Double-site catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of electrocatalysts, particularly discloses a double-site catalyst as well as a preparation method and application thereof, and provides a preparation scheme of an electrolytic water anode catalyst, which adopts a mild low-temperature hydrothermal method and an ethylene glycol in-situ thermal reduction process. A catalytic site-proton transmission site double-site synergistic system is successfully constructed, and the flaky niobium oxyphosphate carrier provides a large specific surface area and excellent proton conductivity, so that protons can be rapidly conducted into an electrolyte, negative effects caused by proton accumulation are avoided, and the stability of the electrolyte is improved. The preparation method effectively inhibits metal iridium dissolution and shedding caused by local microenvironment acidification, maintains the thermodynamic stability of the catalyst, enables metal iridium nanoparticles to be loaded on a sheet-shaped niobium oxide phosphate carrier, enables metal iridium to serve as a reaction active site, provides efficient precipitation reaction activity, and enables the separation reaction activity to be improved by taking the niobium oxide phosphate carrier as a proton conductive site. The reaction efficiency is improved through cooperation with metal iridium, and the catalytic activity and stability are remarkably improved through the synergistic effect of the two.

Description

Technical Field

[0001] This invention relates to the field of electrocatalyst technology, and specifically discloses a two-site catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen production through renewable energy coupled with water electrolysis has a low CO2 emission footprint, meeting the growing demand for low-carbon emission reduction. Currently, proton exchange membrane electrolysis (PEMWE) hydrogen production technology employs a zero-gap electrolyzer structure, offering advantages such as wide load capacity and high operating current density. It can be directly adapted to fluctuating renewable energy sources like wind and solar power, enabling large-scale, efficient hydrogen production. As the cost of PEMWE hydrogen production decreases, the number of megawatt-scale and above PEMWE deployments both domestically and internationally is increasing year by year.

[0003] Renewable energy coupled with proton exchange membrane electrolysis (PEMWE) for hydrogen production is a key pathway to achieving dual-carbon goals. The oxygen evolution reaction (OER) occurring at the anode of PEMWE exhibits slow kinetics and requires long-term operation under strong acidity and high oxidation potential. Currently, commercial anodes primarily rely on the scarce and expensive noble metal iridium (Ir)-based catalyst IrO2. Its extremely low reserves result in high costs, severely limiting the megawatt-scale deployment of PEMWE.

[0004] One of the main strategies for reducing iridium usage is to develop inexpensive supported IrO2 catalysts. This reduces iridium usage by increasing the dispersion of active sites. Existing research mainly focuses on developing support materials with high conductivity, high specific surface area, and high stability, such as transition metal nitrides and various ion-doped oxides. Thiele et al. (Appl. Catal. B, 2020, 269, 118762.) used titanium dioxide (TiO2) as a support and coated its surface with an IrO2 layer to obtain a core-shell structured catalyst (50 wt% IrO2@TiO2). At 1 A cm⁻¹, the catalyst achieved high conductivity. -2 The cell voltage at the current density was 1.67 V (iridium content in the membrane electrode was 0.4 mg). Ir cm -2 Shi et al. (Angew. Chem. Int. Ed. 2022, 61, e202212341) used niobium pentoxide (Nb2O5) as a support, loading 60 wt% metallic iridium nanoparticles onto its surface at 3 A cm⁻¹. -2 The cell voltage at the current density was 1.839 V (iridium content in the membrane electrode was 1.8 mg). Ir cm -2Khan et al. (Mater. Chem. Physics. 2023, 308, 128192) used antimony-doped tin oxide (ATO) as a conductive carrier, loaded 35 wt% metallic iridium nanoparticles on its surface, and applied the resulting material at 1.65 V. RHE The mass activity at voltage is 777 A g. Ir -1 This is 2.6 times that of commercial IrO2 catalysts. Li et al. (J.Am. Chem. Soc. 2025, 147, 32, 29505-29516) used zirconium phosphide (ZrP) as a support and investigated the mechanism by which the proton conductor support enhances the activity of the oxygen evolution reaction by modifying the surface of the support with different functional groups (-OH and -CH3). They loaded 9.24 wt% metallic iridium nanoparticles onto its surface at 1.53 V. RHE The mass activity at voltage is 798 A g. Ir -1 It is 26.6 times that of commercial IrO2 catalysts.

[0005] Developing supported catalysts with low iridium loading, high activity, and high stability is an urgent need in the industry. To reduce iridium usage, researchers are dedicated to developing novel support materials to improve the dispersion of active sites. Traditional inert oxide supports, such as TiO2 and Nb2O5, while exhibiting good stability, have extremely poor conductivity, often requiring high iridium loading to form conductive pathways, resulting in low utilization of precious metals. Furthermore, doped conductive oxides such as ATO are prone to dopant ion dissolution in acidic OER environments, leading to support passivation and loss of active components.

