rolled flat, and the titanium fiber felt had a thickness of 0.4 mm.

[0033] Example 2

[0034] S1, 30 mg of ruthenium chloride trihydrate and 20 mg of iridium acetylacetonate were respectively weighed into a supercritical device, titanium fibers with a diameter of 20 μm were placed at the bottom of the device, carbon dioxide gas was introduced at a flow rate of 220 mL / min, the device was heated to 200 ℃, and the pressure was increased to 15 MPa, so that the noble metal precursors and carbon dioxide in the device reached the critical fluid state, the stirring speed was 100 r / min, and the deposition time was 20 min; the device was depressurized to 5 MPa at 300 ℃, hydrogen gas was introduced at a flow rate of 500 mL / min for 2 h, and a titanium fiber coated with a layer was obtained.

[0035] S2, the modified titanium fiber and water-soluble vinylon fiber with a diameter of 7 μm are mixed in a mass ratio of 9:1, and are placed in deionized water for ultrasonic dispersion for 3 h until uniformly dispersed, and then are formed into a titanium fiber felt with uniform thickness by a sheet former to obtain a titanium fiber felt with a basis weight of 50 g / m 2 ;

[0036] S3, 4 layers of the titanium fiber felt prepared in S2 are placed in order and then are pressed, and then are placed in a 1000℃ vacuum sintering furnace for sintering for 4 h, and are kept warm for 2 h, and finally are rolled flat, and the thickness of the titanium fiber felt is 0.2 mm.

[0037] Example 3

[0038] S1, 50 mg of [bis(2,2,6,6-tetramethyl-3,5-heptanedioic acid)(1,5-cyclooctadiene)ruthenium] and 20 mg of acetylacetone iridium are respectively placed in a supercritical device, titanium fibers with a diameter of 50 μm are placed at the bottom of the device, carbon dioxide gas is introduced at a flow rate of 520 mL / min, the device is heated to 400℃, and is pressurized to 18 MPa, so that the noble metal precursors and carbon dioxide in the device reach a critical fluid state, the stirring speed is 200 r / min, and the deposition time is 30 min; the device is depressurized to 5 MPa at 300℃, hydrogen gas is introduced at a flow rate of 700 mL / min, and the time is 2 h, to obtain titanium fibers modified by a plating layer;

[0039] S2, the modified titanium fiber and water-soluble vinylon fiber with a diameter of 20 μm are mixed in a mass ratio of 8:2, and are placed in deionized water for ultrasonic dispersion for 3 h until uniformly dispersed, and then are formed into a titanium fiber felt with uniform thickness by a sheet former to obtain a titanium fiber felt with a basis weight of 400 g / m 2 ;

[0040] S3, 2 layers of the titanium fiber felt prepared in S2 are placed in order and then are pressed, and then are placed in a 1000℃ vacuum sintering furnace for sintering for 4 h, and are kept warm for 2 h, and finally are rolled flat, and the thickness of the titanium fiber felt is 0.8 mm.

[0041] Example 4

[0042] S1, titanium fibers with a diameter of 20 μm and water-soluble vinylon fibers with a diameter of 15 μm are mixed in a mass ratio of 8:2, and are placed in deionized water for ultrasonic dispersion for 3 h until uniformly dispersed, and then are formed into a titanium fiber felt with uniform thickness by a sheet former to obtain a titanium fiber felt with a basis weight of 100 g / m 2 ;

[0043] S2, the titanium fiber felt obtained in S1 is stacked in order and then pressed, and then placed in a 1000℃ vacuum sintering furnace for sintering for 4h, with heat preservation for 2h, and finally rolled flat, and the prepared titanium fiber felt has a thickness of 0.39mm;

[0044] S3, the titanium fiber felt in S2 is first cleaned with a methanol solution, then immersed in a 15% oxalic acid solution for 20min, and then repeatedly washed with deionized water until the surface of the titanium fiber felt is neutral, and then dried to obtain a titanium fiber felt substrate to be deposited;

[0045] S4, 30mg of ruthenium chloride trihydrate and 20mg of [bis(2,2,6,6-tetramethyl-3,5-heptanedioic acid)(1,5-cyclooctadiene)ruthenium] are placed in a supercritical device, the titanium fiber felt substrate to be deposited is placed at the bottom of the device, carbon dioxide gas with a flow rate of 220mL / min is introduced, the device is heated to 200℃, and the pressure is increased to 16MPa, so that the noble metal precursor and carbon dioxide in the device reach a critical fluid state, the stirring speed is 100r / min, and the deposition time is 20min; the device is depressurized to 5MPa at 300℃, and hydrogen gas with a flow rate of 500mL / min is introduced for 2h; a titanium fiber felt with a ruthenium coating is obtained, and the titanium fiber felt has a thickness of 0.4mm.