[0006] In recent years, phosphate materials with certain proton conductivity have attracted attention. US patent application US20100009190A1 discloses a method for preparing nanoscale phosphate material particles using a sol-gel method by adding a chelating agent, and explores its proton conductivity performance. The product prepared by this method is mainly zero-dimensional nanoparticles. During the construction of the catalytic layer, a large amount of grain boundary contact resistance exists between the particles, hindering long-range rapid proton transport. The nanoparticles are also prone to aggregation during long-term operation. CN 114736175 A proposes a metal ion-doped niobium-based phosphate with mesoporous and macroporous structures for catalyzing biomass conversion. To improve mass transfer, its synthesis route introduces Ca, Sr... Heteroatoms such as Fe are difficult to prepare using complex steps such as hydrogen peroxide digestion and organic gelation, and there is a risk of dissolution in strongly acidic water electrolysis environments, which may compromise the stability of the crystal structure. Existing technologies, whether traditional inert / doped oxides or existing particulate or porous phosphate materials, cannot simultaneously meet the comprehensive requirements of PEMWE anodes for high proton / electron conductivity, high specific surface area, and extreme acid resistance. Therefore, existing supports cannot simultaneously satisfy high conductivity, high specific surface area, and high stability. A relatively high iridium loading is still required to maintain the overall conductivity and structural stability of the catalyst. Therefore, developing supports with high proton / electron conductivity, high specific surface area, and high stability, and highly dispersing iridium active sites on the support surface, has become a bottleneck in overcoming the high activity and high stability of low-iridium catalysts. Summary of the Invention

[0007] To address the problems existing in the prior art, the first aspect of this invention proposes a method for preparing a two-site catalyst, comprising the following steps: Step 101: After mixing niobium salt, phosphoric acid solution, and water, sodium fluoride and polyvinylpyrrolidone are added to obtain the first mixture. After adjusting the pH of the first mixture, the temperature is controlled to separate the precipitate. Step 102: After the precipitate is dried, it is heated to the target temperature in an air atmosphere and calcined to obtain sheet-like proton carrier niobium oxyphosphate. Step 103: Iridium salt, sheet-like proton carrier niobium oxyphosphate, and ethylene glycol are mixed and sonicated to obtain a second mixture; Step 104: The second mixture is subjected to temperature control, reaction, separation, and drying to obtain the catalyst Ir / NbOPO4.

[0008] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the niobium salt is selected from one or a mixture of ammonium oxalate niobate, niobium pentachloride, niobium ethanol, niobium isopropoxide, and niobium hydroxide.

[0009] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the phosphoric acid solution is an aqueous solution of phosphoric acid, and the mass concentration of the aqueous solution of phosphoric acid is 70~87wt%. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the phosphoric acid solution is an aqueous solution of phosphoric acid, and the mass concentration of the aqueous solution of phosphoric acid is optionally 73wt%, 76wt%, 79wt%, 82wt%, or 85wt%.

[0010] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the volume of phosphoric acid solution added per 1L of water is 15~20mL. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the volume of phosphoric acid solution added per 1L of water is optionally 16mL, 17mL, 18mL, 19mL, or 20mL.

[0011] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the mass of niobium salt added per 1L of water is 35~45g. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the mass of niobium salt added per 1L of water is optionally 37g, 39g, 41g, or 43g.

[0012] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the mass of sodium fluoride added per 1L of water is 1.5~2.0g. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the mass of sodium fluoride added per 1L of water is optionally 1.6g, 1.7g, 1.8g, or 1.9g.

[0013] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the mass of polyvinylpyrrolidone added per 1L of water is 10~15g. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the mass of polyvinylpyrrolidone added per 1L of water is optionally 11g, 12g, 13g, or 14g.

[0014] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, polyvinylpyrrolidone is selected from one or a mixture of polyvinylpyrrolidone K30, polyvinylpyrrolidone K15, polyvinylpyrrolidone K60, and polyvinylpyrrolidone K90.

[0015] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the pH of the first mixture is adjusted to 3-4.

[0016] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the temperature of the first mixture is controlled to 150~200 ℃. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the temperature of the first mixture is controlled to an optional 160 ℃, 170 ℃, 180 ℃, or 190 ℃.

[0017] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 101, the precipitate is separated by centrifugation and / or filtration.

[0018] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 102, the precipitate is dried at 60~80°C for 10~14h. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 102, the precipitate is dried at 64°C, 68°C, 72°C, or 76°C for 11h, 12h, or 13h respectively.

[0019] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 102, the temperature programmable method is to increase the temperature from room temperature to 300-500°C at a heating rate of 5-10°C / min. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 102, the temperature programmable method is optionally to increase the temperature from room temperature to 320°C, 340°C, 360°C, 380°C, 400°C, 420°C, 440°C, 460°C, or 480°C at heating rates of 6°C / min, 7°C / min, 8°C / min, or 9°C / min.

[0020] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, the target temperature in step 102 is 300~500℃. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, the target temperature in step 102 is optionally 320℃, 340℃, 360℃, 380℃, 400℃, 420℃, 440℃, 460℃, or 480℃.

[0021] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 103, the iridium salt is selected from one or more of chloroiridium acid, IrCl3, and (NH4)2IrCl6.