[0046] Example 5

[0047] S1, titanium fibers with a diameter of 18μm and water-soluble vinylon fibers with a diameter of 15μm are mixed in a mass ratio of 8:2, and then placed in deionized water for ultrasonic dispersion for 3h until uniformly dispersed, and then sheeted by a sheeting machine to form a titanium fiber felt with uniform thickness, and the obtained titanium fiber felt has a basis weight of 50g / m 2 ;

[0048] S2, the titanium fiber felt obtained in S1 is stacked in order and then pressed, and then placed in a 1000℃ vacuum sintering furnace for sintering for 4h, with heat preservation for 2h, and finally rolled flat, and the prepared titanium fiber felt has a thickness of 0.23mm;

[0049] S3, the titanium fiber felt in S2 is first cleaned with a methanol solution, then immersed in a 20% oxalic acid solution for 20min, and then repeatedly washed with deionized water until the surface of the titanium fiber felt is neutral, and then dried to obtain a titanium fiber felt substrate to be deposited;

[0050] S4, 30 mg of ruthenium chloride trihydrate, 20 mg of [bis(2,2,6,6-tetramethyl-3,5-heptanedioic acid)(1,5-cyclooctadiene)ruthenium] and 10 mg of acetylacetone iridium were put into a supercritical device, the titanium fiber felt substrate to be deposited was placed at the bottom of the device, carbon dioxide gas with a flow rate of 320 mL / min was introduced, the device was heated to 200°C, and pressurized to 16 MPa, so that the noble metal precursor and carbon dioxide in the device reached a critical fluid state, the stirring speed was 100 r / min, and the deposition time was 20 min; the device was depressurized to 5 MPa at 300°C, and hydrogen gas with a flow rate of 500 mL / min was introduced for 1.5 h; a titanium fiber felt containing a ruthenium coating was obtained, and the thickness of the titanium fiber felt was 0.25 mm.

[0051] Example 6

[0052] S1, titanium fibers with a diameter of 50 μm and water-soluble vinylon fibers with a diameter of 20 μm were mixed in a mass ratio of 8:2 and then dispersed uniformly in deionized water by ultrasonic treatment for 3 h, and then sheeted by a sheeting machine to form a titanium fiber felt with uniform thickness, and the obtained titanium fiber felt had a basis weight of 500 g / m 2 ;

[0053] S2, two layers of the titanium fiber felt obtained in S1 were stacked and pressed, and then sintered in a 1000°C vacuum sintering furnace for 4 h, and then rolled flat, and the prepared titanium fiber felt had a thickness of 0.9 mm;

[0054] S3, the titanium fiber felt in S2 was first cleaned with a methanol solution, then immersed in a 20% oxalic acid solution for 20 min, and then repeatedly washed with deionized water until the surface of the titanium fiber felt was neutral, and then dried to obtain a titanium fiber felt substrate to be deposited;

[0055] S4, 30 mg of ruthenium chloride trihydrate, 20 mg of [bis(2,2,6,6-tetramethyl-3,5-heptanedioic acid)(1,5-cyclooctadiene)ruthenium] and 10 mg of acetylacetone iridium were put into a supercritical device, the titanium fiber felt substrate to be deposited was placed at the bottom of the device, carbon dioxide gas with a flow rate of 320 mL / min was introduced, the device was heated to 200°C, and pressurized to 16 MPa, so that the noble metal precursor and carbon dioxide in the device reached a critical fluid state, the stirring speed was 100 r / min, and the deposition time was 20 min; the device was depressurized to 5 MPa at 300°C, and hydrogen gas with a flow rate of 500 mL / min was introduced for 1.5 h; a titanium fiber felt containing a ruthenium coating was obtained, and the thickness of the titanium fiber felt was 0.25 mm.

[0056] Comparative Example 1

[0057] S1. Titanium fiber with a diameter of 20 μm and water-soluble vinylon fiber with a diameter of 15 μm were mixed at a mass ratio of 8:2, and ultrasonically dispersed in deionized water for 3 hours until uniformly dispersed. Then, the mixture was formed into a titanium fiber felt with uniform thickness by a sheet forming machine. The obtained titanium fiber felt had a weight of 100 g / m 2 ;

[0058] S2, stacking 4 layers of the titanium fiber felt prepared in S1 neatly and pressing them, then placing them in a vacuum sintering furnace at 1000°C for 4 hours, keeping them warm for 2 hours, and then rolling them flat. The thickness of the titanium fiber felt prepared is 0.39 mm;

[0059] S3, the titanium fiber felt in S2 is first cleaned with a methanol solution, then immersed in a 15% oxalic acid solution for 20 minutes, and then repeatedly rinsed with deionized water until the surface of the titanium fiber felt is neutral, and finally dried to obtain a titanium fiber felt substrate to be deposited;

[0060] S4. Take 2g of phenolic resin and 1g of dispersant and completely dissolve them in 30g of isopropanol, then add 35g of iridium powder and disperse them evenly by ultrasonication to obtain a conductive metal slurry; apply the conductive metal slurry to the titanium fiber felt substrate to be deposited in S3, and then dry it in an oven at 120°C for 1h to obtain a titanium fiber felt containing an iridium coating, and the thickness of the titanium fiber felt is 0.4mm.

[0061] The resistivity of the anode gas transport layers prepared in Examples 1-6 and Comparative Example 1 and the polarization curves after assembling the electrolytic cell were tested.