[0022] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 103, the mass of iridium salt added to each 1L of ethylene glycol is 15~20g. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 103, the mass of iridium salt added to each 1L of ethylene glycol is optionally 16g, 17g, 18g, or 19g.

[0023] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 103, the mass of the sheet-like proton carrier niobium oxyphosphate added to each 1L of ethylene glycol is 4~6g. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 103, the mass of the sheet-like proton carrier niobium oxyphosphate added to each 1L of ethylene glycol is optionally 4g, 5g, or 6g.

[0024] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 104, the temperature of the second mixture is controlled by using an oil bath to control the temperature to 150~170°C. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 104, the temperature of the second mixture is controlled by using an oil bath to control the temperature to an optional 155°C, 160°C, or 165°C.

[0025] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 104, the separation method is centrifugation.

[0026] In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 104, the drying method is vacuum drying at 50~70°C. In some specific embodiments of the dual-site catalyst preparation method described in the first aspect, in step 104, the drying method is optionally vacuum drying at 54°C, 58°C, 62°C, or 66°C.

[0027] The second aspect of the present invention provides a two-site catalyst Ir / NbOPO4 obtained by any of the preparation methods described in the first aspect.

[0028] A third aspect of the present invention provides a membrane electrode comprising a cathode catalytic layer, a proton exchange membrane, and an anode catalytic layer, characterized in that the anode catalytic layer comprises the dual-site catalyst Ir / NbOPO4 described in the second aspect.

[0029] The fourth aspect of this invention proposes the application of the catalyst Ir / NbOPO4 described in the second aspect in electrocatalysis.

[0030] The fifth aspect of the present invention provides a catalyst film comprising the two-site catalyst Ir / NbOPO4 described in the second aspect and a proton-conducting ionomer.

[0031] The sixth aspect of the present invention provides a proton exchange membrane electrolysis water production device, the device comprising the membrane electrode described in the third aspect.

[0032] In this invention, H2IrCl6 can be replaced with other soluble iridium salts, such as IrCl3, (NH4)2IrCl6, etc., as long as they can form metallic iridium nanoparticles under polyol reduction conditions.

[0033] "Room temperature" refers to the indoor ambient temperature, which can be 12℃~37℃, 20℃~30℃, 25℃~30℃, or approximately 25℃.

[0034] Figure 3 Medium, 4cm 2 geo This refers to the size of the membrane electrode being 4cm. 2 ; Figure 4 In the middle, 3 A / cm 2 @80℃ indicates a temperature of 3 A / cm 2 And tested at 80℃; 0.8 mg Ir cm -2 , indicating the iridium loading of a commercial IrO2 catalyst; 220.2 µV h -1 The value represents the decay rate obtained from testing with a commercial IrO2 catalyst; 0.2 mg Ir cm -2 , indicating the iridium loading of the Ir / NbOPO4 catalyst; 1 µV h -1 This represents the decay rate obtained from testing the Ir / NbOPO4 catalyst. The reagents used in this invention have not undergone further purification and are all purchased from the open and legal market. For example, they are purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., Xilong Scientific Co., Ltd., Sinopharm Chemical Reagent Co., Ltd., and Shanghai McLean Biochemical Technology Co., Ltd. Commercial IrO2 is purchased from Suzhou Sinero.

[0035] Advantages of this invention: This invention first prepares niobium oxyphosphate via a hydrothermal method, using ammonium niobate oxalate as the niobium source, phosphoric acid as the phosphorus source, and deionized water as the solvent. NaF and polyvinylpyrrolidone are added to adjust the crystal morphology. Fluoride ions interact with niobium ions and phosphate ions, inhibiting the growth of certain crystal planes and promoting the rapid growth of others, thus forming a plate-like structure. Surfactants help control the crystal growth direction, ensuring a uniform plate-like morphology. Calcination further improves the crystallinity and stability of niobium oxyphosphate. The prepared plate-like niobium oxyphosphate exhibits excellent proton-conducting properties, and its crystal structure contains phosphate ions (PO4). 3-Containing protonable P-OH groups, these groups donate protons in acidic environments, thereby promoting proton conduction; niobium ions (Nb) 5+ The interaction with phosphate ions stabilizes the crystal structure, supporting the acidic properties and proton conduction capability of the material. In addition, the sheet-like structure provides a larger surface contact area, which is beneficial to improve the exposure of active sites and enhance the electron and proton conduction efficiency between catalysts. By utilizing the reducing properties of ethylene glycol at high temperatures, chloroiridium acid adsorbed on the sheet-like niobium oxyphosphate is reduced in situ to metallic iridium nanoparticles. By fully dispersing iridium nanoparticles on the sheet-like support, the utilization rate of active sites is improved. At the same time, the proton conduction capability of the exposed niobium oxyphosphate support is used to quickly remove protons generated in the reaction, avoid the accumulation of surface charge, effectively reduce the energy barrier of the reaction, and improve catalytic efficiency.