[0062] pass Figure 1 It can be seen from the data that the resistivity of the anode gas transport layer prepared in Examples 1-6 is lower than that in Comparative Example 1 at the same pressure, indicating that the titanium fiber felt prepared by the method of the present invention has higher conductivity.

[0063] according to Figure 2 The data show that the anode gas transport layer prepared in Examples 1-6 has a high conductivity at 2000 A / cm 2 The electrolysis voltage when the operating current is dense is significantly lower than that in Comparative Example 1, indicating that the titanium fiber felt prepared by the present invention has higher catalytic activity.

[0064] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for modifying a titanium-based porous transport layer using supercritical fluid technology, characterized in that: The following steps are performed in sequence: S11. Place the precursor of the precious metal in a supercritical device, place the titanium fiber at the bottom of the device, seal the container, introduce carbon dioxide gas at a gas flow rate of 220 to 520 mL / min, and keep the carbon dioxide gas flowing while heating the supercritical device to a temperature of 200 to 400°C and a pressure of 15 to 18 MPa. The precious metal precursor and carbon dioxide in the device reach a supercritical fluid state. Maintain magnetic stirring throughout the entire heating process at a stirring speed of 100 to 200 r / min to make the deposition more uniform. The deposition time is 20 to 30 min. After the deposition is completed, the pressure is released to 5 MPa, and hydrogen is introduced at a gas flow rate of 500 to 700 mL / min. The temperature of the pressure relief process is 300°C and the time is 2 h. After the pressure relief is completed, titanium fiber modified by coating is obtained. S12, mixing the titanium fiber modified by plating and the water-soluble vinylon fiber in a mass ratio of (8-9): (1-2), placing them in deionized water and ultrasonically treating them for 3 hours until they are uniformly dispersed, and then forming them into sheets using a sheet forming machine to form a titanium fiber felt with uniform thickness, wherein the titanium fiber felt has a basis weight of 50-400 g / m2; S13, laminating and pressing the titanium fiber felt prepared in step S12, and then placing it in a vacuum sintering furnace at 1000° C. for 4 hours to remove impurities and some adhesive components in the production process, holding the temperature for 2 hours, and finally rolling and leveling the titanium fiber felt to a thickness of 0.2 to 0.8 mm; In step S11, the precursor of the precious metal is one or more of ruthenium chloride trihydrate, [bis(2,2,6,6-tetramethyl-3,5-heptanediol)(1,5-epoxydiene)ruthenium], and iridium acetylacetonate.

2. The method for modifying a titanium-based porous transport layer using supercritical fluid technology according to claim 1, characterized in that: In step S11 , the diameter of the titanium fiber is 18 to 50 μm.

3. The method for modifying a titanium-based porous transport layer using supercritical fluid technology according to claim 1, characterized in that: In step S12, the diameter of the water-soluble vinylon fiber is 7 to 20 μm.

4. A method for modifying a titanium-based porous transport layer using supercritical fluid technology, characterized in that: The following steps are performed in sequence: S51, titanium fiber and water-soluble vinylon fiber are mixed in a mass ratio of 8:2, and placed in deionized water for 3 hours for ultrasonication until uniform dispersion is achieved, and then sheeted by a sheet forming machine to form a titanium fiber felt of uniform thickness, wherein the obtained titanium fiber felt has a basis weight of 50 to 500 g / m2; S52, laminating and pressing the titanium fiber felt obtained in S51, and then placing it in a vacuum sintering furnace at 1000° C. for 4 hours, keeping it warm for 2 hours, and finally rolling it flat. The thickness of the prepared titanium fiber felt is 0.23 to 0.90 mm; S53, the titanium fiber felt in S52 is first cleaned with a methanol solution, then immersed in a 15-20% by mass oxalic acid solution for 20 minutes, and then repeatedly rinsed with deionized water until the surface of the titanium fiber felt is neutral, and then dried to obtain a titanium fiber felt substrate to be deposited; S54. Place the precious metal precursor in a supercritical device, place the titanium fiber felt substrate to be deposited at the bottom of the device, introduce carbon dioxide gas at a flow rate of 220 to 600 mL / min, heat the device to 200° C., and pressurize it to 16 to 18 MPa, so that the precious metal precursor and carbon dioxide in the device reach a critical fluid state, stir at a speed of 100 to 180 r / min, and deposit for 20 to 30 min. Then, depressurize the device to 5 MPa, introduce hydrogen at a flow rate of 500 mL / min for 2 h at 300° C., and obtain a titanium fiber felt containing a ruthenium coating, wherein the thickness of the titanium fiber felt is 0.25 to 0.93 mm. In step S54 , the precursor of the precious metal is one or more of ruthenium chloride trihydrate, [bis(2,2,6,6-tetramethyl-3,5-heptanedioate)(1,5-epoxydiene)ruthenium], and iridium acetylacetonate.

5. The method for modifying a titanium-based porous transport layer using supercritical fluid technology according to claim 4, characterized in that: In step S51, the diameter of the titanium fiber is 18 to 50 μm, and the diameter of the water-soluble vinylon fiber is 15 to 20 μm.

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