[0036] This invention provides a proton exchange membrane water electrolysis anode catalyst preparation scheme that abandons expensive alkoxide organometallic precursors and harsh anhydrous environments. Employing a mild low-temperature hydrothermal method and in-situ ethylene glycol thermal reduction process, it successfully constructs a dual-site synergistic system of "catalytic site (metallic iridium) - proton transport site (sheet-like niobium oxyphosphate)". The sheet-like niobium oxyphosphate support provides a large specific surface area and excellent proton conductivity, ensuring that protons generated during the reaction can be rapidly conducted to the electrolyte, avoiding the negative effects of proton accumulation. This effectively inhibits the dissolution and shedding of metallic iridium caused by local microenvironment acidification, helping to maintain the thermodynamic stability of the catalyst and promoting reaction kinetics. This invention loads metallic iridium nanoparticles onto the sheet-like niobium oxyphosphate support. The metallic iridium acts as a reactive site, providing highly efficient oxygen evolution reaction activity; simultaneously, the niobium oxyphosphate support, as a proton conducting site, synergistically improves reaction efficiency with the metallic iridium. The synergistic effect of these two components significantly enhances catalytic activity and stability. Attached Figure Description

[0037] Figure 1 This is a scanning electron microscope image of the sheet-like niobium oxyphosphate prepared in this invention; Figure 2 This is a graph showing the electrochemical mass activity of the dual-site catalyst prepared in this invention. Figure 3 PEM water electrolysis performance curve of the dual-site catalyst membrane electrode prepared in this invention; Figure 4 This is a stability test diagram of the dual-site catalyst membrane electrode prepared in this invention. Detailed Implementation

[0038] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0039] Example 1 Preparation of proton carrier niobium oxyphosphate Step 1: Ammonium niobate oxalate (10 mmol based on niobium atoms, NH4NbO6·xH2O·C2H2O4) and 1.5 mL of phosphoric acid aqueous solution (85 wt% H3PO4) were mixed in 75 mL of deionized water and sonicated for 15 minutes to obtain a niobium phosphoric acid solution. 0.15 g of sodium fluoride was added to the niobium phosphoric acid solution and stirred to dissolve. Then, 1.0 g of polyvinylpyrrolidone K30 was added to obtain a precursor mixture. During this process, the mixture was stirred continuously. Sodium fluoride and polyvinylpyrrolidone helped control the crystallization of niobium phosphate and promoted the formation of a plate-like morphology.

[0040] Step 2: Adjust the pH of the precursor mixture to 3-4 using 25 wt% ammonia water to maintain the stability of the niobium phosphate precipitate. Transfer the adjusted solution to a reaction vessel and carry out a hydrothermal reaction at 150-200 ℃ for 12-24 h. After the reaction is completed, centrifuge at 10000 rpm for 3 min to obtain the precipitate. Wash the precipitate with deionized water 3-4 times.

[0041] Step 3: Place the washed precipitate in a vacuum drying oven at 60~80 ℃ and dry for 12 hours to obtain dried sheet NbOPO4. Place the dried sheet NbOPO4 in a muffle furnace and heat it from room temperature to the target temperature of 300~500℃ at a heating rate of 5~10 ℃ / min under air atmosphere. Maintain the target temperature for 2~4 hours to remove organic residues and improve the crystallinity and stability of the material, thus obtaining sheet-like proton carrier niobium oxyphosphate.

[0042] Active metal site loading: S1. Disperse chloroiridium acid (H2IrCl6·xH2O, 0.35 g based on iridium atoms) in 50 mL of ethylene glycol and sonicate for 15 minutes to obtain an iridium source dispersion. Disperse 1.0 g of sheet-like proton carrier niobium oxyphosphate in 150 mL of ethylene glycol solution and sonicate for 15 minutes to obtain a carrier dispersion. Mix the iridium source dispersion and the carrier dispersion and sonicate for 0.5~1 h to allow the surface of the sheet-like proton carrier niobium oxyphosphate to fully adsorb iridium, thus obtaining a mixed solution.

[0043] S2. Place the mixture in an oil bath at 150~170℃, stir and keep warm for 2~4 hours. After the reaction is complete, place the solution in an ice-water bath to cool to room temperature, centrifuge for 3 minutes to remove ethylene glycol, and obtain the catalyst precursor.

[0044] S3. Wash the catalyst precursor with deionized water 3-4 times, and place the washed catalyst precursor in a vacuum drying oven at 60 °C for 12 hours to obtain sheet-like NbOPO4 loaded with iridium nanoparticles, which is used as the PEM water electrolysis anode catalyst Ir / NbOPO4, denoted as Cat-1.

[0045] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that sodium fluoride is not added in step 1 of the preparation process of the proton carrier niobium oxyphosphate. The rest is the same as in Example 1, and the catalyst Cat-2 is obtained.

[0046] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in step 1 of the preparation process of the proton carrier niobium oxyphosphate powder, polyvinylpyrrolidone K30 is not added. The rest is the same as in Example 1, and the catalyst Cat-3 is obtained.

[0047] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in step 1 of the preparation process of the proton carrier niobium oxyphosphate, polyvinylpyrrolidone K30 is not added, but an equal mass of polyvinyl alcohol PVA-1788 is added. The rest is the same as in Example 1, and the catalyst Cat-4 is obtained.

[0048] Comparative Example 4 The difference between Comparative Example 4 and Example 1 lies in the loading process of the active metal sites, specifically: 1.0 g of the sheet-like proton carrier niobium oxyphosphate prepared in Example 1 was dispersed in 150 mL of deionized water, and chloroiridium acid (H2IrCl6 xH2O, 0.35 g based on iridium atoms) was added and stirred for 30 min. Subsequently, an aqueous solution of sodium borohydride (NaBH4 to Ir molar ratio of 5:1 to 8:1) was slowly added dropwise at room temperature as an excess reducing agent. After stirring for 2 hours, the mixture was filtered, washed, and vacuum dried to obtain the catalyst supported on metallic iridium. The rest of the process was the same as in Example 1, yielding catalyst Cat-5.

[0049] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the preparation of the proton-conducting support niobium oxyphosphate is not performed. Instead, niobium pentoxide powder is used as the support during the loading process at the active metal sites. Specifically: S1. Disperse chloroiridium acid (H2IrCl6·xH2O, 0.35 g based on iridium atoms) in 50 mL of ethylene glycol and sonicate for 15 minutes to obtain an iridium source dispersion. Disperse 1.0 g of niobium pentoxide powder carrier in 150 mL of ethylene glycol solution and sonicate for 15 minutes to obtain a carrier dispersion. Mix the iridium source dispersion and the carrier dispersion and sonicate for 0.5~1 h to obtain a mixed solution.

[0050] S2. Place the mixture in an oil bath at 150~170℃, stir and keep warm for 2~4 hours. After the reaction is complete, place the solution in an ice-water bath to cool to room temperature, centrifuge for 3 minutes to remove ethylene glycol, and obtain the catalyst precursor.

[0051] S3. Wash the catalyst precursor with deionized water 3-4 times, and then place the washed catalyst precursor in a vacuum drying oven at 60 °C for 12 hours to obtain the catalyst, denoted as Cat-6.

[0052] Comparative Example 6 The difference between Comparative Example 6 and Example 1 lies in the preparation process of the proton carrier niobium oxyphosphate. The high-temperature calcination step in step 3 (i.e., the step of heating from room temperature to the target temperature of 300-500°C at a rate of 5-10°C / min and holding for 2-4 hours) is omitted. Specifically: The precipitate was obtained in the manner described in steps 1 and 2 of Example 1; After washing the precipitate in step 2, centrifuge and dry it, then place it in a vacuum drying oven at 60~80 ℃ for 12 hours. The resulting support is directly used in the subsequent active metal site loading step, which is the same as in Example 1. The resulting catalyst is denoted as Cat-7.

[0053] Comparative Example 7 The preparation method of metallic iridium nanoparticles (Ir NPs) is as follows: S1. Disperse chloroiridic acid (H2IrCl6·xH2O, 0.35 g based on iridium atoms) in 50 mL of ethylene glycol, sonicate for 15 minutes to obtain an iridium source dispersion, then add 150 mL of ethylene glycol solution, sonicate for 15 minutes to obtain a mixture.

[0054] S2. Place the mixture in an oil bath at 150~170℃, stir and keep warm for 2~4h. After the reaction is complete, place the solution in an ice-water bath to cool to room temperature, centrifuge for 3min to remove ethylene glycol, and obtain a solid. Wash the solid with deionized water 3~4 times, and place the washed catalyst precursor in a vacuum drying oven at 60℃ for 12h to obtain metallic iridium nanoparticles Ir NPs.

[0055] Example 2 Electrochemical performance testing: 1. Weigh 2 mg of the catalyst Ir / NbOPO4 from Example 1 into a container, add 0.6 mL of deionized water and 0.39 mL of isopropanol, and sonicate for 15 minutes to obtain a catalyst dispersion. Then add 10 μL of 5 wt% Nafion D520 solution and sonicate for 15 minutes to obtain catalyst ink.

[0056] 2. The electrode area is 0.196 cm². 2 The glassy carbon electrode was cleaned and polished, and then 10 μL of catalyst ink was dropped onto the surface of the glassy carbon electrode using a pipette. After drying under an infrared lamp, a catalyst film was formed.

[0057] 3. Add 0.5 M H2SO4 solution to the electrolytic cell. Use a mercury / mercurous sulfate electrode as the reference electrode, a carbon rod as the counter electrode, and a glassy carbon electrode with a catalyst film on its surface as mentioned above as the working electrode.

[0058] 4. The electrode rotation speed was set to 1600 rpm, and the electrochemical performance of different catalysts was tested at a test potential of 1.4 V. RHE -1.6V RHE Record the current in response.

[0059] 5. Normalize the current to the mass of the noble metal to calculate the mass of the noble metal iridium on the glassy carbon electrode. Then normalize the response current to the mass of the noble metal iridium. The final current-voltage curve is the mass activity of the catalyst. Fix the overpotential to 320 mV, i.e., the potential to 1.55 V, and record the mass current at this potential.

[0060] like Figure 2 As shown, the dual-site catalyst Ir / NbOPO4 prepared in Example 1 of this invention exhibits superior electrochemical performance in the acidic oxygen evolution reaction. Specifically, at the reaction initiation stage near 1.46 V, its mass activity reached 48.9 times that of commercial IrO2 catalysts. At a working potential of 1.55 V, i.e., an overpotential of 320 mV, its mass activity remained 4.0 times that of Ir NPs (iridium nanoparticles), which is higher than that of Ir NPs. This significant performance improvement demonstrates that the sheet-like niobium phosphate support not only achieves high dispersion of the precious metal iridium through its high specific surface area, greatly improving the atomic utilization of the active sites, but more importantly, the excellent proton conduction capability of the support forms a highly efficient "dual-site" synergistic effect with the active sites of the iridium metal, significantly reducing the reaction initiation potential and activation barrier. This means that, while meeting the same electrolysis performance, the solution of this invention can significantly reduce the amount of scarce precious metal iridium used, significantly reducing the raw material cost of the membrane electrode.

[0061] Example 3 Membrane electrode fabrication: 1. Add deionized water, PEM water electrolysis anode catalyst, perfluorosulfonic acid solution with proton conduction function (ionomer solution, optionally Nafion™ D2021CS perfluorosulfonic acid, in 10 wt% of the catalyst mass), and alcohol to a glass bottle in sequence. Place the glass bottle on a magnetic stirrer and stir to disperse. Then transfer the solution to a ball mill jar containing grinding balls and ball mill under constant temperature conditions. The mass of PEM water electrolysis anode catalyst accounts for 15~40 wt% of the total mass of the slurry.

[0062] The alcohol is a liquid alcohol, such as one or more of ethanol, n-propanol, isopropanol, propylene glycol, etc., and the mass ratio of added deionized water to total liquid alcohol is between 5:5 and 8:2.

[0063] The ball milling conditions were as follows: ZrO2 ball milling beads of 2.0~4.5 mm were used, and the balls were milled at a constant temperature of 15~25 ℃, with a rotation speed of 300~1000 rpm and a time of 2~12 h.

[0064] 2. After ball milling and dispersion, the slurry is mixed and degassed using a degassing machine to obtain the anode catalyst layer slurry.

[0065] 3. Coat the PTFE membrane using a slot coater (loading 0.10~1.0 mg Ir / cm). 2 ).

[0066] 4. After drying, XRF testing was performed to determine whether the average iridium loading in the catalyst coating met the standard.

[0067] 5. Subsequently, a coating with a loading of 0.2 mg Pt / cm³ was applied to the PTFE membrane. 2 The cathode catalyst layer and the 115 proton exchange membrane are prepared into a catalyst coating membrane (CCM) by hot pressing transfer.

[0068] Example 4 Multi-channel device performance testing: A membrane electrode assembly (MEA) loaded with the catalyst Ir / NbOPO4 from Example 1 was prepared as described in Example 3. The electrolytic cell was assembled sequentially with the following components: insulating end plate, cathode plate, 0.15 mm gasket, carbon paper, membrane electrode assembly (CCM), 2.05 mm gasket, titanium felt, titanium mesh, and anode plate. The MEA was then tightened diagonally using a torque wrench (3 N•m) and the electrode clamps were attached. Electrochemical performance tests, including polarization performance tests and 3 A / cm² tests, were conducted by purging water under test conditions of 80 °C and atmospheric pressure (p_ambient). 2 Stability test under current density.

[0069] Polarization performance testing method: During the PEMWE operating condition test, the program was set up to sequentially record current densities starting from a low current density of 0.025 A / cm².2 Up to high current density 5 A / cm 2 The cell voltage of the electrolytic cell was plotted as a function of current density, and the results are as follows: Figure 3 .

[0070] Depend on Figure 3 The polarization curves show that in the range of 0~5 A / cm 2 Within the current density range, the membrane electrode prepared using the Ir / NbOPO4 dual-site catalyst of this invention exhibits significantly lower cell voltages than membrane electrodes using commercial IrO2. In the low current density region, Ir / NbOPO4 shows a lower onset potential, indicating that the Ir / NbOPO4 catalyst has higher intrinsic catalytic activity and effectively reduces the reaction activation energy. In the high current density region, the voltage difference further increases with increasing current density, such as at 2 A / cm². 2 At that time, the cell voltage of the sample of the present invention was approximately 1.62 V, while the cell voltage of the commercial sample was approximately 1.73 V; at 3 A / cm 2 At high current densities, the cell voltage of the sample of this invention is about 1.70 V, while that of commercial samples is as high as about 1.85 V. This means that, under the same hydrogen production capacity, the use of the catalyst of this invention can significantly reduce energy consumption and improve system efficiency.

[0071] like Figure 3 As shown, when only 0.2 mg Ir / cm 2 (Anode: 0.2 mg Ir cm) -2 Even with an ultra-low loading, it still achieved performance superior to commercial catalysts, which fully demonstrates that the high specific surface area of ​​the sheet-like niobium oxyphosphate support effectively disperses the active sites, greatly improves the utilization rate of the precious metal iridium, and significantly reduces the raw material cost of the membrane electrode.

[0072] Figure 3 As can be seen from the slope of the curve, the Ir / NbOPO4 curve of this invention is in the range of 1~4 A / cm. 2 The slope of the linear region is less than that of the commercial IrO2 curve, indicating that the membrane electrode prepared by the catalyst in Example 1 of this invention has a lower ohmic resistance R. The niobium phosphate support constructed in Example 1 of this invention has excellent proton conductivity. The pores constructed by the sheet-like structure are conducive to gas-liquid transport, ensuring mass transfer stability under high current, efficiently opening the proton transport channel in the catalyst layer, and reducing the internal resistance of the membrane electrode. Figure 3 As shown, at >4 A / cm 2 No obvious mass transfer polarization inflection point was observed in the high current density range.

[0073] like Figure 4As shown, the Ir / NbOPO4 catalyst prepared in this invention exhibits excellent long-term operational stability at industrial-grade high current densities. At 80℃ and 3 A / cm², [the catalyst demonstrates this stability]. 2 At high power loads, this catalyst requires only 0.2 mg cm⁻¹. -2 With a low Ir metal loading, it can operate continuously and stably for nearly 1000 hours, and the voltage rise rate is only 1μV h. -1 This is far superior to the higher Ir metal loading (0.8 mg). cm -2 And the voltage decay is severe (220.2 μV h). -1 Commercial IrO2 catalysts have been demonstrated to have extremely high durability and economic benefits in practical PEM electrolyzer applications.

[0074] Example 5 Using the same three-electrode system as in Example 2, and with 0.5 M H₂SO₄ solution as the electrolyte, any of the catalysts prepared in Example 1 and Comparative Examples 1-6 were coated onto a glassy carbon electrode. Electrochemical impedance spectroscopy (EIS) was performed at the oxygen evolution reaction working potential of 1.55 V (vs. RHE). The frequency range was 100 kHz to 0.1 Hz, and the amplitude was 5 mV. The charge transfer resistance R₀ obtained by fitting a Nyquist plot was... ct The data is recorded in Table 1: Table 1 Comparison of electrochemical impedance spectroscopy data for various catalysts

[0075] As shown in Table 1, the two-site catalyst prepared in Example 1 exhibits extremely low charge transfer resistance R. ct Only 2.35 Ω·cm 2 This method is significantly superior to the Nb₂O₅ support used in Comparative Example 5. The support fabrication process in Example 1 successfully induced a sheet-like structure by introducing NaF, which, combined with the abundant P-OH groups in the niobium oxyphosphate framework, constructed a highly efficient proton transport channel. In contrast, although Comparative Example 1 also used niobium oxyphosphate, the lack of NaF sheet-like structure for directional induction resulted in dense particle packing, hindering proton transport and increasing the impedance to 8.42 Ω·cm. 2 Building upon NaF-directed induction, Example 1 further promoted the formation of plate-like crystals using polyvinylpyrrolidone (K30). Combined with a mild ethylene glycol polyol thermal reduction method, this significantly improved proton transport efficiency and significantly reduced charge transfer resistance R. ct .

[0076] Example 6 Using the same three-electrode system as in Example 2, the electrochemical active surface area (ECSA) of the catalysts prepared in Examples 1 and Comparative Examples 1-6 was evaluated by measuring the double-layer capacitance (Cdl). Cyclic voltammetry scans were performed in the non-Radial range of 0.8-0.9 V vs. RHE at different scan rates of 10, 20, 40, 60, 80, and 100 mV / s. The Cdl value was proportional to the number of exposed active sites. The results are shown in Table 2.

[0077] Table 2 Comparison of active area under different preparation processes

[0078] The ethylene glycol polyol thermal reduction method used in Example 1 has significant advantages over the traditional strong reducing agent used in Comparative Example 4. The mild reduction rate of ethylene glycol allows iridium nanoparticles to grow uniformly in situ on the sheet-like support, avoiding the metal agglomeration phenomenon caused by the violent reaction of sodium borohydride. The Ir particles obtained by the mild reduction of ethylene glycol are smaller in size and more uniformly distributed, avoiding the instantaneous nucleation and agglomeration of metal particles caused by strong reducing agents, which greatly reduces the disadvantage of electrochemical active area. At the same time, the data of Comparative Example 2 shows that the addition of PVP surfactant in the support synthesis stage is crucial for the formation of a support with a high specific surface area. It proves that PVP can not only effectively prevent the stacking of niobium oxyphosphate sheets and increase the specific surface area of ​​the support, but also assist in the formation of a more favorable pore structure for iridium loading through interaction with niobate ions. Its regulatory effect is significantly better than that of PVA. Using an appropriate calcination temperature in the support preparation step is beneficial for removing organic residues and constructing electron transport channels, thereby helping to expose active sites.

[0079] Example 7 Accelerated aging test and ion dissolution analysis Using the same three-electrode system as in Example 2, the catalyst was subjected to constant current accelerated aging tests, with the current density set at 100 mA / cm². 2 The system was run continuously for 500 hours. After the operation was completed, the electrolyte was collected, and the concentrations of dissolved iridium and niobium ions in the electrolyte were detected by inductively coupled plasma mass spectrometry (ICP-MS) to evaluate the corrosion resistance stability of the catalyst under a strongly acidic environment. The results are shown in Table 3.

[0080] Table 3 Comparison of ion dissolution and voltage decay after 500 hours of accelerated aging

[0081] The data in Table 3 show that the iridium leaching amount of Comparative Example 4, prepared by the sodium borohydride chemical reduction method, is more than 40 times that of Example 1. Compared with Comparative Example 4, the ethylene glycol high-temperature thermal reduction method used in Example 1 can induce a strong metal-support interaction between metallic iridium and the niobium phosphate support at high temperature, thereby anchoring the active site. This method has significant technical advantages and can significantly prevent the dissolution of active sites or even physical shedding of the catalyst due to bubble impact during the reaction.

[0082] A comparison of Example 1 and Comparative Example 1 (without a fluorine source) shows that the niobium leaching amount in Comparative Example 1 is significantly higher than that in Example 1, approximately 30 times higher. This is because the support in Comparative Example 1 has a lower proton conduction efficiency compared to the support in Example 1, resulting in the inability to remove protons from the reaction interface in a timely manner under high current density. This leads to a sharp drop in local pH value, and this localized strong acid environment exacerbates the chemical corrosion of the support. In contrast, the sheet-like structure of Example 1 of this invention constructs a highly efficient proton transport channel, which can quickly remove protons generated in the reaction, thereby inhibiting local acidification and effectively protecting the structural stability of the support.

[0083] Comparative Example 6, lacking a high-temperature calcination step, produced a catalyst with high Nb dissolution and voltage decay rates during testing. The uncalcined niobium oxyphosphate was in an unstable state with poor crystallinity, making it prone to phase transition or dissolution collapse under strong acidic electrolytes and oxidation potentials, thus shortening the catalyst's lifespan. The catalyst prepared in Example 1 of this invention, through a reasonable calcination temperature, obtained a highly crystalline phase, thereby ensuring the long-term thermodynamic stability of the catalyst under harsh operating conditions.

[0084] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A process for the preparation of a dual site catalyst characterised in that, Including the following steps: Step 101: After mixing niobium salt, phosphoric acid solution, and water, sodium fluoride and polyvinylpyrrolidone are added to obtain the first mixture. After adjusting the pH of the first mixture, the temperature is controlled to separate the precipitate. Step 102: After the precipitate is dried, it is heated to the target temperature in an air atmosphere and calcined to obtain sheet-like proton carrier niobium oxyphosphate. Step 103: Iridium salt, sheet-like proton carrier niobium oxyphosphate, and ethylene glycol are mixed to obtain a second mixture; Step 104: The second mixture is subjected to temperature control, separation, and drying to obtain the catalyst Ir / NbOPO4.

2. The process for the preparation of a dual site catalyst according to claim 1, characterized in that, In step 101, the niobium salt is selected from one or a mixture of ammonium oxalate niobate, niobium pentachloride, niobium ethoxide, niobium isopropoxide, and niobium hydroxide; the mass of the niobium salt added per 1L of water is 35~45g; the mass of the sodium fluoride added per 1L of water is 1.5~2.0g; and the polyvinylpyrrolidone is selected from one or a mixture of polyvinylpyrrolidone K30, polyvinylpyrrolidone K15, polyvinylpyrrolidone K60, and polyvinylpyrrolidone K90.

3. The process for the preparation of a dual site catalyst according to claim 1, characterized in that, In step 102, the precipitate is dried at 60-80℃ for 10-14 hours; the temperature is programmed to rise from room temperature to 300-500℃ at a rate of 5-10℃ / min.

4. The process for the preparation of a dual site catalyst according to claim 1, characterized in that, In step 103, the iridium salt is selected from one or more of H2IrCl6·xH2O, IrCl3, and (NH4)2IrCl6; the mass of the iridium salt added to each 1L of ethylene glycol is 15~20g; the mass of the sheet-like proton carrier niobium oxyphosphate added to each 1L of ethylene glycol is 4~6g.

5. The process for the preparation of a dual site catalyst according to claim 1, characterized in that, In step 104, the temperature of the second mixture is controlled by using an oil bath to maintain the temperature at 150~170℃; the drying method is vacuum drying at 50~70℃.

6. A dual site catalyst Ir / NbOPO4, characterized in that, It is obtained by the preparation method described in any one of claims 1 to 5.

7. A membrane electrode, comprising a cathode catalytic layer, a proton exchange membrane, and an anode catalytic layer, characterized in that, The anode catalyst layer comprises the dual-site catalyst Ir / NbOPO4 as described in claim 6.

8. The application of the dual-site catalyst Ir / NbOPO4 of claim 6 in electrocatalysis.

9. A catalyst film, characterized in that, The catalyst film comprises the dual-site catalyst Ir / NbOPO4 of claim 6 and a proton-conducting ionomer.

10. A proton exchange membrane water electrolysis device, characterized in that, The device comprises the membrane electrode of claim 7.

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